No matter how well you plan, sometimes a system does not run as you expect. If you find you need more swap space, it is simple enough to add. You have three ways to increase swap space: adding a new hard drive, enabling swap over NFS, and creating a swap file on an existing partition.
For information on how to encrypt swap space, what options for this task exist and why it should be done, please refer to Section 18.17 of the Handbook.
The best way to add swap, of course, is to use this as an excuse to add another hard drive. You can always use another hard drive, after all. If you can do this, go reread the discussion of swap space in Section 11.2 of the Handbook for some suggestions on how to best arrange your swap.
Swapping over NFS is only recommended if you do not have a local hard disk to swap to; NFS swapping will be limited by the available network bandwidth and puts an additional burden on the NFS server.
You can create a file of a specified size to use as a swap file. In our example here we will use a 64MB file called /usr/swap0. You can use any name you want, of course.
Example 11-1. Creating a Swapfile on FreeBSD
Be certain that your kernel configuration includes the memory disk driver (md(4)). It is default in GENERIC kernel.
device md # Memory "disks"
Create a swapfile (/usr/swap0):
# dd if=/dev/zero of=/usr/swap0 bs=1024k count=64
Set proper permissions on (/usr/swap0):
# chmod 0600 /usr/swap0
Enable the swap file in /etc/rc.conf:
swapfile="/usr/swap0" # Set to name of swapfile if aux swapfile desired.
Reboot the machine or to enable the swap file immediately, type:
# mdconfig -a -t vnode -f /usr/swap0 -u 0 && swapon /dev/md0