pidof is a Linux utility that returns the process identifier (PID) of a running process or processes. On other operating systems, pgrep and ps are often used instead.
pidof is implemented in the same program as killall5 (see readlink $(command -v pidof)), the Linux name for the System Vkillall program used by the runlevel scripts. pidof is usually a symbolic link to killall5, and the name the program is called under is what determines its behavior.
Some examples that return the process identifiers of several processes using pidof: