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\author{Robert Heller \\ Deepwoods Software \\ Wendell, MA, USA \thanks{Copyright (C) 2006 Robert
heller.}}
\date{March 17, 2006}
\title{Partitioning for Linux}
\emergencystretch=8pt
\begin{document}
\maketitle

\begin{abstract}
This article discusses some of the things to consider when
planning the partitioning of a Linux system.  These considerations
include thoughts on how different directories will be used and how the
usage of different directories might suggest how to partition your disk
space.  Also my thoughts on the relationship between backup strategies
and partitioning are covered.
\end{abstract}

\tableofcontents

\section{The unified UNIX directory tree.}

The overall file system structure on a UNIX system\footnote{Linux's file
system structure is a UNIX file system structure.} is always a single
tree, no matter how many or how few physical or logical disks might be
connected to it.  This differs from MS-Windows, where each disk
(physical or logical) gets its own drive letter and has its own
independent directory tree root.  Under UNIX (or Linux), having more
than one physical or logical disk is generally invisible to the user,
since each disk is seamlessly integrated into the directory tree.  This
means there is never an absolute need to have everything on one disk and
means it is possible to have any number of physical or logical disks and
that having more than one physical or logical disk has no effect on how
the operating system is laid out and has no effect in terms of how
programs are installed and installed programs can always find their data
and configuration files in standard places without needing to know which
logical or physical disk a given directory resides on.

\section{One big partition vs. many smaller partitions.}

Many people would like to install Linux (or other UNIX style operating
systems) all on a single partition.  Yes, one can do this and generally
it will work fine.  There are, however, various reasons to install
Linux/UNIX on a number of different partitions.  These reasons relate to
efficient backup strategies, user and system protection issues
(protecting users from system problems and protecting the system from
user problems and protecting users from each other) and to help the
system cope with unusual disk usage issues by certain daemon processes.

\section{Common partitioning schemes.}

The most common partitioning scheme separates the directory tree into 4
classes: core system, system volatile, user static, and user volatile
file areas.  Generally this scheme starts out with four
partitions\footnote{We will ignore the swap partition for the time
being, since the swap partition is generally never part of the visible
system directory tree.}: root (mounted under /), var (mounted under
/var), usr (mounted under /usr) and home (mounted under /home). 
Generally the root and var file systems can be relatively small (about
1 gig for a typical modern Linux distribution) and the usr and home
file system can be somewhat larger (about 4-6 gig for usr and arbitrary
large for home).  

The root file system contains the core system files. This includes the
kernel itself (generally in /boot), the base set of user and system
utilities (in /bin and /sbin), the system configuration (in /etc), the
essential libraries and kernel modules (in /lib), and the device files
(in /dev). These directories contain the minimal set of files and
directories needed to boot up a Linux system, at least into single user
mode.  Most of the files on this file system do not change much.  Mostly
only a few of the files under /etc change at all (generally manually by
the system administrator), once the system has been installed and
configured.

The var partition contains the system volatile data files.  This includes
daemon\footnote{A UNIX server process is known as a ``daemon''.} pid
and lock files as well as the spool and data directories used by various
daemons. This file system (mounted under /var) is expected to be
constantly changing over the course of normal system operations, mostly
by daemon processes.

The usr partition contains the bulk of the programs, libraries,
documentation, and constant data used by the normal user(s) of the
computer system.  Except when new system software is installed or
existing software is upgraded, files on this file system change not at
all. 

Finally, the home file system contains the personal files of the
end-user(s) of the computer.  The files on this partition are regularly
being created, deleted, and changed, generally at the whim of the
end-user(s).

