linux resolves high concurrent socket maximum connections limit, TCP default 1024 connections

Linux as a server system, when the socket is running high concurrent TCP programs, the connection is usually established to a certain number of cases can no longer establish a connection

I am at work, testing high concurrent TCP program (GPS server-side program), multiple tests, found each connection established to 1000 or so, can no longer establish a TCP connection, the most total Internet search, Linux system default ulimit for 1024 access users can open the maximum number of programs. Typically a port has a maximum connection of 2 to 16 square 65535

• The first step, modify the/etc/security/limits.conf file, add the following line in the file (* Refer to the System user name), modify the Linux system on the user's number of open files soft limit and hard limit:

　　　　

6553565535

• In the second step, modify the/etc/pam.d/login file to add the following line to the file:

Session required/lib/security/pam_limits.so

If it is a 64bit system, it should be:
Session required/lib64/security/pam_limits.so

• In the third step, modify the/etc/sysctl.conf file to add the following line in the file (clear the original contents of the file) (Modify the Network kernel restrictions on TCP connections):

Net.ipv4.ip_local_port_range = 1024x768 65535net.core.rmem_max=16777216net.core.wmem_max=16777216net.ipv4.tcp_rmem= 4096 87380 16777216net.ipv4.tcp_wmem=4096 65536 16777216net.ipv4.tcp_fin_timeout = 10net.ipv4.tcp_tw_recycle = 1net.ipv4.tcp_timestamps = 0net.ipv4.tcp_window_scaling = 0net.ipv4.tcp_sack = 0net.core.netdev_max_backlog = 30000net.ipv4.tcp_no_metrics_save=1net.core.somaxconn = 262144net.ipv4.tcp_syncookies = 0net.ipv4.tcp_max_orphans = 262144net.ipv4.tcp_max_syn_backlog = 262144net.ipv4.tcp_synack_retries = 2net.ipv4.tcp_syn_retries = 2

• Fourth step, execute the following command (to make the above settings effective):

　　　　

/sbin/sysctl-p/etc/sysctl.conf/sbin/sysctl-w net.ipv4.route.flush=1

• Fifth step, execute the following command (Linux system optimized network must be high to allow the number of open files to support large concurrency, default 1024 is far from enough):

　

echo ULIMIT-HSN 65536 >>/etc/rc.local echo ulimit-hsn 65536 >>/root/.bash_profile ULIMIT-HSN 65536

• Sixth step, restart the machine.

By modification, TCP can reach 20,000 connections with no problem at all

linux resolves high concurrent socket maximum connections limit, TCP default 1024 connections