setuid()

Set the real, effective and saved user IDs

Synopsis:

#include <unistd.h>

int setuid( uid_t uid );

Arguments:

uid
The user ID that you want to use for the process.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The setuid() function lets the calling process set its real and effective user IDs and its saved set-user ID to its real or effective user ID, its saved set-user ID, or any user ID identified by the PROCMGR_AID_SETUID ability (see procmgr_ability()).

Note: 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-UID.

If you wish to change only the effective user ID, you should consider using the seteuid() function.

Returns:

0 for success, or -1 if an error occurs (errno is set).

Errors:

EINVAL
The value of uid is out of range.
EPERM
The process doesn't have the PROCMGR_AID_SETUID ability enabled, and uid doesn't match the real user ID or saved set-user ID.

Examples:

/*
 * This process sets its userid to 0 (root)
 */
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>

int main( void )
{
    uid_t ouid;

    ouid = getuid();
    if( setuid( 0 ) == -1 ) {
        perror( "setuid" );
        return EXIT_FAILURE;
    }

    printf( "userid %d switched to 0\n", ouid );
    return EXIT_SUCCESS;
}

Classification:

POSIX 1003.1

Safety:  
Cancellation point No
Interrupt handler No
Signal handler Yes
Thread Yes