1 /*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
4 This file is part of systemd.
6 Copyright 2012 Harald Hoyer, Lennart Poettering
8 systemd is free software; you can redistribute it and/or modify it
9 under the terms of the GNU Lesser General Public License as published by
10 the Free Software Foundation; either version 2.1 of the License, or
11 (at your option) any later version.
13 systemd is distributed in the hope that it will be useful, but
14 WITHOUT ANY WARRANTY; without even the implied warranty of
15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 Lesser General Public License for more details.
18 You should have received a copy of the GNU Lesser General Public License
19 along with systemd; If not, see <http://www.gnu.org/licenses/>.
26 #include <sys/mount.h>
31 #include "path-util.h"
32 #include "switch-root.h"
34 #include "base-filesystem.h"
37 int switch_root(const char *new_root) {
39 /* Don't try to unmount/move the old "/", there's no way to do it. */
40 static const char move_mounts[] =
46 _cleanup_close_ int old_root_fd = -1;
47 struct stat new_root_stat;
49 const char *i, *temporary_old_root;
52 if (path_equal(new_root, "/"))
55 /* When using pivot_root() we assume that /mnt exists as place
56 * we can temporarily move the old root to. As we immediately
57 * unmount it from there it doesn't matter much which
58 * directory we choose for this, but it should be more likely
59 * than not that /mnt exists and is suitable as mount point
60 * and is on the same fs as the old root dir */
61 temporary_old_root = strappenda(new_root, "/mnt");
62 mkdir_p(temporary_old_root, 0755);
64 old_root_remove = in_initrd();
66 if (stat(new_root, &new_root_stat) < 0) {
67 log_error("Failed to stat directory %s: %m", new_root);
71 /* Work-around for a kernel bug: for some reason the kernel
72 * refuses switching root if any file systems are mounted
73 * MS_SHARED. Hence remount them MS_PRIVATE here as a
76 * https://bugzilla.redhat.com/show_bug.cgi?id=847418 */
77 if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0)
78 log_warning("Failed to make \"/\" private mount: %m");
80 NULSTR_FOREACH(i, move_mounts) {
81 char new_mount[PATH_MAX];
84 snprintf(new_mount, sizeof(new_mount), "%s%s", new_root, i);
85 char_array_0(new_mount);
87 mkdir_p(new_mount, 0755);
89 if ((stat(new_mount, &sb) < 0) ||
90 sb.st_dev != new_root_stat.st_dev) {
92 /* Mount point seems to be mounted already or
93 * stat failed. Unmount the old mount
95 if (umount2(i, MNT_DETACH) < 0)
96 log_warning("Failed to unmount %s: %m", i);
100 if (mount(i, new_mount, NULL, MS_MOVE, NULL) < 0) {
101 log_error("Failed to move mount %s to %s, forcing unmount: %m", i, new_mount);
103 if (umount2(i, MNT_FORCE) < 0)
104 log_warning("Failed to unmount %s: %m", i);
108 r = base_filesystem_create(new_root);
110 log_error("Failed to create the base filesystem: %s", strerror(-r));
114 if (chdir(new_root) < 0) {
115 log_error("Failed to change directory to %s: %m", new_root);
119 if (old_root_remove) {
120 old_root_fd = open("/", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_NOCTTY|O_DIRECTORY);
122 log_warning("Failed to open root directory: %m");
125 /* We first try a pivot_root() so that we can umount the old
126 * root dir. In many cases (i.e. where rootfs is /), that's
127 * not possible however, and hence we simply overmount root */
128 if (pivot_root(new_root, temporary_old_root) >= 0) {
130 /* Immediately get rid of the old root. Since we are
131 * running off it we need to do this lazily. */
132 if (umount2("/mnt", MNT_DETACH) < 0) {
133 log_error("Failed to umount old root dir /mnt: %m");
137 } else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0) {
138 log_error("Failed to mount moving %s to /: %m", new_root);
142 if (chroot(".") < 0) {
143 log_error("Failed to change root: %m");
147 if (chdir("/") < 0) {
148 log_error("Failed to change directory: %m");
152 if (old_root_fd >= 0) {
155 if (fstat(old_root_fd, &rb) < 0)
156 log_warning("Failed to stat old root directory, leaving: %m");
158 rm_rf_children(old_root_fd, false, false, &rb);