Arch Linux

Dreameen

Member

From: Poland

Registered: 2004-09-06

Posts: 252

/dev/shm <--what fs it uses?

The thing is that the output of 'df' shows that the Filesystem of /dev/shm/ is 'none' and according to fstab the type is 'tmpfs'. Could someone explain this to me. Is it using 'tmpfs' on /dev/shm/ or not?

$ df 
Filesystem:
-none                    256660         0    256660   0% /dev/shm

/etc/fstab:
# <file system>        <dir>         <type>    <options>          <dump> <pass>
none                   /dev/pts      devpts    defaults            0      0
none                   /dev/shm      tmpfs     defaults            0      0
tmpfs                  /tmp          tmpfs     defaults            0      0
usbfs                  /proc/bus/usb usbfs  defaults            0      0

If it's not using tmpfs I need to enable it, because I'm running WinXp on qemu and I've read on their forums that 'tmpfs' gives it a nice boost.

i3839

Member

Registered: 2004-02-04

Posts: 1,185

Re: /dev/shm <--what fs it uses?

Yes it is. The "none" is for the device, e.g. /dev/hda. But tmpfs is virtual, so there it's ignored, so people put in "none" to avoid confusion.

/dev/shm is used for posix shared memory.

Dreameen

Member

From: Poland

Registered: 2004-09-06

Posts: 252

Re: /dev/shm <--what fs it uses?

Thanks for clear explanation Now, I only have to give it a bit more memory. Something like 270/280Mb.

i3839

Member

Registered: 2004-02-04

Posts: 1,185

Re: /dev/shm <--what fs it uses?

To quote the man page of mount:

The  following  parameters  accept  a  suffix  k, m or g for Ki, Mi, Gi
       (binary kilo, mega and giga) and can be changed on remount.

       size=nbytes
              Override default maximum size of the filesystem.   The  size  is
              given  in  bytes, and rounded down to entire pages.  The default
              is half of the memory.

So putting size=275m in /etc/fstab should do the trick. By executing df -h you can see how much is actually used. Tmpfs doesn't use more memory than needed, so the df numbers aret he memory usage, and size is just the max size.