linux

general

• echo -n - do not output a trailing newline
• _COMMAND_1_; _COMMAND_2_ - sequential/multiple commands
• = in less - show current position in the document
• -N then CR in less - show line numbers
• globbing - pattern matching, not regex; * - any character any number of times; ? - one character; [abc] - a or b or c; [0-9] - digits
• grep -F - normal search, no regex

networking

• sudo ip link set _INTERFACE_ { down | up } - enable/disable interface
• sudo ip a add _IP_/_PREFIX_ dev _INTERFACE_ - add an IP to interface
• sudo ip a del _IP_/_PREFIX_ dev _INTERFACE_ - remove an IP address from interface
• ip r get _IP_ - show route for an IP
• sudo ip r add _IP_/_PREFIX_ via _GATEWAY_IP_ [ dev _INTERFACE_ ] - add a route
• sudo ip r del _IP_/_PREFIX_ via _GATEWAY_IP_ [ dev _INTERFACE_ ] - delete a route

firewalld

• sudo firewall-cmd --list-all - show active config
• firewall-cmd --get-services - show services
• firewall-cmd --info-service _SERVICE_ - show info about a service
• /usr/lib/firewalld/ - directory with firewalld XML files
• sudo firewall-cmd --add-service=_SERVICE_ - add a service to firewall, only valid until reboot, add --permananent to make it persistent through the reboot
• sudo firewall-cmd --add-port=_PORT_/_PROTOCOL_ - add a protocol; protocol is in { tcp | udp | sctp | dccp }
• sudo firewall-cmd --remove-service=_SERVICE_ - remove a service
• sudo firewall-cmd --remove-port=_PORT_/_PROTOCOL_ - remove a port
• sudo firewall-cmd --reload - reload rules to update the running config