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?
It is important to decide what type of machine you are creating. This will determine disk space requirements and affect your partitioning scheme.
There are a number of default ``Profiles'' which Debian offers for your convenience (see Select and Install Profiles, Section 7.20). Profiles 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 profile has a size of the resulting system after installation is complete. Even if you don't use these profiles, 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 profiles and their sizes:
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.
VMEbus systems using the TEAC FC-1 SCSI floppy drive will see it as normal SCSI disk. To make identification of the drive simpler the installation software will create a symbolic link to the appropriate device and name it ``/dev/sfd0''.
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 the other hand, Atari Falcons and Macs feel pain when swapping, so instead of making a large swap partition, get as much RAM as possible.
Note that Linux for your architecture
will not use more than 128 megabytes of swap on
a single swap partition. However, you can make multiple swap
partitions by hand and edit /etc/fstab after you've
installed to get more than 128 megabytes of swap. If your swap
requirements are this high, however, you should probably try to spread
the swap across different disks (also called ``spindles''). Or you can
try the more recent Linux kernels (2.2 and higher) where this limitation
was relaxed (be careful, it may require other changes in your system).
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 boot process (``Partition a Hard Disk'', Section 7.6). If you have a machine with more than one operating system on it, you generally should let the native operating system create it's 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.
If you are running AmigaOS, you can use the HDToolBox
program to partition your disk prior to installation. Here's how:
HDToolBox, select the disk you want to use, click
on the ``Partition Drive'' button and select or create the partition
you want to use as the Debian root filesystem.
HDToolBox
you have installed)
HDToolBox and select ``Save
changes to drive''. Think twice before actually clicking on ``Yes'' --
have you chosen the correct partitions? No important data could get
lost now if you made a mistake? Then click ``OK''. If required, the
Amiga will reboot after this.
Atari partition IDs are three ASCII characters, use ``LNX'' for data and ``SWP'' for swap partitions. If using the low memory installation method, a small Minix partition is also needed (about 2 MB), for which the partition ID is ``MNX''. Failure to set the appropriate partition IDs not only prevents the Debian installation process from recognizing the partitions, but also results in TOS attempting to use the Linux partitions, which confuses the harddisk driver and renders the whole disk inaccessible.
There are a multitude of third party partitioning tools available (the
Atari harddisk utility doesn't permit changing the
partition ID); this manual cannot give detailed descriptions for all
of them. The following description covers SCSITool (from
Hard+Soft GmBH).
SCSITool and select the disk you want to partition
(``Disk'' menu, item ``select'').
For the ``Change'' option, select the partition to change in the selection list, and select ``other systems'' in the dialog box. The next window lists detailed information about the location of this partition, and lets you change the partition ID. Save changes by leaving the window with the ``Ok'' button.
SCSITool using the ``Quit'' item from the ``File''
menu. The computer will reboot to make sure the changed partition
table is used by TOS. If you changed any TOS/GEM partitions, they will
be invalidated and have to be reinitialized (we told you to back up
everything on the disk, didn't we?).
There is a partitioning tool for Linux/m68k called
atari-fdisk in the installation system, but for now we
recommend you partition your disk using a TOS partition editor or some
disk tool. If your partition editor doesn't have an option to edit the
partition type, you can do this crucial step at a later stage (from
the booted temporary install ramdisk). SCSITool is only
one of the partition editors we know of which supports selection of
arbitrary partition types. There may be others; select the tool that
suits your needs.
Partitioning tools for Macintosh tested include HD SC
Setup 7.3.5 (Apple), HDT 1.8 (FWB),
SilverLining (LaCie), and DiskTool (Tim
Endres, GPL). Full versions are required for HDT and
SilverLining. The Apple tool requires a patch in order
to recognize third-party disks (a description on how to patch HD
SC Setup using ResEdit can be found at http://www.euronet.nl/users/ernstoud/patch.html).
The following recipe is for partition with Apple's HD SC Setup.
Whatever tool you use, the partition type has to be set to
``Apple_Unix_SVR2''. The partition names need to be ``A/UX
Root'', ``A/UX Root&Usr'' or ``A/UX Usr'' for data partitions; and
``A/UX swap'' for swap partitions. HD SC Setup will use
the right names and type when creating A/UX partitions in a ``Custom''
partition scheme. Partitions are selected for deletion, creation or
resizing using the mouse, the partition name and type can be selected
from a list of predefined types. DiskTool can create A/UX
type partitions but requires that the user type in the partition names
manually. Descriptions for other tools are welcome.