SSH : server unexpectedly closed network connection

marliyev · 07-24-2020, 01:37 AM

ssh too small and simple, no need to debug or investigate deep, all info, errors in real-time located on status message -> login attempts, port, ip, status, wrong login, wrong passwd etc. just try to login and look to systemctl status sshd.service, you will see whats wrong, thats all

michaelk · 07-24-2020, 04:43 AM

marliyev, I do not want to discourage participation but while ssh appears simple it is not. We are trying to help you as well as the OP and being argumentative with members that have more knowledge and experience is counterproductive.

Looking at authentication messages is a start but there are subtle errors that occur where additional debug information is required. Some errors like file permissions are just ignored. To say that all information is provided by login messages may be misleading for others who search here with similar problems.

marliyev · 07-24-2020, 04:58 AM

Quote:

Originally Posted by michaelk

marliyev, I do not want to discourage participation but while ssh appears simple it is not. We are trying to help you as well as the OP and being argumentative with members that have more knowledge and experience is counterproductive.

Looking at authentication messages is a start but there are subtle errors that occur where additional debug information is required. Some errors like file permissions are just ignored. To say that all information is provided by login messages may be misleading for others who search here with similar problems.

disagree about knowledge and experience, if you have moderator or LQ Guru label its not proof that you better than me

its not right way to give advice for simple question long comment, everybody can paste label moderator or Guru and begin searching google for answer

i know very well how you all answering questions))) if you are guru in linux, i have open thread go and answer for it, moderator)))

ondoho · 07-24-2020, 05:37 AM

In my case systemctl & journalctl give the exact same output for sshd.
Decreasing the priority of shown messages in journalctl has no effect. It's possible that would be different if I had actual errors happening, like OP.
In any case, journalctl seems to give more granular control.

@OP:

Code:

journalctl -n999 --no-pager -p7 | grep sshd

Turbocapitalist · 07-24-2020, 05:47 AM

You can refine that even more, if you have a system infected with systemd:

Code:

sudo journalctl --priority 7 --unit ssh

sudo journalctl --priority 7 --unit ssh --grep 'somepcre'

However, depending on how busy the SSH sever is there, the log may be too much noisy to conveniently find the problem. The method in #8 above works well in a production environment and creates an isolated but complete set of logs for easy analysis.

TB0ne · 07-24-2020, 07:55 AM

Quote:

Originally Posted by marliyev

ssh too small and simple, no need to debug or investigate deep, all info, errors in real-time located on status message -> login attempts, port, ip, status, wrong login, wrong passwd etc. just try to login and look to systemctl status sshd.service, you will see whats wrong, thats all

Still wrong; either you didn't understand what was said or you won't listen. Again, showing the status of the service won't tell you much at all.

Quote:

Originally Posted by marliyev

disagree about knowledge and experience, if you have moderator or LQ Guru label its not proof that you better than me its not right way to give advice for simple question long comment, everybody can paste label moderator or Guru and begin searching google for answer i know very well how you all answering questions))) if you are guru in linux, i have open thread go and answer for it, moderator)))

It is obvious you disagree about knowledge and experience, because it appears you have neither, and have no interest in learning. If you think all people do is Google, then its surprising that YOU haven't been able to figure out the problem and don't know better than to just suggest a status command.

And throwing out sarcastic insults then telling people to go answer your question is pretty funny. Why do you think ANYONE would want to help you at this point?

Quote:

Originally Posted by Turbocapitalist

You can refine that even more, if you have a system infected with systemd:

Code:

sudo journalctl --priority 7 --unit ssh
sudo journalctl --priority 7 --unit ssh --grep 'somepcre'

However, depending on how busy the SSH sever is there, the log may be too much noisy to conveniently find the problem. The method in #8 above works well in a production environment and creates an isolated but complete set of logs for easy analysis.

Agreed, but the OP is using Putty, ostensibly on a Windows system. The normal things for a SSH client to see verbosity may not work; not familiar enough with Putty to know that for certain, mind you. You can log connection attempts to a file and review it later, but the "-vvv" on the CLI is much easier (to me).

marliyev · 07-24-2020, 08:27 AM

Quote:

Originally Posted by TB0ne

Still wrong; either you didn't understand what was said or you won't listen. Again, showing the status of the service won't tell you much at all.

It is obvious you disagree about knowledge and experience, because it appears you have neither, and have no interest in learning. If you think all people do is Google, then its surprising that YOU haven't been able to figure out the problem and don't know better than to just suggest a status command.

And throwing out sarcastic insults then telling people to go answer your question is pretty funny. Why do you think ANYONE would want to help you at this point?

Agreed, but the OP is using Putty, ostensibly on a Windows system. The normal things for a SSH client to see verbosity may not work; not familiar enough with Putty to know that for certain, mind you. You can log connection attempts to a file and review it later, but the "-vvv" on the CLI is much easier (to me).

LQ Guru, how you doing?

are you seeking for job in internet cafe?

marliyev · 07-24-2020, 08:30 AM

attention for root and moderators!!! if someone steps on my foot, I will not be silent, give advice to your fake Guru users!!!

scasey · 07-24-2020, 01:55 PM

Quote:

Originally Posted by marliyev

LQ Guru, how you doing?

are you seeking for job in internet cafe?

Reported. Please review the LQ Rules...specifically.

Quote:

Do not post any messages that are obscene, vulgar, sexually-orientated, hateful, threatening, hostile or insulting.
Personal attacks on others will not be tolerated.
Flame Wars will not be tolerated.
Do not post if you do not have anything constructive to say in the post.

scasey · 07-24-2020, 05:29 PM

Back to the topic...
Had to jump over to a Windows box to review how PuTTY worked.

On the connection dialog there is a Logging tab where logging can be turned on:

Click image for larger version

Name: PuttyLog.JPG
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Size: 55.0 KB
ID: 33709

Capturing everything should yield some clues.

jeremy · 07-24-2020, 05:53 PM

marliyev, your posting privileges have been suspended for 24 hours. If you'd like to continue participating at LQ moving forward, please do ensure you follow the rules. If you have any questions, do feel free to contact me directly.

--jeremy