virt-rescue - Run a rescue shell on a virtual machine
virt-rescue [--options] -d domname virt-rescue [--options] -a disk.img [-a disk.img ...] [-i]
virt-rescue [--options] domname virt-rescue [--options] disk.img [disk.img ...]
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.
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 -i virt-rescue --ro -a /path/to/disk.img -i 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. There is an empty directory called /sysroot where you can mount filesystems.
To automatically mount the virtual machine’s filesystems under /sysroot use the -i option. This uses libguestfs inspection to find the filesystems and mount them in the right place. You can also mount filesystems individually using the -m option.
><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 USB drives, SD cards and hard disks.
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.
- This parameter sets the sector size of the disk image. It affects all explicitly added subsequent disks after this parameter. Using --blocksize with no argument switches the disk sector size to the default value which is usually 512 bytes. See also "guestfs_add_drive_opts" in guestfs(3).
- -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.
- -e none
- Disable the escape key.
- -e KEY
- Set the escape key to the given key sequence. The default is "^]". To specify the escape key you can use:
- Control key + "x" key.
- -e none means there is no escape key, escapes are disabled.
See "ESCAPE KEY" below for further information.
- 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).
- Using virt-inspector(1) code, inspect the disks looking for an
operating system and mount filesystems as they would be mounted on the
real virtual machine.
The filesystems are mounted on /sysroot in the rescue environment.
- --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.
- -m dev[:mountpoint[:options[:fstype]]]
- --mount dev[:mountpoint[:options[:fstype]]]
- Mount the named partition or logical volume on the given mountpoint in
the guest (this has nothing to do with mountpoints in the host).
If the mountpoint is omitted, it defaults to /. You have to mount something on /.
The filesystems are mounted under /sysroot in the rescue environment.
The third (and rarely used) part of the mount parameter is the list of mount options used to mount the underlying filesystem. If this is not given, then the mount options are either the empty string or "ro" (the latter if the --ro flag is used). By specifying the mount options, you override this default choice. Probably the only time you would use this is to enable ACLs and/or extended attributes if the filesystem can support them:
The fourth part of the parameter is the filesystem driver to use, such as "ext3" or "ntfs". This is rarely needed, but can be useful if multiple drivers are valid for a filesystem (eg: "ext2" and "ext3"), or if libguestfs misidentifies a filesystem.
- 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
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.
- This option is provided for backwards compatibility and does nothing.
- --smp N
- Enable N ≥ 2 virtual CPUs in the rescue appliance.
- This option was used in older versions of virt-rescue to suggest what
commands you could use to mount filesystems under /sysroot. For the
current version of virt-rescue, it is easier to use the -i option
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, -d and -m options so that disks
are added and mounts are done read-write.
See "OPENING DISKS FOR READ AND WRITE" in guestfish(1).
- 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 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
exec 3<>/dev/tcp/redhat.com/80 echo "GET /" >&3 cat <&3
See bash(1) for more details.
Virt-rescue supports various keyboard escape sequences which are entered by pressing "^]" (Control key + "]" key).
You can change the escape key using the -e option on the command line (see above), and you can disable escapes completely using -e none. The rest of this section assumes the default escape key.
The following escapes can be used:
- "^] ?"
- "^] h"
- Prints a brief help text about escape sequences.
- "^] i"
- Prints brief libguestfs inspection information for the guest. This only works if you used -i on the virt-rescue command line.
- "^] q"
- "^] x"
- Quits virt-rescue immediately.
- "^] s"
- Synchronize the filesystems (sync).
- "^] u"
- Unmounts all the filesystems, except for the root (appliance) filesystems.
- "^] z"
- Suspend virt-rescue (like pressing "^Z" except that it affects virt-rescue rather than the program inside the rescue shell).
- "^] ^]"
- Sends the literal character "^]" (ASCII 0x1d) through to the rescue shell.
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.
- 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
- 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.
- 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
- 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
- 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
- Before exiting virt-rescue, unmount (or at least sync) the disks:
><rescue> umount /tmp/mnt ><rescue> exit
- 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.
- This configuration file controls the default read-only or read-write mode (--ro or --rw).
Richard W.M. Jones http://people.redhat.com/~rjones/
Copyright (C) 2009-2020 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: 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.