ARCHIVED: In Unix, how can I check whether a networked computer has crashed?

To see whether a networked computer has crashed or otherwise become unavailable, try using the Unix ping command, which reports whether a computer at a particular address or IP number is responding. The syntax for ping is:

  ping address

Replace address with the name of the computer you want to check. Because ping may be stored in a directory that is not included in your path, you may have to include the full path name for the program in order to use it. Often, ping is located in the /etc, /sbin, or /usr/sbin directory, so you may need to enter one of the following:

  /etc/ping address

  /sbin/ping address

  /usr/sbin/ping address

Replace address with the hostname of the computer in question. For example, to check whether the host mail-relay.iu.edu is up, you would enter:

  /etc/ping mail-relay.iu.edu

On some systems, ping will simply respond with a message indicating whether the system is up or down, though typically this behavior can be modified. On other systems, ping sends packets to the remote host and returns information in one second intervals (by default) about how the host responds. If the version of ping on your system does not do this, but simply reports if a host is alive or not, you may be able to change this by including -s in the command, for example:

  /etc/ping -s mail-relay.iu.edu

Press Ctrl-c to stop ping from sending out any more packets; ping then will produce a summary of the remote host's responses. The summary will include the number of packets transmitted, the number received, the percentage of packets lost, and how long it took for each packet to be received and returned. Ideally, the number of packets received should be equal to the number transmitted. If the remote host has a problem, packet loss may occur (i.e., the number of packets received will be fewer than the number transmitted).

Note: In some situations, a remote computer may respond to ping, but not be reachable by other network tools such as SFTP or rlogin.

For more information about the ping command, at the Unix prompt, enter man ping.