freebsd-dev/share/man/man8/picobsd.8

.\" -*- nroff-fill -*-
.\" $FreeBSD$
.Dd June 20, 2001
.Os
.Dt PICOBSD 8
.Sh NAME
.Nm picobsd
.Nd floppy disk based FreeBSD system
.Sh SYNOPSIS
.Nm
.Op options
.Op Ar floppy-type Op Ar site-name
.Sh DESCRIPTION
.Nm
is a script which can be used to produce a minimal implementation of
.Fx
(historically called
.Nm PicoBSD )
which typically fits on one floppy disk, or can be downloaded as a
single image file from some media such as CDROM, flash memory, or through
.Xr etherboot .
.Pp
.Nm picobsd
has been originally created to build simple standalone systems
such as firewalls or bridges, but because of the ability to
cross-build images with different source trees than the one
in the server, it can be extremely useful to developers to
test their code without having to reinstall the system.
.Pp
The boot media (typically a floppy disk) contains a boot loader and a
compressed kernel which includes a memory file system.
Depending on the media, it might also contain a number of
additional files, which can be updated at run time, and are
used to override/update those in the memory file system.
.Pp
The system loads the kernel in the normal way, uncompresses
the memory file system and mounts it as root.
It then updates the memory
filesystem with files from the boot media (if present),
and executes a specialized version of
.Pa /etc/rc .
The boot media (floppy etc.) is
required for loading only, and typically used as readonly.
After the boot phase, the system runs entirely from ram.
.Pp
The following options are available (but also check the
.Nm
script for more details):
.Pp
.Bl -tag -width "xxxxxx" -compact
.It Fl -src Ar SRC_PATH
Use the source tree at
.Ar SRC_PATH
instead the one at
.Ar /usr/src .
Can be useful for cross-building floppy images.
When using this option, you must also create initialize the subtree at
.Ar SRC_PATH/../usr
with the correct include files, libraries and tools (such as the
.Xr config 8
program) that are necessary for the cross-build (see the
.Fl -init
option below).
The source files are unmodified by the
.Nm picobsd
script. However the source tree is not completely readonly,
because
.Xr config 8
expects the kernel configuration file to be in one of
its subdirectories, and also the process of initializing the
.Ar usr
subtree touches some parts of the source tree (this is a bug
in the release build scripts which might go away with time).
.Pp
.It Fl -init
When used together with the
.Fl -src
option, it initializes the
.Ar SRC_PATH/../usr
subtree as necessary to subsequently build picobsd images.
.Pp
.It Fl -modules
Also build kernel modules. They are not stored on the floppy
image but are left available in the build directory.
.Pp
.It Fl n
Make the script non interactive. Do not show the initial menu, and
proceed in the build process without requiring user input.
.Pp
.It Fl v
Make the script verbose, showing the various commands to execute and
waiting for user input before each of them. Useful when debugging.
.Pp
.It Fl -all_in_mfs
Puts the entire content of the filesystem in the memory filesystem
image which is contained in the kernel. This is the default behaviour,
and is extremely useful as the kernel itself can be loaded using
.Xr etherboot
or
.Xr pxeboot
to have a fully functional system.
.Pp
.It Fl -no_all_in_mfs
Leaves files contained into the
.Ar floppy.tree
on the floppy image, so they can be loaded separately from the kernel
(and updated individually to customize the floppy image).
.Pp
.It Fl -floppy_size Ar size
Set the size of the floppy image. Values other than 1440 can
be used for images that are burned into a CDROM.
.Pp
.It Fl c
.It Fl clean
Clean the product of previous builds.
.Xr etherboot
.El
.Sh ENVIRONMENT
As a result of the extreme size limitations, the
.Nm
environment differs from the normal
.Fx
in a number of ways:
.Bl -bullet
.It
There are no dynamic libraries, and there is no directory
.Pa /usr/lib .
As a result, only static executables may be executed.
.It
In order to reduce the size of the executables, all executables on a specific
floppy are joined together as a single executable built with
.Xr crunchgen 1 .
.It
Some programs are supplied in minimalistic versions, specifically
.Nm ns ,
a cut-down version of
.Xr netstat 1 ,
and
.Nm vm ,
a cut-down version of
.Xr vmstat 8 .
.El
.Sh BUILDING picobsd
The
.Nm
sources reside in the hierarchy
.Pa /usr/src/release/picobsd .
In the following discussion, all relative path names are relative to this
directory.  The
.Nm
build process has changed slightly over time, in order to cope
with the unavoidable increase of code size, which requires more and more
tricks to cram as much as possible on
to the floppies.
Starting from
.Fx 4.3 ,
the supported build script is
.Pa /usr/src/release/picobsd/build/picobsd
which can be run from anywhere.
When run in interactive mode (the default without the
.Fl -n
option), the script will let you configure the various parameters
used to build the floppy image.
The following kinds of floppy are envisaged, and we try to keep them
functional and fitting in the 1.44MB floppy despite the unavoidable
increases in the size of the kernel and its applications:
.Bl -hang -width "install  "
.It bridge
is a configuration suitable for bridges, routers and firewalls
.El
.Pp
The following configurations are also present but for reference
only. Many of them are irrimediably out of date and no effort
is done to keep them in good shape:
.Bl -hang -width "install  "
.It dial
is a configuration suitable for dial-out (ppp) networking.
