1virt-rescue(1) Virtualization Support virt-rescue(1)
2
6 virt-rescue - Run a rescue shell on a virtual machine
7
9 virt-rescue [--options] -d domname
10 virt-rescue [--options] -a disk.img [-a disk.img ...] [-i]
12 Old style:
14 virt-rescue [--options] domname
16 virt-rescue [--options] disk.img [disk.img ...]
18
20 Using "virt-rescue" in write mode on live virtual machines, or
21 concurrently with other disk editing tools, can be dangerous,
22 potentially causing disk corruption. The virtual machine must be shut
23 down before you use this command, and disk images must not be edited
24 concurrently.
25 Use the --ro (read-only) option to use "virt-rescue" safely if the disk
27 image or virtual machine might be live. You may see strange or
28 inconsistent results if running concurrently with other changes, but
29 with this option you won't risk disk corruption.
30
32 virt-rescue is like a Rescue CD, but for virtual machines, and without
33 the need for a CD. virt-rescue gives you a rescue shell and some
34 simple recovery tools which you can use to examine or rescue a virtual
35 machine or disk image.
36 You can run virt-rescue on any virtual machine known to libvirt, or
38 directly on disk image(s):
39 virt-rescue -d GuestName -i
41 virt-rescue --ro -a /path/to/disk.img -i
43 virt-rescue -a /dev/sdc
45 For live VMs you must use the --ro option.
47 When you run virt-rescue on a virtual machine or disk image, you are
49 placed in an interactive bash shell where you can use many ordinary
50 Linux commands. What you see in / (/bin, /lib etc) is the rescue
51 appliance. You must mount the virtual machine’s filesystems. There is
52 an empty directory called /sysroot where you can mount filesystems.
53 To automatically mount the virtual machine’s filesystems under /sysroot
55 use the -i option. This uses libguestfs inspection to find the
56 filesystems and mount them in the right place. You can also mount
57 filesystems individually using the -m option.
58 Another way is to list the logical volumes (with lvs(8)) and partitions
60 (with parted(8)) and mount them by hand:
61 ><rescue> lvs
63 LV VG Attr LSize Origin Snap% Move Log Copy% Convert
64 lv_root vg_f15x32 -wi-a- 8.83G
65 lv_swap vg_f15x32 -wi-a- 992.00M
66 ><rescue> mount /dev/vg_f15x32/lv_root /sysroot
67 ><rescue> mount /dev/vda1 /sysroot/boot
68 ><rescue> ls /sysroot
69 Another command to list available filesystems is virt-filesystems(1).
71 To run commands in a Linux guest (for example, grub), you should chroot
73 into the /sysroot directory first:
74 ><rescue> chroot /sysroot
76 NOTES
78 Virt-rescue can be used on any disk image file or device, not just a
79 virtual machine. For example you can use it on a blank file if you
80 want to partition that file (although we would recommend using
81 guestfish(1) instead as it is more suitable for this purpose). You can
82 even use virt-rescue on things like USB drives, SD cards and hard
83 disks.
84 You can get virt-rescue to give you scratch disk(s) to play with. This
86 is useful for testing out Linux utilities (see --scratch).
87 Virt-rescue does not require root. You only need to run it as root if
89 you need root to open the disk image.
90 This tool is just designed for quick interactive hacking on a virtual
92 machine. For more structured access to a virtual machine disk image,
93 you should use guestfs(3). To get a structured shell that you can use
94 to make scripted changes to guests, use guestfish(1).
95
97 --help
98 Display brief help.
99 -a FILE
101 --add FILE
102 Add "FILE" which should be a disk image from a virtual machine. If
103 the virtual machine has multiple block devices, you must supply all
104 of them with separate -a options.
105 The format of the disk image is auto-detected. To override this
107 and force a particular format use the --format=.. option.
108 -a URI
110 --add URI
111 Add a remote disk. See "ADDING REMOTE STORAGE" in guestfish(1).
112 --append KERNELOPTS
114 Pass additional options to the rescue kernel.
115 --blocksize=512
117 --blocksize=4096
118 --blocksize
119 This parameter sets the sector size of the disk image. It affects
120 all explicitly added subsequent disks after this parameter. Using
121 --blocksize with no argument switches the disk sector size to the
122 default value which is usually 512 bytes. See also
123 "guestfs_add_drive_opts" in guestfs(3).
124 -c URI
126 --connect URI
127 If using libvirt, connect to the given URI. If omitted, then we
128 connect to the default libvirt hypervisor.
129 If you specify guest block devices directly (-a), then libvirt is
131 not used at all.
132 -d guest
134 --domain guest
135 Add all the disks from the named libvirt guest. Domain UUIDs can
136 be used instead of names.
137 -e none
139 Disable the escape key.
140 -e KEY
142 Set the escape key to the given key sequence. The default is "^]".
143 To specify the escape key you can use:
144 "^x"
146 Control key + "x" key.
147 "none"
149 -e none means there is no escape key, escapes are disabled.
150 See "ESCAPE KEY" below for further information.
152 --format=raw|qcow2|..
