Boost Linux Server Performance: Essential Kernel and Sysctl Tweaks

Permanently Disable SELinux

SELinux improves security but can cause trouble; to disable edit /etc/selinux/config, change SELINUX=enforcing to SELINUX=disabled, save and reboot.

# vim /etc/selinux/config
# reboot

Set System Runlevel to 3

Running at runlevel 3 saves resources. Edit /etc/inittab to set initdefault to 3 or use init 3.

# grep 3:initdefault /etc/inittab
id:3:initdefault:
# init 3

Increase Maximum File Descriptors

Edit /etc/security/limits.conf and set higher soft and hard limits for nofile and nproc for all users.

* soft nofile 65536
* hard nofile 65536
* soft nproc 65536
* hard nproc 65536

Explanation: * applies to all users; nofile is max open files; nproc is max processes.

Adjust Kernel Network Parameters (/etc/sysctl.conf)

Modify network settings to improve load handling and prevent packet loss.

net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_tw_recycle = 1
net.ipv4.tcp_fin_timeout = 30
net.ipv4.tcp_keepalive_time = 1200
net.ipv4.ip_local_port_range = 1024 65000
net.ipv4.tcp_max_syn_backlog = 8192
net.nf_conntrack_max = 655360

Enables SYN cookies, reuses TIME‑WAIT sockets, recycles them, reduces FIN timeout, shortens keepalive interval, expands local port range, enlarges SYN backlog, and raises conntrack table size.

Firewall‑Related Sysctl Settings

Add the above parameters to the end of /etc/sysctl.conf (or sysctl.conf.first) and apply with sysctl -p.

Common Exceptions

Too many open files – caused by high concurrency or not closing I/O; resolve by increasing file descriptor limits.

Connection timeout – often due to many TIME_WAIT sockets; fix by correcting application behavior and adjusting kernel/network settings.

Useful Commands

Check network socket states:

netstat -n | awk '/^tcp/ {++state[$NF]} END {for(key in state) print key, "\t", state[key]}'

State descriptions: CLOSED, LISTEN, SYN_RECV, SYN_SENT, ESTABLISHED, FIN_WAIT1, FIN_WAIT2, TIME_WAIT, LAST_ACK, etc.

Conclusion

Linux offers many tunable kernel parameters; proper adjustments can significantly boost server processing capability.