Commands tagged protocol (3)

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

    echo "foo" > /dev/tcp/
    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(('', 25), SocketServer.BaseRequestHandler).serve_forever()" Show Sample Output

    echo foo | netcat 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

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

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Bash: escape '-' character in filename

Delete an IPtable rules based on row number

Generate QR code for a WiFi hotspot
Prompts for network name (SSID) and password, and generates (as qr-wifi.png) a WiFi QR code (e.g. "WIFI:S:mynet;T:WPA;P:mypass;;" for mynet/mypass). Dependencies [sudo apt-get install]: qrencode zenity

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
This will create a 10 MB file named testfile.txt. Change the count parameter to change the size of the file. As one commenter pointed out, yes /dev/random can be used, but the content doesn't matter if you just need a file of a specific size for testing purposes, which is why I used /dev/zero. The file size is what matters, not the content. It's 10 MB either way. "Random" just referred to "any file - content not specific"

cat stdout of multiple commands
Concatenate the stdout of multiple commands.

Virtualbox: setup hardware
where - memory 256 assign 256 Mb RAM - acpi on enable ACPI (mandatory if you use Winfog 2000 - ioapic off disable the IO APIC. Not useful if you use one CPU (on virtual machine or a 32 bit operative system). As ACPI, this switch is mandatory for Winbug 2000 - pae on enable the Phisical Address Extension how to use more than 4Gb of RAM on x86 CPU - hwvirtex on enables hardware virtualization extensions for microprocessors that have this feature (which should be also enabled in the BIOS of the motherboard) - nestedpaging on allows part of the processes of memory management hardware are made directly

rgrep: recursive grep without .svn
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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