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.
The size of your swap should be equal to twice your computer's
physical RAM for up to 2 GB of physical RAM. For physical RAM above
2 GB, the size of your swap should be equal to the amount of
physical RAM above 2 GB. The size of your swap should never less
than 32 MB.
Using this basic 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.
Unfortunately, deciding on the amount of swap to allocate to Red
Hat Enterprise Linux is more of an art than a science, so hard
rules are not possible. Each system's most used applications should
be accounted for when determining swap size.
File systems and LVM2 volumes assigned as swap space cannot be in use when being modified. For example,
no system processes can be assigned the swap space, as well as no
amount of swap should be allocated and used by the kernel. Use the
free and cat
/proc/swaps commands to verify how much and where swap is in
The best way to achieve swap space modifications is to boot your
system in rescue mode, and then follow the instructions (for each
scenario) in the remainder of this chapter. Refer to Chapter 5 Basic System Recovery for
instructions on booting into rescue mode. When prompted to mount
the file system, select Skip.