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Move miscellaneous documentation from examples/ to docs/.

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Wasn't very logical putting these doc files in the examples directory.
This commit is contained in:
Richard W.M. Jones
2015-10-21 11:12:23 +01:00
parent eb36df827b
commit 6219e61cba
12 changed files with 118 additions and 78 deletions
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68
examples/Makefile.am
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@@ -20,10 +20,6 @@ include $(top_srcdir)/subdir-rules.mk
EXTRA_DIST = \
LICENSE \
guestfs-examples.pod \
guestfs-faq.pod \
guestfs-performance.pod \
guestfs-recipes.pod \
guestfs-testing.pod \
copy-over.c \
create-disk.c \
debug-logging.c \
@@ -34,11 +30,7 @@ EXTRA_DIST = \
virt-dhcp-address.c
CLEANFILES = \
stamp-guestfs-examples.pod \
stamp-guestfs-faq.pod \
stamp-guestfs-performance.pod \
stamp-guestfs-recipes.pod \
stamp-guestfs-testing.pod
stamp-guestfs-examples.pod
noinst_PROGRAMS = create-disk debug-logging display-icon inspect-vm
if HAVE_LIBVIRT
@@ -139,18 +131,8 @@ virt_dhcp_address_LDADD = \
$(top_builddir)/src/libguestfs.la
endif
man_MANS = \
guestfs-examples.3 \
guestfs-faq.1 \
guestfs-performance.1 \
guestfs-recipes.1 \
guestfs-testing.1
noinst_DATA = \
$(top_builddir)/html/guestfs-examples.3.html \
$(top_builddir)/html/guestfs-faq.1.html \
$(top_builddir)/html/guestfs-performance.1.html \
$(top_builddir)/html/guestfs-recipes.1.html \
$(top_builddir)/html/guestfs-testing.1.html
man_MANS = guestfs-examples.3
noinst_DATA = $(top_builddir)/html/guestfs-examples.3.html
guestfs-examples.3 $(top_builddir)/html/guestfs-examples.3.html: stamp-guestfs-examples.pod
@@ -170,47 +152,3 @@ stamp-guestfs-examples.pod: guestfs-examples.pod copy-over.c create-disk.c debug
--license examples \
$<
touch $@
guestfs-faq.1 $(top_builddir)/html/guestfs-faq.1.html: stamp-guestfs-faq.pod
stamp-guestfs-faq.pod: guestfs-faq.pod
$(PODWRAPPER) \
--section 1 \
--man guestfs-faq.1 \
--html $(top_builddir)/html/guestfs-faq.1.html \
--license LGPLv2+ \
$<
touch $@
guestfs-performance.1 $(top_builddir)/html/guestfs-performance.1.html: stamp-guestfs-performance.pod
stamp-guestfs-performance.pod: guestfs-performance.pod
$(PODWRAPPER) \
--section 1 \
--man guestfs-performance.1 \
--html $(top_builddir)/html/guestfs-performance.1.html \
--license LGPLv2+ \
$<
touch $@
guestfs-recipes.1 $(top_builddir)/html/guestfs-recipes.1.html: stamp-guestfs-recipes.pod
stamp-guestfs-recipes.pod: guestfs-recipes.pod
$(PODWRAPPER) \
--section 1 \
--man guestfs-recipes.1 \
--html $(top_builddir)/html/guestfs-recipes.1.html \
--license examples \
$<
touch $@
guestfs-testing.1 $(top_builddir)/html/guestfs-testing.1.html: stamp-guestfs-testing.pod
stamp-guestfs-testing.pod: guestfs-testing.pod
$(PODWRAPPER) \
--section 1 \
--man guestfs-testing.1 \
--html $(top_builddir)/html/guestfs-testing.1.html \
--license LGPLv2+ \
$<
touch $@

1382
examples/guestfs-faq.pod
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585
examples/guestfs-performance.pod
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@@ -1,585 +0,0 @@
=head1 NAME
guestfs-performance - engineering libguestfs for greatest performance
=head1 DESCRIPTION
This page documents how to get the greatest performance out of
libguestfs, especially when you expect to use libguestfs to manipulate
thousands of virtual machines or disk images.
Three main areas are covered. Libguestfs runs an appliance (a small
Linux distribution) inside qemu/KVM. The first two areas are:
minimizing the time taken to start this appliance, and the number of
times the appliance has to be started. The third area is shortening
the time taken for inspection of VMs.
=head1 BASELINE MEASUREMENTS
Before making changes to how you use libguestfs, take baseline
measurements.
=head2 Baseline: Starting the appliance
On an unloaded machine, time how long it takes to start up the
appliance:
time guestfish -a /dev/null run
Run this command several times in a row and discard the first few
runs, so that you are measuring a typical "hot cache" case.
=head3 Explanation
This command starts up the libguestfs appliance on a null disk, and
then immediately shuts it down. The first time you run the command,
it will create an appliance and cache it (usually under
F</var/tmp/.guestfs-*>). Subsequent runs should reuse the cached
appliance.
=head3 Expected results
You should expect to be getting times under 6 seconds. If the times
you see on an unloaded machine are above this, then see the section
L</TROUBLESHOOTING POOR PERFORMANCE> below.
=head2 Baseline: Performing inspection of a guest
For this test you will need an unloaded machine and at least one real
guest or disk image. If you are planning to use libguestfs against
only X guests (eg. X = Windows), then using an X guest here would be
most appropriate. If you are planning to run libguestfs against a mix
of guests, then use a mix of guests for testing here.
Time how long it takes to perform inspection and mount the disks of
the guest. Use the first command if you will be using disk images,
and the second command if you will be using libvirt.
time guestfish --ro -a disk.img -i exit
time guestfish --ro -d GuestName -i exit
Run the command several times in a row and discard the first few runs,
so that you are measuring a typical "hot cache" case.
=head3 Explanation
This command starts up the libguestfs appliance on the named disk
image or libvirt guest, performs libguestfs inspection on it (see
L<guestfs(3)/INSPECTION>), mounts the guest's disks, then discards all
these results and shuts down.
The first time you run the command, it will create an appliance and
cache it (usually under F</var/tmp/.guestfs-*>). Subsequent runs
should reuse the cached appliance.
=head3 Expected results
You should expect times which are E<le> 5 seconds greater than
measured in the first baseline test above. (For example, if the first
baseline test ran in 5 seconds, then this test should run in E<le> 10
seconds).
=head1 UNDERSTANDING THE APPLIANCE AND WHEN IT IS BUILT/CACHED
The first time you use libguestfs, it will build and cache an
appliance. This is usually in F</var/tmp/.guestfs-*>, unless you have
set C<$TMPDIR> or C<$LIBGUESTFS_CACHEDIR> in which case it will be
under that temporary directory.
