switch_root.c

   1 /*
   2  * switchroot.c - switch to new root directory and start init.
   3  *
   4  * Copyright 2002-2008 Red Hat, Inc.  All rights reserved.
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 2 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  18  *
  19  * Authors:
  20  *      Peter Jones <pjones@redhat.com>
  21  *      Jeremy Katz <katzj@redhat.com>
  22  */
  23
  24 #define _GNU_SOURCE 1
  25
  26 #include <sys/mount.h>
  27 #include <sys/types.h>
  28 #include <sys/stat.h>
  29 #include <sys/param.h>
  30 #include <fcntl.h>
  31 #include <stdio.h>
  32 #include <stdlib.h>
  33 #include <unistd.h>
  34 #include <string.h>
  35 #include <errno.h>
  36 #include <ctype.h>
  37
  38 #ifndef MS_MOVE
  39 #define MS_MOVE 8192
  40 #endif
  41
  42 #ifndef MNT_DETACH
  43 #define MNT_DETACH 0x2
  44 #endif
  45
  46 enum {
  47         ok,
  48         err_no_directory,
  49         err_usage,
  50 };
  51
  52 static int switchroot(const char *newroot)
  53 {
  54         /*  Don't try to unmount the old "/", there's no way to do it. */
  55         const char *umounts[] = { "/dev", "/proc", "/sys", NULL };
  56         int errnum;
  57         int i;
  58
  59         for (i = 0; umounts[i] != NULL; i++) {
  60                 char newmount[PATH_MAX];
  61                 strcpy(newmount, newroot);
  62                 strcat(newmount, umounts[i]);
  63                 if (mount(umounts[i], newmount, NULL, MS_MOVE, NULL) < 0) {
  64                         fprintf(stderr, "Error mount moving old %s %s %m\n",
  65                                 umounts[i], newmount);
  66                         fprintf(stderr, "Forcing unmount of %s\n", umounts[i]);
  67                         umount2(umounts[i], MNT_FORCE);
  68                 }
  69         }
  70
  71         if (chdir(newroot) < 0) {
  72           errnum=errno;
  73           fprintf(stderr, "switchroot: chdir failed: %m\n");
  74           errno=errnum;
  75           return -1;
  76         }
  77
  78         if (mount(newroot, "/", NULL, MS_MOVE, NULL) < 0) {
  79                 errnum = errno;
  80                 fprintf(stderr, "switchroot: mount failed: %m\n");
  81                 errno = errnum;
  82                 return -1;
  83         }
  84
  85         if (chroot(".")) {
  86                 errnum = errno;
  87                 fprintf(stderr, "switchroot: chroot failed: %m\n");
  88                 errno = errnum;
  89                 return -2;
  90         }
  91         return 1;
  92 }
  93
  94 static void usage(FILE *output)
  95 {
  96         fprintf(output, "usage: switchroot <newrootdir> <init> <args to init>\n");
  97         if (output == stderr)
  98                 exit(err_usage);
  99         exit(ok);
 100 }
 101
 102 int main(int argc, char *argv[])
 103 {
 104         char *newroot = argv[1];
 105         char *init = argv[2];
 106         char **initargs = &argv[2];
 107
 108         if (newroot == NULL || newroot[0] == '\0' ||
 109             init == NULL || init[0] == '\0' ) {
 110                 usage(stderr);
 111         }
 112
 113         if (switchroot(newroot) < 0) {
 114           fprintf(stderr, "switchroot has failed.  Sorry.\n");
 115           return 1;
 116         }
 117         if (access(initargs[0], X_OK))
 118           fprintf(stderr, "WARNING: can't access %s\n", initargs[0]);
 119         execv(initargs[0], initargs);
 120 }
 121
 122 /*
 123  * vim:noet:ts=8:sw=8:sts=8
 124  */