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SETUID(2)                   BSD System Calls Manual                  SETUID(2)

NAME
     setuid, seteuid, setgid, setegid -- set user and group ID

SYNOPSIS
     #include <&lt;unistd.h>&gt;

     int
     setuid(uid_t uid);

     int
     seteuid(uid_t euid);

     int
     setgid(gid_t gid);

     int
     setegid(gid_t egid);

DESCRIPTION
     The setuid() function sets the real and effective user IDs and the saved
     set-user-ID of the current process to the specified value.  The setuid()
     function is permitted if the effective user ID is that of the superuser,
     or if the specified user ID is the same as the effective user ID.  If
     not, but the specified user ID is the same as the real user ID, setuid()
     will set the effective user ID to the real user ID.

     The setgid() function sets the real and effective group IDs and the saved
     set-group-ID of the current process to the specified value.  The setgid()
     function is permitted if the effective user ID is that of the superuser,
     or if the specified group ID is the same as the effective group ID.  If
     not, but the specified group ID is the same as the real group ID,
     setgid() will set the effective group ID to the real group ID.  Supple-
     mentary group IDs remain unchanged.

     The seteuid() function (setegid()) sets the effective user ID (group ID)
     of the current process.  The effective user ID may be set to the value of
     the real user ID or the saved set-user-ID (see intro(2) and execve(2));
     in this way, the effective user ID of a set-user-ID executable may be
     toggled by switching to the real user ID, then re-enabled by reverting to
     the set-user-ID value.  Similarly, the effective group ID may be set to
     the value of the real group ID or the saved set-group-ID.

RETURN VALUES
     The setuid(), seteuid(), setgid(), and setegid() functions return the
     value 0 if successful; otherwise the value -1 is returned and the global
     variable errno is set to indicate the error.

ERRORS
     setuid() and seteuid() will succeed unless:

     [EPERM]            The user is not the superuser and the requested uid or
                        euid is not the process's real, effective, or saved
                        UID.

     setgid() and setegid() will succeed unless:

     [EPERM]            The user is not the superuser and the requested gid or
                        egid is not the process's real, effective, or saved
                        GID.

SEE ALSO
     getgid(2), getuid(2), issetugid(2), setgroups(2), setregid(2),
     setresgid(2), setresuid(2), setreuid(2)

STANDARDS
     The setuid(), seteuid(), setgid(), and setegid() functions conform to
     IEEE Std 1003.1-2008 (``POSIX.1'').

HISTORY
     The setuid() system call first appeared in Version 1 AT&T UNIX; setgid()
     in Version 4 AT&T UNIX; and seteuid() and setegid() in 4.2BSD.

BSD                            September 9, 2014                           BSD