virt-diff1

Usage

Overview

"virt-diff" lists the differences between files in two virtual machines or disk images. The usual use case is to show the changes in a VM after it has been running for a while, by taking a snapshot, running the VM, and then using this tool to show what changed between the new VM state and the old snapshot.

This tool will find differences in filenames, file sizes, checksums, extended attributes, file content and more from a virtual machine or disk image. However it does not look at the boot loader, unused space between partitions or within filesystems, "hidden" sectors and so on. In other words, it is not a security or forensics tool.

To specify two guests, you have to use the -a or -d option(s) for the first guest, and the -A or -D option(s) for the second guest. The common case is:

 virt-diff -a old.img -A new.img

or using names known to libvirt:

 virt-diff -d oldguest -D newguest

Options

--help

Display brief help.

-a file

--add file

Add file which should be a disk image from the first 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).

--all

Same as --extra-stats --times --uids --xattrs.

--atime

The default is to ignore changes in file access times, since those are unlikely to be interesting. Using this flag shows atime differences as well.

-A file

-A URI

Add a disk image from the second virtual machine.

--blocksize=512

--blocksize=4096

--blocksize

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).

--checksum

--checksum=crc|md5|sha1|sha224|sha256|sha384|sha512

Use a checksum over file contents to detect when regular files have changed content.

With no argument, this defaults to using md5. Using an argument, you can select the checksum type to use. If the flag is omitted then file times and size are used to determine if a file has changed.

-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.

--csv

Write out the results in CSV format (comma-separated values). This format can be imported easily into databases and spreadsheets, but read "NOTE ABOUT CSV FORMAT" below.

--dir-links

The default is to ignore changes in the number of links in directory entries, since those are unlikely to be interesting. Using this flag shows changes to the nlink field of directories.

--dir-times

The default is to ignore changed times on directory entries, since those are unlikely to be interesting. Using this flag shows changes to the time fields of directories.

-d guest

--domain guest

Add all the disks from the named libvirt guest, as the first guest. Domain UUIDs can be used instead of names.

-D guest

Add all the disks from the named libvirt guest, as the second guest. Domain UUIDs can be used instead of names.

--echo-keys

When prompting for keys and passphrases, virt-diff normally turns echoing off so you cannot see what you are typing. If you are not worried about Tempest attacks and there is no one else in the room you can specify this flag to see what you are typing.

--extra-stats

Display extra stats.

--format=raw|qcow2|..

--format

The default for the -a/-A option is to auto-detect the format of the disk image. Using this forces the disk format for -a/-A options which follow on the command line. Using --format with no argument switches back to auto-detection for subsequent -a/-A options.

For example:

 virt-diff --format=raw -a disk.img [...]

forces raw format (no auto-detection) for disk.img.

 virt-diff --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).

-h

--human-readable

Display file sizes in human-readable format.

--key SELECTOR

Specify a key for LUKS, to automatically open a LUKS device when using the inspection.

--key NAME:key:KEY_STRING

--key UUID:key:KEY_STRING

--key all:key:KEY_STRING

"NAME" is the libguestfs device name (eg. "/dev/sda1"). "UUID" is the device UUID. "all" means try the key against any encrypted device.

Use the specified "KEY_STRING" as passphrase.

--key NAME:file:FILENAME

--key UUID:file:FILENAME

--key all:file:FILENAME

Read the passphrase from FILENAME.

--key NAME:clevis

--key UUID:clevis

--key all:clevis

Attempt passphrase-less unlocking for the device with Clevis, over the network. Please refer to "ENCRYPTED DISKS" in guestfs(3) for more information on network-bound disk encryption (NBDE).

Note that if any such option is present on the command line, QEMU user networking will be automatically enabled for the libguestfs appliance.

--keys-from-stdin

Read key or passphrase parameters from stdin. The default is to try to read passphrases from the user by opening /dev/tty.

If there are multiple encrypted devices then you may need to supply multiple keys on stdin, one per line.

--times

Display time fields.

--time-days

Display time fields as days before now (negative if in the future).

Note that 0 in output means "up to 1 day before now", or that the age of the file is between 0 and 86399 seconds.

--time-relative

Display time fields as seconds before now (negative if in the future).

--time-t

Display time fields as seconds since the Unix epoch.

--uids

Display UID and GID fields.

-v

--verbose

Enable verbose messages for debugging.

-V

--version

Display version number and exit.

-x

Enable tracing of libguestfs API calls.

--xattrs

Display extended attributes.

Note about CSV format

Comma-separated values (CSV) is a deceptive format. It seems like it should be easy to parse, but it is definitely not easy to parse.

Myth: Just split fields at commas. Reality: This does not work reliably. This example has two columns:

 "foo,bar",baz

Myth: Read the file one line at a time. Reality: This does not work reliably. This example has one row:

 "foo
 bar",baz

For shell scripts, use "csvtool" (https://github.com/Chris00/ocaml-csv also packaged in major Linux distributions).

For other languages, use a CSV processing library (eg. "Text::CSV" for Perl or Python’s built-in csv library).

Most spreadsheets and databases can import CSV directly.

Exit status

This program returns 0 if successful, or non-zero if there was an error.