The simplest "is it alive" check
ping sends ICMP Echo Request packets and measures how long the Echo Reply takes to come back. It answers two questions at once: is the host reachable, and how fast is the round-trip. Despite being the oldest network tool in the kit, it's still the very first thing to reach for when something feels off.
Reading the output
Each reply line gives you four numbers worth knowing:
- icmp_seq — sequence number; gaps indicate packet loss.
- ttl — Time To Live; counts down by 1 at every router. A high TTL implies few hops; a low one implies many.
- time — round-trip in milliseconds; lower is faster.
- packet loss % — at the summary line; 0 % is good, 1–2 % is borderline, more is a real problem.
When ping lies
Some hosts and firewalls block ICMP. A failing ping doesn't always mean the host is dead — it might just be configured to ignore. Pair it with nc -zv host port on a service port (22, 443) when you need to confirm reachability beyond "will it answer pings."