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 return log_error_errno(errno, "Failed to stat directory %s: %m", new_root);
62 /* Work-around for kernel design: the kernel refuses switching
63 * root if any file systems are mounted MS_SHARED. Hence
64 * remount them MS_PRIVATE here as a work-around.
66 * https://bugzilla.redhat.com/show_bug.cgi?id=847418 */
67 if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0)
68 log_warning_errno(errno, "Failed to make \"/\" private mount: %m");
70 NULSTR_FOREACH(i, move_mounts) {
71 char new_mount[PATH_MAX];
74 snprintf(new_mount, sizeof(new_mount), "%s%s", new_root, i);
75 char_array_0(new_mount);
77 mkdir_p_label(new_mount, 0755);
79 if ((stat(new_mount, &sb) < 0) ||
80 sb.st_dev != new_root_stat.st_dev) {
82 /* Mount point seems to be mounted already or
83 * stat failed. Unmount the old mount
85 if (umount2(i, MNT_DETACH) < 0)
86 log_warning_errno(errno, "Failed to unmount %s: %m", i);
90 if (mount(i, new_mount, NULL, mountflags, NULL) < 0) {
91 if (mountflags & MS_MOVE) {
92 log_error_errno(errno, "Failed to move mount %s to %s, forcing unmount: %m", i, new_mount);
94 if (umount2(i, MNT_FORCE) < 0)
95 log_warning_errno(errno, "Failed to unmount %s: %m", i);
97 if (mountflags & MS_BIND)
98 log_error_errno(errno, "Failed to bind mount %s to %s: %m", i, new_mount);
103 /* Do not fail, if base_filesystem_create() fails. Not all
104 * switch roots are like base_filesystem_create() wants them
105 * to look like. They might even boot, if they are RO and
106 * don't have the FS layout. Just ignore the error and
107 * switch_root() nevertheless. */
108 (void) base_filesystem_create(new_root);
110 if (chdir(new_root) < 0)
111 return log_error_errno(errno, "Failed to change directory to %s: %m", new_root);
113 if (old_root_remove) {
114 old_root_fd = open("/", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_NOCTTY|O_DIRECTORY);
116 log_warning_errno(errno, "Failed to open root directory: %m");
119 /* We first try a pivot_root() so that we can umount the old
120 * root dir. In many cases (i.e. where rootfs is /), that's
121 * not possible however, and hence we simply overmount root */
122 if (pivot_root(new_root, temporary_old_root) >= 0) {
124 /* Immediately get rid of the old root, if detach_oldroot is set.
125 * Since we are running off it we need to do this lazily. */
126 if (detach_oldroot && umount2(oldroot, MNT_DETACH) < 0)
127 log_error_errno(errno, "Failed to lazily umount old root dir %s, %s: %m",
129 errno == ENOENT ? "ignoring" : "leaving it around");
131 } else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0)
132 return log_error_errno(errno, "Failed to mount moving %s to /: %m", new_root);
135 return log_error_errno(errno, "Failed to change root: %m");
138 return log_error_errno(errno, "Failed to change directory: %m");
140 if (old_root_fd >= 0) {
143 if (fstat(old_root_fd, &rb) < 0)
144 log_warning_errno(errno, "Failed to stat old root directory, leaving: %m");
146 rm_rf_children(old_root_fd, false, false, &rb);