For more information about how the appliance is constructed, see
L<supermin(1)/SUPERMIN APPLIANCES>.
Every time libguestfs runs it will check that no host files used by
the appliance have changed. If any have, then the appliance is
rebuilt. This usually happens when a package is installed or updated
on the host (eg. using programs like C<yum> or C<apt-get>). The
reason for reconstructing the appliance is security: the new program
that has been installed might contain a security fix, and so we want
to include the fixed program in the appliance automatically.
These are the performance implications:
=over 4
=item *
The process of building (or rebuilding) the cached appliance is slow,
and you can avoid this happening by using a fixed appliance (see
below).
=item *
If not using a fixed appliance, be aware that updating software on the
host will cause a one time rebuild of the appliance.
=item *
F</var/tmp> (or C<$TMPDIR>, C<$LIBGUESTFS_CACHEDIR>) should be on a
fast disk, and have plenty of space for the appliance.
=back
=head1 USING A FIXED APPLIANCE
To fully control when the appliance is built, you can build a fixed
appliance. This appliance should be stored on a fast local disk.
To build the appliance, run the command:
libguestfs-make-fixed-appliance <directory>
replacing C<E<lt>directoryE<gt>> with the name of a directory where
the appliance will be stored (normally you would name a subdirectory,
for example: F</usr/local/lib/guestfs/appliance> or
F</dev/shm/appliance>).
Then set C<$LIBGUESTFS_PATH> (and ensure this environment variable is
set in your libguestfs program), or modify your program so it calls
C<guestfs_set_path>. For example:
export LIBGUESTFS_PATH=/usr/local/lib/guestfs/appliance
Now you can run libguestfs programs, virt tools, guestfish etc. as
normal. The programs will use your fixed appliance, and will not ever
build, rebuild, or cache their own appliance.
(For detailed information on this subject, see:
L<libguestfs-make-fixed-appliance(1)>).
=head2 Performance of the fixed appliance
In our testing we did not find that using a fixed appliance gave any
measurable performance benefit, even when the appliance was located in
memory (ie. on F</dev/shm>). However there are two points to
consider:
=over 4
=item 1.
Using a fixed appliance stops libguestfs from ever rebuilding the
appliance, meaning that libguestfs will have more predictable start-up
times.
=item 2.
The appliance is loaded on demand. A simple test such as:
time guestfish -a /dev/null run
does not load very much of the appliance. A real libguestfs program
using complicated API calls would demand-load a lot more of the
appliance. Being able to store the appliance in a specified location
makes the performance more predictable.
=back
=head1 REDUCING THE NUMBER OF TIMES THE APPLIANCE IS LAUNCHED
By far the most effective, though not always the simplest way to get
good performance is to ensure that the appliance is launched the
minimum number of times. This will probably involve changing your
libguestfs application.
Try to call C<guestfs_launch> at most once per target virtual machine
or disk image.
Instead of using a separate instance of L<guestfish(1)> to make a
series of changes to the same guest, use a single instance of
guestfish and/or use the guestfish I<--listen> option.
Consider writing your program as a daemon which holds a guest open
while making a series of changes. Or marshal all the operations you
want to perform before opening the guest.
You can also try adding disks from multiple guests to a single
appliance. Before trying this, note the following points:
=over 4
=item 1.
Adding multiple guests to one appliance is a security problem because
it may allow one guest to interfere with the disks of another guest.
Only do it if you trust all the guests, or if you can group guests by
trust.
=item 2.
There is a hard limit to the number of disks you can add to a single
appliance. Call L<guestfs(3)/guestfs_max_disks> to get this limit.
For further information see L<guestfs(3)/LIMITS>.
=item 3.
Using libguestfs this way is complicated. Disks can have unexpected
interactions: for example, if two guests use the same UUID for a
filesystem (because they were cloned), or have volume groups with the
same name (but see C<guestfs_lvm_set_filter>).
=back
L<virt-df(1)> adds multiple disks by default, so the source code for
this program would be a good place to start.
=head1 SHORTENING THE TIME TAKEN FOR INSPECTION OF VMs
The main advice is obvious: Do not perform inspection (which is
expensive) unless you need the results.
If you previously performed inspection on the guest, then it may be
safe to cache and reuse the results from last time.
Some disks don't need to be inspected at all: for example, if you are
creating a disk image, or if the disk image is not a VM, or if the
disk image has a known layout.
Even when basic inspection (C<guestfs_inspect_os>) is required,
auxiliary inspection operations may be avoided:
=over 4
=item *
Mounting disks is only necessary to get further filesystem
information.
=item *
Listing applications (C<guestfs_inspect_list_applications>) is an
expensive operation on Linux, but almost free on Windows.
=item *
Generating a guest icon (C<guestfs_inspect_get_icon>) is cheap on
Linux but expensive on Windows.
=back
=head1 PARALLEL APPLIANCES
Libguestfs appliances are mostly I/O bound and you can launch multiple
appliances in parallel. Provided there is enough free memory, there
should be little difference in launching 1 appliance vs N appliances
in parallel.
On a 2-core (4-thread) laptop with 16 GB of RAM, using the (not
especially realistic) test Perl script below, the following plot shows
excellent scalability when running between 1 and 20 appliances in
parallel:
12 ++---+----+----+----+-----+----+----+----+----+---++
+ + + + + + + + + + *
| |
| * |
11 ++ ++
| |
| |
| * * |
10 ++ ++
| * |
| |
s | |
9 ++ ++
e | |
| * |
c | |
8 ++ * ++
o | * |
| |
n 7 ++ ++
| * |
d | * |
| |
s 6 ++ ++
| * * |
| * |
| |
5 ++ ++
| |
| * |
| * * |
4 ++ ++
| |
| |
+ * * * + + + + + + + +
3 ++-*-+----+----+----+-----+----+----+----+----+---++
0 2 4 6 8 10 12 14 16 18 20
number of parallel appliances
It is possible to run many more than 20 appliances in parallel, but if
you are using the libvirt backend then you should be aware that out of
the box libvirt limits the number of client connections to 20.
