How to raise ServerLimit and MaxClient

If your server starts getting more and more traffic you’ll need to lift up number of allowed Apache connections. This guide works only on cPanel/WHM powered servers.

The easy way
Log in at WHM and to go to Service Configuration > Apache Configuration > Global Configuration. In there find ServerLimit and MaxClients and set those to some nice value (eg. 1024 or 2048 depends how much memory you have). Save and that should be it.

The geek way
Edit of httpd.conf (usually located at /usr/local/apache/conf folder). It should look something like this (depending on your server specification):

StartServers        5
MinSpareServers     5
MaxSpareServers     10
ServerLimit         1024
MaxClients          1024
MaxRequestsPerChild 10000

Save, Distill settings, restart Apache:

/usr/local/cpanel/bin/apache_conf_distiller --update
/scripts/rebuildhttpdconf
/etc/init.d/httpd restart

Check
After you do something like this you simply MUST take a look at your Apache error_log file (usually located at /usr/local/apache/logs folder). If you see following line in Apache error_log:

** [warn] WARNING: Attempt to change ServerLimit ignored during restart

You should stop and run the Apache again since ServerLimit can’t be changed by restarting Apache. To do so execute following at SSH:

apachectl stop
apachectl start
Tags: serverlimit, apache serverlimit, WARNING: Attempt to change ServerLimit ignored during restart, serverlimit maxclients, serverlimit vs maxclients, serverlimit apache, apache serverlimit vs maxclients, server limit vs maxclient

Big file downloads stops at random

After migrating a site to new server I run into a strange problem with big file downloads that just stop/break without any specific reason at anytime. Downloads are not direct than are done using PHP (I’ll write more about that soon and I’ll link to that post from in here when I do) suddenly break without any notice. Browser reports that file has been successfully downloaded, Apache doesn’t report any errors but file is broken and not downloaded entirely.

I was pulling my hair for days, since sometimes downloads were working fine but sometimes they would just stop. Things got worse in case of downloading multiple files at the same time. Sometimes one or two downloads would break, sometimes all, sometimes none. It was driving me mad. Since I have been traveling those days across Northern Europe, I have been able to test the file download from multiple locations/countries and various connection types (ADSL, Cable, WiFi hot spots) and was still experienced same problems.

The setup on that server was bit complex and it used Apache to serve dynamic content, separate web server for static content. Downloads were done using PHP or using mod_xsendfile but either way problem persisted. So I figured out that something must be timing out and that is braking the connection. Since it would happen that out of 4-5 simultaneous downloads one or two would breakĀ and few would download normally. Finally, I tried increasing Apache timeout from 10 seconds to 30 seconds and it worked out! I was so pissed of and happy at the same time… The solution was so easy and in front of my nose but I needed so much time to figure it out… I felt so stupid for a second but then I solved the problem and I’ve learned something new…

It turns out that if there were no communication between server and client for 10 seconds the Apache would simply close connection and download would break. Nothing will be reported on both sides since it’s “normal” way to end the communication. This was also going on when mod_xsendfile was used to serve/download files. The problem was even greater when internet connection was worse (WiFi) and when I was downloading more files at once since than the connection would have to be split on few files.

So if you’re making a download server for larger files make sure you setup your Apache timeout to some reasonable value (30 seconds or more). Under term “larger files” I consider everything larger than pictures, but basically 50mb file could be called “larger file” since for it’s download it is required some time and of course open connection.

Tags: apache large file download timeout, downloads stop randomly

Web host is adding ?PHPSESSID to the end of all URLs

Today I a customer of mine came to me with a problem with web site that he have just moved from one host to another. And on that new host all his links on his site suddenly had ?PHPSESSID=k234j2knk… in the end. Since that is totally unusable since that site doesn’t even uses sessions and could affect his search engine rankings, he wanted it out of the way. The new host he moved that site to was shared and it doesn’t allow editing of php.ini any way so I had to make some other solution.

After failing with adding one of those on top of php files, as suggested on most pages that I found on Google:

// stop PHP from automatically embedding PHPSESSID on local URLs
ini_set('session.use_trans_sid', false);

// only use cookies (no url based sessions)
ini_set('session.use_only_cookies', true);

I suggested him to just switch hosts again, but he said he already paid up front for the whole year… and that it’s not an option… and that he wants that off his site… So, I’ve Googled some more and finally found a simple solution (that doesn’t require editing of 100’s of files in his case because of poorly programmed site). All I had to do is just put one line of code in .htaccess file and BOOM! All those nasty ?PHPSESSID were gone!

php_flag session.use_trans_sid off