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[febootstrap.git] / febootstrap.pod

diff --git a/febootstrap.pod b/febootstrap.pod
index c76b4eb..6620976 100644 (file)
--- a/febootstrap.pod
+++ b/febootstrap.pod
@@ -48,52 +48,16 @@ name and what abbreviations are allowed depends on the package
 manager.
 
 The supermin appliance that febootstrap writes consists of two files
 manager.
 
 The supermin appliance that febootstrap writes consists of two files

-called C<hostfiles> and C<base.img> (it is common for users to add
-more files).  By default these are written to the current directory.
-If you specify the I<-o OUTPUTDIR> option then these files are written
-to the named directory instead (traditionally this directory is named
+called C<hostfiles> and C<base.img> (see L</SUPERMIN APPLIANCES>
+below).  By default these are written to the current directory.  If
+you specify the I<-o OUTPUTDIR> option then these files are written to
+the named directory instead (traditionally this directory is named

 C<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
 I<not> do cross-builds.
 
 C<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
 I<not> do cross-builds.
 

-=head2 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 C<febootstrap-minimize> for this
-purpose, but it is no longer provided.  Instead you can post-process
-C<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.
-
-=head2 KERNEL AND KERNEL MODULES
-
-Usually the kernel and kernel modules are I<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.
-
-=head2 BOOTING AND CACHING THE SUPERMIN APPLIANCE
-
-To instantiate and boot the supermin appliance you need to use the
-separate tool L<febootstrap-supermin-helper(8)>.  For fastest boot
-times you should cache the output of that tool.  See the libguestfs
-source file C<src/appliance.c> for an example of how this is done.
-
-=head2 ENFORCING AVAILABILITY OF HOSTFILES
-
-L<febootstrap-supermin-helper(8)> builds the appliance by copying in
-host files as listed in C<hostfiles>.  For this to work those host
-files must be available.  We usually enforce this by adding
-requirements (eg. RPM C<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.
-

 =head1 OPTIONS
 
 =over 4
 =head1 OPTIONS
 
 =over 4


@@ -139,8 +103,170 @@ Enable verbose messages.
 
 Print the package name and version number, and exit.
 
 
 Print the package name and version number, and exit.
 

+=item B<--yum-config CONFIGFILE>
+
+(Yum/RPM package handler only).  Use an alternate configuration file
+instead of C</etc/yum.conf>.  If you also want to specify alternate
+repositories then you can put them in this file directly or add a
+C<reposdir> option to this file.  For more information on the file
+format see L<yum.conf(5)>.
+
+=back
+
+=head1 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 C</bin/bash> and
+C</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:
+
+=over 4
+
+=item B<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 C<*.repo> files into the appliance.
+
+Each pathname in the file should start with a C</> character.  (In
+older versions of febootstrap, paths started with C<./> and were
+relative to the root directory, but you should not do that in new
+files).
+
+=item B<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 C<hostfiles>, paths and directories in the base image
+don't need to have any relationship to the host filesystem.
+

 =back
 
 =back
 

+=head2 RECONSTRUCTING THE APPLIANCE
+
+The separate tool L<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
+C<supermin.d> directory path as an argument.
+
+In this way extra files can be added to the appliance just by creating
+another cpio file (C<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.
+
+=head3 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.
+
+=head3 LEXICOGRAPHICAL ORDER
+
+febootstrap-supermin-helper visits the supermin control files in
+lexicographical order.  Thus in the example above, in the order
+C<base.img> -E<gt> C<extra.img> -E<gt> C<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.
+
+=head3 EXAMPLE OF CREATING EXTRA CPIO FILE
+
+You can create a file like C<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.
+
+=head2 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 C<febootstrap-minimize> for this
+purpose, but it is no longer provided.  Instead you can post-process
+C<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
+
+=head2 KERNEL AND KERNEL MODULES
+
+Usually the kernel and kernel modules are I<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.
+
+=head2 BOOTING AND CACHING THE SUPERMIN APPLIANCE
+
+For fastest boot times you should cache the output of
+febootstrap-supermin-helper.  See the libguestfs source file
+C<src/appliance.c> for an example of how this is done.
+
+=head2 ENFORCING AVAILABILITY OF HOSTFILES
+
+febootstrap-supermin-helper builds the appliance by copying in host
+files as listed in C<hostfiles>.  For this to work those host files
+must be available.  We usually enforce this by adding requirements
+(eg. RPM C<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.
+

 =head1 SEE ALSO
 
 L<febootstrap-supermin-helper(8)>,
 =head1 SEE ALSO
 
 L<febootstrap-supermin-helper(8)>,