The simple Perl script below was used to collect the data for the plot
above, but there is much more information on this subject, including
more advanced test scripts and graphs, available in the following blog
postings:
L<http://rwmj.wordpress.com/2013/02/25/multiple-libguestfs-appliances-in-parallel-part-1/>
L<http://rwmj.wordpress.com/2013/02/25/multiple-libguestfs-appliances-in-parallel-part-2/>
L<http://rwmj.wordpress.com/2013/02/25/multiple-libguestfs-appliances-in-parallel-part-3/>
L<http://rwmj.wordpress.com/2013/02/25/multiple-libguestfs-appliances-in-parallel-part-4/>
#!/usr/bin/env perl
use strict;
use threads;
use warnings;
use Sys::Guestfs;
use Time::HiRes qw(time);
sub test {
my $g = Sys::Guestfs->new;
$g->add_drive_ro ("/dev/null");
$g->launch ();
# You could add some work for libguestfs to do here.
$g->close ();
}
# Get everything into cache.
test (); test (); test ();
for my $nr_threads (1..20) {
my $start_t = time ();
my @threads;
foreach (1..$nr_threads) {
push @threads, threads->create (\&test)
}
foreach (@threads) {
$_->join ();
if (my $err = $_->error ()) {
die "launch failed with $nr_threads threads: $err"
}
}
my $end_t = time ();
printf ("%d %.2f\n", $nr_threads, $end_t - $start_t);
}
=head1 USING USER-MODE LINUX
Since libguestfs 1.24, it has been possible to use the User-Mode Linux
(uml) backend instead of KVM
(see L<guestfs(3)/USER-MODE LINUX BACKEND>). This section makes some
general remarks about this backend, but it is B<highly advisable> to
measure your own workload under UML rather than trusting comments or
intuition.
=over 4
=item *
UML usually performs the same or slightly slower than KVM, on baremetal.
=item *
However UML often performs the same under virtualization as it does on
baremetal, whereas KVM can run much slower under virtualization (since
hardware virt acceleration is not available).
=item *
Upload and download is as much as 10 times slower on UML than KVM.
Libguestfs sends this data over the UML emulated serial port, which is
far less efficient than KVM's virtio-serial.
=item *
UML lacks some features (eg. qcow2 support), so it may not be
applicable at all.
=back
For some actual figures, see:
L<http://rwmj.wordpress.com/2013/08/14/performance-of-user-mode-linux-as-a-libguestfs-backend/#content>
=head1 TROUBLESHOOTING POOR PERFORMANCE
=head2 Ensure hardware virtualization is available
Use F</proc/cpuinfo> and this page:
http://virt-tools.org/learning/check-hardware-virt/
to ensure that hardware virtualization is available. Note that you
may need to enable it in your BIOS.
Hardware virt is not usually available inside VMs, and libguestfs will
run slowly inside another virtual machine whatever you do. Nested
virtualization does not work well in our experience, and is certainly
no substitute for running libguestfs on baremetal.
=head2 Ensure KVM is available
Ensure that KVM is enabled and available to the user that will run
libguestfs. It should be safe to set 0666 permissions on F</dev/kvm>
and most distributions now do this.
=head2 Processors to avoid
Avoid processors that don't have hardware virtualization, and some
processors which are simply very slow (AMD Geode being a great
example).
=head2 Xen dom0
In Xen, dom0 is a virtual machine, and so hardware virtualization is
not available.
=head1 DETAILED TIMINGS USING TS
Use the L<ts(1)> command (from moreutils) to show detailed
timings:
$ guestfish -a /dev/null run -v |& ts -i '%.s'
0.000022 libguestfs: launch: program=guestfish
0.000134 libguestfs: launch: version=1.29.31fedora=23,release=2.fc23,libvirt
0.000044 libguestfs: launch: backend registered: unix
0.000035 libguestfs: launch: backend registered: uml
0.000035 libguestfs: launch: backend registered: libvirt
0.000032 libguestfs: launch: backend registered: direct
0.000030 libguestfs: launch: backend=libvirt
0.000031 libguestfs: launch: tmpdir=/tmp/libguestfsw18rBQ
0.000029 libguestfs: launch: umask=0002
0.000031 libguestfs: launch: euid=1000
0.000030 libguestfs: libvirt version = 1002012 (1.2.12)
[etc]
The timestamps are seconds (incrementally since the previous line).
=head1 DETAILED TIMINGS USING SYSTEMTAP
You can use SystemTap (L<stap(1)>) to get detailed timings from
libguestfs programs.
Save the following script as F<time.stap>:
global last;
function display_time () {
now = gettimeofday_us ();
delta = 0;
if (last > 0)
delta = now - last;
last = now;
printf ("%d (+%d):", now, delta);
}
probe begin {
last = 0;
printf ("ready\n");
}
/* Display all calls to static markers. */
probe process("/usr/lib*/libguestfs.so.0")
.provider("guestfs").mark("*") ? {
display_time();
printf ("\t%s %s\n", $$name, $$parms);
}
/* Display all calls to guestfs_* functions. */
probe process("/usr/lib*/libguestfs.so.0")
.function("guestfs_[a-z]*") ? {
display_time();
printf ("\t%s %s\n", probefunc(), $$parms);
}
Run it as root in one window:
# stap time.stap
ready
It prints "ready" when SystemTap has loaded the program. Run your
libguestfs program, guestfish or a virt tool in another window. For
example:
$ guestfish -a /dev/null run
In the stap window you will see a large amount of output, with the
time taken for each step shown (microseconds in parenthesis). For
example:
xxxx (+0): guestfs_create
xxxx (+29): guestfs_set_pgroup g=0x17a9de0 pgroup=0x1
xxxx (+9): guestfs_add_drive_opts_argv g=0x17a9de0 [...]
xxxx (+8): guestfs_int_safe_strdup g=0x17a9de0 str=0x7f8a153bed5d
xxxx (+19): guestfs_int_safe_malloc g=0x17a9de0 nbytes=0x38
xxxx (+5): guestfs_int_safe_strdup g=0x17a9de0 str=0x17a9f60
xxxx (+10): guestfs_launch g=0x17a9de0
xxxx (+4): launch_start
[etc]
You will need to consult, and even modify, the source to libguestfs to
fully understand the output.
=head1 DETAILED DEBUGGING USING GDB
You can attach to the appliance BIOS/kernel using gdb. If you know
what you're doing, this can be a useful way to diagnose boot
regressions.
Firstly, you have to change qemu so it runs with the C<-S> and C<-s>
options. These options cause qemu to pause at boot and allow you to
attach a debugger. Read L<qemu(1)> for further information.
