How to create swap in linux

[Saman]

These are the steps to add swap space to your Linux system through the use of swap files. Be sure to login as root user.

1. Determine the amount of existing swap space
   

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   more /proc/swaps

   This will list any swap partitions and swap files currently in use. Your swap space should be at least twice the amount of physical RAM installed for best results. For example, a system with 512MB of physical RAM should have at least 1GB of swap space.
   To configure 2GB of swap, we can make one 2GB swap file or two 1GB swap files. We'll do two 1GB swap files because one 2GB swap file might not work depending on Linux kernel support for large files (file over 2GB).
2. Make swap files named swapfile1 and swapfile2 in /var/tmp

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   cd /var/tmp
   dd if=/dev/zero of=swapfile1 bs=1024 count=1048576
   dd if=/dev/zero of=swapfile2 bs=1024 count=1048576

   This creates the files /var/tmp/swapfile1 and /var/tmp/swapfile2, each 1GB in size. Using the "dd" command ensures that the files have no holes.
3. Turn each swap file into a swap area

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   /sbin/mkswap -c -v1 /var/tmp/swapfile1
   /sbin/mkswap -c -v1 /var/tmp/swapfile2

4. Turn on swap files

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   # swapon /var/tmp/swapfile1
   # swapon /var/tmp/swapfile2

   If you getting the error message, swapon: swapfile: Operation not permitted. then you must be in a VPS without rights to create swap files. Make sure you are logged in as root as well.
5. Verify that the system is using the swap file

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   more /proc/swaps

   You should see entries for /var/tmp/swapfile1 and swapfile2.
6. Set up your system to load the swap space at startup
   
   In /etc/rc.d/rc.sysinit, look for a line that contains:

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   swapon -a

   Append this command to enable your swap files at startup:

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   swapon /var/tmp/swapfile1
   swapon /var/tmp/swapfile2

   The line should now look something like this:

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   action "Activating swap partitions" swapon -a swapon /var/tmp/swapfile1 swapon /var/tmp/swapfile2