Hi!
It happens time to time on our x2go server, that the CPU usage goes almost 100% on a single CPU. The high usage is caused by the sshd process which runs the <username>@notty, in PS it looks like this:
root 32768 25441 7 Apr28 ? 03:14:44 sshd: myuser@notty
An strace of the process shows that the number of open files reached the predefined limit:
...
accept(7, 0x7fff6d2bccb0, [128]) = -1 EMFILE (Too many open files)
socket(PF_FILE, SOCK_DGRAM|SOCK_CLOEXEC, 0) = -1 EMFILE (Too many open files)
select(4096, [3 5 7 8 9], [], NULL, NULL) = 1 (in [7])
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
...
Increasing the limit "nofile" solves the high CPU problem only temporarily, as the number of open files increases with the time monotonously (at a rate of ~1/20 sec).
Checking the files opened by the given process shows, the following
...
sshd 32768 root 8499u IPv4 1542181459 0t0 TCP loopback:30028->loopback:51585 (CLOSE_WAIT)
...
The number of such CLOSE_WAIT entries is several thousands.
Netstat shows a similar view:
...
tcp 0 0 127.0.0.1:30028 127.0.0.1:38163 CLOSE_WAIT 32768/sshd
...
After increasing the limit of open files I logged the strace of the process during a period when the number of CLOSE_WAIT connections increases (see attached file).
The user is doing nothing, he is just logged in with x2go, but doesn't run any active processes, he doesn't even use the server.
Has anyone experienced the same problem or has any explanation for this behaviour?
Regards
Swizzly
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