Libguestfs invokes qemu several times (to scan the help output and so
on) and you only want the final invocation of qemu to use these
options, so use a qemu wrapper script like this:
#!/bin/bash -
# Set this to point to the real qemu binary.
qemu=/usr/bin/qemu-kvm
if [ "$1" != "-global" ]; then
# Scanning help output etc.
exec $qemu "$@"
else
# Really running qemu.
exec $qemu -S -s "$@"
fi
Now run guestfish or another libguestfs tool with the qemu wrapper
(see L<guestfs(3)/QEMU WRAPPERS> to understand what this is doing):
LIBGUESTFS_HV=/path/to/qemu-wrapper guestfish -a /dev/null -v run
This should pause just after qemu launches. In another window, attach
to qemu using gdb:
$ gdb
(gdb) set architecture i8086
The target architecture is assumed to be i8086
(gdb) target remote :1234
Remote debugging using :1234
0x0000fff0 in ?? ()
(gdb) cont
At this point you can use standard gdb techniques, eg. hitting C<^C>
to interrupt the boot and C<bt> get a stack trace, setting
breakpoints, etc. Note that when you are past the BIOS and into the
Linux kernel, you'll want to change the architecture back to 32 or 64
bit.
=head1 SEE ALSO
L<supermin(1)>,
L<guestfish(1)>,
L<guestfs(3)>,
L<guestfs-examples(3)>,
L<libguestfs-make-fixed-appliance(1)>,
L<stap(1)>,
L<qemu(1)>,
L<gdb(1)>,
L<http://libguestfs.org/>.
=head1 AUTHORS
Richard W.M. Jones (C<rjones at redhat dot com>)
=head1 COPYRIGHT
Copyright (C) 2012-2015 Red Hat Inc.

689
examples/guestfs-recipes.pod
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@@ -1,689 +0,0 @@
=begin comment
We break with tradition here and don't use ALL CAPS for the section
headings, as this makes them much easier to read.
=end comment
=head1 NAME
guestfs-recipes - libguestfs, guestfish and virt tools recipes
=head1 DESCRIPTION
This page contains recipes for and links to things you can do using
libguestfs, L<guestfish(1)> and the virt tools.
=head1 Access a remote disk image using guestfish
If the disk image is on a remote server which is accessible using SSH,
HTTP, FTP, NBD, iSCSI, or similar, then you can open it directly. See
L<guestfish(1)/ADDING REMOTE STORAGE> for several examples. This
requires libguestfs E<ge> 1.22 and qemu E<ge> 1.5.
=head1 Audit a virtual machine for setuid files
See: L<virt-ls(1)/EXAMPLES>.
=head1 Audit a virtual machine for vulnerabilities and security problems
See:
L<https://rwmj.wordpress.com/2013/05/16/scanning-offline-guests-using-openscap-and-guestmount/#content>
=head1 Change the background image in a Windows XP VM
The links below explain how to use L<guestfish(1)> to change the
background image for a user of a Windows XP VM. Unfortunately the
technique appears to be substantially different for each version of
Windows.
L<https://lists.fedoraproject.org/pipermail/virt/2011-May/002655.html>
L<https://lists.fedoraproject.org/pipermail/virt/2011-May/002658.html>
=head1 Checksum a file or device within a disk image
To checksum a whole device, or a partition, LV etc within a disk image:
guestfish --ro -a disk.img run : checksum-device md5 /dev/sda1
Replace C<md5> with the type of checksum you want. See
L<guestfs(3)/guestfs_checksum_device> for a list of supported types.
F</dev/sda1> means "the first partition". You could use F</dev/sda>
to checksum the whole disk image, or the name of a logical volume or
RAID device.
To checksum a single file:
guestfish --ro -a disk.img -i checksum sha256 /etc/passwd
or for a Windows guest:
guestfish --ro -a disk.img -i \
checksum sha256 'win:\windows\system32\config\SOFTWARE'
=head1 Cloning a virtual machine
Use a combination of tools like L<cp(1)>, L<dd(1)>, and
virt tools like L<virt-sysprep(1)>, L<virt-sparsify(1)>
and L<virt-resize(1)>.
For more details, see: L<virt-sysprep(1)/COPYING AND CLONING>.
=head1 Convert a CD-ROM / DVD / ISO to a tarball
This converts input F<cd.iso> to output F<cd.tar.gz>:
guestfish --ro -a cd.iso -m /dev/sda tgz-out / cd.tar.gz
To export just a subdirectory, eg. F</files>, do:
guestfish --ro -a cd.iso -m /dev/sda tgz-out /files cd.tar.gz
=head1 Convert from one format/filesystem to another
If you have a data disk in one format / filesystem / partition /
volume manager, you can convert it another using this technique.
In this example, we start with a data disk that has a single partition
containing a filesystem, and we want to create another disk that
contains the same files but on an ext3 filesystem embedded in a
logical volume on a sparse raw-format disk.
First create the formatted-but-empty target disk:
truncate -s 10G target.img
virt-format -a target.img --partition=mbr --lvm --filesystem=ext3
Now, pipe two guestfish instances together to transfer the old data to
the new disk:
guestfish --ro -a source.img -m /dev/sda1 -- tar-out / - | \
guestfish --rw -a target.img -m /dev/VG/LV -- tar-in - /
To browse the final disk image, do:
guestfish --ro -a target.img -m /dev/VG/LV
><fs> ll /
This technique is quite powerful, allowing you for example to split up
source directories over the target filesystems.
Note this won't work (at least, not directly) for bootable virtual
machine disks because it doesn't copy over the boot loader.
=head1 Convert Windows DVD to bootable USB key
L<http://rwmj.wordpress.com/2013/05/09/tip-convert-a-windows-dvd-iso-to-a-bootable-usb-key-using-guestfish/#content>
=head1 Convert Xen-style partitionless image to partitioned disk image
Xen disk images are often partitionless, meaning that the filesystem
starts directly at the beginning of the disk with no partition table.
You can in fact use these directly in KVM (provided the guest isn't
Windows), but some people like to convert them to regular partitioned
disk images, and this is required for Windows guests. Here is how to
use guestfish to do this:
guestfish
><fs> add-ro input.img
><fs> sparse output.img 10G # adjust the output size
><fs> run
# Create a partition table on the output disk:
><fs> part-init /dev/sdb mbr
><fs> part-add /dev/sdb p 2048 -2048
# Copy the data to the target partition:
><fs> copy-device-to-device /dev/sda /dev/sdb1 sparse:true
# Optionally resize the target filesystem. Use ntfsresize
# for Windows guests:
><fs> resize2fs /dev/sdb1
Such a disk image won't be directly bootable. You may need to boot it
with an external kernel and initramfs (see below). Or you can use the
guestfish commands C<syslinux> or C<extlinux> to install a SYSLINUX
bootloader.
=head1 Create empty disk images
The L<virt-format(1)> tool can do this directly.
Use L<virt-make-fs(1)> to create a disk image with content. This can
also create some standard disk images such as virtual floppy devices
(VFDs).
You can also use the L<guestfish(1)> I<-N> option to create empty disk
images. The useful guide below explains the options available.
L<https://rwmj.wordpress.com/2010/09/08/new-guestfish-n-options-in-1-5-9/#content>
L<virt-builder(1)> can create minimal guests.
=head1 Delete a file (or other simple file operations)
Use guestfish. To delete a file:
guestfish -a disk.img -i rm /file/to/delete
To touch a file (bring it up to date or create it):
guestfish -a disk.img -i touch /file/to/touch
To stat a file. Since this is a read-only operation, we can make it
safer by adding the I<--ro> flag.
guestfish --ro -a disk.img -i stat /file/to/stat
There are dozens of these commands. See L<guestfish(1)> or the output
of C<guestfish -h>
=head1 Diff two guests; compare a snapshot to the current version
Since libguestfs E<ge> 1.26, use L<virt-diff(1)> to look for
differences between two guests (for example if they were originally
cloned from the same source), or between two snapshots from the same
guest. In earlier versions of libguestfs, use L<virt-ls(1)>.
=head1 Disable a systemd service
The following is the equivalent of C<systemctl mask ...>. To disable
the C<cloud-init> service so it doesn't start at next boot:
guestfish -a disk.img -i \
ln-sf /dev/null /etc/systemd/system/cloud-init.service
To disable tmp-on-tmpfs:
guestfish -a disk.img -i \
ln-sf /dev/null /etc/systemd/system/tmp.mount
One problem with the commands above is there is no feedback if you get
the name of the service you are trying to mask wrong. But you can use
L<virt-ls(1)> to list the available systemd services like this:
virt-ls -a /tmp/fedora-19.img -R /lib/systemd/system
=head1 Dump raw filesystem content from inside a disk image or VM
You can use the L<guestfish(1)> C<download> command to extract the raw
filesystem content from any filesystem in a disk image or a VM (even
one which is encrypted or buried inside an LV or RAID device):
guestfish --ro -a disk.img run : download /dev/sda1 sda1.img
guestfish --ro -d Guest run : download /dev/vg_guest/lv_root lv.img
To download to stdout, replace the filename with a C<-> character:
guestfish --ro -a disk.img run : download /dev/sda1 - | gzip > sda1.gz
To list the filesystems in a disk image, use L<virt-filesystems(1)>.
See also L</Uploading raw filesystem content>.
=head1 Edit grub configuration in a VM
You can use this to:
=over 4
=item *
Fix a virtual machine that does not boot.
=item *
Change which kernel is used to boot the VM.
=item *
Change kernel command line options.
=back
Use L<virt-edit(1)> to edit the grub configuration:
virt-edit -d BrokenGuest /boot/grub2/grub.cfg
or for general tinkering inside an unbootable VM use L<virt-rescue(1)>
like this:
virt-rescue -d BrokenGuest
=head1 Export any directory from a VM
To export F</home> from a VM into a local directory use
L<virt-copy-out(1)>:
virt-copy-out -d Guest /home .
Notes:
=over 4
=item *
The final dot of the command is not a printing error. It means we
want to copy out to the current directory.
=item *
This creates a directory called C<home> under the current directory.
=back
If the guest is a Windows guest then you can use drive letters and
backslashes, but you must prefix the path with C<win:> and quote it to
protect it from the shell, like this:
virt-copy-out -d WinGuest 'win:c:\windows\system32\config' .
To get the output as a compressed tarball, do:
virt-tar-out -d Guest /home - | gzip --best > home.tar.gz
Although it sounds tempting, this is usually not a reliable way to get
a backup from a running guest. See the entry in the FAQ:
L<http://libguestfs.org/FAQ.html#backup>
=head1 Find out which user is using the most space
This simple script examines a Linux guest to find out which user is
using the most space in their home directory:
#!/bin/sh -
set -e
vm="$1"
dir=/home
eval $(guestfish --ro -d "$vm" -i --listen)
for d in $(guestfish --remote ls "$dir"); do
echo -n "$dir/$d"
echo -ne '\t'
guestfish --remote du "$dir/$d";
done | sort -nr -k 2
guestfish --remote exit
=head1 Export external kernel and initramfs (initrd)
If a Linux guest doesn't have a boot loader or it is broken, then you
can usually boot it using an external kernel and initramfs. In this
configuration, the hypervisor acts like a bootloader, loading the
kernel from the host disk into guest memory and jumping straight into
the kernel.
However you may wonder how to get the right kernel corresponding to
the disk image you have. Since libguestfs E<ge> 1.24
L<virt-builder(1)> can get the latest kernel and corresponding
initramfs for you:
mkdir outputdir
virt-builder --get-kernel disk.img -o outputdir
ls -lh outputdir
=head1 Get DHCP address from a VM
The link below explains the many different possible techniques for
getting the last assigned DHCP address of a virtual machine.
L<https://rwmj.wordpress.com/2011/03/31/tip-code-for-getting-dhcp-address-from-a-virtual-machine-disk-image/#content>
In the libguestfs source examples directory you will find the latest
version of the F<virt-dhcp-address.c> program.
=head1 Get the operating system product name string
Save the following script into a file called F<product-name.sh>:
#!/bin/sh -
set -e
eval "$(guestfish --ro -d "$1" --i --listen)"
root="$(guestfish --remote inspect-get-roots)"
guestfish --remote inspect-get-product-name "$root"
guestfish --remote exit
Make the script executable and run it on a named guest:
# product-name.sh RHEL60x64
Red Hat Enterprise Linux Server release 6.0 (Santiago)
You can also use an XPath query on the L<virt-inspector(1)> XML using
the C<xpath> command line tool or from your favourite programming
language:
# virt-inspector RHEL60x64 > xml
# xpath '//product_name' < xml
Found 1 nodes:
-- NODE --
<product_name>Red Hat Enterprise Linux Server release 6.0 (Santiago)</product_name>
=head1 Get the default boot kernel for a Linux VM
The link below contains a program to print the default boot kernel for
a Linux VM.
L<https://rwmj.wordpress.com/2010/10/30/tip-use-augeas-to-get-the-default-boot-kernel-for-a-vm/#content>
It uses Augeas, and the technique is generally applicable for many
different tasks, such as:
=over 4
=item *
listing the user accounts in the guest
=item *
what repositories is it configured to use
=item *
what NTP servers does it connect to
=item *
what were the boot messages last time it booted
=item *
listing who was logged in recently
=back
L<http://augeas.net/>
=head1 Hanging guests
There are various ways to use libguestfs to find out why a guest
is hanging or unresponsive:
=over 4
=item 1.
Read the log files using virt-cat:
virt-cat Guest /var/log/messages | less
=item 2.
Read the Windows Event Log (Windows Vista or later only):
L<https://rwmj.wordpress.com/2011/04/17/decoding-the-windows-event-log-using-guestfish/#content>
=item 3.
