Need help with /dev/shm
Mark Phillips
mark at phillipsmarketing.biz
Sun Sep 9 15:00:50 MST 2012
Lisa,
Thank-you for your fast response.
Now, do I get the award for the absolutely dumbest question to every be
posted to the plug list? My award should be banishment to the world of
Windoze.
My apologies for wasting everyone's time... :(
Mark
On Sun, Sep 9, 2012 at 1:25 PM, Lisa Kachold <lisakachold at obnosis.com>wrote:
> Hi Mark,
>
> On Sun, Sep 9, 2012 at 12:50 PM, Mark Phillips <mark at phillipsmarketing.biz
> > wrote:
>
>> I have been having some issues with an old server running a jsp
>> applicaition (tomcat web server and java 1.5....I said it was old!). I
>> looked at the partitions and found:
>>
>> Last login: Sun Sep 9 11:57:49 2012 from 192.168.25.150
>> mark at gandalf:~$ df -h
>> Filesystem Size Used Avail Use% Mounted on
>> /dev/hda6 110G 61G 44G 58% /
>> tmpfs 63M 0 63M 0% /dev/shm
>> /dev/hda1 30M 7.3M 21M 27% /boot
>> mark at gandalf:~$
>>
>> tmpfs or /dev/shm is at 0%. Usually, a zero anywhere is bad thing....;)
>> so should I do something about this?
>>
>> This is 63M with 0 used above.
>
> You can expand it for better performance, but I doubt that your
> utilization issues are /dev/shm kernel intermessage processing related. In
> a J2EE system, it would be memory, garbage collection, or a kernel based
> known memory error.
>
> But if you are running Ultramonkey or a databasae, you could use all of
> /dev/shm during heavy network use, so you can easily expand /dev/shm (see
> below).
>
>
> Reference:
> http://www.cyberciti.biz/tips/what-is-devshm-and-its-practical-usage.html
>
>
>> I goolged /dev/shm and understand that it is a ram disk for interprocess
>> communications. Wonderful. Should I be worried it is at 0% Should I
>> increase the size? Running top shows these resources in the system"
>>
>> Tasks: 60 total, 1 running, 59 sleeping, 0 stopped, 0 zombie
>> Cpu(s): 1.0% us, 0.3% sy, 0.0% ni, 98.4% id, 0.0% wa, 0.3% hi, 0.0% si
>> Mem: 127152k total, 124740k used, 2412k free, 6896k buffers
>> Swap: 489940k total, 0k used, 489940k free, 45500k cached
>>
>>
>> If I should increase the size of /dev/shm, would I edit fstab and add
>> this line
>>
>> none /dev/shm tmpfs defaults,size=8G 0 0
>>
>> and then
>>
>> mount -o remount /dev/shm
>>
>> You can use /dev/shm to improve the performance of application<http://www.cyberciti.biz/tips/what-is-devshm-and-its-practical-usage.html#>software such as Oracle or overall Linux system
> performance<http://www.cyberciti.biz/tips/what-is-devshm-and-its-practical-usage.html#>.
> On heavily loaded system, it can make tons of difference. For example
> VMware workstation/server can be optimized to improve your Linux host's
> performance (i.e. improve the performance of your virtual machines).
>
> In this example, remount /dev/shm with 8G size as follows:
> # mount -o remount,size=8G /dev/shm
> To be frank, if you have more than 2GB RAM + multiple Virtual machines<http://www.cyberciti.biz/tips/what-is-devshm-and-its-practical-usage.html#>,
> this hack always improves performance. In this example, you will give you
> tmpfs instance on /disk2/tmpfs which can allocate 5GB RAM/SWAP in 5K inodes
> and it is only accessible by root:
> # mount -t tmpfs -o size=5G,nr_inodes=5k,mode=700 tmpfs /disk2/tmpfs
> Where,
>
> - *-o opt1,opt2 * : Pass various options with a -o flag followed by a
> comma separated string of options. In this examples, I used the following
> options:
> - *remount* : Attempt to remount an already-mounted filesystem. In
> this example, remount the system and increase its size.
> - *size=8G or size=5G* : Override default maximum size of the
> /dev/shm filesystem. he size is given in bytes, and rounded up to entire
> pages. The default is half of the memory. The size parameter also accepts a
> suffix % to limit this tmpfs instance to that percentage of your pysical
> RAM: the default, when neither size nor nr_blocks is specified, is
> size=50%. In this example it is set to 8GiB or 5GiB. The tmpfs mount
> options for sizing ( size, nr_blocks, and nr_inodes) accept a suffix k, m
> or g for Ki, Mi, Gi (binary kilo, mega and giga) and can be changed on
> remount.
> - *nr_inodes=5k* : The maximum number of inodes for this instance.
> The default is half of the number of your physical RAM pages, or (on a
> machine with highmem) the number of lowmem RAM pages, whichever is the
> lower.
> - *mode=700* : Set initial permissions of the root directory.
> - *tmpfs* : Tmpfs is a file system which keeps all files in virtual
> memory.
>
> *How do I restrict or modify size of /dev/shm permanently?*
>
> You need to add or modify entry in /etc/fstab file so that system can read
> it after the reboot. Edit, /etc/fstab as a root user, enter:
> # vi /etc/fstab
> Append or modify /dev/shm entry as follows to set size to 8G
>
> none /dev/shm tmpfs defaults,size=8G 0 0
>
> Save and close the file. For the changes to take effect immediately
> remount /dev/shm:
> # mount -o remount /dev/shm
>
>> Thanks,
>>
>>
>
>
>> Mark
>>
>> P.S. The issues I am having with the application may have nothing to do
>> with this situation...could be some bad programming....ie a bug.
>>
>> P.P.S. I am running Linux version 2.6.8-2-386 (
>> horms at tabatha.lab.ultramonkey.org) (gcc version 3.3.5 (Debian
>> 1:3.3.5-13)) (yes, I said it was old....) Consider it my contribution to
>> keeping old hardware out of the dump!
>>
>>
>>
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