.It install
is a configuration suitable for software installation.
.It isp
is a configuration suitable for dial-in (ppp) networking.
.It net
is a configuration suitable for general networking.
.It router
is a configuration suitable for use as a router.  This particular configuration
aims to work on minimal hardware.
.El
.Pp
These configurations serve only as examples to build your own.
Not all of them have been tested, and you might need small tweaks
to the configuration files to make them work or even fit into
the available disk space as code size increases.
.Pp
You can define your own floppy type, by creating a directory
with a name of your choice (e.g. FOO) which contains
some of the following files and directories. For more
information on how to construct these files, look at one
of the standard
.Nm picobsd
configurations as a reference.
.Pp
.Bl -tag -width "xxxxx" -compact
.It Pa PICOBSD
The kernel configuration file (required). This is a mostly standard
kernel configuration file, possibly stripped down by removing
unnecessary drivers and options to reduce the kernel's size.
.Pp
To be recognised as a
.Nm
kernel config file, the file must also contain the line
beginning with #PicoBSD below, and a matching MD_ROOT_SIZE
option:
.Pp
.Bd -literal -offset indent

#marker    def_sz  init   MFS_inodes    floppy_inodes
#PicoBSD   4200    init   8192          32768
options MD_ROOT_SIZE=4200      # same as def_sz
.Ed
.Pp
to inform the script on the size of the memory filesystem and
a few other information on how to build the image.
.Pp
.It Pa crunch.conf
crunchgen configuration (required). See the
.Xr crunchgen 1
manpage for the syntax.
.Pp
.It Pa config
shell variables, sourced by the
.Pa picobsd
script (optional). Again, look at the standard
.Pp
.It Pa floppy.tree.exclude
files from the standard floppy tree which are not needed (optional).
.Pp
.It Pa floppy.tree/
local additions to the standard floppy tree (optional).
.Pp
.It Pa floppy.tree. Ns ${site}
same as above, site-specific (optional).
.El
.Pp
More information on the build process can be found in the
comments in the
.Pa picobsd
script.
Sample configurations can be found in
.Pa /usr/src/release/picobsd/ Ns ${type} Ns /
.Sh USING ALTERNATE SOURCE TREES
The build script can be instructed use an alternate source tree
using the
.Fl -src Ar SRC_PATH
option.
The tree that you specify must contain full sources for the kernel
and for all programs that you want to include in your image.
As an example, to cross-build the "bridge" floppy
using RELENG_4 sources, you can do the following:
.Bd -literal -offset indent
  cd <some_empty_directory>
  mkdir FOO
  (cd FOO; cvs -d <my_repository> co -r RELENG_4 src )
  picobsd --src FOO/src --init	# this is needed only once
  picobsd --src FOO/src -n -v bridge
.Ed
.Pp
If the build is successful, the directory
.Ar build_dir-bridge/
will contain a
.Ar kernel
that can be downloaded with
.Xr etherboot 8 ,
a floppy image called
.Ar picobsd.bin ,
plus the products of the compilation in other directories.
If you want to modify the source tree in
.Ar FOO/src ,
a new image can be produced by simply running
.Bd -literal -offset indent
  picobsd --src FOO/src -n -v bridge
.Ed
.Pp
whereas if the change affects include files or libraries
you first need to update them e.g. by running first
.Bd -literal -offset indent
  picobsd --src FOO/src --init  # this is needed only once
.Ed
.Pp
as you would normally do for any change of this kind.
.Pp
.Sh BOOTING PicoBSD
To boot
.Nm ,
insert the floppy and reset the machine.  The boot procedure is similar to the
standard
.Fx
boot, but proceeds at a snail's pace.  From the end of the POST
(BIOS Power On Self Test) until the system is up and running takes
anywhere between 1 and 3 minutes.
.Pp
To speed up booting, you can use
.Xr etherboot
to load the preloaded, uncompressed kernel image
which is a byproduct of the
.Nm
build.
In this case
the load time is a matter of a few seconds, even on a 10Mbit/s
ethernet.
.Ss Swap space
After booting,
.Nm
runs entirely from the memory file system.  The floppies are no longer used, and
even if there are hard disk drivers in the
.Nm
kernel, it does not access the drives.  In particular, there is no swap space,
so if you run out of memory, unpredictable things can happen.
.Pp
If you have a disk driver and a disk with a swap partition on it, and the swap
partition does not contain a dump you want to keep, you can use this swap with
.Nm .
Use the
.Xr swapon 8
command.
.Sh SEE ALSO
.Xr crunchgen 1 ,
.Xr swapon 8 ,
.Xr vnconfig 8
.Sh AUTHORS
.An -nosplit
.An Andrzej Bialecki Aq abial@FreeBSD.org ,
with subsequent work on the scripts by
.An Luigi Rizzo Aq luigi@iet.unipi.it
and others.
Man page and
.Pa Makefiles
created by
.An Greg Lehey Aq grog@lemis.com .
.Sh BUGS
In order to build
.Nm ,
the kernel of the system on which it is built must have the
.Xr vn 4
driver installed.
.Pp
The build process must be run as
.Dq root
because of the need of running
.Xr vnconfig 8
and
.Xr mount 8 .
.Pp
Building
.Nm
is still a black art.  The biggest problem is determining what will fit on the
floppies, and the only practical method is trial and error.