Although it is theoretically possible to use a full disk to house your Linux system, this is almost never done in practice. Instead, full disk block devices are split up in smaller, more manageable block devices. On systems, these are called partitions.

Partitions are divided in three types: primary, extended and logical.

A primary partition is a partition which has its information stored in the MBR (master boot record). As an MBR is very small (512 bytes) only four primary partitions can be defined (for instance, /dev/sda1 to /dev/sda4).

An extended partition is a special primary partition (meaning the extended partition must be one of the four possible primary partitions) which contains more partitions. Such a partition didn't exist originally, but as four partitions were too few, it was brought to life to extend the formatting scheme without losing backward compatibility.

A logical partition is a partition inside the extended partition. Their definitions aren't placed inside the MBR, but are declared inside the extended partition.

If you are not interested in drawing up a partitioning scheme for your system, you can use the partitioning scheme we use throughout this book:

If you are interested in knowing how big a partition should be, or even how many partitions you need, read on. Otherwise continue now with partitioning your disk by reading Using fdisk to Partition your Disk.

The number of partitions is highly dependent on your environment. For instance, if you have lots of users, you will most likely want to have your /home separate as it increases security and makes backups easier. If you are installing Gentoo to perform as a mailserver, your /var should be separate as all mails are stored inside /var. A good choice of filesystem will then maximise your performance. Gameservers will have a separate /opt as most gaming servers are installed there. The reason is similar for /home: security and backups. You will definitely want to keep /usr big: not only will it contain the majority of applications, the Portage tree alone takes around 500 Mbyte excluding the various sources that are stored in it.

As you can see, it very much depends on what you want to achieve. Separate partitions or volumes have the following advantages:

• You can choose the best performing filesystem for each partition or volume
• Your entire system cannot run out of free space if one defunct tool is continuously writing files to a partition or volume
• If necessary, file system checks are reduced in time, as multiple checks can be done in parallel (although this advantage is more with multiple disks than it is with multiple partitions)
• Security can be enhanced by mounting some partitions or volumes read-only, nosuid (setuid bits are ignored), noexec (executable bits are ignored) etc.

However, multiple partitions have disadvantages as well. If not configured properly, you will have a system with lots of free space on one partition and none on another. Another nuisance is that separate partitions - especially for important mountpoints like /usr or /var - often require the administrator to boot with an initramfs to mount the partition before other boot scripts start. This isn't always the case though, so your results may vary.

There is also a 15-partition limit for SCSI and SATA.

As an example partitioning, we show you one for a 20GB disk, used as a demonstration laptop (containing webserver, mailserver, gnome, ...):

$ df -h
Filesystem    Type    Size  Used Avail Use% Mounted on
/dev/sda5     ext4    509M  132M  351M  28% /
/dev/sda2     ext4    5.0G  3.0G  1.8G  63% /home
/dev/sda7     ext4    7.9G  6.2G  1.3G  83% /usr
/dev/sda8     ext4   1011M  483M  477M  51% /opt
/dev/sda9     ext4    2.0G  607M  1.3G  32% /var
/dev/sda1     ext2     51M   17M   31M  36% /boot
/dev/sda6     swap    516M   12M  504M   2% <not mounted>
(Unpartitioned space for future usage: 2 GB)

/usr is rather full (83% used) here, but once all software is installed, /usr doesn't tend to grow that much. Although allocating a few gigabytes of disk space for /var may seem excessive, remember that Portage uses this partition by default for compiling packages. If you want to keep /var at a more reasonable size, such as 1GB, you will need to alter your PORTAGE_TMPDIR variable in /etc/make.conf to point to the partition with enough free space for compiling extremely large packages such as OpenOffice.

The following parts explain how to create the example partition layout described previously, namely:

Change your partition layout according to your own preference.

fdisk is a popular and powerful tool to split your disk into partitions. Fire up fdisk on your disk (in our example, we use /dev/sda):

# fdisk /dev/sda

Once in fdisk, you'll be greeted with a prompt that looks like this:

Command (m for help): 

Type p to display your disk's current partition configuration:

Command (m for help): p

Disk /dev/sda: 240 heads, 63 sectors, 2184 cylinders
Units = cylinders of 15120 * 512 bytes

Device Boot    Start       End    Blocks   Id  System
/dev/sda1             1        14    105808+  83  Linux
/dev/sda2            15        49    264600   82  Linux swap
/dev/sda3            50        70    158760   83  Linux
/dev/sda4            71      2184  15981840    5  Extended
/dev/sda5            71       209   1050808+  83  Linux
/dev/sda6           210       348   1050808+  83  Linux
/dev/sda7           349       626   2101648+  83  Linux
/dev/sda8           627       904   2101648+  83  Linux
/dev/sda9           905      2184   9676768+  83  Linux

Command (m for help): 

This particular disk is configured to house seven Linux filesystems (each with a corresponding partition listed as "Linux") as well as a swap partition (listed as "Linux swap").

