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 -c URI
117 --connect URI
118 If using libvirt, connect to the given URI. If omitted, then we
119 connect to the default libvirt hypervisor.
120 If you specify guest block devices directly (-a), then libvirt is
122 not used at all.
123 -d guest
125 --domain guest
126 Add all the disks from the named libvirt guest. Domain UUIDs can
127 be used instead of names.
128 -e none
130 Disable the escape key.
131 -e KEY
133 Set the escape key to the given key sequence. The default is "^]".
134 To specify the escape key you can use:
135 "^x"
137 Control key + "x" key.
138 "none"
140 -e none means there is no escape key, escapes are disabled.
141 See "ESCAPE KEY" below for further information.
143 --format=raw|qcow2|..
145 --format
146 The default for the -a option is to auto-detect the format of the
147 disk image. Using this forces the disk format for -a options which
148 follow on the command line. Using --format with no argument
149 switches back to auto-detection for subsequent -a options.
150 For example:
152 virt-rescue --format=raw -a disk.img
154 forces raw format (no auto-detection) for disk.img.
156 virt-rescue --format=raw -a disk.img --format -a another.img
158 forces raw format (no auto-detection) for disk.img and reverts to
160 auto-detection for another.img.
161 If you have untrusted raw-format guest disk images, you should use
163 this option to specify the disk format. This avoids a possible
164 security problem with malicious guests (CVE-2010-3851).
165 -i
167 --inspector
168 Using virt-inspector(1) code, inspect the disks looking for an
169 operating system and mount filesystems as they would be mounted on
170 the real virtual machine.
171 The filesystems are mounted on /sysroot in the rescue environment.
173 --memsize MB
175 Change the amount of memory allocated to the rescue system. The
176 default is set by libguestfs and is small but adequate for running
177 system tools. The occasional program might need more memory. The
178 parameter is specified in megabytes.
179 -m dev[:mountpoint[:options[:fstype]]]
181 --mount dev[:mountpoint[:options[:fstype]]]
182 Mount the named partition or logical volume on the given mountpoint
183 in the guest (this has nothing to do with mountpoints in the host).
184 If the mountpoint is omitted, it defaults to /. You have to mount
186 something on /.
187 The filesystems are mounted under /sysroot in the rescue
189 environment.
190 The third (and rarely used) part of the mount parameter is the list
192 of mount options used to mount the underlying filesystem. If this
193 is not given, then the mount options are either the empty string or
194 "ro" (the latter if the --ro flag is used). By specifying the
195 mount options, you override this default choice. Probably the only
196 time you would use this is to enable ACLs and/or extended
197 attributes if the filesystem can support them:
198 -m /dev/sda1:/:acl,user_xattr
200 The fourth part of the parameter is the filesystem driver to use,
202 such as "ext3" or "ntfs". This is rarely needed, but can be useful
203 if multiple drivers are valid for a filesystem (eg: "ext2" and
204 "ext3"), or if libguestfs misidentifies a filesystem.
205 --network
207 Enable QEMU user networking in the guest. See "NETWORK".
208 -r
210 --ro
211 Open the image read-only.
212 The option must always be used if the disk image or virtual machine
214 might be running, and is generally recommended in cases where you
215 don't need write access to the disk.
216 See also "OPENING DISKS FOR READ AND WRITE" in guestfish(1).
218 --scratch
220 --scratch=N
221 The --scratch option adds a large scratch disk to the rescue
222 appliance. --scratch=N adds "N" scratch disks. The scratch
223 disk(s) are deleted automatically when virt-rescue exits.
224 You can also mix -a, -d and --scratch options. The scratch disk(s)
226 are added to the appliance in the order they appear on the command
227 line.
228 --selinux
230 This option is provided for backwards compatibility and does
231 nothing.
232 --smp N
234 Enable N ≥ 2 virtual CPUs in the rescue appliance.
235 --suggest
237 This option was used in older versions of virt-rescue to suggest
238 what commands you could use to mount filesystems under /sysroot.
239 For the current version of virt-rescue, it is easier to use the -i
240 option instead.
241 This option implies --ro and is safe to use even if the guest is up
243 or if another virt-rescue is running.
244 -v
246 --verbose
247 Enable verbose messages for debugging.
248 -V
250 --version
251 Display version number and exit.
252 -w
254 --rw
255 This changes the -a, -d and -m options so that disks are added and
256 mounts are done read-write.
257 See "OPENING DISKS FOR READ AND WRITE" in guestfish(1).
259 -x Enable tracing of libguestfs API calls.
261
263 Previous versions of virt-rescue allowed you to write either:
264 virt-rescue disk.img [disk.img ...]
266 or
268 virt-rescue guestname
270 whereas in this version you should use -a or -d respectively to avoid
272 the confusing case where a disk image might have the same name as a
273 guest.
274 For compatibility the old style is still supported.
276
278 Adding the --network option enables QEMU user networking in the rescue
279 appliance. There are some differences between user networking and
280 ordinary networking:
281 ping does not work
283 Because the ICMP ECHO_REQUEST protocol generally requires root in
284 order to send the ping packets, and because virt-rescue must be
285 able to run as non-root, QEMU user networking is not able to
286 emulate the ping(8) command. The ping command will appear to
287 resolve addresses but will not be able to send or receive any
288 packets. This does not mean that the network is not working.
289 cannot receive connections
291 QEMU user networking cannot receive incoming connections.
292 making TCP connections
294 The virt-rescue appliance needs to be small and so does not include
295 many network tools. In particular there is no telnet(1) command.
