SETREUID(2) System Calls Manual SETREUID(2)
setreuid - set real and effective user IDs
int setreuid(ruid, euid)
int ruid, euid;
setreuid() is used to set the real and effective user IDs of the call-
ing process. If ruid is -1, the real user ID is not changed; if euid
is -1, the effective user ID is not changed. The real and effective
user IDs may be set to different values in the same call.
If the effective user ID of the calling process is super-user, the real
user ID and the effective user ID can be set to any legal value.
If the effective user ID of the calling process is not super-user,
either the real user ID can be set to the effective user ID, or the
effective user ID can either be set to the saved set-user ID from
execve(2V) or the real user ID. Note: if a set-UID process sets its
effective user ID to its real user ID, it can still set its effective
user ID back to the saved set-user ID.
In either case, if the real user ID is being changed (that is, if ruid
is not -1), or the effective user ID is being changed to a value not
equal to the real user ID, the saved set-user ID is set equal to the
new effective user ID.
0 on success.
-1 on failure and sets errno to indicate the error.
setreuid() will fail and neither of the user IDs will be changed if:
EINVAL The value of ruid or euid is less than 0 or greater than
USHRT_MAX (defined in <<sys/limits.h>>).
EPERM The calling process' effective user ID is not the super-
user and a change other than changing the real user ID
to the effective user ID, or changing the effective user
ID to the real user ID or the saved set-user ID, was
execve(2V), getuid(2V), setregid(2), setuid(3V)
21 January 1990 SETREUID(2)