virt-rescue(1) Virtualization Support virt-rescue(1)
virt-rescue - Run a rescue shell on a virtual machine
virt-rescue [--options] -d domname
virt-rescue [--options] -a disk.img [-a disk.img ...]
virt-rescue --suggest (-d domname | -a disk.img ...)
virt-rescue [--options] domname
virt-rescue [--options] disk.img [disk.img ...]
You must not use "virt-rescue" on live virtual machines. Doing so will probably result in disk corruption in the VM. "virt-rescue" tries
to stop you from doing this, but doesn't catch all cases.
However if you use the --ro (read only) option, then you can attach a shell to a live virtual machine. The results might be strange or
inconsistent at times but you won't get disk corruption.
virt-rescue is like a Rescue CD, but for virtual machines, and without the need for a CD. virt-rescue gives you a rescue shell and some
simple recovery tools which you can use to examine or rescue a virtual machine or disk image.
You can run virt-rescue on any virtual machine known to libvirt, or directly on disk image(s):
virt-rescue -d GuestName
virt-rescue --ro -a /path/to/disk.img
virt-rescue -a /dev/sdc
For live VMs you must use the --ro option.
When you run virt-rescue on a virtual machine or disk image, you are placed in an interactive bash shell where you can use many ordinary
Linux commands. What you see in "/" ("/bin", "/lib" etc) is the rescue appliance. You must mount the virtual machine's filesystems by
hand. There is an empty directory called "/sysroot" where you can mount filesystems.
You can get virt-rescue to suggest mount commands for you by using the --suggest option (in another terminal):
$ virt-rescue --suggest -d Fedora15
Inspecting the virtual machine or disk image ...
This disk contains one or more operating systems. You can use these
mount commands in virt-rescue (at the ><rescue> prompt) to mount the
# /dev/vg_f15x32/lv_root is the root of a linux operating system
# type: linux, distro: fedora, version: 15.0
# Fedora release 15 (Lovelock)
mount /dev/vg_f15x32/lv_root /sysroot/
mount /dev/vda1 /sysroot/boot
mount --bind /dev /sysroot/dev
mount --bind /dev/pts /sysroot/dev/pts
mount --bind /proc /sysroot/proc
mount --bind /sys /sysroot/sys
Another way is to list the logical volumes (with lvs(8)) and partitions (with parted(8)) and mount them by hand:
LV VG Attr LSize Origin Snap% Move Log Copy% Convert
lv_root vg_f15x32 -wi-a- 8.83G
lv_swap vg_f15x32 -wi-a- 992.00M
><rescue> mount /dev/vg_f15x32/lv_root /sysroot
><rescue> mount /dev/vda1 /sysroot/boot
><rescue> ls /sysroot
Another command to list available filesystems is virt-filesystems(1).
To run commands in a Linux guest (for example, grub), you should chroot into the /sysroot directory first:
><rescue> chroot /sysroot
Virt-rescue can be used on any disk image file or device, not just a virtual machine. For example you can use it on a blank file if you
want to partition that file (although we would recommend using guestfish(1) instead as it is more suitable for this purpose). You can even
use virt-rescue on things like SD cards.
You can get virt-rescue to give you scratch disk(s) to play with. This is useful for testing out Linux utilities (see --scratch).
Virt-rescue does not require root. You only need to run it as root if you need root to open the disk image.
This tool is just designed for quick interactive hacking on a virtual machine. For more structured access to a virtual machine disk image,
you should use guestfs(3). To get a structured shell that you can use to make scripted changes to guests, use guestfish(1).
Display brief help.
Add file which should be a disk image from a virtual machine. If the virtual machine has multiple block devices, you must supply all
of them with separate -a options.
The format of the disk image is auto-detected. To override this and force a particular format use the --format=.. option.
Add a remote disk. See "ADDING REMOTE STORAGE" in guestfish(1).
Pass additional options to the rescue kernel.
If using libvirt, connect to the given URI. If omitted, then we connect to the default libvirt hypervisor.
If you specify guest block devices directly (-a), then libvirt is not used at all.
Add all the disks from the named libvirt guest. Domain UUIDs can be used instead of names.
The default for the -a option is to auto-detect the format of the disk image. Using this forces the disk format for -a options which
follow on the command line. Using --format with no argument switches back to auto-detection for subsequent -a options.
virt-rescue --format=raw -a disk.img
forces raw format (no auto-detection) for "disk.img".
virt-rescue --format=raw -a disk.img --format -a another.img
forces raw format (no auto-detection) for "disk.img" and reverts to auto-detection for "another.img".
If you have untrusted raw-format guest disk images, you should use this option to specify the disk format. This avoids a possible
security problem with malicious guests (CVE-2010-3851).
Change the amount of memory allocated to the rescue system. The default is set by libguestfs and is small but adequate for running
system tools. The occasional program might need more memory. The parameter is specified in megabytes.
Enable QEMU user networking in the guest. See "NETWORK".
Open the image read-only.
The option must always be used if the disk image or virtual machine might be running, and is generally recommended in cases where you
don't need write access to the disk.
See also "OPENING DISKS FOR READ AND WRITE" in guestfish(1).
The --scratch option adds a large scratch disk to the rescue appliance. --scratch=N adds "N" scratch disks. The scratch disk(s) are
deleted automatically when virt-rescue exits.
You can also mix -a, -d and --scratch options. The scratch disk(s) are added to the appliance in the order they appear on the command
Enable SELinux in the rescue appliance. You should read "SELINUX" in guestfs(3) before using this option.
Enable N >= 2 virtual CPUs in the rescue appliance.
Inspect the disk image and suggest what mount commands should be used to mount the disks. You should use the --suggest option in a
second terminal, then paste the commands into another virt-rescue.
This option implies --ro and is safe to use even if the guest is up or if another virt-rescue is running.
Enable verbose messages for debugging.
Display version number and exit.
This changes the -a and -d options so that disks are added and mounts are done read-write.
See "OPENING DISKS FOR READ AND WRITE" in guestfish(1).
-x Enable tracing of libguestfs API calls.
OLD-STYLE COMMAND LINE ARGUMENTS
Previous versions of virt-rescue allowed you to write either:
virt-rescue disk.img [disk.img ...]
whereas in this version you should use -a or -d respectively to avoid the confusing case where a disk image might have the same name as a
For compatibility the old style is still supported.
Adding the --network option enables QEMU user networking in the rescue appliance. There are some differences between user networking and
ping does not work
Because the ICMP ECHO_REQUEST protocol generally requires root in order to send the ping packets, and because virt-rescue must be able
to run as non-root, QEMU user networking is not able to emulate the ping(8) command. The ping command will appear to resolve addresses
but will not be able to send or receive any packets. This does not mean that the network is not working.
cannot receive connections
QEMU user networking cannot receive incoming connections.
making TCP connections
The virt-rescue appliance needs to be small and so does not include many network tools. In particular there is no telnet(1) command.
You can make TCP connections from the shell using the magical "/dev/tcp/<hostname>/<port>" syntax:
echo "GET /" >&3
See bash(1) for more details.
CAPTURING CORE DUMPS
If you are testing a tool inside virt-rescue and the tool (not virt-rescue) segfaults, it can be tricky to capture the core dump outside
virt-rescue for later analysis. This section describes one way to do this.
1. Create a scratch disk for core dumps:
truncate -s 4G /tmp/corefiles
virt-format --partition=mbr --filesystem=ext2 -a /tmp/corefiles
virt-filesystems -a /tmp/corefiles --all --long -h
2. When starting virt-rescue, attach the core files disk last:
virt-rescue --rw [-a ...] -a /tmp/corefiles
NB. If you use the --ro option, then virt-rescue will silently not write any core files to "/tmp/corefiles".
3. Inside virt-rescue, mount the core files disk. Note replace "/dev/sdb1" with the last disk index. For example if the core files disk
is the last of four disks, you would use "/dev/sdd1".
><rescue> mkdir /tmp/mnt
><rescue> mount /dev/sdb1 /tmp/mnt
4. Enable core dumps in the rescue kernel:
><rescue> echo '/tmp/mnt/core.%p' > /proc/sys/kernel/core_pattern
><rescue> ulimit -Hc unlimited
><rescue> ulimit -Sc unlimited
5. Run the tool that caused the core dump. The core dump will be written to "/tmp/mnt/core.PID".
><rescue> ls -l /tmp/mnt
-rw------- 1 root root 1941504 Dec 7 13:13 core.130
drwx------ 2 root root 16384 Dec 7 13:00 lost+found
6. Before exiting virt-rescue, unmount (or at least sync) the disks:
><rescue> umount /tmp/mnt
7. Outside virt-rescue, the core dump(s) can be removed from the disk using guestfish(1). For example:
guestfish --ro -a /tmp/corefiles -m /dev/sda1
><fs> ll /
><fs> download /core.NNN /tmp/core.NNN
Several environment variables affect virt-rescue. See "ENVIRONMENT VARIABLES" in guestfs(3) for the complete list.
Libvirt guest names can contain arbitrary characters, some of which have meaning to the shell such as "#" and space. You may need to quote
or escape these characters on the command line. See the shell manual page sh(1) for details.
This configuration file controls the default read-only or read-write mode (--ro or --rw).
guestfs(3), guestfish(1), virt-cat(1), virt-edit(1), virt-filesystems(1), libguestfs-tools.conf(5), http://libguestfs.org/.
Richard W.M. Jones http://people.redhat.com/~rjones/
Copyright (C) 2009-2013 Red Hat Inc.
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, write to the Free Software Foundation,
Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
To get a list of bugs against libguestfs, use this link:
To report a new bug against libguestfs, use this link:
When reporting a bug, please supply:
o The version of libguestfs.
o Where you got libguestfs (eg. which Linux distro, compiled from source, etc)
o Describe the bug accurately and give a way to reproduce it.
o Run libguestfs-test-tool(1) and paste the complete, unedited output into the bug report.
libguestfs-1.22.6 2013-08-24 virt-rescue(1)