man : getresuid(2)
SETRESUID(2) OpenBSD Programmer's Manual SETRESUID(2)
getresgid, getresuid, setresgid, setresuid - get or set real, effective
and saved user or group ID
getresgid(gid_t *rgid, gid_t *egid, gid_t *sgid);
getresuid(uid_t *ruid, uid_t *euid, uid_t *suid);
setresgid(gid_t rgid, gid_t egid, gid_t sgid);
setresuid(uid_t ruid, uid_t euid, uid_t suid);
The setresuid() function sets the real, effective and saved user IDs of
the current process. The analogous setresgid() sets the real, effective
and saved group IDs.
Privileged processes may set these IDs to arbitrary values. Unprivileged
processes are restricted in that each of the new IDs must match one of
the current IDs.
Passing -1 as an argument causes the corresponding value to remain
The getresgid() and getresuid() calls retrieve the real, effective, and
saved group and user IDs of the current process, respectively.
Upon success, these functions return 0; otherwise -1 is returned.
[EPERM] The calling process was not privileged and tried to change
one or more IDs to a value which was not the current real
ID, the current effective ID nor the current saved ID.
[EFAULT] An address passed to getresgid() or getresuid() was
getegid(2), geteuid(2), getgid(2), getuid(2), issetugid(2), setgid(2),
setregid(2), setreuid(2), setuid(2)
These functions are not part of the IEEE Std 1003.1 (``POSIX'')
specification. While they are not completely portable, they are the
least ambiguous way to manage user and group IDs.
These functions first appeared in HP-UX.
OpenBSD 4.9 May 31, 2007 OpenBSD 4.9