setgid (2)

#include <sys/types.h>

#include <unistd.h>

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.

EINVAL

The group ID specified in gid is not valid in this user namespace.

EPERM

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.

SVr4, POSIX.1-2001.

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.

getgid(2), setegid(2), setregid(2), capabilities(7), credentials(7), user_namespaces(7)

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