Cygwin supports both Win32- and POSIX-style paths, where directory delimiters may be either forward or back slashes. UNC pathnames (starting with two slashes and a network name) are also supported. POSIX operating systems (such as Linux) do not have the concept of drive letters. Instead, all absolute paths begin with a slash (instead of a drive letter such as "c:") and all file systems appear as subdirectories (for example, you might buy a new disk and make it be the /disk2 directory). Because many programs written to run on UNIX systems assume the existance of a single unified POSIX file system structure, Cygwin maintains a special internal POSIX view of the Win32 file system that allows these programs to successfully run under Windows. Cygwin uses this mapping to translate between Win32 and POSIX paths as necessary. The mount utility program is used to to map Win32 drives and network shares into Cygwin's internal POSIX directory tree. This is a similar concept to the typical UNIX mount program. For those people coming from a Windows background, the mount utility is very similar to the old DOS join, in that it makes your drive letters appear as subdirectories somewhere else. The mapping is stored in the current user's Cygwin mount table in the Windows registry so that the information will be retrieved next time the user logs in. Because it is sometimes desirable to have system-wide as well as user-specific mounts, there is also a system-wide mount table that all Cygwin users inherit. The system-wide table may only be modified by a user with the appropriate priviledges (Administrator priviledges in Windows NT). The current user's table is located under "HKEY_CURRENT_USER/Software/Cygnus Solutions/Cygwin/mounts v<version>" where <version> is the latest registry version associated with the Cygwin library (this version is not the same as the release number). The system-wide table is located under the same subkeys under HKEY_LOCAL_SYSTEM. By default, the POSIX root / points to the system partition but it can be relocated to any directory in the Windows file system using the mount command. Whenever Cygwin generates a POSIX path from a Win32 one, it uses the longest matching prefix in the mount table. Thus, if C: is mounted as /c and also as /, then Cygwin would translate C:/foo/bar to /c/foo/bar. Invoking mount without any arguments displays Cygwin's current set of mount points. In the following example, the C drive is the POSIX root and D drive is mapped to /d. Note that in this case, the root mount is a system-wide mount point that is visible to all users running Cygwin programs, whereas the /d mount is only visible to the current user. c:\cygnus\> mount Device Directory Type Flags D: /d user textmode C: / system textmode You can also use the mount command to add new mount points, and the umount to delete them. See and for more information on how to use these utilities to set up your Cygwin POSIX file system. Whenever Cygwin cannot use any of the existing mounts to convert from a particular Win32 path to a POSIX one, Cygwin will automatically default to an imaginary mount point under the default POSIX path /cygdrive. For example, if Cygwin accesses Z:\foo and the Z drive is not currently in the mount table, then Z:\ would be automatically converted to /cygdrive/Z. The default prefix of /cygdrive may be changed (see the for more information). It is possible to assign some special attributes to each mount point. Automatically mounted partitions are displayed as "auto" mounts. Mounts can also be marked as either "textmode" or "binmode" -- whether text files are read in the same manner as binary files by default or not (see for more information on text and binary modes. Which set of mounts is right for a given Cygwin user depends largely on how closely you want to simulate a POSIX environment, whether you mix Windows and Cygwin programs, and how many drive letters you are using. If you want to be very POSIX-like (assuming "CygwinRoot" is the top directory of your Cygwin distribution), you may want to do something like this: C:\> mount c:\Cygnus\CygwinRoot / C:\> mount c:\ /c C:\> mount d:\ /d C:\> mount e:\ /cdrom However, if you mix Windows and Cygwin programs a lot, you might want to create an "identity" mapping, so that conversions between the two (see ) can be eliminated: C:\> mount c:\ \ C:\> mount d:\foo /foo C:\> mount d:\bar /bar C:\> mount e:\grill /grill You'd have to repeat this for all top-level subdirectories on all drives, but then you'd always have the top-level directories available as the same names in both systems. The cygpath program provides the ability to translate between Win32 and POSIX pathnames in shell scripts. See for the details. The HOME, PATH, and LD_LIBRARY_PATH environment variables are automatically converted from Win32 format to POSIX format (e.g. from C:\cygnus\cygwin-b20\H-i586-cygwin32\bin to /bin, if there was a mount from that Win32 path to that POSIX path) when a Cygwin process first starts. Symbolic links can also be used to map Win32 pathnames to POSIX. For example, the command ln -s //pollux/home/joe/data /data would have about the same effect as creating a mount point from //pollux/home/joe/data to /data using mount, except that symbolic links cannot set the default file access mode. Other differences are that the mapping is distributed throughout the file system and proceeds by iteratively walking the directory tree instead of matching the longest prefix in a kernel table. Note that symbolic links will only work on network drives that are properly configured to support the "system" file attribute. Many do not do so by default (the Unix Samba server does not by default, for example). Windows filenames invalid under Windows are also invalid under Cygwin. This means that base filenames such as AUX, COM1, LPT1 or PRN (to name a few) cannot be used in a regular Cygwin Windows or POSIX path, even with an extension (prn.txt). However the special names can be used as filename extensions (file.aux). You can use the special names as you would under DOS, for example you can print on your default printer with the command cat filename > PRN (make sure to end with a Form Feed). There is no need to create a POSIX /dev directory as it is simulated within Cygwin automatically. It supports the following devices: /dev/null, /dev/tty and /dev/comX (the serial ports). These devices cannot be seen with the command ls /dev although commands such as ls /dev/tty work fine. FIXME: Are there other devices under /dev. What about the funny ones mounted by default, such as /dev/fd1. What do they really do? Executable program filenames end with .exe but the .exe need not be included in the command, so that traditional UNIX names can be used. However, for programs that end in ".bat" and ".com", you cannot omit the extension. As a side effect, the ls filename gives information about filename.exe if filename.exe exists and filename does not. In the same situation the function call stat("filename",..) gives information about filename.exe. The two files can be distinguished by examining their inodes, as demonstrated below. C:\Cygnus\> ls * a a.exe b.exe C:\Cygnus\> ls -i a a.exe 445885548 a 435996602 a.exe C:\Cygnus\> ls -i b b.exe 432961010 b 432961010 b.exe If a shell script myprog and a program myprog.exe coexist in a directory, the program has precedence and is selected for execution of myprog. The gcc compiler produces an executable named filename.exe when asked to produce filename. This allows many makefiles written for UNIX systems to work well under Cygwin. Unfortunately, the install and strip commands do distinguish between filename and filename.exe. They fail when working on a non-existing filename even if filename.exe exists, thus breaking some makefiles. This problem can be solved by writing install and strip shell scripts to provide the extension ".exe" when needed. To circumvent the limitations on shell line length in the native Windows command shells, Cygwin programs expand their arguments starting with "@" in a special way. If a file pathname exists, the argument @pathname expands recursively to the content of pathname. Double quotes can be used inside the file to delimit strings containing blank space. Embedded double quotes must be repeated. In the following example compare the behaviors of the bash built-in echo and of the program /bin/echo. /Cygnus$ echo 'This is "a long" line' > mylist /Cygnus$ echo @mylist @mylist /Cygnus$ /bin/echo @mylist This is a long line /Cygnus$ rm mylist /Cygnus$ /bin/echo @mylist @mylist