                        Introduction to NanoBSD

  Daniel Gerzo

   Copyright (c) 2006 The FreeBSD Documentation Project

   $FreeBSD: doc/en_US.ISO8859-1/articles/nanobsd/article.sgml,v 1.7
   2010/07/13 04:06:37 maxim Exp $

   FreeBSD is a registered trademark of the FreeBSD Foundation.

   Many of the designations used by manufacturers and sellers to
   distinguish their products are claimed as trademarks. Where those
   designations appear in this document, and the FreeBSD Project was
   aware of the trademark claim, the designations have been followed
   by the "(TM)" or the "(R)" symbol.

   This document provides information about the NanoBSD tools, which
   can be used to create FreeBSD system images for embedded
   applications, suitable for use on a Compact Flash card (or other
   mass storage medium).

     --------------------------------------------------------------

1 Introduction to NanoBSD

   NanoBSD is a tool currently developed by Poul-Henning Kamp
   <phk@FreeBSD.org>. It creates a FreeBSD system image for embedded
   applications, suitable for use on a Compact Flash card (or other
   mass storage medium).

   It can be used to build specialized install images, designed for
   easy installation and maintenance of systems commonly called
   "computer appliances". Computer appliances have their hardware and
   software bundled in the product, which means all applications are
   pre-installed. The appliance is plugged into an existing network
   and can begin working (almost) immediately.

   The features of NanoBSD include:

     * Ports and packages work as in FreeBSD -- Every single
       application can be installed and used in a NanoBSD image, the
       same way as in FreeBSD.

     * No missing functionality -- If it is possible to do something
       with FreeBSD, it is possible to do the same thing with
       NanoBSD, unless the specific feature or features were
       explicitly removed from the NanoBSD image when it was created.

     * Everything is read-only at run-time -- It is safe to pull the
       power-plug. There is no necessity to run fsck(8) after a
       non-graceful shutdown of the system.

     * Easy to build and customize -- Making use of just one shell
       script and one configuration file it is possible to build
       reduced and customized images satisfying any arbitrary set of
       requirements.

     --------------------------------------------------------------

2 NanoBSD Howto

  2.1 The design of NanoBSD

   Once the image is present on the medium, it is possible to boot
   NanoBSD. The mass storage medium is divided into three parts by
   default:

     * Two image partitions: code#1 and code#2.

     * The configuration file partition, which can be mounted under
       the /cfg directory at run time.

   These partitions are normally mounted read-only.

   The /etc and /var directories are md(4) (malloc) disks.

   The configuration file partition persists under the /cfg
   directory. It contains files for /etc directory and is briefly
   mounted read-only right after the system boot, therefore it is
   required to copy modified files from /etc back to the /cfg
   directory if changes are expected to persist after the system
   restarts.

   Example 1. Making persistent changes to /etc/resolv.conf

 # vi /etc/resolv.conf
 [...]
 # mount /cfg
 # cp /etc/resolv.conf /cfg
 # umount /cfg

     Note: The partition containing /cfg should be mounted only at
     boot time and while overriding the configuration files.

     Keeping /cfg mounted at all times is not a good idea, especially
     if the NanoBSD system runs off a mass storage medium that may be
     adversely affected by a large number of writes to the partition
     (i.e. when the filesystem syncer flushes data to the system
     disks).

     --------------------------------------------------------------

  2.2 Building a NanoBSD image

   A NanoBSD image is built using a simple nanobsd.sh shell script,
   which can be found in the /usr/src/tools/tools/nanobsd directory.
   This script creates an image, which can be copied on the storage
   medium using the dd(1) utility.

   The necessary commands to build a NanoBSD image are:

 # cd /usr/src/tools/tools/nanobsd (1)
 # sh nanobsd.sh (2)
 # cd /usr/obj/nanobsd.full (3)
 # dd if=_.disk.full of=/dev/da0 bs=64k (4)

   (1)
           Change the current directory to the base directory of the
           NanoBSD build script.
   (2)
           Start the build process.
   (3)
           Change the current directory to the place where the built
           images are located.
   (4)
           Install NanoBSD onto the storage medium.

     --------------------------------------------------------------

  2.3 Customizing a NanoBSD image

   This is probably the most important and most interesting feature
   of NanoBSD. This is also where you will be spending most of the
   time when developing with NanoBSD.

   Invocation of the following command will force the nanobsd.sh to
   read its configuration from the myconf.nano file located in the
   current directory:

 # sh nanobsd.sh -c myconf.nano

   Customization is done in two ways:

     * Configuration options

     * Custom functions

     --------------------------------------------------------------

    2.3.1 Configuration options

   With configuration settings, it is possible to configure options
   passed to both the buildworld and installworld stages of the
   NanoBSD build process, as well as internal options passed to the
   main build process of NanoBSD. Through these options it is
   possible to cut the system down, so it will fit on as little as
   64MB. You can use the configuration options to trim down FreeBSD
   even more, until it will consists of just the kernel and two or
   three files in the userland.

   The configuration file consists of configuration options, which
   override the default values. The most important directives are:

     * NANO_NAME -- Name of build (used to construct the workdir
       names).

     * NANO_SRC -- Path to the source tree used to build the image.

     * NANO_KERNEL -- Name of kernel configuration file used to build
       kernel.

     * CONF_BUILD -- Options passed to the buildworld stage of the
       build.

     * CONF_INSTALL -- Options passed to the installworld stage of
       the build.

