Ch7. Monitor and Manage Linux Processes

 

What is a process?

- A process is a program which is being executed
- Any process may create a child process. All processes are descendants of the first system process, which is systemd on a RHEL7 system.

[root@master ~]# echo $$   (To see the PID of your current shell process)
	4085
[root@master ~]# bash
[root@master ~]# echo $$
	8686
[root@master ~]# exit
	exit
[root@master ~]# echo $$
	4085**

Listing processes:

[root@master ~]# ps
[root@master ~]# ps aux
[root@master ~]# ps -aux
[root@master ~]# ps -aux | less
[root@master ~]# ps aux | grep -i syslogd
[root@master ~]# ls /proc/
[root@master ~]# ps aux | grep 264             (which shown in /proc)
[root@master ~]# pidof vim                     or [root@master ~]# pgrep vim
[root@master ~]# ps -l                         (To display Parent PID PPID)
[root@master ~]# ps -ef                        (To display Parent PID PPID and nice values)

a.... all processes attached to a terminal
u.... provides more columns
x.... all other processes

[root@master ~]# pstree                        (process status tree)
OR
[root@master ~]# ps fax                        (process status tree)
[root@master ~]# pstree -p                     (Display PID of each process)

- Processes in brackets (usually at the top) are scheduled kernel threads.

Real-time process monitoring:

**[root@master ~]# uptime
[root@master ~]# grep "model name" /proc/cpuinfo  (to know nu of CPUs)
[root@master ~]# top**

• type 1 to show all cpu cores

• type s to change the default refresh rate which is 3 seconds

• type h for help

• type k to kill a process

• type r to renice a process

• type M to change the display to sort by the amount of memory

• type P to change the display to sort by the CPU utilization

• type n to change the number of processes shown

• type w to save current display configuration

• type q to quit

• PID ... The process ID

• USER ... The process owner

• VIRT ... (Virtual memory) All memory the process is using including swap

• RES ... (Resident memory) The physical memory used by the process

• TIME ... CPU time, the total processing time since the process started

GUI tools to manage processes:

[root@master ~]# gnome-system-monitor 
OR)
Applications.. System Tools.. System Monitor

Controlling Jobs:

- Background processes display a question mark (?) in the TTY column in a ps aux command.

[root@master ~]# dd if=/dev/zero of=/dev/null
[root@master ~]# sleep 100000 &                (Running a job in the background)
	[1] 5151

[root@master ~]# jobs
	[1]+  Running       sleep 100000 &

[root@master ~]# fg %1
	sleep 100000

	^Z                                            (To resend to the background)
	[1]+  Stopped       sleep 100000

[root@master ~]# bg %1                          (To restart the process in the background)              
	[1]+ sleep 100000 &

OR
	[root@master ~]# bg 5151

^C                                               (End the process)

Killing Processes:

[root@master ~]# kill -l           (List all signals)
[root@master ~]# man 7 signal

1)SIGHUP   Causes the process to re-read the configuration file
9)SIGKILL  Should be used with caution
15)SIGTERM  The   default

[root@master ~]# pidof vim
	4123
[root@master ~]# kill 4123         (Default is SIGTERM 15)

[root@master ~]# pidof vim
	7073
[root@master ~]# kill -9 7073
[root@master ~]# kill -SIGKILL 7073

[root@master ~]# pkill vim         (Default is SIGTERM 15)
[root@master ~]# killall vim

Managing Process Priorities:

- Processes are scheduled according to priority.
- negative values are allowed only to root.

[root@master ~]# ps l                      (To show nice values)

-The nice command is used to start a process with a user defined priority.
[root@master ~]# nice vim text &           (Default is 10)
[1] 9182

[root@master ~]# nice -n 15 vim text &

-The renice command is used to change the priority of a currently running process.
[root@master ~]# renice 19 9182            (19 is the new value)

---