Linux Process Management Basics

[Ageek]

Linux Process Management

A process can be identified as a set of instructions loaded to the memory. Every process has UID and GID.

Who is the owner of the ‘firefox’ program?

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stat /usr/bin/firefox
	stat $(which firefox)

Observe,
Get PID, Executed User, Real User, Common Name

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ps axo pid,euser,ruser,comm |grep firefox
ps axo pid,euser,ruser,comm |egrep ‘init|firefox’

Get PID, %CPU, % MEM, Executed User, Real User, Common Name

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	ps axo pid,%cpu,%mem,tty,euser,ruser,comm |less

find the parent process

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pstree |less

What is a Signal in Linux

This a UNIX concept which is used to inter-process communication. Using Signal can send a message directly to a process. There are many Signal types are available. Most frequently use signal are;
HUP (1) -> re-read the config file
KILL (9) -> Terminate immediately
TERM (15) -> Terminate gracefully

Further, observe

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man 7 signal

Command use for sending Signals

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kill
killall
pkill
pgrep

Exersises:

Observe:

1.

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        $ pgrep crond
	$ pgrep cupsd

	# kill -HUP $(pgrep crond)
	# kill -HUP $(pgrep cupsd)

	$ pgrep crond	-> has PID got changed?
	$ pgrep cupsd  	-> has PID got changed?

	# kill -9 $(pgrep cupsd)
	$ pgrep cupsd

	# service crond start
	$ pgrep crond 	-> check the PID

2.

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        $ firefox &
	$ killall firefox		->Observe the firefox
	
	$ pkill firefox

3.

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$ firefox
	$ ctrl + z

	$ jobs 	-> find the job id
	$ bg %1	-> resume the background process 1
	
	$ fg %1	
	$ kill %1

Start Stop Services

All init script of the process are usually in /etc unless if you have given a installing prefix when compiling the packages.

How to use;

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/etc/init.d/servicename start|stop|reload|restart|status

OR

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service servicename start|stop|reload|restart|status

Start Stop service while Boot and Shutdown time

At the booting process kernel start the init process, which is the master process of the system. Then read the /etc/inittab to decide the default runlevel.

Observ:

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cat /etc/inittab

|
|
# Default runlevel. The runlevels used are:
# 0 - halt (Do NOT set initdefault to this)
# 1 - Single user mode
# 2 - Multiuser, without NFS (same as 3, do not have networking)
# 3 - Full multiuser mode
# 4 - unused
# 5 - X11
# 6 - reboot (Do NOT set initdefault to this)
#
id:5:initdefault: # default runlevel
According to the runlevel defined the appropriate directory is used to run the initial script.

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				|- rc0.d
				|
				|- rc1.d
				|
				|- rc2.d
				|
	/etc/rc.d/|- rc3.d
				|	
				|- rc4.d
				|
				|- rc5.d
				|
				|- rc6.d

Observ:

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	ls -al /etc/rc.d/rc5.d

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K95cgconfig -> ../init.d/cgconfig
K95firstboot -> ../init.d/firstboot
S02lvm2-monitor -> ../init.d/lvm2-monitor
S07iscsid -> ../init.d/iscsid

Anatomy of the init scripts

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                     S 07 iscsid
S for start at boot _|	|	|_  init script			
K dont start		|_ prority level			

Create a script to start at the beginning will be discussed later on

[Neo]

This is extremely useful. Well done!

[Nipuna]

I like Linux.