A couple years ago, my coworker wrote a great post on finding disk space issues in Linux and how to resolve them. Helped me out this weekend when a critical server was having issues, so wanted to post it here:
http://www.randomlyexpressed.com/diagnosing-linux-disk-usage/
For future reference (after reading the post above)
Show filesystem usage:
~$ df -h
Show all
Duo has thorough documentation for adding MFA to your SSH sessions, but there are a couple additional steps needed to also integrate with Active Directory. This post will go through the installation for both Duo and Active Directory for Ubuntu 16.04. For other Linux distros, the Duo documentation linked above has you covered.
If you are using Duo Security MFA (highly recommended), you may want high-availability for your Duo Radius servers. Duo doesn't currently have a "supported" solution for this, but keepalived worked great after a quick call to support. This is also assuming you have followed Duo's instructions to install their radius server (found here)
First, install keepalived (basic instructions
If you need to debug traffic going to a linux server or appliance, you can use tcpdump to generate a pcap file you can analyze in wireshark.
For example, ssh into the server, and use the following command:
tcpdump -s0 port 80 and host 192.168.1.10 -wDebugTraffic.pcap
This will capture all traffic coming into port 80 from