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Functions

Check if TCP port 25 is open

Terminal - Check if TCP port 25 is open
sudo lsof -iTCP:25
2013-11-20 08:26:37
User: netaxiz
Functions: sudo
-2
Check if TCP port 25 is open

Alternatives

There is 1 alternative - vote for the best!

Terminal - Alternatives
(echo >/dev/tcp/localhost/25) &>/dev/null && echo "TCP port 25 open" || echo "TCP port 25 close"
2013-11-12 02:11:01
User: YouM
Functions: echo
0

Check trough unix sockets if tcp port is open or close

netstat -tln | grep :25
2013-11-12 16:47:06
User: Peteches
Functions: grep netstat
0

netstat will list all open ports on the system, unix sockets, tcp sockets and udp sockets. the t flag limits to tcp ports the l flag limits to listening ports and the n flag disables the translation of port to service ( ie :25 displayed instead of :smtp ). then grep for the port you are interested in preceeded by a colon.

sudo lsof -iTCP:25 -sTCP:LISTEN
nc -zv localhost 25
2013-11-21 22:04:00
User: toaster
0

Using netcat (nc)

25 can be replaced with the friendly value (smtp). Check error code for result or use -v option to echo output

nc -z localhost smtp && echo open || echo closed

nc -zv host protocol

netstat -lntp

Know a better way?

If you can do better, submit your command here.

What others think

That would include outgoing connections that are not listening.

Comment by pdxdoughnut 208 weeks and 4 days ago

I use:

netstat -lnpt4|grep :25
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Comment by scott154 10 weeks and 6 days ago

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