os/doc
3
0
Fork 0
Code Issues Pull requests Projects Releases Wiki Activity

A new article explaining how best to use FreeBSD on solid state media.

Browse source 
Submitted by:	John Kozubik <john@kozubik.com>
This commit is contained in:
Nik Clayton 2001-06-20 16:12:33 +00:00
parent 5f4f6b445d
commit 35c396b859
Notes: svn2git 2020-12-08 03:00:23 +00:00 
svn path=/head/; revision=9649
2 changed files with 654 additions and 0 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

24
en_US.ISO8859-1/articles/solid-state/Makefile Normal file
View file

@ -0,0 +1,24 @@
#
# $FreeBSD: doc/en_US.ISO8859-1/articles/committers-guide/Makefile,v 1.4 2001/04/08 17:26:59 nik Exp $
#
#
DOC?= article
FORMATS?= html
INSTALL_COMPRESSED?= gz
INSTALL_ONLY_COMPRESSED?=
JADEFLAGS+= -V %generate-article-toc%
#
# SRCS lists the individual SGML files that make up the document. Changes
# to any of these files will force a rebuild
#
# SGML content
SRCS= article.sgml
DOC_PREFIX?= ${.CURDIR}/../../..
.include "${DOC_PREFIX}/share/mk/doc.project.mk"

630
en_US.ISO8859-1/articles/solid-state/article.sgml Normal file
View file

@ -0,0 +1,630 @@
<!-- Copyright (c) 2001 The FreeBSD Documentation Project
Redistribution and use in source (SGML DocBook) and 'compiled' forms
(SGML, HTML, PDF, PostScript, RTF and so forth) with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code (SGML DocBook) must retain the above
copyright notice, this list of conditions and the following
disclaimer as the first lines of this file unmodified.
2. Redistributions in compiled form (transformed to other DTDs,
converted to PDF, PostScript, RTF and other formats) must reproduce
the above copyright notice, this list of conditions and the
following disclaimer in the documentation and/or other materials
provided with the distribution.
THIS DOCUMENTATION IS PROVIDED BY THE FREEBSD DOCUMENTATION PROJECT "AS
IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL NIK CLAYTON BE LIABLE FOR ANY
DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
ANY WAY OUT OF THE USE OF THIS DOCUMENTATION, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
$FreeBSD$
-->
<!DOCTYPE article PUBLIC "-//FreeBSD//DTD DocBook V4.1-Based Extension//EN" [
<!ENTITY % man PUBLIC "-//FreeBSD//ENTITIES DocBook Manual Page Entities//EN">
%man;
<!ENTITY legalnotice SYSTEM "../../share/sgml/legalnotice.sgml">
]>
<article>
<articleinfo>
<title>FreeBSD and Solid State Devices</title>
<authorgroup>
<author>
<firstname>John</firstname>
<surname>Kozubik</surname>
<affiliation>
<address><email>john@kozubik.com</email></address>
</affiliation>
</author>
</authorgroup>
<pubdate>$FreeBSD$</pubdate>
<copyright>
<year>2001</year>
<holder>The FreeBSD Documentation Project</holder>
</copyright>
&legalnotice;
<abstract>
<para>This article covers the use of solid state disk devices in FreeBSD
to create embedded systems.</para>
<para>Embedded systems have the advantage of increased stability due to
the lack of integral moving parts (hard drives). Account must be
taken, however, for the generally low disk space available in the
system and the durability of the storage medium.</para>
<para>Specific topics to be covered include the types and attributes of
solid state media suitable for disk use in FreeBSD, kernel options
that are of interest in such an environment, the
<filename>rc.diskless</filename> mechanisms that automate the
initialization of such systems and the need for read-only filesystems,
and building file systems from scratch. The article will conclude
with some general strategies for small and read-only FreeBSD
environments.</para>
</abstract>
</articleinfo>
<sect1 id="intro">
<title>Solid State Disk Devices</title>
<para>The scope of this article will be limited to solid state disk
devices made from flash memory. Flash memory is a solid state memory
(no moving parts) that is non-volatile (the memory maintains data even
after all power sources have been disconnected). Flash memory can
withstand tremendous physical shock and is reasonably fast (the flash
memory solutions covered in this article are slightly slower than a EIDE
hard disk for write operations, and much faster for read operations).
