<h2>Unix Shell Scripting Interview Questions and Answers</h2>
<h3>1Q) What is UNIX? </h3>
Ans: It is a portable operating system that is designed for both efficient multi-tasking and multi-user functions. Its portability allows it to run on different hardware platforms. It was written in C and lets the user do processing and control under a shell.
<h3>2Q) What is Shell? </h3>
Ans: A shell acts as an interface between the user and the system. As a command interpreter, the shell takes commands and sets them up for execution.
<h3>3Q) What is the Zombie process in UNIX? How do you find the Zombie process in UNIX? </h3>
Ans: When a program forks and the child finishes before the parent, the kernel still keeps some of its information about the child in case the parent might need it.
for example, the parent may need to check the child&rsquo;s exit status. To be able to get this information, the parent calls &lsquo;wait()&rsquo;; 
In the interval between the child terminating and the parent calling &lsquo;wait()&rsquo;, the child is said to be a &lsquo;zombie&rsquo; (If you do &lsquo;ps&rsquo;, the child will have a &lsquo;Z&rsquo; in its status field to indicate this.)
<h3>4Q) What is nohup in UNIX? </h3>
Ans: Nohup is a special command which is used to run the process in the background, but it is slightly different than &amp; which is normally used for putting a process in the background. A UNIX process started with nohup will not stop even if the user who has stared log off from the system. While the background process started with &amp; will stop as soon as the user log off.
<h3>5Q) What type of buffer is supported by Unix?</h3>
Ans:
<ul>
<li>Fully Buffered.</li>
<li>Line Buffered.</li>
<li>Un-Buffered.</li>
</ul>
<blockquote>
Interested in mastering Unix Shell Scripting Training? Enroll now for FREE demo on "<a style="color: #e03e2d;" href="unix-shell-scripting-training" target="_blank" rel="noopener">Unix Shell Scripting Training</a>"
</blockquote>
<h3>6Q) What are signals? </h3>
Ans: Signals are software interrupts. Signal provides a way of handling asynchronous events: a user at a terminal typing the interrupt key to stop a program or the next program in the pipeline terminating prematurely.
<h3>7Q) What is the session?</h3>
Ans: A Session is a collection of one or more process groups. A process establishes a new session by calling setsid function. This function return process groupid ok.
<h3>8Q) What is &lsquo;ps&rsquo; command for? </h3>
Ans: The ps command prints the process status for some or all of the running processes. The information given are the process identification number (PID),the amount of time that the process has taken to execute so far, etc.
<h3>9Q) How are devices represented in UNIX? </h3>
Ans: All devices are represented by files called special files that are located in/dev directory. Thus, device files and other files are named and accessed in the same way. A &lsquo;regular file&rsquo; is just an ordinary data file in the disk.
<h3>10Q) What are the different type of variables used in a Shell Script ? </h3>
Ans: In a shell script we can use two types of variables :
<ul>
<li>System-defined variables</li>
<li>User-defined variables</li>
</ul>
System-defined variables are defined or created by Operating System(Linux) itself. These variables are generally defined in Capital Letters and can be viewed by &ldquo;set&rdquo; command.
<h3>11Q) How to use Argument in a script? </h3>
Ans: First argument: $1,
Second argument : 
$2 Example : 
Script will copy file (arg1) to destination (arg2) ./copy.sh file1.txt /tmp/ cat copy.sh #!/bin/bash cp $1 $2
<h3>12Q) How to check if previous command run successful? $? How to check if file exist on filesystem?</h3>
Ans: if [ -f /var/log/messages ]
then echo &ldquo;File exists&rdquo;
<h3>13Q) What does it mean #!/BIN/SH OR #!/BIN/BASH at beginning of every script? </h3>
Ans: That line tells which shell to use. #!/bin/bash script to execute using /bin/bash. In the case of python script, there will be #!/usr/bin/python.
<h3>14Q) What is the first symbol in the bash script file?</h3>
Ans: #
What would be the output of command: `{` -Z &ldquo;&rdquo; `}` &amp;&amp; ECHO 0 || ECHO 1? &nbsp;
<h3>15Q) What difference between &amp; And &amp;&amp;?</h3>
Ans:
<ul>
<li>&amp; &ndash; we using it when want to put the script to the background</li>
<li>&amp;&amp; &ndash; when we want to execute command/script if first script was finished successfully.</li>
</ul>
<h3>16Q) What would be the output of the command: ECHO ${NEW:-VARIABLE}?</h3>
Ans:
<ul>
<li>Variable</li>
</ul>
<h3>17Q) How to redirect STDOUT and STDERR Streams to LOG.TXT file from the script inside?</h3>
Ans: Add &ldquo;exec &gt;log.txt 2&gt;&amp;1&rdquo; as the first command in the script.
<h3>18Q) How to get HOME_DIR with echo command only if string variable=&rdquo;USER:123:321:/HOME/DIR&rdquo; is given? </h3>
Ans: echo ${variable#*:*:*:} or
echo ${variable##*:}
<h3>19Q) How to list users that UID less than100(awk)?</h3>
Ans: awk -F: &lsquo;$3&lt;100&rsquo; /etc/passwd
<h3>20Q) How to change the standard field separator to&ldquo;:&rdquo; in bash shell?</h3>
Ans: IFS=&rdquo;:&rdquo;
<h3>21Q) How to print all arguments provided to the script?</h3>
Ans: echo $* or echo $@
<h3> 22Q) How to define an array in bash? </h3>
Ans: array=(&ldquo;Hi&rdquo; &ldquo;my&rdquo; &ldquo;name&rdquo; &ldquo;is&rdquo;)
<h3>23Q) How will you pass and access arguments to a script in Linux? </h3>
Ans: Arguments can be passed as: script name&nbsp;&ldquo;Arg1&rdquo; &ldquo;Arg2&rdquo;&hellip;.&rdquo;Argn&rdquo; and can be accessed inside the script as $1 , $2 .. $n.
<h3>24Q) How do you write the contents of 3 files into a single file? </h3>
Ans: cat file1 file2 file3 &gt; file
<h3>25Q) Write a command to find the sum of bytes (size of the file) of all files in a directory? </h3>
Ans: 
<pre class="language-javascript"><code>ls -l | grep '^-'|

awk 'BEGIN {sum=0}

{sum = sum + $5}

END

{print sum}'

</code></pre>
<h3>26Q) Write a command to select only those lines containing "july" as a whole word?</h3>
Ans:
grep -w july filename The '-w' option makes the grep command to search for exact whole words. If the specified pattern is found in a string, then it is not considered as a whole word. 
For example: In the string "mikejulymak", the pattern "july" is found. However "july" is not a whole word in that string.
<h3>27Q) Write a command to duplicate each line in a file? </h3>
Ans: sed 'p' &lt; filename
<h3>28Q) Write a command to list the files in '/usr' directory that start with 'ch' and then display the number of lines in each file? </h3>
Ans: wc -l /usr/ch* Another way is find /usr -name 'ch*' -type f -exec wc -l {} ;
<h3>29Q) Write a command to remove the prefix of the string ending with '/'? </h3>
Ans: The basename utility deletes any prefix ending in /. The usage is mentioned below: basename /usr/local/bin/file This will display the only file.

Unix Shell Scripting Interview Questions and Answers

unix-shell-scripting-interview-questions-answers

&nbsp;
<h3>1Q) What is UNIX?</h3>
Ans: It is a portable operating system that is designed for both efficient multi-tasking and multi-user functions. Its portability allows it to run on different hardware platforms. It was written in C and lets the user do processing and control under a shell.
<h3>2Q) What is Shell?</h3>
Ans: A shell acts as an interface between the user and the system. As a command interpreter, the shell takes commands and sets them up for execution.
<h3>3Q) What is <a href="https://en.wikipedia.org/wiki/Zombie" target="_blank" rel="noopener">Zombie</a> process in UNIX? How do you find Zombie process in UNIX?</h3>
Ans: When a program forks and the child finishes before the parent, the kernel still keeps some of its information about
the child in case the parent might need it for example, the parent may need to check the child&rsquo;s exit status. To be
able to get this information, the parent calls &lsquo;wait()&rsquo;; In the interval between the child terminating and the parent
calling &lsquo;wait()&rsquo;, the child is said to be a &lsquo;zombie&rsquo; (If you do &lsquo;ps&rsquo;, the child will have a &lsquo;Z&rsquo; in its status field to indicate this.)
<h3>4Q) What is nohup in UNIX?</h3>
Ans: Nohup is a special command which is used to run process in background, but it is slightly different than &amp; which is normally used for putting a process in background. A <a href="unix-shell-scripting-training/">UNIX</a> process started with nohup will not stop even if the user who has stared log off from system. While background process started with &amp; will stop as soon as user logoff.
<h3>5Q) What type of buffer is supported by Unix?</h3>
Ans:
<ul>
<li>Fully Buffered.</li>
<li>Line Buffered.</li>
<li>Un-Buffered.</li>
</ul>
<h3>6Q) What are signals?</h3>
Ans: Signals are software interrupts . Signal provides a way of handling asynchronous events: a user at a terminal typing the iterrupt key to stop a program or the next program in the pipeline termnating prematurely.
<blockquote style="box-sizing: border-box; margin: 0px 0px 1rem; border-left: none; padding: 15px; line-height: 36px; color: #333333; font-family: quicksand, sans-serif; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: #ffffff; text-decoration-style: initial; text-decoration-color: initial;">
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</blockquote>
<h3>7Q) What is the session?</h3>
Ans: A Session is a collection of one or more process group. A process establish a new session by calling setsid function. This function return process groupid ok.
<h3>8Q) What is &lsquo;ps&rsquo; command for?</h3>
Ans: The ps command prints the process status for some or all of the running processes. The information given are the process identification number (PID),the amount of time that the process has taken to execute so far etc.
<h3>9Q) How are devices represented in UNIX?</h3>
Ans: All devices are represented by files called special files that are located in/dev directory. Thus, device files and other files are named and accessed in the same way. A &lsquo;regular file&rsquo; is just an ordinary data file in the disk.
<h3>10Q) What are the different type of variables used in a Shell Script ?</h3>
Ans: In a <a href="understanding-unix-programms/">shell script</a> we can use two types of variables :
<ul>
<li>System-defined variables</li>
<li>User-defined variables</li>
</ul>
System-defined variables are defined or created by Operating System(Linux) itself. These variables are generally defined in Capital Letters and can be viewed by &ldquo;set&rdquo; command.
<h3>11Q) How to use Argument in a script?</h3>
Ans: First argument: $1,
Second argument : $2
Example : Script will copy file (arg1) to destination (arg2)
./copy.sh file1.txt /tmp/
cat copy.sh
#!/bin/bash
cp $1 $2
<h3>12Q) How to check if previous command run successful?</h3>
Ans: $?
<h3>13Q)How to check if file exist on filesystem?</h3>
Ans: if [ -f /var/log/messages ]
then
echo &ldquo;File exists&rdquo;
<h3>14Q) What it means #!/BIN/SH OR #!/BIN/BASH at beginning of every script?</h3>
Ans: That line tells which shell to use. #!/bin/bash script to execute using /bin/bash. In case of python script there there will be #!/usr/bin/python.
<h3>15Q) What is the first symbol in the bash script file?</h3>
Ans: #
<h3>16Q) What difference between &amp; And &amp;&amp; ?</h3>
Ans:
<ul>
<li>&amp; &ndash; we using it when want to put script to background</li>
<li>&amp;&amp; &ndash; when we want to execute command/script if first script was finished successfully.</li>
</ul>
<h3>17Q)What would be the output of command: ECHO ${NEW:-VARIABLE}?</h3>
Ans:
<ul>
<li>Variable</li>
</ul>
<h3>18Q) How to redirect STDOUT and STDERR Streams to LOG.TXT file from the script inside?</h3>
Ans: Add &ldquo;exec &gt;log.txt 2&gt;&amp;1&rdquo; as the first command in the script.
<h3>19Q) How to get HOME_DIR with echo command only if string variable=&rdquo;USER:123:321:/HOME/DIR&rdquo; is given?</h3>
Ans:
echo ${variable#*:*:*:}
or
echo ${variable##*:}
<h3>20Q) How to list users which UID less than100(awk)?</h3>
Ans: awk -F: &lsquo;$3&lt;100&rsquo; /etc/passwd
<h3>21Q) How to change standard field separator to&ldquo;:&rdquo; in bash shell?</h3>
Ans: IFS=&rdquo;:&rdquo;
<h3>22Q) How to print all arguments provided to the script?</h3>
Ans: echo $*
or
echo $@
<h3>23Q)How to define array in bash?</h3>
Ans: array=(&ldquo;Hi&rdquo; &ldquo;my&rdquo; &ldquo;name&rdquo; &ldquo;is&rdquo;)
<h3>24Q) How will you pass and access arguments to a script in Linux?</h3>
Ans: Arguments can be passed as:
scriptName &ldquo;Arg1&rdquo; &ldquo;Arg2&rdquo;&hellip;.&rdquo;Argn&rdquo; and can be accessed inside the script as $1 , $2 .. $n.
<h3>25Q) How do you write the contents of 3 files into a single file?</h3>
Ans: cat file1 file2 file3 &gt; file
<h3>26Q) Write a command to find the sum of bytes (size of the file) of all files in a directory?</h3>
Ans: ls -l | grep '^-'| awk 'BEGIN {sum=0} {sum = sum + $5} END {print sum}'
<h3>27Q) Write a command to select only those lines containing "july" as a whole word?</h3>
Ans: grep -w july filename
The '-w' option makes the grep command to search for exact whole words. If the specified pattern is found in a string, then it is not considered as a whole word. For example: In the string "mikejulymak", the pattern "july" is found. However "july" is not a whole word in that string.
<h3>28Q) Write a command to duplicate each line in a file?</h3>
Ans: sed 'p' &lt; filename
<h3>29Q) Write a command to list the files in '/usr' directory that start with 'ch' and then display the number of lines in each file?</h3>
Ans: wc -l /usr/ch*
Another way is
find /usr -name 'ch*' -type f -exec wc -l {} ;
<h3>30Q) Write a command to remove the prefix of the string ending with '/'?</h3>
Ans: The basename utility deletes any prefix ending in /. The usage is mentioned below:
basename /usr/local/bin/file
This will display the only file.
<h3>31Q) Write down syntax for all loops in shell scripting?</h3>
Ans: 
<pre class="language-javascript"><code>for loop :

