Text in fstab page about /dev/shm

Jeremy Utley jerutley at gmail.com
Wed Feb 22 20:03:12 PST 2006


On 2/22/06, Chris Staub <chris at beaker67.com> wrote:
> In the "Creating /etc/fstab" section, there is this paragraph:
>
> The /dev/shm mount point for tmpfs is included to allow enabling
> POSIX-shared memory. The kernel must have the required support built
> into it for this to work (more about this is in the next section).
> Please note that very little software currently uses POSIX-shared
> memory. Therefore, consider the /dev/shm mount point optional. For more
> information, see Documentation/filesystems/tmpfs.txt in the kernel
> source tree.
>
> I don't really know much of anything about the subject myself, but it
> seems strange that it says /dev/shm is "optional" when it's described as
> required during the LFS system build. Is that paragraph simply out-of-date?

As indicated by the email from Greg earlier, we do create /dev/shm as
a directory during the install process.  However, mounting a tmpfs
filesystem there to allow POSIX shared memory support is an optional,
although recommended and default, thing to do.

There's actually some docs (I believe either glibc or the kernel)
where it is notated that this mount *should* occur, and in fact,
nearly every GNU/Linux distribution today does this (I think the one
exception is Slackware, and while it's a great distro, it's always
been somewhat of a different beast).

So, the moral of the story is, while not completely necessary,
mounting a tmpfs filesystem at /dev/shm is not an absolute
requirement, but is recommended.

HTH,

Jeremy



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