I will briefly introduce the commands that manipulate the process.
Please use it for learning, LPIC, LinuC measures, etc.
Also, if you think it's processed cheese, I highly recommend browser back.
A program running on Linux is called a process.
The following commands that handle such a process are introduced with usage examples. (The one in parentheses is a bonus)
| command | Description |
|---|---|
| pgrep | Search for the running process ID based on username, UID, GID, etc. |
| top | View running processes in real time |
| ps | Get process information |
| pstree | View currently running processes in a tree format |
| nice | Change process priority |
| renice | Change the priority of running processes |
| jobs | View running processes |
| bg | Make it a background job |
| fg | Make it a foreground job |
| kill | Send a signal to the process |
| killall | Send a signal to the process |
| (free) | Show the amount of free and used memory in the system |
pgrep
A command to search for a running process ID based on user name, UID, GID, etc.
$ pgrep -u root
1
2
3
4
6
...(abridgement)
$ pgrep -U 0
1
2
3
4
6
...(abridgement)
You can specify the user name with -u and the UID with -U.
Root UID is 0 in LINUX
top
A command to display the running process in real time
top - 22:06:29 up 1 day, 16:36, 1 user, load average: 0.00, 0.02, 0.00
Tasks: 96 total, 1 running, 55 sleeping, 0 stopped, 0 zombie
%Cpu(s): 0.0 us, 0.3 sy, 0.0 ni, 99.7 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
KiB Mem : 1002108 total, 150664 free, 517700 used, 333744 buff/cache
KiB Swap: 0 total, 0 free, 0 used. 330584 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
17870 mysql 20 0 1309152 319372 0 S 0.7 31.9 6:43.18 mysqld
32132 ubuntu 20 0 44524 3928 3320 R 0.3 0.4 0:00.01 top
1 root 20 0 159948 6360 3880 S 0.0 0.6 0:04.36 systemd
2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd
3 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 rcu_gp
Running ps with no options shows only processes launched from the current shell You can also see the mysqld that I used to play in my environment and the process of the top command that I'm running now. The screen is automatically updated and displayed in descending order of CPU usage Monitoring ends when you press "q"
"PID" means the process ID, "USER" means the user who executed the process, "% CPU" means the percentage of CPU consumed, and "% MEM" means the percentage of memory consumed.
ps
PS (ProceSs) command is a command to get process information
$ ps
PID TTY TIME CMD
31249 pts/0 00:00:00 bash
31348 pts/0 00:00:00 ps
If you execute without options, a list of processes started on that terminal will be displayed. "PID" is the process ID, "TTY" is the name of the terminal that executed the process, "TIME" is the execution time of the process, and "CMD" is the execution command. From the results, we can see that the shell uses bash.
| option | Description |
|---|---|
| a | View other users' processes |
| u | Also display the user name |
| x | Also show processes that are not executed from the terminal |
| e | Display information about all processes except kernel processes |
| f | Generate a complete list |
| o | Customize the columns to display |
ps aux
$ ps aux
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 1 0.0 0.6 159948 6268 ? Ss Aug27 0:04 /sbin/init
root 2 0.0 0.0 0 0 ? S Aug27 0:00 [kthreadd]
root 3 0.0 0.0 0 0 ? I< Aug27 0:00 [rcu_gp]
...abridgement...
ubuntu 31248 0.0 0.3 107980 3628 ? S 14:17 0:00 sshd: ubuntu@pts/0
ubuntu 31249 0.0 0.5 23112 5064 pts/0 Ss 14:17 0:00 -bash
ubuntu 31351 0.0 0.3 40088 3504 pts/0 R+ 14:22 0:00 ps aux
ps -efThere is also a method
$ ps -ef
UID PID PPID C STIME TTY TIME CMD
root 1 0 0 Aug27 ? 00:00:04 /sbin/init
root 2 0 0 Aug27 ? 00:00:00 [kthreadd]
root 3 2 0 Aug27 ? 00:00:00 [rcu_gp]
...abridgement...
