seteuid()

Updated: May 06, 2022

Set the effective user ID

Synopsis:

#include <unistd.h>

int seteuid( uid_t uid );

Arguments:

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

The real and saved user IDs aren't changed.

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.
QNX recommends that you do not use a negative value for a user ID.

Returns:

0
Success.
-1
An error occurred (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 the saved set-user ID.

Examples:

/*
 * This process sets its effective userid to 0 (root).
 */

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>

int main( void )
{
    uid_t oeuid;

    oeuid = geteuid();
    if( seteuid( 0 ) == -1 ) {
        perror( "seteuid" );
        return EXIT_FAILURE;
    }

    printf( "effective userid now 0, was %d\n",
        oeuid );

    return EXIT_SUCCESS;
}

Classification:

POSIX 1003.1

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