We will first remove all existing partitions from the disk. Type d to delete a partition. For instance, to delete an existing /dev/sda1:

Command (m for help): d
Partition number (1-4): 1

The partition has been scheduled for deletion. It will no longer show up if you type p, but it will not be erased until your changes have been saved. If you made a mistake and want to abort without saving your changes, type q immediately and hit enter and your partition will not be deleted.

Now, assuming that you do indeed want to wipe out all the partitions on your system, repeatedly type p to print out a partition listing and then type d and the number of the partition to delete it. Eventually, you'll end up with a partition table with nothing in it:

Disk /dev/sda: 30.0 GB, 30005821440 bytes
240 heads, 63 sectors/track, 3876 cylinders
Units = cylinders of 15120 * 512 = 7741440 bytes

Device Boot    Start       End    Blocks   Id  System

Command (m for help):

Now that the in-memory partition table is empty, we're ready to create the partitions. We will use a default partitioning scheme as discussed previously. Of course, don't follow these instructions to the letter if you don't want the same partitioning scheme!

We first create a small boot partition. Type n to create a new partition, then p to select a primary partition, followed by 1 to select the first primary partition. When prompted for the first cylinder, hit enter. When prompted for the last cylinder, type +32M to create a partition 32 Mbyte in size:

Command (m for help): n
Command action
  e   extended
  p   primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-3876, default 1): (Hit Enter)
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-3876, default 3876): +32M

Now, when you type p, you should see the following partition printout:

Command (m for help): p

Disk /dev/sda: 30.0 GB, 30005821440 bytes
240 heads, 63 sectors/track, 3876 cylinders
Units = cylinders of 15120 * 512 = 7741440 bytes

Device Boot    Start       End    Blocks   Id  System
/dev/sda1          1        14    105808+  83  Linux

We need to make this partition bootable. Type a to toggle the bootable flag on a partition and select 1. If you press p again, you will notice that an * is placed in the "Boot" column.

Let's now create the swap partition. To do this, type n to create a new partition, then p to tell fdisk that you want a primary partition. Then type 2 to create the second primary partition, /dev/sda2 in our case. When prompted for the first cylinder, hit enter. When prompted for the last cylinder, type +512M to create a partition 512MB in size. After you've done this, type t to set the partition type, 2 to select the partition you just created and then type in 82 to set the partition type to "Linux Swap". After completing these steps, typing p should display a partition table that looks similar to this:

Command (m for help): p

Disk /dev/sda: 30.0 GB, 30005821440 bytes
240 heads, 63 sectors/track, 3876 cylinders
Units = cylinders of 15120 * 512 = 7741440 bytes

Device Boot    Start       End    Blocks   Id  System
/dev/sda1 *        1        14    105808+  83  Linux
/dev/sda2         15        81    506520   82  Linux swap

Finally, let's create the root partition. To do this, type n to create a new partition, then p to tell fdisk that you want a primary partition. Then type 3 to create the third primary partition, /dev/sda3 in our case. When prompted for the first cylinder, hit enter. When prompted for the last cylinder, hit enter to create a partition that takes up the rest of the remaining space on your disk. After completing these steps, typing p should display a partition table that looks similar to this:

Command (m for help): p

Disk /dev/sda: 30.0 GB, 30005821440 bytes
240 heads, 63 sectors/track, 3876 cylinders
Units = cylinders of 15120 * 512 = 7741440 bytes

Device Boot    Start       End    Blocks   Id  System
/dev/sda1 *        1        14    105808+  83  Linux
/dev/sda2         15        81    506520   82  Linux swap
/dev/sda3         82      3876  28690200   83  Linux

To save the partition layout and exit fdisk, type w.

Command (m for help): w

Now that your partitions are created, you can continue with Creating Filesystems.

Now that your partitions are created, it is time to place a filesystem on them. If you don't care about what filesystem to choose and are happy with what we use as default in this handbook, continue with Applying a Filesystem to a Partition. Otherwise read on to learn about the available filesystems...

To create a filesystem on a partition or volume, there are tools available for each possible filesystem:

For instance, to have the boot partition (/dev/sda1 in our example) in ext2 and the root partition (/dev/sda3 in our example) in ext4 (as in our example), you would use:

# mkfs.ext2 /dev/sda1
# mkfs.ext4 /dev/sda3

Now create the filesystems on your newly created partitions (or logical volumes).

mkswap is the command that is used to initialize swap partitions:

# mkswap /dev/sda2

To activate the swap partition, use swapon:

# swapon /dev/sda2

Create and activate the swap with the commands mentioned above.