ubuntu 31248 31155 0 14:17 ? 00:00:00 sshd: ubuntu@pts/0
ubuntu 31249 31248 0 14:17 pts/0 00:00:00 -bash
ubuntu 31355 31249 0 14:27 pts/0 00:00:00 ps -ef
It's nice to customize the display as you like
$ ps -o pid,nice,user,cmd
PID NI USER CMD
3614 0 ubuntu -bash
4341 0 ubuntu ps -o pid,nice,user,cmd
pstree
A command to display the currently running process in a tree format
Below is an example of running on AWS EC2
$ pstree
systemd─┬─accounts-daemon───2*[{accounts-daemon}]
├─acpid
├─2*[agetty]
├─amazon-ssm-agen───8*[{amazon-ssm-agen}]
├─atd
├─containerd───8*[{containerd}]
├─cron
├─dbus-daemon
├─dockerd───9*[{dockerd}]
├─lvmetad
├─lxcfs───10*[{lxcfs}]
├─mysqld───38*[{mysqld}]
├─networkd-dispat───{networkd-dispat}
├─polkitd───2*[{polkitd}]
├─rsyslogd───3*[{rsyslogd}]
├─snapd───8*[{snapd}]
├─sshd───sshd───sshd───bash───pstree
├─systemd───(sd-pam)
├─systemd-journal
├─systemd-logind
├─systemd-network
├─systemd-resolve
├─systemd-timesyn───{systemd-timesyn}
├─systemd-udevd
└─unattended-upgr───{unattended-upgr}
You can see that bash is started from sshd required to access EC2 and pstree is running from that bash
nice
Change process priority
Process priorities are defined as -20 from -20 to 19, with lower priorities being higher.
When executed with no arguments, the priority is incremented by 10.
$ sleep 15 &
[2] 2644
[1] Done nice sleep 15
$ ps -o pid,nice,user,cmd
PID NI USER CMD
2521 0 ubuntu -bash
2644 0 ubuntu sleep 15
2645 0 ubuntu ps -o pid,nice,user,cmd
$ nice sleep 15 &
[1] 2634
$ ps -o pid,nice,user,cmd
PID NI USER CMD
2521 0 ubuntu -bash
2634 10 ubuntu sleep 15
2635 0 ubuntu ps -o pid,nice,user,cmd
renice
Change the priority of running processes
$ sleep 15 &
[1] 2651
$ ps -o pid,nice,user,cmd
PID NI USER CMD
2521 0 ubuntu -bash
2651 0 ubuntu sleep 15
2652 0 ubuntu ps -o pid,nice,user,cmd
$ renice 10 2651
2651 (process ID) old priority 0, new priority 10
$ ps -o pid,nice,user,cmd
PID NI USER CMD
2521 0 ubuntu -bash
2651 10 ubuntu sleep 15
2655 0 ubuntu ps -o pid,nice,user,cmd
jobs
(Background) View running jobs. A job is a unit of processing seen by the user, and there are foreground jobs that are visible to the user and background jobs that are invisible to the user. You can make it a background job by prepending the bg command or prepending the "&" to the execution command.
$ sleep 60 &
[1] 3810
$ jobs
[1]+ Running sleep 60 &
$ kill -s SIGKILL %1
$ jobs
[1]+ Killed sleep 60
[1]Or%1Is called the job id and is assigned to each user.
bg
Make it a background job
Type Ctrl + z in the running program, or
&Even if it is executed with, it becomes a background job.
fg
Make it a foreground job
In bash, only one program can run in the foreground job
kill
You can use the kill command to signal a process
| Signal ID | Signal name | motion |
|---|---|---|
| 1 | SIGUP | Termination by disconnecting the terminal |
| 2 | SIGINT | End by interrupt |
| 9 | SIGKILL | forced termination |
| 15 | SIGTERM | Exit (default) |
| 18 | SIGCONT | Resume |
If it is SIGTERM, the program termination process is executed, but SIGKILL is forcibly terminated as it is.
By the way, SIGINT is sent when ending with "Control + c"
If you want to terminate the process with process ID 32147, do as follows
$ kill -15 32147
You can also end by specifying the signal ID
$ kill -s SIGTERM 32147
Specify the signal ID
$ kill -9 32147
Specify the signal name
$ kill -s SIGKILL 32147
killall
Send a signal to the process by specifying the process name
Even if the same program is executed multiple times, different PIDs are assigned to each process, but if killall is used, processes with the same name can be terminated at once.
$ vi a.txt &
[1] 3728
$ ps
PID TTY TIME CMD
3614 pts/0 00:00:00 bash
3728 pts/0 00:00:00 vi
3732 pts/0 00:00:00 ps
$ killall -15 vi
$ ps
PID TTY TIME CMD
3614 pts/0 00:00:00 bash
3728 pts/0 00:00:00 vi
3734 pts/0 00:00:00 ps
$ killall -SIGKILL vi
[1]+ Killed vi a.txt
$ ps
PID TTY TIME CMD
3614 pts/0 00:00:00 bash
3736 pts/0 00:00:00 ps
free
Show the amount of free and used memory in the system
When combined with the -t option, it also displays a line showing the total of physical memory and swap memory.
$ free -t
total used free shared buff/cache available
Mem: 1002108 516296 104900 812 380912 331188
Swap: 0 0 0
Total: 1002108 516296 104900
You can get to know the kernel program (at least in terms) just by elaborating on the process. Let's live a fun Linux life while being aware of what programs are running on your computer.
It was a topic about the process for the first time in a year. Nice to meet you too.