Don't guess at the HostID; save everybody time by getting it right the first time!
The easiest procedure is often to download/install IDL first, and then let IDL itself display the HostID it uses.
However, sometimes the Wizard itself displays two or three MAC addresses.
So, here are some ways to select the correct MAC address out of multiple possibilities; that of the ethernet adapter.
Mac OS X
Open a terminal window and run the script
/Applications/exelis/idl/bin/lmhostid  (The "Terminal" program is in /Applications/Utilities/. Run it, and in the terminal window type out the above command, and press Return.)
The hostID will be a 12-character hex code.
In the case of Mac OS X 10.8 and 10.9 this is the WiFi hardware address (en1/ether); for earlier versions of Mac OS X, it is the Ethernet (en0/ether) hardware address.
WindowsDownload and install IDL/ENVI. Then run IDL Licensing Wizard (it may run automatically at the completion of installation).
The License Wizard program is in the main ("Start") All Programs menu, in the IDL or ENVI folder, the "Tools" subfolder.
Choose "Request a license if you don't have internet access". (even though you really do have internet access...)
This produces some text for "Offline License Request".
The information you need is just the Hostname and Host ID.
The Host ID is usually a single 12-character code; however, if there are two or more such 12-character codes, you can determine which one is the right one to use, by typing a simple command into a terminal (command window).
ipconfig /allOpen a command window by typing cmd into the search window:
In the command terminal type "ipconfig /all" and in the lengthy output look for each Host ID suggested by the License Authorization Wizard. The one that corresponds to Ethernet adapter Local Area Connection is the one that you want.
Linux/SolarisOpen a terminal window and cd to the IDL bin directory (in /usr/local/exelis/idl/bin or in /usr/local/itt/idl/bin) and run the script
The hostID will be a 12-character hex code (Linux) or an 8-character hex code (Solaris).
(The standard installation directory for IDL and ENVI is
ITT_DIR=/usr/local/exelis, and the "lmhostid"
script will be in some subdirectory.)
For a Host ID on which to base a license file
(IDL or ENVI or any number of other software licenses)
it is smart to choose the MAC address which is likely
to always be "on".
In the past, this would have been the Ethernet hardware address, which will be active whenever the computer is turned on.
The "Mountain Lion" version of Mac OS X has begun using the Wifi MAC address instead, since that is becoming universal.