3

I have a network device (a scanner) that can scan to SFTP. Unfortunately, it's giving me problems. I can see from the SSH logs that it's able to login, but I can't see what it's doing after that. I think it's running into a file or directory not found situation. The device has no verbose logging capability. So I have to do this on the server somehow.

How can I monitor/log what happens after it has successfully establish an SSH connection?

  • What is this device? Does it have shell access, can you run strace and restart the SSH daemon? Can you not run sshd more verbosely and/or run it in the foreground? – slm Sep 1 '18 at 21:53
  • I see why the confusion. I amended the question. It's a scanner. It uses SFTP. I can run strace and restart the ssh daemon. I'll see what it does. – 010110110101 Sep 1 '18 at 22:10
  • I just did a bit ago. – slm Sep 2 '18 at 3:38
1

Per this solution from the RHEL forums titled: How to configure SSH to debug mode?

Method #1 - sshd on another port

$ /usr/sbin/sshd -ddd -D -p (port) 2>&1

Then to connect to it:

$ ssh -p (port)

Method #2 - change sshd's config file

$ vim /etc/ssh/sshd_config

Then change the loglevel:

LogLevel DEBUG3

And then restart sshd.

$ service sshd restart

sshd_config man page

$ man sshd_config
...
LogLevel:

Gives the verbosity level that is used when logging messages from sshd.  
The possible values are: QUIET, FATAL, ERROR, INFO, VER-BOSE, DEBUG, DEBUG1, 
DEBUG2 and DEBUG3. The default is INFO. DEBUG and DEBUG1 are equivalent. DEBUG2 
and DEBUG3 each specify higher levels of debugging output. Logging with a DEBUG 
level violates the privacy of users and is not recommended.
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0

The best solution would be to enable TTY logging so it shows up in audit logs

echo "session     required      pam_tty_audit.so enable=*" >> /etc/pam.d/password-auth-ac
echo "session     required      pam_tty_audit.so enable=*" >> /etc/pam.d/system-auth-ac

Then, to view the logs you can use:

aureport --tty
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