Find out which files were last updated in a guest:
L<https://rwmj.wordpress.com/2012/02/27/using-libguestfs-to-find-out-why-a-windows-guest-was-hanging/#content>
This might give you a clue as to what program is running.
=back
=head1 Hex-dumping sectors from the guest
Hex-dump the boot partition (Master Boot Record / first sector):
guestfish --ro -a disk.img run : pread-device /dev/sda 0x200 0 |
hexdump -C
(C<0x200> = 512 bytes which is the size of traditional PC sectors)
To hexdump the N'th partition, substitute a number for C<N> in the
following command:
guestfish --ro -a disk.img \
run : pread-device /dev/sda 0x200 $((N*0x200)) |
hexdump -C
=head1 Hex-editing sectors in the guest
Hex-edit the boot partition (Master Boot Record / first sector):
guestfish --rw -a disk.img run : hexedit /dev/sda 0x200
=head1 Install packages (RPMs, Debian packages) in a guest
Since libguestfs 1.26, L<virt-builder(1)>, L<virt-customize(1)> and
L<virt-sysprep(1)> have an I<--install> option for installing packages
in Linux guests. (Use virt-customize if you have an existing guest,
or virt-builder if you want to create a guest from scratch).
For example:
virt-builder fedora-20 --install emacs
=head1 Install packages from an alternate repository
Since libguestfs 1.26, you can use L<virt-builder(1)>,
L<virt-customize(1)> or L<virt-sysprep(1)> I<--edit> option to edit
repository metadata before installing packages
For example this would install packages from the updates-testing
repository in Fedora:
virt-builder fedora-20 \
--edit '/etc/yum.repos.d/fedora-updates-testing.repo:
s/enabled=0/enabled=1/' \
--install emacs
=head1 Install SYSLINUX bootloader in a guest
SYSLINUX is a small, easy to configure bootloader for Linux and
Windows guests. If your guest is not bootable, you can install the
SYSLINUX bootloader using either the guestfish commands C<syslinux>
(for FAT-based guests) or C<extlinux> (for ext2/3/4 and btrfs-based
guests).
This guide assumes a Linux guest where F</dev/sda1> is F</boot>,
F</boot/vmlinuz> is the guest kernel, and F</dev/sda3> is the root
partition. For a Windows guest you would need a FAT-formatted boot
partition and you would need to use the C<syslinux> command instead.
Create a F<syslinux.cfg> configuration file. You should check the
SYSLINUX documentation at L<http://www.syslinux.org> but it may look
something like this:
DEFAULT linux
LABEL linux
SAY Booting the kernel
KERNEL vmlinuz
INITRD initrd
APPEND ro root=/dev/sda3
Locate the syslinux master boot record (a file called something like
F</usr/share/syslinux/mbr.bin>).
guestfish -a disk.img -i
# Upload the master boot record and configuration file:
><fs> upload ..../mbr.bin /boot/mbr.bin
><fs> upload ..../syslinux.cfg /boot/syslinux.cfg
# Put the MBR into the boot sector:
><fs> copy-file-to-device /boot/mbr.bin /dev/sda size:440
# Install syslinux on the first partition:
><fs> extlinux /boot
# Set the first partition as bootable:
><fs> part-set-bootable /dev/sda 1 true
See also:
L<http://rwmj.wordpress.com/2013/04/04/new-in-libguestfs-use-syslinux-or-extlinux-to-make-bootable-guests/#content>
=head1 List applications installed in a VM
Save the following to a file F<list-apps.sh>:
#!/bin/sh -
set -e
eval "$(guestfish --ro -d "$1" --i --listen)"
root="$(guestfish --remote inspect-get-roots)"
guestfish --remote inspect-list-applications "$root"
guestfish --remote exit
Make the file executable and then you can run it on any named
virtual machine:
# list-apps.sh WinGuest
[0] = {
app_name: Mozilla Firefox (3.6.12)
app_display_name: Mozilla Firefox (3.6.12)
app_epoch: 0
app_version: 3.6.12 (en-GB)
app_release:
app_install_path: C:\Program Files\Mozilla Firefox
app_trans_path:
app_publisher: Mozilla
app_url: http://www.mozilla.com/en-GB/
app_source_package:
app_summary:
app_description: Mozilla Firefox
}
[1] = {
app_name: VLC media player
app_display_name: VLC media player 1.1.5
app_epoch: 0
app_version: 1.1.5
app_release:
app_install_path: C:\Program Files\VideoLAN\VLC
app_trans_path:
app_publisher: VideoLAN
app_url: http://www.videolan.org/
app_source_package:
app_summary:
app_description:
}
If you want to run the script on disk images (instead of libvirt
virtual machines), change C<-d "$1"> to C<-a "$1">. See also
L<virt-inspector(1)>.
=head1 List files and directories in a VM
Use L<virt-ls(1)>.
=head1 List services in a Windows VM
The link below contains a script that can be used to list out the
services from a Windows VM, and whether those services run at boot
time or are loaded on demand.
L<https://rwmj.wordpress.com/2010/12/10/tip-list-services-in-a-windows-guest/#content>
=head1 Make a disk image sparse
Use L<virt-sparsify(1)>.
=head1 Monitor disk usage over time
You can use L<virt-df(1)> to monitor disk usage of your guests over
time. The link below contains a guide.
L<http://virt-tools.org/learning/advanced-virt-df/>
=head1 Reading the Windows Event Log from Windows Vista (or later)
L<guestfish(1)> plus the tools described in the link below can be used
to read out the Windows Event Log from any virtual machine running
Windows Vista or a later version.
L<https://rwmj.wordpress.com/2011/04/17/decoding-the-windows-event-log-using-guestfish/#content>
=head1 Remove root password (Linux)
Using the L<virt-edit(1)> I<-e> option you can do simple replacements
on files. One use is to remove the root password from a Linux guest:
virt-edit -d domname /etc/passwd -e 's/^root:.*?:/root::/'
virt-edit -a disk.img /etc/passwd -e 's/^root:.*?:/root::/'
=head1 Remove Administrator password (Windows)
The link below contains one technique for removing the Administrator
password from a Windows VM, or to be more precise, it gives you a
command prompt the next time you log in which you can use to bypass
any security:
L<https://mdbooth.wordpress.com/2010/10/18/resetting-a-windows-guests-administrator-password-with-guestfish/>
=head1 Sysprepping a virtual machine (Windows)
It is possible to do a "sysprep" using libguestfs alone, although not
straightforward. Currently there is code in the Aeolus Oz project
which does this (using libguestfs). It is likely we will add this to
L<virt-sysprep(1)> in future.
