About Swap Space

Adding Swap Space
Sometimes it is necessary to add more swap space after installation. For example, you may upgrade the amount of RAM in your system from 128 MB to 256 MB, but there is only 256 MB of swap space. It might be advantageous to increase the amount of swap space to 512 MB if you perform memory-intense operations or run applications that require a large amount of memory.
You have three options: create a new swap partition, create a new swap file, or extend swap on an existing LVM2 logical volume. It is recommended that you extend an existing logical volume.

Extending Swap on an LVM2 Logical Volume
To extend an LVM2 swap logical volume (assuming /dev/VolGroup00/LogVol01 is the volume you want to extend):
1. Disable swapping for the associated logical volume:
2. # swapoff -v /dev/VolGroup00/LogVol01
3. Resize the LVM2 logical volume by 256 MB:
4. # lvm lvresize /dev/VolGroup00/LogVol01 -L +256M
5. Format the new swap space:
6. # mkswap /dev/VolGroup00/LogVol01
7. Enable the extended logical volume:
8. # swapon -va
9. Test that the logical volume has been extended properly:
10. # cat /proc/swaps # free

Creating an LVM2 Logical Volume for Swap
To add a swap volume group (assuming /dev/VolGroup00/LogVol02 is the swap volume you want to add):
1. Create the LVM2 logical volume of size 256 MB:
2. # lvm lvcreate VolGroup00 -n LogVol02 -L 256M
3. Format the new swap space:
4. # mkswap /dev/VolGroup00/LogVol02
5. Add the following entry to the /etc/fstab file:
6. /dev/VolGroup00/LogVol02 swap swap defaults 0 0
7. Enable the extended logical volume:
8. # swapon -va
9. Test that the logical volume has been extended properly:
10. # cat /proc/swaps # free

Creating a Swap File
To add a swap file:
1. Determine the size of the new swap file in megabytes and multiply by 1024 to determine the number of blocks. For example, the block size of a 64 MB swap file is 65536.
2. At a shell prompt as root, type the following command with count being equal to the desired block size:
3. dd if=/dev/zero of=/swapfile bs=1024 count=65536
4. Setup the swap file with the command:
5. mkswap /swapfile
6. To enable the swap file immediately but not automatically at boot time:
7. swapon /swapfile
8. To enable it at boot time, edit /etc/fstab to include the following entry:
9. /swapfile swap swap defaults 0 0
The next time the system boots, it enables the new swap file.
10. After adding the new swap file and enabling it, verify it is enabled by viewing the output of the command cat /proc/swaps or free.

Removing Swap Space

Sometimes it can be prudent to reduce swap space after installation. For example, say you downgraded the amount of RAM in your system from 1 GB to 512 MB, but there is 2 GB of swap space still assigned. It might be advantageous to reduce the amount of swap space to 1 GB, since the larger 2 GB could be wasting disk space.
You have three options: remove an entire LVM2 logical volume used for swap, remove a swap file, or reduce swap space on an existing LVM2 logical volume.

Reducing Swap on an LVM2 Logical Volume
To reduce an LVM2 swap logical volume (assuming /dev/VolGroup00/LogVol01 is the volume you want to extend):
1. Disable swapping for the associated logical volume:
2. # swapoff -v /dev/VolGroup00/LogVol01
3. Reduce the LVM2 logical volume by 512 MB:
4. # lvm lvreduce /dev/VolGroup00/LogVol01 -L -512M
5. Format the new swap space:
6. # mkswap /dev/VolGroup00/LogVol01
7. Enable the extended logical volume:
8. # swapon -va
9. Test that the logical volume has been reduced properly:
10. # cat /proc/swaps # free

Removing an LVM2 Logical Volume for Swap
The swap logical volume cannot be in use (no system locks or processes on the volume). The easiest way to achieve this it to boot your system in rescue mode. Refer to for instructions on booting into rescue mode. When prompted to mount the file system, select Skip.
To remove a swap volume group (assuming /dev/VolGroup00/LogVol02 is the swap volume you want to remove):
1. Disable swapping for the associated logical volume:
2. # swapoff -v /dev/VolGroup00/LogVol02
3. Remove the LVM2 logical volume of size 512 MB:
4. # lvm lvremove /dev/VolGroup00/LogVol02
5. Remove the following entry from the /etc/fstab file:
6. /dev/VolGroup00/LogVol02 swap swap defaults 0 0
7. Test that the logical volume has been extended properly:
8. # cat /proc/swaps # free

Removing a Swap File
To remove a swap file:
1. At a shell prompt as root, execute the following command to disable the swap file (where /swapfile is the swap file):
2. # swapoff -v /swapfile
3. Remove its entry from the /etc/fstab file.
4. Remove the actual file:
5. # rm /swapfile