29 November 2009

Store volatile data in RAM using tmpfs

There are several reasons why you might want to hold certain data in non-permanent memory. Applications that create a lot of temporary data, causing system slowdown and strain on the storage medium, are an example, or you want the data to be gone after every power cycle because it is of no use anymore at that point, or the data would simply eat up too much storage over time.

Unix-like platforms support a file system named tmpfs, which is a RAM filesystem growing and shrinking dynamically with its contents. Setup is straightforward. To mount /tmp as tmpfs, you add the following line to /etc/fstab, after the physical partition mounts:

none /tmp tmpfs defaults 0 0

Be sure to clear out the contents of the old /tmp directory before remounting, because the mount will "overlay" what was previously there and the data will not be accessible but still occupy space.

Other locations that are good candidates for a tmpfs: /var/tmp, /home/username/tmp, /var/cache/apt/archives, web browser and other caches in your home directory. Don't be tempted to put /var/log on a tmpfs because the logs are important information sources for troubleshooting and forensics. Use logrotate instead for limiting the amount of log storage.

When you are done setting up the temporary file systems, issue a mount -a to remount everything from fstab.

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