L<https://github.com/clalancette/oz>
L<https://www.redhat.com/archives/virt-tools-list/2011-May/msg00019.html>
=head1 Unpack a live CD
Linux live CDs often contain multiple layers of disk images wrapped
like a Russian doll. You can use L<guestfish(1)> to look inside these
multiple layers, as outlined in the guide below.
L<https://rwmj.wordpress.com/2009/07/15/unpack-the-russian-doll-of-a-f11-live-cd/#content>
=head1 Uploading and downloading files
The link below contains general tips on uploading (copying in)
and downloading (copying out) files from VMs.
L<https://rwmj.wordpress.com/2010/12/02/tip-uploading-and-downloading/#content>
=head1 Uploading raw filesystem content
You can use L<guestfish(1)> to upload whole filesystems into a VM,
even into a filesystem which is encrypted or buried inside an LV or
RAID device:
guestfish --rw -a disk.img run : upload sda1.img /dev/sda1
guestfish --rw -d Guest run : upload lv.img /dev/vg_guest/lv_root
One common problem is that the filesystem isn't the right size for the
target. If it is too large, there's not much you can do with
libguestfs - you have to prepare the filesystem differently. But if
the filesystem needs to expand into the target, you can use guestfish
to resize it to the right size:
guestfish --rw -d Guest run : \
upload lv.img /dev/vg_guest/lv_root : \
resize2fs /dev/vg_guest/lv_root
(or use C<ntfsresize> if the filesystem is NTFS).
=head1 Use libguestfs tools on VMware ESX guests
The link below explains how to use libguestfs, L<guestfish(1)> and the
virt tools on any VMware ESX guests, by first sharing the VMware VMFS
over sshfs.
L<https://rwmj.wordpress.com/2011/05/10/tip-use-libguestfs-on-vmware-esx-guests/#content>
=head1 SEE ALSO
L<guestfs(3)>,
L<guestfish(1)>,
L<guestfs-examples(3)>,
L<guestfs-erlang(3)>,
L<guestfs-golang(3)>,
L<guestfs-java(3)>,
L<guestfs-lua(3)>,
L<guestfs-ocaml(3)>,
L<guestfs-perl(3)>,
L<guestfs-python(3)>,
L<guestfs-ruby(3)>,
L<http://libguestfs.org/>.
=head1 AUTHORS
Richard W.M. Jones (C<rjones at redhat dot com>)
=head1 COPYRIGHT
Copyright (C) 2009-2015 Red Hat Inc.

397
examples/guestfs-testing.pod
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@@ -1,397 +0,0 @@
=head1 NAME
guestfs-testing - manual testing of libguestfs, you can help!
=head1 DESCRIPTION
This page has manual tests you can try on libguestfs. Everyone has a
slightly different combination of platform, hardware and guests, so
this testing is very valuable. Thanks for helping out!
Tests marked with a B<*> (asterisk) can B<destroy data> if you're not
careful. The others are safe and won't modify anything.
Most of these tests will work with any libguestfs E<ge> 1.14. Some of
these tests (marked) require libguestfs E<ge> 1.22.
You can report bugs you find through this link:
L<https://bugzilla.redhat.com/enter_bug.cgi?component=libguestfs&product=Virtualization+Tools>
or post on the mailing list (registration is B<not> required, but if
you're not registered then you'll have to wait for a moderator to
manually approve your message):
L<https://www.redhat.com/mailman/listinfo/libguestfs>
=head1 TESTS
=head2 Run libguestfs-test-tool
Run:
libguestfs-test-tool
This command does a very simple, non-destructive test that basic
libguestfs is functioning. You don't need to run it as root.
If it I<doesn't> print C<===== TEST FINISHED OK =====>, report it as a
bug. It is very important that you include the B<complete, unedited>
output of C<libguestfs-test-tool> in your bug report. See the
L</BUGS> section at the end of this page.
=head2 Check KVM acceleration is being used.
If your host has hardware virt acceleration, then with a hot cache
libguestfs should be able to start up in a few seconds. Run the
following command a few times:
time guestfish -a /dev/null run
After a few runs, the time should settle down to a few seconds (under
5 seconds on fast 64 bit hardware).
How to check for hardware virt:
L<http://virt-tools.org/learning/check-hardware-virt/>
If the command above does not work at all, use
L<libguestfs-test-tool(1)>.
=head2 Check which version of libguestfs, qemu, libvirt, etc is being used.
Look at the output of C<libguestfs-test-tool> and check:
=over 4
=item *
Which version of libguestfs is being used? Near the beginning of the
output you'll see a line like:
library version: 1.22.0fedora=19,release=1.fc19,libvirt
=item *
Is libvirt being used? You can tell the difference by looking
for the backend:
guestfs_get_backend: direct
or:
guestfs_get_backend: libvirt
=item *
Which version of qemu is being used? It may be printed out:
libguestfs: qemu version 1.5
but note that if you're using libvirt then libguestfs doesn't have
this information.
=item *
Which kernel is being used? L<supermin(1)> will try to pick the
latest kernel installed on your machine. You can see the version in
the appliance output, eg:
[ 0.000000] Linux version 3.9.2-200.fc18.x86_64 [...]
=back
=head2 Try to open a local guest image with guestfish.
You can use any guest disk image for this test. Make sure you use the
C<--ro> flag so that L<guestfish(1)> will open the disk image
read-only.
guestfish --ro -a /path/to/disk.img -i
If the command is successful, it should print out the guest operating
system name and put you at the guestfish C<E<gt>E<lt>fsE<gt>> prompt.
You can use guestfish commands like S<C<ll />> to look inside the disk
image. To exit, type C<exit>.
If you get an error, try enabling debugging (add C<-v> to the command
line). Also make sure that L<libguestfs-test-tool(1)> succeeds.
=head2 Try to open a remote guest image with guestfish.
B<Note> this test requires S<libguestfs E<ge> 1.22> and S<qemu E<ge> 1.5>.
You may also have to disable libvirt by setting this:
export LIBGUESTFS_BACKEND=direct
If you have a disk image available over HTTP/FTP, try to open it.
guestfish --ro -i --format=raw -a http://www.example.com/disk.img
For SSH you will need to make sure that ssh-agent is set up so you
don't need a password to log in to the remote machine. Then a command
similar to this should work:
guestfish --ro -i --format=raw \
-a ssh://remote.example.com/path/to/disk.img
If you get an error, try enabling debugging (add C<-v> to the command
line). Also make sure that L<libguestfs-test-tool(1)> succeeds.
=head2 Run virt-alignment-scan on all your guests.
Run L<virt-alignment-scan(1)> on guests or disk images:
virt-alignment-scan -a /path/to/disk.img
or:
virt-alignment-scan -d Guest
Does the alignment report match how the guest partitions are aligned?