One very important aspect of flash memory, the ramifications of which
will be discussed later in this article, is that each sector has a
limited rewrite capacity. You can only write, erase, and write again to
a sector of flash memory a certain number of times before the sector
becomes permanently unusable. Although many flash memory products
automatically map bad blocks, and although some even distribute write
operations evenly throughout the unit, the fact remains that there
exists a limit to the amount of writing that can be done to the device.
Competitive units have between 1,000,000 and 10,000,000 writes per
sector in their specification. This figure varies due to the
temperature of the environment.</para>
<para>Specifically, we will be discussing ATA compatible compact-flash
units and the M-Systems Disk-On-Chip flash memory unit. ATA compatible
compact-flash cards are quite popular as storage media for digital
cameras. Of particular interest is the fact that they pin out directly
to the IDE bus and are compatible with the ATA command set. Therefore,
with a very simple and low-cost adaptor, these devices can be attached
directly to an IDE bus in a computer. Once implemented in this manner,
operating systems such as FreeBSD see the device as a normal hard disk
(albeit small). The M-Systems Disk-On-Chip product is based on the same
underlying flash memory technology as ATA compatible compact-flash
cards, but resides in a DIP form factor and is not ATA compatible. To
use such a device, not only must you install it on a motherboard that
has a Disk-On-Chip socket, you must also build the `fla` driver into any
FreeBSD kernel you wish to use it with. Further, there is critical,
manufacturer-specific data residing in the boot sector of this device,
so you must take care not to install the FreeBSD (or any other) boot
loader when using this.</para>
<para>Other solid state disk solutions do exist, but their expense,
obscurity, and relative unease of use places them beyond the scope of
this article.</para>
</sect1>
<sect1 id="kernel">
<title>Kernel Options</title>
<para>A few kernel options are of specific interest to those creating
an embedded FreeBSD system.</para>
<para>First, all embedded FreeBSD systems that use flash memory as system
disk will be interested in memory disks and memory filesystems. Because
of the limited number of writes that can be done to flash memory, the
disk and the filesystems no the disk will most likely be mounted
read-only. In this environment, filesystems such as
<filename>/tmp</filename> and <filename>/var</filename> are mounted as
memory filesystems to allow the system to create logs and update
counters and temporary files. Memory filesystems are a critical
component to a successful solid state FreeBSD implementation.</para>
<para>You should make sure the following lines exist in your kernel
configuration file:</para>
<programlisting>options MFS # Memory Filesystem
options MD_ROOT # md device usable as a potential root device
pseudo-device md # memory disk</programlisting>
<para>Second, if you will be using the M-Systems Disk-On-Chip product, you
must also include this line:</para>
<programlisting>device fla0 at isa?</programlisting>
</sect1>
<sect1 id="ro-fs">
<title><filename>rc.diskless</filename> and Read-Only Filesystems</title>
<para>The post-boot initialization of an embedded FreeBSD system is
controlled by <filename>/etc/rc.diskless2</filename>
(<filename>/etc/rc.diskless1</filename> is for BOOTP diskless boot).
This initialization script is invoked by placing a line in
<filename>/etc/rc.conf</filename> as follows:</para>
<programlisting>diskless_mount=/etc/rc.diskless2</programlisting>
<para><filename>rc.diskless2</filename> mounts <filename>/var</filename>
as a memory filesystem, makes a configurable list of directories in
<filename>/var</filename> with the &man.mkdir.1; command, changes modes
on some of those directories, and extracts a list of device entries to
copy to a writable (again, a memory filesystem)
<filename>/dev</filename> partition. In the execution of
<filename>/etc/rc.diskless2</filename>, one other
<filename>rc.conf</filename> variable comes into play -
<literal>varsize</literal>. The <filename>/etc/rc.diskless2</filename>
file creates a <filename>/var</filename> partition based on the value of
this variable in <filename>rc.conf</filename>:</para>
<programlisting>varsize=8192</programlisting>
<para>Remember that this value is in sectors. The creation of the
<filename>/dev</filename> partition by
<filename>/etc/rc.diskless2</filename>, however, is governed by a
hard-coded value of 4096 sectors. It is trivial to change this entry in
the <filename>/etc/rc.diskless2</filename> file itself, although you
shouldn't need more space than that for
<filename>/dev</filename>.</para>
<para>It is important to remember that the
<filename>/etc/rc.diskless2</filename> script assumes that you have
already removed your conventional <filename>/tmp</filename> partition
and replaced it with a symbolic link to <filename>/var/tmp</filename>.
