&nbsp;
<h2>Unix/Linux Tutorials Overview</h2>
Welcome to Unix/Linux Tutorials by Linux Experts. The objective of these tutorials is to provide an in-depth understanding of the Linux Operating System. In these tutorials, we will cover topics such as Architecture, OS Commands, Vi Editor, and File Permissions. We will also cover advanced topics such as Scheduling Jobs, User Administration, Disk Partitioning, Package Management, and Troubleshooting of common issues.
In addition to the free Linux tutorials, we will also cover common interview questions, issues, and how to's of the Linux operating system.
<h3>Index</h3>
<ul>
<li><a href="features-unixlinux/" target="_blank" rel="noopener">Features of UNIX/LINUX</a></li>
<li><a href="unix-introduction/" target="_blank" rel="noopener">UNIX Introduction</a></li>
<li><a href="unix-commands-2/" target="_blank" rel="noopener">UNIX Commands</a></li>
<li><a href="system-usage-accounting-services-unix/" target="_blank" rel="noopener">System Usage Accounting Services in UNIX</a></li>
<li><a href="history-features-unix/" target="_blank" rel="noopener">History and Features of UNIX</a></li>
<li><a href="daemon-process-unix/" target="_blank" rel="noopener">Daemon process in UNIX</a></li>
<li><a href="understanding-unix-programms/" target="_blank" rel="noopener">Understanding of Unix Programs</a></li>
<li><a href="unix-system-architecture-explination/" target="_blank" rel="noopener">Unix System Architecture And Its Explanation</a></li>
<li><a href="functional-layers-models-unix/" target="_blank" rel="noopener">Functional layers &amp; Models in Unix</a></li>
<li><a href="architecture-unix/" target="_blank" rel="noopener">Architecture of UNIX</a></li>
<li><a href="working-wait-unix/" target="_blank" rel="noopener">Working With Wait() In UNIX</a></li>
<li><a href="unix-shell-scripting-training" target="_blank" rel="noopener">Unix Shell Scripting</a></li>
</ul>
<h3 style="text-align: justify;">Introduction to UNIX</h3>
<ul style="text-align: justify;">
<li>UNIX is a CUI Operating system.</li>
<li>LINUX is not just for UNIX wizards. <a href="https://www.linux.com/" target="_blank" rel="noopener">LINUX</a> is a clone of O/S.</li>
<li>Linux is the most important achievement of free software, it has been developed for business, education &amp; personal productivity.</li>
<li>Everyone has to start somewhere, and Linux administrators and engineers are no exception. Of you have purchased this book, I imagine that your goal is to pass the Red Hat exams (RHCSA &amp; RHCE) while acquiring or improving your current Linux skills.</li>
<li>These Linux skills and commands are all essential for knowing how to work with Linux, not just Red Hat.</li>
</ul>
<h2 style="text-align: justify;">Operating System(O/S)</h2>
<ul style="text-align: justify;">
<li>The operating system is an interface between user &amp; computer (or) it is system software.</li>
<li>The operating system is the most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs.</li>
<li>Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers.</li>
<li>It is classified into two types.</li>
</ul>
<img class="alignnone wp-image-5228" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/11/2406.png" alt="Unix/Linux" width="451" height="207" />
Single user systems: Provides a platform for only one user at a time. They are popularly associated with the DeskTop Operating System which runs on standalone systems where no user accounts are required.
Example: DOS
Multi-User Systems: More than one user can access the same system resources (CPU, applications, memory, printers &hellip;&hellip;&hellip;etc) at the same time known as multiuse.
Example: UNIX, LINUX
<blockquote>
Inclined to build a profession as Linux Developer? Then here is the blog post on, explore <a title="Linux Training" href="linux-training" target="_blank" rel="noopener">Linux Training</a>
</blockquote>
<h3 style="text-align: justify;">Feature of Linux</h3>
Multiuser: A multi-user Operating system allows more than one user to share the same computer system at the same time.
Multi-Tasking: More than one program can be run at a time. The main concept of multitasking is maximum utilizing CPU resources
Open System: The UNIX is open source code i.e Any user can modify Unix open-source code according to there ideas and requirements
<ul style="text-align: justify;">
<li>Using UNIX open source codeSun Micro Systems+ Adding additional features =Sun SalariesIBM+Adding additional feature &nbsp;= &nbsp;IBM-AIXHP+Adding additional feature= HP=UXSunta Curuz + Adding additional feature= SCO-UnixSilicon Graphics &nbsp; +Adding additional feature= &nbsp; IRIXMicro Soft+Adding additional feature &nbsp;= &nbsp; &nbsp;xenix</li>
</ul>
<ul style="text-align: justify;">
<li>Any operating system developed based on UNIX open-source code known as flavors of UNIX</li>
<li>The Linux was given to GPL (General Public License) Organized by GNU.</li>
<li>Linux Torvalds, who was then a student at the University of Helsinki in fin land, developed Linux in 1991. Linux is also an open system</li>
</ul>
<h3 style="text-align: justify;">Distributors of Linux</h3>
<ul>
<li style="text-align: justify;">Red Hat</li>
<li style="text-align: justify;">Suse</li>
<li style="text-align: justify;">Ubuntu</li>
<li style="text-align: justify;">Puppy</li>
<li style="text-align: justify;">Slackware</li>
<li style="text-align: justify;">Centos</li>
<li style="text-align: justify;">OEL</li>
<li style="text-align: justify;">Fedora</li>
<li style="text-align: justify;">White box</li>
<li style="text-align: justify;">Mandrake</li>
</ul>
Security: One of the most valued advantages of Linux over the other platforms lies with the high-security levels it ensures. Every Linux user is happy to work in a virus-Free environment and use the regular virus &ndash; prevention time needed when working with other operating systems for another more important task.
--&gt; UNIX/LINUX has given two levels of securities.
<ul style="text-align: justify;">
<li>System-level Security: It's controlled by the system administrator.</li>
<li>File-level Security: It's&nbsp;controlled by the owner of the file.</li>
</ul>
Portability: Portability means Independent of hardware &amp; processors
Communication: The main concept of communication facility Exchanging of information or files from one user account to another user account.
Programming Facility: UNIX o/s provides shell. Shell works like a programming language. It provides commands and keywords.
<table style="width: 587px; height: 256px;" border="1" cellspacing="1" cellpadding="1">
<tbody>
<tr>
<td>Script Language</td>
<td>Programming Language</td>
</tr>
<tr>
<td>It is an interpreter based language.</td>
<td>Compiler based language</td>
</tr>
<tr>
<td>Interpreter Converts high level</td>
<td>The whole program is a single short into machine language.</td>
</tr>
<tr>
<td>Doesn&rsquo;t create .exe files</td>
<td>Create .exe files</td>
</tr>
<tr>
<td>No need to compile the program.</td>
<td>Need to compile the program</td>
</tr>
<tr>
<td>It takes fewer lines of code</td>
<td>Takes numerous lines of code.</td>
</tr>
<tr>
<td>Reduces cost of maintenance</td>
<td>Increases the cost of maintenance.</td>
</tr>
</tbody>
</table>
Help facility: It is a beautiful feature of UNIX/ LINUX Operating systems. Don&rsquo;t know the information about the given command just go through the helpline.
Example:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
#Man &lt;command name&gt;
(or)
#info &lt;Command name&gt;
(or)
#&lt;command name&gt; --help
&nbsp;
<a style="background-color: #e94350; color: #ffffff; padding: 10px 20px;" href="interview-questions-on-linux" target="_blank" rel="noopener">Linux Interview Questions</a>
&nbsp;
<h2 style="text-align: justify;">For an in-depth understanding of Linux click on</h2>
<ul>
<li class="title"><a class="current-page" href="http://tekslate.com/features-unixlinux/" target="_blank" rel="noopener">Features of UNIX/LINUX</a></li>
<li class="title"><a href="http://tekslate.com/architecture-os/" target="_blank" rel="noopener">The architecture&nbsp;of O/S</a></li>
<li class="title"><a class="current-page" href="http://tekslate.com/unix-introduction/" target="_blank" rel="noopener">UNIX Introduction</a></li>
<li class="title"><a class="current-page" href="http://tekslate.com/basic-commands-unix/" target="_blank" rel="noopener">Basic commands</a></li>
<li class="title"><a class="current-page" href="http://tekslate.com/user-administration-linux/" target="_blank" rel="noopener">User Administration</a></li>
</ul>

Best UNIX/LINUX E Learning | Tutorials By LINUX Experts

Unix/Linux Tutorials

unixlinux

Linux Interview Questions and Answers

linux-interview-questions-answers

Linux Interview Questions

interview-questions-on-linux

&nbsp;
<h2 style="text-align: justify;">Linux Features</h2>
Multiuser: A multi-user Operating system allows more than one user to share the same computer system at the same time.
Multi-Tasking: More than one program can be run at a time. The main concept of multitasking is maximum utilizing CPU resources
Open System: The UNIX is open source code i.e Any user can modify Unix open-source code according to their ideas and requirements
<ul style="text-align: justify;">
<li>Using UNIX open source codeSun Micro Systems+ Adding additional features =Sun SalariesIBM+Adding additional feature &nbsp;= &nbsp;IBM-AIXHP+Adding additional feature= HP=UXSunta Curuz + Adding additional feature= SCO-UnixSilicon Graphics &nbsp; +Adding additional feature= &nbsp; IRIXMicro Soft+Adding additional feature &nbsp;= &nbsp; &nbsp;xenix</li>
<li>Any operating system developed based on UNIX open-source code known as flavours of UNIX</li>
<li>The<a href="https://www.linux.com/" target="_blank" rel="noopener"> Linux </a>was given to GPL (General Public License) Organized by GNU.</li>
<li>Linux Torvalds, who was then a student at the University of Helsinki in fin land, developed Linux in 1991. Linux is also an open system</li>
</ul>
<h2 style="text-align: justify;">Distributors of Linux</h2>
<ul>
<li style="text-align: justify;">Red Hat</li>
<li style="text-align: justify;">Suse</li>
<li style="text-align: justify;">Ubuntu</li>
<li style="text-align: justify;">Puppy</li>
<li style="text-align: justify;">Slackware</li>
<li style="text-align: justify;">Centos</li>
<li style="text-align: justify;">OEL</li>
<li style="text-align: justify;">Fedora</li>
<li style="text-align: justify;">White box</li>
<li style="text-align: justify;">Mandrake</li>
</ul>
Do you want to master Linux? Then enrol in<a href="linux-training" target="_blank" rel="noopener"> "Linux Training"</a> This course will help you to master Linux
Security: One of the most valued advantages of Linux over the other platforms lies with the high-security levels it ensures. Every Linux user is happy to work in a virus-Free environment and use the regular virus prevention time needed when working with other operating systems for another more important task.
UNIX/LINUX has given two levels of securities.
<ul style="text-align: justify;">
<li>System-level Security: It's controlled by the system administrator.</li>
<li>File-level Security: It's&nbsp;controlled by the owner of the file.</li>
</ul>
Portability: Portability means Independent of hardware &amp; processors
Communication: The main concept of communication facility Exchanging of information or files from one user account to another user account.
Programming Facility: UNIX o/s provides shell. Shell works like a programming language. It provides commands and keywords.
<table style="width: 587px; height: 256px;" border="1" cellspacing="1" cellpadding="1">
<tbody>
<tr>
<td style="text-align: center;">Script Language</td>
<td style="text-align: center;">Programming Language</td>
</tr>
<tr>
<td>It is an interpreter based language.</td>
<td>Compiler based language</td>
</tr>
<tr>
<td>Interpreter Converts high level</td>
<td>The whole program in a single short into&nbsp;machine language.</td>
</tr>
<tr>
<td>Doesn&rsquo;t create .exe files</td>
<td>Create .exe files</td>
</tr>
<tr>
<td>No need to compile the program.</td>
<td>Need to compile the program</td>
</tr>
<tr>
<td>It takes fewer lines of code</td>
<td>Takes numerous lines of code.</td>
</tr>
<tr>
<td>Reduces cost of maintenance</td>
<td>Increases the cost of maintenance.</td>
</tr>
</tbody>
</table>
Help facility: It is a beautiful feature of UNIX/ <a href="unixlinux" target="_blank" rel="noopener">LINUX</a> Operating systems. Don&rsquo;t know the information about the given command just go through the helpline.
Example:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
#Man &lt;command name&gt;
(or)
&shy;&shy;&shy;&shy; #info &lt;Command name&gt;
(or)
#&lt;command name&gt; --help
<a style="background-color: #e94350; color: #ffffff; padding: 10px 20px;" title="Explore Linux Interview Questions" href="interview-questions-on-linux" target="_blank" rel="noopener">Linux Interview Questions</a>
<h2>For an in-depth understanding of Linux click on</h2>
<ul>
<li class="title"><a class="current-page" title="Unix Architecture" href="http://tekslate.com/architecture-os/" target="_blank" rel="noopener">Architecture of O/S</a></li>
<li class="title"><a class="current-page" title="Introduction to Unix" href="http://tekslate.com/unix-introduction/" target="_blank" rel="noopener">UNIX Introduction</a></li>
<li class="title"><a class="current-page" title="Unix Commands" href="http://tekslate.com/basic-commands-unix/" target="_blank" rel="noopener">Basic commands</a></li>
<li class="title"><a class="current-page" title="User Administration in Linux" href="http://tekslate.com/user-administration-linux/" target="_blank" rel="noopener">User Administration</a></li>
</ul>
<div class="tags">&nbsp;</div>

Features of UNIX | LINUX Features - Updated 2022

Features of UNIX/LINUX

features-unixlinux

&nbsp;
<h2>File system Architecture</h2>
It is a method of storing the data in an organized fashion on the disk. Every partition on the disk except MBR and the extended partition should be assigned with some file system to make them store the data. The file system is applied to the partition by formatting it with a particular type of file system.
<h3>Types of file systems</h3>
Disk file systems: A disk file system is a file system designed for the storage of a file on a data storage device, most commonly a disk drive, which might be directly or indirectly connected to the computer.
Ex: FAT, FAT32, NTFS, CDFS, HFS, ext2, ext3, ISO 9660
Network file systems:&nbsp;A network file system is a file system that acts as a client for a remote file access protocol, providing access to files on a server.
Ex: DFS, NFS, SMB, FTP
Virtual file system: The purpose of VFS is to allow client applications to access different types of concrete file systems uniformly. It can be used to bridge the differences in Windows, Mac OS, and Unix file system, so that applications can access files on local file systems of those types without having to know what types of the file system they are accessing.
<h3>File system Hierarchy system</h3>
<img class="wp-image-5269 aligncenter" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/11/560-460x126.png" alt="file system" width="552" height="151" />
This is a top-level working directory.&nbsp; It is a parent directory for all other directories. It is called as &nbsp;&nbsp;&ldquo;ROOT&rdquo; directory. It is represented by forward-slash (/)
<blockquote>
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</blockquote>
Root: It is the home directory for the root users (Superuser). It provides a working environment for the root user.
Home: It is the home directory for other users.&nbsp; It provides a working environment for other users (except root).
Bin: (Binary files): It contains commands used by all users.
Sbin:&nbsp;(Superuser binary files): It contains commands used by the only superuser (root).
Boot: It contains system bootable files, boot loader information, kernel related information for <a href="https://www.linux.com/" target="_blank" rel="noopener">LINUX</a>
etc:&nbsp;It contains all system configuration files. /etc/hosts,/etc/resolv.conf
Usr:&nbsp;By default soft wares are installed in / usr directory. (UNIX sharable resources).
Opt: It is an optional directory for users. It contains third party soft wares.
Dev: It contains all device files information. Similar to devise manager of windows. In UNIX/LINUX every device is treated as a file. &nbsp;
Var: It is containing variable files information like emails, print, log files.
Mnt: It is the default removable media working directory. It is empty by default.
Lib: It contains library files which are used by OS. It is similar to the dell files of windows.
Tmp:&nbsp;It contains temporary files of information.
Media:&nbsp;It contains all of the removable media like CD-ROM, pen drive.
Proc: It contains process files. Its contents are not permanent, they keep changing It's also called a virtual directory. Its file contains useful information used by OS. Like&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /proc/meminfo&hellip;&hellip;&hellip; /proc/cpuinfo&hellip;&hellip;&hellip;&hellip;
&nbsp;
<a style="background-color: #e94350; color: #ffffff; padding: 10px 20px;" href="interview-questions-on-linux" target="_blank" rel="noopener">Linux Interview Questions</a>
&nbsp;
<h2>For an in-depth understanding of Linux click on</h2>
<ul>
<li class="title"><a class="current-page" title="Features of UNIX/LINUX" href="https://tekslate.com/features-unixlinux/" target="_blank" rel="noopener">Features of UNIX/LINUX</a></li>
<li class="title"><a class="current-page" title="Architecture of O/S" href="https://tekslate.com/architecture-os/" target="_blank" rel="noopener">Architecture of O/S</a></li>
<li class="title"><a class="current-page" title="UNIX Introduction" href="https://tekslate.com/unix-introduction/" target="_blank" rel="noopener">UNIX Introduction</a></li>
<li class="title"><a class="current-page" title="Basic commands" href="https://tekslate.com/basic-commands-unix/" target="_blank" rel="noopener">Basic commands</a></li>
<li class="title"><a class="current-page" title="User Administration" href="https://tekslate.com/user-administration-linux/" target="_blank" rel="noopener">User Administration</a></li>
</ul>

