Version : 2024.01
Last update : 2024/11/27 08:50
A process is a binary file that is loaded into memory and executed. When the file is loaded it needs the operating system to supply it with information such that it can execute correctly. Collectively, this information is refered to as the process environment and includes:
This information is stored in the /proc directory:
[root@redhat9 ~]# cd /proc; ls -d [0-9]* 1 10446 10597 17 22 28 34 406 423 465 504 535 540 5671 5705 5724 5737 5765 5950 6 6200 6384 6444 6462 6571 6668 708 7429 76 77 79 8946 9400 10 10590 12 18 23 29 35 415 43 47 51 536 541 5675 5707 5725 5742 5787 5952 6049 6206 6410 6451 6473 6599 6674 709 743 7618 78 7900 90 9490 10062 10591 13 2 24 3 36 42 434 48 511 537 542 5698 5708 5728 5743 58 5956 61 629 6432 6452 6477 6611 69 710 7430 7619 7896 8 9357 95 10066 10592 14 20 242 30 38 420 44 49 52 538 543 57 5710 5734 5744 5851 5963 614 6318 6433 6453 6479 6617 705 711 7431 7620 7897 80 9365 9543 10223 10595 15 2014 245 32 4 421 45 5 53 539 55 5700 5714 5735 5757 5863 5968 6195 6377 6436 6454 6482 6626 706 712 7432 7621 7898 81 9369 96 10383 10596 16 21 27 33 403 422 46 50 534 54 56 5704 5717 5736 5763 59 5975 62 6381 6439 6455 6486 6640 707 742 7433 7622 7899 853 9392 9896
Each directory refers to a process PID. It contains data from the process environment, for example :
[root@redhat9 proc]# cd 1 ; ls -l total 0 -r--r--r--. 1 root root 0 Sep 25 15:29 arch_status dr-xr-xr-x. 2 root root 0 Sep 25 12:44 attr -rw-r--r--. 1 root root 0 Sep 25 15:29 autogroup -r--------. 1 root root 0 Sep 25 15:29 auxv -r--r--r--. 1 root root 0 Sep 25 12:44 cgroup --w-------. 1 root root 0 Sep 25 15:29 clear_refs -r--r--r--. 1 root root 0 Sep 25 12:44 cmdline -rw-r--r--. 1 root root 0 Sep 25 12:44 comm -rw-r--r--. 1 root root 0 Sep 25 15:29 coredump_filter -r--r--r--. 1 root root 0 Sep 25 15:29 cpu_resctrl_groups -r--r--r--. 1 root root 0 Sep 25 15:29 cpuset lrwxrwxrwx. 1 root root 0 Sep 25 14:56 cwd -> / -r--------. 1 root root 0 Sep 25 12:44 environ lrwxrwxrwx. 1 root root 0 Sep 25 12:44 exe -> /usr/lib/systemd/systemd dr-x------. 2 root root 0 Sep 25 12:44 fd dr-xr-xr-x. 2 root root 0 Sep 25 14:56 fdinfo -rw-r--r--. 1 root root 0 Sep 25 12:44 gid_map -r--------. 1 root root 0 Sep 25 15:29 io -r--------. 1 root root 0 Sep 25 15:29 ksm_merging_pages -r--r--r--. 1 root root 0 Sep 25 15:29 limits -rw-r--r--. 1 root root 0 Sep 25 12:44 loginuid dr-x------. 2 root root 0 Sep 25 15:29 map_files -r--r--r--. 1 root root 0 Sep 25 12:44 maps -rw-------. 1 root root 0 Sep 25 15:29 mem -r--r--r--. 1 root root 0 Sep 25 12:44 mountinfo -r--r--r--. 1 root root 0 Sep 25 12:44 mounts -r--------. 1 root root 0 Sep 25 15:29 mountstats dr-xr-xr-x. 53 root root 0 Sep 25 12:44 net dr-x--x--x. 2 root root 0 Sep 25 12:44 ns -r--r--r--. 1 root root 0 Sep 25 15:29 numa_maps -rw-r--r--. 1 root root 0 Sep 25 15:29 oom_adj -r--r--r--. 1 root root 0 Sep 25 15:29 oom_score -rw-r--r--. 1 root root 0 Sep 25 15:29 oom_score_adj -r--------. 1 root root 0 Sep 25 15:29 pagemap -r--------. 1 root root 0 Sep 25 15:29 patch_state -r--------. 1 root root 0 Sep 25 15:29 personality -rw-r--r--. 1 root root 0 Sep 25 15:29 projid_map lrwxrwxrwx. 1 root root 0 Sep 25 12:44 root -> / -rw-r--r--. 1 root root 0 Sep 25 15:29 sched -r--r--r--. 1 root root 0 Sep 25 15:29 schedstat -r--r--r--. 1 root root 0 Sep 25 12:44 sessionid -rw-r--r--. 1 root root 0 Sep 25 12:44 setgroups -r--r--r--. 1 root root 0 Sep 25 15:29 smaps -r--r--r--. 1 root root 0 Sep 25 15:29 smaps_rollup -r--------. 1 root root 0 Sep 25 15:29 stack -r--r--r--. 1 root root 0 Sep 25 14:56 stat -r--r--r--. 1 root root 0 Sep 25 15:29 statm -r--r--r--. 1 root root 0 Sep 25 12:44 status -r--------. 1 root root 0 Sep 25 15:29 syscall dr-xr-xr-x. 3 root root 0 Sep 25 12:44 task -rw-r--r--. 1 root root 0 Sep 25 15:29 timens_offsets -r--r--r--. 1 root root 0 Sep 25 15:29 timers -rw-rw-rw-. 1 root root 0 Sep 25 15:29 timerslack_ns -rw-r--r--. 1 root root 0 Sep 25 12:44 uid_map -r--r--r--. 1 root root 0 Sep 25 15:29 wchan
Important - Note that the content of the files is of little or of no direct use to a System Administrator.
