A useful selection of open source/freeware tools that no system administrator should be without
Nmap – A security scanner useful for network inventory, checking for rogue systems on your network and helpful when firewall hardening. The program boasts a large number of command switches, and the author Fyodor has even released a book all about the program
Nessus – Free for home, licensed for business use. A very effective vulnerability scanner. Regular updates mean that the software is always aware of the very latest in documented OS vulnerabilities. You can setup Nessus to scan a single, or range of IP’s, and the intensity of the scan can also be adjusted (safe scan – useful if you’re worried about the stability of specific systems). Very customisable scanning options include variable port ranges, TCP, UDP and SNMP specific scans are just a few of the options available. A very effective tool to assist every system administrator or security consultant.
BartPE Builder – Used very recently (aligning disks blog entry) to create boot media. There are many freeware plugins, such as disk management, AV, spyware scanning tools and plenty more that can be integrated into the build
PRTG – The free version of PRTG allows you to monitor up to 10 sensors (20 if you place a link on your website to paessler.com – see website). This is a very useful tool for monitoring bandwidth on SNMP enabled devices. I personally use this on my home Juniper SSG firewall to monitor the traffic flowing through the Internal, External and DMZ interfaces.
Elog – A web-based logging system. Very useful to help comply with PCIDSS standards, and a good reference point if used as a change log system.