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I have read somewhere that one can put a file on a linux system into memory, and loading it will be superfast.

How do I do this? How do I verify the file is loaded from memory?

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up vote 10 down vote accepted

On Linux, you probably already have an tmpfs filesystem that you can write to at /dev/shm.

$ >/dev/shm/foo
$ df /dev/shm/foo
Filesystem           1K-blocks      Used Available Use% Mounted on
tmpfs                   224088         0    224088   0% /dev/shm

This may use swap, however. For a true ramdisk (that won't swap), you need to use the ramfs filesystem.

mount ramfs -t ramfs /mountpoint
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Will this be then available to apache/php? I am interested in using this for a chat app and plan to save/retrieve recent lines from memory to avoid HDD write/read overhead. – Majid Fouladpour Jan 2 '14 at 1:03

It's called a ramdisk. You can simply mount your RAM as follows:

mount tmpfs <mountpoint> -t tmpfs -o size=2G

This creates a ramdisk of 2 GiB. For more information see man mount and search for tmpfs.

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2  
This is not truly a ramdisk, tmpfs can swap. – Chris Down Dec 24 '12 at 11:05

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