Linux

APC is one of PHP Opcode Cache on the « market ». It is free and should be bundled inside the next revision of PHP, version 6.

I won’t go deep into how OpCode caches work, you will find a lot of docs, just google for APC, Xcache, eAccelerator… What I can say is that APC (as other caches do) will « save » binary parts of your PHP code into memory and use it when you call for the same PHP function again. This way you save all the PHP file opening, parsing, etc.

Maybe you noticed I said « into memory ». Yes. When you start APC it take a small amount (64 or 32Mo standard) of memory and store the binary parts in it.
This is fine but what if you have a really big website with lots of functions, classes, includes… like when you’re using Typo3 and tons of extensions ?

One thing you won’t come accross often on internet is « How (the hell) do I know if APC is performing well ? »

First, most of the time, the PHP page generation time is halved when you activate APC. This is a good clue. Great.
But what about memory consumption ?

During my tests, I found that APC completly flush the memory if it cannot add a new object. I don’t know if it’s a normal behaviour but it’s what I noted. This is why you have to extensively do your testing and tune the memory size before going to production.

This can be done really easyly with the apc.php page provided in the  APC package. You may not have it if you used some Linux package installer like yum or aptitude. If so, you’ll have to download the APC source from their website and copy apc.php to your web DocumentRoot or wherever you want it. As this is giving sensible informations, I would recomment to put it in a secured place.
We are using Typo3 here so I put the page in the /typo3 folder, which is protected and only accessible by the backend users. This is secure enough for now. Else, use the default login process, user « apc » and password « password ». This can be changed in the page. Disable it if you put the file inside an already protected location.

Browse to your apc.php page and see what happen. First, you’ll get a nasty PHP error if you don’t have APC PHP module enabled. Ensure it is enables in /etc/php.d/apc.conf (on CentOS, can be somewhere else on other distro).

What you see here is, on the left, some metrics and informations of the versions, uptime…
On the right you have the memory utilisation and the cache hit/miss representation. Also, you can see the fragmentation of the memory. You don’t want that but actualy I’m not sure you have a way to reduce it…

The things you need to check are on the left side, in the panel « File Cache Information ».

Hits : how many objects were already in the cache and were used

Miss : how many objects were NOT in the cache, for whatever reason : first request for it, memory full, object can’t be cached…

Cache Full Count : how many times the cache (memory) was full and flushed

This last one is one of the most important and need to be checked first when you website start to slow.

Monitoring

Now you want to monitor this with your Nagios/Centreon or whatever… Well.
I found a « APC monitoring project » out there, APC-PHP-MONITOR on GitHub. This was my starting point as this one is really basic.

As they do, I made a PHP script you have to put in your PHP website somewhere. I used a basic check to ensure only the right IP can access this script. In my case, 10.1.1.88.

Then I modified the PHP script so I can use it from Nagios or whatever. I named the file check_php_apc_cache.php. It’s not a superbe PHP script. It’s just dirty working fine for now.

You can then create a Nagios check or Template. Mine looks like this :

Finaly, the result :

Believe it or not, but latest Ubuntu release 1) does not include the latest PHP yet and 2) does not include mssql module.

Reading the newsgroups and forums, it seems nobody have a real tutorial on how to add it. You will also notice that Ubuntu builders have no plan to include it one day… (even if it is free, not under specific licence and need almost no dependency (Freetds is needed but I don’t know if it is mandatory to build).

Whatever, I need this module, and I came with a working solution :

apt-get source php5
cd /usr/lib/php5/php5-5.2.3/ext/mssql
phpize
./configure
make
make install

Just create a ini file in /etc/php5/conf.d/mssql.ini with :

# configuration for php MsSQL
moduleextension=mssql.so

And restart you Apache server.

!! Be warned that the module may be removed at the next package upgrade !! You will have to compile it again.

I’m really supprised today to see how applications uses Jack (the Linux – and other now – audio patch).

The Jack plus name is made of two parts : the application name and the « channel » name. The application name must be unique globaly, and the channel must be unique in each application.
While some seems to be configurable in both parts, some are not :

Darkice, by defaults, create a « darkice-PID:left » and  « darkice-PID:right », where PID is the real process ID of Darkice. This ensure 2 darkice will not have the same name. The drowback is that it is very hard to find which darkice is which, moreover if you want to script that.
I made a patch for darkice so you can freely change that.

With Ecasound, a command line sound mixer and processing you can only change the channel name. If you start more Ecasound, you will have another process ecasound_2, then ecasound_3… which is not really better than the way Darkice is doing it natively.
Another issue is when you kill one Ecasound, they all die ! This is a huge issue I will have to work on quickly, but I’m pretty sure this is due to a jack naming issue.

Then what should the convention be ?

As the important part is the application name, not the channel name, it seems that this part should be configurable.  Then the channel name could be, by default, either a direction and a number, or a direction and a name :

- ecasound-test1:in_1
-  ecasound-test1:in_2
- ecasound-test1:out_1
- ecasound-test1:ou_2

- ecasound-filter2:in_left
- ecasound-filter2:in_right

Devs, please, think of it !

This has always been a mess for sysadmins. Even good onces always get fooled by UNIX file rights and umask calculation.
The base is simple :
take 777 and substract the umask. If umask is 022, you’ll get a file permission of 755, which mean rwx-rwx-rwx.
Remember that 7 is 0111 in binary, so the rights are only triggered if a 1 is set.
First number is the « setUID bit », second the read, then the write, and the execute right.

But how to do this in C++ ?
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Meme si je n’utilise pas ubuntu, ca peut tjrs etre utile. Je viens de passer dessus, donc je vous en fais profiter : http://www.prendreuncafe.com/blog/post/2006/09/05/489-installer-et-configurer-apache2-trac-et-subversion-sur-ubuntu