One way to check that computers are online (or responsive) is through ping.
This command demonstrates how much information (packets) is transmitted and how
many are received.
If both transmitted and received have the same number, then the computer is
online and accessible.
euid123@computer1:~$ ping computer2
PING computer2 (10.144.120.1) 56(84) bytes of data.
64 bytes from computer2 (10.144.120.1): icmp_seq=1 ttl=64 time=0.457 ms
64 bytes from computer2 (10.144.120.1): icmp_seq=2 ttl=64 time=0.486 ms
64 bytes from computer2 (10.144.120.1): icmp_seq=3 ttl=64 time=0.380 ms
^C
--- computer2 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 1998ms
rtt min/avg/max/mdev = 0.380/0.441/0.486/0.044 ms
To get out of ping, Cntrl+C must be used.
If the computer isn’t on the same network, then a hostname issue will be
returned.
If the computer is offline, an “unreachable” message will be returned.