154 --format
155 The default for the -a option is to auto-detect the format of the
156 disk image. Using this forces the disk format for -a options which
157 follow on the command line. Using --format with no argument
158 switches back to auto-detection for subsequent -a options.
159 For example:
161 virt-rescue --format=raw -a disk.img
163 forces raw format (no auto-detection) for disk.img.
165 virt-rescue --format=raw -a disk.img --format -a another.img
167 forces raw format (no auto-detection) for disk.img and reverts to
169 auto-detection for another.img.
170 If you have untrusted raw-format guest disk images, you should use
172 this option to specify the disk format. This avoids a possible
173 security problem with malicious guests (CVE-2010-3851).
174 -i
176 --inspector
177 Using virt-inspector(1) code, inspect the disks looking for an
178 operating system and mount filesystems as they would be mounted on
179 the real virtual machine.
180 The filesystems are mounted on /sysroot in the rescue environment.
182 --memsize MB
184 Change the amount of memory allocated to the rescue system. The
185 default is set by libguestfs and is small but adequate for running
186 system tools. The occasional program might need more memory. The
187 parameter is specified in megabytes.
188 -m dev[:mountpoint[:options[:fstype]]]
190 --mount dev[:mountpoint[:options[:fstype]]]
191 Mount the named partition or logical volume on the given mountpoint
192 in the guest (this has nothing to do with mountpoints in the host).
193 If the mountpoint is omitted, it defaults to /. You have to mount
195 something on /.
196 The filesystems are mounted under /sysroot in the rescue
198 environment.
199 The third (and rarely used) part of the mount parameter is the list
201 of mount options used to mount the underlying filesystem. If this
202 is not given, then the mount options are either the empty string or
203 "ro" (the latter if the --ro flag is used). By specifying the
204 mount options, you override this default choice. Probably the only
205 time you would use this is to enable ACLs and/or extended
206 attributes if the filesystem can support them:
207 -m /dev/sda1:/:acl,user_xattr
209 The fourth part of the parameter is the filesystem driver to use,
211 such as "ext3" or "ntfs". This is rarely needed, but can be useful
212 if multiple drivers are valid for a filesystem (eg: "ext2" and
213 "ext3"), or if libguestfs misidentifies a filesystem.
214 --network
216 Enable QEMU user networking in the guest. See "NETWORK".
217 -r
219 --ro
220 Open the image read-only.
221 The option must always be used if the disk image or virtual machine
223 might be running, and is generally recommended in cases where you
224 don't need write access to the disk.
225 See also "OPENING DISKS FOR READ AND WRITE" in guestfish(1).
227 --scratch
229 --scratch=N
230 The --scratch option adds a large scratch disk to the rescue
231 appliance. --scratch=N adds "N" scratch disks. The scratch
232 disk(s) are deleted automatically when virt-rescue exits.
233 You can also mix -a, -d and --scratch options. The scratch disk(s)
235 are added to the appliance in the order they appear on the command
236 line.
237 --selinux
239 This option is provided for backwards compatibility and does
240 nothing.
241 --smp N
243 Enable N ≥ 2 virtual CPUs in the rescue appliance.
244 --suggest
246 This option was used in older versions of virt-rescue to suggest
247 what commands you could use to mount filesystems under /sysroot.
248 For the current version of virt-rescue, it is easier to use the -i
249 option instead.
250 This option implies --ro and is safe to use even if the guest is up
252 or if another virt-rescue is running.
253 -v
255 --verbose
256 Enable verbose messages for debugging.
257 -V
259 --version
260 Display version number and exit.
261 -w
263 --rw
264 This changes the -a, -d and -m options so that disks are added and
265 mounts are done read-write.
266 See "OPENING DISKS FOR READ AND WRITE" in guestfish(1).
268 -x Enable tracing of libguestfs API calls.
270
272 Previous versions of virt-rescue allowed you to write either:
273 virt-rescue disk.img [disk.img ...]
275 or
277 virt-rescue guestname
279 whereas in this version you should use -a or -d respectively to avoid
281 the confusing case where a disk image might have the same name as a
282 guest.
283 For compatibility the old style is still supported.
285
287 Adding the --network option enables QEMU user networking in the rescue
288 appliance. There are some differences between user networking and
289 ordinary networking:
290 ping does not work
292 Because the ICMP ECHO_REQUEST protocol generally requires root in
293 order to send the ping packets, and because virt-rescue must be
294 able to run as non-root, QEMU user networking is not able to
295 emulate the ping(8) command. The ping command will appear to
296 resolve addresses but will not be able to send or receive any
297 packets. This does not mean that the network is not working.
298 cannot receive connections
300 QEMU user networking cannot receive incoming connections.
301 making TCP connections
303 The virt-rescue appliance needs to be small and so does not include
304 many network tools. In particular there is no telnet(1) command.
305 You can make TCP connections from the shell using the magical
306 /dev/tcp/<hostname>/<port> syntax:
307 exec 3<>/dev/tcp/redhat.com/80
309 echo "GET /" >&3
310 cat <&3
311 See bash(1) for more details.
313
315 Virt-rescue supports various keyboard escape sequences which are
316 entered by pressing "^]" (Control key + "]" key).
