freebsd man page for getresuid

SETRESUID(2)						      BSD System Calls Manual						      SETRESUID(2)

NAME
     getresgid, getresuid, setresgid, setresuid -- get or set real, effective and saved user or group ID

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/types.h>
     #include <unistd.h>

     int
     getresgid(gid_t *rgid, gid_t *egid, gid_t *sgid);

     int
     getresuid(uid_t *ruid, uid_t *euid, uid_t *suid);

     int
     setresgid(gid_t rgid, gid_t egid, gid_t sgid);

     int
     setresuid(uid_t ruid, uid_t euid, uid_t suid);

DESCRIPTION
     The setresuid() system call 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 unchanged.

     The getresgid() and getresuid() calls retrieve the real, effective, and saved group and user IDs of the current process, respectively.

RETURN VALUES
     Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the
     error.

ERRORS
     [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 invalid.

SEE ALSO
     getegid(2), geteuid(2), getgid(2), getuid(2), issetugid(2), setgid(2), setregid(2), setreuid(2), setuid(2)

HISTORY
     These functions first appeared in HP-UX.

BSD
								 February 7, 2015							       BSD