SETUID(2) BSD System Calls Manual SETUID(2)
setuid, seteuid, setgid, setegid -- set user and group ID
The setuid() function sets the real and effective user IDs and the saved set-user-ID of the
current process to the specified value. The setuid() function is permitted if the effective
user ID is that of the super user, or if the specified user ID is the same as the effective
user ID. If not, but the specified user ID is the same as the real user ID, setuid() will
set the effective user ID to the real user ID.
The setgid() function sets the real and effective group IDs and the saved set-group-ID of
the current process to the specified value. The setgid() function is permitted if the
effective user ID is that of the super user, or if the specified group ID is the same as the
effective group ID. If not, but the specified group ID is the same as the real group ID,
setgid() will set the effective group ID to the real group ID.
The seteuid() function (setegid()) sets the effective user ID (group ID) of the current
process. The effective user ID may be set to the value of the real user ID or the saved
set-user-ID (see intro(2) and execve(2)); in this way, the effective user ID of a set-user-
ID executable may be toggled by switching to the real user ID, then re-enabled by reverting
to the set-user-ID value. Similarly, the effective group ID may be set to the value of the
real group ID or the saved set-user-ID.
Upon success, these functions return 0; otherwise -1 is returned.
If the user is not the super user, or the uid specified is not the real, effective ID, or
saved ID, these functions return -1.
The setuid() and setgid() functions are compliant with the ISO/IEC 9945-1:1990 (``POSIX.1'')
specification with _POSIX_SAVED_IDS defined, with the extensions allowed in section B.4.2.2.
The seteuid() and setegid() functions are extensions based on the POSIX concept of
_POSIX_SAVED_IDS, and have been proposed for a future revision of the standard.
4.2 Berkeley Distribution June 4, 1993 4.2 Berkeley Distribution