I have 2 machines A and B.
In machine A, I do
echo "Hello World" > /dev/tcp/{Bs_ip}/12345
In machine B, how do I write a script that runs in the background, listens on port 12345, and prints whatever it receives from port 12345 to stdout?
BTW both machines are running Red Hat Enterprise Linux AS 4.
Thanks
You can do that using netcat:
nc -l -p 123456
If you want to be able to handle multiple connections you will have to use a loop.
You can use netcact (nc) or netcat on steroids, ie socat. I gave a link to the examples section of the man page, so that you can see how powerful socat is.
socat TCP4-LISTEN:12345 -
Should do what you want
Related
I have a command which out outputs certain data which i store in a ext file using a '>>' command.Now Instead of doing that I want to have a socket or a port on any server which will catch the output of the command.Basically i want to output all my script data to a socket or url which ever is possible.
Any help in this direction is most welcomed.
You can use socat to listening on a port 12345 and echo any data sent to it like this:
socat -u TCP-LISTEN:12345,keepalive,reuseaddr,fork STDOUT
If you want to capture it to a file as well (file.log), you can use the same command with tee:
socat -u TCP-LISTEN:12345,keepalive,reuseaddr,fork STDOUT | tee file.log
You can run your program to output to bash's TCP virtual device:
./prog > /dev/tcp/localhost/12345
If you don't want to use bash magic then you can also use socat to send the data:
./prog | socat - TCP-CONNECT:localhost:12345
The above example assume you are running your program and "logger" on the same system but you can replace "localhost" with the hostname or address of the system you wish to send to (where the socat is listening).
I have my home computer A and a work computer C that I want to synchronise using unison. In the middle is a work computer B. A can communicate with B and B can communicate with C directly but A and C can't directly connect to each other. In fact the communication diagram looks like A->B<->C. That is A can connect to B but B can't connect to A.
To give an example how I use this setup, I currently do the following if I want to ssh from A to C
ssh -t -X -C me_B#B ssh -X me_C#C
How can I run unison from A and sync with C, maybe using ssh port forwarding?
To make it a little clearer, C has unfiltered outgoing connectivity to the Internet. B has unfiltered in and outgoing connectivity to both C and the Internet. A is my home computer.
Update
The following command line works for me to at least copy files from A to C
scp -oProxyCommand="ssh me_B#B nc -v %h %p" foo/* me_C#C:foo
Is there some way to use this idea to get unison to work?
Yes, ssh port forwarding can be used for that. Use the following command on A if you want to forward ssh on port 22 at C to the local port 3000 (for example):
# Create the tunnel
ssh -L 3000:C:22 userB#B -N
After you have issued the command, you can login into C from A using:
# Connect using the tunnel
ssh -p 3000 userC#localhost
Note: During the discussion below it turned out, that in OP's network, the connection trough the tunnel can only be established using the following command:
ssh -p 3000 -l userC localhost
Note that I'm using -l userC instead of userC#.
Now you can use unison like this:
unison directory ssh://userC#localhost:3000 directory
I am running embedded linux program, so that the kernel init script automatically start the program, and the stdin/stdout are going through the serial device, which is also the shell.
When I connect to target with telnet, I don't see the same stdin/stdout of the program.
Maybe I can redirect console stdin/stdout to telnet connection ?
What ways do I have to gain such capabilities using the telnet connection ?
Thanks,
Ran
I don't know if it is possible with telnet, but you can mock it through netcat. Just like below:
<STDOUT> | netcat -t www.example.com 80
I'm using Expect to connect to my server over a (virtual) serial port. (HP iLo, to be specific)
When booting from a Linux OS ISO image, you eventually get to the 'boot:' prompt. When my server reaches that prompt, I would like to enter my own custom boot options and press enter. Easy, right?
This is how the boot prompt looks when you're watching my Expect script execute (looks normal):
boot:
However, I have not been able to match 'boot:'. Looking at the Expect Buffer in my logfile, this is what is being captured for that line:
ESC\[25;01HbbESC\[25;01HESC\[25;02HooESC\[25;02HESC\[25;03HooESC\[25;03HESC\[25;04HttESC\[25;04HESC\[25;05H::ESC\[25;05HESC\[25;06H ESC\[25;06HESC\[25;07H"
I think all those control sequences are screwing up my match. If you look closely 'boot:' is actually in there, but it's surrounded by what I believe are ANSI control sequences.
In fact, the logfile is absolutely full of ANSI control characters.
Relevant pieces of the Expect script I've been playing around with:
bash #] expect -d -c '
.....
# SSH to the Virtual Serial Port Management server
spawn ssh user#1.2.3.4
.....
# Access the Virtual Serial Port for the server being booted
send "vsp\r"
.....
# After rebooting the server, when the boot: prompt appears, enter boot options
expect {
"boot:" {send $bootOptions \r\n"}
timeout {send_user "Never found boot prompt\n"; send_user "$expect_out(buffer)"; exit 1}
}
.....
exit'
Any ideas about what the best way to handle those control characters would be? I've tried exporting TERM=dumb and TERM=vt1000 on the machine I'm running the script on. Didn't make much of a difference.
Not sure if this will help, but you could create a wrapper for ssh and exec that instead of ssh and then have
ssh <host> | perl -pe 's/\e([^\[\]]|\[.*?[a-zA-Z]|\].*?\a)//g' | col -b
perhaps take out the col -b which filters newlines if you don't need that.
Is there a way to quickly bind to a TCP port/ip address and simply print out all information to STDOUT? I have a simple debugging solution which writes things to 127.0.0.1:4444 and I'd like to be able to simply bind up a port from bash and print everything that comes across. Is there an easy way to do this?
$ nc -k -l 4444 > filename.out
see nc(1)
Just because you asked how to do it in bash, though netcat answer is very valid:
$ exec 3<>/dev/tcp/127.0.0.1/4444
$ cat <&3
That is working as you expecting:
nc -k -l 4444 |bash
and then you
echo "ls" >/dev/tcp/127.0.0.1/4444
then you see the listing performed by bash.
[A Brief Security Warning]
Of course if you leave a thing like this running on your computer, you have a wide open gateway for all kinds of attacks because commands can be sent from any user account on any host in your network. This implements no security (authentication, identification) whatsoever and sends all transmitted commands unencrypted over the network, so it can very easily be abused.
Adding an answer using ncat that #Freedom_Ben alluded to:
ncat -k -l 127.0.0.1 4444
and explanation of options from man ncat:
-k, --keep-open Accept multiple connections in listen mode
-l, --listen Bind and listen for incoming connections