Because <filename>tmp</filename> is one of the directories created in
<filename>/var</filename> by the <filename>/etc/rc.diskless2</filename>
script, and because <filename>/var</filename> is a memory file system
(which is mounted read-write), <filename>/tmp</filename> will now be a
directory that is read-write as well.</para>
<para>The fact that <filename>/var</filename> and
<filename>/dev</filename> are read-write filesystems is an important
distinction, as the <filename>/</filename> partition (and any other
partitions you may have on your flash media) should be mounted
read-only. Remember that in <xref linkend="intro"> we detailed the
limitations of flash memory - specifically the limited write capability.
The importance of not mounting filesystems on flash media read-write,
and the importance of not using a swap file cannot be overstated. A
swap file on a busy system can burn through a piece of flash media in
less than one year. Heavy logging or temporary file creation and
destruction can do the same. Therefore, in addition to removing the
<literal>swap</literal> and <literal>/proc</literal> entries from your
<filename>/etc/fstab</filename> file, you should also change the Options
field for each filesystem to <literal>ro</literal> as follows:</para>
<programlisting># Device Mountpoint FStype Options Dump Pass#
/dev/ad0s1a / ufs ro 1 1</programlisting>
<para>A few applications in the average system will immediately begin to
fail as a result of this change. For instance, ports will not install
from the ports tree because the
<filename>/var/db/port.mkversion</filename> file does not exist. cron
will not run properly as a result of missing cron tabs in the
<filename>/var</filename> created by
<filename>/etc/rc.diskless2</filename>, and syslog and dhcp will
encounter problems as well as a result of the read-only filesystem and
missing items in the <filename>/var</filename> that
<filename>/etc/rc.diskless2</filename> has created. These are only
temporary problems though, and are addressed, along with solutions to
the execution of other common software packages in
<xref linkend="strategies">.</para>
<para>An important thing to remember is that a filesystem that was mounted
read-only with <filename>/etc/fstab</filename> can be made read-write at
any time by issuing the command:</para>
<screen>&prompt.root; <userinput>/sbin/mount -uw <replaceable>partition</replaceable></userinput></screen>
<para>and can be toggled back to read-only with the command:</para>
<screen>&prompt.root; <userinput>/sbin/mount -ur <replaceable>partition</replaceable></userinput></screen>
</sect1>
<sect1>
<title>Building a File System From Scratch</title>
<para>Because ATA compatible compact-flash cards are seen by FreeBSD as
normal IDE hard drives, as is a M-Systems Disk-On-Chip product (when you
are running a kernel with the fla driver built in) you could
theoretically install FreeBSD from the network using the kern and
mfsroot floppies or from a CD. Other than the fact that you should not
write a boot-loader of any kind to the M-Systems device, no special
instructions are needed.</para>
<para>However, even a small installation of FreeBSD using normal
installation procedures can produce a system in size of greater than 200
megabytes. Because most people will be using smaller flash memory
devices (128 megabytes is considered fairly large - 32 or even 16
megabytes is common) an installation using normal mechanisms is not
possible&mdash;there is simply not enough disk space for even the
smallest of conventional installations.</para>
<para>The easiest way to overcome this space limitation is to install
FreeBSD using conventional means to a normal hard disk. After the
installation is complete, pare down the operating system to a size that
will fit onto your flash media, then tar the entire filesystem. The
following steps will guide you through the process of preparing a piece
of flash memory for your tarred filesystem. Remember, because a normal
installation is not being performed, operations such as partitioning,
labeling, file-system creation, etc. need to be performed by hand. In
addition to the kern and mfsroot floppy disks, you will also need to use
the fixit floppy. If you are using a M-Systems Disk-On-Chip, the kernel
on your kern floppy must have the <literal>fla</literal> option detailed
in <xref linkend="kernel"> compiled into it. Please see
<xref linkend="kern.flp"> for instructions on creating a new kernel for
<filename>kern.flp</filename>.</para>
