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bashwake-on-lan

Bash one-line command to send wake on LAN magic packet without specific tool

Is it possible to forge a wake on LAN magic packet and send it in just a one-line bash command?

Of course, I know there are specific tools for doing this that solve the problem in one line, but it could be useful to know the minimal requirements for WOL forging. This is: how to deal with wake on LAN without specific tools.

Solution

  • The minimum requirements I can think off:

    • Bash supporting brace expansion (I think it is v3.5.1 and above).
    • The sed command (1).
    • NetCat.

    Assuming:

    • WOL package for LAN, broadcast to 255.255.255.255.

    The command line would be:

    echo -e $(echo $(printf 'f%.0s' {1..12}; printf "$(echo $MAC | sed 's/://g')%.0s" {1..16}) | sed -e 's/../\\x&/g') | nc -w1 -u -b 255.255.255.255 4000

    Replace $MAC by the destination MAC. Or, this time in a two-liner :-) command:

    MAC=11:22:33:44:55:66
echo -e $(echo $(printf 'f%.0s' {1..12}; printf "$(echo $MAC | sed 's/://g')%.0s" {1..16}) | sed -e 's/../\\x&/g') | nc -w1 -u -b 255.255.255.255 4000

    So, in a more generic notation:

    MAC=11:22:33:44:55:66
Broadcast=255.255.255.255
PortNumber=4000
echo -e $(echo $(printf 'f%.0s' {1..12}; printf "$(echo $MAC | sed 's/://g')%.0s" {1..16}) | sed -e 's/../\\x&/g') | nc -w1 -u -b $Broadcast $PortNumber

    Explanations:

    • The WOL magic packet is composed of ffffffffffff (12 times f) followed by 16 times the destination MAC without colons (:).
    • The sed command is used here to remove colons (:) from the MAC and to add the \x hex specificator (so that 11 becomes \x11, 22 becomes \x22 ... and so on) prior to sending the string to the network stack.
    • The forged wake on LAN package is sent to the network stack piping it to NetCat. SoCat can be used instead (syntax will differ, of course).

    Tested working on Ubuntu, Kali and even CygWin (Windows 7 SP 1 64 bits ).

    To take under consideration:

    • CygWin's NetCat version doesn't need for -b parameter.
    • NetCat's OpenBSD version has a bug as for today (Juy 2015) on broadcast data sending (-b), so you will have to replace it by NetCat Traditional version (netcat-traditional package on apt-get installers).
    • This example uses UDP port 4.000. The specific port number seems not to be important on WOL.
    • The above one-line bash command should work too for wake on LAN via internet. In this case replace $Broadcast address by the destination public IP, and open/forward the specified $PortNumber (UDP) on destination.
    • echo -e can be replaced by printf.

    WOL magic packet string for the above example:

    FFFFFFFFFFFF112233445566112233445566112233445566112233445566112233445566112233445566112233445566112233445566112233445566112233445566112233445566112233445566112233445566112233445566112233445566112233445566

    (1) Well, indeed, sed is not explicitly required. It is used here to remove ':' and add \x to each pair of characters in the magic packet's forged string. I know there are ways to replace sed by some shell expansion or so.