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Cygwin on portable storage devices

Ali Devin Sezer
Feb 5, 2005

Cygwin is a software package that enables one to work in a UNIX-like environment under a Windows machine. It is fast, reliable and easy to install. It has most of the applications one uses on UNIX (gcc, X, xfig, latex, Perl, bash, ps tools, textutils,...) and most of it is covered by the GNU public license. Cygwin supports many flavors of Windows:XP, 2000, 98, etc. For more info on cygwin go

The goal of this page is to describe a way of installing cygwin on a portable storage device like a portable hard drive or a USB memory stick. The main use of such a setup, obviously, is that it enables you to carry a UNIX like system in your pocket everywhere you go and use any Windows machine (e.g. Windows pc's at your university library) with your own powerful cygwin/UNIX tools.

Choice of Portable device

The choice of device doesn't really change the installation process. However here are some notes on this issue:
  • USB memory stick: A core cygwin installation doesn't need more than a couple of hundred MBs. Thus a 1 GB USB memory stick easily gives you the capacity you need to install cygwin. But, remember that USB memory sticks are slow (bearable with NTFS crawling with FAT32) if you install a big file system  on them.
The rest of this note is independent of the choice of portable storage device.

Choice of Filesystem

You have two realistic choices for a file system (FS) on your portable storage device:fat32 and ntfs. (For those who are not familiar with FSs: FS is what is installed on a storage device when you format it. The formatting software asks you which kind of FS you want). Although NTFS is a much better FS, I had read/write permission problems with it when using different computers on which i had different accounts. A simplistic solution to this problem is to use fat32. That's what I do.  


I assume that your portable storage device is already formatted. Here are the steps:
  • Go to and install cygwin on your portable storage device.  Let's designate your portable storage device with "E:\" and assume that you installed cygwin in "E:\cygwin".

    As is, this installation will work only when your portable storage device is connected to the computer on which you performed the installation. What follows is  what you need to do so that your cygwin can work with any host windows computer.

  • Unless it is not there, create the directory "E:\cygwin\home". Then create the directory "E:\cygwin\home\username", where username is a user name that you pick. (e.g. your name). This will be your home directory: whenever you start an rxvt or an xterm it will start with this directory as the current directory.
  • Copy profile to E:\cygwin\etc. Open it with an editor (e.g. notepad) and replace the phrase "username" (it occurs twice) with the user name you have chosen above.
  • Download and put it in "E:\". Rename it "X.bat" [*]. This script assumes that you installed cygwin under "E:\cygwin" on your storage device. If you installed it in some other directory you will need to modify this script to reflect that ( X.bat figures out the drive label of the portable device [assumed to be E in this discussion] on its own. So you have to change X.bat only if cygwin is installed in some directory other than "cygwin" in the root directory of your portable storage device). X.bat inserts several keys into the windows registry. This is required for cygwin to work. It also saves any key values that it might alter. Finally it starts a copy of the X server and a terminal (assuming that  X and rxvt were installed in step 1).[**]
  • Download and put it in "E:\". Rename it to "uninstall.bat" [*]. Run this script once you are done using cygwin and quit all cygwin software. It restores any registry keys that might have been altered when running "X.bat".
This is it. double clicking "X.bat" will make cygwin operational and start an X server as well as an rxvt. When you exit all cygwin software, double click "uninstall.bat".

If you are using a very old windows, replace

 for /f %%A in ('cd') do set WD=%%A
in "X.bat" with
set WD=%1
and start "X.bat" from "Run" in the Start menu by typing "X.bat [DRIVE]:\" in the Run box, where [DRIVE] is the letter that Windows assigned to your portable storage device (`E' in the above examples). 

[*] This script is based on a script by Fergus in the CD-ROM related postings at (see the links above).

[**]The scripts ``X.bat'' and ``uninstall.bat'' modify host's registry. They insert several keys in the CURRENT USER and LOCAL MACHINE sections of the registry. These keys are modified through the ``mount'' command of cygwin and are  referred to by cygwin to find out which directories on the Windows directory structure are going to be mapped to /bin, /lib and /. If cygwin is already installed on the host, "X.bat" will save these entries before changing them. The modified entries are later restored when you are done using your portable cygwin and run the "uninstall.bat" script.