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# netstat -at
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 localhost:30037         *:*                     LISTEN
tcp        0      0 localhost:ipp           *:*                     LISTEN
tcp        0      0 *:smtp                  *:*                     LISTEN
tcp6       0      0 localhost:ipp           [::]:*                  LISTEN

What does the asterisk * in *:smtp mean ?

Why is there no IP address shown?

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up vote 3 down vote accepted

It is a wildcard meaning "any".

For example, in the third line:

tcp        0      0 *:smtp                  *:*                     LISTEN

The first *, in *:smtp, means the process is listening on all of the IP addresses the machine has. The second *, in *:*, means connections can come from any IP address. The third *, in *:*, means the connection can originate from any port on the remote machine.

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Thank you, that helped. Is it right to say, the first * means 'listen on all network interfaces the system has' ? – John Threepwood Aug 10 '12 at 22:14
Yes, in the "Local Address" column. (It has different meaning in the "Foreign Address" column) – dsh Aug 10 '12 at 22:16
Does this mean that it listens on both IPv4 and IPv6? – Anton Rudeshko Jun 2 '15 at 14:30

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