<procedure>
<step>
<title>Partitioning your flash media device</title>
<para>After booting with the kern and mfsroot floppies, choose
<literal>custom</literal> from the installation menu. In the custom
installation menu, choose <literal>partition</literal>. In the
partition menu, you should delete all existing partitions using the
<keycap>d</keycap> key. After deleting all existing partitions,
create a partition using the <keycap>c</keycap> key and accept the
default value for the size of the partition. When asked for the
type of the partition, make sure the value is set to
<literal>165</literal>. Now write this partition table to the disk
by pressing the <keycap>w</keycap> key (this is a hidden option on
this screen). When presented with a menu to choose a boot manager,
take care to select <literal>None</literal> if you are using an
M-Systems Disk-On-Chip. If you are using a ATA compatible compact
flash card, you should choose the FreeBSD Boot Manager. Now press
the <keycap>q</keycap> key to quit the partition menu. You will be
shown the boot manager menu once more - repeat the choice you made
earlier.</para>
</step>
<step>
<title>Creating file systems on your flash memory device</title>
<para>Exit the custom installation menu, and from the main
installation menu choose the <literal>fixit</literal> option. After
entering the fixit environment, enter the following commands:</para>
<informaltable frame="none">
<tgroup cols="2">
<thead>
<row>
<entry align="center">ATA compatible</entry>
<entry align="center">Disk-On-Chip</entry>
</row>
</thead>
<tbody>
<row>
<entry><para><screen>&prompt.root; <userinput>mknod /dev/ad0c c 116 0</userinput>
&prompt.root; <userinput>mknod /dev/ad0c c 116 2</userinput>
&prompt.root; <userinput>disklabel -e /dev/ad0c</userinput></screen></para></entry>
<entry><para><screen>&prompt.root; <userinput>mknod /dev/fla0c c 102 2</userinput>
&prompt.root; <userinput>mknod /dev/fla0c c 102 2</userinput>
&prompt.root; <userinput>disklabel -e /dev/fla0c</userinput></screen></para></entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>At this point you will have entered the vi editor under the
auspices of the disklabel command. If you are using Disk-On-Chip,
the first step will be to change the type value near the beginning
of the file from <literal>ESDI</literal> to
<literal>DOC2K</literal>. Next, regardless of whether you are using
Disk-On-Chip or ATA compatible compact flash media, you need to add
an a: line at the end of the file. This <literal>a:</literal> line
should look like:</para>
<programlisting>a: <replaceable>123456</replaceable> 0 4.2BSD 0 0</programlisting>
<para>Where <replaceable>123456</replaceable> is a number that is
exactly the same as the number in the existing <literal>c:</literal>
entry for size. Basically you are duplicating the existing
<literal>c:</literal> line as an <literal>a:</literal> line, making
sure that fstype is <literal>4.2BSD</literal>. Save the file and
exit.</para>
<informaltable frame="none">
<tgroup cols="2">
<thead>
<row>
<entry align="center">ATA compatible</entry>
<entry align="center">Disk-On-Chip</entry>
</row>
</thead>
<tbody>
<row>
<entry><para><screen>&prompt.root; <userinput>disklabel -B -r /dev/ad0c</userinput>
&prompt.root; <userinput>newfs /dev/ad0a</userinput></screen></para></entry>
<entry><para><screen>&prompt.root; <userinput>disklabel -B -r /dev/fla0c</userinput>
&prompt.root; <userinput>newfs /dev/fla0a</userinput></screen></para></entry>
</row>
</tbody>
</tgroup>
</informaltable>
</step>
<step>
<title>Placing your filesystem on the flash media</title>
<para>Mount the newly prepared flash media:</para>
<informaltable frame="none">
<tgroup cols="2">
<thead>
<row>
<entry align="center">ATA compatible</entry>
<entry align="center">Disk-On-Chip</entry>
</row>
</thead>
<tbody>
<row>
<entry><para><screen>&prompt.root; <userinput>mount /dev/ad0a /flash</userinput></screen></para></entry>
<entry><para><screen>&prompt.root; <userinput>mount /dev/fla0 /flash</userinput></screen></para></entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>Bring this machine up on the network so we may transfer our tar
file and explode it onto our flash media filesystem. One example of
how to do this is:</para>
<screen>&prompt.root; <userinput>ifconfig xl0 192.168.0.10 netmask 255.255.255.0</userinput>
&prompt.root; <userinput>route add default 192.168.0.1</userinput></screen>
<para>Now that the machine is on the network, transfer your tar file.
