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setreuid() - Unix, Linux System Call
setreuid, setregid - set real and/or effective user or group ID
int setreuid(uid_t ruid, uid_t euid);
int setregid(gid_t rgid, gid_t egid);
setreuid() sets real and effective user IDs of the current process.
Supplying a value of -1 for either the real or effective user ID forces
the system to leave that ID unchanged.
Unprivileged processes may only set the effective user ID to the real user ID,
the effective user ID or the saved set-user-ID.
POSIX: It is unspecified whether unprivileged processes may set the
real user ID to the real user ID, the effective user ID or the
Linux: Unprivileged users may only set the real user ID to
the real user ID or the effective user ID.
Linux: If the real user ID is set or the effective user ID is set to a value
not equal to the previous real user ID,
the saved set-user-ID will be set to the new effective user ID.
setregid() sets real and effective group IDs of the current process,
and all of the above holds with "group" instead of "user".
On success, zero is returned. On error, -1 is returned, and
errno is set appropriately.
The current process is not privileged
(Linux: does not have the
CAP_SETUID capability in the case of
setreuid(), or the
CAP_SETGID capability in the case of
setregid()) and a change other than (i)
swapping the effective user (group) ID with the real user (group) ID,
or (ii) setting one to the value of the other or (iii) setting the
effective user (group) ID to the value of the
saved set-user-ID (saved set-group-ID) was specified.
Setting the effective user (group) ID to the
saved set-user-ID (saved set-group-ID) is
possible since Linux 1.1.37 (1.1.38).
POSIX.1-2001, 4.3BSD (the
setregid() function calls first appeared in 4.2BSD).