Job Control

Job Control #

Commands #

Niceness and Priority #

40 niceness values. -20 is highest and 19 is lowest. Default is 0. Child processes inherit niceness of parent. Users can renice processes they own. root can renice any process.

  • nice (1) - run a program with modified scheduling priority
  • renice (1) - alter priority of running processes

Print process list with priority and niceness columns:

ps -efl

[root@server1 ~]# ps -efl | head
F S UID          PID    PPID  C PRI  NI ADDR SZ WCHAN  STIME TTY          TIME CMD
4 S root           1       0  0  80   0 - 43106 ep_pol Mar02 ?        00:00:01 /usr/lib/systemd/systemd rhgb --switched-root --system --deserialize 31
1 S root           2       0  0  80   0 -     0 kthrea Mar02 ?        00:00:00 [kthreadd]
1 I root           3       2  0  60 -20 -     0 rescue Mar02 ?        00:00:00 [rcu_gp]
1 I root           4       2  0  60 -20 -     0 rescue Mar02 ?        00:00:00 [rcu_par_gp]
1 I root           5       2  0  60 -20 -     0 rescue Mar02 ?        00:00:00 [slub_flushwq]
1 I root           6       2  0  60 -20 -     0 rescue Mar02 ?        00:00:00 [netns]
1 I root           8       2  0  60 -20 -     0 worker Mar02 ?        00:00:00 [kworker/0:0H-events_highpri]
1 I root          10       2  0  60 -20 -     0 rescue Mar02 ?        00:00:00 [mm_percpu_wq]
1 I root          12       2  0  80   0 -     0 rcu_ta Mar02 ?        00:00:00 [rcu_tasks_kthre]

View default niceness with nice command:

[root@server1 ~]# nice
0

Process Signals #

List available signals with kill -l:

[root@server1 ~]# 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

Most common process signals:

Signal Number Signal Name Action
1 SIGHUP Hang up signal causes a process to disconnect itself from a closed terminal that it was tied to. Also used to instruct a running daemon to re-read its configuration without a restart
2 SIGINT The ^c (Ctrl+c) signal issued on the controlling terminal to interrupt the execution of a process.
9 SIGKILL Terminates a process abruptly.
15 SIGTERM Sends a soft termination signal to stop a process in an orderly fashion. This is the default signal if none is specified with the command.
18 SIGCONT Same as using the bg command to resume.
19 SIGSTOP Same as using the Ctrl+z to suspend a job.
20 SIGTSTP Same as using the fg command.

Commands #

  • kill (1) - terminate a process
  • pkill (1) - look up, signal, or wait for processes based on name and other attributes