File system in unix linux

File system

file-system-unix-linux

&nbsp;
<h2>Wild Card Characters In Unix/Linux</h2>
*: It matches zero (or) more characters in the given file &nbsp;
Ex:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
$&nbsp; ls a* ----&gt;Displaying files star with &lsquo;a&rdquo;.
$&nbsp; ls&nbsp; i*----&gt;Start with &lsquo;I&rdquo; end with &lsquo;g&rsquo;
$ ls&nbsp;&nbsp; *g----&gt;list out&nbsp; end with &lsquo;g&rsquo; only
$ rm I *----&gt;removes start with i
$cp&nbsp; a* Documents/copies start with a
$ cp - rf I * g Documents /
$&nbsp; cp - rvf * / backup copies current directory all files
? : It matches any single character in the given file &nbsp;
Ex:&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; &nbsp;
$ ls ?----&gt;Display single character files.
$ ls ??----&gt;Two character files
$ ls a ??? ----&gt;list four character files but first one is &lsquo;a&rsquo;.
$ rm ?? &nbsp;----&gt;Removes two character files.
$ cp ??? Documents/ copies three character files.
[&nbsp;&nbsp;&nbsp;&nbsp; ]: It matches any single characters in the given list.
<blockquote>
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</blockquote>
Ex: $ ls [aeiou] ----&gt;Displays given matching character files.
$ ls [aeiou] * ----&gt;Displays start with a,e,I,o,u files.
$ rm [aeiou] *----&gt;Removing start with a,e,I,o,u
$ cp [aeiou] * Unix/copying start with a,e,I,o,u &nbsp; &nbsp;
[&nbsp; -&nbsp;&nbsp; ] : It matches any single characters in the given range.
Ex: &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
$ ls [a-f]&nbsp; *----&gt;Displays start with a,b,c,d,e,f
$ ls [a-f, o-v] * ----&gt;Display start with a-e &amp; o-v
$ rm&nbsp; [a-f] *----&gt;Removes a-f
$ cp&nbsp; [a-f, 1-9]&nbsp; *&nbsp; Unix/copying files a-f &amp; 1-9
&nbsp;
<a style="background-color: #e94350; color: #ffffff; padding: 10px 20px;" href="unixlinux" target="_blank" rel="noopener">Linux Tutorials</a>
&nbsp;
<h2>For an in-depth understanding of Linux click on</h2>
<ul>
<li class="title"><a class="current-page" href="http://tekslate.com/features-unixlinux/" target="_blank" rel="noopener">Features of UNIX/LINUX</a></li>
<li class="title"><a class="current-page" href="http://tekslate.com/architecture-os/" target="_blank" rel="noopener">Architecture of O/S</a></li>
<li class="title"><a class="current-page" href="http://tekslate.com/unix-introduction/" target="_blank" rel="noopener">UNIX Introduction</a></li>
<li class="title"><a class="current-page" href="http://tekslate.com/basic-commands-unix/" target="_blank" rel="noopener">Basic commands</a></li>
<li class="title"><a class="current-page" href="http://tekslate.com/user-administration-linux/" target="_blank" rel="noopener">User Administration</a></li>
</ul>
<div class="tags">&nbsp;</div>
&nbsp;

Wild card characters in Unix Linux | Learn Linux Online

Meta characters (or) wild card characters

meta-characters-wild-card-characters-unix-linux

&nbsp;
<h2>Process Management In Linux</h2>
<ul>
<li>A process is a program under execution. (or)</li>
<li>A process is an instance of a running program.</li>
<li>The process has its own address space in memory, a thread of execution, and characteristics such as security context, environment and current priority.</li>
<li>The <a href="https://www.linux.com/" target="_blank" rel="noopener">Linux</a> kernel tracks every aspect of a process by its process ID number information about each process is advertised by the kernel to user program through the / process/ PID</li>
<li>When a process starts another program, the new process is called a child process. This original process is the parent process of its child process. Child process inherit characteristics from its parents, such as its environment and the user and groups it's as which it's run.</li>
<li>There are two types of process in Linux:</li>
</ul>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;1. Foreground process.
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;2. Background process.
<h3>Foreground process: </h3>
In Foreground users can execute only one process (or) job.
Ex: $ firefox &nbsp;
To kill the foreground job in Linux:
Ctrl + C EX: $cp file1 file2 &nbsp;
<h3>Background Process:</h3>
In the Background, users can execute many jobs at a time.
Ex: &nbsp;$fire fox &amp; $ cp file1 file2&nbsp;
To check the jobs list in Linux:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
$jobs PS: &nbsp;Displays information about the running process. $ps
To view the process with more detailed information:
$ ps U &nbsp;
I can detail a particular process:
$ ps aux / grep ssh (or) $ ps aux
Kill: Terminates a process
Syn: $kill PID $ kill 4286 Sometimes if the kill command doesn&rsquo;t work the way you intended it to, you can also call it with the 9 option to give it a priority on the system.
$Kill -94286 &nbsp; Signal
Signal: The operating system communicates to the process through signals. These signals report events or error situations to processes. In many cases, signals will result in the process existing
<ul>
<li>One typical signal is SIGTERM, which terminates the process; it asks it to exit cleanly.</li>
<li>Another is SIGKILL, which kills the process; the process is required to exit immediately.</li>
</ul>
<h3>To find the PID(s_ belonging to the SSH service)</h3>
$ pidof sshd (or) $ Pgrep sshd
Top: Monitors system resources (similar to task manager in windows)
Options: $top
S ---&gt;To change the time interval for updating top results (Sec&rsquo;s)
R ---&gt;&nbsp;&nbsp; To sort by PID number
U ---&gt;&nbsp;&nbsp; Username to get only that user process details
P ---&gt;&nbsp; &nbsp;To sort by CPU utilization.
M ---&gt;&nbsp; &nbsp;To sort by RAM utilization.
C ---&gt;&nbsp; &nbsp;To display or hide command full path.
R ---&gt;&nbsp;&nbsp; To renice a process
K ---&gt;&nbsp;&nbsp; To kill a process
W ---&gt;&nbsp;&nbsp; To save the modified configuration
Z ---&gt;&nbsp; &nbsp;to Quit
When you&rsquo;re comfortable working with processes, you can then make some more advanced adjustments, such as changing the priority of a particular process.
Renice: Adjusts the priority of a particular process.
Syn: renice &lt;priority&gt; [options] -p changes process priority for a particular PID -u changes process priority for a particular user(s)
The priority value range from -20 (first priority) to 20 (dead last priority). Only the root user may set processes to use a priority under o. #renice -23874 * 
Note: If all ready processes have the same priority, they will share the processor equally. Priority only has an effect when two processes at different priority levels are computing for CPU time, In which case the lower priority process will get less time &amp; appear to run more slowly.
Nohup: The nohup jobs will create in the server account so nohup jobs will execute even the user disconnects from his account. Ex:$nohup cp files1,file2 &amp; $nohup firefox&nbsp; &nbsp;&nbsp;
<h3>Communication commands</h3>
The main concept of communication facility exchanging of information or files from one user to another user.
Write: It is used to write a message to another user account, but he should be logged into the user. $write user name/terminal name ----------------------- Ctrl+d&nbsp; (Save &amp; quit)
<ul>
<li>To deny messages: $mesg n</li>
<li>To allow messages: $mesg y</li>
</ul>
Wall: It is used for to send a broadcast message to all users who are connected to server $ wall Welcome to Linux ______________ Ctrl+d (save &amp; quit)
Mail: Using the mail command you can quickly and efficiently circulate memos and other written information to your co-workers you can even send and receive emails from people outside your organization. $ mail&nbsp; <a href="mailto:user1@server254.example.com" target="_blank" rel="noopener">user1@server254.example.com</a> single user $mail user1,user2,user3&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
multiple users at a time $ mail&nbsp; user1&lt;stud It translates files to the user. $ mail user2&lt;backup-file
<ul>
<li>Mails are stored in mailbox: (/var/spool/mail/username)</li>
<li>Go open the mailbox: $mail</li>
</ul>
<blockquote>
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</blockquote>
Note: By default, all mails will store in the primary mailbox (Nor/spool/mail).&nbsp; It will open mails in the primary mailbox transferred to the secondary mailbox (i.e mbox) &agrave;To open secondary mailbox: $mail &ndash; f
The primary mailbox only maintains unread mails.
<h3>Mail box options: &nbsp;&nbsp;&nbsp;&nbsp;</h3>
Q ---&gt;quit &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
d --&gt;delete
R ---&gt;reply&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
d2 ---&gt; delete 2nd mail
P ---&gt; print&nbsp;
w filename --&gt; IT writes to new file * 
&nbsp;
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&nbsp;
<h3>One Bit Equals to how many bytes</h3>
The bit is the smallest component of data and byte is larger than bit size. The size 1000 can be replaced with 1024 and still be correct using the other acceptable standards. Both of these standards are correct depending on what type of storage you are referring to.
Processor (or) virtual storage&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Disk Storage 
1&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; bit&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =&nbsp;&nbsp;&nbsp; Binary digit&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;1 bit&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;=&nbsp; &nbsp;binary digit
8&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; bits&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =&nbsp;&nbsp;&nbsp; 1 byte&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;8 bits&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; =&nbsp; &nbsp;1 byte
1024&nbsp;&nbsp;&nbsp; bytes&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =&nbsp;&nbsp;&nbsp; 1 kilobyte&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;1000 bytes&nbsp; &nbsp;=&nbsp; &nbsp;1 kilo
1024&nbsp;&nbsp;&nbsp; kilo&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =&nbsp;&nbsp;&nbsp; 1 mega&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;1000 kilo&nbsp; &nbsp; &nbsp; &nbsp;=&nbsp; 1 mega
1024&nbsp;&nbsp;&nbsp; mega&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =&nbsp;&nbsp;&nbsp; 1 Giga&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 1000 mega&nbsp; &nbsp; &nbsp;=&nbsp; 1Giga
1024&nbsp;&nbsp;&nbsp; Giga&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =&nbsp;&nbsp;&nbsp; 1 Tera&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 1000 Giga&nbsp; &nbsp; &nbsp; &nbsp; =&nbsp; 1 Tera
1024&nbsp;&nbsp;&nbsp; Tera&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =&nbsp;&nbsp;&nbsp; 1 Peta&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;1000 Tera&nbsp; &nbsp; &nbsp; &nbsp; =&nbsp; 1 Peta
1024&nbsp;&nbsp;&nbsp; peta&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =&nbsp;&nbsp;&nbsp; 1 exa&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;1000 peta&nbsp; &nbsp; &nbsp; &nbsp; =&nbsp; 1 Exa
1024&nbsp;&nbsp;&nbsp; exa&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =&nbsp;&nbsp;&nbsp; 1 zetta&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 1000 Exa&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; =&nbsp; 1Zetta
1024 &nbsp;&nbsp; zetta&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =&nbsp;&nbsp;&nbsp; 1 yotta&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;1000 Zetta&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =&nbsp; 1 Yotta
1024&nbsp;&nbsp;&nbsp; yotta&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =&nbsp;&nbsp;&nbsp; 1bronto&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 1000 Yotta&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =&nbsp; 1 Bronto
1024&nbsp;&nbsp;&nbsp; Bronto&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =&nbsp;&nbsp;&nbsp; 1 Geo&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 1000 Bronto&nbsp;&nbsp;&nbsp;&nbsp; =&nbsp; 1 Geo
<h2>For an in-depth understanding of Linux click on</h2>
<ul>
<li class="title"><a class="current-page" href="http://tekslate.com/features-unixlinux/" target="_blank" rel="noopener">Features of UNIX/LINUX</a></li>
<li class="title"><a class="current-page" href="http://tekslate.com/architecture-os/" target="_blank" rel="noopener">Architecture of O/S</a></li>
<li class="title"><a class="current-page" href="http://tekslate.com/unix-introduction/" target="_blank" rel="noopener">UNIX Introduction</a></li>
<li class="title"><a class="current-page" href="http://tekslate.com/basic-commands-unix/" target="_blank" rel="noopener">Basic commands</a></li>
<li class="title"><a class="current-page" href="http://tekslate.com/user-administration-linux/" target="_blank" rel="noopener">User Administration</a></li>
</ul>