296 You can make TCP connections from the shell using the magical
297 /dev/tcp/<hostname>/<port> syntax:
298 exec 3<>/dev/tcp/redhat.com/80
300 echo "GET /" >&3
301 cat <&3
302 See bash(1) for more details.
304
306 Virt-rescue supports various keyboard escape sequences which are
307 entered by pressing "^]" (Control key + "]" key).
308 You can change the escape key using the -e option on the command line
310 (see above), and you can disable escapes completely using -e none. The
311 rest of this section assumes the default escape key.
312 The following escapes can be used:
314 "^] ?"
316 "^] h"
317 Prints a brief help text about escape sequences.
318 "^] i"
320 Prints brief libguestfs inspection information for the guest. This
321 only works if you used -i on the virt-rescue command line.
322 "^] q"
324 "^] x"
325 Quits virt-rescue immediately.
326 "^] s"
328 Synchronize the filesystems (sync).
329 "^] u"
331 Unmounts all the filesystems, except for the root (appliance)
332 filesystems.
333 "^] z"
335 Suspend virt-rescue (like pressing "^Z" except that it affects
336 virt-rescue rather than the program inside the rescue shell).
337 "^] ^]"
339 Sends the literal character "^]" (ASCII 0x1d) through to the rescue
340 shell.
341
343 If you are testing a tool inside virt-rescue and the tool (not virt-
344 rescue) segfaults, it can be tricky to capture the core dump outside
345 virt-rescue for later analysis. This section describes one way to do
346 this.
347 1. Create a scratch disk for core dumps:
349 truncate -s 4G /tmp/corefiles
351 virt-format --partition=mbr --filesystem=ext2 -a /tmp/corefiles
352 virt-filesystems -a /tmp/corefiles --all --long -h
353 2. When starting virt-rescue, attach the core files disk last:
355 virt-rescue --rw [-a ...] -a /tmp/corefiles
357 NB. If you use the --ro option, then virt-rescue will silently not
359 write any core files to /tmp/corefiles.
360 3. Inside virt-rescue, mount the core files disk. Note replace
362 /dev/sdb1 with the last disk index. For example if the core files
363 disk is the last of four disks, you would use /dev/sdd1.
364 ><rescue> mkdir /tmp/mnt
366 ><rescue> mount /dev/sdb1 /tmp/mnt
367 4. Enable core dumps in the rescue kernel:
369 ><rescue> echo '/tmp/mnt/core.%p' > /proc/sys/kernel/core_pattern
371 ><rescue> ulimit -Hc unlimited
372 ><rescue> ulimit -Sc unlimited
373 5. Run the tool that caused the core dump. The core dump will be
375 written to /tmp/mnt/core.PID.
376 ><rescue> ls -l /tmp/mnt
378 total 1628
379 -rw------- 1 root root 1941504 Dec 7 13:13 core.130
380 drwx------ 2 root root 16384 Dec 7 13:00 lost+found
381 6. Before exiting virt-rescue, unmount (or at least sync) the disks:
383 ><rescue> umount /tmp/mnt
385 ><rescue> exit
386 7. Outside virt-rescue, the core dump(s) can be removed from the disk
388 using guestfish(1). For example:
389 guestfish --ro -a /tmp/corefiles -m /dev/sda1
391 ><fs> ll /
392 ><fs> download /core.NNN /tmp/core.NNN
393
395 Several environment variables affect virt-rescue. See "ENVIRONMENT
396 VARIABLES" in guestfs(3) for the complete list.
397
399 $XDG_CONFIG_HOME/libguestfs/libguestfs-tools.conf
400 $HOME/.libguestfs-tools.rc
401 $XDG_CONFIG_DIRS/libguestfs/libguestfs-tools.conf
402 /etc/libguestfs-tools.conf
403 This configuration file controls the default read-only or read-
404 write mode (--ro or --rw).
405 See libguestfs-tools.conf(5).
407
409 guestfs(3), guestfish(1), virt-cat(1), virt-edit(1),
410 virt-filesystems(1), libguestfs-tools.conf(5), http://libguestfs.org/.
411
413 Richard W.M. Jones http://people.redhat.com/~rjones/
414
416 Copyright (C) 2009-2019 Red Hat Inc.
417
419 This program is free software; you can redistribute it and/or modify it
420 under the terms of the GNU General Public License as published by the
421 Free Software Foundation; either version 2 of the License, or (at your
422 option) any later version.
423 This program is distributed in the hope that it will be useful, but
425 WITHOUT ANY WARRANTY; without even the implied warranty of
426 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
427 General Public License for more details.
428 You should have received a copy of the GNU General Public License along
430 with this program; if not, write to the Free Software Foundation, Inc.,
431 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
432
434 To get a list of bugs against libguestfs, use this link:
435 https://bugzilla.redhat.com/buglist.cgi?component=libguestfs&product=Virtualization+Tools
436 To report a new bug against libguestfs, use this link:
438 https://bugzilla.redhat.com/enter_bug.cgi?component=libguestfs&product=Virtualization+Tools
439 When reporting a bug, please supply:
441 · The version of libguestfs.
443 · Where you got libguestfs (eg. which Linux distro, compiled from
445 source, etc)
446 · Describe the bug accurately and give a way to reproduce it.
448 · Run libguestfs-test-tool(1) and paste the complete, unedited output
450 into the bug report.
451libguestfs-1.40.1 2019-01-17 virt-rescue(1)