Andy Smith wrote: > > On Thu, Aug 20, 2020 at 12:09:03PM +0700, Victor Sudakov wrote: > > There is a process listening on 127.0.0.1:8081 but for some reason > > netstat/sockstat/ss do not show it listening on IPv4. Is this a bug or a > > feature? > > I think it's listening on an IPv4-mapped IPv6 address so it can > accept either v4 or v6. Does this answer your question? > > https://unix.stackexchange.com/questions/152612/netstat-why-are-ipv4-daemons-listening-to-ports-listed-only-in-a-inet6 > > Daemons that want to receive connections will do the equivalent of: > > bind(address, port) > > The address will determine the interface and whether it is v4 or v6 > or whatever. If they instead do: > > bind(INADDR_ANY, port) > > then this will bind to every interface whether it's v4 or v6 and the > daemon will get udp6 or tcp6 sockets that can from fromn/to a v4 address. Thank you, Andy, that explains it. It's different in *BSD which got me confused. In *BSD, even if you bind to INADDR_ANY, you'll see something like this in sockstat output: root dovecot 39601 21 tcp4 *:110 *:* root dovecot 39601 22 tcp6 *:110 *:* root dovecot 39601 23 tcp4 *:995 *:* root dovecot 39601 24 tcp6 *:995 *:* -- Victor Sudakov, VAS4-RIPE, VAS47-RIPN 2:5005/49@fidonet http://vas.tomsk.ru/
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