setluid(S)                     6 January 1993                     setluid(S)


 Name

    setluid - set login user ID

 Syntax


    cc  . . .  -lprot


    #include  <sys/types.h>
    #include  <sys/security.h>
    #include  <sys/audit.h>
    #include  <prot.h>

    int setluid (uid)
    unsigned short uid;


 Description

    The setluid routine is used to set the login user ID of the calling pro-
    cess.  The login user ID, or LUID, should be set at login time.  Only the
    super user can set the LUID.  Once set, the LUID cannot be reset, even by
    the super user.

    Until the LUID is set, the setuid(S) and setgid(S) routines fail.  This
    ensures that the LUID is set before any identity changes in the other
    (effective and real)  user IDs.

    The setluid routine is invoked by the login(C) program just prior to the
    identity changes caused by setuid(S) and setgid(S) calls.  It is also
    used by at(C) and crontab(C) job entries before starting a non-
    interactive session for a user.

    The LUID is an accurate representation of the user who logged into the
    system and cannot be altered during the session.  The LUID is needed
    because both the effective and real user IDs can be altered by use of
    setuid(S) or the setuid bits on an executable file, and consequently, at
    times during a session, do not accurately reflect the login user.

    The LUID is inherited by all children of the process.  If the LUID was
    not set before a fork(S), the child would also contain an unset LUID.

 Return value

    Upon successful completion, the setluid routine returns a value of 0.
    Otherwise, a value of -1 is returned and errno is set to indicate the
    appropriate error.

 Diagnostics

    If one of the following conditions occurs, the setluid routine fails and
    errno is set to the corresponding value:

    [EINVAL]  user ID is out of range.

    [EPERM]   The LUID has already been set for this process or some ancestor
              of this process.


 See also

    getluid(S), getuid(S), setuid(S), setgid(S), stat(S)

 Standards conformance

    The setluid routine is an extension of AT&T System V provided by the
    Santa Cruz Operation.