pipcs -qa gives me somthing like this :

POSIX IPC status as of Thu Apr 27 15:59:08 2006
T MODE OWNER GROUP REFCNT QNUM MNUM QBYTES NAME
POSIX Message Queues:
q rw-rw---- abmd AZZX 1 0 100000 22 /abLVxy
q rw-rw---- abcd ABZY 13 0 50000 256 /abgxy
q rw-rw---- abcd ABZY 3 0 1000 256 /abILxy
q rw-rw---- abcd ABZY 1 0 50000 256 /ab0xy
q rw-rw---- abcd ABZY 1 0 50000 256 /abMD1xy
... etc
q rw-rw---- acc4d AZZX 0 0 1024 256 /abSOxy
q rw-rw---- acc4d AZZX 0 901 1024 256 /ab0Axy
q rw-rw---- acc4d AZZX 0 4 1024 256 /ab10xy
q rw-rw---- abcd ABZY 0 0 100000 14 /abB1xy
q rw-rw---- u91134 ABZY 0 0 100 10 /aby
q rw-rw---- acc4d AZZX 0 5 1024 256 /abITxy
q rw-rw---- abcd ABZY 2 0 100000 14 /abW1xy

And if I try to create a new one, with msg size 32 and queue length 128 :

mqopen 128 32 -c /test_32x128

There is no pb.

...but if I use :

mqopen 1024 10000 -c /test (this also is ok)
mqopen 1024 10000 -c /test2 (this fails ...)
mq_open(): No space left on device

It's ok, if I reduce the number of messages on the queue :
mq_open -b 1024 -m 5000 -c /test2 (this works)

The pb is that we have 12 Go of physical RAM available...

This link http://docs.hp.com/en/32650-90879/ch03s03.html says :
"
MESSAGE [ENOSPC] No space left on device. (POSIX.1 ERROR 28)

CAUSE During a write() function on a regular file, or when extending a directory, there was no free space left on the device.

ACTION Deallocate unneeded disk space.
"

Here the error occurs when we try to create a new queue not when we try to write a message on a queue.

Under Linux kernel 2.6 and probably under FreeBSD 7, posix queues use a "virtual file system" to make permanent the content of the queue between reboot and use shared memory. This is something like a filesystem in memory... in turn shared memory is implemented using ipc sys v shared memory system calls : shmat(), etc ...We already allow max usage os shared mem with kernel params. I try to know what is limiting us now ? Max adressable space for shared mem is 1.75 GB under HP-UX, but we cannot create any queue after that all existing queues use approx. 900 MB...

Of course there is a lot of apps running and sharing the same space of 1.75 GB. vmstat says we still have 407000 free page (if a page is 4096 Bytes), this gives 450 MB available. Of course I don't know if this RAM is contiguous or fragmented... this perhaps explain why we fail with a queue of 10 MB and not 5MB... I don't know if there is a way to unfragment memory without rebooting...

It's very strange that on a system with 12GB RAM, HP-UX fixed the shared memory adress range from 0x8000 0000 to 0xefff ffff... Is this the way they understand virtual memory ? Or perhaps I misunderstand their man pages...

Thank you again for your interest on this problem,
Cengiz ADANIR.