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wiki:development:debugging

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X2Go Server Debugging

If you want to track down problems with the x2goserver or the cups-x2go code, it is possible to enable output of debug information into the systems syslog facility (normally /var/log/syslog).

The default log levels for x2goserver and cups-x2go are set to notice. Available log levels are: emerg, crit, alert, err, warning, notice, info, debug.

Log File Watching

While testing your X2Go server, you can open another terminal on the server and watch the syslog file:

root@x2goserver:~$ tail -f /var/log/syslog | grep x2go

Debugging x2goserver

The x2goserver log level can be set by editing:

root@x2goserver:~$ editor /etc/x2go/x2goserver.conf

Debugging cups-x2go

For debugging cups-x2go there are two files to look at:

  • /var/log/cups/error_log - in case cups-x2go code has a bug (e.g. a syntax error) or fails otherhow
  • /var/log/syslog - in case anything goes wrong while cups-x2go is processing a print job

For setting the log level of your CUPS server, please investigate the cupsd.conf man page:

$ man cupsd.conf

The cups-x2go log level can be set by editing:

root@x2goserver:~$ editor /etc/cups/cups-x2go

Customizing Debug Messages

All X2go server scripts are ready for syslogging, though not all of them actually do log to syslog. If you want to add your own syslog messages for debugging purposes, please take a look at the code of files that already do report to syslog. Here is a little howto that explains how to add extra log output to X2go server scripts:

Logging in X2Go Perl Scripts

Whereever you want to write a line to syslog from an X2Go Perl script, place this command:

syslog('debug', '<My message to syslog...>');

Logging in X2go Shell/Bash Scripts

Whereever you want to write a line to syslog from an X2Go Shell/Bash script, place this command:

$X2GO_LIB_PATH/x2gosyslog "$0" "debug" "<My message to syslog...>"

Python X2Go / PyHoca Debugging

The PyHoca clients both have a –libdebug option. Run pyhoca-gui or pyhoca-cli from the command line with that option enabled and you get blasted with debug output.

How To fix error - "Access denied. Authentication that can continue: publickey,keyboard-interactive"

Sometime in the past year or two of Ubuntu & Debian operating system updates something changed which caused the normal x2goclient session profile that requires the UserID -and- Password to be entered to fail giving an error message on the client that says: Access denied. Authentication that can continue: publickey,keyboard-interactive

Here's how to fix it.

Start a terminal session with your x2goserver and edit /etc/ssh/sshd_config

sudo nano /etc/ssh/sshd_config

in /etc/ssh/sshd_config (example was copied from Ubuntu 12.04) you will see the following entries:

# Change to yes to enable challenge-response passwords (beware issues with
# some PAM modules and threads)
ChallengeResponseAuthentication yes

# Change to no to disable tunnelled clear text passwords
PasswordAuthentication no

HOW TO FIX THIS

ChangeE PasswordAuthentication to “yes” and save the file.

then restart ssh

sudo /etc/init.d/ssh restart

REASON for the failure & change of behavior from previous/older versions of Ubuntu.

I installed several older versions of Ubuntu going back to Ubuntu 9.10 and found that the installations of the Ubuntu Server changed the content of the /etc/ssh/sshd_config file!

In older systems the entry for PasswordAuthentication either said:

# Change to no to disable tunnelled clear text passwords
# PasswordAuthentication no

where the PasswordAuthentication line was commented out … which then defaulted it to “YES”

-or-

the Password Authentication line was actually uncommented BUT set to “YES”

# Change to no to disable tunnelled clear text passwords
PasswordAuthentication yes

So those older OS versions and x2go would work using login ID's and Passwords.

Sometime during one of the Ubuntu 11.x releases the PasswordAuthentication entry was actually changed to “no” as is the case in Ubuntu 12.04 servers and the line was left not commented out so it was active…

# Change to no to disable tunnelled clear text passwords
PasswordAuthentication no

That is what caused the failure of x2go logins using passwords and would present the user with that error message:

Access denied. Authentication that can continue: publickey,keyboard-interactive

wiki/development/debugging.1335368278.txt.gz · Last modified: 2013/03/08 13:31 (external edit)