Is there some way to tell what processes are attached to a shared memory segment? We have a system on which I perform "icps -ma" and there are several segments pending deletion having numerous processes attached to them and I can't tell what processes they are. Neither the creator's pid nor last pid that touched them, as listed by ipcs -mp, exist. I'm at a loss.... Is there a command I can execute that will tell me what is attached?
I think just do only a our write a code
Because Kernel is process management director and itself do it automatically..
For example let be we have two process and we share the same memory segment.
Firstly we use shmget() syscall for create memory portion
The key value in here "key" gives a identifier for memory portion "size" gives a shared memory size "shmflag" is used to choose "0700" .Because we want to create new memory portion..
If function success then return value gives to us "shared memory segment ID"..So Then return value from shmget gives shmid value..
For add to address space we use shmat()
let it be shmaddr = NULL -- > let the kernel choose a suitable address at which to attach the our shared mem segment portion.. shmflg = 0 --> because of NULL no neccessary set the flag
And then if shmat is successfull it returns shared mem segment address..
So we get the SHR address
We create 4K SHR memory space..And we have a address pointer that called name shmptr..Then anyway we use it in our process (in c code..)
I know how to use a shared memory segment in code. What I'm asking for is a command that will tell me all the processes PIDs that have called shmat for the memory. More specifically, all the processes that have called shmat and have not subsequently called shmdt. The kernel knows this, because the it holds the memory mapping for all processes. I just need to know how to make it tell me.
For more specifics, in the case I'm experiencing, some process has called shmctl asking for it to be deleted (second parameter passed as IPC_RMID) and until all processes have called shmdt the kernel must hold the segment. It flags this (as shown by ipcs) two ways: 1) it changes the key to 0xFFFFFFFF (in Linux it is 0x00000000), and 2) it shows a 'D' in the first character of the MODE column (don't see this in Linux). The first is not sufficient to say it's pending deletion because process private keys are also listed as 0xFFFFFFFF (0x00000000 in Linux). So, in Linux it seems there is no good way to see (via ipcs) that the segment is pending deletion. Either way, the shared memory segment will linger until every processes has called shmdt. Therefore, I need to know what processes need to be killed so it goes away.
P.S. It is quite annoying that the kernel switches the key.... I believe I know why it does it, and that's because a subsequent create for the key must succeed. But, it's just bloody annoying because at the very least it could hold the old value and list that with ipcs...but...whatever. Just means I'm guessing as to which key is being held on too longer than it should be.
Last edited by DreamWarrior; 05-06-2010 at 01:49 PM..
pmap (in Linux) will show shared memory attachments. Unfortunatly pmap does not exist for AIX and it's "equivallent" as listed by IBM (procmap) doesn't show shared memory attachments.
I'm have no access to AIX machine right now to verify, but you could try svmon, check this article.
---------- Post updated at 10:10 PM ---------- Previous update was at 09:45 PM ----------
Just to add that those segments may be orphans now (and the processes gone, it is often the case with crashed Oracle database instances, then you need to issue ipcrm carefully ).
Well...it looks like that would work...alas, svmon is not executable by anyone other than root on our machines.... I'll see if I can get that fixed. Thanks!
Any other commands that may do it in light of the root problem?
---------- Post updated at 04:32 PM ---------- Previous update was at 04:29 PM ----------
How can that happen? The kernel should clean up after the process ends, so while it is possible that no one ever flagged the segment to be deleted, if it does get flagged, when every process ends/dies it should go away.
Hi, i have 2 identical web servers using AIX. I use nmon analyser to check their performance.
The server A exceeds 20% memory usage for system, 5% for cache and the rest 75% for processes. While, it uses 4% of Paging Space.
The server B exceeds 20% for system, 45% for cache and 35% for processes.... (24 Replies)
Platform: Oracle Linux 6.4
To find the most memory consuming processes, I tried the following 2 methods
1. Method1
# ps aux | head -1 ; ps aux | sort -nk +4 | tail -7
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 95 0.0 0.0 0 0 ? ... (2 Replies)
Hello.
I am new to this forum and I would like to ask for advice about low level POSIX programming.
I have to implement a POSIX compliant C shared library.
A file will have some variables and the shared library will have some functions which need those variables.
There is one special... (5 Replies)
Hi again!
I have 2 questions ..:
How can i create exactly one number of processes ?
For example i want to create l*n processes and i tried this:
for(i=0;i<l*n;i++){
pid=fork()}
But it creates more than l*n
Also, i want each child to run another x.c program with 3 command line... (1 Reply)
Hi again!
I have 2 questions ..:
How can i create exactly one number of processes ?
For example i want to create l*n processes and i tried this:
for(i=0;i<l*n;i++){
pid=fork()}
But it creates more than l*n
Also, i want each child to run another x.c program with 3 command line... (1 Reply)
When I run 'top' command,I see the following
Memory: 32G real, 12G free, 96G swap free
Though it shows as 12G free,I am not able to account for processes that consume the rest 20G.
In my understanding some process should be consuming atleast 15-16 G but I am not able to find them.
Is... (1 Reply)
Hello ,
I would like to know how to check if a given process id belongs to particualr shared memory segment .
Please help
Thanks in advance (3 Replies)
Using pmap, I was able to get a memory map of an Oracle process. It had the following id:
0000000380000000 4194320K rwxsR
Converting that Hex ID to decimal gave:
352321658
So, then I did ipcs -am:
IPC status from <running system> as of Thu Jun 18 15:43:17 MDT 2009
T ID ... (1 Reply)
Hi All,
I'm facing the following issue with my shared libraries in AIX.
memory related calls such as memset, memcpy, malloc etc are failing miserably.
there is something wrong with stack/memory which i can't guess.
i've used the following flags to build my libraray:
ld -G... (0 Replies)