2001-12-16 00:27:04

by Hua Zhong (hzhong)

Subject: use shmfs

Hi:

Currently I'm using shmfs as a volatile storage. I am using Monta Vista's
kernel (2.4.2). I added the following line in /etc/fstab:

tmpfs /dev/shm shm defaults 0 0

# df /dev/shm
Filesystem 1k-blocks Used Available Use% Mounted on
tmpfs 0 0 0 - /dev/shm

the "0" number of blocks seems fishy.

I cannot write to the filesystem. write returns EINVAL. I can create an
empty file, however.

What should I do to make it work? Thanks.

By the way, I know tmpfs is a replacement of shmfs, but it's not in the
2.4.2 kernel I am using (can't find in config). Is it in any newer kernels
(especially 2.4.9)? Is it stable enough?

Thanks

2001-12-16 05:31:25

by Robert Love

Subject: Re: use shmfs

On Sat, 2001-12-15 at 19:26, Hua Zhong wrote:

> Currently I'm using shmfs as a volatile storage. I am using Monta Vista's
> kernel (2.4.2). I added the following line in /etc/fstab:
>
> tmpfs /dev/shm shm defaults 0 0
> <snip>
> I cannot write to the filesystem. write returns EINVAL. I can create an
> empty file, however.

It is confusing: tmpfs is used both for abstracting POSIX shared memory
(shm) and for a page-cache-based dynamic RAM disk. The line above, that
you are adding, is for the shm support. You need to add another line to
create the tmpfs filesystem at a given mount point. Example:

tmpfs /var/cheese tmpfs defaults,size=4m 0 0

Would create a tmpfs at /var/cheese. The (optional) size parameter
specifies a maximum fs size of 4MB.

See Documentation/filesystems/tmpfs.txt for more information.

Robert Love