284 lines
8.3 KiB
Groff
284 lines
8.3 KiB
Groff
.\" -*- nroff-fill -*-
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.\" $FreeBSD$
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.Dd 23 December 1999
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.Os FreeBSD
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.Dt PicoBSD 8
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.Sh NAME
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.Nm PicoBSD
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.Nd Floppy disk based FreeBSD system
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.Sh SYNOPSIS
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.Nm
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is a minimal implementation of FreeBSD on one or more floppy disks. The
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floppies are required for loading only; the system runs from ramdisk and is thus
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not limited to the speed of the floppies.
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.Sh DESCRIPTION
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The first (and only required)
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.Nm
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floppy contains a compressed kernel and compressed MFS root file system, as well
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as some files in the
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.Pa /etc
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directory. The system loads the kernel in the normal way, uncompresses the file
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system and mounts it as root. It then copies the files in the floppy
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.Pa /etc
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directory to the MFS
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.Pa /etc
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directory and executes a specialized version
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.Pa /etc/rc .
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The standard version of
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.Pa /etc/rc
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prompts for additional floppies and reads them in to the MFS file system.
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.Sh ENVIRONMENT
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As a result of the extreme size limitations, the
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.Nm
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environment differs from the normal FreeBSD in a number of ways:
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.Bl -bullet
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.It
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There are no dynamic libraries, and there is no directory
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.Pa /usr/lib .
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As a result, only static executables may be executed.
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.It
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In order to reduce the size of the executables, all executables on a specific
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floppy are joined together as a single executable built with
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.Xr crunchgen 1 .
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.It
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Some programs are supplied in minimalistic versions, specifically
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.Nm ns ,
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a cut-down version of
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.Nm netstat ,
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and
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.Nm vm ,
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a cut-down version of
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.Nm vmstat .
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.El
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.Sh BUILDING PicoBSD
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The
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.Nm
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sources reside in the hierarchy
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.Pa /usr/src/release/picobsd .
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In the following discussion, all relative path names are relative to this
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directory. The
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.Nm
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build process is designed to be flexible in order to cram as much as possible on
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to the floppies. In particular, the following possibilities exist:
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.Bl -bullet
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.It
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The old style of building uses a script called
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.Pa build/build .
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To use it, change directory to
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.Pa build/
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and run
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.Cm build .
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.Cm build
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is an interactive script which will ask for parameter entries and then build the
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appropriate single floppy version. Five kinds of floppy are envisaged:
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.Bl -hang
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.It dial
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is a configuration suitable for dial-out (ppp) networking.
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.It install
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is a configuration suitable for software installation.
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.It isp
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is a configuration suitable for dial-in (ppp) networking.
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.It net
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is a configuration suitable for general networking.
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.It router
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is a configuration suitable for use as a router. This particular configuration
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aims to work on minimal hardware.
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.El
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.It
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The new style of building uses
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.Cm make .
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The file
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.Pa Makefile
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will build in the directory
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.Pa custom .
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.El
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.Pp
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The build process involves the following steps. In the examples, the
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subdirectory
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.Pa custom
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is used, but the principle also applies to the subdirectories
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.Pa dial ,
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.Pa install ,
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.Pa isp ,
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.Pa net
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and
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.Pa router .
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.Bl -hang
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.It Em Build the kernel.
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Each directory contains a configuration file with a name starting with
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.Pa PICOBSD .
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When building a custom
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.Nm PicoBSD ,
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it is important to review this file carefully. The smallest possible kernel
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occupies about 600 kB after compression, and it is easy to have a kernel as
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large as 900 kB. It is probably not possible to build a first
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.Nm
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floppy with a kernel of 900 kB.
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.It Em Create the MFS image.
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The MFS image for the first floppy is created as a
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.Nm vnode
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file system which is subsequently mounted as
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.Pa /dev/vn0
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on
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.Pa custom/mmnt .
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.It Em Create the crunched executables.
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The executables for the first floppy are built in the directory
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.Pa crunch/crunch1/ .
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The contents of this executable are determined by the file
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.Pa crunch/crunch1/crunch.conf .
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.It Em Build the floppy image.
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A second file system image, which will later become the first floppy, is built
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and mounted as
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.Pa /dev/vn1
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on
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.Pa custom/fmnt .
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It receives the compressed kernel, the compressed MFS file system, the contents
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of the tree
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.Pa floppy.tree/
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and
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.Pa floppy.tree/custom/
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if the latter directory exists. This dual method allows specific files in
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.Pa floppy.tree/custom/
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to overlay files from
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.Pa floppy.tree/ .
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.It Em Create the image for the second floppy.