There are three types of process:
A process can be in one of nine process states :
The output from this command shows the processes attached to the current terminal:
[root@redhat9 1]# cd ~
[root@redhat9 ~]# ps
PID TTY TIME CMD
10062 pts/0 00:00:00 su
10066 pts/0 00:00:00 bash
10602 pts/0 00:00:00 ps
You can get more details by using the -l switch:
[root@redhat9 ~]# ps -l F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD 4 S 0 10062 9400 0 80 0 - 58719 do_wai pts/0 00:00:00 su 4 S 0 10066 10062 0 80 0 - 56056 do_wai pts/0 00:00:00 bash 4 R 0 10604 10066 0 80 0 - 56370 - pts/0 00:00:00 ps
Note in this output :
| F | Process flag. The value of 4 means the process is using root privileges. |
|---|---|
| S | The process state - S (sleeping), R (In run queue), Z (zombie), N (low priority), D (uninterruptible sleep), T (Traced) |
| UID | User ID of the user who has stated the process |
| PID | Process ID |
| PPID | Parent PID |
| C | Prority factor |
| PRI | Process priority |
| NI | Process nice value |
| ADDR | Memory address |
| SZ | Virtual memory usage |
| WCHAN | Name of the kernel function in which the process is asleep |
| TTY | Name of the terminal in which the process was started |
| TIME | Processing time |
| CMD | The command that generated the process |
To view the process table, use the ps command with the l and x switches:
[root@redhat9 ~]# ps lx | more F UID PID PPID PRI NI VSZ RSS WCHAN STAT TTY TIME COMMAND 4 0 1 0 20 0 190992 17880 ep_pol Ss ? 0:13 /usr/lib/systemd/systemd rhgb --switched-root --system --deserialize 31 1 0 2 0 20 0 0 0 kthrea S ? 0:00 [kthreadd] 1 0 3 2 0 -20 0 0 rescue I< ? 0:00 [rcu_gp] 1 0 4 2 0 -20 0 0 rescue I< ? 0:00 [rcu_par_gp] 1 0 5 2 0 -20 0 0 rescue I< ? 0:00 [slub_flushwq] 1 0 6 2 0 -20 0 0 rescue I< ? 0:00 [netns] 1 0 8 2 0 -20 0 0 worker I< ? 0:00 [kworker/0:0H-events_highpri] 1 0 10 2 0 -20 0 0 rescue I< ? 0:00 [mm_percpu_wq] 1 0 12 2 20 0 0 0 rcu_ta I ? 0:00 [rcu_tasks_kthre] 1 0 13 2 20 0 0 0 rcu_ta I ? 0:00 [rcu_tasks_rude_] 1 0 14 2 20 0 0 0 rcu_ta I ? 0:00 [rcu_tasks_trace] 1 0 15 2 20 0 0 0 smpboo S ? 0:00 [ksoftirqd/0] 1 0 16 2 20 0 0 0 rcu_gp I ? 0:01 [rcu_preempt] 1 0 17 2 -100 - 0 0 smpboo S ? 0:00 [migration/0] 1 0 18 2 -51 - 0 0 smpboo S ? 0:00 [idle_inject/0] 1 0 20 2 20 0 0 0 smpboo S ? 0:00 [cpuhp/0] 1 0 21 2 20 0 0 0 smpboo S ? 0:00 [cpuhp/1] 1 0 22 2 -51 - 0 0 smpboo S ? 0:00 [idle_inject/1] 1 0 23 2 -100 - 0 0 smpboo S ? 0:00 [migration/1] 1 0 24 2 20 0 0 0 smpboo S ? 0:00 [ksoftirqd/1] 1 0 27 2 20 0 0 0 smpboo S ? 0:00 [cpuhp/2] 1 0 28 2 -51 - 0 0 smpboo S ? 0:00 [idle_inject/2] 1 0 29 2 -100 - 0 0 smpboo S ? 0:00 [migration/2] 1 0 30 2 20 0 0 0 smpboo S ? 0:00 [ksoftirqd/2] 1 0 32 2 0 -20 0 0 worker I< ? 0:00 [kworker/2:0H-events_highpri] 1 0 33 2 20 0 0 0 smpboo S ? 0:00 [cpuhp/3] 1 0 34 2 -51 - 0 0 smpboo S ? 0:00 [idle_inject/3] 1 0 35 2 -100 - 0 0 smpboo S ? 0:00 [migration/3] 1 0 36 2 20 0 0 0 smpboo S ? 0:00 [ksoftirqd/3] 1 0 38 2 0 -20 0 0 worker I< ? 0:00 [kworker/3:0H-events_highpri] 5 0 42 2 20 0 0 0 devtmp S ? 0:00 [kdevtmpfs] 1 0 43 2 0 -20 0 0 rescue I< ? 0:00 [inet_frag_wq] 1 0 44 2 20 0 0 0 kaudit S ? 0:00 [kauditd] 1 0 45 2 20 0 0 0 watchd S ? 0:00 [khungtaskd] 1 0 46 2 20 0 0 0 oom_re S ? 0:00 [oom_reaper] 1 0 47 2 0 -20 0 0 rescue I< ? 0:00 [writeback] 1 0 48 2 20 0 0 0 kcompa S ? 0:02 [kcompactd0] 1 0 49 2 25 5 0 0 ksm_sc SN ? 0:00 [ksmd] 1 0 50 2 39 19 0 0 khugep SN ? 0:00 [khugepaged] 1 0 51 2 0 -20 0 0 rescue I< ? 0:00 [cryptd] 1 0 52 2 0 -20 0 0 rescue I< ? 0:00 [kintegrityd] 1 0 53 2 0 -20 0 0 rescue I< ? 0:00 [kblockd] 1 0 54 2 0 -20 0 0 rescue I< ? 0:00 [blkcg_punt_bio] 1 0 55 2 0 -20 0 0 rescue I< ? 0:00 [tpm_dev_wq] 1 0 56 2 0 -20 0 0 rescue I< ? 0:00 [md] 1 0 57 2 0 -20 0 0 rescue I< ? 0:00 [md_bitmap] 1 0 58 2 0 -20 0 0 rescue I< ? 0:00 [edac-poller] 1 0 59 2 -51 - 0 0 kthrea S ? 0:00 [watchdogd] 1 0 61 2 0 -20 0 0 worker I< ? 0:00 [kworker/0:1H-kblockd] 1 0 62 2 20 0 0 0 kswapd S ? 0:00 [kswapd0] 1 0 69 2 0 -20 0 0 rescue I< ? 0:00 [kthrotld] 1 0 76 2 0 -20 0 0 rescue I< ? 0:00 [acpi_thermal_pm] 1 0 77 2 0 -20 0 0 rescue I< ? 0:00 [kmpath_rdacd] 1 0 78 2 0 -20 0 0 rescue I< ? 0:00 [kaluad] --More-- [q]
This output contains some additional information:
| VSZ | The same thing as SZ in the previous example |
|---|---|
| RSS | Memory in KB used by the process |
| STAT | The same thing as S in the previous example |
Using the a, u and x switches you obtain the following output:
