Directory Structure FHS – Difference Between /tmp and /var/tmp

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On most FHS systems, there is a /tmp folder as well as a /var/tmp folder. What is the functional difference between the two?

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/tmp is meant as fast (possibly small) storage with a short lifetime. Many systems clean /tmp very fast - on some systems it is even mounted as RAM-disk. /var/tmp is normally located on a physical disk, is larger and can hold temporary files for a longer time. Some systems also clean /var/tmp, but less often.

Also note that /var/tmp might not be available in the early boot-process, as /var and/or /var/tmp may be mountpoints. Thus it is a little bit comparable to the difference between /bin and /usr/bin. The first is available during early boot - the latter after the system has mounted everything. So most boot-scripts will use /tmp and not /var/tmp for temporary files.

Another (upcoming) location on Linux for temporary files is /dev/shm.

Related Solutions

Yum user temp files (/var/tmp/yum*) fills up with repo data

When you run yum under not privileged user it uses as a cache directory the directory /var/tmp or what is set by the shell variable TMPDIR. So you can change the default behavior by running yum like this:

TMPDIR=/tmp yum check-update
TMPDIR=/tmp yum makecache

The same way you can run yum to clean up the cache directory:

TMPDIR=/tmp yum clean metadata
TMPDIR=/tmp yum clean all

When you use clean all option, ignore the warnings about rpmdb files as the user doesn't have priviledges to do so.

Finally, you can export the TMPDIR variable to not use it repeatedly when running yum:

export TMPDIR=/tmp
yum check-update
yum clean metadata

Ubuntu – Difference between /run and /var/run

From the Wikipedia page on the Filesystem Hierarchy Standard:

Modern Linux distributions include a /run directory as a temporary filesystem (tmpfs) which stores volatile runtime data, following the FHS version 3.0. According to the FHS version 2.3, this data should be stored in /var/run but this was a problem in some cases because this directory isn't always available at early boot. As a result, these programs have had to resort to trickery, such as using /dev/.udev, /dev/.mdadm, /dev/.systemd or /dev/.mount directories, even though the device directory isn't intended for such data. Among other advantages, this makes the system easier to use normally with the root filesystem mounted read-only.

So if you have already made a temporary filesystem for /run, linking /var/run to it would be the next logical step (as opposed to keeping the files on disk or creating a separate tmpfs).

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Related Solutions

Yum user temp files (/var/tmp/yum*) fills up with repo data

Ubuntu – Difference between /run and /var/run

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