You may be faced with a bit of a dilemma at this point - if your
flash memory part is 128 megabytes, for instance, and your tar file
is larger than 64 megabytes, you cannot have your tar file on the
flash media at the same time as you explode it - you will run out of
space. One solution to this problem, if you are using ftp, is to
untar the file while it is transferred over ftp. If you perform
your transfer in this manner, you will never have the tar file and
the tar contents on your disk at the same time:</para>
<screen><prompt>ftp></prompt> <userinput>get tarfile.tar "| tar xvf -"</userinput></screen>
<para>If your tarfile is gzipped, you can accomplish this as
well:</para>
<screen><prompt>ftp></prompt> <userinput>get tarfile.tar "| zcat | tar xvf -"</userinput></screen>
<para>After the contents of your tarred filesystem are on your flash
memory file system, you can unmount the flash memory and
reboot:</para>
<screen>&prompt.root; <userinput>cd /</userinput>
&prompt.root; <userinput>umount /flash</userinput>
&prompt.root; <userinput>exit</userinput></screen>
<para>Assuming that you configured your filesystem correctly when it
was built on the normal hard disk (with your filesystems mounted
read-only, and with the necessary options compiled into the kernel)
you should now be successfully booting your FreeBSD embedded
system.</para>
</step>
</procedure>
</sect1>
<sect1 id="kern.flp">
<title>Building a <filename>kern.flp</filename> Installation Floppy with
the fla Driver</title>
<note>
<para>This section of the article is relevant only to those using
M-Systems Disk-On-Chip flash media.</para>
</note>
<para>It is possible that your <filename>kern.flp</filename> boot floppy
does not have a kernel with the <devicename>fla</devicename> driver
compiled into it necessary for the system to recognize the Disk-On-Chip.
If you have booted off of the installation floppies and are told that no
disks are present, then you are probably lacking the
<devicename>fla</devicename> driver in your kernel.</para>
<para>After you have built a kernel with <devicename>fla</devicename>
support that is smaller than 1.4 megabytes, you can create a custom
<filename>kern.flp</filename> floppy image with it by following these
instructions:</para>
<procedure>
<step>
<para>Obtain an existing kern.flp image file</para>
</step>
<step>
<para><screen>&prompt.root; <userinput>vnconfig vn0c kern.flp</userinput></screen></para>
</step>
<step>
<para><screen>&prompt.root; <userinput>mount /dev/vn0c /mnt</userinput></screen></para>
</step>
<step>
<para>Place your kernel file into <filename>/mnt</filename>, replacing
the existing one</para>
</step>
<step>
<para><screen>&prompt.root; <userinput>vnconfig -d vn0c</userinput></screen></para>
</step>
</procedure>
<para>Your <filename>kern.flp</filename> file now has your new kernel on it.</para>
</sect1>
<sect1 id="strategies">
<title>System Strategies for Small and Read Only Environments</title>
<para>In <xref linkend="ro-fs">, it was pointed out that the
<filename>/var</filename> filesystem constructed by
<filename>/etc/rc.diskless2</filename> and the presence of a read-only
root filesystem causes problems with many common software packages used
with FreeBSD. In this article, suggestions for successfully running
cron, syslog, ports installations, and the Apache web server will be
provided.</para>
<sect2>
<title>cron</title>
<para>In <filename>/etc/rc.diskless2</filename> there is a variable
named <literal>var_dirs</literal>. This variable consists of a
space-delimited list of directories that will be created inside of
<filename>/var</filename> after it is mounted as a memory filesystem.
<filename>cron</filename> and <filename>cron/tabs</filename> are not
in that list, and without those directories, cron will complain. By
inserting <literal>cron</literal>, <literal>cron/tabs</literal>, and
perhaps even <literal>at</literal>, and <literal>at/jobs</literal> as
elements of that variable, you will facilitate the running of the
&man.cron.8; and &man.at.1; daemons.</para>
<para>However, this still does not solve the problem of maintaining cron
tabs across reboots. When the system reboots, the
<filename>/var</filename> filesystem that is in memory will disappear
and any cron tabs you may have had in it will also disappear.