for i in $( ls );

do echo item: $i

done

while loop :

#!/bin/bash

COUNTER=0

while [ $COUNTER -lt 10 ]; do

echo The counter is

$COUNTER let COUNTER=COUNTER+1

done

until loop :

#!/bin/bash

COUNTER=20 until [ $COUNTER -lt 10 ]; do

echo COUNTER $COUNTER

let COUNTER-=1

done

</code></pre>
32Q)How to get part of string variable with echo command only ?
Ans: echo ${variable:x:y}
x - start position
y - length
example:
variable="My name is Petras, and I am developer."
echo ${variable:11:6} # will display Petras

Unix Shell Scripting Interview Questions

interview-questions-on-unix-shell-scripting

Ten ESSENTIAL UNIX Commands These are ten commands that you really need to know in order to get started with UNIX. They are probably similar to commands you already know for another operating system.
<table width="90%">
<tbody>
<tr>
<td>Command</td>
<td>Example</td>
<td>Description</td>
</tr>
<tr>
<td>
<ol>
<li>&nbsp; &nbsp;ls</li>
</ol>
</td>
<td>ls ls &ndash;alF</td>
<td>Lists files in current directory List in long format</td>
</tr>
<tr>
<td>
<ol start="2">
<li>&nbsp; &nbsp;cd</li>
</ol>
</td>
<td>cd tempdir cd .. cd ~dhyatt/web-docs</td>
<td>Change directory to tempdir Move back one directory Move into dhyatt's web-docs directory</td>
</tr>
<tr>
<td>
<ol start="3">
<li>&nbsp; &nbsp;mkdir</li>
</ol>
</td>
<td>mkdir graphics</td>
<td>Make a directory called graphics</td>
</tr>
<tr>
<td>
<ol start="4">
<li>&nbsp; &nbsp;rmdir</li>
</ol>
</td>
<td>rmdir emptydir</td>
<td>Remove directory (must be empty)</td>
</tr>
<tr>
<td>
<ol start="5">
<li>&nbsp; &nbsp;cp</li>
</ol>
</td>
<td>cp file1 web-docs cp file1 file1.bak</td>
<td>Copy file into directory Make backup of file1</td>
</tr>
<tr>
<td>
<ol start="6">
<li>&nbsp; &nbsp;rm</li>
</ol>
</td>
<td>rm file1.bak rm *.tmp</td>
<td>Remove or delete file Remove all file</td>
</tr>
<tr>
<td>
<ol start="7">
<li>&nbsp; &nbsp;mv</li>
</ol>
</td>
<td>mv old.html new.html</td>
<td>Move or rename files</td>
</tr>
<tr>
<td>
<ol start="8">
<li>&nbsp; &nbsp;more</li>
</ol>
</td>
<td>more index.html</td>
<td>Look at file, one page at a time</td>
</tr>
<tr>
<td>
<ol start="9">
<li>&nbsp; &nbsp;lpr</li>
</ol>
</td>
<td>lpr index.html</td>
<td>Send file to printer</td>
</tr>
<tr>
<td>
<ol>
<li>&nbsp;man</li>
</ol>
</td>
<td>man ls</td>
<td>Online manual (help) about command</td>
</tr>
</tbody>
</table>
&nbsp; Ten VALUABLE UNIX Commands Once you have mastered the basic UNIX commands, these will be quite valuable in managing your own account.
<table width="90%">
<tbody>
<tr>
<td>Command</td>
<td>Example</td>
<td>Description</td>
</tr>
<tr>
<td>
<ol>
<li>&nbsp; &nbsp;grep &lt;str&gt;&lt;files&gt;</li>
</ol>
</td>
<td>grep "bad word" *</td>
<td>Find which files contain a certain word</td>
</tr>
<tr>
<td>
<ol start="2">
<li>&nbsp; &nbsp;chmod &lt;opt&gt; &lt;file&gt;</li>
</ol>
</td>
<td>chmod 644 *.html chmod 755 file.exe</td>
<td>Change file permissions read only Change file permissions to executable</td>
</tr>
<tr>
<td>
<ol start="3">
<li>&nbsp; &nbsp;passwd</li>
</ol>
</td>
<td>passwd</td>
<td>Change passwd</td>
</tr>
<tr>
<td>
<ol start="4">
<li>&nbsp; &nbsp;ps &lt;opt&gt;</li>
</ol>
</td>
<td>ps aux ps -ef &nbsp;&nbsp;|&nbsp;&nbsp; grep java</td>
<td>List all running processes by #ID List process #ID's running by java</td>
</tr>
<tr>
<td>
<ol start="5">
<li>&nbsp; &nbsp;kill &lt;opt&gt; &lt;ID&gt;</li>
</ol>
</td>
<td>kill -9 8453</td>
<td>Kill process with ID #8453</td>
</tr>
<tr>
<td>
<ol start="6">
<li>&nbsp; &nbsp;gcc (g++) &lt;source&gt;</li>
</ol>
</td>
<td>gcc file.c -o file g++ fil2.cpp -o fil2</td>
<td>Compile a program written in C Compile a program written in C++</td>
</tr>
<tr>
<td>
<ol start="7">
<li>&nbsp; &nbsp;gzip &lt;file&gt;</li>
</ol>
</td>
<td>gzip bigfile gunzip bigfile.gz</td>
<td>Compress file Uncompress file</td>
</tr>
<tr>
<td>
<ol start="8">
<li>&nbsp; &nbsp;mail (pine)</li>
</ol>
</td>
<td>mail me@tjhsst.edu&nbsp;&lt;&nbsp;file1 pine</td>
<td>Send file1 by email to someone Read mail using pine</td>
</tr>
<tr>
<td>
<ol start="9">
<li>&nbsp; &nbsp;telnet &lt;host&gt; ssh &lt;host&gt;</li>
</ol>
</td>
<td>telnet vortex.tjhsst.edu ssh -l dhyatt jazz.tjhsst.edu</td>
<td>Open a connection to vortex Open a secure connection to jazz as user dhyatt</td>
</tr>
<tr>
<td>
<ol>
<li>&nbsp;ftp &lt;host&gt; ncftp &lt;host/directory&gt;</li>
</ol>
</td>
<td>ftp station1.tjhsst.edu ncftp metalab.unc.edu</td>
<td>Upload or Download files to station1 Connect to archives at UNC</td>
</tr>
</tbody>
</table>
&nbsp; Ten FUN UNIX Commands These are ten commands that you might find interesting or amusing. They are actually quite helpful at times, and should not be considered idle entertainment.
<table width="90%">
<tbody>
<tr>
<td>Command</td>
<td>Example</td>
<td>Description</td>
</tr>
<tr>
<td>
<ol>
<li>&nbsp; &nbsp;who</li>
</ol>
</td>
<td>who</td>
<td>Lists who is logged on your machine</td>
</tr>
<tr>
<td>
<ol start="2">
<li>&nbsp; &nbsp;finger</li>
</ol>
</td>
<td>finger</td>
<td>Lists who is on computers in the lab</td>
</tr>
<tr>
<td>
<ol start="3">
<li>&nbsp; &nbsp;ytalk &lt;user@place&gt;</li>
</ol>
</td>
<td>ytalk dhyatt@threat</td>
<td>Talk online with dhyatt who is on threat</td>
</tr>
<tr>
<td>
<ol start="4">
<li>&nbsp; &nbsp;history</li>
</ol>
</td>
<td>history</td>
<td>Lists commands you've done recently</td>
</tr>
<tr>
<td>
<ol start="5">
<li>&nbsp; &nbsp;fortune</li>
</ol>
</td>
<td>fortune</td>
<td>Print random humerous message</td>
</tr>
<tr>
<td>
<ol start="6">
<li>&nbsp; &nbsp;date</li>
</ol>
</td>
<td>date</td>
<td>Print out current date</td>
</tr>
<tr>
<td>
<ol start="7">
<li>&nbsp; &nbsp;cal &lt;mo&gt; &lt;yr&gt;</li>
</ol>
</td>
<td>cal 9 2000</td>
<td>Print calendar for September 2000</td>
</tr>
<tr>
<td>
<ol start="8">
<li>&nbsp; &nbsp;xeyes</li>
</ol>
</td>
<td>xeyes &amp;</td>
<td>Keep track of cursor (in "background")</td>
</tr>
<tr>
<td>
<ol start="9">
<li>&nbsp; &nbsp;xcalc</li>
</ol>
</td>
<td>xcalc &amp;</td>
<td>Calculator ("background" process)</td>
</tr>
<tr>
<td>
<ol>
<li>&nbsp;mpage &lt;opt&gt; &lt;file&gt;</li>
</ol>
</td>
<td>mpage -8 file1 &nbsp;&nbsp;|&nbsp;&nbsp;lpr</td>
<td>Print 8 pages on a single sheet and send to printer (the font will be small!)</td>
</tr>
</tbody>
</table>
&nbsp; Ten HELPFUL UNIX Commands These ten commands are very helpful, especially with graphics and word processing type applications.
<table width="90%">
<tbody>
<tr>
<td>Command</td>
<td>Example</td>
<td>Description</td>
</tr>
<tr>
<td>
<ol>
<li>&nbsp; &nbsp;netscape</li>
</ol>
</td>
<td>netscape &amp;</td>
<td>Run Netscape browser</td>
</tr>
<tr>
<td>
<ol start="2">
<li>&nbsp; &nbsp;xv</li>
</ol>
</td>
<td>xv &amp;</td>
<td>Run graphics file converter</td>
