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git.ipfire.org Git - thirdparty/systemd.git/blob - src/core/switch-root.c
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 int r
, old_root_fd
= -1;
45 struct stat new_root_stat
;
48 _cleanup_free_
char *temporary_old_root
= NULL
;
50 if (path_equal(new_root
, "/"))
53 /* When using pivot_root() we assume that /mnt exists as place
54 * we can temporarily move the old root to. As we immediately
55 * unmount it from there it doesn't matter much which
56 * directory we choose for this, but it should be more likely
57 * than not that /mnt exists and is suitable as mount point
58 * and is on the same fs as the old root dir */
59 temporary_old_root
= strappend(new_root
, "/mnt");
60 if (!temporary_old_root
)
63 old_root_remove
= in_initrd();
65 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 if ((stat(new_mount
, &sb
) < 0) ||
88 sb
.st_dev
!= new_root_stat
.st_dev
) {
90 /* Mount point seems to be mounted already or
91 * stat failed. Unmount the old mount
93 if (umount2(i
, MNT_DETACH
) < 0)
94 log_warning("Failed to unmount %s: %m", i
);
98 if (mount(i
, new_mount
, NULL
, MS_MOVE
, NULL
) < 0) {
99 log_error("Failed to move mount %s to %s, forcing unmount: %m", i
, new_mount
);
101 if (umount2(i
, MNT_FORCE
) < 0)
102 log_warning("Failed to unmount %s: %m", i
);
106 if (chdir(new_root
) < 0) {
108 log_error("Failed to change directory to %s: %m", new_root
);
112 if (old_root_remove
) {
113 old_root_fd
= open("/", O_RDONLY
|O_NONBLOCK
|O_CLOEXEC
|O_NOCTTY
|O_DIRECTORY
);
115 log_warning("Failed to open root directory: %m");
118 /* We first try a pivot_root() so that we can umount the old
119 * root dir. In many cases (i.e. where rootfs is /), that's
120 * not possible however, and hence we simply overmount root */
121 if (pivot_root(new_root
, temporary_old_root
) >= 0) {
123 /* Immediately get rid of the old root. Since we are
124 * running off it we need to do this lazily. */
125 if (umount2(temporary_old_root
, MNT_DETACH
) < 0) {
127 log_error("Failed to umount old root dir %s: %m", temporary_old_root
);
131 } else if (mount(new_root
, "/", NULL
, MS_MOVE
, NULL
) < 0) {
133 log_error("Failed to mount moving %s to /: %m", new_root
);
137 if (chroot(".") < 0) {
139 log_error("Failed to change root: %m");
143 if (chdir("/") < 0) {
145 log_error("Failed to change directory: %m");
149 if (old_root_fd
>= 0) {
152 if (fstat(old_root_fd
, &rb
) < 0)
153 log_warning("Failed to stat old root directory, leaving: %m");
155 rm_rf_children(old_root_fd
, false, false, &rb
);
163 if (old_root_fd
>= 0)
164 close_nointr_nofail(old_root_fd
);