febootstrap - Bootstrapping tool for creating supermin appliances
febootstrap [-o OUTPUTDIR] --names LIST OF PKGS ... febootstrap [-o OUTPUTDIR] PKG FILE NAMES ...
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.
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.
Display brief command line usage, and exit.
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.
Provide a list of package names, instead of providing packages directly. In this mode febootstrap may require network access. See BASIC OPERATION above.
Don't print warnings about packaging problems.
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.
Enable verbose messages.
Print the package name and version number, and exit.
(Yum/RPM package handler only). Use an alternate configuration file
instead of /etc/yum.conf. If you also want to specify alternate
repositories then you can put them in this file directly or add a
reposdir option to this file. For more information on the file
format see yum.conf(5).
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:
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).
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.
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.
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.
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.
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.
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
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)).
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.
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.
febootstrap-supermin-helper(8), http://people.redhat.com/~rjones/febootstrap/, guestfs(3), http://libguestfs.org/.
Richard W.M. Jones http://people.redhat.com/~rjones/
Matthew Booth mbooth@redhat.com
Copyright (C) 2009-2010 Red Hat Inc.
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