Process Management in Unix/Linux

Monitoring system performance (or) process Management

monitoring-system-performance-process-management-linux

&nbsp;
<h2>Links In Linux</h2>
To give a pointer to the source file called a link.
In Unix/Linux two types of links.
<ul>
<li>Soft links</li>
<li>Hard links.</li>
</ul>
<h2>Soft links</h2>
The inode number of the source file, link file are different.
<ul>
<li>It can be created across the file system.</li>
<li>Editing of the original file will be replicated in the link files.</li>
<li>The size of the soft link file equals the number of characters in the original file path.</li>
<li>If the source file is deleted the link file will not be accessible.</li>
<li>It is also be called a shortcut link</li>
</ul>
Syn: $ ln-s&lt;source file&gt; &lt;link file&gt;
Ex: $ ln-s/backup/linux /root/desktop/linux
<h2>Hard links</h2>
&agrave; Source file, link file has same inode numbers.
<ul>
<li>It can&rsquo;t be created across the file system.</li>
<li>Editing of the original file will replicate in the link files.</li>
<li>The size of the hard link file is the same as the original file.</li>
<li>The source file is deleted the link file we can access.</li>
<li>It is a backup link.</li>
</ul>
Syn: $/n&lt;source file&gt;&lt;link file&gt;
Ex: $ /n/root/ backup/root/ desktop/ backup &nbsp;
*Shell concept: Shell is a command-line interpreter. The shell access request from the user and the checks command existence, if the command exists then it converts into kernel understandable language (Machine language) and it sends the given request to kernel.
The shell access interface b/w user and kernel
<blockquote>
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</blockquote>
<h3>Types of shells&nbsp;</h3>
<table style="width: 500px;" border="1" cellspacing="1" cellpadding="1">
<tbody>
<tr>
<td>Shell name</td>
<td>Developed By</td>
<td>Prompt</td>
<td>Interpreter name</td>
</tr>
<tr>
<td>Bourne shell</td>
<td>Stephen Bourne</td>
<td>$</td>
<td>sh</td>
</tr>
<tr>
<td>Korn Shell</td>
<td>David korn</td>
<td>$</td>
<td>ksh</td>
</tr>
<tr>
<td>C shell</td>
<td>Bill joy</td>
<td>%</td>
<td>csh</td>
</tr>
<tr>
<td>Bash shell</td>
<td>Stephen Bourne</td>
<td>$</td>
<td>bash</td>
</tr>
<tr>
<td>Z shell</td>
<td>paul</td>
<td>$</td>
<td>z sh</td>
</tr>
</tbody>
</table>
Note: The advanced version of the Bourne shell is the bash shell.
<ul>
<li>Bash means &ldquo;Bourne again shell&rdquo;</li>
<li>Bash shell is the default in Linux.</li>
</ul>
Default shell name&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Flavour name 
Bash Shell&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Linux
Bourne Shell&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; SCo_Unix, Solaris, HP_UX
Korn Shell&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; IBM_AIX
C shell&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; IRIX (Silicon Graphics) &nbsp;
<table style="width: 500px;" border="1" cellspacing="1" cellpadding="1">
<tbody>
<tr>
<td>Default shell name</td>
<td>Flavour name</td>
</tr>
<tr>
<td>Bash Shell</td>
<td>Linux</td>
</tr>
<tr>
<td>Bourne Shell</td>
<td>SCo_Unix, Solaris, HP_UX</td>
</tr>
<tr>
<td>Korn Shell</td>
<td>IBM_AIX</td>
</tr>
<tr>
<td>C shell</td>
<td>IRIX (Silicon Graphics)</td>
</tr>
</tbody>
</table>
<h3>Features of shells</h3>
<ul>
<li>Word completion</li>
<li>Command History.</li>
<li>Command alias.</li>
</ul>
To check the shells:
#cat / etc/shells
To check the parent shell of the current user:
# echo $ SHELL &nbsp;
To view the available shells:
#Cd /bin #ls&nbsp; *&nbsp; sh
To shift from bash shell to sh shell:
#sh
To shift from sh shell to k shell:
#ksh
To check the current working shell:
#echo $ʘ
To exit the shell:
#exist
&nbsp;
<a style="background-color: #e94350; color: #ffffff; padding: 10px 20px;" href="unixlinux" target="_blank" rel="noopener">Linux Tutorials</a>
&nbsp;
<h3>Command completion:</h3>
<a href="https://www.linux.com/" target="_blank" rel="noopener">Linux </a>automatic command completion is a tool or program that can identify what you are typing in the Linux command line terminal and can complete that command, words, or sentence for you. This is really cool feature in Linux
<ul>
<li>When the &lt;TAB&gt; key is pressed, any command starting with the given string will be completed by the system automatically.</li>
<li>For multiple commands that starting with the given string, pressing the &lt;TAB&gt; key twice will list down all those matched files or commands.</li>
<li>If there are no match of any command, files, or folders, then, the automatic word completion will not show, a &lsquo;ting&rsquo; sound will buzz.</li>
</ul>
Ex: $cd /var/l&lt;tab&gt;Lib/lock/ log/
<h3>Command History:&nbsp;&nbsp; </h3>
The history command performs one of several operations related to recently &ndash; executed commands recorded in a history list. Each of these recorded commands is referred to as an &lsquo;event&rsquo;, when specifying an event to the history command. &nbsp;
$history
$history 10
$history &ndash;c&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Lock the history.
$history &ndash;r &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Unlock history.
$rm.bash_history&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;Removes the history
<h3>Command alias:</h3>
<ul>
<li>Alias is a built-in shell command in Linux/Unix operating systems.</li>
<li>It can save you a lot of typing by assigning a name to long commands.</li>
<li>The alias command can be useful if you want to create a &lsquo;shortcut&rsquo; to a command.</li>
</ul>
Syn: Alias name=&rsquo;command&rsquo;
Ex:&nbsp;&nbsp;&nbsp;
$alias&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;U= user add
$alias&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;C= Clear
$alias&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Display alias list
$unalias U&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Disable alias
$Vim. bashrc&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Permanent alias names
<h2>For an in-depth understanding of Linux click on</h2>
<ul>
<li class="title"><a class="current-page" title="Features of UNIX/LINUX" href="http://tekslate.com/features-unixlinux/" target="_blank" rel="noopener">Features of UNIX/LINUX</a></li>
<li class="title"><a class="current-page" title="Architecture of O/S" href="http://tekslate.com/architecture-os/" target="_blank" rel="noopener">Architecture of O/S</a></li>
<li class="title"><a title="Linux Tutorials" href="http://tekslate.com/tutorials/unixlinux/" target="_blank" rel="noopener">Linux Tutorials</a></li>
<li class="title"><a class="current-page" title="Basic commands" href="http://tekslate.com/basic-commands-unix/" target="_blank" rel="noopener">Basic commands</a></li>
<li class="title"><a class="current-page" title="User Administration" href="http://tekslate.com/user-administration-linux/" target="_blank" rel="noopener">User Administration</a></li>
</ul>

Links in Linux

Links

linux-links

&nbsp;
<h2>File Permissions In Linux</h2>
<ul>
<li>Just like every operating system,<a href="https://www.linux.com/" target="_blank" rel="noopener"> Linux </a>comes with a set of permissions that it uses to protect files, directories, and devices on the system.</li>
<li>These permissions can be manipulated to allow (or) disallow access to files and directories on different parts of the system.</li>
</ul>
<h2>Basic file permissions</h2>
Let&rsquo;s look at how permissions work first. Linux permissions are implemented through the properties of files and are defined by three separate categories.
&nbsp; <img class="alignnone wp-image-5336" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/11/g.png" alt="File Permissions " width="327" height="183" />
User: The person who owns the file.
Group: The group that owns the file.
Other: All other users on the system.
Permissions in Linux can be assigned one of two ways. You can use the mnemonic or a single digit to represent the permission level.
<table style="width: 622px; height: 179px;" border="1" cellspacing="1" cellpadding="1">
<tbody>
<tr>
<td>Operation</td>
<td>Digit&nbsp;</td>
<td>Mnemonic&nbsp;</td>
<td>Description</td>
</tr>
<tr>
<td>Read</td>
<td>r</td>
<td>4</td>
<td>View file contents.</td>
</tr>
<tr>
<td>Write</td>
<td>w</td>
<td>2</td>
<td>Write to me or change.</td>
</tr>
<tr>
<td>Execute</td>
<td>x</td>
<td>1</td>
<td>Run the file.</td>
</tr>
</tbody>
</table>
<h3>Default file permissions</h3>
Umask: Universal mask is a default value that always gets dedicated from maximum file permission allocated for every file &amp; directory.
For super user umask value is # 022.
For Normal user, the umask value is $002
<h2>For superuser:</h2>
Maximum permission of a file 666-Umask (-)022
Default file permission&nbsp;------&gt;&nbsp; 644
Maximum permission of a directory 777-Umask (-)022
Default directory permission 755
<blockquote>
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</blockquote>
<h2>For Normal user:</h2>
Maximum permission of a file ---- 666----Umask (-)_002---664
Maximum permission of a directory---777 umask---002 (-)775
To see the umask # umask
To change the umask # umask 222
To view umask value from the fiel # vim /etc/ bashrc
<h4>Operators:</h4>
+&nbsp; ---&gt;To add a permission.
-&nbsp; ---&gt;To remove permission.
= ---&gt;To override the permission.
Here are some of the commands you can use to work with permissions:
Chmod:- It is used to change the permission of a file and directory. It can be used by the owner of the file (or) by root.
Syn: Chmod [options] [permission]&nbsp;&nbsp; [file]
R ---&gt; Acts recursively.
V ---&gt; Provides verbose output.
Ex:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
1) # Chmod u+rw,g+r, o+x&nbsp;&nbsp; linux # Chmod 641 linux
2) #chmod ugo =rw backup (or) # chmod 666 backup
3) #chmod U-W, g-r, o-x&nbsp; linux
4) #chmod-R U+W, g+r, o+x linux
5) #chmod-R 777 unix
6) # chmod 755 Unix
&nbsp;
<a style="background-color: #e94350; color: #ffffff; padding: 10px 20px;" href="unixlinux" target="_blank" rel="noopener">Linux Tutorials</a>
&nbsp;
Chgrp: &agrave; By using this command we can change the group of the file.
Syn: Chgrp [options] [group name] [file]
R ---&gt; Recursively
V ---&gt; Verbose
Ex: #ls-l linux #chgrp sales linux
Chown: This command is used so we can change the owner of the file, as well as owner &amp; group at a time.
Syn: Chown [options] [user:group] [file]
R---&gt; Recursively
V---&gt; Verbose.
Ex: &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
#Chown Raju Linux&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;To Change the only owner.
#Chown Raju: sales Linux&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;To Change owner &amp; group
#Chown &ndash;R Ramu: color Unix&nbsp; &nbsp; &nbsp;Recursively to change.
To view the symbolic as well as a numeric mode of permission
# stat Linux
To change the permissions in GUI mode
#navtilus &amp;
Assign the permissions in GUI mode:
Right-click on file -----&gt;properties----&gt;permissions.
<h2>For an in-depth understanding of Linux click on</h2>
<ul>
<li class="title"><a class="current-page" title="Features of UNIX/LINUX" href="http://tekslate.com/features-unixlinux/" target="_blank" rel="noopener">Features of UNIX/LINUX</a></li>
<li class="title"><a class="current-page" title="Architecture of O/S" href="http://tekslate.com/architecture-os/" target="_blank" rel="noopener">Architecture of O/S</a></li>
<li class="title"><a class="current-page" title="UNIX Introduction" href="http://tekslate.com/unix-introduction/" target="_blank" rel="noopener">UNIX Introduction</a></li>
<li class="title"><a class="current-page" title="Basic commands" href="http://tekslate.com/basic-commands-unix/" target="_blank" rel="noopener">Basic commands</a></li>
<li class="title"><a class="current-page" title="User Administration" href="http://tekslate.com/user-administration-linux/" target="_blank" rel="noopener">User Administration</a></li>
</ul>

File Permissions in Linux - Unix

File Permissions

file-permissions-in-linux

&nbsp;
<h2>Scheduling Jobs in Linux</h2>
<ul>
<li>In any operating system, it is possible to create jobs that you want to reoccur. This process known as job scheduling is usually done based on user-defined jobs. As an administrator, however, you can define your own jobs and allow your users to create them as well. The importance of the job scheduling is that the critical tasks like taking backups, which the clients usually want to be taken in nights, can easily be performed without the intervention of the administrator by scheduling a cron job.</li>
<li>If the cron job is scheduled carefully that the backup will be taken at any given time of the client and there will be no need for the administrator to remain back at nights to take the backup. For Red Hat or any other<a href="https://www.linux.com/" target="_blank" rel="noopener"> Linux</a>, this process is handled by the cron service or a daemon called cron, which can be used to schedule tasks (also called jobs) By default, <a href="https://www.redhat.com/en" target="_blank" rel="noopener">Red Hat</a> comes with a set of predefined jobs that occur on the system (hourly, daily, weekly, monthly, and with arbitrary periodicity)</li>
<li>There are two tools for scheduling jobs.</li>
</ul>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;1. at
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 2. cron tab
<h2>At Jobs</h2>
&nbsp;&ldquo;at&rdquo; is used to schedule the job for a particular time or interval, in other words, it is used only for one time or only for one interval.
Syn: at [options]
<ul>
<li>l&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;lists all jobs in the queue</li>
<li>d&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Removes a job from the queue</li>
<li>f&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Reads input from the file</li>
<li>m&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Sends mail to the user when the job is complete.</li>
</ul>
Examples:
1. $ at 9am At&gt; date Ctrl+d (save &amp; quit)
2. $at now +3 days At&gt; /bin/echo &ldquo;hello world&rdquo; Ctrl+d (save &amp; quit)
3. $ at 03222013 At&gt; ls Ctrl +d (save &amp; quit)
4. $at 1:30&nbsp;&nbsp;&nbsp;&nbsp; 3/22/2013 At&gt; cp file1&nbsp; file2 Ctrl+d (Save &amp; quit)
5. $at &ndash;f filename&nbsp; 11pm At&gt; /bin/echo &ldquo;hello world&rdquo; Ctrl+d (save &amp; quit)
<blockquote>
Inclined to build a profession as Linux Developer? Then here is the blog post on, explore <a title="Linux Training" href="linux-training" target="_blank" rel="noopener">Linux Training</a>
</blockquote>
<h3>View the currently queued jobs:</h3>
$ at&nbsp; - l (or) $ atq
<h3>Delete the job from the queue: </h3>
$ at &ndash; d 1 (or) $ atrm 1
<h3>Verify that the job is truly gone: </h3>
$at q
To View the job details:
$ at&nbsp; -c 2
<h3>Restricting a user from using at jobs:</h3>
The atd service uses two files to control access to the services
/etc/at.allow /etc/at.deny The /etc/at.allow file:
If it exists, only these users are allowed (at.deny is ignored).
If it doesn&rsquo;t exist, all users except at deny are permitted.
The /etc/at.deny file:
If it exists and is empty, all users are allowed (red hat default)
<h3>For both files: </h3>
If neither file exists, root only.
&nbsp;
<a style="background-color: #e94350; color: #ffffff; padding: 10px 20px;" href="interview-questions-on-linux" target="_blank" rel="noopener">Linux Interview Questions</a>
&nbsp;
<h2>Cron jobs</h2>
The default setting for a red hat allows any user to create a cron job. As the root user, you also have the ability to edit and remove any cron job you want. Let&rsquo;s jump into creating a cron job for the system. You can use the crontab command to create, edit, and delete jobs.
Syn: Crontab [-u use] [option]
Options: &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
<ul>
<li>e &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Edits the users crontab</li>
<li>l&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Lists the user&rsquo;s crontab</li>
<li>d&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Deletes the user&rsquo;s crontab</li>
<li>i&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Prompts before deleting the user&rsquo;s crontab.&nbsp; &nbsp;</li>
</ul>
Before you start using the crontab command, however, you should look over the format it uses so you understand how to create and edit cron jobs. Each user has her own crontab file in /var/spool/cron, based on the username of each user. Any &ldquo;allow&rdquo; actions taken by the cron service are logged to /var/log/cron. &nbsp;
<h3>To view the /etc/crontab file t understand its syntax:</h3>
&nbsp; <img class="alignnone wp-image-5343" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/11/660-460x275.png" alt="Automation jobs" width="561" height="335" /> &nbsp;
Examples:
# Crontab &nbsp;&ndash;e
*/01&nbsp;&nbsp;&nbsp; *&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; *&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; *&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; *&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; date
*/30&nbsp;&nbsp;&nbsp; 11&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; *&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; *&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; *&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; cp file1 file2
45&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 10,22&nbsp;&nbsp; 03&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; *&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; *&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /bin/echo&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &ldquo;Hello world&rdquo;
50&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 22&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 01,11&nbsp;&nbsp; 10&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; *&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; logname
59&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 23&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 31&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 12&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; *&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /bin/echo&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &ldquo;Happy New Year&rdquo; */01&nbsp;&nbsp;&nbsp; *&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; *&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; *&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 0,6&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /bin/echo&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &ldquo;Today is weekend&rdquo; : wq !
To check assigned cronjobs:
# crontab &ndash;l
<h3>To check the cronjob service:</h3>
# service crond status
<h3>Restart the cron service:</h3>
#Service crond restart #Chkconfig crond on
<h3>To set up user 01&rsquo;s crontab:</h3>
#corntab &ndash;u&nbsp; user01&nbsp; -e *&nbsp;&nbsp;&nbsp;&nbsp; *&nbsp;&nbsp;&nbsp;&nbsp; *&nbsp;&nbsp;&nbsp;&nbsp; *&nbsp;&nbsp;&nbsp;&nbsp; *&nbsp;&nbsp; /tmp/sample_script :wq!
<h3>To remove a user&rsquo;s crontab jobs:</h3>
#crontab&nbsp; -U user01&nbsp;&nbsp;&nbsp; -r
<h3>You can verify the log file:</h3>
# tail /var/log/cron *&nbsp; 
Note: What do you think happens if you set up cron jobs to run during the night (say, to run some reports) and you shut down the system right before you go home? Well, it runs out that there is another great feature of cron. The /etc/anacrontab file defines fobs that should be run every time the system is started. If your system is turned off during the time that a cron job should have run, when the system boots again, the cron service will call/etc/anacrontab to make sure that all missed cron jobs are run.
<h3>Let&rsquo;s look at the /etc/anacrontab file:</h3>
# cat / etc/anacrontab
<h3>Control access to the cron service:</h3>
<ul>
<li>To start working with cron, first need to know at the two config files that control access to the cron service:</li>
<li>These two files are</li>
</ul>
/etc/cron.allow. /etc/cron.deny.
<h3>The /etc/cron.allow file:</h3>
If it exists, only these users are allowed (cron.deny is ignored)
If it doesn&rsquo;t exist, all users except cron. Deny is permitted.
<h3>The /etccron.deny file:</h3>
If it exists and is empty, all users are allowed (red hat default)
<h3>For both files:</h3>
If neither file exists, root only.
<h2>For an in-depth understanding of Linux click on</h2>
<ul>
<li class="title"><a class="current-page" title="Features of UNIX/LINUX" href="https://tekslate.com/features-unixlinux/" target="_blank" rel="noopener">Features of UNIX/LINUX</a></li>
<li class="title"><a class="current-page" title="Architecture of O/S" href="https://tekslate.com/architecture-os/" target="_blank" rel="noopener">Architecture of O/S</a></li>
<li class="title"><a class="current-page" title="UNIX Introduction" href="https://tekslate.com/unix-introduction/" target="_blank" rel="noopener">UNIX Introduction</a></li>
<li class="title"><a class="current-page" title="Basic commands" href="https://tekslate.com/basic-commands-unix/" target="_blank" rel="noopener">Basic commands</a></li>
<li class="title"><a class="current-page" title="User Administration" href="https://tekslate.com/user-administration-linux/" target="_blank" rel="noopener">User Administration</a></li>
</ul>

