If you've ever looked at the /tmp file system on a RHEL system, you may have noticed that it is, by default, simply a folder in the root directory.

For example:

# df -h /tmp
Filesystem               Size  Used Avail Use% Mounted on
/dev/mapper/centos-root  100G  4.6G   96G   5% /

The risk of having this is, that anyone can fill up the root file system, by writing temporary data to the /tmp folder, which is risky for system stability.

Red Hat Enterprise Linux 7 offers the ability to use /tmp as a mount point for a temporary file storage system (tmpfs), but unfortunately, it is not enabled by default.

When enabled, this temporary storage appears as a mounted file system, but stores its content in volatile memory instead of on a persistent storage device. And when using this, no files in /tmp are stored on the hard drive except when memory is low, in which case swap space is used. This also means that the contents of /tmp are not persisted across a reboot.

To enable this feature, execute the following commands:

# systemctl enable tmp.mount
# systemctl start tmp.mount

RHEL uses a default size of half the memory size for the in-memory /tmp file system. For example on a system with 16 GB of memory, an 8 GB /tmp file system is set up after enabling the tmp.mount feature:

# df -h /tmp
Filesystem               Size  Used Avail Use% Mounted on
/dev/mapper/centos-root  100G   53G   48G  53% /
# systemctl enable tmp.mount
# systemctl start tmp.mount
# df -h /tmp
Filesystem      Size  Used Avail Use% Mounted on
tmpfs           7.8G     0  7.8G   0% /tmp

By having this in place, it's no longer possible to fill up the root file system, when writing files and/or data to the /tmp file system. The downside, however, is that this uses memory, and when filling up the memory, may be using the swap space. As such, having a dedicated file system on disk for the /tmp folder is still the better solution.



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