Partitioning your disk simply refers to the act of breaking up your disk into sections. Each section is then independent of the others. It's roughly equivalent to putting up walls in a house; if you add furniture to one room it doesn't affect any other room.
If you already have an operating system on your system (Windows95, Windows NT, OS/2, MacOS, Solaris, FreeBSD, …) and want to stick Linux on the same disk, you will probably need to repartition the disk. In general, changing a partition with a filesystem already on it will destroy any information there. Thus you should always make backups before doing any repartitioning. Using the analogy of the house, you would probably want to move all the furniture out of the way before moving a wall or you risk destroying it.
At a bare minimum, GNU/Linux needs one partition for itself. You can have a single partition containing the entire operating system, applications, and your personal files. Most people feel that the swap partition is also a necessity, although it's not strictly true. ``Swap'' is scratch space for an operating system, which allows the system to use cheap disk storage as ``virtual memory''. By putting swap on a separate partition, Linux can make much more efficient use of it. It is possible to force Linux to use a regular file as swap, but it is not recommended.
Most people choose to give GNU/Linux more than the minimum number of partitions, however. There are two reasons you might want to break up the filesystem into a number of smaller partitions. The first is for safety. If something happens to corrupt the file system, generally only one partition is affected. Thus, you only have to replace (from the backups you've been carefully keeping) a portion of your system. At a bare minimum, you should consider creating what is commonly called a ``root partition''. This contains the most essential components of the system. If any other partitions get corrupted, you can still boot into GNU/Linux to fix the system. This can save you the trouble of having to reinstall the system from scratch.
The second reason is generally more important in a business setting, but it
really depends on your use of the machine. Suppose something runs out of
control and starts eating disk space. If the process causing the problem
happens to have root privileges (the system keeps a percentage of the disk away
from users), you could suddenly find yourself out of disk space. This is not
good as the OS needs to use real files (besides swap space) for many things.
It may not even be a problem of local origin. For example, getting spammed
with e-mail can easily fill a partition. By using more partitions, you protect
the system from many of these problems. Using mail as an example again, by
putting /var/spool/mail on its own partition, the bulk of the
system will work even if you get spammed.
The only real drawback to using more partitions is that it is often difficult to know in advance what your needs will be. If you make a partition too small then you will either have to reinstall the system or you will be constantly moving things around to make room in the undersized partition. On the other hand, if you make the partition too big, you will be wasting space that could be used elsewhere. Disk space is cheap nowadays, but why throw your money away?
The following list describes some important directories. It should help you to find out what your partitioning scheme should be. If this is too confusing for you, just ignore it and reread it when you read the rest of the installation manual.
/: root represents the starting point of the directory hierarchy.
It contains the essential programs that the computer can boot. This includes
the kernel, system libraries, configuration files in /etc and
various other needed files. Typically 30-50 MB are needed but this may vary.
Note: do not partition /etc, /bin,
/sbin, /lib or /dev as its own
partition; you won't be able to boot.
/dev: this directory contains the various device files which are
interfaces to the various hardware components. For more information see Device Names in Linux, Section
4.3.
/usr: all user programs (/usr/bin), libraries
(/usr/lib), documentation (/usr/share/doc), etc., are
in this directory. This part of the filesystem needs most of the space. You
should at least provide 300-500 MB of disk space. If you want to install more
packages you should increase the amount of space you give this directory.
/home: every user will put his data into a subdirectory of this
directory. The size of this depends on how many users will be using the system
and what files are to be stored in their directories. Depending on your
planned usage you should reserve about 100 MB for each user, but adapt this
value to your needs.
/var: all variable data like news articles, e-mails, websites,
APT's cache, etc. will be placed under this directory. The size of this
directory depends greatly on the usage of your computer, but for most people
will be dictated by the package management tool's overhead. If you are going
to do a full installation of just about everything Debian has to offer, all in
one session, setting aside 2 or 3 gigabytes of space for /var
should be sufficient. If you are going to install in pieces (that is to say,
install services and utilities, followed by text stuff, then X, ...), you can
get away with 2-5 hundred megabytes of room in /var. If harddrive
space is at a premium and you don't plan on using APT, at least not for major
updates, you can get by with as little as 30 or 40 megabytes in
/var.
/tmp: if a program creates temporary data it will most likely go
in there. 20-50 MB should be usually enough.
/proc: this is a virtual file system which doesn't reside on the
harddisk. Thus no harddisk space is needed. It provides interesting and also
vital information about the running system.
It is important to decide what type of machine you are creating. This will determine disk space requirements and affect your partitioning scheme.
This has changed for Potato -- we need to update it. There are a number of common task applications What does this need to be called? which Debian offers for your convenience (see Select and Install Profiles, Section 7.21). Common task applications are simply sets of package selections which make it easier for you, in that a number of packages are automatically marked for installation.
Each given common task application has a size of the resulting system after installation is complete. Even if you don't use these common task applications, this discussion is important for planning, since it will give you a sense of how large your partition or partitions need to be.
The following are some of the available common task applications and their sizes: The various applications and sizes should probably go here.
Remember that these sizes don't include all the other materials which are
usually to be found, such as user files, mail, and data. It is always best to
be generous when considering the space for your own files and data. Notably,
the Debian /var partition contains a lot of state information.
The dpkg files (with information on all installed packages) can
easily consume 20MB; with logs and the rest, you should usually allocate at
least 50MB for /var.