[root@redhat9 ~]# ps aux | more USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 1 0.0 0.2 190992 17880 ? Ss Sep25 0:13 /usr/lib/systemd/systemd rhgb --switched-root --system --deserialize 31 root 2 0.0 0.0 0 0 ? S Sep25 0:00 [kthreadd] root 3 0.0 0.0 0 0 ? I< Sep25 0:00 [rcu_gp] root 4 0.0 0.0 0 0 ? I< Sep25 0:00 [rcu_par_gp] root 5 0.0 0.0 0 0 ? I< Sep25 0:00 [slub_flushwq] root 6 0.0 0.0 0 0 ? I< Sep25 0:00 [netns] root 8 0.0 0.0 0 0 ? I< Sep25 0:00 [kworker/0:0H-events_highpri] root 10 0.0 0.0 0 0 ? I< Sep25 0:00 [mm_percpu_wq] root 12 0.0 0.0 0 0 ? I Sep25 0:00 [rcu_tasks_kthre] root 13 0.0 0.0 0 0 ? I Sep25 0:00 [rcu_tasks_rude_] root 14 0.0 0.0 0 0 ? I Sep25 0:00 [rcu_tasks_trace] root 15 0.0 0.0 0 0 ? S Sep25 0:00 [ksoftirqd/0] root 16 0.0 0.0 0 0 ? I Sep25 0:01 [rcu_preempt] root 17 0.0 0.0 0 0 ? S Sep25 0:00 [migration/0] root 18 0.0 0.0 0 0 ? S Sep25 0:00 [idle_inject/0] root 20 0.0 0.0 0 0 ? S Sep25 0:00 [cpuhp/0] root 21 0.0 0.0 0 0 ? S Sep25 0:00 [cpuhp/1] root 22 0.0 0.0 0 0 ? S Sep25 0:00 [idle_inject/1] root 23 0.0 0.0 0 0 ? S Sep25 0:00 [migration/1] root 24 0.0 0.0 0 0 ? S Sep25 0:00 [ksoftirqd/1] root 27 0.0 0.0 0 0 ? S Sep25 0:00 [cpuhp/2] root 28 0.0 0.0 0 0 ? S Sep25 0:00 [idle_inject/2] root 29 0.0 0.0 0 0 ? S Sep25 0:00 [migration/2] root 30 0.0 0.0 0 0 ? S Sep25 0:00 [ksoftirqd/2] root 32 0.0 0.0 0 0 ? I< Sep25 0:00 [kworker/2:0H-events_highpri] root 33 0.0 0.0 0 0 ? S Sep25 0:00 [cpuhp/3] root 34 0.0 0.0 0 0 ? S Sep25 0:00 [idle_inject/3] root 35 0.0 0.0 0 0 ? S Sep25 0:00 [migration/3] root 36 0.0 0.0 0 0 ? S Sep25 0:00 [ksoftirqd/3] root 38 0.0 0.0 0 0 ? I< Sep25 0:00 [kworker/3:0H-events_highpri] root 42 0.0 0.0 0 0 ? S Sep25 0:00 [kdevtmpfs] root 43 0.0 0.0 0 0 ? I< Sep25 0:00 [inet_frag_wq] root 44 0.0 0.0 0 0 ? S Sep25 0:00 [kauditd] root 45 0.0 0.0 0 0 ? S Sep25 0:00 [khungtaskd] root 46 0.0 0.0 0 0 ? S Sep25 0:00 [oom_reaper] root 47 0.0 0.0 0 0 ? I< Sep25 0:00 [writeback] root 48 0.0 0.0 0 0 ? S Sep25 0:02 [kcompactd0] root 49 0.0 0.0 0 0 ? SN Sep25 0:00 [ksmd] root 50 0.0 0.0 0 0 ? SN Sep25 0:00 [khugepaged] root 51 0.0 0.0 0 0 ? I< Sep25 0:00 [cryptd] root 52 0.0 0.0 0 0 ? I< Sep25 0:00 [kintegrityd] root 53 0.0 0.0 0 0 ? I< Sep25 0:00 [kblockd] root 54 0.0 0.0 0 0 ? I< Sep25 0:00 [blkcg_punt_bio] root 55 0.0 0.0 0 0 ? I< Sep25 0:00 [tpm_dev_wq] root 56 0.0 0.0 0 0 ? I< Sep25 0:00 [md] root 57 0.0 0.0 0 0 ? I< Sep25 0:00 [md_bitmap] root 58 0.0 0.0 0 0 ? I< Sep25 0:00 [edac-poller] root 59 0.0 0.0 0 0 ? S Sep25 0:00 [watchdogd] root 61 0.0 0.0 0 0 ? I< Sep25 0:00 [kworker/0:1H-kblockd] root 62 0.0 0.0 0 0 ? S Sep25 0:00 [kswapd0] root 69 0.0 0.0 0 0 ? I< Sep25 0:00 [kthrotld] root 76 0.0 0.0 0 0 ? I< Sep25 0:00 [acpi_thermal_pm] root 77 0.0 0.0 0 0 ? I< Sep25 0:00 [kmpath_rdacd] root 78 0.0 0.0 0 0 ? I< Sep25 0:00 [kaluad] --More-- [q]
This output contains some additional information:
| USER | The user associated with the process |
|---|---|
| %CPU | % of the processor ressources used by the process |
| %MEM | % of the memory ressources used by the process |
The command line switches for this command are :
[root@redhat9 ~]# ps --help all
Usage:
ps [options]
Basic options:
-A, -e all processes
-a all with tty, except session leaders
a all with tty, including other users
-d all except session leaders
-N, --deselect negate selection
r only running processes
T all processes on this terminal
x processes without controlling ttys
Selection by list:
-C <command> command name
-G, --Group <GID> real group id or name
-g, --group <group> session or effective group name
-p, p, --pid <PID> process id
--ppid <PID> parent process id
-q, q, --quick-pid <PID>
process id (quick mode)
-s, --sid <session> session id
-t, t, --tty <tty> terminal
-u, U, --user <UID> effective user id or name
-U, --User <UID> real user id or name
The selection options take as their argument either:
a comma-separated list e.g. '-u root,nobody' or
a blank-separated list e.g. '-p 123 4567'
Output formats:
-F extra full
-f full-format, including command lines
f, --forest ascii art process tree
-H show process hierarchy
-j jobs format
j BSD job control format
-l long format
l BSD long format
-M, Z add security data (for SELinux)
-O <format> preloaded with default columns
O <format> as -O, with BSD personality
-o, o, --format <format>
user-defined format
s signal format
u user-oriented format
v virtual memory format
X register format
-y do not show flags, show rss vs. addr (used with -l)
--context display security context (for SELinux)
--headers repeat header lines, one per page
--no-headers do not print header at all
--cols, --columns, --width <num>
set screen width
--rows, --lines <num>
set screen height
Show threads:
H as if they were processes
-L possibly with LWP and NLWP columns
-m, m after processes
-T possibly with SPID column
Miscellaneous options:
-c show scheduling class with -l option
c show true command name
e show the environment after command
k, --sort specify sort order as: [+|-]key[,[+|-]key[,...]]
