Re: [gentoo-user] Setting size of /dev/shm or cleaning up ancient /etc/fstab

[Paul Hartman <paul.hartman+gentoo@gmail.com>]

On Wed, May 8, 2013 at 12:55 AM, Walter Dnes <waltdnes@waltdnes.org> wrote:
>   I'm running mdev, so that may be related.  Here's my story... a script
> I run to automatically process digital photos started blowing up on me.
> After much bashing of head against brick wall, I determined that
> /dev/shm now has an absolute max size of 10 megabytes!  Any larger files
> could not be written to it.  Here's all the uncommented stuff in /etc/fstab
>
>
> /dev/sda5               /         ext2     noatime,nodiratime,async        0 1
> /dev/sda7               /home     reiserfs noatime,nodiratime,async,notail 0 1
> /home/bindmounts/opt    /opt      auto     bind                            0 0
> /home/bindmounts/var    /var      auto     bind                            0 0
> /home/bindmounts/usr    /usr      auto     bind                            0 0
> /home/bindmounts/tmp    /tmp      auto     bind                            0 0
> /dev/sda6               none            swap            sw              0 0
> /dev/cdrom              /mnt/cdrom      iso9660         noauto,users,ro 0 0
> /dev/sr0                /mnt/dvd        auto            noauto,users,ro  0 0
> devpts  /dev/pts devpts defaults 0 0
> none              /dev/shm        tmpfs rw,noatime,noexec,nosuid,nodev 0 0
>
>   Meanwhile, my netbook, with the /dev/shm line commented out, runs just
> fine and handles large files in /dev/shm.  I followed the example at
> http://wiki.gentoo.org/wiki/Complete_Handbook/Configuring_the_system
> with slightly more paranoid settings, e.g. noexec.  What gives?

You can forcefully specify the size of /dev/shm like this:

none        /dev/shm  tmpfs   defaults,size=10G          0 0

But it should default to 50% of your system RAM... weird... do you
have any local scripts that are remounting it, maybe?

There's a lot more information in the kernel documentation:
/usr/src/linux//Documentation/filesystems/tmpfs.txt


The default fstab from latest baselayout does not contain /dev/shm at all:

# /etc/fstab: static file system information.
#
# noatime turns off atimes for increased performance (atimes normally aren't
# needed); notail increases performance of ReiserFS (at the expense of storage
# efficiency).  It's safe to drop the noatime options if you want and to
# switch between notail / tail freely.
#
# The root filesystem should have a pass number of either 0 or 1.
# All other filesystems should have a pass number of 0 or greater than 1.
#
# See the manpage fstab(5) for more information.
#

# <fs>                  <mountpoint>    <type>          <opts>
 <dump/pass>

# NOTE: If your BOOT partition is ReiserFS, add the notail option to opts.
/dev/BOOT               /boot           ext2            noauto,noatime  1 2
/dev/ROOT               /               ext3            noatime         0 1
/dev/SWAP               none            swap            sw              0 0
/dev/cdrom              /mnt/cdrom      auto            noauto,ro       0 0
/dev/fd0                /mnt/floppy     auto            noauto          0 0