[phpa] Re: SHM Permissions
- From: "Nick Lindridge" <nick@xxxxxxxxxxxxxxxxxxxxx>
- To: <phpa@xxxxxxxxxxxxx>
- Date: Wed, 15 May 2002 08:44:10 -0000 ()
> so ... now to the bogo ... I got the nearly the same problem as Marco.
> I installed Version 1.3 of PHPa and everything is fine on running
> default values.
> But by changing
>
> phpa.shm_perms = 644
> phpa.shm_user="httpd"
> phpa.shm_group="httpd"
>
> I noticed that phpa_cache_admin could not even connectd to the shared
> memory.
> The child process is running as httpd but the Apache is started as
> root.
The above looks fine.
> phpa_cache_admin is telling me:
>
> [root]>phpa_cache_admin -m
> 8388608:8374184:32768:32768:8337260:4156:0:1021427005:m
> [root]>su httpd
> [httpd]>phpa_cache_admin -m
> Unable to acquire shm sems - Permission denied
> Unable to access cache shared memory - Permission denied
> No shm cache available with key 0x0c0deb00
> [httpd]>ipcs -m
> ------ Shared Memory Segments --------
> key shmid owner perms bytes nattch status
> 0x0c0deb00 12292 root 644 8388608 9
> 0x00000000 12294 httpd 600 92164 9 dest
hmm, that's strange. What happens is that apache/php/phpa first runs as
root, and phpa creates the shm. Then it switches the user/group of the
shared memory. My system at home shows the following:
root@pod:/usr/local/builds/apache-1.3.22/bin > ipcs
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x00280267 0 root 644 1048576 1
0x0c0deb00 110081 nobody 644 8388608 21
0x00000000 109058 nobody 600 46084 21 dest
so you can see ownership of the shm is now nobody. You might try
stopping apache, checking that the shm was removed, and then
restarting. If the shm is still owned by root and not showing as httpd,
then take a look in the apache error log for any messages. Send me a
private email if it's still root.
> In fact, the script could read the shared memory ... so why it tell me
> that there is no such key available ? Isn't it enought for the stats
to
> read the shared mem ... maybe to flush I have to write, but to get the
> status also ?
This isn't quite correct. The message about no shm is misleading, but
what it really means is that it couldn't access both the shm and the
semaphores. The locking mechanism and crash detection mechanism require
that phpa_cache_admin writes to the shm in order to read it, and it
needs to acquire some semaphores.
nick
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