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;
52 if (path_equal(new_root, "/"))
55 temporary_old_root = strappenda(new_root, oldroot);
56 mkdir_p_label(temporary_old_root, 0755);
58 old_root_remove = in_initrd();
60 if (stat(new_root, &new_root_stat) < 0) {
61 log_error("Failed to stat directory %s: %m", new_root);
65 /* Work-around for a kernel bug: for some reason the kernel
66 * refuses switching root if any file systems are mounted
67 * MS_SHARED. Hence remount them MS_PRIVATE here as a
70 * https://bugzilla.redhat.com/show_bug.cgi?id=847418 */
71 if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0)
72 log_warning("Failed to make \"/\" private mount: %m");
74 NULSTR_FOREACH(i, move_mounts) {
75 char new_mount[PATH_MAX];
78 snprintf(new_mount, sizeof(new_mount), "%s%s", new_root, i);
79 char_array_0(new_mount);
81 mkdir_p_label(new_mount, 0755);
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, mountflags, NULL) < 0) {
95 if (mountflags & MS_MOVE) {
96 log_error("Failed to move mount %s to %s, forcing unmount: %m", i, new_mount);
98 if (umount2(i, MNT_FORCE) < 0)
99 log_warning("Failed to unmount %s: %m", i);
101 if (mountflags & MS_BIND)
102 log_error("Failed to bind mount %s to %s: %m", i, new_mount);
107 r = base_filesystem_create(new_root);
109 log_error("Failed to create the base filesystem: %s", strerror(-r));
113 if (chdir(new_root) < 0) {
114 log_error("Failed to change directory to %s: %m", new_root);
118 if (old_root_remove) {
119 old_root_fd = open("/", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_NOCTTY|O_DIRECTORY);
121 log_warning("Failed to open root directory: %m");
124 /* We first try a pivot_root() so that we can umount the old
125 * root dir. In many cases (i.e. where rootfs is /), that's
126 * not possible however, and hence we simply overmount root */
127 if (pivot_root(new_root, temporary_old_root) >= 0) {
129 /* Immediately get rid of the old root, if detach_oldroot is set.
130 * Since we are running off it we need to do this lazily. */
131 if (detach_oldroot && umount2(oldroot, MNT_DETACH) < 0) {
132 log_error("Failed to umount old root dir %s: %m", oldroot);
136 } else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0) {
137 log_error("Failed to mount moving %s to /: %m", new_root);
141 if (chroot(".") < 0) {
142 log_error("Failed to change root: %m");
146 if (chdir("/") < 0) {
147 log_error("Failed to change directory: %m");
151 if (old_root_fd >= 0) {
154 if (fstat(old_root_fd, &rb) < 0)
155 log_warning("Failed to stat old root directory, leaving: %m");
157 rm_rf_children(old_root_fd, false, false, &rb);