Installation guide

Chapter 14.
91
Swap Space
14.1. What is Swap Space?
Swap space in Linux is used when the amount of physical memory (RAM) is full. If the system needs
more memory resources and the RAM is full, inactive pages in memory are moved to the swap space.
While swap space can help machines with a small amount of RAM, it should not be considered a
replacement for more RAM. Swap space is located on hard drives, which have a slower access time
than physical memory.
Swap space can be a dedicated swap partition (recommended), a swap file, or a combination of swap
partitions and swap files.
Swap should equal 2x physical RAM for up to 2 GB of physical RAM, and then an additional 1x
physical RAM for any amount above 2 GB, but never less than 32 MB.
So, if:
M = Amount of RAM in GB, and S = Amount of swap in GB, then
If M < 2
S = M *2
Else
S = M + 2
Using this formula, a system with 2 GB of physical RAM would have 4 GB of swap, while one with
3 GB of physical RAM would have 5 GB of swap. Creating a large swap space partition can be
especially helpful if you plan to upgrade your RAM at a later time.
For systems with really large amounts of RAM (more than 32 GB) you can likely get away with a
smaller swap partition (around 1x, or less, of physical RAM).
Important
File systems and LVM2 volumes assigned as swap space should not be in use when being
modified. Any attempts to modify swap will fail if a system process or the kernel is using swap
space. Use the free and cat /proc/swaps commands to verify how much and where swap is
in use.
Red Hat advises that you modify swap space while the system is booted in rescue mode; for
instructions on how to boot in rescue mode, refer to the Installation Guide. When prompted to
mount the file system, select Skip.
14.2. Adding Swap Space
Sometimes it is necessary to add more swap space after installation. For example, you may upgrade
the amount of RAM in your system from 128 MB to 256 MB, but there is only 256 MB of swap space.
It might be advantageous to increase the amount of swap space to 512 MB if you perform memory-
intense operations or run applications that require a large amount of memory.
You have three options: create a new swap partition, create a new swap file, or extend swap on an
existing LVM2 logical volume. It is recommended that you extend an existing logical volume.