/home

The /home directory contains the personal files of users. Placing /home on a separate partition allows you to reinstall the system without having to reinstall personal files  – all you need to do is create users with the same names as on the previous install.

These days, 100GB per user seems a reasonable minimum, but you can also allocate whatever disk space is left over from the other partitions to /home. However, be aware that automatic running of fsck during boot up can take up to five minutes with a very large home partition.

/swap

The old rule used to be that a swap directory should be twice the size as a system's RAM. However, today when computers have several gigabytes of RAM, this rule is wasteful. If you have two or more gigabytes of RAM, you generally need no more than 2GB of swap, unless you are doing extremely intensive computations or multimedia work.

In fact, on a modern system, casual users have little need of a swap partition and can easily do without. However, if you decide you need one, you can use the mkswap command to create a swap file, which is only slightly less efficient than a swap directory, and then activate it with swapon -a. If necessary, you can have 32 swap files or directories per system.

/tmp

Working files for both the system and applications are stored in /tmp, including some files downloaded from the Internet. These files change frequently and increase as you open more programs.

Although most of these working files are small, they could cause the system to crash if left on a crowded root partition. You can avoid this potential problem by placing /tmp on its own 1GB partition on a workstation. A 2GB partition should be more than adequate on a typical server.