Linux add a swap file howto
Q. I need additional swap space to improve my system performance. How do I add a swap file to Linux system?
A. In Linux, as in most other Unix-like operating systems, it is common to use a whole partition of a hard disk for swapping. However, with the 2.6 Linux kernel, swap files are just as fast[7] as swap partitions, although Red Hat recommends using a swap partition. The administrative flexibility of swap files outweighs that of partitions; since modern high capacity hard drives can remap physical sectors, no partition is guaranteed to be contiguous. You can add swap file as a dedicated partition or use following instructions to create a swap file.
Procedure to add a swap file
You need to use dd command to create swapfile. Next you need to use mkswap command to set up a Linux swap area on a device or in a file.
a) Login as the root user
b) Type following command to create 512MB swap file (1024 * 512MB = 524288 block size):
# dd if=/dev/zero of=/swapfile1 bs=1024 count=524288
c) Set up a Linux swap area:
# mkswap /swapfile1
d) Activate /swapfile1 swap space immediately:
# swapon /swapfile1
e) To activate /swapfile1 after Linux system reboot, add entry to /etc/fstab file. Open this file using text editor such as vi:
# vi /etc/fstab
Append following line:
/swapfile1 swap swap defaults 0 0
So next time Linux comes up after reboot, it enables the new swap file for you automatically.
g) How do I verify swap is activated or not?
Simply use free command:
$ free -m
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January 17th, 2007 at 10:00 pm
TYPO: vi /etc/fstatb
It should be fstab
January 17th, 2007 at 10:16 pm
anon,
Thanks for heads up!
June 1st, 2007 at 2:35 am
If you don’t want to reboot the machine to enable the new swapfile, after step f) you can issue these commands:
swapoff -a
swapon -a
to first stop and then start all swaps in /etc/fstab
October 20th, 2007 at 8:25 am
Thanks for the help. But how would I go about deleting this swapfile? Also, how does creating a swapfile this way differ from creating a separate partition for one? I only ask because I would like to have multiple installs of linux on my system, and I would like them to share the same swapfile.
Recently, I’ve been trying to create a swapfile partition and it’s not being recognized, so I’ve been having trouble.
May 7th, 2008 at 6:29 pm
Thanks, I have been looking for the last step for months heh.