$ Linux Command

Processes

pidof

Find the process ID of a running program.

pidprocessrunningfindproc

Additional Notes

pidof returns the process IDs (PIDs) of running programs that match the given name. It searches through the /proc filesystem to find processes whose executable name matches the specified program name.

System administrators use pidof in scripts to check if a program is running, send signals to processes by name, or get PIDs for monitoring tools. It is simpler than parsing the output of ps or grep and is available on most Linux systems as part of the sysvinit-utils or procps-ng packages.

Syntax

pidof [options] [program-name...]

Parameters

  • program-name: The exact name of the program (or programs) whose PIDs to find.

Common Options

  • -s: Return only a single PID (the first one found).
  • -c: Return only PIDs running with the same root directory. Useful in containers or chroot environments.
  • -x: Also return PIDs of scripts started by the named program (shell scripts, etc.).
  • -o PID: Omit the specified PID from the result. Can be used multiple times.
  • -q: Quiet mode. Do not print PIDs, only set the exit status.
  • -S: Separate PIDs with spaces instead of newlines (default behavior).
  • --help: Show help and exit.
  • --version: Show version information.

Examples

pidof bash

Show the PID(s) of all running bash processes.

pidof -s nginx

Show only the first PID of the nginx master process.

pidof -o $$ systemd

Find systemd PIDs, excluding the current shell's PID ($$ is the current shell PID).

pidof rsyslogd sshd cron

Find PIDs for multiple programs at once.

if pidof -q nginx; then echo "nginx is running"; fi

Check if nginx is running without printing PIDs.

kill -TERM $(pidof myapp)

Send SIGTERM to all processes named myapp.

Practical Notes

  • pidof matches the exact program name as shown in /proc/PID/comm or /proc/PID/exe. It is not affected by command-line arguments.
  • For matching command lines with arguments, use pgrep which supports regular expressions and other advanced filters.
  • pidof -s is useful when you need the main process PID (e.g., the nginx master process).
  • The exit status is 0 if at least one PID was found, non-zero otherwise.
  • Use killall to kill processes by name without needing pidof first.