SETPGID

setpgid, getpgid, setpgrp, getpgrp ? set/get process group

#include <unistd.h>

int setpgid(pid_t pid, pid_t pgid);
pid_t getpgid(pid_t pid);
int setpgrp(void);
pid_t getpgrp(void);

setpgid sets the process group ID of the process specified by pid to pgid. If pid is zero, the process ID of the current process is used. If pgid is zero, the process ID of the process specified by pid is used. If setpgid is used to move a process from one process group to another (as is done by some shells when creating pipelines), both process groups must be part of the same session. In this case, the pgid specifies an existing process group to be joined and the session ID of that group must match the session ID of the joining process.

getpgid returns the process group ID of the process specified by pid. If pid is zero, the process ID of the current process is used.

In the Linux DLL 4.4.1 library, setpgrp simply calls setpgid(0,0).

getpgrp is equivalent to getpgid(0). Each process group is a member of a session and each process is a member of the session of which its process group is a member.

Process groups are used for distribution of signals, and by terminals to arbitrate requests for their input: Processes that have the same process group as the terminal are foreground and may read, while others will block with a signal if they attempt to read. These calls are thus used by programs such as csh(1) to create process groups in implementing job control. The TIOCGPGRP and TIOCSPGRP calls described in termios(4) are used to get/set the process group of the control terminal.

If a session has a controlling terminal, CLOCAL is not set and a hangup occurs, then the session leader is sent a SIGHUP. If the session leader exits, the SIGHUP signal will be sent to each process in the foreground process group of the controlling terminal.

If the exit of the process causes a process group to become orphaned, and if any member of the newly-orphaned process group is stopped, then a SIGHUP signal followed by a SIGCONT signal will be sent to each process in the newly-orphaned process group.

On success, setpgid and setpgrp return zero. On error, ?1 is returned, and errno is set appropriately.

getpgid returns a process group on success. On error, ?1 is returned, and errno is set appropriately.

getpgrp always returns the current process group.

EINVAL

pgid is less than 0.

EPERM

Various permission violations.

ESRCH

pid does not match any process.

SVr4, POSIX, 4.4BSD.

The functions setpgid and getpgrp conform to POSIX.1. The function setpgrp is from BSD 4.2. The function getpgid conforms to SVr4.

getuid(2), setsid(2), tcsetpgrp(3), termios(4)