[LINUX] Kernel parameters to modify often

What I personally fix well

When there are not enough file descriptors

Socket is also included in the FD, but it is overlooked. This kind of error occurs almost first. Nginx Too many open files error etc. Check with ʻulimit -n`, but note that it is executed by the user who encountered the error. It may be different for root.

[anyuser]$ ulimit -n
1024

In this case, only 1024 FDs can be used.

counter-measure

Modify limits.conf. Note that depending on the case, only root is often set to FD, and if nothing is set, the default will be 1024. Change both the soft limit and the hard limit. The value is determined as appropriate. The following is when changing the FD of anyuser.

/etc/security/limits.conf


*                soft    core            unlimited
*                hard    core            unlimited
root             soft    nofile          65536
root             hard    nofile          65536
anyuser soft nofile 65536 ← Add here
anyuser hard nofile 65536 ← Add here

Confirmation method

Even if it is described in /etc/security/limits.conf, it may not be reflected. Ssh to the server, check the process ID of the process, and check with cat / proc / <process_ID> / limits.

port depletion or something

If throughput does not come out even though it is not a resource bottleneck, any port may be exhausted.

In most cases, if you check the server with netstat, a large amount of TIME_WAIT may occur and any port may be used up.

It is quite common. https://qiita.com/kuni-nakaji/items/c07004c7d9e5bb683bc2 This can be confirmed with the following command.

[[email protected]]# netstat -antp
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 0.0.0.0:111             0.0.0.0:               LISTEN      1/systemd
tcp        0      0 127.0.0.1:25            0.0.0.0:               LISTEN      1211/master
tcp        0      0 0.0.0.0:12127           0.0.0.0:               LISTEN      8689/sshd
tcp        0      0 10.140.180.223:12127    10.140.50.217:61738     ESTABLISHED 14604/sshd: appladm 
tcp6       0      0 :::40042                :::                    LISTEN      12232/java
tcp6       0      0 :::111                  :::                    LISTEN      1/systemd
tcp6       0      0 :::8080                 :::                    LISTEN      12232/java
tcp6       0      0 :::34710                :::                    LISTEN      12232/java
tcp6       0      0 :::12120                :::                    LISTEN      12232/java
tcp6       0      0 ::1:25                  :::                    LISTEN      1211/master
tcp6       0      0 :::12127                :::                    LISTEN      8689/sshd
tcp6       0      0 10.140.180.223:42881    10.140.197.150:3306     ESTABLISHED 12232/java 

counter-measure

Modify the following ip_local_port_range and modify tcp_tw_reuse to 1. (Add if there is no entry for tcp_tw_reuse.) It is not recommended to modify other parameters.

/etc/sysctl.conf


net.ipv4.ip_local_port_range = 30000 65500
net.ipv4.tcp_tw_reuse = 0

Reflect with sysctl -p when completed.

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