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febootstrap - Bootstrapping tool for creating supermin appliances
SYNOPSIS
febootstrap [-o OUTPUTDIR] --names LIST OF PKGS ...
febootstrap [-o OUTPUTDIR] PKG FILE NAMES ...
DESCRIPTION
febootstrap is a tool for building supermin appliances. These are tiny
appliances (similar to virtual machines), usually around 100KB in size,
which get fully instantiated on-the-fly in a fraction of a second when
you need to boot one of them.
Originally "fe" in febootstrap stood for "Fedora", but this tool is now
distro-independent and can build supermin appliances for several
popular Linux distros, and adding support for others is reasonably
easy.
Note that this manual page documents febootstrap 3.x which is a
complete rewrite and quite different from version 2.x. If you are
looking for the febootstrap 2.x tools, then this is not the right
place.
BASIC OPERATION
There are two modes for using febootstrap. With the --names parameter,
febootstrap takes a list of package names and creates a supermin
appliance containing those packages and all dependencies that those
packages require. In this mode febootstrap usually needs network
access because it may need to consult package repositories in order to
work out dependencies and download packages.
Without --names, febootstrap takes a list of packages (ie. filenames
of locally available packages). This package set must be complete and
consistent with no dependencies outside the set of packages you
provide. In this mode febootstrap does not require any network access.
It works by looking at the package files themselves.
By "package" we mean the RPM, DEB, (etc.) package. A package name
might be the fully qualified name (eg. "coreutils-8.5-7.fc14.x86_64")
or some abbreviation (eg. "coreutils"). The precise format of the name
and what abbreviations are allowed depends on the package manager.
The supermin appliance that febootstrap writes consists of two files
called "hostfiles" and "base.img" (see "SUPERMIN APPLIANCES" below).
By default these are written to the current directory. If you specify
the -o OUTPUTDIR option then these files are written to the named
directory instead (traditionally this directory is named "supermin.d"
but you can call it whatever you want).
In all cases febootstrap can only build a supermin appliance which is
identical in distro, version and architecture to the host. It does not
do cross-builds.
OPTIONS--help
Display brief command line usage, and exit.
--exclude REGEXP
After doing dependency resolution, exclude packages which match the
regular expression.
This option is only used with --names, and it can be given multiple
times on the command line.
--names
Provide a list of package names, instead of providing packages
directly. In this mode febootstrap may require network access.
See "BASIC OPERATION" above.
--no-warnings
Don't print warnings about packaging problems.
-o outputdir
Select the output directory where the two supermin appliance files
are written ("hostfiles" and "base.img"). The default directory is
the current directory. Note that if this files exist already in
the output directory then they will be overwritten.
--packager-config CONFIGFILE
Set the configuration file for the package manager. This allows
you to specify alternate software repositories.
For ArchLinux, this sets the pacman configuration file (default
"/etc/pacman.conf"). See pacman.conf(5).
For Yum/RPM distributions, this sets the yum configuration file
(default "/etc/yum.conf"). See yum.conf(5).
--save-temps
Don't remove temporary files and directories on exit. This is
useful for debugging.
--use-installed
If packages are already installed, use the contents (from the local
filesystem) instead of downloading them.
Note that this can cause malformed appliances if local files have
been changed from what was originally in the package. This is
particularly a problem for configuration files.
However this option is useful in some controlled situations: for
example when using febootstrap inside a freshly installed chroot.
-v
--verbose
Enable verbose messages.
-V
--version
Print the package name and version number, and exit.
--yum-config CONFIGFILE
This is a deprecated alias for --packager-config CONFIGFILE.
SUPERMIN APPLIANCES
Supermin appliances consist of just enough information to be able to
build an appliance containing the same operating system (Linux version,
distro, release etc) as the host OS. Since the host and appliance
share many common files such as "/bin/bash" and "/lib/libc.so" there is
no reason to ship these files in the appliance. They can simply be
read from the host on demand when the appliance is launched. Therefore
to save space we just store the names of the host files that we want.
There are some files which cannot just be copied from the host in this
way. These include configuration files which the host admin might have
edited. So along with the list of host files, we also store a skeleton
base image which contains these files and the outline directory
structure.
Therefore the supermin appliance normally consists of at least two
control files:
hostfiles
The list of files that are to be copied from the host. This is a
plain text file with one pathname per line. Directories are
included in this file.