=head2 Run virt-cat on some files in guests.
L<virt-cat(1)> can display files from guests. For a Linux guest, try:
virt-cat LinuxGuest /etc/passwd
A recent feature is support for Windows paths, for example:
virt-cat WindowsGuest 'c:\windows\win.ini'
An even better test is if you have a Windows guest with multiple
drives. Do C<D:>, C<E:> etc paths work correctly?
=head2 B<*> Copy some files into a B<shut off> guest.
L<virt-copy-in(1)> can recursively copy files and directories
into a guest or disk image.
virt-copy-in -d Guest /etc /tmp
This should copy local directory F</etc> to F</tmp/etc> in the guest
(recursively). If you boot the guest, can you see all of the copied
files and directories?
Shut the guest down and try copying multiple files and directories:
virt-copy-in -d Guest /home /etc/issue /tmp
=head2 Copy some files out of a guest.
L<virt-copy-out(1)> can recursively copy files and directories
out of a guest or disk image.
virt-copy-out -d Guest /home .
Note the final space and period in the command is not a typo.
This should copy F</home> from the guest into the current directory.
=head2 Run virt-df.
L<virt-df(1)> lists disk space. Run:
virt-df
You can try comparing this to the results from L<df(1)> inside the
guest, but there are some provisos:
=over 4
=item *
The guest must be idle.
=item *
The guest disks must be synched using L<sync(1)>.
=item *
Any action such as booting the guest will write log files causing the
numbers to change.
=back
We don't guarantee that the numbers will be identical even under these
circumstances. They should be similar. It would indicate a bug if
you saw greatly differing numbers.
=head2 Try importing virt-df CSV output into a spreadsheet or database.
Run:
virt-df --csv > /tmp/report.csv
Now try to load this into your favorite spreadsheet or database. Are
the results reproduced faithfully in the spreadsheet/database?
L<http://www.postgresql.org/docs/8.1/static/sql-copy.html>
L<http://dev.mysql.com/doc/refman/5.1/en/load-data.html>
=head2 B<*> Edit a file in a B<shut off> guest.
L<virt-edit(1)> can edit files in guests. Try this command on
a RHEL or Fedora guest:
virt-edit LinuxGuest /etc/sysconfig/network
On other Linux guests try editing other files such as:
virt-edit LinuxGuest /etc/motd
Are the changes seen inside the guest when it is booted?
=head2 Display the filesystems / partitions / LVs in a guest.
L<virt-filesystems(1)> can be used to display filesystems in
a guest. Try this command on any disk image or guest:
virt-filesystems -a /path/to/disk.img --all --long -h
or:
virt-filesystems -d Guest --all --long -h
Do the results match what is seen in the guest?
=head2 Run virt-inspector on all your guests.
Use L<virt-inspector(1)> to get a report on all of your guests or disk
images:
virt-inspector -a /path/to/disk.img | less
or:
virt-inspector -d Guest | less
Do the results match what is actually in the guest?
=head2 Try the auditing features of virt-ls on all your guests.
List all setuid or setgid programs in a Linux virtual machine:
virt-ls -lR -d Guest / | grep '^- [42]'
List all public-writable directories in a Linux virtual machine:
virt-ls -lR -d Guest / | grep '^d ...7'
List all Unix domain sockets in a Linux virtual machine:
virt-ls -lR -d Guest / | grep '^s'
List all regular files with filenames ending in '.png':
virt-ls -lR -d Guest / | grep -i '^-.*\.png$'
Display files larger than 10MB in home directories:
virt-ls -lR -d Guest /home | awk '$3 > 10*1024*1024'
Find everything modified in the last 7 days:
virt-ls -lR -d Guest --time-days / | awk '$6 <= 7'
Find regular files modified in the last 24 hours:
virt-ls -lR -d Guest --time-days / | grep '^-' | awk '$6 < 1'
Do the results match what is in the guest?
=head2 Create a disk image from a tarball.
Use L<virt-make-fs(1)> to create a disk image from any tarball
that you happen to have:
virt-make-fs --partition=mbr --type=vfat /any/tarball.tar.gz output.img
Add 'output.img' as a raw disk to an existing guest. Check the guest
can see the files. This test is particularly useful if you try it
with a Windows guest.
Try other partitioning schemes, eg. I<--partition=gpt>.
Try other filesystem formats, eg. I<--type=ntfs>, I<--type=ext2>.
=head2 B<*> Run virt-rescue on a B<shut off> disk image or guest.
Use L<virt-rescue(1)> to examine, rescue or repair a B<shut off> guest
or disk image:
virt-rescue -a /path/to/disk.img
or:
virt-rescue -d Guest
Can you use ordinary shell commands to examine the guest?
=head2 B<*> Resize your guests.
Use L<virt-resize(1)> to give a guest some more disk space. For
example, if you have a disk image that is smaller than 30G, increase
it to 30G by doing:
truncate -s 30G newdisk.img
virt-filesystems -a /path/to/olddisk.img --all --long -h
virt-resize /path/to/olddisk.img newdisk.img --expand /dev/sda1
qemu-kvm -m 1024 -hda newdisk.img
Does the guest still boot? Try expanding other partitions.
=head2 B<*> Sparsify a guest disk.
Using L<virt-sparsify(1)>, make a disk image more sparse:
virt-sparsify /path/to/olddisk.img newdisk.img
Is F<newdisk.img> still bootable after sparsifying? Is the resulting
disk image smaller (use C<du> to check)?
=head2 B<*> "sysprep" a B<shut off> Linux guest.
B<Note> that this really will mess up an existing guest, so it's
better to clone the guest before trying this.
virt-sysprep --hostname newhost.example.com -a /path/to/disk.img
Was the sysprep successful? After booting, what changes were made and
were they successful?
=head2 Dump the Windows Registry from your Windows guests.
Use L<virt-win-reg(1)> to dump out the Windows Registry from
any Windows guests that you have.
virt-win-reg --unsafe-printable-strings WindowsGuest 'HKLM\Software' |
less
virt-win-reg --unsafe-printable-strings WindowsGuest 'HKLM\System' |
less
Does the output match running C<regedit> inside the guest?
A recent feature is the ability to dump user registries, so try this,
replacing I<username> with the name of a local user in the guest:
virt-win-reg --unsafe-printable-strings WindowsGuest 'HKEY_USERS\username' |
less
=head1 SEE ALSO
L<guestfs(3)>,
L<guestfish(1)>,
L<guestfs-examples(3)>,
L<http://libguestfs.org/>.
=head1 AUTHORS
Richard W.M. Jones (C<rjones at redhat dot com>)
=head1 COPYRIGHT
Copyright (C) 2011-2012 Red Hat Inc.