Therefore, one solution would be to create cron tabs for the users
that need them, mount your <filename>/</filename> filesystem as
read-write and copy those cron tabs to somewhere safe, like
<filename>/etc/tabs</filename>, then add a line to the end of
<filename>/etc/rc.diskless2</filename> that copies those crontabs into
<filename>/var/cron/tabs</filename> after that directory has been
created during system initialization. You may also need to add a line
that changes modes and permissions on the directories you create and
the files you copy with <filename>/etc/rc.diskless2</filename>.</para>
</sect2>
<sect2>
<title>syslog</title>
<para><filename>syslog.conf</filename> specifies the locations of
certain log files that exist in <filename>/var/log</filename>. These
files are not created by <filename>/etc/rc.diskless2</filename> upon
syste initialization. Therefore, somewhere in
<filename>/etc/rc.diskless2</filename>, after the section that creates
the directories in <filename>/var</filename>, you will need to add
something like this:</para>
<screen>&prompt.root; <userinput>touch /var/log/security /var/log/maillog /var/log/cron /var/log/messages</userinput>
&prompt.root; <userinput>chmod 0644 /var/log/*</userinput></screen>
<para>You will also need to add the log directory to the list of
directories that <filename>/etc/rc.diskless2</filename>
creates.</para>
</sect2>
<sect2>
<title>ports installation</title>
<para>Before discussing the changes necessary to successfully use the
ports tree, a reminder is necessary regarding the read-only nature of
your filesystems on the flash media. Since they are read-only, you
will need to temporarily mount them read-write using the mount syntax
shown in <xref linkend="ro-fs">. You should always remount those
filesystems read-only when you are done with any maintenance - it is
dangerous to leave them in read-write mode lest a process begin
logging or otherwise writing regularly to the flash media and wearing
it out over time.</para>
<para>To make it possible to enter a ports directory and successfully
run <command>make install</command>, it is necessary for the file
<filename>/var/db/port.mkversion</filename> to exist, and that it have
a correct date in it. Further, we must create a packages directory on
a non-memory filesystem that will keep track of our packages across
reboots. Because it is necessary to mount your filesystems as
read-write for the installation of a package anyway, it is sensible to
assume that an area on the flash media can also be used for package
information to be written to.</para>
<para>First, create a package database directory. This is normally in
<filename>/var/db/pkg</filename>, but we cannot place it there as it
will disappear every time the system is booted.</para>
<screen>&prompt.root; <userinput>mkdir /etc/pkg</userinput></screen>
<para>Now, add a line to <filename>/etc/rc.diskless2</filename> that
links the <filename>/etc/pkg</filename> directory to
<filename>/var/db/pkg</filename>. An example:</para>
<screen>&prompt.root; <userinput>ln -s /etc/pkg /var/db/pkg</userinput></screen>
<para>Add another line in <filename>/etc/rc.diskless2</filename> that
creates and populates
<filename>/var/db/port.mkversion</filename></para>
<screen>&prompt.root; <userinput>touch /var/db/port.mkversion</userinput>
&prompt.root; <userinput>chmod 0644 /var/db/port.mkversion</userinput>
&prompt.root; <userinput>echo <replaceable>20010412</replaceable> >> /var/db/port.mkversion</userinput></screen>
<para>where <replaceable>20010412</replaceable> is a date that is
appropriate for your particular release of FreeBSD</para>
<para>Now, any time that you mount your file systems as read-write and
install a package, the <command>make install</command> will work
because it finds a suitable
<filename>/var/db/port.mkversion</filename>, and package information
will be written successfully to <filename>/etc/pkg</filename> (because
the filesystem will, at that time, be mounted read-write) which will
always be available to the operating system as
<filename>/var/db/pkg</filename>.</para>
</sect2>
<sect2>
<title>Apache Web Server</title>
<para>Apache keeps pid files and logs in
<filename><replaceable>apache_install</replaceable>/logs</filename>.
Since this directory no doubt exists on a read-only file system, this
will not work. It is necessary to add a new directory to the
<filename>/etc/rc.diskless2</filename> list of directories to create
in <filename>/var</filename>, to link
<filename><replaceable>apache_install</replaceable>/logs</filename> to
<filename>/var/log/apache</filename>. It is also necessary to set
permissions and ownership on this new directory.</para>
<para>First, add the directory <literal>log/apache</literal> to the list
of directories to be created in
<filename>/etc/rc.diskless2</filename>.</para>
<para>Second, add these commands to
<filename>/etc/rc.diskless2</filename> after the directory creation
section:</para>
<screen>&prompt.root; <userinput>chmod 0774 /var/log/apache</userinput>
&prompt.root; <userinput>chown nobody:nobody /var/log/apache</userinput></screen>
<para>Finally, remove the existing
<filename><replaceable>apache_install</replaceable>/logs</filename>
directory, and replace it with a link:</para>
<screen>&prompt.root; <userinput>rm -rf (apache_install)/logs</userinput>
&prompt.root; <userinput>ln -s /var/log/apache (apache_install)/logs</userinput></screen>
</sect2>
</sect1>
</article>