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Sysctl is a great way to optimize Linux. sysctl has a dozens of values which could drastically improve server networking and overall performance.
One of the many heplful variables to optimize the way the Linuz kernel works on busy servers is net.ipv4.ip_local_port_range .
The default sysctl setting for net.ipv4.ip_local_port_range on Debian, Ubuntu Fedora, RHEL, CentOS is:
net.ipv4.ip_local_port_range = 32768 65536
This means that the kernel and the corresponding server running services instructing the Linuz kernel open new port sockets can only open local ports in the range of 32768 – 65536 .
On a regular Desktop GNU/Linux machine or a not high iron server this settins is perfectly fine, however on a high scale servers the local port range in the interval of 32768-65536 might be insufficient at times, especially if there are programs which require binding of many local ports.
Therefore on a high load servers, generally it’s a good to raise the port range to be assigned by kernel to 8912 – 65536 , to do so the setting has to be changed like shown below:
linux:~# sysctl -w net.ipv4.ip_local_port_range = 8192 65536
If changing this setting on the server doesn’t show any negative impact on performance in few hours time or a day or even better decreases the server average load, it’s a good idea that it be added to sysctl.conf to load up the setting on next kernel boot.
linux:~# echo 'net.ipv4.ip_local_port_range' >> /etc/sysctl.conf