OpenBSD has a file system called mfs which stands for memory file system. It allows you to create an entire file system in memory (RAM). Since CompactFlash disk have a limited amount of write cycles we will use this feature to our advantage. We will create the following directories in mfs:
by adding the following lines to /etc/fstab:
swap /tmp mfs rw,-s=65536,nodev,noatime,noexec,nosuid 0 0
swap /var/log mfs rw,-s=131072,nodev,noatime,noexec,nosuid 0 0
swap /var/run mfs rw,-s=2048,nodev,noatime,noexec,nosuid 0 0
swap /var/tmp mfs rw,-s=16384,nodev,noatime,noexec,nosuid 0 0
As you have no doubt noticed the –s switch in the mount options specifies the actual size of the mfs partition in 512 byte blocks. Hence 65536 are actually 32 megabytes.
We specify a few additional security and performance options:
nodev no device files will be interpreted
noatime the access times of the files won't be updated
noexec no executable files on this file system
nosuid Ignore set-user-identifier and set-group-identifier
These partitions will be mounted on top of existing directories and the original content will not be accessible unless the mfs file systems are umounted.