     * CONF_WORLD -- Options passed to both the buildworld and the
       installworld stage of the build.

     * FlashDevice -- Defines what type of media to use. Check the
       FlashDevice.sub file for more details.

     --------------------------------------------------------------

    2.3.2 Custom functions

   It is possible to fine-tune NanoBSD using shell functions in the
   configuration file. The following example illustrates the basic
   model of custom functions:

 cust_foo () (
         echo "bar=baz" > \
                 ${NANO_WORLDDIR}/etc/foo
 )
 customize_cmd cust_foo

   A more useful example of a customization function is the
   following, which changes the default size of the /etc directory
   from 5MB to 30MB:

 cust_etc_size () (
         cd ${NANO_WORLDDIR}/conf
         echo 30000 > default/etc/md_size
 )
 customize_cmd cust_etc_size

   There are a few default pre-defined customization functions ready
   for use:

     * cust_comconsole -- Disables getty(8) on the VGA devices (the
       /dev/ttyv* device nodes) and enables the use of the COM1
       serial port as the system console.

     * cust_allow_ssh_root -- Allow root to login via sshd(8).

     * cust_install_files -- Installs files from the nanobsd/Files
       directory, which contains some useful scripts for system
       administration.

     --------------------------------------------------------------

    2.3.3 Adding packages

   Packages can be added to a NanoBSD image using a custom function.
   The following function will install all the packages located in
   /usr/src/tools/tools/nanobsd/packages:

 install_packages () (
 mkdir -p ${NANO_WORLDDIR}/packages
 cp /usr/src/tools/tools/nanobsd/packages/* ${NANO_WORLDDIR}/packages
 chroot ${NANO_WORLDDIR} sh -c 'cd packages; pkg_add -v *;cd ..;'
 rm -rf ${NANO_WORLDDIR}/packages
 )
 customize_cmd install_packages

     --------------------------------------------------------------

    2.3.4 Configuration file example

   A complete example of a configuration file for building a custom
   NanoBSD image can be:

 NANO_NAME=custom
 NANO_SRC=/usr/src
 NANO_KERNEL=MYKERNEL
 NANO_IMAGES=2

 CONF_BUILD='
 NO_KLDLOAD=YES
 NO_NETGRAPH=YES
 NO_PAM=YES
 '

 CONF_INSTALL='
 NO_ACPI=YES
 NO_BLUETOOTH=YES
 NO_CVS=YES
 NO_FORTRAN=YES
 NO_HTML=YES
 NO_LPR=YES
 NO_MAN=YES
 NO_SENDMAIL=YES
 NO_SHAREDOCS=YES
 NO_EXAMPLES=YES
 NO_INSTALLLIB=YES
 NO_CALENDAR=YES
 NO_MISC=YES
 NO_SHARE=YES
 '

 CONF_WORLD='
 NO_BIND=YES
 NO_MODULES=YES
 NO_KERBEROS=YES
 NO_GAMES=YES
 NO_RESCUE=YES
 NO_LOCALES=YES
 NO_SYSCONS=YES
 NO_INFO=YES
 '

 FlashDevice SanDisk 1G

 cust_nobeastie() (
         touch ${NANO_WORLDDIR}/boot/loader.conf
         echo "beastie_disable=\"YES\"" >> ${NANO_WORLDDIR}/boot/loader.conf
 )

 customize_cmd cust_comconsole
 customize_cmd cust_install_files
 customize_cmd cust_allow_ssh_root
 customize_cmd cust_nobeastie

     --------------------------------------------------------------

  2.4 Updating NanoBSD

   The update process of NanoBSD is relatively simple:

    1. Build a new NanoBSD image, as usual.

    2. Upload the new image into an unused partition of a running
       NanoBSD appliance.

       The most important difference of this step from the initial
       NanoBSD installation is that now instead of using the
       _.disk.full file (which contains an image of the entire disk),
       the _.disk.image image is installed (which contains an image
       of a single system partition).

    3. Reboot, and start the system from the newly installed
       partition.

    4. If all goes well, the upgrade is finished.

    5. If anything goes wrong, reboot back into the previous
       partition (which contains the old, working image), to restore
       system functionality as fast as possible. Fix any problems of
       the new build, and repeat the process.

   To install new image onto the running NanoBSD system, it is
   possible to use either the updatep1 or updatep2 script located in
   the /root directory, depending from which partition is running the
   current system.

   According to which services are available on host serving new
   NanoBSD image and what type of transfer is preferred, it is
   possible to examine one of these three ways:

     --------------------------------------------------------------

    2.4.1 Using ftp(1)

   If the transfer speed is in first place, use this example:

 # ftp myhost
 get _.disk.image "| sh updatep1"

     --------------------------------------------------------------

    2.4.2 Using ssh(1)

   If a secure transfer is preferred, consider using this example:

 # ssh myhost cat _.disk.image.gz | zcat | sh updatep1

     --------------------------------------------------------------

    2.4.3 Using nc(1)

   Try this example if the remote host is not running neither ftp(1)
   or sshd(8) service:

    1. At first, open a TCP listener on host serving the image and
       make it send the image to client:

 myhost# nc -l 2222 < _.disk.image

         Note: Make sure that the used port is not blocked to receive
         incoming connections from NanoBSD host by firewall.

    2. Connect to the host serving new image and execute updatep1
       script:

 # nc myhost 2222 | sh updatep1

     --------------------------------------------------------------