Scheduling Jobs in Linux

Automation Jobs

job-scheduling-linux

&nbsp;
<h2>User Administration in Linux</h2>
<ul>
<li>User is nothing but an individual who uses the available Hardware &amp; Software resources</li>
<li>In Red hat Linux, there are three different types of users.</li>
</ul>
<h3>Superuser (or) root user: </h3>
--&gt;The root user account is the equivalent of the administrator (or) Enterprise admin account in the windows world.
<ul>
<li>It is the most powerful account on the system and has access to everything.</li>
</ul>
<h3>System users: </h3>
---&gt; A system account is similar to a normal user account. The main difference is that system users normally don&rsquo;t have a home directory and can&rsquo;t log in the way normal users do
<ul>
<li>May system users are created or associated with applications or services to help run them more securely.</li>
<li>For example, if we install Apache it will create as user apache. These kinds of users are known as system users.</li>
</ul>
<h3>Normal user&rsquo;s: </h3>
---&gt; Normal users are the users created by the root user. They are normal users like &nbsp;&nbsp;Rahul, &nbsp;sara, Raju----- etc.
<ul>
<li>Normal user accounts have no write access to anything on the system except their home directory (they can reed and explore much of the system, however), which is created when the user account is added</li>
<li>As an Administrator, you can assign access rights to different files &amp; directories, allowing your users to gain access to different areas of the system (outside their home directory).</li>
</ul>
<h3>Some important points related to user administration:</h3>
<ul>
<li>Users &amp; Groups are used to control access to files and resources.</li>
<li>Users login to the system by supplying their username &amp; password</li>
<li>Every file on the system is owned by a user and associated with a group.</li>
<li>Every process has an owner and group affiliation, and can only access the resources owner or group can access.</li>
<li>Every user of the system is assigned a unique user ID number.</li>
<li>Users name and UID are stored in /etc/ passwd.</li>
<li>Users password is stored in /etc/shadow in encrypted form</li>
<li>Users are assigned a home directory and a program that is run when they login (usually a shell).</li>
<li>Users can&rsquo;t read, write, or Execute each other&rsquo;s files without permission.</li>
</ul>
<h3>Types of users in Linux &amp; their attributes:- &nbsp;</h3>
<table style="width: 656px; height: 173px;" border="1" cellspacing="1" cellpadding="1">
<tbody>
<tr>
<td>Type</td>
<td>Example</td>
<td>UID</td>
<td>GID</td>
<td>Home Directory</td>
</tr>
<tr>
<td>Superuser</td>
<td>Root</td>
<td>ʘ</td>
<td>ʘ</td>
<td>/root</td>
</tr>
<tr>
<td>System user</td>
<td>ftp, ssh, nobody</td>
<td>1-499</td>
<td>1-499</td>
<td>/var/ftp</td>
</tr>
<tr>
<td>Normal user</td>
<td>Visitor, sara</td>
<td>500-60,000</td>
<td>500-60,000</td>
<td>/home/user</td>
</tr>
</tbody>
</table>
<h3>Whenever a user is created in Linux things created by default: </h3>
<ul>
<li>A home directory is created (/home/username)</li>
<li>A mailbox is created (/var/spool mail)</li>
<li>Unique UID &amp; GID are given to user.</li>
</ul>
<h2>User private Group(UPG):- </h2>
In Red Hat, Linux uses user private Group (UPG) schema. According to the UPG scheme, you create any user account, the user consists of the primary group with the same name and same ID.
---&gt;&nbsp;For Example if a user is created with the name Raju, then a primary group of that user will be raju only. &nbsp;
<h3>The user information maintained by the two database files: </h3>
(a) &nbsp;&nbsp;/etc/passwd: &agrave; This file maintains user-related information. Syn: &nbsp;&lt;username&gt; : &lt;password&gt; :&lt;UID&gt;: &lt;GID&gt; : &lt;comments&gt; : &lt;Homedir&gt; : &lt;shell&gt;
(b)&nbsp; /etc/shadow: &agrave; This file maintains user-related password information
Syn: &lt;username&gt; : &lt;encrypted password&gt; : &lt;last passwd change&gt; : &lt;min&gt;: &lt;max&gt; : &lt;warn&gt; : &lt;inactive&gt; : expires&gt; : &lt;not used&gt;
<h3>Complexity Requirements of password in linux:-</h3>
A root user can change the password of self and any user in the system, there are no rules for root to assign a password. The root can assign any length of password either long or short, it can be an alphabet or numeric or both, on the whole, there is no limitation for root for assigning a password.
A normal user can change only its password. A valid password for a normal user should add here to the following rules.
<ul>
<li>It should be at least 7 characters but not more than 255 characters</li>
<li>At least one character should be upper case.</li>
<li>At least one character should be lower case.</li>
<li>At least one character should be a symbol and number.</li>
<li>It should not match the previous password</li>
<li>The login name and the password can&rsquo;t be the same.</li>
</ul>
<h3>User Administration </h3>
To manage user accounts, you can use the following Linux commands 
User add:- create user (or) system accounts.
Syn: Useradd [options] LOGIN
Options:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
<ul>
<li>U &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; userid</li>
<li>c&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; comment</li>
<li>e&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Expire &ndash;Date</li>
<li>s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; SHELL</li>
<li>r&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Creates a system account</li>
<li>d&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Home directory</li>
<li>g&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; primary group id</li>
<li>G&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Secondary group id</li>
</ul>
 Ex: Create a user in linux
#useradd raju
<ul>
<li>
<h3>To check the user you just created </h3>
</li>
</ul>
# cat /etc/passwd/grep raju
<ul>
<li>
<h3>Let&rsquo;s create a user with our own attributes</h3>
</li>
</ul>
# useradd &ndash;u 555 &ndash;c &ldquo;linux user&rdquo;&nbsp; -d /opt/india &ndash;s /bin/sh india
<ul>
<li>
<h3>To check the user:</h3>
</li>
</ul>
#cat/etc passwd/ grep india
Tip:- As a good practice, you should provide a label or some description for each account; otherwise, after time, you will forget what it is for.
 User mod:- Modifies user accounts.
Syn: User mod [options] LOGIN
Note:- All the options which are used with the user add command can be used and,
<ul>
<li>l To change the login name</li>
<li>L To Lock account</li>
<li>U To unlock the account</li>
</ul>
Ex: &agrave; Changing the name of the user
#usermod &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -l newname oldname
<ul>
<li>To lock the user account</li>
</ul>
# Usermod&nbsp; &nbsp;&nbsp;&nbsp; -L Username
<ul>
<li>To unlock the user account</li>
</ul>
#usermod &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -U username
Note: &nbsp;When an account is locked it will show! (Exclamation mark) in /etc/shadow file.
 Userdel: &nbsp;Removes a user or system account.
Syn: &nbsp;Userdel [options] LOGIN
<ul>
<li>f &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; forces deletion of the user even if he&rsquo;s still logged in.</li>
<li>r&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Removes the user&rsquo;s home directory and mail spool.</li>
</ul>
Ex: #userdel username
<blockquote>
Inclined to build a profession as Linux Developer? Then here is the blog post on, explore <a title="Linux Training" href="linux-training" target="_blank" rel="noopener">Linux Training</a>
</blockquote>
Passwd: Sets a password or resets a password for a user account
Syn: passwd [options] [LOGIN] -l &agrave; Locks a user&rsquo;s account -u &agrave; Unlocks a user&rsquo;s account
Ex: #passwd raju
<ul>
<li>Let&rsquo;s look at how the password files work</li>
</ul>
#cat/etc/shadow/grep raju
<h3>Chage: </h3>
Enables you to modify the parameters surrounding passwords (complexity, age, expiration)
Syn: Chage [options] user
<ul>
<li>d &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Indicates the day the password was last changed.</li>
<li>E&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Sets the account expiration date</li>
<li>I&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; change the password in an inactive state after the account expires.</li>
<li>l&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; shows the account of aging information.</li>
<li>m&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; sets the minimum number of days between password Change</li>
<li>M&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Sets the maximum number of days a password is valid.</li>
<li>W&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Sets the number of days to warn before the password expires.</li>
</ul>
Ex: Find the user&rsquo;s password information #chage &ndash;l user
<ul>
<li>Sets user account to expire in one week</li>
</ul>
#chage &ndash;E 2013-03-28 raju &nbsp;
PWCK: verifies the consistency of passwords across database files.
<ul>
<li>When you create or delete users, sometimes things don&rsquo;t always work out properly. This can cause the password file to become inconsistent you can use the pwck command to verify the consistency between the /etc/passwd &amp; /etc/shadow file</li>
</ul>
#pwck
<h2>For an in-depth understanding of Linux click on</h2>
<ul>
<li class="title"><a class="current-page" title="Features of UNIX/LINUX" href="http://tekslate.com/features-unixlinux/" target="_blank" rel="noopener">Features of UNIX/LINUX</a></li>
<li class="title"><a class="current-page" title="Architecture of O/S" href="http://tekslate.com/architecture-os/" target="_blank" rel="noopener">Architecture of O/S</a></li>
<li class="title"><a class="current-page" title="UNIX Introduction" href="http://tekslate.com/unix-introduction/" target="_blank" rel="noopener">UNIX Introduction</a></li>
<li class="title"><a class="current-page" title="Basic commands" href="http://tekslate.com/basic-commands-unix/" target="_blank" rel="noopener">Basic commands</a></li>
<li class="title"><a class="current-page" title="User Administration" href="http://tekslate.com/user-administration-linux/" target="_blank" rel="noopener">User Administration</a></li>
</ul>

