setgid man page


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

setgid — set-group-ID


#include <unistd.h>

int setgid(gid_t gid);


If the process has appropriate privileges, setgid() shall set the real group ID, effective group ID, and the saved set-group-ID of the calling process to gid.

If the process does not have appropriate privileges, but gid is equal to the real group ID or the saved set-group-ID, setgid() shall set the effective group ID to gid; the real group ID and saved set-group-ID shall remain unchanged.

The setgid() function shall not affect the supplementary group list in any way.

Any supplementary group IDs of the calling process shall remain unchanged.

Return Value

Upon successful completion, 0 is returned. Otherwise, -1 shall be returned and errno set to indicate the error.


The setgid() function shall fail if:

The value of the gid argument is invalid and is not supported by the implementation.
The process does not have appropriate privileges and gid does not match the real group ID or the saved set-group-ID.

The following sections are informative.


Refer to the Rationale section in setuid().

See Also

exec, getegid(), geteuid(), getgid(), getuid(), setegid(), seteuid(), setregid(), setreuid(), setuid()

The Base Definitions volume of POSIX.1‐2008, <sys_types.h>, <unistd.h>