</tr>
<tr>
<td>
<ol start="3">
<li>&nbsp; &nbsp;xfig / xpaint</li>
</ol>
</td>
<td>xfig &amp; (xpaint &amp;)</td>
<td>Run drawing program</td>
</tr>
<tr>
<td>
<ol start="4">
<li>&nbsp; &nbsp;gimp</li>
</ol>
</td>
<td>gimp &amp;</td>
<td>Run photoshop type program</td>
</tr>
<tr>
<td>
<ol start="5">
<li>&nbsp; &nbsp;ispell &lt;fname&gt;</li>
</ol>
</td>
<td>ispell file1</td>
<td>Spell check file1</td>
</tr>
<tr>
<td>
<ol start="6">
<li>&nbsp; &nbsp;latex &lt;fname&gt;</li>
</ol>
</td>
<td>latex file.tex</td>
<td>Run LaTeX, a scientific document tool</td>
</tr>
<tr>
<td>
<ol start="7">
<li>&nbsp; &nbsp;xemacs / pico</li>
</ol>
</td>
<td>xemacs (or pico)</td>
<td>Different editors</td>
</tr>
<tr>
<td>
<ol start="8">
<li>&nbsp; &nbsp;soffice</li>
</ol>
</td>
<td>soffice &amp;</td>
<td>Run StarOffice, a full word processor</td>
</tr>
<tr>
<td>
<ol start="9">
<li>&nbsp; &nbsp;m-tools (mdir, mcopy, mdel, mformat, etc. )</li>
</ol>
</td>
<td>mdir a: mcopy file1 &nbsp; a:</td>
<td>DOS commands from UNIX (dir A:) Copy file1 to A:</td>
</tr>
<tr>
<td>
<ol>
<li>&nbsp;gnuplot</li>
</ol>
</td>
<td>gnuplot</td>
<td>Plot data graphically</td>
</tr>
</tbody>
</table>
&nbsp; Ten USEFUL UNIX Commands: These ten commands are useful for monitoring system access, or simplifying your own environment.
<table width="90%">
<tbody>
<tr>
<td>Command</td>
<td>Example</td>
<td>Description</td>
</tr>
<tr>
<td>
<ol>
<li>&nbsp; &nbsp;df</li>
</ol>
</td>
<td>df</td>
<td>See how much free disk space</td>
</tr>
<tr>
<td>
<ol start="2">
<li>&nbsp; &nbsp;du</li>
</ol>
</td>
<td>du -b subdir</td>
<td>Estimate disk usage of directory in Bytes</td>
</tr>
<tr>
<td>
<ol start="3">
<li>&nbsp; &nbsp;alias</li>
</ol>
</td>
<td>alias lls="ls -alF"</td>
<td>Create new command "lls" for long format of ls</td>
</tr>
<tr>
<td>
<ol start="4">
<li>&nbsp; &nbsp;xhost</li>
</ol>
</td>
<td>xhost + threat.tjhsst.edu xhost -</td>
<td>Permit window to display from x-window program from threat Allow no x-window access from other systems</td>
</tr>
<tr>
<td>
<ol start="5">
<li>&nbsp; &nbsp;fold</li>
</ol>
</td>
<td>fold -s file1 &nbsp;&nbsp;|&nbsp;&nbsp; lpr</td>
<td>Fold or break long lines at 60 characters and send to printer</td>
</tr>
<tr>
<td>
<ol start="6">
<li>&nbsp; &nbsp;tar</li>
</ol>
</td>
<td>tar -cf subdir.tar subdir tar -xvf subdir.tar</td>
<td>Create an archive called subdir.tar of a directory Extract files from an archive file</td>
</tr>
<tr>
<td>
<ol start="7">
<li>&nbsp; &nbsp;ghostview (gv)</li>
</ol>
</td>
<td>gv filename.ps</td>
<td>View a Postscript file</td>
</tr>
<tr>
<td>
<ol start="8">
<li>&nbsp; &nbsp;ping (traceroute)</li>
</ol>
</td>
<td>ping threat.tjhsst.edu traceroute www.yahoo.com</td>
<td>See if machine is alive Print data path to a machine</td>
</tr>
<tr>
<td>
<ol start="9">
<li>&nbsp; &nbsp;top</li>
</ol>
</td>
<td>top</td>
<td>Print system usage and top resource hogs</td>
</tr>
<tr>
<td>
<ol>
<li>&nbsp;logout (exit)</li>
</ol>
</td>
<td>logout or exit</td>
<td>How to quit a UNIX shell.</td>
</tr>
</tbody>
</table>
&nbsp; To check your disk utilization on Solaris or Linux, use the iostat -D &lt;interval&gt; command, where the interval value determines how many seconds you want to elapse between monitoring cycles. To check your CPU utilization, simply leave off the -D flag (iostat &lt;interval&gt;). For Windows, use the Performance Monitor tool (perfmon), to monitor both your disk and CPU utilization. &nbsp; TCP (transmission control protocol) socket performance, set the tcp_time_wait_interval parameter as follows: ndd -set /dev/tcp tcp_time_wait_interval 60000 &nbsp; Check the amount of data transferred between the application and the application server, and between the application server and the database server. netstat -s -P tcp &nbsp; Use&nbsp;Kill -3&nbsp;PID, where&nbsp;PID&nbsp;is the root of the process tree. To obtain the root PID, perform a: ps -efHl | grep 'java' **. ** &nbsp; Check out our Related Courses <a href="https://tekslate.com/tutorials/weblogic-tutorials-how-to/">Weblogic Tutorials</a> <a href="https://tekslate.com/introduction-clustering-weblogic/">Introduction to Clustering Weblogic</a> <a href="https://tekslate.com/weblogic-server-administration-training/" target="_blank" rel="noopener">WebLogic Server Admin Training in Houston</a> <a href="https://tekslate.com/weblogic-server-installation/">Oracle Weblogic Server Installation</a>
<div id="malwarebytes-root"></div>

UNIX Commands-2

UNIX Commands

unix-commands-2

<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. LINUX is a clone of O/S.</li>
<li>Linux is the most important achievement of free soft ware, 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 <a href="https://www.redhat.com/en" target="_blank" rel="noopener">Red Hat</a> 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 <a href="https://www.linux.com/" target="_blank" rel="noopener">linux</a>, not just Red Hat.</li>
</ul>
<pre style="text-align: center;">Desired to gain proficiency on Linux ? Explore the blog post on <a href="https://tekslate.com/linux-training/" target="_blank" rel="noopener">Linux training</a> to become a pro in Linux.</pre>
Operating System(O/S)
<ul style="text-align: justify;">
<li>Operating system is a interface between user &amp; computer (or) it is a 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 basis tasks, such as recognizing input from the keyboard, sending out put 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="2" width="451" height="207" />
<ol>
<li style="text-align: justify;">Single user systems; Provides a platform for only one user at a time. They are popularly associated with Desk Top operating System which run on standalone systems where no user accounts are required.
<ol>
<li>Example: DOS</li>
</ol>
</li>
<li>Multi User Systems: More than one user can access same system resources (CPU, applications, memory, printers &hellip;&hellip;&hellip;etc) at the same time known as multiuse.
<ol>
<li style="text-align: justify;">Example: UNIX, LINUX</li>
</ol>
</li>
</ol>
For indepth understanding of&nbsp;Linux click on
<ul>
<li class="title"><a class="current-page" href="https://tekslate.com/features-unixlinux/">Features of UNIX/LINUX</a></li>
<li class="title"><a class="current-page" href="https://tekslate.com/architecture-os/">Architecture of O/S</a></li>
<li class="title"><a href="https://tekslate.com/tutorials/unixlinux/" target="_blank" rel="noopener">Linux Tutorials</a></li>
<li class="title"><a class="current-page" href="https://tekslate.com/basic-commands-unix/">Basic commands</a></li>
<li class="title"><a class="current-page" href="https://tekslate.com/user-administration-linux/">User Administration</a></li>
</ul>

