/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/ /*** This file is part of systemd. Copyright 2012 Harald Hoyer, Lennart Poettering systemd is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. systemd is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with systemd; If not, see <http://www.gnu.org/licenses/>. ***/ #include <sys/stat.h> #include <stdbool.h> #include <errno.h> #include <string.h> #include <sys/mount.h> #include <unistd.h> #include <fcntl.h> #include "util.h" #include "path-util.h" #include "switch-root.h" #include "missing.h" int switch_root(const char *new_root) { /* Don't try to unmount/move the old "/", there's no way to do it. */ static const char move_mounts[] = "/dev\0" "/proc\0" "/sys\0" "/run\0"; _cleanup_close_ int old_root_fd = -1; struct stat new_root_stat; bool old_root_remove; const char *i, *temporary_old_root; if (path_equal(new_root, "/")) return 0; /* When using pivot_root() we assume that /mnt exists as place * we can temporarily move the old root to. As we immediately * unmount it from there it doesn't matter much which * directory we choose for this, but it should be more likely * than not that /mnt exists and is suitable as mount point * and is on the same fs as the old root dir */ temporary_old_root = strappenda(new_root, "/mnt"); old_root_remove = in_initrd(); if (stat(new_root, &new_root_stat) < 0) { log_error("Failed to stat directory %s: %m", new_root); return -errno; } /* Work-around for a kernel bug: for some reason the kernel * refuses switching root if any file systems are mounted * MS_SHARED. Hence remount them MS_PRIVATE here as a * work-around. * * https://bugzilla.redhat.com/show_bug.cgi?id=847418 */ if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0) log_warning("Failed to make \"/\" private mount: %m"); NULSTR_FOREACH(i, move_mounts) { char new_mount[PATH_MAX]; struct stat sb; snprintf(new_mount, sizeof(new_mount), "%s%s", new_root, i); char_array_0(new_mount); if ((stat(new_mount, &sb) < 0) || sb.st_dev != new_root_stat.st_dev) { /* Mount point seems to be mounted already or * stat failed. Unmount the old mount * point. */ if (umount2(i, MNT_DETACH) < 0) log_warning("Failed to unmount %s: %m", i); continue; } if (mount(i, new_mount, NULL, MS_MOVE, NULL) < 0) { log_error("Failed to move mount %s to %s, forcing unmount: %m", i, new_mount); if (umount2(i, MNT_FORCE) < 0) log_warning("Failed to unmount %s: %m", i); } } if (chdir(new_root) < 0) { log_error("Failed to change directory to %s: %m", new_root); return -errno; } if (old_root_remove) { old_root_fd = open("/", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_NOCTTY|O_DIRECTORY); if (old_root_fd < 0) log_warning("Failed to open root directory: %m"); } /* We first try a pivot_root() so that we can umount the old * root dir. In many cases (i.e. where rootfs is /), that's * not possible however, and hence we simply overmount root */ if (pivot_root(new_root, temporary_old_root) >= 0) { /* Immediately get rid of the old root. Since we are * running off it we need to do this lazily. */ if (umount2(temporary_old_root, MNT_DETACH) < 0) { log_error("Failed to umount old root dir %s: %m", temporary_old_root); return -errno; } } else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0) { log_error("Failed to mount moving %s to /: %m", new_root); return -errno; } if (chroot(".") < 0) { log_error("Failed to change root: %m"); return -errno; } if (chdir("/") < 0) { log_error("Failed to change directory: %m"); return -errno; } if (old_root_fd >= 0) { struct stat rb; if (fstat(old_root_fd, &rb) < 0) log_warning("Failed to stat old root directory, leaving: %m"); else { rm_rf_children(old_root_fd, false, false, &rb); old_root_fd = -1; } } return 0; }