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This is a common error I see in couple of my servers when they experience syn flood attacks. I have always thought this troubleshooting is included in my blog, but I got surprised today after searching It was not there. Anyway, sometimes, you may experience issues like your public network stop responding to requests even though there is no outage from your datacenter. Public network comes online once the iptables is restarted but goes back again after a while. This usually happens due to the iptable’s connection tracking table becomes full. You can find whether this is the issue or not by typing dmesg in your shell window or if you KVM then it should execute automatically in the KVM window. The error should look like this:

ip_conntrack: table full, dropping packet

To resolve this you need to increase the value of this table. To check the current set value, type this:

cat /proc/sys/net/ipv4/ip_conntrack_max

To find the current usage of the table type this:

cat /proc/sys/net/ipv4/netfilter/ip_conntrack_count

You can temporary resolve with a echo to the ip_conntrack_max file:

echo 191072 > /proc/sys/net/ipv4/ip_conntrack_max

Though, as it is a kernel variable, you can set this variable using sysctl too. To do that, go to /etc and edit the sysctl.conf file. You need to put the following line at the bottom of the conf file:

net.ipv4.ip_conntrack_max=191072

You can then run the sysctl load to load the latest configured kernel values by typing:

sysctl -p

It will also allow you to set the ip_conntrack_max value to this one after the reboot.

Happy troubleshooting

Today I was working on optimizing one of my server for maximum cpu and memory utilization while I found a daemon called Yum-updatesd. I was always thinking before that this daemon not only checks the updates available for the server rather install them as well. But I was totally wrong. This daemon only finds the latest update and send the notification via email. If you are using cpanel, this is a fully worthless daemon. I have seen it was taking around 200 MB RAM and at the runtime it was halting around 2% of the cpu. Even I have experienced better IO performance at the time of CRON running after killing this daemon. So, Kill it, it is nothing but a memory hunter of your server

Today, one of my client was having an issue with his wordpress. He was using the headline premium theme with his wordpress and couldn’t use the featured panel offered by that theme. It was because that option couldn’t be saved in the theme settings. I have tried searching a lot in google, but couldn’t find a solution. One of the solution I got in wordpress forum hit my mind was stating about mod_security. I have tried disabling it but couldn’t get a proper result. After that, I had gone through the process trace information using strace and found the settings couldn’t be save because of the php memory limit. I tried increasing that value using a custom php.ini file for that customer and viola

Hope this is going to come handy for my readers

Today, One of my client was reporting the following error in roundcube:

SERVICE CURRENTLY NOT AVAILABLE!

Error No. [0×01F4]

I tried to check the roundcube error log and it seems the roundcube database was crashed. To reinstall roundcube, there is a script available for cpanel users can be used as following:


/usr/local/cpanel/bin/update-roundcube --force


And viola, this fixed my issue

I have faced a sudden issue with whmcs today morning. After the reply, it was showing blank page. I changed the site template today which includes some modification of whmcs as well, I forgot to change templates_c folder 777 permission which is required by WHMCS. After I did a recursive chmod on templates_c to 777, the blank page was gone. Hope this helps some people.

mod_geoip is a grate module for geo targeting the traffic within apache. MaxMind also comes with a free geoip database which can be used with the mod_geoip. To complete the installation, we would need to complete two steps:

1. Install the GeoIP Library
2. Install mod_geoip module.

To install GeoIP Library, first you need to download the available GeoIP library from here:

http://www.maxmind.com/app/c

While I was doing my job, the latest free built was 1.4.6 and the download URL was the following:

http://geolite.maxmind.com/download/geoip/api/c/GeoIP-1.4.6.tar.gz

cd /usr/src
wget http://geolite.maxmind.com/download/geoip/api/c/GeoIP-1.4.6.tar.gz

I had downloaded the tarred source file under /usr/src, here I would extract it and install it.

tar -xvzf GeoIP*
cd GeoIP*
./configure
make
make install


After running the above commands, GeoIP library should be installed under /usr/src/GeoIP-version-number, once this is completed, we would proceed to the next section to install mod_geoip.

As I was using apache 2 here, I took the mod_geoip source from here:

http://www.maxmind.com/download/geoip/api/mod_geoip2

After downloading the latest version of mod_geoip, I had extracted it and used the below commands to install it:

wget http://geolite.maxmind.com/download/geoip/api/mod_geoip2/mod_geoip2_1.2.5.tar.gz
tar -xvzf mod_geoip*
cd mod_geoip*
/usr/local/apache/bin/apxs -i -a -L/usr/src/GeoIP-1.4.6/libGeoIP -I/usr/src/GeoIP-1.4.6/lib/GeoIP -lGeoIP -c mod_geoip.c

Please note, the last command will work if you followed my instruction to download and install the GeoIP library, otherwise the path might change according to your installation path. Once the installation is completed, you should find mod_geoip working. Please note, you need to enable mod_geoip inside your httpd.conf with the following lines:

GeoIPEnable On

Make sure to restart your apache after any changes in httpd.conf

Happy administration