"Remote side unexpectedly closed network connection" - where is it logged? O_o

Help! (Home for newbies)
1

Hello,

Those last days, I am getting a LOT of “Remote side unexpectedly closed network connection” errors in my WinSCP client, when attempting to connect by SFTP to websites I host on my dedi (Debian 10, virtualmin, webmin).

The connection gets eventually done, but sometimes it will work on the first attempt, some other times on the 6th, see the idea?

I would very much like to investigate what may cause it, unfortunately, I don’t find where this kind of event appears to be logged. I searched for my IP in the log files listed in webmin > system > system logs, and nothing relevant came up.
In case my IP is changed or it’s either IPv4 or IPv6 that shows up, I loaded in my web browser a bogus filethatdoesnotexist.jpg on a domain, and found my IP on that domain’s apache error log when searching for filethatdoesnotexist.jpg, so I’m confident I searched the right IP number for me.

All monitored services are up, there’s no bottleneck in the server’s resources (CPU, RAM, disk, etc), so it must be something software-related, thus: something that is logged. I’ve just gotta find where it is logged :smiley:

If you can help me with a suggestion or a “duh, it’s logged there (and here’s why your IP wasn’t in there)”, I will be very grateful, thank you!

2

Could be /var/log/secure, but could also be journalctl -u ssh or journalctl -u sshd.

3

could also be in /var/log/auth.log and/or /var/log/proftpd/sftp.log…

4

You can know for sure whether it is in the proftpd sftp log, as it is only in play on port 2222.

5

Hello!

Thank you for the replies, I am sorry I forgot to reply when it was fresh.

I come back with a conclusion, this was not a virtualmin problem, actually. Two other persons tested connecting on their side, and didn’t meet any of the problems I faced, despite multiple tests.

As I changed my IP multiple times, tried on a second computer, and still had that issue nonetheless, I can only conclude it’s an odd issue with “the tubes”, something between my router and my dedicated server, in the way, has issues. The frequency of connexions failing also varies over time, up or down, apparently at random, so clearly it’s something outside of my reach, with its own reasons.
I can only imagine it will eventually be fixed with a random maintenance somewhere ¯_(ツ)_/¯