UNIX Introduction

unix-introduction

<h3>Text Editors in Unix</h3>
Being able to use a text editor is probably one of the most critical skills to have as a system administrator. You constantly need to edit con fig files, write scripts or make changes to system files &hellip;&hellip;.. all of which require you to use a text editor.
<ul>
<li>The three most popular editors available today include</li>
</ul>
Vi(or) Vim:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Text editor with great flexibility. Emacs&nbsp; :&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; similar to vi, an advanced text editor with many features. Nano&nbsp;&nbsp; :&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; A basic text editor for quick editing
<ul>
<li>Vi (or) Vim Editor:</li>
<li>Using this editor to create new files, open the files and modifying the data into a existing files.</li>
<li>The Vi Editor is most popular</li>
<li>It has three modes:
<ul>
<li>Command mode</li>
<li>Insert mode</li>
<li>Execution (or) colon mode</li>
</ul>
</li>
<li>By default mode is command mode</li>
</ul>
Syn: &nbsp;Vim [arguments]&nbsp;&nbsp; [file] Arguments:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; R &nbsp; &nbsp;-----&gt;&nbsp;opens a file in read &ndash;only mode -&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; o &nbsp; &nbsp;-----&gt;&nbsp;Open two files at a time + &nbsp; &nbsp; &nbsp;-----&gt;&nbsp;Starts at the end of the file +&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;rum&gt; &nbsp; &nbsp;-----&gt;&nbsp;Start at line &lt;num&gt; &nbsp; <img class="alignnone wp-image-5299" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/11/1343-460x254.png" alt="1" width="504" height="277" /> &nbsp; Insert mode options: i --------&gt;&nbsp;To begin insert mode at the current cursor position. I --------&gt;To Insert at the beginning of the current line a--------&gt;To append to the next word&rsquo;s letter. A&nbsp;--------&gt; To append at the end of the line o &nbsp;--------&gt;To insert a new line below the cursor position. O &nbsp;--------&gt; &nbsp;To Insert a new line above the cursor position. &nbsp; Commands for command mode: e &nbsp;--------&gt; Moves to the end of a word b &nbsp;--------&gt; Moves to the beginning of a word. $ &nbsp;--------&gt;Moves to the end of a line. ˄ &nbsp; --------&gt;Moves to the beginning of a line H --------&gt;Moves to the first line onscreen M --------&gt;&nbsp;Moves to the middle line onscreen L &nbsp;--------&gt;Moves to the last line onscreen x (nx) --------&gt;Deletes current character. dd (ndd)--------&gt;Deletes the current line dw (ndw)--------&gt;Deletes current word. Yy(nyy) &nbsp;--------&gt; yanks (copies) the current line p --------&gt;paste below the cursor line P &nbsp;--------&gt;paste above the cursor line U--------&gt;undo the last action. gg(ngg)--------&gt;go to beginning of the file G --------&gt;End of the file. W (n)--------&gt;To move the cursor forward, word by word. b(n) --------&gt;&nbsp;To move the cursor back word, word by word Ctrl +f --------&gt;To forward one page. Ctrl +b --------&gt;To back word one page. / &nbsp;--------&gt;To search a word in the file. n --------&gt;Find next occurrence of search word. N --------&gt;&nbsp;find previous occurrence of search word. . &nbsp;--------&gt; Repeat last command action. Commands for last line mode: :q &nbsp;--------&gt;To quit without saving :w &nbsp; --------&gt;To save the changes &nbsp; :wq &nbsp;&nbsp; --------&gt;To save &amp; quit &nbsp; :wq! &nbsp;(or)&nbsp;&nbsp;&nbsp;:x &nbsp;--------&gt; &nbsp;To save &amp; quit with forcefully. &nbsp; :set nu &nbsp;(or) &nbsp; &nbsp;:se nu -------&gt;&nbsp;To setting line numbers. &nbsp; &nbsp; :set nonu &nbsp;&nbsp;(or) &nbsp;&nbsp;:se nonu------&gt; To remove line numbers. &nbsp; :n &nbsp;------&gt;Jumps to line n :$d ------&gt;To delete last line :! &lt;unixcmd&gt; ------&gt;&nbsp;To execute unix cmds :x &nbsp;------&gt;To give password to the file and remove password. :/storing / ------&gt;search a word in the file.
<pre style="text-align: center;">Desired to gain proficiency on Linux ? 
Explore the blog post on <a href="https://tekslate.com/linux-training/" target="_blank" rel="noopener">Linux training online</a> to become a pro in Linux.</pre>
<ul>
<li>To find &amp; Replace:</li>
</ul>
: % S/root/dog/&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp; To replace storing &ldquo;dog&rdquo; for the first instance : %s/root/dog/g&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; For each instance of a line. : %s/root/dog/gi&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; To ignore case sensitive : %s/root/dog/gc&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp; ask for confirmation &nbsp; &nbsp;
<ul>
<li>Executing unix commands in vi:</li>
</ul>
Any unix command can be Executed from the vi command line by typing an &ldquo;!&rdquo; before the unix command. EX: : ! Pwd : r ! data &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;Reads the results from the date command into a new line following the cursor : r ! cat file1
<ul>
<li>I want to copy 1,4 lines to paste after 10th line:</li>
</ul>
: &nbsp;1,4 CO 10
<ul>
<li>I want to move 3,7 lines after 8th line:</li>
</ul>
: 3,7 mo 8
<ul>
<li>I want to copy 1,30 lines create a new file:</li>
</ul>
: 1,30 w test1
<ul>
<li>I want to append the data into a existing file:</li>
</ul>
: &nbsp;8,20 w &gt;&gt; test1
<ul>
<li>I want to insert end of the line (or) we require line</li>
</ul>
: r/etc/passwd &nbsp; Managing two files at time: $vim &nbsp;&nbsp; -0 file1 file2 (or) $vim file1 file2 Options: :n &nbsp; &nbsp;----&gt;&nbsp;edit next file (file2) :rew &nbsp;&nbsp;----&gt;&nbsp;Rewind to the file (file1) (or)
<ul>
<li>To move one file to another file (ctrl + W)</li>
</ul>
Press two times
<div class="tags">&nbsp;</div>

Using a Text Editor in unix

Using a Text Editor

using-text-editor-in-unix

UNIX Architecture &nbsp;
<ul>
<li>Typical computer system consists of
<ul>
<li>Hardware</li>
<li>Operating system</li>
<li>Applications and utilities</li>
</ul>
</li>
</ul>
&nbsp;
<ul>
<li>Typical as includes a user interface or command interpreter.</li>
</ul>
&nbsp;
<ul>
<li>Unix is somewhat unique in that the command interpreter is not integrated with the os but it is a separate program.</li>
</ul>
&nbsp; <img class="alignnone wp-image-9414" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/154-460x337.png" alt="1" width="545" height="398" /> &nbsp; &nbsp; &nbsp;
<div id="malwarebytes-root"></div>

Architecture of UNIX

architecture-unix

<h2>Levels of Unix Software</h2>
<ul>
<li>Unix users a layer approach of defining software layered approach is basis for Unix Security.</li>
<li>At the lowest level, the level closest to the hardware, are the basic hardware interface modules
<ul>
<li>process scheduling</li>
<li>Memory management</li>
<li>interrupt handling</li>
<li>low level device control</li>
<li>disk system management &amp; data buffering</li>
<li>process synchronization and inter &ndash; process communication ( 1pc)</li>
</ul>
</li>
</ul>
<h3>&nbsp;</h3>
<h3>Unix Functional layer Model</h3>
&nbsp; &nbsp; <img class="alignnone wp-image-9418" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/224-460x345.png" alt="2" width="511" height="383" /> &nbsp; &nbsp;
<h3>Kernel Service layer </h3>
&nbsp; <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />File / disk access service <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />process creation and termination <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />Mapping between user requests and device driver actions. <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />The next level provides all the kernel services <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />The user system call is converted to a Kernel service call that actually &nbsp;performs&nbsp; the requests service <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />I/O service <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />Terminal handling services &nbsp;
<h3>System call Interface Layer </h3>
&nbsp; <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />The system call interface layer converts a process running in user mode to a protected kernel mode process. &nbsp; <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />This allows the program to invoke protected kernel routines to perform system functions. &nbsp;
<h3>User process Layer&nbsp;</h3>
The uppermost layer consists of user process running :
<ul>
<li>shell</li>
</ul>
<ul>
<li>Unix commands</li>
</ul>
<ul>
<li>Utility programs</li>
</ul>
<ul>
<li>User application program</li>
</ul>
&nbsp;
<h3>&nbsp; User process</h3>
*protected from other users *Have no access to Unix Kernel routines except through system call interface *cannot directly access Kernel memory space. &nbsp;
<h3>Kernel&nbsp;&nbsp; VS User space</h3>
<img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />&nbsp; In addition to the software levels, Unix also features two&nbsp; &ldquo;rings of protection &rdquo; from inadvertent programming errors or malisons attacks&nbsp; &nbsp;that might damage other user&rsquo;s processes&nbsp; or the kernel&rsquo;s processes and data structures. <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />The inner protected ring is known as kernel space <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />The outer ring is called user space.&nbsp; &nbsp; &nbsp;
<h3>User Space </h3>
<img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />User space is the area in memory &nbsp;when user process are run <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />This consist of memory starting above the kernel and includes the4 rest of available memory. <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />This memory is protected ; the system prevents one user from interfering with another. <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />Only Kernel process can access a user process. <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />A process operating in this memory region is said to be in user mode. &nbsp;
<h3>Kernel Space </h3>
<img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />Kernel space is the region at memory where all kernel service are provided via kernel process. <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />Any process executing in kernel space is said to be executing in kernel mode. <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />Kernel Space is a privileged area ; the area the user has access to it only through the system call interface. <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />A user does not have direct access to either all machine instructions or devices. <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />A kernel process does have direct access to both. <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />Also, a kernel process can modify the memory map, an operation frequently required to perform process scheduling. <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />A user process becomes a kernel process when it executes a system call and starts executes kernel code. &nbsp;
<h3>Data Flow Between Kernel and user Space </h3>
&nbsp; <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />Since users and the kernel do not share memory address space , the mechanism for moving data between them is important. <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />When a system call is executed , the arguments to the call and the corresponding kernel routine&nbsp; identification are passed from user space to kernel space. <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />Kernel routine ID is usually passed either via a hardware machine register or via the stack. <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />System call arguments are passed in the user area of the calling process. <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />User area of a process contains information a bout the process the Kernel needs while the process is running. <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />Open files , root, current directory, arguments to current system call , and process text, stack and data segment sizes. <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />A pointer to the process table entry containing information for scheduling such as priority. <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />User file descriptor table and information about open files. <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />Kernel Stack for the process. <img class="alignnone size-full wp-image-8553" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Untitled1.png" alt="Untitled" width="36" height="12" />Remember , user can not access Kernel space but Kernel space can access user space. &nbsp; &nbsp; &nbsp;

Functional layers & Models in Unix

functional-layers-models-unix

<h2>Unix Command Interface and commands </h2>
&nbsp;
<ul>
<li>Unix command interface &nbsp;is a separate program referred to as shell.</li>
<li>The shell provides the user interface between the user and the Kernel.</li>
<li>Unix commands and Utilities , like the shell , are also separate programs.</li>
<li>They are part of a Unix distribution , and are considered part of Unix but not part of the Kernel.</li>
</ul>
&nbsp; Unix System Services
<ul>
<li>Unix Provides a number&nbsp; of system services such as system administration , system reconfiguration and file system maintenance.</li>
<li>Other services include
<ul>
<li>Customization of system parameters</li>
<li>Rebuilding of kernel with user device</li>
<li>Creation and definition of user accounts.</li>
<li>Setup and maintenance of access control parameters for files and peripherals.</li>
<li>Most service are built in to the kernel as system calls.</li>
</ul>
</li>
</ul>
&nbsp; Unix System calls &nbsp;
<ul>
<li>System calls provide a programming interface that allows user programs&nbsp; to access Kernel function.</li>
<li>There are a large number of system calls that perform functions to manage system resources such as memory , disk storage , and peripherals.</li>
<li>System calls are defined in a run time library that provides a mapping of the system call interface to the Kernel routines that platform the system functions.</li>
<li>The shell also provides functionality equivalent to many of the system calls.</li>
</ul>
&nbsp;
<h2>System Usage Accounting Services</h2>
Unix provides some general accounting services. As each process terminations , an accounting record is mode available discoing the resources used by the process.
<ul>
<li>Name of the process</li>
<li>Amount of user and system CPU time used</li>
<li>Elapsed time</li>
<li>Average amount of memory used.</li>
<li>Number of disk I/O operations done</li>
<li>UID and GID of the process</li>
<li>Terminal from which process was Started.</li>
</ul>
<div id="malwarebytes-root"></div>