So, the first pass at creating partitions for a Linux installation would be
something like this subset of the file systems on my home desktop
machine (36gig SCSI disk):

\vspace*{\baselineskip}

\begin{tabular}{lrrrrl}
Filesystem & Size & Used & Avail & Use\% & Mounted on \\
/dev/sda1  & 1011M& 151M &  809M &  16\% & / \\
/dev/sda7  &  5.9G& 2.7G &  2.9G &  47\% & /home \\
/dev/sda3  &  5.9G& 3.5G &  2.1G &  63\% & /usr \\
/dev/sda5  & 1011M& 230M &  730M &  24\% & /var \\
\end{tabular}

\vspace*{\baselineskip}

This uses roughly 14 gig worth of disk space.  If you have additional
disk space, you can make the /home file system larger\footnote{But
don't forget about a swap partition!}. I often limit the size of the
/home partition, since that keeps my backups limited in size and use the
``extra'' space on the disk for a not backed up scratch file system. 
This scratch file system (which I usually mount under /scratch)
contains random files I don't need to back up, such as files I
downloaded from the Internet (which I can always download again) or
things like image files from a photo CD (which are implicitly backed
up on the CD itself).

Here is another example, from my laptop, which has a 40 gig IDE disk:

\vspace*{\baselineskip}

\begin{tabular}{lrrrrl}
Filesystem & Size & Used & Avail & Use\% & Mounted on\\
/dev/hda1  &  966M & 285M & 632M & 32\% & /\\
/dev/hda5  &  3.8G & 255M & 3.4G &  7\% & /home\\
/dev/hda6  &  3.8G & 1.8G & 1.8G & 51\% & /mp3s\\
/dev/hda7  &   24G & 3.7G &  20G & 16\% & /scratch\\
/dev/hda3  &  3.8G & 2.2G & 1.5G & 61\% & /usr\\
\end{tabular}

\vspace*{\baselineskip}

I've set aside a 4 gig partition to hold my MP3 files--I use my laptop
as a sort of big bulky IPod.  Virtually all of the MP3 files are ripped
from CDs I own.  Thus all of the files on the /mp3s file system are
re-creatable, especially since I do have a backup of the scripts I used
to extract and convert the audio files on the CDs on my desktop machine.

And yet another example from my model railroad control system:

\vspace*{\baselineskip}

\begin{tabular}{lrrrrl}
Filesystem & Size & Used & Avail & Use\% & Mounted on\\
/dev/hda1  &  966M & 232M & 685M & 26\% & /\\
/dev/hda6  &  7.6G & 139M & 7.1G &  2\% & /home\\
/dev/hda7  &   12G & 3.1G & 7.7G & 29\% & /scratch\\
/dev/hda3  &  5.7G & 2.2G & 3.2G & 42\% & /usr\\
/dev/hda5  &  1.9G & 198M & 1.6G & 11\% & /var\\
/dev/hda8  &  2.9G & 1.8G & 931M & 67\% & /WBL3\\
\end{tabular}

\vspace*{\baselineskip}

In addition to a (large) scratch file system, I also have a file system
that contains ISO images of the operating system's distribution CDs
(/WBL3--White Box Linux 3.0).

\section{Additional thoughts about special sorts of server classes.}

On a server machine, it is often reasonable and very desirable to set
aside one or more file systems (generally mounted somewhere under /var)
for the volatile data used by the server's daemons:

\vspace*{\baselineskip}

\begin{centering}
\begin{tabular}{|l|r|p{1.125in}|}
\hline
Daemon&Typical mount point&Description \\
\hline
Mail server (sendmail) & /var/spool/mail& Mail spool
and queue files \\
&/var/spool/mqueue& \\
\hline
News server (inn) & /var/spool/news& News articles \\
\hline
Print server (lpd, cups) & /var/spool/lpd & Spooled print jobs \\
\hline
Web server (Apache) & /var/www & Web pages \\
\hline
Database server (PostgreSQL) & /var/lib/pgsql & Database files \\
\hline
\end{tabular} \\
\end{centering}

\section{Conclusions.}

In conclusion, I'd like to say that there is no one ``one size fits
all'' solution to how to partition your hard drive in preparation to the
installation of Linux.  There are many factors that need to be
considered, including who will be using the system, how will they be
using the system, how you plan on backing up files, how you (as system
administrator) plan on resolving disk usage disputes amongst users, and
considerations regarding server process disk needs.  With a little
careful thought and planning it is possible to come up with a well
crafted partitioning scheme that will serve you for the life of the
system (or at least the life of the hard drive(s)).

\end{document}