setuid(S)                      6 January 1993                      setuid(S)


 Name

    setuid, setgid - set user and groupIDs

 Syntax


    cc  . . .  -lc


    int setuid (uid)
    uid_t uid;

    int setgid (gid)
    gid_t gid;


 Description

    The setuid routine is used to set the real user ID and effective user ID
    of the calling process.  If the effective user ID of the calling process
    is root, the real user ID and effective user ID are set to uid.  If the
    effective user ID of the calling process is not root, but its real user
    ID is equal to uid, the effective user ID is set to uid.  If the
    effective user ID of the calling process is not root, but the saved set-
    user ID from exec(S) is equal to uid, the effective user ID is set to
    uid, except when the saved set-user ID from exec() is root.

    The setgid routine precisely parallels the setuid routine except that it
    sets group IDs rather than user IDs.

    The setgid routine is used to set the real group ID and effective group
    ID of the calling process.  If the effective user ID of the calling pro-
    cess is root, the real group ID and effective group ID are set to gid.
    If the effective user ID of the calling process is not root, but its real
    group ID is equal to gid, the effective group ID is set to gid.  If the
    effective user ID of the calling process is not root, but the saved set-
    group ID from exec(S) is equal to gid, the effective group ID is set to
    gid.

 Return value

    Upon successful completion, setuid and setgid return a value of 0.  If
    these routines fail, they return a value of -1 and errno is set to indi-
    cate the appropriate error.

 Diagnostics

    If one of the following conditions occurs, the setuid (setgid) routine
    fails and errno is set to the corresponding value:

    [EINVAL]  The uid (gid) is out of range.

    [EPERM]   The real user (group) ID of the calling process is not equal to
              uid (gid) and its effective user ID is not root.


 See also

    getuid(S)

 Standards conformance

    setgid and setuid are conformant with:
    AT&T SVID Issue 2;
    X/Open Portability Guide, Issue 3, 1989;
    IEEE POSIX Std 1003.1-1990 System Application Program Interface (API) [C
    Language] (ISO/IEC 9945-1);
    and NIST FIPS 151-1.