Notes by woolf
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Created by woolf on July 31, 2011 12:30:20
Last update: July 31, 2011 12:30:20
The DNS (Domain Name System) server uses port 53 (UDP and TCP). From Wikipedia :
DNS primarily uses User Datagram Protocol (UDP) on port number 53 to serve requests. DNS queries consist of a single UDP request from the client followed by a single UDP reply from the server. The Transmission Control Protocol (TCP) is used when the response data size exceeds 512 bytes, or for tasks such as zone transfers. Some operating systems, such as HP-UX, are known to have resolver implementations that use TCP for all queries, even when UDP would suffice.
Created by woolf on July 05, 2011 15:38:52
Last update: July 05, 2011 15:39:55
By default VirtualBox enables one network adapter ("Adapter 1") with NAT. Connection from the guest OS to the outside world works natually when the guest network adapter is assigned an IP address by the VirtualBox DHCP server. Use VBoxManage to see a list of DHCP servers:
$ VBoxManage list dhcpservers NetworkName: H... The guest IP address is not visible from the outside world. If you need to access a server on the guest OS, you need to set up port forwarding in VirtualBox settings: Settings -> Network -> Adapter 1 -> Advanced -> Port Forwarding . Beware that on Linux/Unix, port forwarding may not work if you bind to a privileged port (port number < 1024) but you are not root. Bridged networking can be...
Created by woolf on February 10, 2011 13:25:20
Last update: February 10, 2011 13:25:20
If Command Extensions are enabled (which is enabled by default), then there are several dynamic environment variables that can be expanded but which don't show up in the list of variables displayed by SET . These variable values are computed dynamically each time the value of the variable is expanded (but see example below). If the user explicitly defines a variable with one of these names, then that definition will override the dynamic one described below: %CD% - expands to the current directory string. %DATE% - expands to current date using same format as DATE command. %TIME% - expands to current time using same format as TIME command. %RANDOM% - expands to a random decimal number between 0 and 32767. %ERRORLEVEL% - expands to the...
Created by woolf on February 10, 2011 13:16:34
Last update: February 10, 2011 13:16:49
%PATH:str1=str2% would expand the PATH environment variable, substituting each occurrence of " str1 " in the expanded result with " str2 ". " str2 " can be the empty string to effectively delete all occurrences of " str1 " from the expanded output. " str1 " can begin with an asterisk, in which case it will match everything from the beginning of the expanded output to the first occurrence of the remaining portion of str1. %PATH:~10,5% would expand the PATH environment variable, and then use only the 5 characters that begin at the 11th (offset 10) character of the expanded result. If the length is not specified, then it defaults to the remainder of the variable value. If either number (offset or length) is negative,...
Created by woolf on February 10, 2011 12:51:14
Last update: February 10, 2011 13:06:11
Windows command line shell does not come with a sleep command. One trick is to emulate sleep using the ping command:
C:\>ping /?
Usage: ping [-t] [-a] [-n count...
To sleep for about 5 seconds:
@rem make sure to ping a non-existing IP, otherwis...
If you have the Windows Resource Kit installed, it does provide a sleep command:
C:\>sleep
Usage: sleep time-to-sleep-in-s...