User Administration in Linux

User Administration

user-administration-linux

&nbsp;
<h2>Group Administration in Linux</h2>
The group is nothing but a collection of users using which one can reduce the administration task in the o/s environment. Groups are divided into two types.
(a)&nbsp; primary group:- It is a group in which a user initially belongs in this group the user can access the resource with default permissions.
(b) Secondary group:- Apart from primary, if a user has an account in the other group i.e then it is called a secondary group to the user. ---&gt;&nbsp; The group information is maintained by the two database files.
(i) &nbsp;/etc/group: This file maintains group related information.
Syn: &lt;group name&gt;: &lt;password placeholder&gt; : &lt;GID&gt; : &lt;members&gt;
(ii) /etc/gshadow: This file maintains group password related information.
Syn: &lt;group name&gt; : &lt;password placeholder&gt;: &lt;group admin&gt; : &lt;members&gt; &nbsp;&nbsp;
 Groupadd: Creates a group
Syn: groupadd [options] group name
r&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; creates a system group
g&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; groupid
Ex:&nbsp;---&gt;&nbsp;Let&rsquo;s create a group called sales #groupadd sales
<ul>
<li>To verify the group:</li>
</ul>
#cat/etc/group/grep sales
<ul>
<li>To add the user:</li>
</ul>
#usermod &ndash;G sales user1 #cat/etc/group/grep sales
---&gt;&nbsp;To add another user to the sales group
#usermod&nbsp; -G sales user2
<ul>
<li>Now if you verify, you should see two user accounts in the last field:</li>
</ul>
#cat/etc/group/grep sales
<ul>
<li>Another way you can verify what groups a user belongs to is to user</li>
</ul>
Syn: id [options] [username]
G &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; shows the GID
n&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; shows the name instead of the ID
u&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; shows the UID
 Ex: #id &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -Gn user1
<ul>
<li>If the ID command is called without any options, you can also see what UID &amp; GID the user has: # id user1</li>
</ul>
Groupmod: Modifies the properties of a group
 Syn: &nbsp;groupmod [options] groupname
g&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; groupid
n&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; newgroupname
<h4>---&gt;&nbsp;To change the groupid: </h4>
# groupmod &ndash;g 888 sales
<h4> ---&gt;&nbsp;To change groupname:</h4>
#groupmod &nbsp;&nbsp;&nbsp; -n &lt;new-name&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;Existing name&gt;
<h3> G passwd:</h3>
<ul>
<li>Assign the password to the group:</li>
</ul>
#gpasswd &lt;groupname&gt;
<ul>
<li>Adding and Removing Members t a Group:</li>
</ul>
Syn: g passwd [options] &lt;arguments&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;groupname&gt; &nbsp;
<table style="width: 531px; height: 145px;" border="1" cellspacing="1" cellpadding="1">
<tbody>
<tr>
<td>-a</td>
<td>Add a single user</td>
</tr>
<tr>
<td>-M</td>
<td>Add multiple users</td>
</tr>
<tr>
<td>-A</td>
<td>Group Administrator</td>
</tr>
<tr>
<td>-d</td>
<td>Removing a user from a group</td>
</tr>
</tbody>
</table>
Ex:&nbsp;#g passwd &ndash;a user1 sales #g passwd &ndash;M user2, user3, user4 color #g passwd &ndash;A user3 &nbsp; color
Groupdel:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Deletes a group
<ul>
<li>To removes a group:</li>
</ul>
#groupdel&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;groupname&gt;
Note: &nbsp;
If the group has empty (or) secondary users you can delete the group. In case the group maintains a single primary user, then you can&rsquo;t delete the group account.
<h3> Switching Accounts: </h3>
Su: Enables you to run a command as another user or switch user accounts.
<ul>
<li>To switch accounts, use this command:</li>
</ul>
#SU&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; user1
<ul>
<li>You can also login as the root user using the su command:</li>
</ul>
#su-root
* Tip:- &nbsp;You can log in to the root user account using the SU command with no parameters. So what is the difference between using su and su the su command mover you into the root user&rsquo;s account without initializing any of the root&rsquo;s path or shell variables? When you use su -, everything is initialized as if you were logging in from the console.
<h3>User Account Initialization: &nbsp;</h3>
When a user is created, everything from the /etc/skel directory is copied to the user&rsquo;s newly created home directory (usually /home/ &lt;username&gt;).
<ul>
<li>You can modify these &ldquo;skeleton&rdquo; files or can add your own custom files. The benefit here is that user creation becomes standardized, ensuring that policies are adhered to. The customizable files are broken down into two different sections:</li>
</ul>
(a) User-specific files: &agrave; After a user is created and his home directory is populated, that user can now customize those files to fit his own personal needs.
<ul>
<li>Bashrc Defines functions and aliases</li>
<li>Bash_profile Sets environment variables</li>
<li>Bash_logout Defines any commands that should be executed before the users log out</li>
</ul>
(b) &nbsp;Global user configuration: /etc/bashrc&nbsp;&nbsp;&nbsp;&nbsp; Defines functions an aliases /etc/profile&nbsp;&nbsp;&nbsp;&nbsp; sets environment variables /etc/profile.d&nbsp; specifies a directory that contains scripts that are called by the /etc/profile file.
<ul>
<li>One last file to look at is /etc/login.defs. This file control specifies relating to system-wide user logins and passwords.</li>
</ul>
#grep &nbsp; -˅&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ˄#&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /etc/login.defs (or) #cat /etc/login.defs
<blockquote>
Inclined to build a profession as Linux Developer? Then here is the blog post on, explore <a title="Linux Training" href="linux-training" target="_blank" rel="noopener">Linux Training</a>
</blockquote>
<h3>Group collaboration:</h3>
Group collaboration is an essential part of any business and for any system administrator who deals with users. Here we look at three key features about file directory permissions;
(a) Setuid: This flag is used to allow multiuser access &agrave; For example if you have a script that generates reports for your company, but the script must be run as user1 to succeed, you can set the setuid bit to enable other users to run this command as though they were user1
<ul>
<li>Create a file to hold the report script:</li>
</ul>
#touch reporting- script
<ul>
<li>Set the setuid bit:</li>
</ul>
#chmod &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 4755 &nbsp;&nbsp; reporting-script
(or)
#chmod&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; U+S&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; reporting-script
<ul>
<li>Now view the permissions of the file:</li>
</ul>
#ls&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -l&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; reporting &ndash; script
<ul>
<li>In the file&rsquo;s owner permissions, notice that there is an &lsquo;s&rsquo; in place of the x. This shows that this file has the setuid flag set.</li>
</ul>
*Tip: &agrave; To find all setuid files: # find / -perm 4000
(b) Setgid: This flag is used to allow multi-group access. &agrave; which is similar to setuid but set at the group level instead. With this bit set, all users of the group can execute the file instead of just the user who owns it. The setgid bit allows users to collaborate on files.
Step 1:&nbsp; As root, create the directory:
# mkdir /tmp/oracle
Step 2: &nbsp;Create the group0 and add users to it.
# group add sales
# usermod &nbsp;&nbsp;&nbsp;&nbsp; -G &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; sales &nbsp;&nbsp; user1
# usermod&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -G&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; sales&nbsp;&nbsp;&nbsp; user2
Step 3: &nbsp;Assign the permissions for collaboration:
# chown &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; root: sales &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /tmp/oracle
#chmod&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 2770&nbsp;&nbsp;&nbsp; /tmp/oracle
Step 4: &nbsp;Verify&nbsp; # ls &nbsp;&nbsp;&nbsp;&nbsp; -ld&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /tmp/oracle
<ul>
<li>Now all members of the sales group can read/write to files within this folder. Also, notice that access to this folder is denied for anyone who isn&rsquo;t a member of the sales group.</li>
</ul>
(c) sticky bit: This flag prevents accidental delete by users &amp; groups
Step 1: Set the sticky bit on the /tmp directory:
# chmod&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 1777 /tmp
Step 2: Verify # ls &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -ld / tmp
<ul>
<li>For the sticky bit, there is a &lsquo;t&rsquo; on the end of the permissions listed. Now other users are not able to delete your files; only you can.</li>
<li>This feature might be helpful when you&rsquo;re sharing files and there are particular files you don&rsquo;t want other users to delete.</li>
</ul>
<h2>For an in-depth understanding of Linux click on</h2>
<ul>
<li class="title"><a class="current-page" title="Features of UNIX/LINUX" href="http://tekslate.com/features-unixlinux/" target="_blank" rel="noopener">Features of UNIX/LINUX</a></li>
<li class="title"><a class="current-page" title="Architecture of O/S" href="http://tekslate.com/architecture-os/" target="_blank" rel="noopener">Architecture of O/S</a></li>
<li class="title"><a class="current-page" title="UNIX Introduction" href="http://tekslate.com/unix-introduction/" target="_blank" rel="noopener">UNIX Introduction</a></li>
<li class="title"><a class="current-page" title="Basic commands" href="http://tekslate.com/basic-commands-unix/" target="_blank" rel="noopener">Basic commands</a></li>
<li class="title"><a class="current-page" title="User Administration" href="http://tekslate.com/user-administration-linux/" target="_blank" rel="noopener">User Administration</a></li>
</ul>

Group Administration in Linux

Group Administration

group-administration-in-linux

&nbsp;
<h2>Package Management in Linux</h2>
<ul>
<li>Software is the basis of any operating system, allowing you to install and use different utilities.</li>
<li>In<a href="https://www.linux.com/" target="_blank" rel="noopener"> linux,</a> the software is distributed through the use of packages, which contain the actual software files.</li>
<li>Each distribution of Linux has its own package management system. For <a href="https://www.redhat.com/en" target="_blank" rel="noopener">Red Hat</a>, there are two package management systems: RPM &amp; YUM.</li>
</ul>
<h3>Working with RPM: </h3>
<ul>
<li>RPM stands for (Red Hat Package Manager)</li>
<li>RPM is the default package installation tool in the Linux operating system.</li>
<li>By using RPM we can install, upgrade, Query, verify, and remove the packages.</li>
<li>Before diving into package management, let&rsquo;s look at the naming convention used by the system to describe packages. &nbsp;</li>
</ul>
<h2>Package parameters:</h2>
&nbsp; <img class="alignnone wp-image-5357" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/11/750.png" alt="Packaage parameters" width="438" height="175" />
<h3>Methods of Installation: </h3>
Two ways of Installations.
<ul>
<li>Standalone</li>
<li>Network</li>
</ul>
Standalone: In this type, we can install the packages through any removable media (or) through the dump.
<h2> Installing and Removing packages: </h2>
Syn: #rpm &lt;options&gt; &lt;pkg-name&gt;&nbsp; --force&nbsp; --aid
Options:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
I &nbsp;---&gt; install&nbsp;a given package
V ---&gt;&nbsp;verbose output
H ---&gt;&nbsp;&nbsp;Shows hash progress when installing
U ---&gt;&nbsp;Upgrades a given package
E ---&gt;&nbsp;Removes a given package
---force ---&gt;&nbsp;Install the package with forcefully
---aid &nbsp; &nbsp;---&gt;&nbsp; Install the package along with dependencies
---nodeps ---&gt;&nbsp;&nbsp;To erase an package without dependencies
<h3>Query options (with &ndash; q): </h3>
Syn: #rpm &lt;options&gt; &lt;kg-name&gt;
C &nbsp; &nbsp; &nbsp; ---&gt;&nbsp;Lists all config files.
D &nbsp; &nbsp; &nbsp; &nbsp;---&gt;&nbsp;lists all documentation files.
I &nbsp; &nbsp; &nbsp; ---&gt;Displays information about the package.
L &nbsp; &nbsp; ---&gt;Lists the files in a package.
S &nbsp; &nbsp; &nbsp;---&gt;status of the package.
<h3>Verify options (with-v):</h3>
-a &nbsp; ---&gt;&nbsp;Queries all packages
F &nbsp; ---&gt;&nbsp;displays information about the specified file.
---&gt;&nbsp;For installing an application. #rpm&nbsp; -ivh&nbsp; nano -2.2.6-1.x86_64.rpm
<ul>
<li>For installing an application with forcefully</li>
</ul>
# rpm&nbsp; -ivh nano-2.2.6-1.x86_64.rpm&nbsp; --force
<ul>
<li>If you want to upgrade this package (because you know that it is already installed), you can substitute the &ndash;I option for &ndash;U</li>
</ul>
#rpm&nbsp; - Uvh nano -2.2.6-1.x86_64.rpm
<ul>
<li>For uninstalling a package</li>
</ul>
# rpm&nbsp; -e nano
<ul>
<li>You can always reinstall the package at a later date if you keep the .rpm file on your system</li>
</ul>
#rpm&nbsp; - ivh&nbsp;&nbsp; -replace pkgs nano -2.26-1 .x86_64.rpm
Tip: A common situation to run into on the job is having to install a package that is already installed. You don&rsquo;t have to go through the trouble of uninstalling the package first only to reinstall it. You can use the &ndash;replace pkg option alongside the regular install options to override an existing installation.
<ul>
<li>Query the install&rsquo;ed system package for nano:</li>
</ul>
#rpm&nbsp; -qa&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /&nbsp; grep nano
<ul>
<li>Query the information from the nano package:</li>
</ul>
#rpm&nbsp; -qi nano
<ul>
<li>Suppose you are looking around on your new Red Hat installation and a file but aren&rsquo;t sure what it does. You can use the &ndash;f option to query the package that the file belongs to, possibly giving you a better idea of what that file might be sued for.</li>
<li>Find out where the /etc/syslog. Cong file came from by doing the following</li>
</ul>
#rpm&nbsp;&nbsp; -qf /etc/syslog.comf
<ul>
<li>Use the -c option to find all config files</li>
</ul>
#rpm &nbsp; -qd rsyslog
<ul>
<li>To find the documentation files for a given package.</li>
</ul>
#rpm &nbsp; -qd rsyslog
<ul>
<li>To the listing all files that come with the package.</li>
</ul>
#rpm&nbsp; -q1&nbsp; rsyslog
<ul>
<li>To find out whether a package has any dependencies:</li>
</ul>
#rpm&nbsp; -qr rsyslog
<blockquote>
Inclined to build a profession as Linux Developer? Then here is the blog post on, explore <a title="Linux Training" href="linux-training" target="_blank" rel="noopener">Linux Training</a>
</blockquote>
<h2>Network installation:</h2>
In this level, we can install the package from the server through NFS (or) FTP services.
NFS Service:
<ul>
<li>First, check the communication.</li>
</ul>
#ping 192.168.0.254
<ul>
<li>For accessing the data shared from the server</li>
</ul>
#Mount 192.168.0.254:/var/ftp/pub/server/mnt #cd&nbsp;&nbsp; /mnt #rpm &ndash;ivh vsftpd*&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; --force&nbsp;&nbsp;&nbsp; --aid
FTP Service: In this method to install the package the ftp server should have the dump of o/s under the ftp default sharable location
<ul>
<li>First, check the communication</li>
</ul>
# ping 192/168.0.254
<ul>
<li>For accessing the data shared from the server.</li>
</ul>
#rpm&nbsp; -ivh <a href="ftp://192.168.0.254/pub/server/&lt;pkg-name" target="_blank" rel="noopener">ftp://192.168.0.254/pub/server/&lt;pkg-name</a>&gt;&nbsp;&nbsp; --force --aid
<h3>Working with YUM:</h3>
<ul>
<li>YUM stands for a yellow dog update modifier.</li>
<li>In this section, we look at the same tasks, except this time we use the more flexible yum utility.</li>
<li>The yum command has access to repositories where tons of packages are kept and can install, upgrade, or remove them for you automatically.</li>
<li>Yum also takes care of resolving and installing any dependencies for you, which the rpm command can&rsquo;t do.</li>
<li>Yum is an interactive tool that waits for the confirmation of a user.</li>
<li>Yum is a default package management tool in Red Hat o/s.</li>
<li>Using this tool we can install the required packages</li>
<li>With dependencies.</li>
</ul>
Syn: &nbsp;Yum &lt;options&gt; &lt;command&gt; &lt;package name&gt;
Options: &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
c &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; --&gt;&nbsp;&nbsp; specifies the location of the config file
q &nbsp; &nbsp; &nbsp; &nbsp; --&gt;&nbsp;&nbsp;&nbsp;specifies quit, no output
y &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; --&gt;&nbsp;&nbsp; to always answer yes to prompts.
V &nbsp; &nbsp; &nbsp; --&gt;&nbsp;&nbsp;&nbsp;provides verbose output.
<h3>Commands:</h3>
Clean &nbsp; --&gt;&nbsp;&nbsp;&nbsp;Removes cached data.
Erase &nbsp; --&gt;&nbsp;&nbsp;&nbsp;Removes a package from the system.
List &nbsp; &nbsp; &nbsp; --&gt;&nbsp;&nbsp; Displays available packages
Install &nbsp; --&gt;&nbsp;&nbsp; Install a package on the system.
Search --&gt;&nbsp;&nbsp;&nbsp;Enables you to search for a package.
Update --&gt;&nbsp;&nbsp; Updates a package.
Group list &nbsp; &nbsp; &nbsp; --&gt;&nbsp;&nbsp;Displays available packages groups.
Group installs --&gt;&nbsp;&nbsp; Install packages with in a group.
Group remove --&gt;&nbsp;&nbsp;Removes a packages with in a group
<h3>YUM Server configuration:</h3>
<ul>
<li>Mount the dvd</li>
</ul>
#mount/dev/dvd/mnt
<ul>
<li>Install RPM package (vsftpd)</li>
</ul>
#rpm &ndash; ivh vsftpd*&nbsp; --force &ndash;aid
<ul>
<li>Copy the dump of o/s into the default sharable location ftp.</li>
</ul>
#cp &ndash;rvf /mnt/*&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /var/ftp/pub *&agrave; means all the data under the mount point&nbsp; /mnt.
<ul>
<li>Install the create repo package:</li>
</ul>
#rpm&nbsp; -ivh&nbsp; create repo*&nbsp;&nbsp;&nbsp; ---force&nbsp;&nbsp; --aid &nbsp; &nbsp;
<h3>Create the new repository:</h3>
#create repo&nbsp; -g&nbsp; /var/ftp/pub/server/repo data/comps-rhel5-server-core.xml/ var/ftp/pub
Note: &nbsp;If any errors are showing then remove #rm&nbsp; - fr&nbsp; /var/ftp/pub/repo data
<h3>Open the YUM configuration file:</h3>
#vim /etc/yum.repos.d/linux.repo
<ol>
<li>[linux]</li>
<li>name=yum server</li>
<li>base url = ftp: //192.168.0.254/pub</li>
<li>enable = 1</li>
<li>gpgcheck = 0</li>
</ol>
:wq!
<ul>
<li>Restart the ftp service</li>
</ul>
# service vsftpd restart # yum&nbsp; clean all
<ul>
<li>To list out packages</li>
</ul>
#yum list
<ul>
<li>To install the package</li>
</ul>
# yum install postfix&nbsp; -Y
<ul>
<li>You could also update the postfix package</li>
</ul>
#yum update postfix -y
<ul>
<li>To remove the package</li>
</ul>
#yum remove postfix &nbsp;
Note: One great feature about yum is that instead of updating a single package, you can list all updates that need to be installed for the system. #yum list updates
<ul>
<li>From this list, you can choose to update packages individually or as a whole. If you cant to install all the updates</li>
</ul>
#yum update
<ul>
<li>To get a listing of all available &ldquo;groups&rdquo;,</li>
</ul>
#yum group list
<ul>
<li>You can then install that &ldquo;groups&rdquo;:</li>
</ul>
#yum group installs &ldquo;Development Tools&rdquo;
 Note: Don&rsquo;t forget that Linux doesn&rsquo;t handle whitespace the way that windows do. If you specify a group name, you need to enclose it in quotation marks(&ldquo;&nbsp; &ldquo; ).
<h2> Searching for packages:</h2>
<ul>
<li>Find the postfix package to install:</li>
</ul>
#yum search postfix
<ul>
<li>To find out more information about the postfix package:</li>
</ul>
#yum info postfix ---&gt;&nbsp;&nbsp;To flush the cache, do the following #yum clean all
<h3>Configuring Additional Repositories:</h3>
<ul>
<li>Sometimes you might want to install a package that isn&rsquo;t in the repositories that come preconfigured with Red Hat. If the package is available in someone else&rsquo;s repository, you can add that person&rsquo;s repository to your yum config file.</li>
<li>You can either add your own custom repositories to the main config file /etc/yum.conf (or) create a .repo file in the /etc/yum. Repos.d directory which will be added automatically. Here is what a sample entry for a custom repository looks like:</li>
</ul>
[Unique title]
Name&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; = my custom yum repository.
Base url &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; = <a href="ftp://192.162.0.250/opt/yum/myrepos" target="_blank" rel="noopener">ftp://192.162.0.250/opt/yum/myrepos</a>
Enabled&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =1
Gpgcheck&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =0
:wq!
<ul>
<li>One neat trick that you can do is to create a repository based on an ISO</li>
<li>This trick can be useful in an environment whether there is no Internet access and you&rsquo;d like to install packages from the Red Hat</li>
</ul>
Step 1: Create a folder for the temporary mount: &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; # mkdir&nbsp; /mnt/cd
Step 2: &nbsp;Mount the ISO image (or) cd: &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; # mount&nbsp; -o loop /dev/cdrom / mnt/cd
Note:&nbsp; ---&gt;&nbsp;To create a ISO image.
#dd if =/dev/scdʘ &nbsp;&nbsp;&nbsp;&nbsp; of = /os/rhe/5.iso
To check it which device is mount &nbsp;
<ul>
<li>Read the image file</li>
</ul>
#mount &ndash;o loop&nbsp; /OS/Rhel5.iso&nbsp;&nbsp; /DVD
Step 3: &nbsp;Create a repository in the temporary directory:
# cd&nbsp; / mnt
#createrepo.
This creates an XML file of all the packages from the mounted CD.
 Step 4: &nbsp;&nbsp;You also need to clean the current repository cache:
#yum clean all &nbsp;
Step 5:&nbsp; Create a .repo file for your temporary repository:
#vim /etc/yum.repos.d/sio.repo
[ISO Repo]
Name = My Repository
Base url =file:///mnt/cd
Enabled=1
Gpgcheck=0
:wq!
<h3>Adding your custom packages:</h3>
<ul>
<li>Just as you have already created two different types of custom repositories, you can add packages you have created to them as well.</li>
</ul>
Step 1:&nbsp; copy the file over to your private directory
#cp&nbsp; /usr/src/redhat/RPMS/x86_64/mysample &ndash; 1.0-0.x86_64.rpm
/opt/yum/myrepos
Step 2: Update the repository to recognize your new package:
#createrepo&nbsp; - update
<ul>
<li>Now you should be able to search for your package in your private repository along with other software</li>
</ul>
<h3>Registering your system: </h3>
<ul>
<li>To register your system to the Red Hat Network, you must have an active subscription with Red Hat.</li>
<li>You can register during the installation of your system or manually after the system has already been installed. Use the &lsquo;rhn_register&rsquo; command to begin the registration process. After you finish, you can visit <a href="http://rhn.redhat.com" target="_blank" rel="noopener">http://rhn.redhat.com</a> to start managing your system(s) through the web. You need to make sure that the rhnsd daemon is running for it to be managed.</li>
</ul>
 Step1: &nbsp;Set the daemon to boot on system start
# chkconfig rhnsd on
Step2: You should verify whether the service is currently running
#service rhnsd status
Step3: If it is, you are all set: otherwise, start the service manually:
# service rhnsd start
<h2>For an in-depth understanding of Linux click on</h2>
<ul>
<li class="title"><a class="current-page" title="Features of UNIX/LINUX" href="http://tekslate.com/features-unixlinux/" target="_blank" rel="noopener">Features of UNIX/LINUX</a></li>
<li class="title"><a class="current-page" title="Architecture of O/S" href="http://tekslate.com/architecture-os/" target="_blank" rel="noopener">Architecture of O/S</a></li>
<li class="title"><a class="current-page" title="UNIX Introduction" href="http://tekslate.com/unix-introduction/" target="_blank" rel="noopener">UNIX Introduction</a></li>
<li class="title"><a class="current-page" title="Basic commands" href="http://tekslate.com/basic-commands-unix/" target="_blank" rel="noopener">Basic commands</a></li>
<li class="title"><a class="current-page" title="User Administration" href="http://tekslate.com/user-administration-linux/" target="_blank" rel="noopener">User Administration</a></li>
</ul>

