#!/usr/bin/perl -w
# virt-rescue
# Copyright (C) 2009-2010 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., 675 Mass Ave, Cambridge, MA 02139, USA.

use warnings;
use strict;

use Errno;
use Sys::Guestfs;
use Sys::Guestfs::Lib qw(open_guest);
use Pod::Usage;
use Getopt::Long;
use Locale::TextDomain 'libguestfs';

=encoding utf8

=head1 NAME

virt-rescue - Run a rescue shell on a virtual machine

=head1 SYNOPSIS

 virt-rescue [--options] domname

 virt-rescue [--options] disk.img [disk.img ...]

=head1 WARNING

You must I<not> use C<virt-rescue> on live virtual machines.  Doing so
will probably result in disk corruption in the VM.  C<virt-rescue>
tries to stop you from doing this, but doesn't catch all cases.

However if you use the I<--ro> (read only) option, then you can attach
a shell to a live virtual machine.  The results might be strange or
inconsistent at times but you won't get disk corruption.

=head1 DESCRIPTION

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 GuestName

 virt-rescue --ro /path/to/disk.img

 virt-rescue /dev/sdc

For live VMs you I<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 C</> (C</bin>, C</lib> etc) is the
rescue appliance.  You must mount the virtual machine's filesystems by
hand.  There is an empty directory called C</sysroot> where you can
mount filesystems.

In the example below, we list logical volumes, then choose one to
mount under C</sysroot>:

 ><rescue> lvs
 LV      VG        Attr   LSize   Origin Snap%  Move Log Copy%  Convert
 lv_root vg_f11x64 -wi-a-   8.83G
 lv_swap vg_f11x64 -wi-a- 992.00M
 ><rescue> mount /dev/vg_f11x64/lv_root /sysroot
 ><rescue> ls /sysroot

If you don't know what filesystems are available on the virtual
machine then you can use commands such as L<parted(8)> and L<lvs(8)>
to find out.

=head2 NOTES

Virt-rescue can be used on I<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
L<guestfish(1)> instead as it is more suitable for this purpose).  You
can even use virt-rescue on things like SD cards.

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 L<guestfs(3)>.  To get a structured shell that you can
use to make scripted changes to guests, use L<guestfish(1)>.

=head1 OPTIONS

=over 4

=cut

my $help;

=item B<--help>

Display brief help.

=cut

my $version;

=item B<--version>

Display version number and exit.

=cut

my $append;

=item B<--append kernelopts>

Pass additional options to the rescue kernel.

=cut

my $uri;

=item B<--connect URI> | B<-c URI>

If using libvirt, connect to the given I<URI>.  If omitted, then we
connect to the default libvirt hypervisor.

If you specify guest block devices directly, then libvirt is not used
at all.

=cut

my $format;

=item B<--format> raw

Specify the format of disk images given on the command line.  If this
is omitted then the format is autodetected from the content of the
disk image.

If disk images are requested from libvirt, then this program asks
libvirt for this information.  In this case, the value of the format
parameter is ignored.

If working with untrusted raw-format guest disk images, you should
ensure the format is always specified.

=cut

my $memsize;

=item B<--memsize MB> | B<-m 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.

=cut

my $network;

=item B<--network MB>

Enable QEMU user networking in the guest.

=cut

my $readonly;

=item B<--ro> | B<-r>

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.

=cut

my $selinux;

=item B<--selinux>

Enable SELinux in the rescue appliance.  You should read
L<guestfs(3)/SELINUX> before using this option.

=back

=cut

GetOptions ("help|?" => \$help,
            "version" => \$version,
            "append=s" => \$append,
            "connect|c=s" => \$uri,
            "format=s" => \$format,
            "memsize|m=i" => \$memsize,
            "network" => \$network,
            "ro|r" => \$readonly,
            "selinux" => \$selinux,
    ) or pod2usage (2);
pod2usage (1) if $help;
if ($version) {
    my $g = Sys::Guestfs->new ();
    my %h = $g->version ();
    print "$h{major}.$h{minor}.$h{release}$h{extra}\n";
    exit
}

pod2usage (__"virt-rescue: no image or VM names rescue given")
    if @ARGV == 0;

my @args = (\@ARGV);
push @args, address => $uri if $uri;
push @args, rw => 1 unless $readonly;
push @args, format => $format if defined $format;
my $g = open_guest (@args);

# Setting "direct mode" is required for the rescue appliance.
$g->set_direct (1);

# Set other features.
$g->set_selinux (1) if $selinux;
$g->set_memsize ($memsize) if defined $memsize;
$g->set_network (1) if $network;

# Set the kernel command line, which must include guestfs_rescue=1
# (see appliance/init).
my $str = "guestfs_rescue=1";
$str .= " $append" if defined $append;
$g->set_append ($str);

# Run the appliance.  This won't return until the user quits the
# appliance.
eval { $g->launch (); };

# launch() expects guestfsd to start. However, virt-rescue doesn't run guestfsd,
# so this will always fail with ECHILD when the appliance exits unexpectedly.
die $@ unless $!{ECHILD};

exit 0;

=head1 ENVIRONMENT VARIABLES

Several environment variables affect virt-rescue.  See
L<guestfs(3)/ENVIRONMENT VARIABLES> for the complete list.

=head1 SHELL QUOTING

Libvirt guest names can contain arbitrary characters, some of which
have meaning to the shell such as C<#> and space.  You may need to
quote or escape these characters on the command line.  See the shell
manual page L<sh(1)> for details.

=head1 SEE ALSO

L<guestfs(3)>,
L<guestfish(1)>,
L<virt-cat(1)>,
L<Sys::Guestfs(3)>,
L<Sys::Guestfs::Lib(3)>,
L<Sys::Virt(3)>,
L<http://libguestfs.org/>.

=head1 AUTHOR

Richard W.M. Jones L<http://people.redhat.com/~rjones/>

=head1 COPYRIGHT

Copyright (C) 2009-2010 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., 675 Mass Ave, Cambridge, MA 02139, USA.