Process Management In Linux
- A process is a program under execution. (or)
- A process is an instance of a running program.
- The process has its own address space in memory, a thread of execution, and characteristics such as security context, environment and current priority.
- The Linux 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
- 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.
- There are two types of process in Linux:
1. Foreground process.
2. Background process.
In Foreground users can execute only one process (or) job.
Ex: $ firefox
To kill the foreground job in Linux:
Ctrl + C EX: $cp file1 file2
In the Background, users can execute many jobs at a time.
Ex: $fire fox & $ cp file1 file2
To check the jobs list in Linux:
$jobs PS: Displays information about the running process. $ps
To view the process with more detailed information:
$ ps U
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’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 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
- One typical signal is SIGTERM, which terminates the process; it asks it to exit cleanly.
- Another is SIGKILL, which kills the process; the process is required to exit immediately.
To find the PID(s_ belonging to the SSH service)
$ pidof sshd (or) $ Pgrep sshd
Top: Monitors system resources (similar to task manager in windows)
S --->To change the time interval for updating top results (Sec’s)
R ---> To sort by PID number
U ---> Username to get only that user process details
P ---> To sort by CPU utilization.
M ---> To sort by RAM utilization.
C ---> To display or hide command full path.
R ---> To renice a process
K ---> To kill a process
W ---> To save the modified configuration
Z ---> to Quit
When you’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 <priority> [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 & 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 & $nohup firefox
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 (Save & quit)
- To deny messages: $mesg n
- To allow messages: $mesg y
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 & 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 email@example.com single user $mail user1,user2,user3
multiple users at a time $ mail user1<stud It translates files to the user. $ mail user2<backup-file
- Mails are stored in mailbox: (/var/spool/mail/username)
- Go open the mailbox: $mail
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Note: By default, all mails will store in the primary mailbox (Nor/spool/mail). It will open mails in the primary mailbox transferred to the secondary mailbox (i.e mbox) àTo open secondary mailbox: $mail – f
The primary mailbox only maintains unread mails.
Mail box options:
d2 ---> delete 2nd mail
P ---> print
w filename --> IT writes to new file *
One Bit Equals to how many bytes
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 Disk Storage
1 bit = Binary digit 1 bit = binary digit
8 bits = 1 byte 8 bits = 1 byte
1024 bytes = 1 kilobyte 1000 bytes = 1 kilo
1024 kilo = 1 mega 1000 kilo = 1 mega
1024 mega = 1 Giga 1000 mega = 1Giga
1024 Giga = 1 Tera 1000 Giga = 1 Tera
1024 Tera = 1 Peta 1000 Tera = 1 Peta
1024 peta = 1 exa 1000 peta = 1 Exa
1024 exa = 1 zetta 1000 Exa = 1Zetta
1024 zetta = 1 yotta 1000 Zetta = 1 Yotta
1024 yotta = 1bronto 1000 Yotta = 1 Bronto
1024 Bronto = 1 Geo 1000 Bronto = 1 Geo
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