Adding emergency swap space to linux

6. January 2012 06:00


This is a quick guide to adding emergancy swap space to linux. Which is useful when you know a machine is going to run out memory. Or you need a lot of memory for a single task that cannot be completed without the extra memory.


Step 1


Login as root


Step 2


Create a new file of the size that you want to add using the following command. In this case 512 mbytes of space.


dd if=/dev/zero of=/extraswap1 bs=1024 count=512k


Step 3


Fix the permissions on the file so that only the creator can read / write to it.


chmod 0600 /extraswap1


Step 4


Turn it into a swap file and tell linux to turn on the extra space


mkswap /extraswap1

swapon /extraswap1


Step 5


If you want the swap to be enabled after the next reboot of the machine you will need to add the following line to /etc/fstab


/extraswap1 swap swap defaults 0 0




You can verify that it is working by either using free or by looking directly at the proc filesystem using cat /proc/swaps

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