Networking
How to check IP addresses and network interfaces in Linux
List IP addresses, interfaces, and link state with ip addr and ip link, including a compact one-line brief.
How to check firewall rules in Linux
Check the active firewall rules with firewall-cmd on RHEL/Oracle Linux, ufw on Ubuntu, and nft as the low-level view.
How to test if a remote port is open in Linux
Check whether a TCP port on a remote host is reachable with nc, bash /dev/tcp, and curl, without installing telnet.
How to check listening ports in Linux
List listening TCP and UDP ports and the process owning each with ss -tulpn, the modern replacement for netstat.
How to check the routing table and test connectivity in Linux
View the routing table with ip route and test reachability and the path to a host with ping and traceroute.
How to do a DNS lookup in Linux
Resolve hostnames and check DNS records with dig and host, and see the configured resolvers in /etc/resolv.conf.
How to check network statistics and interface errors in Linux
Check socket summary counts and per-interface packet, error, and drop counters with ss -s and ip -s link.