What are the various levels in ssh -vvv: debug1, debug2, debug3

Question

Is each a different side of the connection or a deeper layer of logging. I am interested because of, for example, this excerpt from a vvv output

debug3: send packet: type 30
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
Connection reset by nnnn port 22

Looking through the output I can't determine which side is saying what.

Thanks for the acceptance! Favour returned: question upvoted! ;-) (I don't know why it attracted a downvote in the first place...) — Fabby, Dec 04 '18 at 12:46

Fabby · Accepted Answer · 2022-07-05T14:20:35.653

6

The short answer:

Yes!

The long answer:

From [man ssh][1]:

-v
Verbose mode. Causes ssh to print debugging messages about its progress. This is helpful in debugging connection, authentication, and configuration problems. Multiple -v options increase the verbosity. The maximum is 3.

To see what it really does, have a look at the [edits on this question][2] as we asked the OP to go from -v to -vvv (Debug levels 2 and 3 for -vv and -vvv respectively)
For even more information, have a look at RFC4252, Section 6 [1]: http://man7.org/linux/man-pages/man1/ssh.1.html [2]: https://unix.stackexchange.com/posts/483302/revisions "SSH forwarded through modem recently started failing"

edited Jul 05 '22 at 14:20

answered Nov 22 '18 at 19:57

Fabby

5,384

So you're saying that -v, -vv, -vvv, are equivalent to LogLevel DEBUG1, LogLevel DEBUG2, LogLevel DEBUG3 in the ~/.ssh/config file. Then, what ssh argument should I use that will be equivalent to LogLevel VERBOSE? – cowlinator May 07 '20 at 01:29
Also, as a note, the debug3 output can be a little cryptic. You may want to look up RFC 4252 section 6 for help with the packet numbers. – cowlinator May 07 '20 at 01:50
@cowlinator Added to answer: Feel free to do this yourself next time! You can edit any answer here! (Due to your rep here, you will go through the review process) As to your LogLevel VERBOSE question: maybe post an additional question??? 0:-) – Fabby May 08 '20 at 09:58

score 3 · Answer 2 · answered Nov 22 '18 at 20:35

In ssh I have noticed that:

ssh -v
    will tell you what is happening mostly on your end
ssh -vv 
    will tell you low level on both ends
ssh -vvv
    will tell you almost everything from both ends.

Hence the conversation :

debug1:Some useful information from 1
debug2:Some useful information from 2
debug1:Some useful information from 1
debug3:Some useful information about what is passing between both and more..

What are the various levels in ssh -vvv: debug1, debug2, debug3

2 Answers2

The short answer:

The long answer: