=head1 NAME

febootstrap-supermin-helper - Reconstruct initramfs from supermin appliance.

=head1 SYNOPSIS

 febootstrap-supermin-helper supermin.img hostfiles.txt host_cpu kernel initrd
 febootstrap-supermin-helper input [...] host_cpu kernel initrd

 febootstrap-supermin-helper -f ext2 input [...] host_cpu kernel initrd appliance

 febootstrap-supermin-helper -f checksum input [...] host_cpu

=head1 DESCRIPTION

I<febootstrap-supermin-helper> reconstructs a bootable kernel and
initramfs from a supermin appliance.  First you should be familiar
with L<febootstrap(8)>.

=head1 PARAMETERS

Of the required parameters, the first few are I<input> files, and the
last two or three are I<output> files.

C<supermin.img> and C<hostfiles.txt> are the input files which
describe the supermin appliance.  (You can also use a directory name
here which is searched for files).

C<host_cpu> should be the host CPU, eg. C<x86_64> or C<i686>.

C<kernel>, C<initrd> and C<appliance> are the temporary output files
that this script produces.  These output files are meant to be used
just for booting the appliance, and should be deleted straight
afterwards.  The extra C<appliance> parameter is only required when
the format is C<ext2>.  None of these parameters are needed for
the checksum output C<-f checksum>.

=head1 OPTIONS

=over 4

=item B<-f fmt>

=item B<--format fmt>

Select the output format for the appliance.  Possible formats are:

=over 4

=item cpio

A Linux initramfs.  This is the default.

In this case you have to supply names for the C<kernel>
and C<initrd>, where the C<initrd> is the appliance.

=item ext2

An ext2 filesystem.

In this case you have to supply names for the C<kernel>, a small
C<initrd> which is used just to locate the appliance, and the
C<appliance> (the ext2 filesystem).

=item checksum

Output a checksum.

This prints a checksum which only changes when one of the input files
changes.

You can use this in order to cache the output of a previous run of
this program: computing the checksum is much quicker than building an
appliance, and you only need to invalidate the cache (and consequently
rebuild the appliance) when the checksum changes.  Note that the
host_cpu and the UID of the current user are included in the checksum.

=back

=item B<-k file>

=item B<--kmods file>

If this option is specified, then C<file> should be a list of
wildcards matching kernel module names, eg:

 virtio*.ko
 scsi*.ko
 piix.ko

In this case, only kernel modules matching those wildcards will be
included in the output appliance.  Note: You must resolve any
dependencies yourself as this does not pull in dependent modules
automatically.

If this option is not specified, then every kernel module from the
host will be included.  This is safer, but can produce rather large
appliances which need a lot more memory to boot.

=item B<-u user>

=item B<--user user>

=item B<-g group>

=item B<--group group>

Run febootstrap-supermin-helper as an alternate user and/or group.
C<user> and C<group> can be specified as either a name, which will
be resolved using the system name service, or a uid/gid.  Use of these
options requires root privileges.

Use of these options is required if running febootstrap-supermin-helper
as root with the effective uid/gid set to non-root.  Bash will reset
the effective uid/gid to the real uid/gid when invoked.  As
febootstrap-supermin-helper uses bash in parts, this will result in the
creation of an appliance with a mixture of ownerships.

=back

=head1 SPEED

In libguestfs, on a mid-range Intel-based PC, we reconstruct the
initramfs using this script in around 1/5th of a second (assuming a
"hot cache" - it's rather slower when run the first time on a cold
cache).

Some tips to improve performance:

=over 4

=item *

Use a kernel module whitelist (the C<--kmods> option), and only
list the kernel modules you really need.

=item *

Minimize the appliance, removing as much extraneous junk as possible.

=back

=head1 ENVIRONMENT VARIABLES

=over 4

=item FEBOOTSTRAP_KERNEL

If this environment variable is set, then automatic selection of the
kernel is bypassed and this kernel is used.

The environment variable should point to a kernel file,
eg. C</boot/vmlinuz-3.0.x86_64>

The corresponding module path is guessed from the kernel name, but you
can override that by setting C<FEBOOTSTRAP_MODULES>.

=item FEBOOTSTRAP_MODULES

If C<FEBOOTSTRAP_KERNEL> and C<FEBOOTSTRAP_MODULES> are both set, then
automatic selection of the kernel is bypassed and the kernel and
module path are set to these values.

The environment variable should point to a module directory,
eg. C</lib/modules/3.0.x86_64/>

This has no effect if C<FEBOOTSTRAP_KERNEL> is not set.

=back

=head1 SEE ALSO

L<febootstrap(8)>.

=head1 AUTHORS

Richard W.M. Jones <rjones @ redhat . com>

=head1 COPYRIGHT

(C) Copyright 2009-2011 Red Hat Inc.,
L<http://people.redhat.com/~rjones/febootstrap>.

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.