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git.ipfire.org Git - thirdparty/systemd.git/blob - src/shared/switch-root.c
2 This file is part of systemd.
4 Copyright 2012 Harald Hoyer, Lennart Poettering
6 systemd is free software; you can redistribute it and/or modify it
7 under the terms of the GNU Lesser General Public License as published by
8 the Free Software Foundation; either version 2.1 of the License, or
9 (at your option) any later version.
11 systemd is distributed in the hope that it will be useful, but
12 WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
16 You should have received a copy of the GNU Lesser General Public License
17 along with systemd; If not, see <http://www.gnu.org/licenses/>.
25 #include <sys/mount.h>
29 #include "base-filesystem.h"
34 #include "path-util.h"
36 #include "stdio-util.h"
37 #include "string-util.h"
38 #include "switch-root.h"
39 #include "user-util.h"
42 int switch_root(const char *new_root
, const char *oldroot
, bool detach_oldroot
, unsigned long mountflags
) {
44 /* Don't try to unmount/move the old "/", there's no way to do it. */
45 static const char move_mounts
[] =
51 _cleanup_close_
int old_root_fd
= -1;
52 struct stat new_root_stat
;
54 const char *i
, *temporary_old_root
;
56 if (path_equal(new_root
, "/"))
59 temporary_old_root
= strjoina(new_root
, oldroot
);
60 mkdir_p_label(temporary_old_root
, 0755);
62 old_root_remove
= in_initrd();
64 if (stat(new_root
, &new_root_stat
) < 0)
65 return log_error_errno(errno
, "Failed to stat directory %s: %m", new_root
);
67 /* Work-around for kernel design: the kernel refuses switching
68 * root if any file systems are mounted MS_SHARED. Hence
69 * remount them MS_PRIVATE here as a work-around.
71 * https://bugzilla.redhat.com/show_bug.cgi?id=847418 */
72 if (mount(NULL
, "/", NULL
, MS_REC
|MS_PRIVATE
, NULL
) < 0)
73 log_warning_errno(errno
, "Failed to make \"/\" private mount: %m");
75 NULSTR_FOREACH(i
, move_mounts
) {
76 char new_mount
[PATH_MAX
];
80 n
= snprintf(new_mount
, sizeof new_mount
, "%s%s", new_root
, i
);
81 if (n
>= sizeof new_mount
) {
82 bool move
= mountflags
& MS_MOVE
;
84 log_warning("New path is too long, %s: %s%s",
85 move
? "forcing unmount instead" : "ignoring",
89 if (umount2(i
, MNT_FORCE
) < 0)
90 log_warning_errno(errno
, "Failed to unmount %s: %m", i
);
94 mkdir_p_label(new_mount
, 0755);
96 if (stat(new_mount
, &sb
) < 0 ||
97 sb
.st_dev
!= new_root_stat
.st_dev
) {
99 /* Mount point seems to be mounted already or
100 * stat failed. Unmount the old mount point. */
101 if (umount2(i
, MNT_DETACH
) < 0)
102 log_warning_errno(errno
, "Failed to unmount %s: %m", i
);
106 if (mount(i
, new_mount
, NULL
, mountflags
, NULL
) < 0) {
107 if (mountflags
& MS_MOVE
) {
108 log_error_errno(errno
, "Failed to move mount %s to %s, forcing unmount: %m", i
, new_mount
);
110 if (umount2(i
, MNT_FORCE
) < 0)
111 log_warning_errno(errno
, "Failed to unmount %s: %m", i
);
113 } else if (mountflags
& MS_BIND
)
114 log_error_errno(errno
, "Failed to bind mount %s to %s: %m", i
, new_mount
);
118 /* Do not fail, if base_filesystem_create() fails. Not all
119 * switch roots are like base_filesystem_create() wants them
120 * to look like. They might even boot, if they are RO and
121 * don't have the FS layout. Just ignore the error and
122 * switch_root() nevertheless. */
123 (void) base_filesystem_create(new_root
, UID_INVALID
, GID_INVALID
);
125 if (chdir(new_root
) < 0)
126 return log_error_errno(errno
, "Failed to change directory to %s: %m", new_root
);
128 if (old_root_remove
) {
129 old_root_fd
= open("/", O_RDONLY
|O_NONBLOCK
|O_CLOEXEC
|O_NOCTTY
|O_DIRECTORY
);
131 log_warning_errno(errno
, "Failed to open root directory: %m");
134 /* We first try a pivot_root() so that we can umount the old
135 * root dir. In many cases (i.e. where rootfs is /), that's
136 * not possible however, and hence we simply overmount root */
137 if (pivot_root(new_root
, temporary_old_root
) >= 0) {
139 /* Immediately get rid of the old root, if detach_oldroot is set.
140 * Since we are running off it we need to do this lazily. */
141 if (detach_oldroot
&& umount2(oldroot
, MNT_DETACH
) < 0)
142 log_error_errno(errno
, "Failed to lazily umount old root dir %s, %s: %m",
144 errno
== ENOENT
? "ignoring" : "leaving it around");
146 } else if (mount(new_root
, "/", NULL
, MS_MOVE
, NULL
) < 0)
147 return log_error_errno(errno
, "Failed to mount moving %s to /: %m", new_root
);
150 return log_error_errno(errno
, "Failed to change root: %m");
153 return log_error_errno(errno
, "Failed to change directory: %m");
155 if (old_root_fd
>= 0) {
158 if (fstat(old_root_fd
, &rb
) < 0)
159 log_warning_errno(errno
, "Failed to stat old root directory, leaving: %m");
161 (void) rm_rf_children(old_root_fd
, 0, &rb
);