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git.ipfire.org Git - thirdparty/systemd.git/blob - src/shared/switch-root.c
1 /* SPDX-License-Identifier: LGPL-2.1+ */
12 #include "base-filesystem.h"
18 #include "mount-util.h"
19 #include "mountpoint-util.h"
20 #include "path-util.h"
22 #include "stdio-util.h"
23 #include "string-util.h"
25 #include "switch-root.h"
26 #include "user-util.h"
29 int switch_root(const char *new_root
,
30 const char *old_root_after
, /* path below the new root, where to place the old root after the transition */
31 bool unmount_old_root
,
32 unsigned long mount_flags
) { /* MS_MOVE or MS_BIND */
34 _cleanup_free_
char *resolved_old_root_after
= NULL
;
35 _cleanup_close_
int old_root_fd
= -1;
41 assert(old_root_after
);
43 if (path_equal(new_root
, "/"))
46 /* Check if we shall remove the contents of the old root */
47 old_root_remove
= in_initrd();
48 if (old_root_remove
) {
49 old_root_fd
= open("/", O_RDONLY
|O_NONBLOCK
|O_CLOEXEC
|O_NOCTTY
|O_DIRECTORY
);
51 return log_error_errno(errno
, "Failed to open root directory: %m");
54 /* Determine where we shall place the old root after the transition */
55 r
= chase_symlinks(old_root_after
, new_root
, CHASE_PREFIX_ROOT
|CHASE_NONEXISTENT
, &resolved_old_root_after
);
57 return log_error_errno(r
, "Failed to resolve %s/%s: %m", new_root
, old_root_after
);
58 if (r
== 0) /* Doesn't exist yet. Let's create it */
59 (void) mkdir_p_label(resolved_old_root_after
, 0755);
61 /* Work-around for kernel design: the kernel refuses MS_MOVE if any file systems are mounted MS_SHARED. Hence
62 * remount them MS_PRIVATE here as a work-around.
64 * https://bugzilla.redhat.com/show_bug.cgi?id=847418 */
65 if (mount(NULL
, "/", NULL
, MS_REC
|MS_PRIVATE
, NULL
) < 0)
66 return log_error_errno(errno
, "Failed to set \"/\" mount propagation to private: %m");
68 FOREACH_STRING(i
, "/sys", "/dev", "/run", "/proc") {
69 _cleanup_free_
char *chased
= NULL
;
71 r
= chase_symlinks(i
, new_root
, CHASE_PREFIX_ROOT
|CHASE_NONEXISTENT
, &chased
);
73 return log_error_errno(r
, "Failed to resolve %s/%s: %m", new_root
, i
);
75 /* Already exists. Let's see if it is a mount point already. */
76 r
= path_is_mount_point(chased
, NULL
, 0);
78 return log_error_errno(r
, "Failed to determine whether %s is a mount point: %m", chased
);
79 if (r
> 0) /* If it is already mounted, then do nothing */
82 /* Doesn't exist yet? */
83 (void) mkdir_p_label(chased
, 0755);
85 if (mount(i
, chased
, NULL
, mount_flags
, NULL
) < 0)
86 return log_error_errno(errno
, "Failed to mount %s to %s: %m", i
, chased
);
89 /* Do not fail if base_filesystem_create() fails. Not all switch roots are like base_filesystem_create() wants
90 * them to look like. They might even boot, if they are RO and don't have the FS layout. Just ignore the error
91 * and switch_root() nevertheless. */
92 (void) base_filesystem_create(new_root
, UID_INVALID
, GID_INVALID
);
94 if (chdir(new_root
) < 0)
95 return log_error_errno(errno
, "Failed to change directory to %s: %m", new_root
);
97 /* We first try a pivot_root() so that we can umount the old root dir. In many cases (i.e. where rootfs is /),
98 * that's not possible however, and hence we simply overmount root */
99 if (pivot_root(new_root
, resolved_old_root_after
) >= 0) {
101 /* Immediately get rid of the old root, if detach_oldroot is set.
102 * Since we are running off it we need to do this lazily. */
103 if (unmount_old_root
) {
104 r
= umount_recursive(old_root_after
, MNT_DETACH
);
106 log_warning_errno(r
, "Failed to unmount old root directory tree, ignoring: %m");
109 } else if (mount(new_root
, "/", NULL
, MS_MOVE
, NULL
) < 0)
110 return log_error_errno(errno
, "Failed to move %s to /: %m", new_root
);
113 return log_error_errno(errno
, "Failed to change root: %m");
116 return log_error_errno(errno
, "Failed to change directory: %m");
118 if (old_root_fd
>= 0) {
121 if (fstat(old_root_fd
, &rb
) < 0)
122 log_warning_errno(errno
, "Failed to stat old root directory, leaving: %m");
124 (void) rm_rf_children(old_root_fd
, 0, &rb
);