setuid()

set the real, effective and saved user IDs

Synopsis:

#include <unistd.h>
int setuid( uid_t uid );

Description:

The setuid() function allows the calling process to set the real, effective and saved user IDs based on the following:

• If the process has appropriate privileges, the setuid() function sets the real user ID, effective user ID and saved user ID to uid.
• If the process doesn't have the appropriate privileges, but uid is equal to the real user ID, setuid() sets the effective user ID to uid; the real and saved user IDs aren't changed.

If you wish to change only the effective user ID, even if you have appropriate privileges, you should consider using the seteuid() function.

Returns:

0

Success

-1

An error occurred. errno is set to indicate the error.

Errors:

EINVAL

The value of uid is invalid.

EPERM

The process doesn't have appropriate privileges, and uid doesn't match the real user ID.

Examples:

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

void main()
  {
    uid_t ouid;

    ouid = getuid();
    if( setuid( 0 ) == -1 ) {
      perror( "setuid" );
      exit( EXIT_FAILURE );
    }
    printf( "userid %d switched to 0\n", ouid );
    exit( EXIT_SUCCESS );
  }

Classification:

POSIX 1003.1

See also:

errno, setegid(), seteuid(), setgid()