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#1 (**permalink**) 01-05-2008, 06:20 AM

AIX 5.2

For 32-bit processes the max. number of shared memory segments
a process can obtain is 11.

To obtain more the "shmat" capability can can be used.
But AFAIK this is an option while *compile time* only.

Q: - Is this true?
- Do we have option to break the limit while runtime?
Eg: setting a variable or system configuration?

thanks guys
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#2 (**permalink**) 01-05-2008, 06:20 AM

mgrd wrote:
> AIX 5.2
>
> For 32-bit processes the max. number of shared memory segments
> a process can obtain is 11.
>
> To obtain more the "shmat" capability can can be used.
> But AFAIK this is an option while *compile time* only.
>
> Q: - Is this true?
> - Do we have option to break the limit while runtime?
> Eg: setting a variable or system configuration?

own follow-up:

I found on IBM's
"Technical Reference: Base Operating System and Extensions, Volume 2",
(http://publib.boulder.ibm.com/infocenter/pseries)
the entry for the "shmat Subroutine":

---snip---
An extended shmat capability is available.
If an environment variable EXTSHM=ON is defined then processes executing
in that environment will be able to create and attach more than eleven
shared memory segments.
---snip---

But I still don't know if setting the variable
EXTSHM=ON
requires the binary in question to be compiled with the shmat
capability or not.

With other words:
Does every program can obtain more than 11 shared memory segments
provided the variable
EXTSHM=ON
is set?

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#3 (**permalink**) 01-05-2008, 06:20 AM

mgrd <mgrd@gmx.net> wrote:
> I found on IBM's
> "Technical Reference: Base Operating System and Extensions, Volume 2",
> (http://publib.boulder.ibm.com/infocenter/pseries)
> the entry for the "shmat Subroutine":
>
> ---snip---
> An extended shmat capability is available.
> If an environment variable EXTSHM=ON is defined then processes executing
> in that environment will be able to create and attach more than eleven
> shared memory segments.
> ---snip---
>
> But I still don't know if setting the variable
> EXTSHM=ON
> requires the binary in question to be compiled with the shmat
> capability or not.
>
> With other words:
> Does every program can obtain more than 11 shared memory segments
> provided the variable
> EXTSHM=ON
> is set?

The quotation seems to say so.
Why don't you try it out?

Yours,
Laurenz Albe

#4 (**permalink**) 01-05-2008, 06:20 AM

Laurenz Albe wrote:
> The quotation seems to say so.
> Why don't you try it out?

Well, I didn't have a machine available but needed the info for a
customer.

However, I tried it now and it works fine:

The environment variable EXTSHM=ON
- increases the numbers of shared mem segments per process over 11
- the program doesn't need to to be compiled with shmat capability

BTW, the variable also seems to remove shared memory id's which
were left over unused (creater procs terminated; not attached to any
other).

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