tmpfs

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tmpfs (temporary file system) (formerly known as shmfs) is a virtual filesystem created to store files in dynamic (volatile) memory. tmpfs is typically created on RAM.

Warning
The volatile memory (such as RAM) cannot keep the files after system shutdown, reboot, or crash. It should be apparent by the name: tmpfs is meant only for ephemeral files. Best practice is to only store recoverable/regeneratable files in tmpfs.

In Linux ramfs (random access memory file system) has been replaced by tmpfs as the old ramfs did not handle well when the system run out of memory. tmpfs allows the filesystem to grow dynamically when it needs more space until it hits the pre-set maximum value it has been allocated; after that it will use swap space if it is available.

There are many cases for using temporary file systems in Linux, one being the /tmp directory which does not need to physically store non-volatile data.

Important
When using systemd, the /tmp directory is mounted by default as tmpfs. See this section to disable this behavior and mount it manually in /etc/fstab.

Installation

Kernel

Users need to activate the following kernel options:

KERNEL Enable tmpfs support

File systems  --->
     Pseudo filesystems  --->
          [*] Tmpfs virtual memory file system support (former shm fs)
          [ ] Optional drivers

Optional drivers
Option	Description
Tmpfs POSIX Access Control Lists	Enable ACL permissions.
Tmpfs extended attributes	Enable metadata support.

Usage

Generate and mount tmpfs in one step:

root #mount -t tmpfs tmpfs /MOUNTPOINT

Users can specify the mount option size to control the maximum size of the filesystem (default: half of system RAM). Note that tmpfs doesn't reserve this memory, but allocates only the needed memory.

systemd

When using systemd the /tmp directory is mounted by default as tmpfs and given a default size which is deemed big enough without chewing up too much RAM.

Users can view mounted temporary filesystems using the following command:

root #findmnt --target /tmp

This will show if the /tmp mount point is a tmpfs filesystem and the size of such filesystem.

In order to disable this behavior and take back control of the directory by using /etc/fstab the user needs to run the following command:

root #systemctl mask tmp.mount

This command will now not mount /tmp as a tmpfs and will automatically switch back to a block device.

Users should now add a new line in /etc/fstab which will create a tmpfs for /tmp manually.

FILE /etc/fstabtmpfs fstab example

tmpfs /tmp tmpfs rw,nosuid,nodev,size=4G,mode=1777 0 0

OpenRC

OpenRC users should simply add the mount point into /etc/fstab:

FILE /etc/fstabtmpfs fstab example

tmpfs /tmp tmpfs rw,nosuid,nodev,size=4G,mode=1777 0 0

Note
If the user is interested in mounting other directories besides /tmp, be sure to first check if they already use tmpfs with the findmnt command:

root #findmnt --target /<directory-to-check>

Conclusion

The outcome of using a temporary filesystem for non volatile files such as the /tmp directory is that the system has a very fast and very responsive access to caching files and stored session media. This also helps when using a browser to surf the web as cookies can be stored on this volatile media speeding up the application; on every reboot they are scrubbed or wiped from RAM. If users need to keep temporary files for analytics then they should avoid using the tmpfs filesystem for /tmp and other directories. All data stored in the tmpfs mount point will be lost when the system is rebooted or powered down.

Advancements in technology

Some hardware manufactures provide devices that are slower than RAM but faster than SSD to be used as cache drives. These devices are usually incorporated on a PCIe add-in card and have either an adapter from PCIe to M.2 slot or the entire memory device is embedded into the PCIe card.

If users need a non-volatile high speed versatile solution faster than SSD/SAS/SATA then these high speed solutions should be considered. Of course users should not mount these devices with tmpfs but instead use a conventional partitioning filesystem.

Technology such as the Intel 3Dx Optane memory cache can be used too, but this technology, although more versatile than SSD, is still subject to wearing out. It does however provide a brilliant midway point that will only get better as the technology progresses in the future and provides us with a much faster computing experience when setup correctly.