Paths can contain wildcards, which are expanded when the appliance
is created, eg:
/etc/yum.repos.d/*.repo
would copy all of the "*.repo" files into the appliance.
Each pathname in the file should start with a "/" character. (In
older versions of febootstrap, paths started with "./" and were
relative to the root directory, but you should not do that in new
files).
base.img
This uncompressed cpio file contains the skeleton filesystem.
Mostly it contains directories and a few configuration files.
All paths in the cpio file should be relative to the root directory
of the appliance.
Note that unlike "hostfiles", paths and directories in the base
image don't need to have any relationship to the host filesystem.
RECONSTRUCTING THE APPLIANCE
The separate tool febootstrap-supermin-helper(8) is used to reconstruct
an appliance from the hostfiles and base image files.
This program in fact iterates recursively over the files and
directories passed to it. A common layout is:
supermin.d/
supermin.d/base.img
supermin.d/extra.img
supermin.d/hostfiles
and then invoking febootstrap-supermin-helper with just the
"supermin.d" directory path as an argument.
In this way extra files can be added to the appliance just by creating
another cpio file ("extra.img" in the example above) and dropping it
into the directory. When the appliance is constructed, the extra files
will appear in the appliance.
DIRECTORIES BEFORE FILES
In order for febootstrap-supermin-helper to run quickly, it does not
know how to create directories automatically. Inside hostfiles and the
cpio files, directories must be specified before any files that they
contain. For example:
/usr
/usr/sbin
/usr/sbin/serviced
It is fine to list the same directory name multiple times.
LEXICOGRAPHICAL ORDER
febootstrap-supermin-helper visits the supermin control files in
lexicographical order. Thus in the example above, in the order
"base.img" -> "extra.img" -> "hostfiles".
This has an important effect: files contained in later cpio files
overwrite earlier files, and directories do not need to be specified if
they have already been created in earlier control files.
EXAMPLE OF CREATING EXTRA CPIO FILE
You can create a file like "extra.img" very easily using a shell
snippet similar to this one:
cd $tmpdir
mkdir -p usr/sbin
cp /path/to/serviced usr/sbin/
echo -e "usr\nusr/sbin\nusr/sbin/serviced" |
cpio --quiet -o -H newc > extra.img
rm -rf usr
Notice how we instruct cpio to create intermediate directories.
MINIMIZING THE SUPERMIN APPLIANCE
You may want to "minimize" the supermin appliance in order to save time
and space when it is instantiated. Typically you might want to remove
documentation, info files, man pages and locales. We used to provide a
separate tool called "febootstrap-minimize" for this purpose, but it is
no longer provided. Instead you can post-process "hostfiles" yourself
to remove any files or directories that you don't want (by removing
lines from the file). Be careful what you remove because files may be
necessary for correct operation of the appliance.
For example:
< supermin.d/hostfiles \
grep -v '^/usr/share/man/' |
grep -v '^/usr/share/doc/' |
grep -v '^/usr/share/info/' > supermin.d/hostfiles-t
mv supermin.d/hostfiles-t supermin.d/hostfiles
KERNEL AND KERNEL MODULES
Usually the kernel and kernel modules are not included in the supermin
appliance. When the appliance is instantiated, the kernel modules from
the host kernel are copied in, and it is booted using the host kernel.
febootstrap-supermin-helper is able to choose the best host kernel
available to boot the appliance. Users can override this by setting
environment variables (see febootstrap-supermin-helper(8)).
BOOTING AND CACHING THE SUPERMIN APPLIANCE
For fastest boot times you should cache the output of febootstrap-
supermin-helper. See the libguestfs source file "src/appliance.c" for
an example of how this is done.
ENFORCING AVAILABILITY OF HOSTFILES
febootstrap-supermin-helper builds the appliance by copying in host
files as listed in "hostfiles". For this to work those host files must
be available. We usually enforce this by adding requirements (eg. RPM
"Requires:" lines) on the package that uses the supermin appliance, so
that package cannot be installed without pulling in the dependent
packages and thus making sure the host files are available.
SEE ALSOfebootstrap-supermin-helper(8),
<http://people.redhat.com/~rjones/febootstrap/>, guestfs(3),
<http://libguestfs.org/>.
AUTHORS
· Richard W.M. Jones <http://people.redhat.com/~rjones/>
· Matthew Booth mbooth@redhat.com
COPYRIGHT
Copyright (C) 2009-2011 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.
febootstrap-3.20 2012-12-22 FEBOOTSTRAP(8)
