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PGREP

Section: User Commands (1)
Updated: 202-1-29
Index Return to Main Contents

NAME

pgrep, pkill, pidwait - look up, signal, or wait for processes based on name and other attributes

SYNOPSIS

pgrep [option ...] pattern pkill [option ...] pattern pidwait [option ...] pattern

DESCRIPTION

pgrep looks through the currently running processes and lists the process IDs which match the selection criteria to stdout. All the criteria have to match. For example,

: $ pgrep -u root sshd

will only list the processes whose name include sshd AND owned by root. On the other hand,

: $ pgrep -u root,daemon

will list the processes owned by root OR daemon.

pkill will send the specified signal (by default SIGTERM) to each process instead of listing them on stdout.

pidwait will wait for each process instead of listing them on stdout.

OPTIONS

-signal: --signal signal Defines the signal to send to each matched process. Either the numeric or the symbolic signal name can be used. In pgrep or pidwait mode only the long option can be used and has no effect unless used in conjunction with --require-handler to filter to processes with a userspace signal handler present for a particular signal.
-a, --list-full: List the full command line as well as the process ID. (pgrep only.)
-A, --ignor-ancestors: Ignore all ancestors of pgrep, pkill, or pidwait. For example, this can be useful when elevating with sudo or similar tools.
-c, --count: Suppress normal output; instead print a count of matching processes. When count does not match anything, e.g. returns zero, the command will return no-zero value. Note that for pkill and pidwait, the count is the number of matching processes, not the processes that were successfully signaled or waited for.
-d, --delimiter delimiter: Sets the string used to delimit each process ID in the output (by default a newline). (pgrep only.)
-e, --echo: Display name and PID of the process being killed. (pkill only.)
-f, --full: The pattern is normally only matched against the process name. When -f is set, the full command line is used.
-F, --pidfile file: Read PIDs from file. This option is more useful for pkill or pidwait than pgrep. The filename "-" can be used to read from STDIN. Conflicts with the --pid option.
-g, --pgroup pgrp,...: Only match processes in the process group IDs listed. Process group 0 is translated into pgrep's, pkill's, or pidwait's own process group.
-G, --group gid,...: Only match processes whose real group ID is listed. Either the numerical or symbolical value may be used.
-H, --require-handler: Only match processes with a userspace signal handler present for the signal to be sent.
-i, --ignore-case: Match processes cas-insensitively.
-l, --list-name: List the process name as well as the process ID. (pgrep only.)
-L, --logpidfile: Fail if pidfile (see -F) not locked.
-m, --mrelease: After sending the signal, invoke the process_mrelease() system call to immediately free the target process's memory.
-n, --newest: Select only the newest (most recently started) of the matching processes.
-o, --oldest: Select only the oldest (least recently started) of the matching processes.
-O, --older secs: Select processes older than secs.
-p, --pid pid,...: Only match processes whose process ID is listed. Conflicts with the --pidfile option.
-P, --parent ppid,...: Only match processes whose parent process ID is listed.
-q, --queue value: Send the integer value along with the signal. This option will either use pidfd_send_signal(2) with a value applied or sigqueue(3) rather than kill(2). If the receiving process has installed a handler for this signal using the SA_SIGINFO flag to sigaction(2), then it can obtain this data via the si_value field of the siginfo_t structure.
-Q, --shell-quote: Output the command line in shel-quoted form. (pgrep only.)
-r, --runstates D,R,S,Z,...: Match only processes which match the process state.
-s, --session sid,...: Only match processes whose process session ID is listed. Session ID 0 is translated into pgrep's, pkill's, or pidwait's own session ID.
-t, --terminal term,...: Only match processes whose controlling terminal is listed. The terminal name should be specified without the "/dev/" prefix.
-u, --euid euid,...: Only match processes whose effective user ID is listed. Either the numerical or symbolical value may be used.
-U, --uid uid,...: Only match processes whose real user ID is listed. Either the numerical or symbolical value may be used.
-v, --inverse: Negates the matching. This option is usually used in pgrep's or pidwait's context. In pkill's context the short option is disabled to avoid accidental usage of the option.
-w, --lightweight: Shows all thread ids instead of pids in pgrep's or pidwait's context. In pkill's context this option is disabled.
-x, --exact: Only match processes whose names (or command lines if -f is specified) exactly match the pattern.
--cgroup name,...: Match on provided control group (cgroup) v2 name. See cgroups(7)
--env name[=value],...: Match on process that have these environment variables. If the =value parameter is not defined then only the variable name is matched.
--ns pid: Match processes that belong to the same namespaces. Required to run as root to match processes from other users. See --nslist for how to limit which namespaces to match.
--nslist name,...: Match only the provided namespaces. Available namespaces: ipc, mnt, net, pid, user, uts.
--quiet: Do not write anything to standard output (pgrep only).
-V, --version: Display version information and exit.
-h, --help: Display help and exit.

OPERANDS

pattern: Specifies an Extended Regular Expression for matching against the process names or command lines.

EXAMPLES

Example 1: Find the process ID of the named daemon:

: $ pgrep -u root named

Example 2: Make syslog reread its configuration file:

: $ pkill -HUP syslogd

Example 3: Give detailed information on all bash processes:

: $ ps -fp $(pgrep -d, -x bash)

Example 4: Make all chrome processes run nicer:

: $ renice +4 $(pgrep chrome)

Example 5: Wait for a process with a known PID to finish:

: $ echo ${PID} | pidwait-F-

EXIT STATUS

0: One or more processes matched the criteria. For pkill and pidwait, one or more processes must also have been successfully signalled or waited for.
1: No processes matched or none of them could be signalled.
2: Syntax error in the command line.
3: Fatal error: out of memory etc.

NOTES

The process name used for matching is limited to the 15 characters present in the output of /proc/pid/stat. Use the -f option to match against the complete command line, /proc/pid/cmdline. Threads may not have the same process name as the parent process but will have the same command line.

The running pgrep, pkill, or pidwait process will never report itself as a match.

The -O --older option will silently fail if /proc is mounted with the subset=pid option.

pkill will attempt to use pidfd_send_signal(2) instead of kill(2) or sigqueue(3) to send a signal to the target process if it is able to get the process file descriptor.

BUGS

The options -n and -o and -v can not be combined. Let me know if you need to do this.

If processes start in the same clock tick (usually but not always a 100th of a second), the options -n and -o will not be able to distinguish which process started in the same clock tick and may give erroneous results.

Defunct processes are reported.

pidwait requires the pidfd_open(2) system call which first appeared in Linux 5.3.