killpgrp

Killpgrp refers to the operation of sending a signal to all processes in a specified process group. In Unix-like systems, process groups are a mechanism used to group related processes (such as the components of a shell pipeline) so signals can be delivered to the entire group as a unit. The effect of killpgrp is to propagate the chosen signal to every member of the target group, subject to the usual rules of signal handling and process privileges.

In practice, there are two common ways to realize a killpgrp. Using the kill system call with a negative process group ID, e.g., kill(-pgrp, SIGTERM), delivers the signal to all processes in the group with ID pgrp. Some systems provide a helper function such as killpg(pgrp, sig) in C libraries, which performs the same action. In shells, the equivalent action is often written as a command using a negative group ID, for example, kill -s SIGTERM -1234 to terminate all processes in group 1234.

Portability and behavior vary by platform. POSIX defines the negative PID convention for signaling a process group, but some details may differ across Unix flavors. Privileges apply: a process can signal only its own group unless it has appropriate privileges; some processes may ignore or handle signals in custom ways (except for SIGKILL or, in many cases, SIGSTOP). Signals targeted at a group affect only active members, not defunct or re-parented processes.

See also: kill, killall, process groups, job control, SIGTERM, SIGKILL.