knock, knockd: add page (#14316)

* knock.md and knockd.md

* Update pages/linux/knock.md

Co-authored-by: Sebastiaan Speck <12570668+sebastiaanspeck@users.noreply.github.com>

* Update pages/linux/knock.md

Co-authored-by: Sebastiaan Speck <12570668+sebastiaanspeck@users.noreply.github.com>

* Update pages/linux/knock.md

Co-authored-by: Wiktor Perskawiec <git@spageektti.cc>

---------

Co-authored-by: Sebastiaan Speck <12570668+sebastiaanspeck@users.noreply.github.com>
Co-authored-by: Wiktor Perskawiec <git@spageektti.cc>

pages/linux/knock.md

@@ -0,0 +1,20 @@
+# 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 {{hostname}} {{portnumber}}`
+
+- Force usage of IPv4/IPv6:
+
+`knock {{-4|-6}} {{hostname}} {{portnumber}}`
+
+- Display errors and details of connection:
+
+`knock -v {{hostname}} {{portnumber}}`

pages/linux/knockd.md

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+# knockd
+
+> Port knocking daemon to listen for port knocking and execute scripts.
+> More information: <https://manned.org/knockd>.
+
+- Start knockd system daemon:
+
+`knockd -d`
+
+- Use specified configuration file for knockd:
+
+`knockd -c {{path/to/file}}.configuration`