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The `ping' command allows the user to check if another system is currently "up" and running. The general form of the command is `ping system'.(11) For example,

ping cs.widener.edu

will tell you if the main machine in Widener University's Computer Science lab is currently online (we certainly hope so!).

Many implementations of `ping' also include an option to let you see how fast a link is running (to give you some idea of the load on the network). For example:

% ping -s cs.swarthmore.edu
PING cs.swarthmore.edu: 56 data bytes
64 bytes from icmp_seq=0 ttl=251 time=66 ms
64 bytes from icmp_seq=1 ttl=251 time=45 ms
64 bytes from icmp_seq=2 ttl=251 time=46 ms
--- cs.swarthmore.edu ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 45/52/66 ms

This case tells us that for `cs.swarthmore.edu' it takes about 46 milliseconds for a packet to go from Widener to Swarthmore College and back again. It also gives the average and worst-case speeds, and any packet loss that may have occurred (e.g. because of network congestion).

While `ping' generally doesn't hurt network performance, you shouldn't use it too often--usually once or twice will leave you relatively sure of the other system's state.

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