Creating A Swap File; Removing Swap Space; Reducing Swap On An Lvm2 Logical Volume - Red Hat ENTERPRISE LINUX 4 System Administration Manual

11.2.3. 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:
dd if=/dev/zero of=/swapfile bs=1024 count=65536
3. Setup the swap file with the command:
mkswap /swapfile
4. To enable the swap file immediately but not automatically at boot time:
swapon /swapfile
5. To enable it at boot time, edit /etc/fstab to include the following entry:
/swapfile
The next time the system boots, it enables the new swap file.
6. 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.

11.3. 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.

11.3.1. 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:
# swapoff -v /dev/VolGroup00/LogVol01
2. Reduce the LVM2 logical volume by 512 MB:
# lvm lvreduce /dev/VolGroup00/LogVol01 -L -512M
swap swap defaults 0 0
Creating a Swap File
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