System Usage Accounting Services in UNIX

system-usage-accounting-services-unix

<h2>Operating System </h2>
&nbsp;
<ul>
<li>OS can be defined as an organized collection of software consisting of procedures for operating a computer.</li>
<li>OS provides an environment for execution of programs.</li>
<li>OS acts as an interface between the user and the hardware of the computer system.</li>
</ul>
&nbsp; <img class="alignnone size-full wp-image-9386" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/220.png" alt="2" width="30" height="12" />Operating system continues interacts with user in two ways.
<ol>
<li>Operating system commands
<ul>
<li>Enables user to interact directly with the O.S</li>
</ul>
</li>
<li>Operating System calls
<ul>
<li>Provides an interface to a running program and the operating system . system calls in UNIX are written in &lsquo;C&rsquo;.</li>
</ul>
</li>
</ol>
&nbsp;
<h2>History of UNIX </h2>
<ul>
<li>Ken Thompson at AT &amp; T Bell laboratories designed UNIX in late 1960&rsquo;s.</li>
<li>Two versions of UNIX that emerged are AT &amp; T UNIX and BSD Unix.</li>
<li>In 1989, AT &amp; T and sun Micro Systems joined together and developed system V release 4(SVR 4)</li>
<li>Two of main standards mainly in use are POSIX and X/open standard. In 1988, MIT formed X consortium developed vendor _ natural X window system.</li>
</ul>
&nbsp; What is LINUX ?
<ul>
<li>An open source UNIX like operating system.</li>
<li>Initially created by LINUX Torvalds for pc Architecture ports exit for alpha and space processors</li>
<li>Developer community world &ndash; wide contribute to its enhancement and growth.</li>
</ul>
&nbsp;
<h2>Features of UNIX &nbsp;</h2>
<ul>
<li>Multi &ndash; User , Multi tasking, time sharing</li>
<li>Portability</li>
<li>Modularity</li>
<li>File structure</li>
<li>Security</li>
<li>Strong network Supporting &amp; advanced graphics</li>
</ul>
<div id="malwarebytes-root"></div>
<div id="malwarebytes-root"></div>
<div id="malwarebytes-root"></div>

History and Features of UNIX

history-features-unix

<h2>Layered Architecture</h2>
&nbsp; <img class="alignnone size-full wp-image-9389" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/320.png" alt="3" width="405" height="342" /> &nbsp; &nbsp; &nbsp;
<h2>Unix System&nbsp; Architecture</h2>
<ul>
<li>Unix system follows a layered approach . It has 4 Layers</li>
<li>The inner most layer is the hardware layer.</li>
<li>In the second layer , the KERNEL is placed.</li>
<li>The utilities and other application programs form 3rd</li>
<li>Fourth layer is the one with which the user actually interacts.</li>
</ul>
&nbsp; Kernel
<ul>
<li>Kernel is that part of OS which directly makes interface with the hardware system.</li>
</ul>
&nbsp; Actions :
<ul>
<li>Provides mechanism for creating and deleting processes.</li>
<li>Provides processor scheduling, memory &amp; I/0 management</li>
<li>Provides inter &ndash; process communication</li>
</ul>
&nbsp; The Shell 
<ul>
<li>A utility program that comes with the UNIX system</li>
</ul>
&nbsp; Features of shell are&nbsp; :
<ul>
<li>Interactive processing</li>
<li>Back ground processing</li>
<li>I/ O Redirection</li>
<li>Pipes</li>
<li>Shell Scripts</li>
<li>Shell Variables</li>
<li>Programming constructs</li>
</ul>
&nbsp; Process Management 
<ul>
<li>A process is a program in execution</li>
<li>Several processes can be executed simultaneously a UNIX system.</li>
<li>A process is generally created using the &ldquo;fork ()&rdquo;.system call</li>
<li>The process that invokes the &ldquo;fork ()&rdquo; system call is the parent process, and the newly created process is called the child process</li>
</ul>
&nbsp; CPU Scheduling 
<ul>
<li>UNIX uses round &ndash; ration scheduling to support its multi-user and time &ndash; sharing feature.</li>
<li>Round &ndash; robin fashion of scheduling is considered to be the oldest, simplest and widely used algorithm.</li>
<li>Every process is given a time slice.</li>
</ul>
&nbsp; &nbsp;&nbsp;&nbsp; &nbsp;Memory Management &nbsp;
<ul>
<li>Virtual memory</li>
<li>Swap area</li>
<li>Demand paging</li>
</ul>
&nbsp; File Management 
<ul>
<li>UNIX uses a hierarchical file system with &lsquo;1&rsquo; as its root</li>
<li>Every non &ndash; leaf node of the tree is called as directory file</li>
<li>Every leaf node can either be a file, or an empty directory.</li>
</ul>
&nbsp; Types of UNIX users
<ul>
<li>Broad classification of users</li>
</ul>
-&nbsp; root - non-root
<ul>
<li>Group</li>
</ul>
- &nbsp;Unix allows user ID&rsquo;s to be grouped -&nbsp; A single user ID can be member of multiple groups
<ul>
<li>Differentiating users with respect to file access</li>
</ul>
-OWNER -Group -others &nbsp; &nbsp; Working with UNIX 
<ul>
<li>User logs in with a valid user ID.</li>
<li>User logs out to terminate the login session.</li>
</ul>
&nbsp; exec() Excel, Excel p, Excel e, Excel v, Excel vp &ndash; executes a file &nbsp; Synopsis # include &lt;Unistd. h&gt; Extern char ** en viron; Int excel&nbsp; (const char&nbsp; * path , const char * arg,&hellip;&hellip;&hellip;&hellip;&hellip;); Int excel p (const char&nbsp; * file , const char * arg,&hellip;&hellip;&hellip;&hellip;&hellip;); Int excel &nbsp;&nbsp;e &nbsp;(const char&nbsp; * path , const char * avg,&hellip;, char * const envp [] ) ; &nbsp; Return Value If any of the exec () functions returns , an error will have occurred. The return value is -1, and the global variable err no will be set to indicate the error. &nbsp; Files /bin/sh &nbsp; System () System&nbsp; - executes a shell command &nbsp; Synopsis # include &lt;stdlib.h&gt; Int system (const char&nbsp; * command;) &nbsp; Description System () executes a command specified&nbsp; in command by calling /bin/sh &ndash; c command, and returns&nbsp; after the command&nbsp;&nbsp; has been completed. Using execution of the command , SIGCHLD will&nbsp; be blocked and SIGINT and SIGQUIT will be ignored. &nbsp; Return Value &lsquo;- 1&rsquo; on error If&nbsp; the value of command is NULL, sys n () returns non &ndash; Zero&nbsp; if the shell is available and if not system () does not effect wait status of at other children . &nbsp; PS: $ PS:
<table>
<tbody>
<tr>
<td width="66">PID</td>
<td width="66">TTY</td>
<td width="66">TIME</td>
<td width="66">CMD</td>
</tr>
<tr>
<td width="66">2561</td>
<td width="66">Pts/0</td>
<td width="66">00:00:00</td>
<td width="66">Bash</td>
</tr>
<tr>
<td width="66">2752</td>
<td width="66">Pts/0</td>
<td width="66">00:00:00</td>
<td width="66">PS</td>
</tr>
</tbody>
</table>
&nbsp; $ bash // opened bash for your own &nbsp; $ Ps &ndash; l: 
<table>
<tbody>
<tr>
<td width="37">F</td>
<td width="37">S</td>
<td width="45">UID</td>
<td width="44">PID</td>
<td width="45">PPIS</td>
<td width="37">0</td>
<td width="41">PRI</td>
<td width="40">NT</td>
<td width="49">ADDR</td>
<td width="44">S7</td>
<td width="62">WCHAN</td>
<td width="46">TTY</td>
<td width="67">TIME</td>
<td width="45">CMD</td>
</tr>
<tr>
<td width="37">0</td>
<td width="37">S</td>
<td width="45">6524</td>
<td width="44">2561</td>
<td width="45">2559</td>
<td width="37">0</td>
<td width="41">75</td>
<td width="40">0</td>
<td width="49">-</td>
<td width="44">1177</td>
<td width="62">wait</td>
<td width="46">Pts/0</td>
<td width="67">00:00:00</td>
<td width="45">Bash</td>
</tr>
<tr>
<td width="37">0</td>
<td width="37">S</td>
<td width="45">6524</td>
<td width="44">2767</td>
<td width="45">2561</td>
<td width="37">0</td>
<td width="41">76</td>
<td width="40">0</td>
<td width="49">-</td>
<td width="44">1176</td>
<td width="62">Wait</td>
<td width="46">Pts/0</td>
<td width="67">00:00:00</td>
<td width="45">Bash</td>
</tr>
<tr>
<td width="37">0</td>
<td width="37">S</td>
<td width="45">6524</td>
<td width="44">2785</td>
<td width="45">2767</td>
<td width="37">0</td>
<td width="41">76</td>
<td width="40">0</td>
<td width="49">-</td>
<td width="44">1084</td>
<td width="62">-</td>
<td width="46">Pts/0</td>
<td width="67">00:00:00</td>
<td width="45">PS</td>
</tr>
</tbody>
</table>
&nbsp; &nbsp; &nbsp; &nbsp;
<div id="malwarebytes-root"></div>
<div id="malwarebytes-root"></div>