Linux disks and partition names may be different from other operating systems. You need to know the names that Linux uses when you create and mount partitions. Here's the basic naming scheme:
The partitions on each disk are represented by appending a decimal number to the disk name: ``sda1'' and ``sda2'' represent the first and second partitions of the first SCSI disk drive in your system.
Here is a real-life example. Let's assume you have a system with 2 SCSI disks, one at SCSI address 2 and the other at SCSI address 4. The first disk (at address 2) is then named ``sda'', and the second ``sdb''. If the ``sda'' drive has 3 partitions on it, these will be named ``sda1'', ``sda2'', and ``sda3''. The same applies to the ``sdb'' disk and its partitions.
Note that if you have two SCSI host bus adapters (i.e., controllers), the order of the drives can get confusing. The best solution in this case is to watch the boot messages, assuming you know yourself the drive models.
As described above, you should definitely have a separate smaller root
partition, and a larger /usr partition, if you have the space.
For examples, see below. For most users, the two partitions initially
mentioned are sufficient. This is especially appropriate when you have a
single small disk, since breaking out lots of partitions can waste space.
In some cases, you might need a separate /usr/local partition if
you plan to install many programs that are not part of the Debian distribution.
If your machine will be a mail server, you might need to make
/var/spool/mail a separate partition. Often, putting
/tmp on its own partition, for instance 20 to 32MB, is a good
idea. If you are setting up a server with lots of user accounts, it's
generally good to have a separate, large /home partition. In
general, the partitioning situation varies from computer to computer depending
on its uses.
For very complex systems, you should see the Multi Disk
HOWTO. This contains in-depth information, mostly of interest to
ISPs and people setting up servers.
With respect to the issue of swap partition size, there are many views. One rule of thumb which works well is to use as much swap as you have system memory, although there probably isn't much point in going over 64MB of swap for most users. It also shouldn't be smaller than 16MB, in most cases. Of course, there are exceptions to these rules. If you are trying to solve 10000 simultaneous equations on a machine with 256MB of memory, you may need a gigabyte (or more) of swap.
On 32-bit architectures (i386, m68k, 32-bit SPARC, and PowerPC), the maximum size of a swap partition is 2GB (on Alpha and SPARC64, it's so large as to be virtually unlimited). This should be enough for nearly any installation. However, if your swap requirements are this high, you should probably try to spread the swap across different disks (also called ``spindles'') and, if possible, different SCSI or IDE channels. The kernel will balance swap usage between multiple swap partitions, giving better performance.
As an example, one of the authors' home machine has 32MB of RAM and a 1.7GB IDE
drive on /dev/hda. There is a 500MB partition for another
operating system on /dev/hda1 (should have made it 200MB as it
never gets used). A 32MB swap partition is used on /dev/hda3 and
the rest (about 1.2GB on /dev/hda2) is the Linux partition.
There are two different times that you can partition: prior to the installation of Debian, or during installation of Debian. If your computer will be solely dedicated to Debian, you should partition as part of the installation process (``Partition a Hard Disk'', Section 7.7). If you have a machine with more than one operating system on it, you generally should let the native operating system create its own partitions.
The following sections contain information regarding partitioning in your native operating system prior to installation. Note that you'll have to map between how the other operating system names partitions, and how Linux names partitions; see Device Names in Linux, Section 4.3.
Tru64 UNIX, formerly known as Digital UNIX, which is in turn formerly known as
OSF/1, uses the partitioning scheme similar to the BSD `disk label', which
allows for up to eight partitions per disk drive. The partitions are numbered
`1' through to `8' in Linux and ``lettered'' `a' through to `h' in UNIX. Linux
kernels 2.2 and higher always correspond `1' to `a', `2' to `b' and so on. For
example, rz0e in Tru64 UNIX would most likely be called
sda5 in Linux.
Partitions in the disk label may overlap. Moreover, the `c' partition is
required to span the entire disk (thus overlapping all other non-empty
partitions). Under Linux this makes sda3 identical to
sda (sdb3 to sdb, if present, and so
on). Apart from satisfying this requirement, there is, however, not much point
in creating overlapping partitions.
Another conventional requirement is for the `a' partition to start from the beginning of the disk, so that it always includes the boot block with the disk label.
Disks can be partitioned with the graphical disk configuration tool that is
accessible through the Application Manager, or with the command-line
disklabel utility. Partition type for the Linux file system
should be set to `resrvd8'. This can only be done via disklabel;
however, all other configuration can easily be performed with the graphical
tool.
It is possible, and indeed quite reasonable, to share a swap partition between
UNIX and Linux. In this case it will be needed to do a mkswap on
that partition every time the system is rebooted from UNIX into Linux, as UNIX
will damage the swap signature. You may want to run mkswap from
the Linux start-up scripts before adding swap space with swapon
-a.
If you want to mount UNIX partitions under Linux, note that Digital UNIX can use two different file system types, UFS and AdvFS, of which Linux only understands the former.
Windows NT uses the PC-style partition table. If you are manipulating existing FAT or NTFS partitions, it is recommended that you use the native Windows NT tools (or, more conveniently, you can also repartition your disk from the AlphaBIOS setup menu). Otherwise, it is not really necessary to partition from Windows; the Linux partitioning tools will generally do a better job. Note that when you run NT, the Disk Administrator may offer you to write a ``harmless signature'' on non-Windows disks if you have any. Never let it do that, as this signature will destroy the partition information.
If you plan to boot Linux from an ARC/AlphaBIOS/ARCSBIOS console, you will need a (small) FAT partition for MILO. One megabyte is quite sufficient. If Windows NT is installed, its 6 Mb bootstrap partition can be employed for this purpose.