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switch_root: new command
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Copied from Dracut project:
git://dracut.git.sourceforge.net/gitroot/dracut

switch_root history in dracut.git repository:

$ git shortlog switch_root.c
Harald Hoyer (5):
      replace switch_root shell script with binary
      add \n to switch_root
      use switch_root code from http://pjones.fedorapeople.org/mkstart/usr/lib/mkstart/switchroot.c
      mount move instead of umount and fix the search for fallback inits
      setsid() and set controlling terminal for real /sbin/init

Victor Lowther (2):
      Simplify switch_root.c a bit
      Remove all files on the initramfs before switching root

Signed-off-by: Peter Jones <pjones@redhat.com>
Signed-off-by: Karel Zak <kzak@redhat.com>
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karelzak committed Jun 22, 2009
1 parent e9799b6 commit 711ea73
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2 changes: 2 additions & 0 deletions AUTHORS
Expand Up @@ -29,6 +29,8 @@ AUTHORS (merged projects & commands):
setarch: Elliot Lee <sopwith@redhat.com>
Jindrich Novy <jnovy@redhat.com>
simpleinit: Richard Gooch <rgooch@atnf.csiro.au>
switch_root: Peter Jones <pjones@redhat.com>
Jeremy Katz <katzj@redhat.com>


CONTRIBUTORS:
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1 change: 1 addition & 0 deletions po/POTFILES.in
Expand Up @@ -180,6 +180,7 @@ sys-utils/renice.c
sys-utils/rtcwake.c
sys-utils/setarch.c
sys-utils/setsid.c
sys-utils/switch_root.c
sys-utils/tunelp.c
text-utils/col.c
text-utils/colcrt.c
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1 change: 1 addition & 0 deletions sys-utils/.gitignore
Expand Up @@ -36,6 +36,7 @@ sparc32.8
sparc32bash.8
sparc64.8
sparc.8
switch_root
tunelp
vidmode.8
x86_64.8
2 changes: 1 addition & 1 deletion sys-utils/Makefile.am
@@ -1,7 +1,7 @@
include $(top_srcdir)/config/include-Makefile.am

bin_PROGRAMS =
sbin_PROGRAMS =
sbin_PROGRAMS = switch_root
usrbinexec_PROGRAMS = flock ipcrm ipcs ipcmk renice setsid
usrsbinexec_PROGRAMS = readprofile

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198 changes: 198 additions & 0 deletions sys-utils/switch_root.c
@@ -0,0 +1,198 @@
/*
* switchroot.c - switch to new root directory and start init.
*
* Copyright 2002-2008 Red Hat, Inc. All rights reserved.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* Authors:
* Peter Jones <pjones@redhat.com>
* Jeremy Katz <katzj@redhat.com>
*/

#define _GNU_SOURCE 1

#include <sys/mount.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/param.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <ctype.h>
#include <dirent.h>

#ifndef MS_MOVE
#define MS_MOVE 8192
#endif

#ifndef MNT_DETACH
#define MNT_DETACH 0x2
#endif

enum {
ok,
err_no_directory,
err_usage,
};

/* remove all files/directories below dirName -- don't cross mountpoints */
static int
recursiveRemove(char * dirName)
{
struct stat sb,rb;
DIR * dir;
struct dirent * d;
char * strBuf = alloca(strlen(dirName) + 1024);

if (!(dir = opendir(dirName))) {
printf("error opening %s: %m\n", dirName);
return 0;
}

if (fstat(dirfd(dir),&rb)) {
printf("unable to stat %s: %m\n", dirName);
closedir(dir);
return 0;
}

errno = 0;
while ((d = readdir(dir))) {
errno = 0;

if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, "..")) {
errno = 0;
continue;
}

strcpy(strBuf, dirName);
strcat(strBuf, "/");
strcat(strBuf, d->d_name);

if (lstat(strBuf, &sb)) {
printf("failed to stat %s: %m\n", strBuf);
errno = 0;
continue;
}

/* only descend into subdirectories if device is same as dir */
if (S_ISDIR(sb.st_mode)) {
if (sb.st_dev == rb.st_dev) {
recursiveRemove(strBuf);
if (rmdir(strBuf))
printf("failed to rmdir %s: %m\n", strBuf);
}
errno = 0;
continue;
}
if (unlink(strBuf)) {
printf("failed to remove %s: %m\n", strBuf);
errno = 0;
continue;
}
}

if (errno) {
closedir(dir);
printf("error reading from %s: %m\n", dirName);
return 1;
}

closedir(dir);

return 0;
}

static int switchroot(const char *newroot)
{
/* Don't try to unmount the old "/", there's no way to do it. */
const char *umounts[] = { "/dev", "/proc", "/sys", NULL };
int errnum;
int i;

for (i = 0; umounts[i] != NULL; i++) {
char newmount[PATH_MAX];
strcpy(newmount, newroot);
strcat(newmount, umounts[i]);
if (mount(umounts[i], newmount, NULL, MS_MOVE, NULL) < 0) {
fprintf(stderr, "Error mount moving old %s %s %m\n",
umounts[i], newmount);
fprintf(stderr, "Forcing unmount of %s\n", umounts[i]);
umount2(umounts[i], MNT_FORCE);
}
}

if (chdir(newroot) < 0) {
errnum=errno;
fprintf(stderr, "switchroot: chdir failed: %m\n");
errno=errnum;
return -1;
}
recursiveRemove("/");
if (mount(newroot, "/", NULL, MS_MOVE, NULL) < 0) {
errnum = errno;
fprintf(stderr, "switchroot: mount failed: %m\n");
errno = errnum;
return -1;
}

if (chroot(".")) {
errnum = errno;
fprintf(stderr, "switchroot: chroot failed: %m\n");
errno = errnum;
return -2;
}
return 1;
}

static void usage(FILE *output)
{
fprintf(output, "usage: switchroot <newrootdir> <init> <args to init>\n");
if (output == stderr)
exit(err_usage);
exit(ok);
}

int main(int argc, char *argv[])
{
char *newroot = argv[1];
char *init = argv[2];
char **initargs = &argv[2];

if (newroot == NULL || newroot[0] == '\0' ||
init == NULL || init[0] == '\0' ) {
usage(stderr);
}

if (switchroot(newroot) < 0) {
fprintf(stderr, "switchroot has failed. Sorry.\n");
return 1;
}
if (access(initargs[0], X_OK))
fprintf(stderr, "WARNING: can't access %s\n", initargs[0]);

/* get session leader */
setsid();
/* set controlling terminal */
ioctl (0, TIOCSCTTY, 1);

execv(initargs[0], initargs);
}

/*
* vim:noet:ts=8:sw=8:sts=8
*/

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