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RedHat 9 (Linux i386) - man page for getpgid (redhat section 2)

SETPGID(2)				      Linux Programmer's Manual 				   SETPGID(2)

NAME
setpgid, getpgid, setpgrp, getpgrp - set/get process group
SYNOPSIS
#include <unistd.h> int setpgid(pid_t pid, pid_t pgid); pid_t getpgid(pid_t pid); int setpgrp(void); pid_t getpgrp(void);
DESCRIPTION
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 exist- ing 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(3) 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.
RETURN VALUE
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.
ERRORS
EINVAL pgid is less than 0 (setpgid, setpgrp). EACCES An attempt was made to change the process group ID of one of the children of the calling process and the child had already performed an execve (setpgid, setpgrp). EPERM An attempt was made to move a process into a process group in a different session, or to change the process group ID of one of the children of the calling process and the child was in a different ses- sion, or to change the process group ID of a session leader (setpgid, setpgrp). ESRCH pid does not match any process.
CONFORMING TO
The functions setpgid and getpgrp conform to POSIX.1. The function setpgrp is from BSD 4.2. The function getpgid conforms to SVr4.
NOTES
POSIX took setpgid from the BSD function setpgrp. Also SysV has a function with the same name, but it is identical to setsid(2). To get the prototypes under glibc, define both _XOPEN_SOURCE and _XOPEN_SOURCE_EXTENDED, or use "#define _XOPEN_SOURCE n" for some integer n larger than or equal to 500.
SEE ALSO
getuid(2), setsid(2), tcsetpgrp(3), termios(3) Linux 1999-09-02 SETPGID(2)


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