Lately, I had some trouble with OpenSSH log (by default on Debian, the file is located at /var/log/auth.log). My problem is that the log file is empty. For example, it is impossible to set up a system, which prevents Brute Force attacks (to prevent this, we need to look into the log). The first thing I did is to restart the SSH server by launching this command:
Unfortunately, it does not work. So, I tried to find the source of the problem in the configuration file. Although I never need to configure OpenSSH to activate log file (by default, OpenSSH writes automatically into a log file), I checked if all variables are correctly configured. In /etc/ssh/sshd_config file, two variable are useful for us:
On Internet, we can find a solution that replace LogLevel INFO by LogLevel VERBOSE:
After replacing and restarting the SSH server, nothing appeared in the log file and it was still blank.
As often, it is a file ownership problem: OpenSSH uses syslog protocol to handle log information. A solution is to restart rsyslog daemon with root privilege:
sudo /etc/init.d/rsyslog restart
I wrote this post because on the one hand, I had this problem several times. So, I will not forget the solution anymore (I have a short memory) and on the other hand, I hope this post will help someone in the same situation as me.