Knock 🚪

knock is a simple, command-line network reachability tester. I made knock because I found myself using telnet to test if I could successfully connect to remote databases, webservers, and the like fairly often and realized that I don't actually need all of the features and historical baggage of that software: I just want to know if I can get from point A to B. knock is designed around this use-case. Other tools like ncat do more and better, but they also bring needless complexity to this task.

Installation

Build from source or download a pre-built binary.

$ ./build.tcl

Usage

You can call knock just like telnet:

$ knock localhost 8080
Failed: connection refused.

Or with a colon:

$ knock 192.168.100.1:22
Succeeded.

Or with option flags:

$ knock -time 10 -dest example.com -port 8000 -net tcp
Failed: connection timed out after 10 seconds.

Normally, any problem connecting will be reported to the user as explicitly as possible. Unlike telnet, knock will never prompt the user for interactive input. As soon as a connection succeeds, knock will hang up and report back that success.

Options

Option	Description
-dest	Network destination address or name
-net	Network type to use (default tcp)
-port	Port number to knock on destination (default 80)
-time	Time to wait in seconds before giving up (default 15)

Networks

Supported network types are tcp, tcp4, tcp6, udp, udp4, udp6, ip, ip4, ip6 , unix, unixgram, and unixpacket. The network types with 4 in their name are IPv4-only, and those with 6 are IPv6-only.

Miscellaneous

Knock is open source-software distributed under the 0BSD license. To report bugs or view source code, see https://codeberg.org/nat-418/knock.