shm filesystem

Posted on 2000-05-12
Last Modified: 2013-12-15
Can someone tell me what I need to do to mount the shm filesystem at start up?   Certain programs require a shared memory segment at startup(so I'm told)and consequently won't run.    From the startup log the shm filesystem isn't being mounted.  
Question by:cliffhanger121599
  • 3
  • 3
LVL 40

Expert Comment

ID: 2807103
"shm filesystem"? I've never heard of such a beast. However the SysV IPC facility does provide for shared memory regions and the shm*() funtions that manipulate it. The functionality must be enabled in the kernel. I believe that it's typically enabled in distributed kernels, but if you've built a custom kernel you might have it disabled.


Author Comment

ID: 2807450
Thanks.  I have the sysv IPC facility enabled in the kernel and then I thought my problem lay here with this piece of text from the kernel doc.

  Shared memory is now implemented using a new (minimal) virtual file
  system, which you need to mount before programs can use shared memory.
  To do this automatically at system startup just add the following line
  to your /etc/fstab:

  none      /var/shm      shm      defaults      0 0

When I added this to fsab I got the message at startup that the file does not exist.   Can you help me further?   I do have a file called shm, but it contains nothing!
LVL 40

Expert Comment

ID: 2807518
Can you give me more of a reference as to where you found that? I've searched the 2.2.12 & 2.2.14 kernel documention and don't see anything like that. Also what program(s) are you trying to use that's complaining?
VMware Disaster Recovery and Data Protection

In this expert guide, you’ll learn about the components of a Modern Data Center. You will use cases for the value-added capabilities of Veeam®, including combining backup and replication for VMware disaster recovery and using replication for data center migration.


Accepted Solution

jyu_88 earned 50 total points
ID: 2807758
you must have the new kernel which now treats shared memory as seperate file system. Your solution is right, just add that line to the /etc/fstab. However, since the mount point /var/shm is not there ( thus the complaint about the fiel doesot exist), you need to make sure the mount point, i.e., /var/shm, exists before attempt to mount it. Mount point will be a directory, do the following as root:
1) mkdir /var/shm
2) chmod 755 /var/shm
3) mount /var/shm
It will work from that point on.

been there done that, with 2.3.99pre5 kernel:-)

Author Comment

ID: 2808321
Thanks.  Your right, I'm running 2.3.99 pre3(and trying to run Midi Player, Hdparm etc.) and apart from this problem it has been fine.    When i read jyu 88's answer I thought , that's it  - but now I find that the 'chmon' command is not recognised on my system. i.e. it doesn't exist.    Where does this come from?   Incidentally, I do have a shm file at /proc/sysvipc, is this relevent?
LVL 40

Expert Comment

ID: 2808410
I think the command you want is chmod, not chmon, and it's found in /bin.

Author Comment

ID: 2808735
Many thanks to jlevie for pointing out my error.    Full marks to jyu 88 though for excellent answer.   One last thing, what does the command 'chmod 755 /var/shm' do(I've just looked at the man file and it's as clear as mud!).

Featured Post

Windows Server 2016: All you need to know

Learn about Hyper-V features that increase functionality and usability of Microsoft Windows Server 2016. Also, throughout this eBook, you’ll find some basic PowerShell examples that will help you leverage the scripts in your environments!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
wifi not working on Raspberry Pi 3? 2 56
nagios remote hosts 9 56
linux 13 50
Upgrade BIOS / EUFI at Scale 4 36
Daily system administration tasks often require administrators to connect remote systems. But allowing these remote systems to accept passwords makes these systems vulnerable to the risk of brute-force password guessing attacks. Furthermore there ar…
I am a long time windows user and for me it is normal to have spaces in directory and file names. Changing to Linux I found myself frustrated when I moved my windows data over to my new Linux computer. The problem occurs when at the command line.…
Learn several ways to interact with files and get file information from the bash shell. ls lists the contents of a directory: Using the -a flag displays hidden files: Using the -l flag formats the output in a long list: The file command gives us mor…
This demo shows you how to set up the containerized NetScaler CPX with NetScaler Management and Analytics System in a non-routable Mesos/Marathon environment for use with Micro-Services applications.

777 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question