Package Management in Linux

Package Management

package-management-in-linux

&nbsp;
<h2>Linux Kernel</h2>
<ul>
<li>The heart of <a href="https://www.redhat.com/en" target="_blank" rel="noopener">Red Hat</a> is the Linux kernel. The kernel is responsible for interacting with the hardware and producing output to the screen. There is also a virtual file system that gets created in the /proc directory to hold information and parameters for the kernel.</li>
<li>Linux is truly just the kernel. Red Hat and the other distributions in existence today are software and configuration files packaged with the <a href="https://www.linux.com/" target="_blank" rel="noopener">linux kernel</a> to bring you an entire operating system. Because the kernel is really what runs everything, understanding how it works is essential.</li>
<li>The Kernel can be used to load new drivers, support new hardware, or even offer a custom kernel for individual needs.</li>
<li>The Linux Kernel is modular, and because of this, you can load and unload kernel modules even after the system has booted.</li>
<li>Let&rsquo;s start with the uname command to find out some info, about the kernel. &nbsp;</li>
</ul>
Uname: Displays information about the Kernel.
Syn: Uname [option]
<ul>
<li>a------&gt;prints all information relating to the kernel</li>
<li>s------&gt;show the kernel name</li>
<li>r------&gt;requests kernel release information</li>
<li>v------&gt;requests the kernel version.</li>
</ul>
------&gt;&nbsp;Let&rsquo;s check &amp;see which version of the kernel is currently running:
#uname&nbsp; -a
Linux root 2.6.32.71.e16.x86_64&hellip; &nbsp;
Note: &nbsp;The kernel version numbering is important here.
<ul>
<li>The first number is the major version of the kernel. The second number is the major release of the first number.</li>
<li>If the release number is even, which it is (6),&nbsp; it means that this is a stable release of the kernel. Odd numbers are development kernels and should not be used for production systems.</li>
<li>The third number is the patch version of the kernel.</li>
<li>The last number (710 is added by Red Hat to represent its release version of the kernel. Also note the el6, which tells you that you are running Red Hat Enter price Linux6. If you couldn&rsquo;t tell, this is an x64 &ndash; bit version of the operating system.</li>
<li>To get the version of the currently installed kernel:</li>
</ul>
#rpm&nbsp; -qa /grep kernel
<ul>
<li>You could also use the following:</li>
</ul>
#rpm&nbsp; - q kernel
<ul>
<li>When it comes to working with kernels, you should be familiar with different locations. Let&rsquo;s look at four of these locations:</li>
</ul>
/boot&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; : the place where the kernel and boot files are kept
/proc&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; :&nbsp; Current hardware configuration &amp; status.
/usr/src&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; : Source code of the kernel.
/lib/modules&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; : Kernel modules.
Lsmod: Lists currently loaded kernel modules
Syn: Lsmod
<ul>
<li>To look at what is currently loaded by the kernel since you booted the system, you use the following command:</li>
</ul>
#lsmod
<table style="width: 544px; height: 196px;" border="1" cellspacing="1" cellpadding="1">
<tbody>
<tr>
<td>Module &nbsp;</td>
<td>Site</td>
<td>Used by</td>
</tr>
<tr>
<td>&nbsp;Autofs4</td>
<td>29253</td>
<td>3</td>
</tr>
<tr>
<td>Hidp</td>
<td>23105</td>
<td>2</td>
</tr>
<tr>
<td>Rfcomm</td>
<td>42457</td>
<td>0</td>
</tr>
<tr>
<td>L2cap</td>
<td>29505</td>
<td>1ʘ hidp, rfcomm</td>
</tr>
<tr>
<td>Ext4</td>
<td>353979</td>
<td>2</td>
</tr>
</tbody>
</table>
&nbsp; [output truncated]
<ul>
<li>The preceding output is truncated due to size.</li>
<li>Show the details of the ext4 kernel module listed previously:</li>
</ul>
Modinfo: Displays information about a kernel module
#modinfo&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ext4
#modinfo&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; cdrom &nbsp;
To find all the kernel Modules:
<ul>
<li>All the kernel modules will be residing in /etc/lib/modules directory.</li>
</ul>
# cd&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /etc/lid/modules # ls
<ul>
<li>To search all the kernel modules in the system using find cmd:</li>
</ul>
#find&nbsp; /&nbsp; -name&nbsp; *.ko&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; (Modules in the system will bending with&nbsp; .ok extension) &nbsp;
Mod probe: &nbsp;&agrave; To remove the loaded module Syn: &nbsp;modprobe &lt;modname&gt; #modprobe &ndash;r&nbsp; vfat
<ul>
<li>Now to check</li>
</ul>
#lsmod&nbsp; /grep&nbsp;&nbsp; -i&nbsp; vfat
<ul>
<li>To install / re-install a module:</li>
</ul>
#modprobe&nbsp; vfat
# lsmod&nbsp;&nbsp; / grep&nbsp; - i&nbsp; vfat &nbsp;
<h2>* Updating the kernel:</h2>
<ul>
<li>View the current version of the kernel:</li>
</ul>
# uname&nbsp; - r
<ul>
<li>To view kernel package information</li>
</ul>
# yum inof kernel (or) #rpm&nbsp; - qi&nbsp;&nbsp; / grep kernel /
<ul>
<li>Using the package manager, you can upgrade the kernel to the latest version:</li>
</ul>
# yum update kernel&nbsp;&nbsp; - y (or) # rpm &ndash; ivh&nbsp; kernel -2.6.18-194.3.lel5 &nbsp;
* Note: &nbsp;when updating a kernel with the rpm command, never use the&nbsp; -U option to update. The reason behind this is that the update option erases the prior kernel when updating, whereas the &ndash;i option installs the newer kernel alongside the old kernel. If something doesn&rsquo;t work or goes wrong, you have an older kernel to revert to.
<blockquote>
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</blockquote>
<h3>Tuning the kernel with /proc/ sys:</h3>
<ul>
<li>The kernel has a virtual file system, / proc/ sys, that allows you to tune the kernel while the system is running.</li>
<li>The kernel creates the / proc/sys virtual file system when the system boots up, which holds all the parameters of the kernel. This virtual file system is used to manipulate kernel parameters for testing purposes (these changes are valid only until the system reboots).</li>
<li>When you have the kernel tuned the way you&rsquo;d like, you can simply have your settings applied when the system boots (through a special config file), or you can compile your own kernel to have them built-in permanently.</li>
<li>As you are testing kernel changes, make sure you don&rsquo;t rely on any settings made within the / proc / sys file system because they are erased when the system reboots. During testing, you can use the echo cmd to change the values of the kernel while the system is running.</li>
</ul>
 Step 1): View the current value in the kernel:
#cat / proc/sys/net/ipv4/ip-forward
Step 2): Change the kernel option that controls packet forwarding:
#echo 1 &gt; /proc/sys/net/ipv4/ip-forward
Step 3): Verify the value has changed:
#cat / proc/sys/net/ipv4/ip &ndash;forward
If you want the changes to be persistent across system reboots, you can put the parameters you&rsquo;d like to remain during boot in the letc/sysctl. conf file.
Sysctl: Enables you to tune kernel
Before you start tuning things, let&rsquo;s look at all the available options:
#sysctl -a
Now, let&rsquo;s make the same changes to the kernel as before.
Step 1): query the parameter responsible for forwarding packets within the kernel
#sysctl&nbsp; - / grep&nbsp;&nbsp; ip_forward
Step 2): Using sysctl&nbsp; to change the option:
#sysctl&nbsp;&nbsp; -w net.ipv4.ip-forward = 1
Enables you to change a setting in the sysctl config file.
Step 3): verify the value has been changed:
# Sysctl&nbsp;&nbsp; - a&nbsp; / grep&nbsp;&nbsp; ip &ndash; forward
Step 4): return the parameter to its original value:
#sysctl&nbsp; -w&nbsp;&nbsp; net.ipv4.ip-forward=ʘ
<h2> For an in-depth understanding of Linux click on</h2>
<ul>
<li class="title"><a class="current-page" title="Features of UNIX/LINUX" href="http://tekslate.com/features-unixlinux/" target="_blank" rel="noopener">Features of UNIX/LINUX</a></li>
<li class="title"><a class="current-page" title="Architecture of O/S" href="http://tekslate.com/architecture-os/" target="_blank" rel="noopener">Architecture of O/S</a></li>
<li class="title"><a class="current-page" title="UNIX Introduction" href="http://tekslate.com/unix-introduction/" target="_blank" rel="noopener">UNIX Introduction</a></li>
<li class="title"><a class="current-page" title="Basic commands" href="http://tekslate.com/basic-commands-unix/" target="_blank" rel="noopener">Basic commands</a></li>
<li class="title"><a class="current-page" title="User Administration" href="http://tekslate.com/user-administration-linux/" target="_blank" rel="noopener">User Administration</a></li>
</ul>
<div class="tags">&nbsp;</div>

