TCP: Fast check for open port

[Kobboi]

I need a more or less quick way to find out if a TCP port on a system on the LAN is open, from a script. I was thinking in the direction of return values of bash's /dev/tcp/<ip>/<port>, but the timeout is pretty high. I succeeded in decreasing it by fiddling with /proc/sys/net/ipv4/tcp_syn_retries. But I guess this will affect every TCP connection on my box.

Any other nice way to do this? (maybe without fiddling with the "global" kernel parameters?)

[vaguy02]

I'd use nmap, but that's just me. I bet there are 100001 programs out there to do it.
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[Kobboi]

It would be nice if it ran from a Gentoo minimal LiveCD, so bash was my first idea. And it works, but the question is about the TCP properties...

[keyson]

Hi,

You have netcat (nc) on the liveCD. You can use that to check for open ports.
ref:
http://www.adamsinfo.com/netcat-tutorial-for-linux-windows-howto-nc/

[OneOfOne]

Perl ftw
perl -m'IO::Socket' -e '$s = new IO::Socket::INET(PeerAddr => $ARGV[0],PeerPort => $ARGV[1], Proto => "tcp", Timeout => 3); print $s "hi server\n"; print(<$s>); print("\n");' host-name port

[timeBandit]

[Kobboi]

But netcat is not on the minimal install CD

[timeBandit]