Unix System  Architecture And Its Explanation

unix-system-architecture-explination

<h2>Daemon process </h2>
At&nbsp;&nbsp; TTY &ndash; if we observe &lsquo;?&rsquo; , it indicates it a Daemon&nbsp; process, which does not need any input and automatically comes&nbsp; into life when the OS is switched ON.&nbsp; &nbsp;And&nbsp; the processes can be seen using commands. &nbsp; Gnome &ndash; terminal Is the parent for the bash. &nbsp; Example on System () call Vi p1.c #include &lt;stdio.h&gt; #include &lt;stdlib.h&gt; Main () { Print f (&ldquo;Process id = % d&hellip;&hellip;&hellip;parent id = %d /n&rdquo;, &nbsp;get p id (), get p p id ()) System (&ldquo;./p2 &rdquo;);// p2 is executable file of p 2.c Print f (&ldquo;After system () call came back to process 1 &rdquo;); } &nbsp; Vi p2.c &nbsp; #include &lt;stdio.h&gt; #include &lt;stdlib.h&gt; Main () { Print f (&ldquo;Process id = % d&hellip;&hellip;&hellip;parent id = %d /n&rdquo;,&nbsp; get p id (), get p p id ()); } Cc&nbsp; -0 p2&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; p2.c Creates executable for p2.c with name p2. &nbsp; &nbsp; Output&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;cc p1.c # ./a.out Process &nbsp;1 id = 2963 &hellip;&hellip;&hellip;.parent id = 2767 &agrave; this is PID of gnome &ndash; terminal Process 2 id = 2964&hellip;&hellip;&hellip;.parent id = 2763 &agrave; this is PID process 1 as process1, called process 2 After System () call came back to process 1 . &nbsp; $echo $PATH / user/ Kerberos/bin : /ur/local/bin :/bin : /user/bin : /home /b59p2/bin These&nbsp; are the paths available in the terminal if we have two executes like ls, cal etc&hellip;&hellip;&hellip; Simply by $ ls, $ cal we can execute, but even through&nbsp; a. out is an executable , $ a. out does not executes why ? $ . pwd /home/b59p2/UNIX/Sys &ndash; exec This is path of you&rsquo;re a .out, Which is not available in above shown paths. Hence, it searches for a. out there in above paths&nbsp; &amp; hence not found, Results, bash : a. out : command not found. Now to execute directly like # a. out , we have two solutions.
<ol>
<li>Copy a. out in any of directory path</li>
</ol>
# cs&nbsp;&nbsp;&nbsp; /home/b59p2/UNIX/Sys- exec/ a. out&nbsp; &nbsp;/home /b59p2/bin # a. out
<ol start="2">
<li>Another way is to update the PATH variable</li>
</ol>
# PATH = $ PATH : /root/b59p2 /UNIX/sys-exec # a. out
<ol>
<li>$ / bin/sh -c command</li>
<li>$ command</li>
</ol>
Ex :-&nbsp; $/bin / sh&nbsp; -c ls $ ls &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Both generates same output &nbsp; Here the major difference is that, in first command&nbsp; bash creates sh and executes command is returns. &nbsp; In 2nd&nbsp; statement executes command in present shell Bash is parent. &nbsp; &nbsp;
<h3>&nbsp;Assignments </h3>
<ol>
<li>create an executable named &ldquo;cme exec &rdquo; , which when used with the i/p command , should be also to execute the command specified..the command is provide from the command line Vi ass1.c</li>
</ol>
Using System () call &nbsp; #include &nbsp;&nbsp;&lt;stdio . h&gt; #include &nbsp;&nbsp;&lt;stdlib . h&gt; Main (int&nbsp; argc, char ** argc ) { If (argc ! = 2) { Print f (&ldquo;usage ./cmd exec&nbsp; &lt;command &gt;&rdquo; ); Return; } System ( arg v [1]); } creating&nbsp; executable cc&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -0&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; cmd exec&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ass1.c &nbsp; Output &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;./cmd exec ls
<ol>
<li>a. out ass1.c cmd exec</li>
</ol>
p1.c p2 p2.c &nbsp; &nbsp;
<h3>Using exec () call</h3>
&nbsp; #include &lt;stdio. h&gt; #include &lt;stdlib. h&gt; Main (int arg c , char ** arg v) { If&nbsp; (argc ! 2) { Print f (&ldquo;Usage :&nbsp; ./cmd exec&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;command&gt; &rdquo;); Return ; } Execlp (&nbsp; args v [1], argv [1], NULL); } &nbsp;
<ol>
<li>Q. a. p to accept any number of commands from the command line and execute them in the same sequence as they are provided.</li>
</ol>
&nbsp;
<h3>Using system () call</h3>
&nbsp; #include &lt;stdio. h&gt; #include &lt;stdlib. h&gt; Main (int arg c , char ** arg v) { Int I ; If&nbsp; (argc == &nbsp;2) { Print f (&ldquo;Usage :&nbsp; ./a. out &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;command 1&gt; &nbsp;&nbsp;&lt;command 2&gt; &hellip;&hellip;&hellip;&hellip;.&rdquo;); Return ; } &nbsp; For (I =1 ; argv [i] ; I ++ ) System (arg v [i] ); } &nbsp; Output ./a .out ls date cal
<ol>
<li>out ass1.c ass2. C ass3. C cmd exec&nbsp; cmd sys p1.c p2 thu Aug 12&nbsp; 00:28:23 1st 2010</li>
</ol>
August 2010 Mon&nbsp;&nbsp; tue wed&nbsp; thu&nbsp;&nbsp; fri&nbsp; sat
<div id="malwarebytes-root"></div>
<div id="malwarebytes-root"></div>

