virt-rescue(1) Virtualization Support virt-rescue(1)NAMEvirt-rescue - Run a rescue shell on a virtual machine
SYNOPSISvirt-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.
DESCRIPTIONvirt-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
NOTES
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).
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 X 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 ALSOguestfs(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.
libguestfs-1.20.4 2013-03-12 virt-rescue(1)
