Re: /dev/tcp

In comp.os.linux.misc, Lawrence DOliveiro <[email protected]> wrote:
> On Wed, 19 Aug 2026 21:20:56 -0000 (UTC), Eli the Bearded wrote:
>> What system(s) have /dev/tcp/* natively?
> Not sure what the point of it is, when you have this
> <https://manpages.debian.org/socat(1)>.

This came up in the context of "how to test network on a system with no
root and no helpful utilities installed."

Normally I use, in preferential order: telnet, nc, perl[*], then curl to
test arbitrary sockets. If I know it runs a webserver, curl will be
first. In this case none of those were installed, and someone came up
with a jshell solution. Bash sockets were discussed, but also ruled out
because bash was not installed.

With jshell, the Java shell, something like this will print "Worked"
if it works:

  var s=new java.net.Socket();
  s.connect(new java.net.InetSocketAddress("www.google.com", 80), 3000);
  System.out.println("Worked");
  s.close();

And if it doesn't work, you get something like:

  |  Exception java.net.SocketTimeoutException: Connect timed out
  |        at NioSocketImpl.timedFinishConnect (NioSocketImpl.java:551)
  |        at NioSocketImpl.connect (NioSocketImpl.java:602)
  |        at SocksSocketImpl.connect (SocksSocketImpl.java:327)
  |        at Socket.connect (Socket.java:633)
  |        at (#2:1)

I was curious if there exist systems where any process that can open
a file (eg, /bin/sh) could use /dev/tcp to test sockets. I don't have
a real need, just a burning curiosity.

Elijah
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[*] knows you can use python, too, but doesn't have the code to do so memorized