virt-rescue(1)
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
Using "virt-rescue" in write mode on live virtual machines, or concurrently with other disk editing tools, can be dangerous, potentially causing disk corruption. The virtual machine must be shut down before you use this command, and disk images must not be edited concurrently. Use the --ro (read-only) option to use "virt-rescue" safely if the disk image or virtual machine might be live. You may see strange or inconsistent results if running concurrently with other changes, but with this option you won't risk 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
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.
-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 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.
FILES
$XDG_CONFIG_HOME/libguestfs/libguestfs-tools.conf
$HOME/.libguestfs-tools.rc
$XDG_CONFIG_DIRS/libguestfs/libguestfs-tools.conf
/etc/libguestfs-tools.conf
This configuration file controls the default read-only or read-
write mode (--ro or --rw).
See libguestfs-tools.conf(5).
SEE ALSO
guestfs(3), guestfish(1), virt-cat(1), virt-edit(1), virt-filesystems(1), libguestfs-tools.conf(5), http://libguestfs.org/.
AUTHOR
Richard W.M. Jones http://people.redhat.com/~rjones/
COPYRIGHT
Copyright (C) 2009-2016 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.
Opportunity
Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.
Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.
Free Software
Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.
Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.
Free Books
The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.
Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.
Education
Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.
Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.
