Set group identity
int setgid(gid_t gid);
setgid() sets the effective group ID of the calling process. If the caller is the superuser, the real GID and saved set-group-ID are also set.
Under Linux, setgid() is implemented like the POSIX version with the _POSIX_SAVED_IDS feature. This allows a set-group-ID program that is not set-user-ID-root to drop all of its group privileges, do some un-privileged work, and then reengage the original effective group ID in a secure manner.
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
The group ID specified in gid is not valid in this user namespace.
The calling process is not privileged (does not have the CAP_SETGID capability), and gid does not match the real group ID or saved set-group-ID of the calling process.
The original Linux setgid() system call supported only 16-bit group IDs. Subsequently, Linux 2.4 added setgid32() supporting 32-bit IDs. The glibc setgid() wrapper function transparently deals with the variation across kernel versions.
This page is part of release 3.74 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at http://www.kernel.org/doc/man-pages/.