ping Command

Use the ping command to find out whether there is IP connectivity to a particular host. The basic syntax is:

/usr/sbin/ping host [timeout]

where host is the host name of the machine in question. The optional timeout argument indicates the time in seconds for ping to keep trying to reach the machine--20 seconds by default. The ping(1M) man page describes additional syntaxes and options.

When you run ping, the ICMP protocol sends a datagram to the host you specify, asking for a response. (ICMP is the protocol responsible for error handling on a TCP/IP network. See "ICMP Protocol" for details.)

Suppose you type:

$ ping elvis

If host elvis is up, this message is displayed:

elvis is alive

indicating that elvis responded to the ICMP request. However, if elvis is down or cannot receive the ICMP packets, you receive the following response from ping:

no answer from elvis

If you suspect that a machine might be losing packets even though it is up, you can use the s option of ping to try to detect the problem. For example, type:

$ ping -s elvis 

ping continually sends packets to elvis until you send an interrupt character or a timeout occurs. The responses on your screen will resemble:

PING elvis: 56 data bytes
64 bytes from 129.144.50.21: icmp_seq=0. time=80. ms
64 bytes from 129.144.50.21: icmp_seq=1. time=0. ms
64 bytes from 129.144.50.21: icmp_seq=2. time=0. ms
64 bytes from 129.144.50.21: icmp_seq=3. time=0. ms
.
.
.
----elvis PING Statistics----
4 packets transmitted, 4 packets received, 0% packet loss
round-trip (ms) min/avg/max = 0/20/80   

The packet-loss statistic indicates whether the host has dropped packets.

If ping fails, check the status of the network reported by ifconfig and netstat, as described in "ifconfig Command" and "netstat Command".