setreuid(SSC)                  6 January 1993                  setreuid(SSC)


 Name

    setreuid - set real and effective user IDs

 Syntax


    int setreuid(ruid, euid)
    int ruid, euid;


 Description

    setreuid is used to set the real and effective user IDs of the calling
    process.  If ruid is -1, the real user ID is not changed; if euid is -1,
    the effective user ID is not changed.  The real and effective user IDs
    may be set to different values in the same call.

    If the effective user ID of the calling process is super-user, the real
    user ID and the effective user ID can be set to any legal value.

    If the effective user ID of the calling process is not super-user, either
    the real user ID can be set to the effective user ID, or the effective
    user ID can either be set to the saved set-user ID from execve(SSC) or
    the real user ID.  Note that if a set-UID process sets its effective user
    ID to its real user ID, it can still set its effective user ID back to
    the saved set-user ID.

    In either case, if the real user ID is changed to a particular value
    (that is, if ruid is not -1), the saved set-user ID is set to that same
    value.

 Return value

    A return value of zero indicates that the call succeeded.  A return value
    of -1 indicates that an error occurred, and in this case an error code is
    stored in the global variable errno.

 Errors

    setreuid will fail and neither of the user IDs will be changed if:

    EPERM          The calling process' effective user ID is not the super-
                   user and a change other than changing the real user ID to
                   the effective user ID, or changing the effective user ID
                   to the real user-id or the saved set-user ID, was speci-
                   fied.

 See also

    getuid(S), execve(S), setregid(SSC), setreuid(SSC) and setuid(S).