setreuid - set real and effective user IDs
int setreuid(uid_t ruid, uid_t euid);
The setreuid() function is used to set the real and effec-
tive user IDs of the calling 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 effec-
tive user ID, or the effective user ID can either be set to
the saved set-user ID from execve() (seeexec(2)) or the real
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.
Upon successful completion, 0 is returned. Otherwise, -1 is
returned, errno is set to indicate the error, and neither of
the user IDs will be changed.
The setreuid() function will fail if:
The value of ruid or euid is less than 0 or greater
than UID_MAX (defined in <limits.h>).
EPERM The calling process's 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 specified.
If a set-user-ID 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.
exec(2), getuid(2), setregid(2), setuid(2)
Man(1) output converted with