Commands tagged protocol (3)

  • this command will send a message to the socket 25 on host 192.168.1.2 in tcp. works on udp and icmp understand only IP address, not hostname. on the other side (192.168.1.2), you can listen to this socket and test if you receive the message. easy to diagnose a firewall problem or not.


    24
    echo "foo" > /dev/tcp/192.168.1.2/25
    mobidyc · 2009-09-12 16:48:05 3
  • Using netcat, usuallly installed on debian/ubuntu. Also to test against a sample server the following two commands may help echo got milk? | netcat -l -p 25 python -c "import SocketServer; SocketServer.BaseRequestHandler.handle = lambda self: self.request.send('got milk?\n'); SocketServer.TCPServer(('0.0.0.0', 25), SocketServer.BaseRequestHandler).serve_forever()" Show Sample Output


    2
    echo foo | netcat 192.168.1.2 25
    pykler · 2009-09-13 01:33:02 0
  • you can use a pair of commands to test firewalls. 1st launch this command at destination machine ncat -l [-u] [port] | cat then use this command at source machine to test remote port echo foo | ncat [-u] [ip address] [port] First command will listen at specified port. It will listen TCP. If you use -u option will listen UDP. Second command will send "foo" through ncat and will reach defined IP and port. Show Sample Output


    -1
    echo foo | ncat [ip address] [port]
    dragonauta · 2012-10-26 10:53:47 0

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Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

Create a random file of a specific size
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cat stdout of multiple commands
Concatenate the stdout of multiple commands.

Virtualbox: setup hardware
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Only excludes .svn from filenames.

Console clock
Shows a simple clock in the console -t param removes the watch header Ctrl-c to exit

Display information sent by browser
Have netcat listen on port 8000, point browser to http://localhost:8000/ and you see the information sent. netcat terminates as soon as your browser disconnects. I tested this command on my Fedora box but linuxrawkstar pointed out that he needs to use $ nc -l -p 8000 instead. This depends on the netcat version you use. The additional '-p' is required by GNU netcat that for example is used by Debian but not by the OpenBSD netcat port used by my Fedora system.


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