Daemon process in UNIX 

daemon-process-unix

Q. W.a. p to accept any number of commands from the command line and execute them in the same sequence as they are provided. &nbsp; Using system () call #include &lt;stdio. h&gt; #include &lt;stdlib. h&gt; Main (int arg c , char ** arg v) { Int I ; If&nbsp; (argc == &nbsp;2) { Print f (&ldquo;Usage :&nbsp; ./a. out &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;command 1&gt; &nbsp;&nbsp;&lt;command 2&gt; &hellip;&hellip;&hellip;&hellip;.&rdquo;); Return ; } &nbsp; For (I =1 ; argv [i] ; I ++ ) System (arg v [i] ); } &nbsp; Output ./a .out ls date cal
<ol>
<li>out ass1.c ass2. C ass3. C cmd exec&nbsp; cmd sys p1.c p2 thu Aug 12&nbsp; 00:28:23 1st 2010</li>
</ol>
August 2010 Mon&nbsp;&nbsp; tue wed&nbsp; thu&nbsp;&nbsp; fri&nbsp; sat&nbsp; &nbsp; &nbsp;
<h2>EX:- 1</h2>
# include &lt;stdio.h&gt; #include &lt;unistd.h&gt; Main () { Print f (&ldquo;Before : process id&nbsp; = % d , parent id = % d/n &rdquo;, get p id (), get&nbsp; p pid ()); Print f (&ldquo;Enter to call fork &rdquo;); Get char (); Fork (); Print f (&ldquo;After&nbsp; : process id&nbsp; = % d , parent id = % d/n &rdquo;, get p id (), get&nbsp; p pid ()); } &nbsp; Output Before : process id = 2069 , parent id = 1835 Enter to call fork After : process id = 2071, parent id = 2069 After : process id = 2069, parent id = 1835 Main () 1835 <img class="alignnone size-full wp-image-9386" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/220.png" alt="2" width="30" height="12" />&nbsp;Bash 2069 <img class="alignnone size-full wp-image-9386" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/220.png" alt="2" width="30" height="12" />&nbsp;process &nbsp; &nbsp; <img class="alignnone size-full wp-image-9397" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Screenshot_160.png" alt="Screenshot_1" width="456" height="264" /> &nbsp; &nbsp;
<h2>Ex :-2</h2>
# include &lt;stdio.h&gt; #include &lt;unistd.h&gt; Main () { Print f (&ldquo;Before : process id&nbsp; = % d , parent id = % d/n &rdquo;, get p id (), get&nbsp; p pid ()); Fork (); Fork (); Print f (&ldquo;After&nbsp; : process id&nbsp; = % d , parent id = % d/n &rdquo;, get p id (), get&nbsp; p pid ()); } Bash : 1835 Main () Process : 2156 <img class="alignnone wp-image-9398" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Screenshot_239-460x376.png" alt="Screenshot_2" width="460" height="376" /> &nbsp; Output: Before:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; process id = 2156 ,&nbsp; parent id = 1835 After&nbsp; :&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; process id = 2158 , parent id = 2157 After&nbsp; :&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; process id = 2157 , parent id = 2156 After&nbsp; :&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; process id = 2159 , parent id = 2156 After&nbsp; :&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;process id = 2156 , parent id = 1839 Last print f is using&nbsp; common code, so it is called duplicate process That is sharing the common code by multiple process. &nbsp; Observation 1. C Main () { Print f (&ldquo;1 : %d %d /n&rdquo;, get p id (), get p pid () ); Fork (); Print f (&ldquo;2: %d %d /n&rdquo;, get p id (), get p pid () ); Fork (); Print f (&ldquo;3 : %d %d /n&rdquo;, get p id (), get p pid () ); Fork (); Print f (&ldquo;14: %d %d /n&rdquo;, get p id (), get p pid () ); &nbsp; Output :- &nbsp; <img class="alignnone wp-image-9399" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Screenshot_340-460x470.png" alt="Screenshot_3" width="471" height="482" /> &nbsp; &nbsp; &nbsp;
<table style="height: 713px;" width="313">
<tbody>
<tr>
<td width="50">1</td>
<td width="50">2470</td>
<td width="50">2439</td>
</tr>
<tr>
<td width="50">2</td>
<td width="50">2471</td>
<td width="50">2470</td>
</tr>
<tr>
<td width="50">2</td>
<td width="50">2470</td>
<td width="50">2439</td>
</tr>
<tr>
<td width="50">3</td>
<td width="50">2473</td>
<td width="50">2470</td>
</tr>
<tr>
<td width="50">4</td>
<td width="50">2474</td>
<td width="50">2473</td>
</tr>
<tr>
<td width="50">4</td>
<td width="50">2473</td>
<td width="50">2470</td>
</tr>
<tr>
<td width="50">3</td>
<td width="50">2470</td>
<td width="50">2439</td>
</tr>
<tr>
<td width="50">4</td>
<td width="50">2475</td>
<td width="50">2470</td>
</tr>
<tr>
<td width="50">4</td>
<td width="50">2470</td>
<td width="50">2439</td>
</tr>
<tr>
<td width="50">3</td>
<td width="50">2472</td>
<td width="50">2471</td>
</tr>
<tr>
<td width="50">3</td>
<td width="50">2471</td>
<td width="50">1</td>
</tr>
<tr>
<td width="50">4</td>
<td width="50">2477</td>
<td width="50">2471</td>
</tr>
<tr>
<td width="50">4</td>
<td width="50">2471</td>
<td width="50">1</td>
</tr>
<tr>
<td width="50">4</td>
<td width="50">2476</td>
<td width="50">2472</td>
</tr>
<tr>
<td width="50">4</td>
<td width="50">2472</td>
<td width="50">1</td>
</tr>
</tbody>
</table>
&nbsp; &nbsp; <img class="alignnone wp-image-9400" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Screenshot_436-460x342.png" alt="Screenshot_4" width="514" height="382" /> &nbsp; &nbsp;
<table style="height: 770px;" width="399">
<tbody>
<tr>
<td width="63">1</td>
<td width="63">2550</td>
<td width="63">2439</td>
</tr>
<tr>
<td width="63">2</td>
<td width="63">2550</td>
<td width="63">2550</td>
</tr>
<tr>
<td width="63">3</td>
<td width="63">2552</td>
<td width="63">2550</td>
</tr>
<tr>
<td width="63">4</td>
<td width="63">2553</td>
<td width="63">2552</td>
</tr>
<tr>
<td width="63">4</td>
<td width="63">2552</td>
<td width="63">2551</td>
</tr>
<tr>
<td width="63">3</td>
<td width="63">2551</td>
<td width="63">2550</td>
</tr>
<tr>
<td width="63">4</td>
<td width="63">2554</td>
<td width="63">2551</td>
</tr>
<tr>
<td width="63">4</td>
<td width="63">2551</td>
<td width="63">2550</td>
</tr>
<tr>
<td width="63">2</td>
<td width="63">2550</td>
<td width="63">2439</td>
</tr>
<tr>
<td width="63">3</td>
<td width="63">2555</td>
<td width="63">2550</td>
</tr>
<tr>
<td width="63">4</td>
<td width="63">2556</td>
<td width="63">2555</td>
</tr>
<tr>
<td width="63">4</td>
<td width="63">2505</td>
<td width="63">2550</td>
</tr>
<tr>
<td width="63">3</td>
<td width="63">2550</td>
<td width="63">2439</td>
</tr>
<tr>
<td width="63">4</td>
<td width="63">2557</td>
<td width="63">2650</td>
</tr>
<tr>
<td width="63">4</td>
<td width="63">2550</td>
<td width="63">2439</td>
</tr>
</tbody>
</table>
&nbsp; &nbsp; &nbsp;
<ol>
<li>Observation 2.c</li>
</ol>
# include &lt;stdio . h&gt; Main () { Int ret; Ret = fork (); If (ret = = -1) { P error (&ldquo;fork &rdquo;); Return ; } Else if (ret = = 0 ) { Print f (&ldquo;Exclusive child code /n &rdquo;); Exit (0); } Else { Print f (&ldquo;Exclusive parent code/ n &rdquo;); Exit (0); } } &nbsp; <img class="alignnone wp-image-9401" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Screenshot_537-460x484.png" alt="Screenshot_5" width="411" height="433" /> &nbsp; &nbsp; Output :- Exclusive child code Exclusive parent code
<h2>&nbsp; &nbsp; &nbsp; &darr;</h2>
Fork on success returns two values &ldquo;Zero &rdquo; &amp; &ldquo;Non - zero&rdquo; collected by child process
<h2>&nbsp; &nbsp; &nbsp;&darr;</h2>
Parent process &nbsp; 4.If memory is not sufficient then fork causes error&nbsp; Race condition&nbsp; in O.S If the out come of a multiprocessing environment involved with 2 tasks&nbsp; &ldquo;T1&rdquo; &amp; &ldquo;T 2&rdquo; , is different from then condition&nbsp; is&nbsp; occurred.
<ul>
<li>Child process always run in background.</li>
<li>Parent process&nbsp; always run in background.</li>
</ul>
<img class="alignnone size-full wp-image-9386" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/220.png" alt="2" width="30" height="12" />If the parent exited before child then it is called orphan. <img class="alignnone size-full wp-image-9386" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/220.png" alt="2" width="30" height="12" />If the child exited but parent is running &nbsp;it is &ldquo;ZOMBIE&rdquo; state. <img class="alignnone size-full wp-image-9386" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/220.png" alt="2" width="30" height="12" />&nbsp;That is exited value is not collected by parent. &nbsp; <img class="alignnone size-full wp-image-9402" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Screenshot_629.png" alt="Screenshot_6" width="209" height="249" /> <img class="alignnone wp-image-9403" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Screenshot_736.png" alt="Screenshot_7" width="307" height="451" /> &nbsp; &nbsp; The exit status must be collected only by wait (); wait (), will be discussed later. &nbsp; <img class="alignnone size-full wp-image-9386" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/220.png" alt="2" width="30" height="12" />W. a. p to execute an application which will be duplicated with four new jobs. That is total no. of jobs hence must be is (i) x <img class="alignnone size-full wp-image-9386" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/220.png" alt="2" width="30" height="12" />&nbsp;x +1 <img class="alignnone size-full wp-image-9386" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/220.png" alt="2" width="30" height="12" />&nbsp;x +2 <img class="alignnone size-full wp-image-9386" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/220.png" alt="2" width="30" height="12" />&nbsp;x +3. Hence two process should&nbsp; not have common&nbsp; parent id. #include &lt;stdio.h&gt; #include &lt;unistd.h&gt; Main () { If (fork ()) {// parent process Print f ( &ldquo;parent : entered process id : % d, parent id + % d/n), get p id (), get p pid()&rdquo;); Sleep (11); Print f ( &ldquo;parent : entered process id : % d, parent id + % d/n), get p id (), get p pid()&rdquo;); } Else { //child 1 process If (fork ()) { Print f ( &ldquo;child 1 : entered process id : % d, parent id + % d/n), get p id (), get p pid()&rdquo;); Sleep (1); Print f ( &ldquo;child 1 : entered process id : % d, parent id + % d/n), get p id (), get p pid()&rdquo;); } Else { If (fork ()) {// child 2 process Print f ( &ldquo;child 2 : entered process id : % d, parent id + % d/n), get p id (), get p pid()&rdquo;); Sleep (3); Print f ( &ldquo;child 2: entered process id : % d, parent id + % d/n), get p id (), get p pid()&rdquo;); } Else {//child 3 process &nbsp; Print f ( &ldquo;child 3: entered process id : % d, parent id + % d/n), get p id (), get p pid()&rdquo;); Sleep (2); Print f ( &ldquo;child 3 : entered process id : % d, parent id + % d/n), get p id (), get p pid()&rdquo;); } } }// end of &lsquo; else &rsquo;&nbsp; paired with main &lsquo;if&rsquo; }// end&nbsp; of main &nbsp; Output &nbsp;
<table>
<tbody>
<tr>
<td width="117">Parent : Entered</td>
<td width="117">Process id =&nbsp; 3272</td>
<td width="117">Parent id = 2439</td>
</tr>
<tr>
<td width="117">Child 1 : Entered</td>
<td width="117">Process id =3273</td>
<td width="117">Parent id =&nbsp; 3272</td>
</tr>
<tr>
<td width="117">Child 2 : Entered</td>
<td width="117">Process id =3274</td>
<td width="117">Parent id = 3273</td>
</tr>
<tr>
<td width="117">Child 3 : Entered</td>
<td width="117">Process id =3275</td>
<td width="117">Parent id =3274</td>
</tr>
<tr>
<td width="117">Child 3 : Exiting</td>
<td width="117">Process id =3275</td>
<td width="117">Parent id =3274</td>
</tr>
<tr>
<td width="117">Child 2 : Exiting</td>
<td width="117">Process id =3274</td>
<td width="117">Parent id =3273</td>
</tr>
<tr>
<td width="117">Child 1 : Exiting</td>
<td width="117">Process id =3273</td>
<td width="117">Parent id =3274</td>
</tr>
<tr>
<td width="117">Parent&nbsp; : Exiting</td>
<td width="117">Process id =3272</td>
<td width="117">Parent id =2439</td>
</tr>
</tbody>
</table>
&nbsp; &nbsp; <img class="alignnone size-full wp-image-9404" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Screenshot_825.png" alt="Screenshot_8" width="451" height="139" /> &nbsp; &nbsp; <img class="alignnone wp-image-9405" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/Screenshot_919-460x460.png" alt="Screenshot_9" width="777" height="777" /> &nbsp; &nbsp; &nbsp; Output :- &nbsp;
<table style="height: 413px;" width="669">
<tbody>
<tr>
<td width="189">Child 3 : Entered</td>
<td width="189">Process id =&nbsp; 2054</td>
<td width="188">Parent id = 2063</td>
</tr>
<tr>
<td width="189">Child 2 : Entered</td>
<td width="189">Process id =2055</td>
<td width="188">Parent id =&nbsp; 2053</td>
</tr>
<tr>
<td width="189">Child 1 : Entered</td>
<td width="189">Process id =2056</td>
<td width="188">Parent id = 2053</td>
</tr>
<tr>
<td width="189">Parent &nbsp;: Entered</td>
<td width="189">Process id =2053</td>
<td width="188">Parent id =1858</td>
</tr>
<tr>
<td width="189">Child 3 : Exiting</td>
<td width="189">Process id =2054</td>
<td width="188">Parent id =2053</td>
</tr>
<tr>
<td width="189">Child 2 : Exiting</td>
<td width="189">Process id =2055</td>
<td width="188">Parent id =2053</td>
</tr>
<tr>
<td width="189">Child 1 : Exiting</td>
<td width="189">Process id =2056</td>
<td width="188">Parent id =2053</td>
</tr>
<tr>
<td width="189">Parent&nbsp; : Exiting</td>
<td width="189">Process id = 2053</td>
<td width="188">Parent id =1853</td>
</tr>
</tbody>
</table>
&nbsp; &nbsp; <img class="alignnone size-full wp-image-9386" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2014/12/220.png" alt="2" width="30" height="12" />W. a. p to execute pwd , cal, date by child 1 , child 2 &amp; child 3 with random delays and observe the sequence&nbsp; of output #include &lt;stdio.h&gt; #include &lt;unistd.h&gt; Main () { If (fork ()) { If (fork ()) { Int t ; Brand (get p id ()); T = rand () % 10 +1; Sleep (t); Execlp (&ldquo;pwd&rdquo;, &lsquo;pwd &rsquo;, NULL); } Else { Int&nbsp; t ; Brand (get p id ()); T = rand () % 10 +1; Sleep (t); Execlp (&ldquo;cal&rdquo;, &lsquo;cal &rsquo;, NULL); } } Else { Int t ; Brand (get p id ()); T = rand () % 10 +1; Sleep (t); Execlp (&ldquo;date&rdquo;, &lsquo;date &rsquo;, NULL); } } Here we can declare &lsquo;t&rsquo; as&nbsp; common local / global variable. It does not be a problem due to concept of &ldquo;copy &ndash; on - write&rdquo;. Output :- July 2011 SU &nbsp;&nbsp;MO TU&nbsp; WE&nbsp; TH&nbsp; FR&nbsp; ST Sat Jul 284:05:34 1st 201 /home /b59p2/UNIX/fork &nbsp; Name # include &lt;stdlib.h&gt; Rand, rand &ndash;r, brand &ndash; pseudo- random number generator int rand (void) ; Int rand-r&nbsp; (unsigned int * seed p); Void brand&nbsp; (unsigned int * seed); &nbsp; Return Value The &nbsp;rand () and rand &ndash; r function return a value between 0 and RAND &ndash; MAX. The brand () function return no&nbsp; value.
<ul>
<li>The rand () function returns a pseudo- random number generator integer between 0 and RAND &ndash; MAX.</li>
<li>The Brand () function sets its argument as the seed for a new sequence of pseudo- random number generator integers to be returned &nbsp;by rand ()</li>
<li>These sequence are repeatable by calling brand() with same seed value.</li>
<li>If no seed value is provided , the rand () function is automatically seeded with a value of 1.</li>
</ul>
&nbsp;

