[svlug] What is /dev/shmfs and how does it relate to API's?

Jeffrey Siegal jbs at quiotix.com
Thu Jul 31 18:26:19 PDT 2003

On Thursday, Jul 31, 2003, at 14:44 America/Denver, M. Drew Streib 

> On Thu, Jul 31, 2003 at 08:28:04PM +0000, M. Drew Streib wrote:
>> /dev/shmfs is 'Shared Memory Filesystem'
>> A direct mapping to a SysV-style shared memory segment of some sort.
>> I'm not sure why you'd want to use a file like this rather than normal
>> APIs. Debug maybe?
> After looking this up more, and with help from Brian Chrisman...
> shmfs is similar to tmpfs in that it is an all RAM/swap filesystem. It
> is basically a ramdisk that can be swapped out, and with variable size.
> It shouldn't need a /dev entry, afaik, as it is fully virtual. Unlike a
> ramdisk, it can be created at any time, and its size is variable 
> depending
> on use (basically limited by swap and ram size).

It doesn't need a /dev entry but is mounted on /dev/shm by convention.  
It could actually be mounted anywhere ("mount -t shmfs none 

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