Why bind-mount /var/tmp to /tmp?

Question

I've read in several places that it is recommended to bind-mount /var/tmp to /tmp. This can be done by adding the following line to /etc/fstab:

/tmp /var/tmp none rw,noexec,nosuid,nodev,bind 0 0

How can this be beneficial? In other words why should we bind-mount /var/tmp to /tmp ?

Answer 1

The Filesystem HierarchyStandard says:

• /tmp/ Temporary files. Often not preserved between system reboots.
• /var/tmp/ Temporary files to be preserved between reboots.

For example: if an processus is launched every 5 minutes and needs to store some data between every launch, it will rather store them in /var/tmp/.

Answer 2

There may be some system safety reason for bind-mounting /var/tmp.

By mounting /var/tmp, the path /var/tmp will stop being an ordinary subdirectory within the / root filesystem and become a distinctly mounted filesystem. This mounting would - as indicated by your example fstab line -

/tmp /var/tmp none rw,noexec,nosuid,nodev,bind 0 0

enable us to trigger some safety related mount options like nosuid and noexec which would act as some additional safety mechanism to avoid the execution of any potentially distrusted temporary data in the /var/tmp path.