Ubuntu – Apache2 setting up Problem with Ubuntu and PHP5

If you are using the Ubuntu package and didn't change things too much, the running process name should be lighttpd and the default user and group names are both www-data. Check the server.username and server.groupname entries in your config file (/etc/lighttpd/lighttpd.conf) to be certain.

Running ps -fC lighttpd should tell you if it is running and the user id that is is running as. On my system the output looks like

• rik@mary:/home/rik$ ps -fC lighttpd
• UID PID PPID C STIME TTY TIME CMD
• www-data 667 1 0 03:50 ? 00:00:00 /usr/sbin/lighttpd -f /etc/lighttpd/lighttpd.conf

Everything you want displayed under your document-root should be readable by the www-data user and the directories need to be executable by www-data as well. To test this you may want to try using find as the user www-data. The sudo command can help with this. sudo -u www-data find /var/www/sites/mysite.com/http/media/css/ should succeed. If not try again one step up with sudo -u www-data find /var/www/sites/mysite.com/http/media/ and so on until find can return file and directory names. Once there the run the chown and chmod commands against that directory without the -R (recursive) flag. Then test again.

If you are comfortable with all of the files and directories under /var/www/sites/mysite.com/http/media being readable by anyone, you may want to chmod all the files as 644 and the dirs as 755. If you have files that need to have the execute bit set this can be a bit more of a problem unless the all have distinctive extensions. This is done using the -type, -exec, and -name flags like:

1. chown -R id:www-data /var/www/sites/mysite.com/http/media

2. find /var/www/sites/mysite.com/http/media -type d -exec chmod 755 {} \;

3. find /var/www/sites/mysite.com/http/media -type f -exec chmod 644 {} \;

4. find /var/www/sites/mysite.com/http/media -type f -name '*.php' -exec chmod 755 {} \;

   If you don't want lighty to access other files an/or dirs in the tree, you will need to handle things differently. It is always easier if you keep files you want readable in a different directory from those you want kept out of the public eye.

I'm not saying this is what's happening but based on my own experience as a CentOS admin, it's most likely runaway apache/php processes taking down the server. I've seen this numerous times on CentOS 5. It's frustrating because there's usually not a trace of what happened in the log files. The machine just grinds to a halt due to physical memory and swap being sucked up by apache/php processes. You would think linux memory management or some daemon would jump in and say "hey stop" but it doesn't. It'll let apache grind your system to a halt.

Having said that, to see what's happening you'll need something that can monitor and log resource usage. I like to use a program called atop. Atop is a lot like the top program but it also takes a snapshot of resource usage at defined intervals. It's pretty simple to install.

wget http://www.atcomputing.nl/Tools/atop/packages/atop-1.23.tar.gz 
tar -zxvf atop-1.23.tar.gz
cd atop-1.23 && make install

Open /etc/atop/atop.daily with a text editor and change INTERVAL=600 to INTERVAL=60

Run the command /etc/atop/atop.daily from a command prompt to start it. Wait a few minutes and run atop -r /var/log/atop/atop_20091118 with the correct date of course.

Hit the t key to go forward in time and T to go back. Next time your server crashes do this and check the MEM free and SWP free lines. If you have memory problems these will be in red. Also look for numerous httpd lines under CMD. If apache/php is your problem there'll be a bunch of them.

If this is the case, I recommend looking at you're MaxClients setting in httpd.conf. If set too high, apache will gladly eat all of your memory causing your machine to crash. Apache/php can easily eat 40-50MB/process. If you multiply 40mb x MaxClients you'll get a rough idea of how much memory apache can potentially use. MaxClients usually defaults to 150 on CentOS so apache can potentially use 6GB of memory by default. This doesn't include memory your system needs for itself and other processes to run. Try setting it to a more realistic value based on the amount of memory you have like 40 if you have 2G of memory and see if that helps. Also if you have KeepAlive On, set KeepAliveTimeout to a low number like 2 or 3.

In my opinion CentOS's apache/php compilation is a real pos that should never have seen the light of day. It's buggy and crash prone. If you run a serious site, I highly recommend compiling your own version of apache/php or even using one of the newer high performance webservers like lighttpd or nginx with fgci php.