L show format specifiers
n display numeric uid and wchan
S, --cumulative include some dead child process data
-y do not show flags, show rss (only with -l)
-V, V, --version display version information and exit
-w, w unlimited output width
--help <simple|list|output|threads|misc|all>
display help and exit
For more details see ps(1).
The pgrep command is used to search for a process based on its name and other properties, then display its PID on the standard output.
For example, the following command displays the PID of the sshd process belonging to root:
[root@redhat9 ~]# pgrep -u root sshd 5734 9357
The following command displays all the PIDs of processes belonging to root or trainee :
[root@redhat9 ~]# pgrep -u root,trainee | more 1 2 3 4 5 6 8 10 12 13 14 15 16 17 18 20 21 22 23 24 27 28 29 30 32 33 34 35 36 38 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 61 62 69 76 77 78 79 --More-- [q]
The command line switches for this command are :
[root@redhat9 ~]# pgrep --help
Usage:
pgrep [options] <pattern>
Options:
-d, --delimiter <string> specify output delimiter
-l, --list-name list PID and process name
-a, --list-full list PID and full command line
-v, --inverse negates the matching
-w, --lightweight list all TID
-c, --count count of matching processes
-f, --full use full process name to match
-g, --pgroup <PGID,...> match listed process group IDs
-G, --group <GID,...> match real group IDs
-i, --ignore-case match case insensitively
-n, --newest select most recently started
-o, --oldest select least recently started
-O, --older <seconds> select where older than seconds
-P, --parent <PPID,...> match only child processes of the given parent
-s, --session <SID,...> match session IDs
-t, --terminal <tty,...> match by controlling terminal
-u, --euid <ID,...> match by effective IDs
-U, --uid <ID,...> match by real IDs
-x, --exact match exactly with the command name
-F, --pidfile <file> read PIDs from file
-L, --logpidfile fail if PID file is not locked
-r, --runstates <state> match runstates [D,S,Z,...]
--ns <PID> match the processes that belong to the same
namespace as <pid>
--nslist <ns,...> list which namespaces will be considered for
the --ns option.
Available namespaces: ipc, mnt, net, pid, user, uts
-h, --help display this help and exit
-V, --version output version information and exit
For more details see pgrep(1).
This command displays processes in a tree structure:
[root@redhat9 ~]# pstree
systemd─┬─ModemManager───3*[{ModemManager}]
├─NetworkManager───2*[{NetworkManager}]
├─accounts-daemon───3*[{accounts-daemon}]
├─at-spi-bus-laun─┬─dbus-daemon
│ └─3*[{at-spi-bus-laun}]
├─at-spi2-registr───2*[{at-spi2-registr}]
├─atd
├─auditd─┬─sedispatch
│ └─2*[{auditd}]
├─avahi-daemon───avahi-daemon
├─colord───3*[{colord}]
├─crond
├─cupsd
├─dbus-broker-lau───dbus-broker
├─firewalld───{firewalld}
├─gdm─┬─gdm-session-wor─┬─gdm-wayland-ses─┬─dbus-run-sessio─┬─dbus-daemon
│ │ │ │ └─gnome-session-b─┬─gnome-shell─┬─Xwayland
│ │ │ │ │ ├─ibus-daemon─┬─ibus-dconf───3*[{ibus-dconf}]
│ │ │ │ │ │ ├─ibus-engine-sim───2*[{ibus-engine-sim}]
│ │ │ │ │ │ └─2*[{ibus-daemon}]
│ │ │ │ │ └─17*[{gnome-shell}]
│ │ │ │ ├─gsd-a11y-settin───3*[{gsd-a11y-settin}]
│ │ │ │ ├─gsd-color───3*[{gsd-color}]
│ │ │ │ ├─gsd-datetime───3*[{gsd-datetime}]
│ │ │ │ ├─gsd-housekeepin───3*[{gsd-housekeepin}]
│ │ │ │ ├─gsd-keyboard───3*[{gsd-keyboard}]
│ │ │ │ ├─gsd-media-keys───3*[{gsd-media-keys}]
│ │ │ │ ├─gsd-power───3*[{gsd-power}]
│ │ │ │ ├─gsd-print-notif───2*[{gsd-print-notif}]
│ │ │ │ ├─gsd-rfkill───2*[{gsd-rfkill}]
│ │ │ │ ├─gsd-screensaver───2*[{gsd-screensaver}]
│ │ │ │ ├─gsd-sharing───3*[{gsd-sharing}]
│ │ │ │ ├─gsd-smartcard───5*[{gsd-smartcard}]
│ │ │ │ ├─gsd-sound───3*[{gsd-sound}]
│ │ │ │ ├─gsd-wacom───3*[{gsd-wacom}]
│ │ │ │ └─3*[{gnome-session-b}]
│ │ │ └─2*[{gdm-wayland-ses}]
│ │ └─2*[{gdm-session-wor}]
│ └─2*[{gdm}]
├─2*[gjs───6*[{gjs}]]
├─gsd-printer───2*[{gsd-printer}]
├─3*[httpd─┬─httpd]
│ ├─httpd───68*[{httpd}]]
│ └─2*[httpd───52*[{httpd}]]]
├─ibus-portal───2*[{ibus-portal}]
├─ibus-x11───2*[{ibus-x11}]
├─irqbalance───{irqbalance}
├─lsmd
├─mcelog
├─polkitd───7*[{polkitd}]
├─power-profiles-───2*[{power-profiles-}]
├─rhsmcertd───{rhsmcertd}
├─rsyslogd───2*[{rsyslogd}]
├─rtkit-daemon───2*[{rtkit-daemon}]
├─sshd───sshd───sshd───bash───su───bash───pstree
├─switcheroo-cont───2*[{switcheroo-cont}]
├─systemd─┬─(sd-pam)
│ ├─dbus-broker-lau───dbus-broker
│ ├─pipewire───2*[{pipewire}]
│ ├─pipewire-pulse───2*[{pipewire-pulse}]
│ └─wireplumber───4*[{wireplumber}]
├─systemd───(sd-pam)
├─systemd-journal
├─systemd-logind
├─systemd-udevd
├─udisksd───4*[{udisksd}]
├─upowerd───2*[{upowerd}]
├─wpa_supplicant
└─xdg-permission-───2*[{xdg-permission-}]
The command line switches for this command are:
[root@redhat9 ~]# pstree --help
pstree: unrecognized option '--help'
Usage: pstree [-acglpsStTuZ] [ -h | -H PID ] [ -n | -N type ]
[ -A | -G | -U ] [ PID | USER ]
or: pstree -V
Display a tree of processes.
