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
The setgid() function shall not affect the supplementary group
list in any way.
Any supplementary group IDs of the calling process shall remain unchanged.
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
The following sections are informative.
Refer to the RATIONALE section in setuid() .
exec() , getegid() , geteuid() , getgid()
, getuid() ,
setegid() , seteuid() , setregid() , setreuid()
, setuid() ,
the Base Definitions volume of IEEE Std 1003.1-2001, <sys/types.h>,
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at