=head1 NAME

virt-tail - Follow (tail) files in a virtual machine

=head1 SYNOPSIS

 virt-tail [--options] -d domname file [file ...]

 virt-tail [--options] -a disk.img [-a disk.img ...] file [file ...]

=head1 DESCRIPTION

C<virt-tail> is a command line tool to follow (tail) the contents of
C<file> where C<file> exists in the named virtual machine (or disk
image).  It is similar to the ordinary command S<C<tail -f>>.

Multiple filenames can be given, in which case each is followed
separately.  Each filename must be a full path, starting at the root
directory (starting with '/').

The command keeps running until:

=over 4

=item *

The user presses the ^C or an interrupt signal is received.

=item *

None of the listed files was found in the guest, or they
all get deleted.

=item *

There is an unrecoverable error.

=back

=head1 EXAMPLE

Follow F</var/log/messages> inside a virtual machine called C<mydomain>:

 virt-tail -d mydomain /var/log/messages

=head1 OPTIONS

=over 4

=item B<--help>

Display brief help.

=item B<-a> file

=item B<--add> file

Add I<file> which should be a disk image from a virtual machine.  If
the virtual machine has multiple block devices, you must supply all of
them with separate I<-a> options.

The format of the disk image is auto-detected.  To override this and
force a particular format use the I<--format=..> option.

=item B<-a URI>

=item B<--add URI>

Add a remote disk.  See L<guestfish(1)/ADDING REMOTE STORAGE>.

=item B<-c> URI

=item B<--connect> 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 (I<-a>), then libvirt is
not used at all.

=item B<-d> guest

=item B<--domain> guest

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

=item B<--echo-keys>

When prompting for keys and passphrases, virt-tail 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.

=item B<-f>

=item B<--follow>

This option is ignored.  virt-tail always behaves like
S<L<tail(1)> I<-f>>.  You don't need to specify the I<-f> option.

=item B<--format=raw|qcow2|..>

=item B<--format>

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

For example:

 virt-tail --format=raw -a disk.img file

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

 virt-tail --format=raw -a disk.img --format -a another.img file

forces raw format (no auto-detection) for F<disk.img> and reverts to
auto-detection for F<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).

=item B<--keys-from-stdin>

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

=item B<-m> dev[:mountpoint[:options[:fstype]]]

=item B<--mount> dev[:mountpoint[:options[:fstype]]]

Mount the named partition or logical volume on the given mountpoint.

If the mountpoint is omitted, it defaults to F</>.

Specifying any mountpoint disables the inspection of the guest and
the mount of its root and all of its mountpoints, so make sure
to mount all the mountpoints needed to work with the filenames
given as arguments.

If you don’t know what filesystems a disk image contains, you can
either run guestfish without this option, then list the partitions,
filesystems and LVs available (see L</list-partitions>,
L</list-filesystems> and L</lvs> commands), or you can use the
L<virt-filesystems(1)> program.

The third (and rarely used) part of the mount parameter is the list of
mount options used to mount the underlying filesystem.  If this is not
given, then the mount options are either the empty string or C<ro>
(the latter if the I<--ro> flag is used).  By specifying the mount
options, you override this default choice.  Probably the only time you
would use this is to enable ACLs and/or extended attributes if the
filesystem can support them:

 -m /dev/sda1:/:acl,user_xattr

Using this flag is equivalent to using the C<mount-options> command.

The fourth part of the parameter is the filesystem driver to use, such
as C<ext3> or C<ntfs>. This is rarely needed, but can be useful if
multiple drivers are valid for a filesystem (eg: C<ext2> and C<ext3>),
or if libguestfs misidentifies a filesystem.

=item B<-v>

=item B<--verbose>

Enable verbose messages for debugging.

=item B<-V>

=item B<--version>

Display version number and exit.

=item B<-x>

Enable tracing of libguestfs API calls.

=back

=head1 LOG FILES

To list out the log files from guests, see the related tool
L<virt-log(1)>.  It understands binary log formats such as the systemd
journal.

=head1 WINDOWS PATHS

C<virt-tail> has a limited ability to understand Windows drive letters
and paths (eg. F<E:\foo\bar.txt>).

If and only if the guest is running Windows then:

=over 4

=item *

Drive letter prefixes like C<C:> are resolved against the
Windows Registry to the correct filesystem.

=item *

Any backslash (C<\>) characters in the path are replaced
with forward slashes so that libguestfs can process it.

=item *

The path is resolved case insensitively to locate the file
that should be displayed.

=back

There are some known shortcomings:

=over 4

=item *

Some NTFS symbolic links may not be followed correctly.

=item *

NTFS junction points that cross filesystems are not followed.

=back

=head1 EXIT STATUS

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

=head1 SEE ALSO

L<guestfs(3)>,
L<guestfish(1)>,
L<virt-copy-out(1)>,
L<virt-cat(1)>,
L<virt-log(1)>,
L<virt-tar-out(1)>,
L<tail(1)>,
L<http://libguestfs.org/>.

=head1 AUTHOR

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

=head1 COPYRIGHT

Copyright (C) 2016 Red Hat Inc.
