Sometimes we find a large number of TIME-WAIT connections on the server, as many as tens of thousands. By modifying the kernel parameters, the system can quickly recycle time-wait {This article is only for your own use, please do not spray}
Check the TCP connection status:
[root@centos ~]# netstat -n | awk '/^tcp/ {++S[$NF]} END {for(a in S) print a, S[a]}'
LAST_ACK 56
SYN_RECV 77
ESTABLISHED 11213
FIN_WAIT1 4013
FIN_WAIT2 1638
CLOSING 3
TIME_WAIT 12261
Modify kernel parameters to quickly recycle time_wait sockets:
[root@centos ~]# echo "net.ipv4.tcp_tw_reuse = 1" >> /etc/sysctl.conf
# means to enable reuse. Allow TIME-WAIT sockets to be reused for new TCP connections, the default is 0, which means close;
[root@centos ~]# echo "net.ipv4.tcp_tw_recycle = 1" >> /etc/sysctl.conf
# Indicates to enable fast recycling of TIME-WAIT sockets in TCP connections, the default is 0, which means close.
[root@centos ~]# sysctl -p
After the modification is completed, look at the TCP connection status. The time-wait connection is significantly reduced, and it feels that accessing Apache is much faster.
[root@centos ~]# netstat -n | awk '/^tcp/ {++S[$NF]} END {for(a in S) print a, S[a]}'
LAST_ACK 26
SYN_RECV 225
ESTABLISHED 9228
FIN_WAIT1 4002
FIN_WAIT2 611
CLOSING 2
TIME_WAIT 415