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CentOS 7.0 - man page for virt-rescue (centos section 1)

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 ...)

       Old style:

	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

	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

       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:

	><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

       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.

       -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.

       -a URI
       --add URI
	   Add a remote disk.  See "ADDING REMOTE STORAGE" in guestfish(1).

       --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

	   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

	   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.

	   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 line.

	   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.

	   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-

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

       -x  Enable tracing of libguestfs API calls.

       Previous versions of virt-rescue allowed you to write either:

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


	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.

       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.

       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

	    ><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

       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

	   See libguestfs-tools.conf(5).

       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

libguestfs-1.22.6			    2013-08-24				   virt-rescue(1)

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