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"
35 int switch_root(const char *new_root) {
37 /* Don't try to unmount/move the old "/", there's no way to do it. */
38 static const char move_mounts[] =
44 _cleanup_close_ int old_root_fd = -1;
45 struct stat new_root_stat;
47 const char *i, *temporary_old_root;
49 if (path_equal(new_root, "/"))
52 /* When using pivot_root() we assume that /mnt exists as place
53 * we can temporarily move the old root to. As we immediately
54 * unmount it from there it doesn't matter much which
55 * directory we choose for this, but it should be more likely
56 * than not that /mnt exists and is suitable as mount point
57 * and is on the same fs as the old root dir */
58 temporary_old_root = strappenda(new_root, "/mnt");
60 old_root_remove = in_initrd();
62 if (stat(new_root, &new_root_stat) < 0) {
63 log_error("Failed to stat directory %s: %m", new_root);
67 /* Work-around for a kernel bug: for some reason the kernel
68 * refuses switching root if any file systems are mounted
69 * MS_SHARED. Hence remount them MS_PRIVATE here as a
72 * https://bugzilla.redhat.com/show_bug.cgi?id=847418 */
73 if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0)
74 log_warning("Failed to make \"/\" private mount: %m");
76 NULSTR_FOREACH(i, move_mounts) {
77 char new_mount[PATH_MAX];
80 snprintf(new_mount, sizeof(new_mount), "%s%s", new_root, i);
81 char_array_0(new_mount);
83 if ((stat(new_mount, &sb) < 0) ||
84 sb.st_dev != new_root_stat.st_dev) {
86 /* Mount point seems to be mounted already or
87 * stat failed. Unmount the old mount
89 if (umount2(i, MNT_DETACH) < 0)
90 log_warning("Failed to unmount %s: %m", i);
94 if (mount(i, new_mount, NULL, MS_MOVE, NULL) < 0) {
95 log_error("Failed to move mount %s to %s, forcing unmount: %m", i, new_mount);
97 if (umount2(i, MNT_FORCE) < 0)
98 log_warning("Failed to unmount %s: %m", i);
102 if (chdir(new_root) < 0) {
103 log_error("Failed to change directory to %s: %m", new_root);
107 if (old_root_remove) {
108 old_root_fd = open("/", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_NOCTTY|O_DIRECTORY);
110 log_warning("Failed to open root directory: %m");
113 /* We first try a pivot_root() so that we can umount the old
114 * root dir. In many cases (i.e. where rootfs is /), that's
115 * not possible however, and hence we simply overmount root */
116 if (pivot_root(new_root, temporary_old_root) >= 0) {
118 /* Immediately get rid of the old root. Since we are
119 * running off it we need to do this lazily. */
120 if (umount2(temporary_old_root, MNT_DETACH) < 0) {
121 log_error("Failed to umount old root dir %s: %m", temporary_old_root);
125 } else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0) {
126 log_error("Failed to mount moving %s to /: %m", new_root);
130 if (chroot(".") < 0) {
131 log_error("Failed to change root: %m");
135 if (chdir("/") < 0) {
136 log_error("Failed to change directory: %m");
140 if (old_root_fd >= 0) {
143 if (fstat(old_root_fd, &rb) < 0)
144 log_warning("Failed to stat old root directory, leaving: %m");
146 rm_rf_children(old_root_fd, false, false, &rb);