-a, --arguments show command line arguments
-A, --ascii use ASCII line drawing characters
-c, --compact-not don't compact identical subtrees
-C, --color=TYPE color process by attribute
(age)
-g, --show-pgids show process group ids; implies -c
-G, --vt100 use VT100 line drawing characters
-h, --highlight-all highlight current process and its ancestors
-H PID, --highlight-pid=PID
highlight this process and its ancestors
-l, --long don't truncate long lines
-n, --numeric-sort sort output by PID
-N TYPE, --ns-sort=TYPE
sort output by this namespace type
(cgroup, ipc, mnt, net, pid, time, user, uts)
-p, --show-pids show PIDs; implies -c
-s, --show-parents show parents of the selected process
-S, --ns-changes show namespace transitions
-t, --thread-names show full thread names
-T, --hide-threads hide threads, show only processes
-u, --uid-changes show uid transitions
-U, --unicode use UTF-8 (Unicode) line drawing characters
-V, --version display version information
-Z, --security-context
show security attributes
PID start at this PID; default is 1 (init)
USER show only trees rooted at processes of this user
top shows a continuous real time list of running processes:
[root@redhat9 ~]# top
top - 14:41:00 up 2 days, 1:56, 1 user, load average: 0.01, 0.01, 0.00
Tasks: 199 total, 1 running, 198 sleeping, 0 stopped, 0 zombie
%Cpu(s): 0.1 us, 0.1 sy, 0.0 ni, 99.8 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
MiB Mem : 7685.1 total, 4518.6 free, 1105.4 used, 2375.3 buff/cache
MiB Swap: 5120.0 total, 5120.0 free, 0.0 used. 6579.8 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
10744 root 20 0 226032 4096 3328 R 0.3 0.1 0:00.04 top
1 root 20 0 190992 17880 10644 S 0.0 0.2 0:13.87 systemd
2 root 20 0 0 0 0 S 0.0 0.0 0:00.05 kthreadd
3 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 rcu_gp
4 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 rcu_par_gp
5 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 slub_flushwq
6 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 netns
8 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 kworker/0:0H-events_highpri
10 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 mm_percpu_wq
12 root 20 0 0 0 0 I 0.0 0.0 0:00.00 rcu_tasks_kthre
13 root 20 0 0 0 0 I 0.0 0.0 0:00.00 rcu_tasks_rude_
14 root 20 0 0 0 0 I 0.0 0.0 0:00.00 rcu_tasks_trace
15 root 20 0 0 0 0 S 0.0 0.0 0:00.05 ksoftirqd/0
16 root 20 0 0 0 0 I 0.0 0.0 0:01.27 rcu_preempt
17 root rt 0 0 0 0 S 0.0 0.0 0:00.31 migration/0
18 root -51 0 0 0 0 S 0.0 0.0 0:00.00 idle_inject/0
20 root 20 0 0 0 0 S 0.0 0.0 0:00.00 cpuhp/0
21 root 20 0 0 0 0 S 0.0 0.0 0:00.00 cpuhp/1
22 root -51 0 0 0 0 S 0.0 0.0 0:00.00 idle_inject/1
23 root rt 0 0 0 0 S 0.0 0.0 0:00.44 migration/1
24 root 20 0 0 0 0 S 0.0 0.0 0:00.02 ksoftirqd/1
27 root 20 0 0 0 0 S 0.0 0.0 0:00.00 cpuhp/2
28 root -51 0 0 0 0 S 0.0 0.0 0:00.00 idle_inject/2
29 root rt 0 0 0 0 S 0.0 0.0 0:00.46 migration/2
30 root 20 0 0 0 0 S 0.0 0.0 0:00.01 ksoftirqd/2
32 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 kworker/2:0H-events_highpri
33 root 20 0 0 0 0 S 0.0 0.0 0:00.00 cpuhp/3
34 root -51 0 0 0 0 S 0.0 0.0 0:00.00 idle_inject/3
35 root rt 0 0 0 0 S 0.0 0.0 0:00.47 migration/3
36 root 20 0 0 0 0 S 0.0 0.0 0:00.02 ksoftirqd/3
38 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 kworker/3:0H-events_highpri
42 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kdevtmpfs
43 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 inet_frag_wq
44 root 20 0 0 0 0 S 0.0 0.0 0:00.01 kauditd
45 root 20 0 0 0 0 S 0.0 0.0 0:00.13 khungtaskd
46 root 20 0 0 0 0 S 0.0 0.0 0:00.00 oom_reaper
47 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 writeback
48 root 20 0 0 0 0 S 0.0 0.0 0:02.29 kcompactd0
49 root 25 5 0 0 0 S 0.0 0.0 0:00.00 ksmd
50 root 39 19 0 0 0 S 0.0 0.0 0:00.93 khugepaged
51 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 cryptd
52 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 kintegrityd
53 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 kblockd
54 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 blkcg_punt_bio
55 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 tpm_dev_wq
56 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 md
57 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 md_bitmap
58 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 edac-poller
59 root -51 0 0 0 0 S 0.0 0.0 0:00.00 wat
...
To display the top command help, press h :
Help for Interactive Commands - procps-ng 3.3.17
Window 1:Def: Cumulative mode Off. System: Delay 3.0 secs; Secure mode Off.
Z,B,E,e Global: 'Z' colors; 'B' bold; 'E'/'e' summary/task memory scale
l,t,m,I Toggle: 'l' load avg; 't' task/cpu; 'm' memory; 'I' Irix mode
0,1,2,3,4 Toggle: '0' zeros; '1/2/3' cpu/numa views; '4' cpus two abreast
f,F,X Fields: 'f'/'F' add/remove/order/sort; 'X' increase fixed-width
L,&,<,> . Locate: 'L'/'&' find/again; Move sort column: '<'/'>' left/right
R,H,J,C . Toggle: 'R' Sort; 'H' Threads; 'J' Num justify; 'C' Coordinates
c,i,S,j . Toggle: 'c' Cmd name/line; 'i' Idle; 'S' Time; 'j' Str justify
x,y . Toggle highlights: 'x' sort field; 'y' running tasks
z,b . Toggle: 'z' color/mono; 'b' bold/reverse (only if 'x' or 'y')
u,U,o,O . Filter by: 'u'/'U' effective/any user; 'o'/'O' other criteria
n,#,^O . Set: 'n'/'#' max tasks displayed; Show: Ctrl+'O' other filter(s)
V,v . Toggle: 'V' forest view; 'v' hide/show forest view children
k,r Manipulate tasks: 'k' kill; 'r' renice
d or s Set update interval
W,Y,! Write config file 'W'; Inspect other output 'Y'; Combine Cpus '!'
q Quit
( commands shown with '.' require a visible task display window )
Press 'h' or '?' for help with Windows,
Type 'q' or <Esc> to continue
Important - To return to the previous display, press q or escape.
