SETGIDSection: Linux Programmer's Manual (2)
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NAMEsetgid - set group identity
DESCRIPTIONsetgid() sets the effective group ID of the current 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 re-engage the original effective group ID in a secure manner.
RETURN VALUEOn success, zero is returned. On error, -1 is returned, and errno is set appropriately.
- The calling process is not privileged (does not have the CAP_SETGID capability), and gid does not match the effective group ID or saved set-group-ID of the calling process.
CONFORMING TOSVr4, POSIX.1-2001.
SEE ALSOgetgid(2), setegid(2), setregid(2), capabilities(7)