whenup

whenup

Start processes when a host is up, or just monitor its status using ICMP

If you're like me and doing lots of reconfigurations to stuff, that require a restart, it's very useful to be able to connect or run a command when the unit is ready again. The 'whenup' tool solves this:

whenup ssh myuser@mythingamabob

This tests for ICMP ping responses from mythingamabob before running the ssh command. The tool automagically figures out that mythingamabob is the host to check, using various hardcoded match patterns - this can be overridden on the command line, and there are lots of options to customize the behaviour.

Example: Terminate ssh and keep reconnecting when host is back up:

whenup -c -k ssh myuser@mythingamabob

Example: Just monitor host availability with toast notifications:

whenup -c -h mythingamabob

Full command line options:

whenup [-h|--host hostname|ip] [-i|--interval 200] [-t|--tolerance 1000] [-d|--delay 2000] [-m|--mode icmp] [-n|--notify true] [-c|--continious false] [-k|--kill false] [--] command [arguments]

• Host: Either a DNS resolvable name or an IP for the host to monitor
• Interval: Test if the host is reachable/ready every N milliseconds
• Tolerance: The host is down if it's not responsive at all after N milliseconds
• Delay: Wait N milliseconds after detecting the host is up, before running the command
• Mode: Test host reachable/ready using ICMP (only option for now)
• Notify: Use toasts to indicate a status change for the monitored host
• Continious: Switch from oneshot command mode to loop mode
• Kill: Terminate the launched process if the host is detected as down

On Linux you'll probably need to allow the binary to send ICMP packets:

setcap cap_net_raw=+ep /path/to/whenup