When launched top's refresh rate is 3 seconds. To change this to 1 second, use the s key:
top - 14:42:15 up 2 days, 1:57, 1 user, load average: 0.00, 0.00, 0.00 Tasks: 199 total, 1 running, 198 sleeping, 0 stopped, 0 zombie %Cpu(s): 0.0 us, 0.1 sy, 0.0 ni, 99.9 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st MiB Mem : 7685.1 total, 4518.6 free, 1105.4 used, 2375.3 buff/cache MiB Swap: 5120.0 total, 5120.0 free, 0.0 used. 6579.8 avail Mem Change delay from 3.0 to 1 ...
To sort the list by memory usage, press M :
[root@redhat9 ~]# top
top - 14:43:12 up 2 days, 1:58, 1 user, load average: 0.00, 0.00, 0.00
Tasks: 199 total, 1 running, 198 sleeping, 0 stopped, 0 zombie
%Cpu(s): 0.0 us, 0.0 sy, 0.0 ni,100.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
MiB Mem : 7685.1 total, 4518.6 free, 1105.4 used, 2375.3 buff/cache
MiB Swap: 5120.0 total, 5120.0 free, 0.0 used. 6579.8 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
6049 gdm 20 0 4453852 242772 120572 S 0.0 3.1 0:23.39 gnome-shell
6617 gdm 20 0 578604 54332 46592 S 0.0 0.7 0:00.05 ibus-x11
6206 gdm 20 0 166808 45312 38144 S 0.0 0.6 0:00.05 Xwayland
5707 root 20 0 350204 44404 18884 S 0.0 0.6 0:00.38 firewalld
6444 gdm 20 0 678348 33608 21888 S 0.0 0.4 0:00.44 gsd-color
5675 polkitd 20 0 2713852 31804 19792 S 0.0 0.4 0:00.54 polkitd
6462 gdm 20 0 661452 29948 22276 S 0.0 0.4 0:00.13 gsd-media-keys
6674 gdm 20 0 2866068 28596 21120 S 0.0 0.4 0:00.06 gjs
6486 gdm 20 0 665628 28568 20996 S 0.0 0.4 0:00.12 gsd-power
6432 gdm 20 0 2931604 27964 20864 S 0.0 0.4 0:00.06 gjs
6439 gdm 20 0 590924 27396 19716 S 0.0 0.3 0:00.12 gsd-wacom
6451 gdm 20 0 590224 26680 19584 S 0.0 0.3 0:00.10 gsd-keyboard
6571 gdm 20 0 598424 24032 17280 S 0.0 0.3 0:00.02 gsd-printer
853 root 20 0 475084 23056 18120 S 0.0 0.3 0:04.02 NetworkManager
5975 gdm 20 0 734740 22260 15744 S 0.0 0.3 0:00.10 gnome-session-b
7620 apache 20 0 2423380 21372 5632 S 0.0 0.3 0:14.02 httpd
7431 apache 20 0 2423380 21316 5632 S 0.0 0.3 0:14.10 httpd
6455 gdm 20 0 594384 20668 16128 S 0.0 0.3 0:00.04 gsd-datetime
7898 apache 20 0 2357844 19356 5632 S 0.0 0.2 0:13.86 httpd
1 root 20 0 190992 17880 10644 S 0.0 0.2 0:13.89 systemd
7621 apache 20 0 2226708 17344 5760 S 0.0 0.2 0:12.83 httpd
7899 apache 20 0 2226708 17292 5760 S 0.0 0.2 0:11.94 httpd
7432 apache 20 0 2226708 17240 5632 S 0.0 0.2 0:12.81 httpd
7622 apache 20 0 2161172 17236 5760 S 0.0 0.2 0:12.70 httpd
7433 apache 20 0 2226708 17196 5632 S 0.0 0.2 0:12.77 httpd
7900 apache 20 0 2226708 17096 5632 S 0.0 0.2 0:12.27 httpd
6381 gdm 9 -11 545148 16128 12800 S 0.0 0.2 0:00.05 wireplumber
5742 root 20 0 395124 15672 11636 S 0.0 0.2 0:00.13 udisksd
6452 gdm 20 0 467300 14876 11136 S 0.0 0.2 0:00.02 gsd-print-notif
6640 colord 20 0 530424 14164 9980 S 0.0 0.2 0:00.06 colord
5851 gdm 20 0 22976 13936 10752 S 0.0 0.2 0:00.11 systemd
9365 trainee 20 0 22984 13812 10624 S 0.0 0.2 0:00.09 systemd
6454 gdm 20 0 603444 13636 10112 S 0.0 0.2 0:04.03 gsd-smartcard
6477 gdm 20 0 530684 13456 8320 S 0.0 0.2 0:00.01 gsd-sound
6599 gdm 20 0 600368 13304 6656 S 0.0 0.2 0:00.07 ibus-daemon
629 root 20 0 36112 13120 9216 S 0.0 0.2 0:00.48 systemd-udevd
5787 root 20 0 387252 13092 9472 S 0.0 0.2 0:00.02 gdm-session-wor
6436 gdm 20 0 678244 12720 9216 S 0.0 0.2 0:00.01 gsd-sharing
5704 root 20 0 391468 12632 10712 S 0.0 0.2 0:00.05 ModemManager
6482 gdm 20 0 524704 12100 7168 S 0.0 0.2 0:01.08 gsd-housekeepin
7429 root 20 0 20368 11608 9176 S 0.0 0.1 0:04.09 httpd
7618 root 20 0 20368 11540 9108 S 0.0 0.1 0:04.28 httpd
6377 gdm 9 -11 326096 11520 8192 S 0.0 0.1 0:00.02 pipewire
5671 root 20 0 21044 11480 9088 S 0.0 0.1 0:02.60 systemd-logind
7896 root 20 0 20368 11464 9032 S 0.0 0.1 0:04.17 httpd
9357 root 20 0 19432 11264 9600 S 0.0 0.1 0:00.02 sshd
5736 root 20 0 247824 11136 9088 S 0.0 0.1 0:00.04 cupsd
614 root 20 0 27084 10880 9728 S 0.0 0.1 0:00.88 systemd-journal
5765 root 20 0 453120 10828 7808 S 0.0 0.1 0:00.02 gdm
...