Understanding of Unix Programs

understanding-unix-programms

<h2>Wait , Wait p id ()</h2>
Wait for process to change state # include &lt;sys / types.h&gt; # include &lt;sys / wait.h&gt; P id &ndash; t Wait&nbsp; (int * status) P id &ndash; t Wait (p id &ndash; t p id, int * status , int options); Int wait id (id type&nbsp; id type, id &ndash; t id, sigin to &ndash; t * in fop, int options); &nbsp;
<h2>Wait () </h2>
The wait () system call suspends executor of the current . process until one of its children terminates the call wait (&amp; status ) is equivalent to Wait p id (- 1, &amp; status , 0); The wait p id () system call&nbsp; suspends execution &nbsp;of the current&nbsp; a&nbsp; child &nbsp;specified by p id argument has changed state , by default&nbsp; wait p id () waits only for terminated children . but this behavior is modified via the options argument as described below &nbsp; &lt; -1 &nbsp;- &nbsp; meaning wait for any child process&nbsp; whose process group ID is equal to the absolute value of P id &nbsp; -1 &nbsp; &nbsp; - &nbsp; &nbsp; meaning wait for any child process &nbsp; 0 &nbsp; &nbsp; -&nbsp; &nbsp; &nbsp;meaning wait for any child process whose process group ID is equal to that of calling process &nbsp; &gt;0 &nbsp; - &nbsp; &nbsp; meaning wait for the child whose process ID is equal to value of Pid &nbsp; Wait ()&nbsp; &nbsp;- &nbsp; is only for parent to wait and not child to wait () for parent&nbsp; &amp; exited value is calls. wait &nbsp;&nbsp;for child &nbsp;exd, this a voids child to be &nbsp; Wait ()&nbsp; - &nbsp; on success, returns the process ID of the terminated child , on error , -1 is returned. &nbsp; Wait P id()&nbsp;- &nbsp;on &nbsp;Success , returns the process ID of the child whose state has changed ; on error , -1 is &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;returned if &lsquo;WNO HAN &amp;&rsquo; &nbsp;was specified and no child specified by p id has yet changed state then o is returned . &nbsp; Wait id ()&nbsp; &nbsp; -&nbsp; &nbsp; &nbsp; Returns&nbsp; 0 on success or if WNO HAN &amp; &nbsp;Was specified and no child specified by id has yet changed state ; on error , -1 is returned. &nbsp;
<h2>Errors </h2>
ECHID &nbsp; &nbsp;- &nbsp; &nbsp; (for wait ())&nbsp; the calling process does not have any un waited &ndash; for children &nbsp; ECHILD&nbsp; - &nbsp; (for&nbsp; wait p id () or wait id ()) [ The process specified&nbsp; by p id (wait p id ()) or id type and id&nbsp; (wait id ()) does not &nbsp;exits or &nbsp;is not &nbsp;&nbsp;a child&nbsp; of the calling process . (This can happen for one&rsquo;s own child if the action for SIGCHILD is set to SIG. IGN) ] &nbsp; EINUAL&nbsp;- &nbsp; The options argument was in valid &nbsp; EINTR &nbsp; - &nbsp; &nbsp;WNDHANG was not set and an unblocked signal or a SIGCHILD was caught. &nbsp;
<h2>Copy &ndash; on &ndash; Write ()</h2>
A separate copy of data will be created , whenever parent/ child modifies the common data. #include &lt;stdio.h&gt; #include &lt;stdlib.h&gt; Int g = 0; Main () { Int l = 0; P F (&ldquo;l &amp; g modified to l= 20, g = 10 globally \n &rdquo;); L = 20; G= 10; If (fork () ) { PF (&ldquo;Parent : l = %d, g = %d\n&rdquo;, l ,g); } Else { PF (&ldquo;Child&nbsp; : l = %d, g = %d\n&rdquo;, l ,g); L ++; G++; PF (&ldquo;l ++, g++ done in child \ n&rdquo;); PF (&ldquo;child : l + % d, g = %d \n&rdquo; l , g); } } Output L = 0, g =0 L &amp; g modified to l = 20, g = 10 globally Child : l =20, g =10 L++, g ++ done in child Child : l =21, g =11 Parent : l =20, g =10 &nbsp;
<ul>
<li>Parent &amp; child share common code</li>
<li>For&rsquo; Data protection &lsquo; data modified in one process will not be reflected in another process</li>
<li>Data protection in done through &lsquo; copy &ndash; on &ndash; write &rsquo;</li>
</ul>
&nbsp; So, data modified by in child is not reflected in parent. &nbsp; Name -exit,&nbsp; - Exit &ndash; terminate the current process #include &lt;unistd.h&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; #include &lt;stdlib.h&gt; Void &ndash; exit (int status )&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Void &ndash; Exit (int status ) &nbsp;
<ul>
<li>The function - Exit () is equivalent to &ndash;exit ()</li>
<li>The function &ndash; exit () terminates the calling process &ldquo;immediately&rdquo; . Any open file descriptors belonging to the process are closed; any children of the process are inherited by process in it, and the process&rsquo;s parent is sent a SIGCHILD signal</li>
<li>The value status is returned to the parent process as the process&rsquo;s exit status and can be effected using one of the wait () family of calls.</li>
</ul>
&nbsp; Return Value 
<ul>
<li>These functions do not return</li>
<li>Exit values are in the range of 0 to 255 and any exit value does not effect the process.</li>
<li>Exit value is short int of 2 bytes and is collected by wait () function in MSB.</li>
</ul>
&nbsp; #include &lt;stdio. h&gt; #include &lt;stdlib.h&gt; Main () { If (fork ()) { Int&nbsp; st, ret Pf(&ldquo;parent executing \ n&rdquo;); Pf(&ldquo;parent Waiting&nbsp; \ n&rdquo;); Ret = Wait&nbsp; (&amp; st); Pf(&ldquo;child exited with&nbsp; % d as collected in MSB \ n&rdquo;, st); St = st &gt;&gt; 8 ;&nbsp; // Hence it is shifted&nbsp; 8 Times Pf(&ldquo;child exited with&nbsp; % d \ n&rdquo;, st); Pf(&ldquo;parent about to exit \ n&rdquo;); Exit (0);&nbsp; // this exit value is returned to bash } Else { Int&nbsp; t ; Srand&nbsp; (get p id ()); T = rand ()&nbsp; % 10 +1 ; Sleep (t); Exit (i); } } &nbsp; Output Parent &nbsp;&nbsp;&nbsp;executing Parent &nbsp;&nbsp;&nbsp;&nbsp;waiting Child &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;exited with 256 as collected in MSB Child &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;exited with 1 Parent &nbsp;&nbsp;&nbsp;about to exit &nbsp; W. a. p to input two small integers (in between 1 to 50) from command line create a new process by fork code. The sum of two integers by the child process and print&nbsp; the result Note These should not be any print statement in child #include &lt;stdio. h&gt; #include &lt;stdlib.h&gt; Main&nbsp; (int argc, char ** arg v) { If (arg c ! =3) { Pf (&ldquo;Usage :&nbsp; ./a.out&nbsp;&nbsp; &lt;Integer 1&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;Integer 2&gt; &rdquo; /n); Return; } If (fork&nbsp; ()) { Int st, ret; Ret = wait (&amp; st); St = st &gt;&gt;8; Print F(&ldquo;Sum = % d /n&rdquo;, st); Exit (0); } Else { Int a, b ; A = a to I (arg V [1]); b= a to I (arg V [2]); exit (a + b); } } &nbsp; Output ./a.out&nbsp;&nbsp; 12&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 14 Sum = 26 &nbsp;
<ol start="2">
<li>W. a. p to create three children from common parent &amp; all the children should delay for randomly generated time of 1 to 10 sec. modify the parent such a manner none of child become orphan.</li>
</ol>
#include &lt;stdio. h&gt; #include &lt;stdlib.h&gt; Main () { If (fork ()) { If (fork ()) { If (fork ()) { //parent process Int st , ret; PF (&ldquo; parent : p id = % d, p pid = % d/n&rdquo; get p id (), get p id ()); While (ret ! = -1) { Ret = wait (&amp; st ), St &gt;&gt;=8; If (st = = 1) PF (&ldquo;child 1 exited with % d /n &rdquo;, st); If (st = = 2) PF (&ldquo;child 2 exited with % d /n &rdquo;, st); If (st = = 3) PF (&ldquo;child 3 exited with % d /n &rdquo;, st); } Exit (0); } Else { //child 3 process Int t; Srand&nbsp;&nbsp; (get p id ()); T = rand () % 10 +1; Sleep (t); PF (&ldquo;child 3 : p id = % d, p pid = %d \ n &rdquo;, get p id (), get p pid ()); Exit (3); } } Else { Int t; Srand&nbsp;&nbsp; (get p id ()); T = rand () % 10 +1; Sleep (t); PF (&ldquo;child 2 : p id = % d, p pid = %d \ n &rdquo;, get p id (), get p pid ()); Exit (2); } } Else { //child 1 process Int t; Srand&nbsp;&nbsp; (get p id ()); T = rand () % 10 +1; Sleep (t); PF (&ldquo;child 3 : p id = % d, p pid = %d \ n &rdquo;, get p id (), get p pid ()); Exit (1); } } &nbsp; OUTPUT Here no child is exited after execution. Hence no child becomes orphan. &nbsp; (ii) Make&nbsp; the parent wait&nbsp; only for 2nd child . If exit states is &lsquo;2&rsquo;, then wait () #include &lt;stdio.h&gt; #include &lt;stdlib.h&gt; Main () { If&nbsp; (fork ()) { If&nbsp; (fork ()) { If&nbsp; (fork ()) { //parent process Int&nbsp; st, ret; PF(&ldquo;Parent : p id = % d, p pid = % d\n &rdquo;, get p id (), get p pid ()); While (ret ! =1) { Ret = wait (&amp; st) St&gt;&gt;8; If (st = = 2) { Pf (&ldquo;child 2 exited with&nbsp; % d \n &rdquo; , st); Exit (0); } Else { //child 3 process Int t ; Srand (get p id ()); T = rand () % 10 +1; Sleep (t); Pf(&ldquo;Child&nbsp; : p id = % d, p pid = % d\n &rdquo;, get p id (), get p pid ()); Exit (3); Else { //child 2 process Int t ; Srand (get p id ()); T = rand () % 10 +1; Sleep (t); Pf(&ldquo;Child &nbsp;2 : p id = % d, p pid = % d\n &rdquo;, get p id (), get p pid ()); } } Else { //child 1process Int t ; Srand (get p id ()); T = rand () % 10 +1; Sleep (t); Pf(&ldquo;Child 1 : p id = % d, p pid = % d\n &rdquo;, get p id (), get p pid ()); } } &nbsp; Output: Hence is child 2 is executed , then child&nbsp; 1 &amp; child 3 becomes orphan. Depending on, random generator&nbsp; of child 2 execution the process that are executed after child 2 becomes orphan.

unix-shell-scripting

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