Linux Kernel

The Kernel

linux-kernel

&nbsp;
<h2>Disk Partitioning in Linux</h2>
<ul>
<li>Disk partitioning is one of the many steps you must take when preparing a system for use.</li>
<li>Partitioning means to divide a single hard drive into many logical drives.</li>
<li>In each system, the physical disk drivers are divided up logically into partitions that allow you to store data on them.</li>
<li>There are also special types of partitions such as RAID that allow for increased performance, redundancy, or both. LVM, like RAID, is an advanced form of partitioning that eases the management of partitions and makes growing them for increased storage capacity simple.</li>
<li>One of the key points to remember when working with partitions is to always plan ahead &nbsp;</li>
</ul>
<h3>Disk partitioning criteria: &nbsp;</h3>
MBR &nbsp;-----&gt;&nbsp; Master Boot Record.
P &nbsp; &nbsp;-----&gt;&nbsp; &nbsp;primary partition
Extended &nbsp;-----&gt;&nbsp; &nbsp;Extended partition
L &nbsp;-----&gt;&nbsp; &nbsp;logical partition
Free &nbsp;-----&gt;&nbsp; Free space &nbsp;
<table>
<tbody>
<tr>
<td rowspan="2" width="31">MB R</td>
<td rowspan="2" width="44">P</td>
<td rowspan="2" width="39">P</td>
<td rowspan="2" width="41">P</td>
<td colspan="3" width="265">Extended</td>
</tr>
<tr>
<td width="61">L</td>
<td width="75">L</td>
<td width="129">FREE</td>
</tr>
</tbody>
</table>
&nbsp;
<ul>
<li>Every disk can have only 3 primary partitions</li>
<li>The primary partition is a partition which usually holds the operating system</li>
<li>The extended partition is a special type of primary partition which can be subdivided into multiple logical partitions</li>
<li>Logical partitions are the partitions which are created under extended partitions</li>
<li>As in the real world, it is the results that matter. It doesn&rsquo;t matter whether you use Disk Druid, fdisk, or parted to create partitions. You can create new partitions at the command line or use GUI front ends to these tools such as the Disk utility.</li>
<li>Remember Disk Druid is available only during the installation process.</li>
<li>You can use two different utilities when partitions disks:</li>
</ul>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; F disk -----&gt; Disk partitioning utility
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; parted -----&gt; Another Disk partitioning utility
<ul>
<li>While f disk is more common, it is slowly being replaced by part, which is more flexible.</li>
</ul>
<h2>Disk identification: </h2>
Different types of disks will be having different initials in Linux
IDE drive will be shown as /dev/had
SCSI/SATA drive will be shown as /dev/sda
the virtual drive will be shown as&nbsp; /dev/vda
Note:&nbsp; The first two letters represent whether the disk is a SCSI (sd) (or) IDE (hd) disk. The third letter represents which disk it actually is If there is a number after the three letters, it is the number of the partition
To view information about the current partition layout,
#cat /proc/partitions / grep hd For IDE
#cat /proc /partitions / grep sd&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; For SCSI / SATA
You need to view their current partitions to see if any exist.
Syn: fdik&nbsp; [options] [device] &nbsp;
Options: 
<ul>
<li>b -----&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; specifies the sector size of the disk</li>
<li>h -----&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; number of heads on the disk</li>
<li>l&nbsp;&nbsp;-----&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; lists current partition table. &nbsp;</li>
</ul>
Note: There are some limitations when it comes to working with partitions. You can have only four partitions to a physical disk with one exception. If you want to make more than the four, you need to create three primary partitions and one extended partition, although the primary partitions aren&rsquo;t required for extended partition,&nbsp; creation. The extended partition can then hold 11 logical partitions (5-16) on it. &nbsp;
<h2>Creating a partition: </h2>
Step 1):&nbsp; # f disk /dev/sda
Step 2): view all the options available to you
command (m for help): m
P-----&gt; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; print the partition table
n -----&gt;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;add a new partition
d -----&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; delete a partition
m -----&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; print this menu
q -----&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; quit without saving changes
t-----&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; change a partition&rsquo;s system-id
w -----&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Write the table to disk and exit
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<ul>
<li>Create a new partition</li>
</ul>
#f disk /dev/sad
:n
First Cylinder (1-1044, default 1 ) :
Using default value 1
Last cylinder or + size&nbsp; &hellip;&hellip;&hellip;..(1-1044,&hellip;&hellip;..) : + 500M
<ul>
<li>Create a second partition:n</li>
</ul>
---------------------
----------------------
----------------------
<ul>
<li>Verify newly created partitions</li>
</ul>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;:P
<ul>
<li>Write the changes to disk:</li>
</ul>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; w
<ul>
<li>Now that two new partitions have been created and written to disk, you should verify their existence. Before doing that, however, you want the kernel to reread the partition table to make sure that it recognizes all disks and partitions correctly. To do this, you use the part probe cmd.</li>
</ul>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Syn: part probe [options] [device]
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;a) d does not actually inform the operating system
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;b) s&nbsp; prints a summary of contents.
<ul>
<li>Now call the part probe command</li>
</ul>
&nbsp; &nbsp; &nbsp; &nbsp; #partprobe /dev/sda
<ul>
<li>Now that you have created partitions with the f disk utility, do it again using the parted command</li>
<li>Create a partition:</li>
</ul>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;#parted / dev/ sda
<ul>
<li>Menu (parted) help</li>
<li>Create your first partition in a similar manner to the fdisk</li>
</ul>
(parted) multipart
partition type? Primary/extended/ logical?
File system type? [ex:2]?
start?
End?
<ul>
<li>Make your second partition again</li>
<li>Before writing changes to disk, you should verify that they have been created the way you want them:</li>
</ul>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;(parted) print
<ul>
<li>Exit the program to save your changes</li>
</ul>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;(parted) quit
<ul>
<li>There are a few things you should notice here. First, you need to specify exactly where you want the start and end of the partition to be. If you don&rsquo;t plan this out ahead of time, you will end up with incorrect partition sizes. You should also take note of the fact that you don&rsquo;t have to write the changes to disk manually; this is done for you when you quit the parted program.</li>
<li>Again, you need to force the kernel to reread the partition table</li>
</ul>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;#part probe
<ul>
<li>Once again, verify that your partitions have been created successfully:</li>
</ul>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;#parted -l
<h3>Deleting a partition: </h3>
Deleting a partition is much easier than creating one because you need to specify only the partition number that you want to delete.
<ul>
<li>Start the f disk utility: # f disk / dev / sda</li>
</ul>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;:p-----&gt;&nbsp;&nbsp; printout the current partition
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;:d-----&gt;&nbsp;&nbsp;Delete a partition
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;:6-----&gt;&nbsp;&nbsp;want to delete 6th partition
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;:w -----&gt;&nbsp;&nbsp;write changes to disk
<ul>
<li>Don&rsquo;t forget to reread the partition table</li>
</ul>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;#part probe /dev/sda
<ul>
<li>Start the parted utility: #parted /dev/sad&nbsp;</li>
</ul>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;(parted) print
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;(parted) rm 5
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;(parted) quit
<h2>In-depth understanding of Linux click on</h2>
<ul>
<li class="title"><a class="current-page" title="Features of UNIX/LINUX" href="http://tekslate.com/features-unixlinux/" target="_blank" rel="noopener">Features of UNIX/LINUX</a></li>
<li class="title"><a class="current-page" title="Architecture of O/S" href="http://tekslate.com/architecture-os/" target="_blank" rel="noopener">Architecture of O/S</a></li>
<li class="title"><a class="current-page" title="UNIX Introduction" href="http://tekslate.com/unix-introduction/" target="_blank" rel="noopener">UNIX Introduction</a></li>
<li class="title"><a class="current-page" title="Basic commands" href="http://tekslate.com/basic-commands-unix/" target="_blank" rel="noopener">Basic commands</a></li>
<li class="title"><a class="current-page" title="User Administration" href="http://tekslate.com/user-administration-linux/" target="_blank" rel="noopener">User Administration</a></li>
</ul>

Disk Partitioning in Linux

Disks & partitioning

disks-partitioning-in-linux

Linux File System

file-system-linux-part-2

&nbsp;
<h2>Linux - System Initialization</h2>
<h3>Boot process: </h3>
Boot process consists of the set of processes from power on the PC to login prompt comes. When a computer boots up, the BIOS is the first program that is run. After it is loaded, the BIOS begins to test the system through the power on Self Test (POST) and then starts loading peripheral devices. The BIOS then looks for the boot device and passes control to it. The boot device contains the Master boot record (MBR), Which starts to boot the system via the boot loader. From here, the Grand unified boot loader (GRUB) looks to boot into the kernel that is labeled as the default. Finally, the kernel calls the init process, which boots up the rest of the system. The GRUB has become the default boot loader for Red Hat, ebonite, and many; other versions of <a href="https://www.linux.com/" target="_blank" rel="noopener">linux</a> as well When GRUB loads, you are given a list of kernels and additional operating systems from which you can choose to boot. By default, there is a configurable 5-second timeout value that chooses the default kernel if you don&rsquo;t make a selection and the timeout there should is reached/ After GRUB loads the kernel, it passes control over to the kernel, which it run begins to initialize and configure the computer&rsquo;s hardware. During the boot process, everything is logged to the /var/ log/ dmesg file. You can also use the dmesg cmd to query information about the boot process after the system has booted. When the system&rsquo;s drivers are in place, the kernel executes the /sbin / init program. In RHEL 6, the boot process has been replaced by a new utility called upstart instead of the traditional system in its style scripts. This utility decreases the time that it takes the system to boot and is already currently being used on other versions of lixun such as ubuntu. The init program is the first process created by the kernel. It is responsible for the rest of the boot process and setting up the environment for the user. First, it consults the /etc/init tab file, which defines how the rest of the boot process will go. The /etc/init tab file lists the default run level to boot into and the system initialization script (etc/rc.d/rc.sysinit). Let&rsquo;s look at the /etc/init tab file to see what the init process goes through #cat/etc/init tab You can see that the default run level is set to 5, although six different run levels are listed. The /etc/init tab file also defines how to handle power failures and virtual terminals. After the init process is done consulting the /etc/init tab file, the /etc/rc.d/rc.sys, init script is run,&nbsp; which handles setting the system clock, networking, setting up the user environment &amp; more. In <a href="https://www.redhat.com/en" target="_blank" rel="noopener">Red Hat Linux</a>, the default run level is 5. This default run level is passed to the /etc/rc.d /rc script, which calls all the programs in the /etc/rc.d/rc#.d directory. The last thing that you should see is the login prompt. If you have a desktop manager installed such as Gnome, you should see a GUI login screen where you can log in to the system; otherwise, you see a text mode login. Working with Grub: The GRUB boot loader is broken down into different stages. The code contained on the MBR is considered GRUB stage 1. It loads GRUB stage 1.5, which tries to identify the file system type (optional), or it can call GRUB stage 2 directly. Stage 2 is what calls the kernel and loads it into memory. In stage 1, GRUB needs to search the MBR looking for an active partition from which to boot the kernel. GRUB has its own format for looking through hard disks. The syntax of this format is (xdn[, m])&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; where xd is the drive
<ul>
<li>n is the number of the disk</li>
<li>m denotes the partition number.</li>
</ul>
<ul>
<li>The syntax is very useful when troubleshooting issues with GRUB because you need to know how GRUB searches for disk drives when trying to find the primary partition. When the primary partition found, GRUB loads the kernel, which is where you move to stage 2. Stage 2 is the place where you will tend to spend the most time troubleshooting boot issues with the system. As stage 2 starts, it presents you with a list of kernels that you can boot from, along with a listing of options that you can use to modify the parameters passed to the kernel during bootup.</li>
</ul>
<h3>Grub Boot options:</h3>
e &nbsp; &nbsp;----&gt; &nbsp; &nbsp; &nbsp; &nbsp; Edit the cmds before booting
a&nbsp;&nbsp; &nbsp;----&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Modify (or) append the kernel arguments before booting
c&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;----&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; open the GRUB cmd line.
<ul>
<li>You can use the &lsquo;a&rsquo; option to modify any parameters you want to pass to the kernel. This includes changing the run level that the system will boot into.</li>
<li>After choosing the &lsquo;a&rsquo; option, you can pass a mode as a parameter to enter into the mode. Here are the different modes that you can booty into:</li>
</ul>
<h3>Single &ndash; User Mode</h3>
------&gt;&nbsp;perform maintenance tasks (or) forget the root password. Run level 2 (or) 3
------&gt;&nbsp;Load only partial services during the boot process Emergency Mode
------&gt;&nbsp;used to perform tasks on an unbootable system. Rescue Mode
------&gt;&nbsp;&nbsp;used to fix boot issues (or) reinstall GRUB. &nbsp;
<h3> The Config file: </h3>
GRUB has only a single config file, /boot/ grub/grub.conf. Two other files actually have soft links to this main config file as well: /boot/grub/menu.lst and /etc/grub.conf. When GRUB starts, it reads its configuration from the main config file # cat /boot/grub/grub.conf Using the C option to enter the GRUB cmd line, you can make changes to the config file, reinstall GRUB, or repair a broken config file.
<blockquote>
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</blockquote>
<h2>The GRUB Command Line: </h2>
How to repair a broken MB You need to make use of the rescue environment, which can be found by booting from the RHEL installation DVD. When you are in the rescue environment, you can repair your broken MBR.
 Step1: Load up the GRUB cmd line to find the disk and partition that contain the grub conf file using the find cmd. Grub&gt; find&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /grub/grub.cong (hd ʘ, ʘ) &agrave;you could also run: Grub&gt;root (hd ʘ, ʘ)
Step 2: Install GRUB on the drive is returned: Grub&gt; setup&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ((hd ʘ) ------&gt;&nbsp;Now that your MBR is fixed, you should be able to boot the system once again.
<ul>
<li>
<h3>Runlevels:</h3>
</li>
</ul>
------&gt; when the system boots up, it queries for the default run level, which is defined in the /etc/init tab file. When the default run level is located, the system boots into that particular run level. ------&gt; There is a six-run level in total which are shown in the /etc/init tab file. Each run level also has a directory called /etc/rc.d/rc#.d, where&nbsp; # is the run level (from 0 to 6).&nbsp;
<h3>Let&rsquo;s look at the different run levels: </h3>
0&nbsp;&nbsp;&nbsp;------&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; halt
1&nbsp;&nbsp;&nbsp;------&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; single-user mode
2&nbsp;&nbsp;&nbsp;------&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; multiuser with partial services
3&nbsp;&nbsp;&nbsp;------&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Full multiuser with networking (text mode)
4&nbsp;&nbsp;&nbsp;------&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; not used
5&nbsp;&nbsp;&nbsp;------&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Full multiuser graphical mode (GUI desktop login)
6&nbsp;&nbsp;&nbsp;------&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Reboot
------&gt; The easiest runlevels to understand are 0 and 6. These two run levels are called by the same cmd with different input. In runlevel 0, essentially the system is off. In run level 6, the system is restarting. Runlevel 1 is used to enter single-user mode, which you would enter if there are issues with the system and you&rsquo;d like to perform maintenance. You can also reset the root user&rsquo;s password at this run level. The remaining runlevels provide various states for different services to run it ------&gt; Don&rsquo;t forget the upstart is the program that actually starts &amp; stops services at each run level now. The /etc/init/ rc.conf file shows how each set of scripts is called: #cat /etc/init/ rc/conf
<h2>Runlevel Utilities: </h2>
Let&rsquo;s now look at the many system utilities that help you manage the system in different run levels. This management cmds are Sys: Shutdown [options] time
<ul>
<li>-k&nbsp;&nbsp;&nbsp;&nbsp; ------&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; doesn&rsquo;t shut down; just warns</li>
<li>-h&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;------&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Halts the system after shutdown</li>
<li>-r&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;------&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Reboots instead of turning off the system</li>
<li>-F&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;------&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Forces a file system check on reboot.</li>
<li>-n&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;------&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; kills all processes quickly (not recommended)</li>
<li>-t&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;------&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; SECS sends a shutdown message but delays shutdown by x seconds.</li>
</ul>
Ex: #shutdown&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -h&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; now #shutdown&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -r&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; now #reboot #shutdown&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
<ul>
<li>-h&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 120&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; Delay the shutdown by 2 minutes.</li>
</ul>
<h3>Halt: </h3>
powers down the system.
------&gt;To turn off the system #shutdown now (or) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; # halt
<h3>Poweroff: </h3>
works the same as the halt cmd.
------&gt;To check the current run level&nbsp; &nbsp;# runlevel (or) #who &ndash;r ------&gt;To change run level 3&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; #init 3
<h2> In-depth understanding of Linux click on</h2>
<ul>
<li><a class="current-page" title="Features of UNIX/LINUX" href="http://tekslate.com/features-unixlinux/" target="_blank" rel="noopener">Features of UNIX/LINUX</a></li>
<li class="title"><a class="current-page" title="Architecture of O/S" href="http://tekslate.com/architecture-os/" target="_blank" rel="noopener">Architecture of O/S</a></li>
<li class="title"><a class="current-page" title="UNIX Introduction" href="http://tekslate.com/unix-introduction/" target="_blank" rel="noopener">UNIX Introduction</a></li>
<li class="title"><a class="current-page" title="Basic commands" href="http://tekslate.com/basic-commands-unix/" target="_blank" rel="noopener">Basic commands</a></li>
<li class="title"><a class="current-page" title="User Administration" href="http://tekslate.com/user-administration-linux/" target="_blank" rel="noopener">User Administration</a></li>
</ul>