To see the zombie and waiting processes, use the i key:
[root@redhat9 ~]# top
top - 14:44:10 up 2 days, 1:59, 1 user, load average: 0.00, 0.00, 0.00
Tasks: 199 total, 1 running, 198 sleeping, 0 stopped, 0 zombie
%Cpu(s): 0.5 us, 0.0 sy, 0.0 ni, 99.3 id, 0.0 wa, 0.2 hi, 0.0 si, 0.0 st
MiB Mem : 7685.1 total, 4518.6 free, 1105.4 used, 2375.3 buff/cache
MiB Swap: 5120.0 total, 5120.0 free, 0.0 used. 6579.8 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
6049 gdm 20 0 4458012 242772 120572 S 1.0 3.1 0:23.41 gnome-shell
10744 root 20 0 226032 4096 3328 R 1.0 0.1 0:00.59 top
To exit top, press q.
The command line switches for this command are :
[root@redhat9 ~]# top --help top: inappropriate '-help' Usage: top -hv | -bcEeHiOSs1 -d secs -n max -u|U user -p pid(s) -o field -w [cols]
Normally commands are executed in the foreground of a terminal. However you can also execute a command in what is known as the background by adding (space)& to the end of the command:
# sleep 9999 &
Important - Note that a background process is said to be asynchronous because it continues independently of its parent, which is the shell. The foreground the process is said to be synchronous.
Linux identifies processes sent to the back ground by job numbers.
The jobs command shows a list of all the current jobs associated with the current terminal:
[root@redhat9 ~]# sleep 9999 & [1] 10749 [root@redhat9 ~]# jobs -l [1]+ 10749 Running sleep 9999 &
Important - The job number is between square brackets whilst the PID is not. The + sign indicates that this is the last job to have been modified.
If you wish to send a process into the background to free up the shell for other commands, you must first suspend the process in question. Normally we suspend a process using the key combination CtrlZ.
For example:
[root@redhat9 ~]# sleep 1234 ^Z [2]+ Stopped sleep 1234
Once suspended, use the bg (background) command followed by % and the job number to send the process to the background:
[root@redhat9 ~]# bg %2 [2]+ sleep 1234 & [root@redhat9 ~]# jobs -l [1]- 10749 Running sleep 9999 & [2]+ 10750 Running sleep 1234 &
Important - Note that when the process is sent to the background it resumes normal execution. The - character which follows the [1] indicates that this is that last but one job to have been modified.
To bring the job back to the foreground you cannot suspend it by using the CtrlZ keys. In this case you will have to send a signal to the process. Signals are sent to processes by using the kill command:
[root@redhat9 ~]# kill -s stop %2 [2]+ Stopped sleep 1234
To bring the process back to the foreground, use the fg command:
[root@redhat9 ~]# fg %2 sleep 1234 ^C
Important - Note that we have used the CtrlC keys to kill the process once in the foreground.
The command line switches for the jobs command are :
[root@redhat9 ~]# help jobs
jobs: jobs [-lnprs] [jobspec ...] or jobs -x command [args]
Display status of jobs.
Lists the active jobs. JOBSPEC restricts output to that job.
Without options, the status of all active jobs is displayed.
Options:
-l lists process IDs in addition to the normal information
-n lists only processes that have changed status since the last
notification
-p lists process IDs only
-r restrict output to running jobs
-s restrict output to stopped jobs
If -x is supplied, COMMAND is run after all job specifications that
appear in ARGS have been replaced with the process ID of that job's
process group leader.
Exit Status:
Returns success unless an invalid option is given or an error occurs.
If -x is used, returns the exit status of COMMAND.
The wait command makes an asynchronous process react like a synchronous process:
[root@redhat9 ~]# jobs -l [1]+ 10749 Running sleep 9999 & [root@redhat9 ~]# wait %1 ^C [root@redhat9 ~]# jobs -l [1]+ 10749 Running sleep 9999 &
Important - Note that using CtrlC kills the process generated by the wait command and not the process generated by the sleep command.
This command is used to change the process priority. The default nice value when a process is started is 10. The highest value of nice is -20, whilst the lowest value is 19:
[root@redhat9 ~]# nice -n -20 sleep 1234 ^Z [2]+ Stopped nice -n -20 sleep 1234 [root@redhat9 ~]# ps lx | grep sleep 0 0 10749 10066 20 0 220952 1792 hrtime S pts/0 0:00 sleep 9999 4 0 10775 10066 0 -20 220952 1792 do_sig T< pts/0 0:00 sleep 1234 0 0 10777 10066 20 0 221664 2304 pipe_r S+ pts/0 0:00 grep --color=auto sleep [root@redhat9 ~]# nice -n 19 sleep 5678 ^Z [3]+ Stopped nice -n 19 sleep 5678 [root@redhat9 ~]# ps lx | grep sleep 0 0 10749 10066 20 0 220952 1792 hrtime S pts/0 0:00 sleep 9999 4 0 10775 10066 0 -20 220952 1792 do_sig T< pts/0 0:00 sleep 1234 0 0 10778 10066 39 19 220952 1792 do_sig TN pts/0 0:00 sleep 5678 0 0 10780 10066 20 0 221664 2304 pipe_r S+ pts/0 0:00 grep --color=auto sleep
As you can see the 6th column contains the nice value that is applied to the 5th column.
Important - Note that only root can give a process a value between 0 and -20.
The command line switches for this command are :
[root@redhat9 ~]# nice --help
Usage: nice [OPTION] [COMMAND [ARG]...]
Run COMMAND with an adjusted niceness, which affects process scheduling.
With no COMMAND, print the current niceness. Niceness values range from
-20 (most favorable to the process) to 19 (least favorable to the process).
Mandatory arguments to long options are mandatory for short options too.
-n, --adjustment=N add integer N to the niceness (default 10)
--help display this help and exit
--version output version information and exit
NOTE: your shell may have its own version of nice, which usually supersedes
the version described here. Please refer to your shell's documentation
for details about the options it supports.
GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
Full documentation <https://www.gnu.org/software/coreutils/nice>
or available locally via: info '(coreutils) nice invocation'
This command is used to change the process priority of an already running process. Only the process owner and root can renice a process:
[root@redhat9 ~]# jobs -l [1] 10749 Running sleep 9999 & [2]- 10775 Stopped nice -n -20 sleep 1234 [3]+ 10778 Stopped nice -n 19 sleep 5678 [root@redhat9 ~]# bg %2 [2]- nice -n -20 sleep 1234 & [root@redhat9 ~]# bg %3 [3]+ nice -n 19 sleep 5678 & [root@redhat9 ~]# jobs -l [1] 10749 Running sleep 9999 & [2]- 10775 Running nice -n -20 sleep 1234 & [3]+ 10778 Running nice -n 19 sleep 5678 & [root@redhat9 ~]# renice +5 10775 10775 (process ID) old priority -20, new priority 5 [root@redhat9 ~]# renice -5 10778 10778 (process ID) old priority 19, new priority -5 [root@redhat9 ~]# ps lx | grep sleep 0 0 10749 10066 20 0 220952 1792 hrtime S pts/0 0:00 sleep 9999 4 0 10775 10066 25 5 220952 1792 do_sys SN pts/0 0:00 sleep 1234 0 0 10778 10066 15 -5 220952 1792 do_sys S< pts/0 0:00 sleep 5678 0 0 10790 10066 20 0 221796 2304 pipe_r S+ pts/0 0:00 grep --color=auto sleep
Important -Note that only root can decrease the priority value with the renice command.
The command line switches for this command are :
[root@redhat9 ~]# renice --help Usage: renice [-n] <priority> [-p|--pid] <pid>... renice [-n] <priority> -g|--pgrp <pgid>... renice [-n] <priority> -u|--user <user>... Alter the priority of running processes. Options: -n, --priority <num> specify the nice value -p, --pid interpret arguments as process ID (default) -g, --pgrp interpret arguments as process group ID -u, --user interpret arguments as username or user ID -h, --help display this help -V, --version display version For more details see renice(1).
This command allows a process to continue after closing the terminal in which is was launched. A child process dies when the parent process dies or terminates. As a connection is a process, when you disconnect, your processes terminate. To avoid remaining connected after launching a long process, use the nohup command:
nohup lp sales.txt &
The command line switches for this command are :
[root@redhat9 ~]# nohup --help
Usage: nohup COMMAND [ARG]...
or: nohup OPTION
Run COMMAND, ignoring hangup signals.
--help display this help and exit
--version output version information and exit
If standard input is a terminal, redirect it from an unreadable file.
If standard output is a terminal, append output to 'nohup.out' if possible,
'$HOME/nohup.out' otherwise.
If standard error is a terminal, redirect it to standard output.
To save output to FILE, use 'nohup COMMAND > FILE'.
NOTE: your shell may have its own version of nohup, which usually supersedes
the version described here. Please refer to your shell's documentation
for details about the options it supports.
GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
Full documentation <https://www.gnu.org/software/coreutils/nohup>
or available locally via: info '(coreutils) nohup invocation'
The kill command sends signals to processes. The list of possible signals can be displayed using the -l option:
[root@redhat9 ~]# kill -l 1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL 5) SIGTRAP 6) SIGABRT 7) SIGBUS 8) SIGFPE 9) SIGKILL 10) SIGUSR1 11) SIGSEGV 12) SIGUSR2 13) SIGPIPE 14) SIGALRM 15) SIGTERM 16) SIGSTKFLT 17) SIGCHLD 18) SIGCONT 19) SIGSTOP 20) SIGTSTP 21) SIGTTIN 22) SIGTTOU 23) SIGURG 24) SIGXCPU 25) SIGXFSZ 26) SIGVTALRM 27) SIGPROF 28) SIGWINCH 29) SIGIO 30) SIGPWR 31) SIGSYS 34) SIGRTMIN 35) SIGRTMIN+1 36) SIGRTMIN+2 37) SIGRTMIN+3 38) SIGRTMIN+4 39) SIGRTMIN+5 40) SIGRTMIN+6 41) SIGRTMIN+7 42) SIGRTMIN+8 43) SIGRTMIN+9 44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13 48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13 52) SIGRTMAX-12 53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9 56) SIGRTMAX-8 57) SIGRTMAX-7 58) SIGRTMAX-6 59) SIGRTMAX-5 60) SIGRTMAX-4 61) SIGRTMAX-3 62) SIGRTMAX-2 63) SIGRTMAX-1 64) SIGRTMAX
Important - You will notice that each signal has a number. These signal numbers are used instead of options. For example, -19 instead of the -stop option.
The most usefull signals are as follows:
| Numéro | Description |
|---|---|
| -1 | A Hang Up is sent to all the child processus of the PID specified |
| -2 | Equivalent to the CtrlC key combination |
| -3 | The same signal as -2 but it generates de debug file |
| -9 | A brutal way of killing a process |
| -15 | The correct way of killing a process |
The command line switches for this command are :
[root@redhat9 ~]# help kill
kill: kill [-s sigspec | -n signum | -sigspec] pid | jobspec ... or kill -l [sigspec]
Send a signal to a job.
Send the processes identified by PID or JOBSPEC the signal named by
SIGSPEC or SIGNUM. If neither SIGSPEC nor SIGNUM is present, then
SIGTERM is assumed.
Options:
-s sig SIG is a signal name
-n sig SIG is a signal number
-l list the signal names; if arguments follow `-l' they are
assumed to be signal numbers for which names should be listed
-L synonym for -l
Kill is a shell builtin for two reasons: it allows job IDs to be used
instead of process IDs, and allows processes to be killed if the limit
on processes that you can create is reached.
Exit Status:
Returns success unless an invalid option is given or an error occurs.
The pkill command is used to send signals to processes identified by their name. For example, the following command forces syslog to reread its configuration file:
[root@redhat9 ~]# pkill -HUP rsyslogd
The command line switches for this command are :
[root@redhat9 ~]# pkill --help
Usage:
pkill [options] <pattern>
Options:
-<sig>, --signal <sig> signal to send (either number or name)
-q, --queue <value> integer value to be sent with the signal
-e, --echo display what is killed
-c, --count count of matching processes
-f, --full use full process name to match
-g, --pgroup <PGID,...> match listed process group IDs
-G, --group <GID,...> match real group IDs
-i, --ignore-case match case insensitively
-n, --newest select most recently started
-o, --oldest select least recently started
-O, --older <seconds> select where older than seconds
-P, --parent <PPID,...> match only child processes of the given parent
-s, --session <SID,...> match session IDs
-t, --terminal <tty,...> match by controlling terminal
-u, --euid <ID,...> match by effective IDs
-U, --uid <ID,...> match by real IDs
-x, --exact match exactly with the command name
-F, --pidfile <file> read PIDs from file
-L, --logpidfile fail if PID file is not locked
-r, --runstates <state> match runstates [D,S,Z,...]
--ns <PID> match the processes that belong to the same
namespace as <pid>
--nslist <ns,...> list which namespaces will be considered for
the --ns option.
Available namespaces: ipc, mnt, net, pid, user, uts
-h, --help display this help and exit
-V, --version output version information and exit
For more details see pgrep(1).
Copyright © 2024 Hugh Norris.