How do I remove a CLOSE WAIT socket connection

Question

I have written a small program that interacts with a server on a specific port  The program works fine  but   Once the program terminated unexpectedly  and ever since that socket connection is shown in CLOSE WAIT state  If I try to run a program it hangs and I have to force it close  which accumulates even more CLOSE WAIT socket connections   Is there a way to flush these connections

User · Answer

It is also worth noting that if your program spawns a new process, that process may inherit all your opened handles. Even after your own program closs, those inherited handles can still be alive via the orphaned child process. And they don't necessarily show up quite the same in netstat. But all the same, the socket will hang around in CLOSE_WAIT while this child process is alive.

I had a case where I was running ADB. ADB itself spawns a server process if its not already running. This inherited all my handles initially, but did not show up as owning any of them when I was investigating (the same was true for both macOS and Windows - not sure about Linux).

User · Answer

I m also having the same issue with a very latest Tomcat server  7 0 40   It goes non-responsive once for a couple of days   To see open connections  you may use   sudo netstat -tonp   grep jsvc   grep --regexp  127 0 0 1 443  --regexp  127 0 0 1 80    grep CLOSE WAIT   As mentioned in this post  you may use  proc sys net ipv4 tcp keepalive time to view the values  The value seems to be in seconds and defaults to 7200  i e  2 hours    To change them  you need to edit  etc sysctl conf   Open create   etc sysctl conf  Add  net ipv4 tcp keepalive time   120  and save the file Invoke  sysctl -p  etc sysctl conf  Verify using  cat  proc sys net ipv4 tcp keepalive time

User · Answer

You can forcibly close sockets with ss command  the ss command is a tool used to dump socket statistics and displays information in similar fashion  although simpler and faster  to netstat   To kill any socket in CLOSE WAIT state  run this  as root     ss --tcp state CLOSE-WAIT --kill

User · Answer

Even though too much of CLOSE WAIT connections means there is something wrong with your code in the first and this is accepted not good practice   You might want to check out  https   github com rghose kill-close-wait-connections  What this script does is send out the ACK which the connection was waiting for   This is what worked for me

User · Answer

It should be mentioned that the Socket instance in both client and the server end needs to explicitly invoke close    If only one of the ends invokes close   then too  the socket will remain in CLOSE WAIT state

User · Answer

As described by Crist Clark      CLOSE WAIT means that the local end of the connection has received a   FIN from the other end  but the OS is waiting for the program at the   local end to actually close its connection       The problem is your program running on the local machine is not   closing the socket  It is not a TCP tuning issue  A connection can    and quite correctly  stay in CLOSE WAIT forever while the program   holds the connection open       Once the local program closes the socket  the OS can send the FIN to   the remote end which transitions you to LAST ACK while you wait for   the ACK of the FIN  Once that is received  the connection is finished   and drops from the connection table  if your end is in CLOSE WAIT you   do not end up in the TIME WAIT state

User · Answer

CLOSE WAIT means your program is still running  and hasn t closed the socket  and the kernel is waiting for it to do so   Add -p to netstat to get the pid  and then kill it more forcefully  with SIGKILL if needed   That should get rid of your CLOSE WAIT sockets  You can also use ps to find the pid   SO REUSEADDR is for servers and TIME WAIT sockets  so doesn t apply here

[linux] How do I remove a CLOSE_WAIT socket connection

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