Re: A note about testing EXEC_BACKEND on recent Linuxen

Added code comment:

/*
* Attach process to shared data structures. If testing
* EXEC_BACKEND on Linux, you must run this as root
* before starting the postmaster:
*
* echo 0 >/proc/sys/kernel/randomize_va_space
*
* This prevents a randomized stack base address that causes
* child shared memory to be at a different address than
* the parent, making it impossible to attached to shared
* memory. Return the value to '1' when finished.
*/
CreateSharedMemoryAndSemaphores(false, 0);

---------------------------------------------------------------------------

Tom Lane wrote:
> I just wasted a couple hours trying to determine why an EXEC_BACKEND
> build would randomly fail on Fedora Core 4. It seems the reason is that
> by default, recent Linux kernels randomize the stack base address ---
> not by a lot, but enough to cause child processes to sometimes be unable
> to attach to the shared memory segment at the same place the postmaster
> did.
>
> You can work around this by doing (as root)
> echo 0 >/proc/sys/kernel/randomize_va_space
> before starting the postmaster. You'll probably want to set it back to
> 1 when done experimenting with EXEC_BACKEND, since address randomization
> is a useful security hack.
>
> Just seems like something that should be in our archives ...
>
> regards, tom lane
>
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