netstat and port question

[Carine Parmentier]

Hi,
Is there anyone who can respond to my 2 outstanding questions :
- in the netstat command without any arguments, you find in the type column stream or datagram. What does stream exactly mean ?
- When you need to add your own applications in the /etc/services port list, is there a quick way to search wheather there are already some particular processes running using a portnr ?
thks for the help
Carine

[harry d brown jr · Accepted solution]

man stream
man UDP

ports: http://www.iana.org/assignments/port-numbers

use lsof to find active processes: http://hpux.ee.ualberta.ca/hppd/hpux/Sysadmin/lsof-4.74/

live free or die
harry d brown jr

[TwoProc]

I think a datagram would be, for example, a request from an http server. That is a simple open connection, get request, submit reply, close connection type of sequence. In the case, the serving process knows to close the connection after the reply automatically. A STREAM would be a constant connection - like an ssh connection to another computer. A program make s a connection to a socket and it remains open and communicating (or at least communicatable) until a close is sent by the process that requested the connection.

I know its possible/probable you wanted a more technical explanation (which I don't have), but this is my impression of the difference.

Second question:
If you're asking whether or not a port is currently in use - netstat -an | grep [port_number]. Or, if it is already listed in /etc/services use - netstat -an | grep [service].

[harry d brown jr]

http://media.wiley.com/product_data/excerpt/31/04712328/0471232831.pdf

live free or die
harry d brown jr

[Carine Parmentier]

Thanks for the useful answers.
John - I was not looking for the used portnr, but the processes.
I already heard about lsof, but I was wondering if you could not find it in standard HP-UX.
thks to both of you

[Amit Agarwal_1]

lsof is not a standard HP-UX commands. You can download one from

ftp://vic.cc.purdue.edu/pub/tools/unix/lsof/

[Bejoy C Alias]

u can use lsof -i : to check whether this port is opened and which process is using that.
e.g : lsof -i tcp:25 , will give u the PID of sendmail if a sendmail daemon is running.
lsof -i udp:53 will give u o/p as named and its PID if a dns server is running on the server