knock(1)

📦
version 0.8.2 · 3 versions
, in alpine 3.22, alpine 3.23, alpine 3.24

💅 knock(1) — the port-knock client, bestie edition ✨

okay so you found the knock(1) man page and you're like "what is this" — don't worry, we're gonna get through it together 🫶 this is the manual for knock, and it's genuinely so much fun once it clicks.

🌸 NAME 🌸

knock — a port-knock client. that's the whole vibe. it knocks. on ports. iconic behavior tbh 👑

✨ SYNOPSIS ✨

knock [options] <host> <port[:proto]> [port[:proto]] ...

so it's knock, then whatever options you want, then the host, then one or more ports — and each port can optionally have :proto stuck on the end if you're feeling fancy 💅

🦋 DESCRIPTION 🦋

knock is a port-knock client, periodt. what it does is send TCP/UDP packets to each port you specify on host, and by doing that it creates a special knock sequence on the listening server. that's the whole trick — the server is listening for a specific little rhythm of knocks and you're out here performing it 🎀

if you wanna know the server side of this whole situation, go read the knockd manpage — that's where the extra info lives 👀

🎀 OPTIONS 🎀

  • -u, --udp — makes all your port hits use UDP instead of TCP (TCP is the default, fyi). but bestie, if you want each port to use a different protocol (some TCP, some UDP), you can just specify the protocol per-port instead. see the examples down below for how that looks ✨
  • -d <t>, --delay <t> — waits <t> milliseconds between each port hit. why would you want this? because sometimes your router sees your stream of SYN packets and is like "omg is this a port scan???" and blocks them 😭 but if you slow the packet rate down with --delay, then the router should let the packets through. crisis averted 💖
  • -4, --ipv4 <version> — forces usage of IPv4 🧚
  • -6, --ipv6 <version> — forces usage of IPv6 🌈
  • -v, --verbose — outputs verbose status messages, so you actually get to see what's happening instead of vibing in the dark 🔥
  • -V, --version — displays the version. short and sweet 🍓
  • -h, --help — syntax help. your little safety net when you forget how anything works 🙈

👑 EXAMPLES 👑

okay these are the moment, fr fr. first one — mixed protocols per port:

knock myserver.example.com 123:tcp 456:udp 789:tcp

see how each port gets its own :tcp or :udp? that's the per-port protocol thing from earlier. slay 🦋

and then this one — all UDP, no per-port labels needed because of -u:

knock -u myserver.example.com 8284 4721 18592 42912

look at that lil sequence of port numbers just knocking away 😭 so satisfying

💜 SEE ALSO 💜

knockd is the accompanying port-knock server — the other half of this whole relationship. you can't knock without somebody listening, iykyk 🫶

🌟 AUTHOR 🌟

Judd Vinet <jvinet@zeroflux.org> — the icon who made this happen 👑

and that's the whole page, bestie!! this version of the knock page comes to you from knockd 0.8.2, dated June 26, 2005 — yeah it's an oldie but it still ate 💅✨ go knock on some ports, you've got this 🎀

📦 where this page comes from