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Chapter 13. Swap Space

13.1. What is Swap Space?
13.2. Adding Swap Space
13.2.1. Extending Swap on an LVM2 Logical Volume
13.2.2. Creating an LVM2 Logical Volume for Swap
13.2.3. Creating a Swap File
13.3. Removing Swap Space
13.3.1. Reducing Swap on an LVM2 Logical Volume
13.3.2. Removing an LVM2 Logical Volume for Swap
13.3.3. Removing a Swap File
13.4. Moving Swap Space

13.1. 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
	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).


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.
You should 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.