Detailed solution to a large number of time wait in linux

Problem description:
In Linux systems, the number of TCP TIME_WAIT sockets frequently reaches two or 30 thousand for High-concurrency Squid servers, and the server is easily dragged to death.
Solution:
By modifying linux kernel parameters, you can reduce the number of IME_WAIT sockets on linux servers.
Vi/etc/sysctl. conf
Add the following lines:
Copy codeThe Code is as follows: net. ipv4.tcp _ fin_timeout = 30
Net. ipv4.tcp _ keepalive_time = 1200
Net. ipv4.tcp _ syncookies = 1
Net. ipv4.tcp _ tw_reuse = 1
Net. ipv4.tcp _ tw_recycle = 1
Net. ipv4.ip _ local_port_range = 1024 65000
Net. ipv4.tcp _ max_syn_backlog = 8192
Net. ipv4.tcp _ max_tw_buckets = 5000

Note:
Net. ipv4.tcp _ syncookies = 1 indicates enabling SYN Cookies. When a SYN wait queue overflows, cookies are enabled to prevent a small number of SYN attacks. The default value is 0, indicating that the process is disabled;
Net. ipv4.tcp _ tw_reuse = 1 indicates enabling reuse. Allow TIME-WAIT sockets to be re-used for a New TCP connection. The default value is 0, indicating that the TCP connection is disabled;
Net. ipv4.tcp _ tw_recycle = 1 indicates to enable quick recovery of TIME-WAIT sockets in TCP connections. The default value is 0, indicating to disable it.
Net. ipv4.tcp _ fin_timeout = 30 indicates that if the socket is disabled by the local end, this parameter determines the time it remains in the FIN-WAIT-2 state.
Net. ipv4.tcp _ keepalive_time = 1200 indicates the frequency of keepalive messages sent by TCP when keepalive is in use. The default value is 2 hours, which is changed to 20 minutes.
Net. ipv4.ip _ local_port_range = 1024 65000 indicates the port range used for external connection. The default value is small: 32768 to 61000, Which is changed to 1024 to 65000.
Net. ipv4.tcp _ max_syn_backlog = 8192 indicates the length of the SYN queue. The default value is 1024. The length of the queue is 8192, which can accommodate more network connections waiting for connection.
Net. ipv4.tcp _ max_tw_buckets = 5000 indicates that the system maintains the maximum number of TIME_WAIT sockets at the same time. If this number is exceeded, the TIME_WAIT socket is immediately cleared and warning information is printed. The default value is 180000, Which is changed to 5000. For servers such as Apache and Nginx, the number of TIME_WAIT sockets can be greatly reduced by parameters in the previous lines, but the effect on Squid is not great. This parameter can control the maximum number of TIME_WAIT sockets to prevent the Squid server from being dragged to death by a large number of TIME_WAIT sockets.
Run the following command to make the configuration take effect:
/Sbin/sysctl-p