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Author Topic: tmpfs and shm confusion  (Read 3805 times)


  • Vectorian
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  • Posts: 774
  • it's enough
tmpfs and shm confusion
« on: February 12, 2011, 03:30:37 am »

Should tmpfs and shm both be mounted at /dev/shm?

Code: [Select]
roarde:$ df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda2             43944444  13103672  30840772  30% /
tmpfs                   222084         0    222084   0% /dev/shm
shm                     222084         0    222084   0% /dev/shm

roarde:$ mount -l
/dev/sda2 on / type reiserfs (rw,noatime)
tmpfs on /dev/shm type tmpfs (rw)
usbfs on /proc/bus/usb type usbfs (rw,devmode=0666)
shm on /dev/shm type tmpfs (rw)

roarde:$ grep "^tmpfs\|^shm" /etc/fstab
tmpfs   /dev/shm    tmpfs defaults 0  0
shm            /dev/shm     tmpfs  defaults        0     0

Trying to track down a performance issue. There's a disk access problem and also processor cache (!) seems to be turned off.


  • Administrator
  • Vectorian
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  • Posts: 4455
Re: tmpfs and shm confusion
« Reply #1 on: February 12, 2011, 05:17:29 am »

Not sure about your configuration, shm and tmpfs is not the same.

I found a good fstab guide here:
scroll down to the tmpfs section.


  • DoucheBag
  • Vectorite
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  • Posts: 115
Re: tmpfs and shm confusion
« Reply #2 on: February 15, 2011, 09:30:02 am »

HI ~ Don't know if this may help:

Generally - if fstab is mis-configured, an error complaint by kernel is output to screen @ bootup

Have you read the /var/log/dmesg file ~ This /var/log directory also contains other helpful log files
In some cases, /tmp content may hold clues (unless a cron task has been set to MT  temporary files)   

Fstab Example:

   proc      /proc      proc   defaults      0 0  <== mandatory_
   shm      /dev/shm   tmpfs   nodev,nosuid,noexec   0 0 <== usual default
 > none       /mnt/tmpfs    tmpfs  <== see URL

Caveat - Tmpfs is "booted" session only - until set as above
Shared memory file system is a "virtual" file management concept
tmpfs  is similar to an initrd content -( temporary)  - usage may be  as suggested in URL
What is the access Problem - drive not found/mounted, DMA *probe not read,  in/out reads fail:

*Hdparm will give drive data -@  present settings
Processor cache would be  a hardware BIOS setting, unless cpu Cfg  utility has  been installed, mis-applied 
'Tho'  I am unaware of any such capability in either

(Without a level one or two CPU cache, you should experience MANY weird results)

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