blob: acbae2bb0d3d8949231ab999322bbfe61f1f54a0 [file] [log] [blame]
/* switch_root.c - Switch from rootfs/initramfs to another filesystem
* Copyright 2005 Rob Landley <>
bool "switch_root"
default y
usage: switch_root [-c /dev/console] NEW_ROOT NEW_INIT...
Use from PID 1 under initramfs to free initramfs, chroot to NEW_ROOT,
and exec NEW_INIT.
-c Redirect console to device in NEW_ROOT
-h Hang instead of exiting on failure (avoids kernel panic)
#define FOR_switch_root
#include "toys.h"
#include <sys/vfs.h>
char *console;
dev_t rootdev;
static int del_node(struct dirtree *node)
if (node->st.st_dev == TT.rootdev && dirtree_notdotdot(node)) {
int flag = 0;
if (S_ISDIR(node->st.st_mode)) {
if (!node->again) return DIRTREE_COMEAGAIN;
unlinkat(dirtree_parentfd(node), node->name, flag);
return 0;
void switch_root_main(void)
char *newroot = *toys.optargs, **cmdline = toys.optargs+1;
struct stat st1, st2;
struct statfs stfs;
int console = console; // gcc's "may be used" warnings are broken.
if (getpid() != 1) error_exit("not pid 1");
// Root filesystem we're leaving must be ramfs or tmpfs
if (statfs("/", &stfs) ||
(stfs.f_type != 0x858458f6 && stfs.f_type != 0x01021994))
error_msg("not ramfs");
goto panic;
// New directory must be different filesystem instance
if (chdir(newroot) || stat(".", &st1) || stat("/", &st2) ||
st1.st_dev == st2.st_dev)
error_msg("bad newroot '%s'", newroot);
goto panic;
// trim any / characters from the init cmdline, as we want to test it with
// stat(), relative to newroot. *cmdline is also used below, but by that
// point we are in the chroot, so a relative path is still OK.
while (**cmdline == '/') (*cmdline)++;
// init program must exist and be an executable file
if (stat(*cmdline, &st1) || !S_ISREG(st1.st_mode) || !(st1.st_mode&0100)) {
error_msg("bad init");
goto panic;
if (TT.console && -1 == (console = open(TT.console, O_RDWR))) {
perror_msg("bad console '%s'", TT.console);
goto panic;
// Ok, enough safety checks: wipe root partition.
dirtree_read("/", del_node);
// Fix the appearance of the mount table in the newroot chroot
if (mount(".", "/", NULL, MS_MOVE, NULL)) {
goto panic;
// Enter the new root before starting init
if (chroot(".")) {
goto panic;
// Make sure cwd does not point outside of the chroot
if (chdir("/")) {
goto panic;
if (TT.console) {
int i;
for (i=0; i<3; i++) if (console != i) dup2(console, i);
if (console>2) close(console);
execv(*cmdline, cmdline);
perror_msg("Failed to exec '%s'", *cmdline);
if (toys.optflags & FLAG_h) for (;;) wait(NULL);