EXAMPLE
       The program below provides a simple implementation of the unshare(1)
       command, which unshares one or more namespaces and executes the command
       supplied in its command-line arguments.  Here's an example of the use
       of this program, running a shell in a new mount namespace, and
       verifying that the original shell and the new shell are in separate
       mount namespaces:

           $ readlink /proc/$$/ns/mnt
           mnt:[4026531840]
           $ sudo ./unshare -m /bin/bash
           [sudo] password for cecilia:
           # readlink /proc/$$/ns/mnt
           mnt:[4026532325]

       The differing output of the two readlink(1) commands shows that the two
       shells are in different mount namespaces.

   Program source
       /* unshare.c

          A simple implementation of the unshare(1) command: unshare
          namespaces and execute a command.
       */
       #define _GNU_SOURCE
       #include <sched.h>
       #include <unistd.h>
       #include <stdlib.h>
       #include <stdio.h>

       /* A simple error-handling function: print an error message based
          on the value in 'errno' and terminate the calling process */

       #define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \
                               } while (0)

       static void
       usage(char *pname)
       {
           fprintf(stderr, "Usage: %s [options] program [arg...]\n", pname);
           fprintf(stderr, "Options can be:\n");
           fprintf(stderr, "    -i   unshare IPC namespace\n");
           fprintf(stderr, "    -m   unshare mount namespace\n");
           fprintf(stderr, "    -n   unshare network namespace\n");
           fprintf(stderr, "    -p   unshare PID namespace\n");
           fprintf(stderr, "    -u   unshare UTS namespace\n");
           fprintf(stderr, "    -U   unshare user namespace\n");
           exit(EXIT_FAILURE);
       }