System Initialization in Linux

System Initialization

system-initialization-linux

&nbsp;
<h2>I lost my Root user password: </h2>
Step 1: &nbsp;Boot into single-user mode by appending the command line during but with the following
Single
 Step 2: when you are presented with a command prompt, change the root user password.
#passwd root
 Step3: Reboot the system and validate that the new root password works correctly:
#reboot
<h2>Password change not available in single-user mode:</h2>
When you enter single-user mode, you may encounter an issue where the root user&rsquo;s password can&rsquo;t be changed.
Step1: Verify the existence of the /etc/shadow file:
#ls /etc/ grep shadow
 Step 2: If the /etc/shadow file doesn&rsquo;t exist, use the pwconv cmd to re-create the /etc/shadow file:
#pwconv
Step 3: Now execute the passwd command to reset or change the root user&rsquo;s password:
#passwd root
Step 4: Reboot the system and validate that the new root password works correctly:
#reboot &nbsp;
<h2>The MBR is corrupt:</h2>
If you are having trouble booting the system and you have determined that the master boot record (MBR) is corrupt you need to boot into rescue mode. Use the Red Hat DVD, boot from it, and choose the option to enter rescue mode.
Step 1: After you boot, enter the GRUB shell:
# grub
Step 2: Locate the root drive:
Grub&gt;root
Step 3: Reinstall the MBR from the GRUB shell:
Grub&gt; setup (hdʘ)
Step 4: Reboot the system to validate that the system boots properly:
#reboot &nbsp;
<h2>Repair the file system: </h2>
When we have an inconsistency to the file /etc/fstab and the file systems listed by blkid utility. Then the system will go to rescue mode
---&gt;&nbsp;To troubleshoot this problem provide the root password for the maintenance
---&gt;&nbsp;When we provide the root password correctly then a shell prompt will be opened
---&gt;&nbsp;At this movement the file system is mounted in read-only mode, hence we can&rsquo;t change the file system table (fstab file)
---&gt;&nbsp;So mount the file system in rw mode
#mount &ndash;o remount, rw/
---&gt;&nbsp;Now open the file /etc/fstab
#vim/etc/fstab
Now remove (or) change the file systems which leads to inconsistency and save the fstab file and reboot the pc
#init 6
(or)
#reboot
<blockquote>
Inclined to build a profession as Linux Developer? Then here is the blog post on, explore <a title="Linux Training" href="linux-training" target="_blank" rel="noopener">Linux Training</a>
</blockquote>
<h2>Assign the grub password: </h2>
The grub password is to be maintained in the file
&ldquo;/boot/grub/grub.cong&rdquo;.
#grub-md5-crypt&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &gt;&gt; /boot / grub /grub.conf
When we type the above command then an encrypted password comes to the last line of the file&nbsp;
/boot/grub/grub.conf
We have to copy that encrypted password and paste in the same file under the line &ldquo;hidden menu&rdquo;
Password &ndash; md5&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;encrypted passwd&gt;
Here we have to paste the encrypted password &nbsp;
<h2>Recover root &amp; grub password: </h2>
Step 1: use the Red Hat DVD, boot from it, and choose the option to enter Rescue mode
Boot: Linux rescues
Select keyboard =&gt; select language =&gt; select networking
Then a shell will be opened
At this moment to give the privilege to the root user to maintain the file system
#chroot /mnt/sysimage
Here we can follow the above-mentioned procedures of recovering the root password and grub password.
<h2>The superblock&nbsp; Has Become corrupt: </h2>
If the superblock on your system has become corrupt, you can re-create it with one of the backup superblocks. If the primary file system has the corruption you may need to use single-user mode or the rescue environment to perform the recovery.
Step 1: Check the state of the file system:
#dumpe2fs&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; h&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /dev/sda 1
Step 2: Find a valid backup superblock:
#dumpe2fs &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /dev/sda 1 / grep &ndash;i superblock
Step 3: Repair the file system with a backup superblock:
#e2fsck &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -f &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -b&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 8193 /dev/sda1
<h2>For an in-depth understanding of Linux click on</h2>
<ul>
<li class="title"><a class="current-page" title="Features of UNIX/LINUX" href="http://tekslate.com/features-unixlinux/" target="_blank" rel="noopener">Features of UNIX/LINUX</a></li>
<li class="title"><a class="current-page" title="Architecture of O/S" href="http://tekslate.com/architecture-os/" target="_blank" rel="noopener">Architecture of O/S</a></li>
<li class="title"><a class="current-page" title="UNIX Introduction" href="http://tekslate.com/unix-introduction/" target="_blank" rel="noopener">UNIX Introduction</a></li>
<li class="title"><a class="current-page" title="Basic commands" href="http://tekslate.com/basic-commands-unix/" target="_blank" rel="noopener">Basic commands</a></li>
<li class="title"><a class="current-page" title="User Administration" href="http://tekslate.com/user-administration-linux/" target="_blank" rel="noopener">User Administration</a></li>
</ul>

Troubleshooting in Linux

Troubleshooting

troubleshooting-linux

<h2>How to do Backup &amp; Restore in Linux</h2>
<ul>
<li>In information technology, a backup or the process of backing up is making copies of data that may be used to restore the original after a data loss event.</li>
<li>Backups have two distinct purposes.</li>
</ul>
1. The primary purpose is to recover data after its loss, be it by data deletion or corruption. Data loss is a very common experience of computer users. 67% of internet users have suffered serious data loss.
2. The secondary purpose of backups is to recover data from an earlier time, according to a user-defined data retention policy, typically configured within a backup application for how long copies of data are required.
<ul>
<li>Backup is the most important job of a system administrator as a system admin it is your duty to take a backup of the data every day.</li>
<li>Many companies have gone out of the market because of poor backup planning.</li>
<li>The easiest way to backup your first is just copying. But if you have too many files to backup, copying and restoring may take a too long time and it is not convenient. If there is a tool that can put many files into one file, the world will be better, fortunately, &lsquo;tar&rsquo; is used to create archive files. &nbsp;</li>
</ul>
<h2> Compression and Archiving:</h2>
<ul>
<li>As you will learn when you become a system administrator, backups are the number one priority.</li>
<li>If something should crash or become corrupt and you can&rsquo;t restore it because you aren&rsquo;t keeping up with your backups or you just don&rsquo;t keep any, you may be looking for a new job. Although we don&rsquo;t address backup programs here, this is a good lead into archiving and compression.</li>
</ul>
 Tar: Tar means tape archiving
<ul>
<li>It is used for compressing and archiving files and directories</li>
<li>A more common use for tar is to simply combine a few files into a single file, for easy storage distribution. &nbsp;</li>
</ul>
Syn:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; tar&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; [options]&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; [FILE]
 Options: &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
<ul>
<li>c &nbsp; &nbsp;-----&gt; &nbsp; &nbsp; &nbsp; &nbsp;creates a new archive</li>
<li>v&nbsp;&nbsp;&nbsp;&nbsp;-----&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; provides verbose output</li>
<li>f&nbsp;&nbsp;&nbsp;&nbsp;-----&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; specifies the archive file to use</li>
<li>t&nbsp;&nbsp;&nbsp;&nbsp;-----&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; lists the files in an archive</li>
<li>x&nbsp;&nbsp;&nbsp;-----&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Extract the backup</li>
<li>z&nbsp;&nbsp;&nbsp;-----&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Zipping</li>
</ul>
<blockquote>
<table style="border-collapse: collapse; width: 100%; height: 24px; background-color: #ECF0F1;" border="1px" cellpadding="10">
<tbody>
<tr style="height: 24px;">
<td style="width: 98.1605%; height: 24px; text-align: center;">Inclined to build a profession as Linux Developer? Then here is the blog post on, explore <a style="color: #236fa1;" title="Linux Training" href="linux-training" target="_blank" rel="noopener">Linux Training</a></td>
</tr>
</tbody>
</table>
</blockquote>
Step 1:&nbsp; create some random blank files:
#touch file 1 file 2 file 3 another _file
 Step 2: create a simple archive containing these files:
#tar &ndash;cvf&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; sample.tar file1&nbsp; file2 file3 another &ndash;file
When an archive is created, you can also apply compression to reduce the amount of space the archive files takes up. Although multiple types of compression are supported with the use of tar we look only at gunzip (.gz) and bzip2 (bz2) here.
Step 3:&nbsp; Let&rsquo;s re-create the archive using the gunzip compression:
#tar&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -cvzf sample.tar.gz&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; file1 file2 file3 another-file
Step 4: view the current directory to see the two current archive files:
#ls
Step 5: To see all the contents within the build file:
#tar &ndash;tvf sample.tar
Step 6: Now extract this build file verbosely:
#tar &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -xvf sample.tar
Step 7:&nbsp; To extract files on a different location
#tar &ndash; xvf sample.tar&nbsp; -c&nbsp; /root/desktop
Cpio: cpio is a tool for creating and extracting archives or copying files from one place to another.
-----&gt;It handles a number of cpio formats as well as reading and writing tar files.
-----&gt;Cpio like tar but can read input from the &ldquo;find&rdquo; command
-----&gt;The basic structure is
:find &ndash;name&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; file/cpio [options]&nbsp; [contraoller]&nbsp; &lt;dest&gt;
 Options:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -o (out)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Controllers:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; O (or)&nbsp; &gt; -out
-i (in)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; I&nbsp;&nbsp; (or) &gt; -in
 Step 1: To take the backup files
#ls&nbsp; file *&nbsp; /cpio&nbsp; -acvf&nbsp; &gt;/root/backup.cpio
Step 2: To see the backup content:
#cpio &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -it &lt;/root/backup.cpio
#cpio&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -it&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -I /root/backup .cpio
Step 3: To restore the backup file:
#cpio&nbsp; -icuvd&nbsp; &lt;/root/backup.cpio
O &nbsp; &nbsp; &nbsp;-----&gt; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Reads the standard input
i &nbsp; &nbsp; &nbsp; &nbsp;-----&gt; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Extract files from the standard input
c &nbsp; &nbsp; &nbsp;-----&gt; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Read or write header information in ASCII character
d &nbsp; &nbsp; &nbsp;-----&gt; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Creates directories as needed
u &nbsp; &nbsp; &nbsp; -----&gt;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Copy unconditionally (older file will not replace a new file)
<h3>DD: (Disk to Disk) </h3>
Used to take the backup of one partition to another, here source partition should be given to &ldquo;if&rdquo; destination partition should be passed to &ldquo;of&rdquo;
<h3>Step 1: To take the backup: </h3>
#dd &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if=/dev/hda6&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; of= /dev/hda7
<h3> Step 2:To recovery: </h3>
#dd &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if = /dev/hda7&nbsp;&nbsp;&nbsp; of=/dev/hda6
<h3>SCP:(Secure copy)</h3>
-----&gt;SCP is used to copy data from one unix or Linux system to another unix or Linux server.
-----&gt;SCP uses a secured shell (ssh) to transfer the data between the remote hosts.
-----&gt;The features of SCP are:
<ul>
<li>Copies files with in the same machine</li>
<li>Copies files from local machine to the remote machine</li>
<li>Copies files from the remote machine to the local machine</li>
<li>Copies files between two different remote servers.</li>
</ul>
Syn: SCP&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; [options]&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; [user from_Host: source_file]&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; {user to _host: Destination_file]
Options:&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
-r&nbsp;&nbsp;&nbsp;-----&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Recursively
-q&nbsp;&nbsp;&nbsp;-----&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Progress bar not displayed
-v&nbsp;&nbsp;&nbsp;&nbsp;-----&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Verbose mode
-p&nbsp;&nbsp;&nbsp;-----&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; copy files using the specified port number.
-----&gt;Copy file from local host to remote server:
#scp&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; filename &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <a href="mailto:root@server254.example.com:/root" target="_blank" rel="noopener">root@server254.example.com:/root</a>
-----&gt;Copy files from remote host to local server: 
#scp &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <a href="mailto:root@server254.example.com:/root/backkup*" target="_blank" rel="noopener">root@server254.example.com:/root/backkup*</a>&nbsp;&nbsp;&nbsp;&nbsp;
&bull; Current directory
-----&gt;Copying a directory: 
#SCP &ndash;r directory <a href="mailto:root@server254.example.com" target="_blank" rel="noopener">root@server254.example.com</a>: /root
-----&gt;Improving the performance of SCP command: 
Using blowfish or arcfour encryption will improve the performance of the SCP command
#SCP&nbsp;&nbsp; -c&nbsp; blowfish filename&nbsp; root@server254.example.com.com:&nbsp; &nbsp; &nbsp;&nbsp;
-----&gt;Specifying the port number: 
#SCP&nbsp;&nbsp; -p&nbsp; 6001&nbsp;&nbsp; backup-file&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <a href="mailto:root@server254.example.com:/tmp" target="_blank" rel="noopener">root@server254.example.com:/tmp</a>
<h2>You Might like</h2>
<ul>
<li class="title"><a class="current-page" title="Features of UNIX/LINUX" href="http://tekslate.com/features-unixlinux/" target="_blank" rel="noopener">Features of UNIX/LINUX</a></li>
<li class="title"><a class="current-page" title="Architecture of O/S" href="http://tekslate.com/architecture-os/" target="_blank" rel="noopener">Architecture of O/S</a></li>
<li class="title"><a class="current-page" title="UNIX Introduction" href="http://tekslate.com/unix-introduction/" target="_blank" rel="noopener">UNIX Introduction</a></li>
<li class="title"><a class="current-page" title="Basic commands" href="http://tekslate.com/basic-commands-unix/" target="_blank" rel="noopener">Basic commands</a></li>
<li class="title"><a class="current-page" title="User Administration" href="http://tekslate.com/user-administration-linux/" target="_blank" rel="noopener">User Administration</a></li>
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