tmpfs is a memory based file system which uses kernel resources relating to the VM system and page cache as a file system. Once mounted, a tmpfs file system provides standard file operations and semantics. tmpfs is so named because files and directories are not preserved across reboot or unmounts, all files residing
on a tmpfs file system that is unmounted will be lost.
tmpfs file systems can be mounted with the command:
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mount -F tmpfs swap directory
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Alternatively, to mount a tmpfs file system on /tmp at multi-user startup time (maximizing possible performance improvements), add the following line to /etc/vfstab:
tmpfs is designed as a performance enhancement which is achieved by caching the writes to files residing on a tmpfs file system. Performance improvements are
most noticeable when a large number of short lived files are written and accessed on a tmpfs file system. Large compilations with tmpfs mounted on /tmp
are a good example of this.
Users of tmpfs should be aware of some constraints involved in mounting a tmpfs file system. The resources used by tmpfs are the same as those
used when commands are executed (for example, swap space allocation). This means that large sized tmpfs files can affect the amount of space left over for programs to execute. Likewise,
programs requiring large amounts of memory use up the space available to tmpfs. Users running into this constraint (for example, running out of space on tmpfs) can
allocate more swap space by using the swap(1M) command.
Another constraint is that the number of files available in a tmpfs file system is calculated based on the physical memory of the machine and not the size of the swap device/partition.
If you have too many files, tmpfs will print a warning message and you will be unable to create new files. You cannot increase this limit by adding swap space.
Normal file system writes are scheduled to be written to a permanent storage medium along with all control information associated with the file (for example, modification time, file permissions). tmpfs control information resides only in memory and never needs to be written to permanent storage. File data remains in core until memory demands are sufficient to cause pages associated with tmpfs to be reused at which time they are copied out to swap.
An additional mount option can be specified to control the size of an individual tmpfs file system.
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