digup is a console tool to update md5sum or shasum digest files. It will read existing digest files, check the current directory for new, updated, modified, renamed, or deleted files, and query the user with a summary of changes. After reviewing the updates, they can be written back to the digest file. This makes digup very useful to update and verify incremental archives like chronological data storages, which are commonly stored and backed up on hard disks. Using a full file digest scan, even slowly creeping bad blocks on old hard disks can be detected. By using a crontab entry, this check can be performed unattended and routinely.
Nagios is a host, service, and network monitoring system that will watch your network and alert you to problems before your clients or end-users do. The system runs checks on hosts and services that you specify using plugins that return status information to Nagios. When problems are encountered, the system will send notifications to system administrators so that they can take action on the problem. The JumpBox for Nagios gives you a head start to using the system. It eliminates the complexity involved in getting the application installed, and allows you to focus on the configuration for your specific environment. Since Nagios is based on plugins, depending on what you want to do this will vary in complexity.
GroundWork Monitor Community Edition can give you insight into your computing infrastructure, allowing you to see the current and historical states of all your computers: servers, desktops, and laptops, all of your network devices, all of your services (like TCP/IP and Web services), and all of your applications (like mail servers and database apps). You can choose to be alerted when something goes awry via pager, SMS, email, or phone, and even set up automatic restarts or fall-overs.
Ganglia is a scalable distributed monitoring system for high-performance computing systems such as clusters and grids. It is based on a hierarchical design targeted at federations of clusters. Ganglia is currently in use on over 500 clusters around the world and has scaled to handle clusters with 2000 nodes.
PortSensor is a powerful Windows/Unix server monitoring tool with Linux/Mac/Windows clients. Sensors can be created to monitor nearly any TCP/UDP service, such as: HTTP, FTP, POP3, SMTP, MySQL, and DNS. Custom sensors can be created to monitor your other critical server metrics, such as processor loads, mail queue loads, disk space usage, and log activity.