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, const char *oldroot, bool detach_oldroot, unsigned long mountflags) {
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;
51 if (path_equal(new_root, "/"))
54 temporary_old_root = strappenda(new_root, oldroot);
55 mkdir_p_label(temporary_old_root, 0755);
57 old_root_remove = in_initrd();
59 if (stat(new_root, &new_root_stat) < 0) {
60 log_error("Failed to stat directory %s: %m", new_root);
64 /* Work-around for kernel design: the kernel refuses switching
65 * root if any file systems are mounted MS_SHARED. Hence
66 * remount them MS_PRIVATE here as a work-around.
68 * https://bugzilla.redhat.com/show_bug.cgi?id=847418 */
69 if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0)
70 log_warning("Failed to make \"/\" private mount: %m");
72 NULSTR_FOREACH(i, move_mounts) {
73 char new_mount[PATH_MAX];
76 snprintf(new_mount, sizeof(new_mount), "%s%s", new_root, i);
77 char_array_0(new_mount);
79 mkdir_p_label(new_mount, 0755);
81 if ((stat(new_mount, &sb) < 0) ||
82 sb.st_dev != new_root_stat.st_dev) {
84 /* Mount point seems to be mounted already or
85 * stat failed. Unmount the old mount
87 if (umount2(i, MNT_DETACH) < 0)
88 log_warning("Failed to unmount %s: %m", i);
92 if (mount(i, new_mount, NULL, mountflags, NULL) < 0) {
93 if (mountflags & MS_MOVE) {
94 log_error("Failed to move mount %s to %s, forcing unmount: %m", i, new_mount);
96 if (umount2(i, MNT_FORCE) < 0)
97 log_warning("Failed to unmount %s: %m", i);
99 if (mountflags & MS_BIND)
100 log_error("Failed to bind mount %s to %s: %m", i, new_mount);
105 /* Do not fail, if base_filesystem_create() fails. Not all
106 * switch roots are like base_filesystem_create() wants them
107 * to look like. They might even boot, if they are RO and
108 * don't have the FS layout. Just ignore the error and
109 * switch_root() nevertheless. */
110 (void) base_filesystem_create(new_root);
112 if (chdir(new_root) < 0) {
113 log_error("Failed to change directory to %s: %m", new_root);
117 if (old_root_remove) {
118 old_root_fd = open("/", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_NOCTTY|O_DIRECTORY);
120 log_warning("Failed to open root directory: %m");
123 /* We first try a pivot_root() so that we can umount the old
124 * root dir. In many cases (i.e. where rootfs is /), that's
125 * not possible however, and hence we simply overmount root */
126 if (pivot_root(new_root, temporary_old_root) >= 0) {
128 /* Immediately get rid of the old root, if detach_oldroot is set.
129 * Since we are running off it we need to do this lazily. */
130 if (detach_oldroot && umount2(oldroot, MNT_DETACH) < 0)
131 log_error("Failed to lazily umount old root dir %s, %s: %m",
133 errno == ENOENT ? "ignoring" : "leaving it around");
135 } else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0) {
136 log_error("Failed to mount moving %s to /: %m", new_root);
140 if (chroot(".") < 0) {
141 log_error("Failed to change root: %m");
145 if (chdir("/") < 0) {
146 log_error("Failed to change directory: %m");
150 if (old_root_fd >= 0) {
153 if (fstat(old_root_fd, &rb) < 0)
154 log_warning("Failed to stat old root directory, leaving: %m");
156 rm_rf_children(old_root_fd, false, false, &rb);