SIGPIPE

Infobox Computing signal
description = Write on a pipe with no one to read it
action = Abnormal termination of the processOn POSIX-compliant platforms, SIGPIPE is the signal raised when a computer program attempts to write to a pipe without a process connected to the other end. The symbolic constant for SIGPIPE is defined in the header file signal.h. Symbolic signal names are used because signal numbers can vary across platforms.

Etymology

"SIG" is a common prefix for signal names. "PIPE" refers to the Unix pipe.

Description

Unix supports the principle of piping, which allows processes to send data to other processes without the need for creating temporary files. When a pipe is broken, the process writing to it is sent the SIGPIPE signal. The default reaction to this signal for a process is to terminate.

A simple example of piping is the following. ps l | headThis command, when run on a Unix-like machine (including Linux), returns a list of processes, limited to ten lines.
* ps l returns a list of all processes (including those of other users).
* head selects the first ten lines.

When ps has written ten lines, head has received all it needs and exits. ps will receive a SIGPIPE when it tries to write the remaining lines, causing it to terminate as well: It is no use writing data that no one will use. It is also possible that the reading process terminates while reading the data. This will also cause SIGPIPE to be sent to the writing process.

One can ignore SIGPIPE (using, for example, the signal system call). In this case, all system calls that would cause SIGPIPE to be sent will return -1 and set errno to EPIPE.