pidof — Find the PID of a running program

Linux / Service and process management / pidof.html

Prints the process IDs of a running program by name.

Basic Information

What is this command?

pidof maps an executable name to the process IDs currently running it.

With several matches it prints them space separated, which suits restart logic in scripts.

What problems does it solve?

• Check for a leftover process before restarting a service.
• Verify whether a program accidentally runs twice.
• Branch on running state inside a script.
• Obtain the PID to signal quickly.

Key features

Lookup by name

Pass the executable name and it prints matching PIDs.

• When to use: When checking whether a program runs
• What you get: PID list or empty output
• Limitations: Matches by name, not by full path

Script branching

Use its output or exit status to decide whether the program runs.

• When to use: When writing restart automation
• What you get: Immediate running/not-running answer
• Limitations: Multiple PIDs may need handling

Single PID selection

The -s option prints only the first matching PID.

• When to use: When a single target is enough
• What you get: One PID
• Limitations: Extra instances stay invisible

Installation and usage

Check whether it is installed

pidof --help

pacman -S sysvinit-tools # Arch (varies by distribution)

Real-world examples

Lookup

Show PIDs of nginx processes.

# Show PIDs of processes named nginx
pidof nginx

Single PID

Print only the first PID.

# Print only the first match
pidof -s nginx

In a script

Restart only when it is running.

# Restart only if it is currently running
pid=$(pidof nginx) && kill -HUP $pid