/dev/shm

[James Board]

I just noticed this in my "df" output:

    >df | grep tmpfs
    tmpfs                   224224         0    224224   0% /dev/shm

There's an entry in /etc/fstab which mounts this automatically. If I interpret that correctly, that's a 224 mbyte ramdisk that is consuming 224 mbytes of system memory whether or not I use it. Is that correct?

If so, will anything break if I unmount it and delete it from /etc/fstab? Do programs typically depend on it? I'd like to reclaim the system memory (low DRAM machine) for other uses.

[Camberwell]

is there anything in that folder?

I've got some stuff in mine from pulseaudio...

[martin@localhost ~]$ ls /dev/shm
pulse-shm-1228622519  pulse-shm-2601782879

I probably wouldn't get rid of it tho, personally

[James Board]

There's nothing in it. And this is about half the memory on this specific machine. I'd love to reclaim all that unused memory.

[robert-e]

Interesting; mine is much bigger:
[bob@localhost ~]$ df | grep tmpfs
tmpfs 772120 312 771808 1% /dev/shm


I looked into it, and it has two lines refering to Pulse Audio. This machine has 1.5 Gbytes of ram, and that is about half of it. I will watch this thead for further comments regarding this ram disk.

Regards,
Bob

[dd_wizard]

I don't think having a a 224MB /dev/shm uses 224MB of RAM, this is linux, not Windoze! I have the following three tmpfs mounts:

Filesystem            Size  Used Avail Use% Mounted on
tmpfs                1001M  328K 1001M   1% /dev/shm
/tmp                 1001M  9.3M  992M   1% /tmp
vartmp               1001M  165M  836M  17% /var/tmp

If you add the sizes up, you get 3,003MB (almost 3GB) on a laptop with only 2GB of RAM. System Monitor tells me that right now, I'm using 558MB (28%) of my RAM, and no swap. My guess is that tmpfs file systems use only as much RAM as they need. And if you get low on RAM, they'll get swapped out if need be. A good description of the usage of /dev/shm is availabe here. My guess is, things could break badly if you umount /dev/shm.

dd_wizard

[robert-e]

dd_wizard,
Thank you; your link helped me understand. I guess in my case, Pulse Audio is using it, even though I am not (listening) using it.
Regards,
Bob