killpgid

Killpgid is a term sometimes used to refer to sending a signal to all processes in a particular process group on Unix-like systems. There is no standard POSIX function actually named killpgid. The portable API is killpg, defined in signal.h, which delivers a signal to every member of a process group identified by a process group ID (PGID). Some codebases implement wrappers or use the concept informally; in portable code, developers may also use kill with a negative PID to target a process group.

Process groups are collections of related processes that share a PGID, a mechanism central to job control in shells. The PGID is usually the PID of the group leader, and signals targeted at the group are delivered to all processes within that group unless a process blocks or handles the signal differently. This makes killpg or equivalent operations suitable for terminating or signaling all processes in a pipeline or job.

The standard function prototype is int killpg(pid_t pgrp, int sig); It sends sig to every process in the group with ID pgrp. On success it returns 0; on error it returns -1 and sets errno. Common errno values include ESRCH when the specified process group does not exist, and EPERM or EACCES when the caller lacks permission. If an invalid signal is supplied (EINVAL), the call fails as well. Note that individual processes can still handle signals in their own way, and some may ignore certain signals.

Usage considerations include the need for appropriate privileges, the potential for terminating critical or child processes, and variability across Unix-like systems regarding the availability of killpg. If killpg is unavailable, signaling a group can often be achieved by using the negative PGID in kill (-pgid, sig) on systems that support it. As a general rule, prefer documented, portable interfaces and consult your platform’s specific man pages.