NAME¶

virt-rescue - Run a rescue shell on a virtual machine

SYNOPSIS¶

 virt-rescue [--options] -d domname
 virt-rescue [--options] -a disk.img [-a disk.img ...]
 virt-rescue --suggest (-d domname | -a disk.img ...)

Old style:

 virt-rescue [--options] domname
 virt-rescue [--options] disk.img [disk.img ...]

WARNING¶

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.

DESCRIPTION¶

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
 filesystems.
 
 # /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:

 ><rescue> lvs
 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

OPTIONS¶

--help

Display brief help.

-a file

--add file

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.

--append kernelopts

Pass additional options to the rescue kernel.

-c URI

--connect URI

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.

-d guest

--domain guest

Add all the disks from the named libvirt guest. Domain UUIDs can be used instead of names.

--format=raw|qcow2|..

--format

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.

For example:

 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).

-m MB

--memsize MB

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.

--network

Enable QEMU user networking in the guest. See "NETWORK".

-r

--ro

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).

--scratch

--scratch=N

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 line.

--selinux

Enable SELinux in the rescue appliance. You should read "SELINUX" in guestfs(3) before using this option.

--smp N

Enable N ≥ 2 virtual CPUs in the rescue appliance.

--suggest

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.

-v

--verbose

Enable verbose messages for debugging.

-V

--version

Display version number and exit.

-w

--rw

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 ...]

or

 virt-rescue guestname

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 guest.

For compatibility the old style is still supported.

NETWORK¶

Adding the --network option enables QEMU user networking in the rescue appliance. There are some differences between user networking and ordinary networking:

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:

 exec 3<>/dev/tcp/redhat.com/80
 echo "GET /" >&3
 cat <&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
 total 1628
 -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
 ><rescue> exit
    

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
    

ENVIRONMENT VARIABLES¶

Several environment variables affect virt-rescue. See "ENVIRONMENT VARIABLES" in guestfs(3) for the complete list.

SHELL QUOTING¶

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.

FILES¶

$HOME/.libguestfs-tools.rc

/etc/libguestfs-tools.conf

This configuration file controls the default read-only or read-write mode (--ro or --rw).

See "OPENING DISKS FOR READ AND WRITE" in guestfish(1).

SEE ALSO¶

guestfs(3), guestfish(1), virt-cat(1), virt-edit(1), virt-filesystems(1), http://libguestfs.org/.

AUTHOR¶

Richard W.M. Jones http://people.redhat.com/~rjones/

COPYRIGHT¶

Copyright (C) 2009-2013 Red Hat Inc.

LICENSE¶

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.

BUGS¶

To get a list of bugs against libguestfs, use this link: https://bugzilla.redhat.com/buglist.cgi?component=libguestfs&product=Virtualization+Tools

To report a new bug against libguestfs, use this link: https://bugzilla.redhat.com/enter_bug.cgi?component=libguestfs&product=Virtualization+Tools

When reporting a bug, please supply:

• The version of libguestfs.
• Where you got libguestfs (eg. which Linux distro, compiled from source, etc)
• Describe the bug accurately and give a way to reproduce it.
• Run libguestfs-test-tool(1) and paste the complete, unedited output into the bug report.