317 You can change the escape key using the -e option on the command line
319 (see above), and you can disable escapes completely using -e none. The
320 rest of this section assumes the default escape key.
321 The following escapes can be used:
323 "^] ?"
325 "^] h"
326 Prints a brief help text about escape sequences.
327 "^] i"
329 Prints brief libguestfs inspection information for the guest. This
330 only works if you used -i on the virt-rescue command line.
331 "^] q"
333 "^] x"
334 Quits virt-rescue immediately.
335 "^] s"
337 Synchronize the filesystems (sync).
338 "^] u"
340 Unmounts all the filesystems, except for the root (appliance)
341 filesystems.
342 "^] z"
344 Suspend virt-rescue (like pressing "^Z" except that it affects
345 virt-rescue rather than the program inside the rescue shell).
346 "^] ^]"
348 Sends the literal character "^]" (ASCII 0x1d) through to the rescue
349 shell.
350
352 If you are testing a tool inside virt-rescue and the tool (not virt-
353 rescue) segfaults, it can be tricky to capture the core dump outside
354 virt-rescue for later analysis. This section describes one way to do
355 this.
356 1. Create a scratch disk for core dumps:
358 truncate -s 4G /tmp/corefiles
360 virt-format --partition=mbr --filesystem=ext2 -a /tmp/corefiles
361 virt-filesystems -a /tmp/corefiles --all --long -h
362 2. When starting virt-rescue, attach the core files disk last:
364 virt-rescue --rw [-a ...] -a /tmp/corefiles
366 NB. If you use the --ro option, then virt-rescue will silently not
368 write any core files to /tmp/corefiles.
369 3. Inside virt-rescue, mount the core files disk. Note replace
371 /dev/sdb1 with the last disk index. For example if the core files
372 disk is the last of four disks, you would use /dev/sdd1.
373 ><rescue> mkdir /tmp/mnt
375 ><rescue> mount /dev/sdb1 /tmp/mnt
376 4. Enable core dumps in the rescue kernel:
378 ><rescue> echo '/tmp/mnt/core.%p' > /proc/sys/kernel/core_pattern
380 ><rescue> ulimit -Hc unlimited
381 ><rescue> ulimit -Sc unlimited
382 5. Run the tool that caused the core dump. The core dump will be
384 written to /tmp/mnt/core.PID.
385 ><rescue> ls -l /tmp/mnt
387 total 1628
388 -rw------- 1 root root 1941504 Dec 7 13:13 core.130
389 drwx------ 2 root root 16384 Dec 7 13:00 lost+found
390 6. Before exiting virt-rescue, unmount (or at least sync) the disks:
392 ><rescue> umount /tmp/mnt
394 ><rescue> exit
395 7. Outside virt-rescue, the core dump(s) can be removed from the disk
397 using guestfish(1). For example:
398 guestfish --ro -a /tmp/corefiles -m /dev/sda1
400 ><fs> ll /
401 ><fs> download /core.NNN /tmp/core.NNN
402
404 Several environment variables affect virt-rescue. See "ENVIRONMENT
405 VARIABLES" in guestfs(3) for the complete list.
406
408 $XDG_CONFIG_HOME/libguestfs/libguestfs-tools.conf
409 $HOME/.libguestfs-tools.rc
410 $XDG_CONFIG_DIRS/libguestfs/libguestfs-tools.conf
411 /etc/libguestfs-tools.conf
412 This configuration file controls the default read-only or read-
413 write mode (--ro or --rw).
414 See libguestfs-tools.conf(5).
416
418 guestfs(3), guestfish(1), virt-cat(1), virt-edit(1),
419 virt-filesystems(1), libguestfs-tools.conf(5), http://libguestfs.org/.
420
422 Richard W.M. Jones http://people.redhat.com/~rjones/
423
425 Copyright (C) 2009-2020 Red Hat Inc.
426
428 This program is free software; you can redistribute it and/or modify it
429 under the terms of the GNU General Public License as published by the
430 Free Software Foundation; either version 2 of the License, or (at your
431 option) any later version.
432 This program is distributed in the hope that it will be useful, but
434 WITHOUT ANY WARRANTY; without even the implied warranty of
435 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
436 General Public License for more details.
437 You should have received a copy of the GNU General Public License along
439 with this program; if not, write to the Free Software Foundation, Inc.,
440 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
441
443 To get a list of bugs against libguestfs, use this link:
444 https://bugzilla.redhat.com/buglist.cgi?component=libguestfs&product=Virtualization+Tools
445 To report a new bug against libguestfs, use this link:
447 https://bugzilla.redhat.com/enter_bug.cgi?component=libguestfs&product=Virtualization+Tools
448 When reporting a bug, please supply:
450 • The version of libguestfs.
452 • Where you got libguestfs (eg. which Linux distro, compiled from
454 source, etc)
455 • Describe the bug accurately and give a way to reproduce it.
457 • Run libguestfs-test-tool(1) and paste the complete, unedited output
459 into the bug report.
460libguestfs-1.45.4 2021-04-03 virt-rescue(1)