How to force the system to donot use the swap memory in fedora 21?

edit

You can turn swap off by issue as root or with sudo this command on the terminal

swapoff -a

or

sudo swapoff -a

If I recall correctly there is also a possibility to set vm.swappiness level via sysctl program

To check current value of this option you can use following command:

sysctl -a | grep vm.swappiness

And with this command:

sysctl -w vm.swappiness=0

you can turn it off completely (system will not swap anymore). Setting this option value to 1 will allow swapping to disk only if RAM is exausted. To permanently save that option accross reboots you can define it in file in /etc/sysctl.d/ directory (/etc/sysctl.d/99-sysctl.conf for example).

As noted in the answer from @aeperezt, you can use swapoff -a to disable swap and swapon -a to enable it again - use swapon -s to see a summary of swap file usage and priority etc.

If you want to permanently remove swap space from your system:

1. Switch to root using:

   sudo -i
   

   Use your password.
2. Disable swap:

   swapoff -a
   

3. Create a backup of the fstab file (we will edit it next):

   cp /etc/fstab{,.orig}
   

4. Edit the /etc/fstab file to remove the swap file entry (use an editor you are comfortable with, for example vi or nano). It will look something like:

   /dev/mapper/HOST-swap   swap   swap   defaults  0 0
   

   The first entry on the line may point to a device file (/dev/VALUE) or possibly a UUID=some-random-long-string -- just look for the swap entries and delete the entire line.
5. IMPORTANT: To avoid running into issues when you next reboot, check that the /etc/fstab file is valid by issuing:

   mount -a
   swapon -s   # to verify swap is not active
   

   If it reports a problem, then fix the problem in the fstab file before continuing (remember you have your backup from step 3).
6. Ideally you would reclaim the disk space by using tools like lvm or btrfs and/or fdisk/gdisk, but the steps needed are very much dependent on whether you are using lvm or btrfs or raw partitions. Too many combinations to list here.