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Finally, the image for the second floppy is built. There is only one file on
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this floppy, which will be copied to the MFS-relative directory
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.Pa /bin
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at boot time. The contents are built in the directory
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.Pa crunch/crunch2/ .
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The contents of this executable are determined by the file
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.Pa crunch/crunch2/crunch.conf .
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.It Em Copy the data to the floppies.
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The previous steps are performed by the
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.Nm make all
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step.
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.Nm make all
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does not copy data to the floppy disks. Instead, use
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.Nm make floppy
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for the first floppy, and
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.Nm make floppy2
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for the second disk.
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.It Em Create additional floppies.
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You can theoretically possible to read a large number of floppies into the MFS.
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Each additional floppy, including the second, is a gzipped tar file containing
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files relative to
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.Pa /bin .
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You can put any statically linked program on a floppy in this form, and the
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startup routines will automatically read it in. Remember that there are no
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dynamic libraries, so the programs must be static.
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.El
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.\" .Sh FILES
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.\" .Sh EXAMPLES
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.\" This next request is for sections 1, 6, 7, 8 & 9 only
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.\" (command return values (to shell) and
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.\" fprintf/stderr type diagnostics)
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.\" .Sh DIAGNOSTICS
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.\" The next request is for sections 2, 3 and 9 error
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.\" and signal handling only.
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.\" .Sh ERRORS
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.Sh BOOTING PicoBSD
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To boot
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.Nm PicoBSD ,
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insert the floppy and reset the machine. The boot procedure is similar to the
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standard FreeBSD boot, but proceeds at a snail's pace. From the end of the POST
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(BIOS Power On Self Test) until the prompt for the second floppy takes about 3
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minutes.
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.Pp
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When the prompt for additional floppies appears, first insert the floppy in the
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drive, then answer
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.Em y .
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When you have no more floppies, enter
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.Em n .
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This version of
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.Nm
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does not have a root password. If you require greater security, you can copy
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your own
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.Pa /etc/master.passwd
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and possibly
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.Pa /etc/group
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to the first boot floppy. These are the only files you need: the boot process
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generates the files
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.Pa /etc/passwd ,
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.Pa /etc/spwd
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and
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.Pa /etc/pwd.db
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automatically.
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.Ss Swap space
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After booting,
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.Nm
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runs entirely from the MFS file system. The floppies are no longer used, and
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even if there are hard disk drivers in the
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.Nm
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kernel, it does not access the drives. In particular, there is no swap space,
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so if you run out of memory, unpredictable things can happen.
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.Pp
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If you have a disk driver and a disk with a swap partition on it, and the swap
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partition does not contain a dump you want to keep, you can use this swap with
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.Nm PicoBSD .
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Use the
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.Xr swapon 8
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command.
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.Sh RECOVERING CRASHED SYSTEMS
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The
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.Em custom
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.Nm
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configuration contains all the programs that are present on the
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.Em fixit
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floppy, so you can use it instead of the fixit floppy.
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.Sh SEE ALSO
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.Xr crunchgen 1 ,
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.Xr swapon 8 ,
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.Xr vnconfig 8
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.\" .Sh STANDARDS
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.\" .Sh HISTORY
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.Sh AUTHORS
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.An Andrzej Bialecki Aq abial@FreeBSD.org .
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Man page and Makefiles created by
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.An Greg Lehey Aq grog@lemis.com .
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.Sh BUGS
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In order to build
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.Nm PicoBSD ,
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the kernel of the system on which it is built must have the
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.Nm vn
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driver installed.
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.Pp
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The build process must be run as
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.Nm root .
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.Pp
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The build process does not search for unused vnode devices; it uses
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.Pa /dev/vn0
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and
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.Pa /dev/vn1 .
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If these files are not in use by other programs, unexpected behaviour may
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result.
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.Pp
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Building
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.Nm
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is still a black art. The biggest problem is determining what will fit on the
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floppies, and the only practical method is trial and error.
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.Pp
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The original version of
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.Nm
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fits on one floppy. Since FreeBSD 4.0, the kernel is so large that most
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configurations will need a second floppy to do any productive work.
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Nevertheless, it should be possible to create minimal kernels which will fit
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alongside sufficient other programs on a single floppy.
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.Pp
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The approach of building executables with
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.Xr crunchgen 1
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means that considerable duplication of libraries occurs between the floppies.
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.Pp
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At the current time (December 1999), the old-style build is broken in FreeBSD
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-CURRENT. In view of the significant increase in size of the 4.x kernel
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compared to the 3.x kernel, it is not certain that it can be fixed.
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.Pp
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.Nm
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has suffered some bit rot in 1999, and currently most of the old-style
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configurations do not build.
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.Pp
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There appears to be no way to get
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.Nm Emacs
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to run on
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.Nm PicoBSD .
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