snippetbashTip

knock — Port knocking client to open specific ports on firewall. More information: <https://manned.org/knock

Submitted by: @import:tldr-pages·Mar 2, 2026·

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portcommandclientspecificknockcliopenknocking

linux

Problem

How to use the knock command: Port knocking client to open specific ports on firewall. More information: <https://manned.org/knock>.

Solution

knock — Port knocking client to open specific ports on firewall. More information: <https://manned.org/knock>.

Knock on ports using different protocols:

knock {{hostname}} {{portnumber}}:{{protocol}}

Knock on port using UDP:

knock {{[-u|--udp]}} {{hostname}} {{portnumber}}

Force usage of IPv4/IPv6:

knock {{-4|-6}} {{hostname}} {{portnumber}}

Display errors and details of connection:

knock {{[-v|--verbose]}} {{hostname}} {{portnumber}}

Code Snippets

Knock on ports using different protocols

knock {{hostname}} {{portnumber}}:{{protocol}}

Knock on port using UDP

knock {{[-u|--udp]}} {{hostname}} {{portnumber}}

Force usage of IPv4/IPv6

knock {{-4|-6}} {{hostname}} {{portnumber}}

Display errors and details of connection

knock {{[-v|--verbose]}} {{hostname}} {{portnumber}}

Context

tldr-pages: linux/knock

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