The CYGWIN environment variable is used to configure many global settings for the Cygwin runtime system. It contains the options listed below, separated by blank characters. Many options can be turned off by prefixing with no. (no)dosfilewarning - If set, Cygwin will warn the first time a user uses an "MS-DOS" style path name rather than a POSIX-style path name. Defaults to set. (no)envcache - If set, environment variable conversions (between Win32 and POSIX) are cached. Note that this may cause problems if the mount table changes, as the cache is not invalidated and may contain values that depend on the previous mount table contents. Defaults to set. (no)export - If set, the final values of these settings are re-exported to the environment as CYGWIN again. Defaults to off. error_start:Win32filepath - if set, runs Win32filepath when cygwin encounters a fatal error, which is useful for debugging. Win32filepath is usually set to the path to gdb or dumper, for example C:\cygwin\bin\gdb.exe. There is no default set. forkchunk:32768 - causes the fork() to copy memory some number of bytes at a time, in the above example 32768 bytes (32Kb) at a time. The default is to copy as many bytes as possible, which is preferable in most cases but may slow some older systems down. proc_retry:n - causes the fork() and exec*() to retry n times when a child process fails due to certain windows-specific errors. These errors usually occur when processes are being started while a user is logging off. (no)glob[:ignorecase] - if set, command line arguments containing UNIX-style file wildcard characters (brackets, question mark, asterisk, escaped with \) are expanded into lists of files that match those wildcards. This is applicable only to programs running from a DOS command line prompt. Default is set. This option also accepts an optional [no]ignorecase modifer. If supplied, wildcard matching is case insensitive. The default is noignorecase (no)reset_com - if set, serial ports are reset to 9600-8-N-1 with no flow control when used. This is done at open time and when handles are inherited. Defaults to set. (no)strip_title - if set, strips the directory part off the window title, if any. Default is not set. (no)title - if set, the title bar reflects the name of the program currently running. Default is not set. (no)tty - if set, Cygwin enables extra support (i.e., termios) for UNIX-like ttys in the Windows console. It is not compatible with some Windows programs. Defaults to not set, in which case the tty is opened in text mode. Note that this has been changed such that ^D works as expected instead of ^Z, and is settable via stty. This option must be specified before starting a Cygwin shell and it cannot be changed in the shell. It should not be set when using other terminals (i.e., rxvt or xterm). (no)upcaseenv - if set, Cygwin converts all environment variables to all-uppercase, when a Cygwin process is started from a non-Cygwin native Windows process. This is how it has been done until Cygwin 1.5. If not set, Cygwin does not change the case of environment variables, except for a restricted set to maintain minimal backward compatibility and for correct handling of certain essential variables. The current list of always uppercased variables is: ALLUSERSPROFILE COMMONPROGRAMFILES COMPUTERNAME COMSPEC HOME HOMEDRIVE HOMEPATH NUMBER_OF_PROCESSORS OS PATH PATHEXT PROCESSOR_ARCHITECTURE PROCESSOR_IDENTIFIER PROCESSOR_LEVEL PROCESSOR_REVISION PROGRAMFILES SYSTEMDRIVE SYSTEMROOT TEMP TERM TMP TMPDIR WINDIR Defaults to not set. (no)winsymlinks - if set, Cygwin creates symlinks as Windows shortcuts with a special header and the R/O attribute set. If not set, Cygwin creates symlinks as plain files with a magic number, a path and the system attribute set. Defaults to not set since plain file symlinks are faster to write and faster to read. Some CYGWIN options have been removed in Cygwin 1.7 for one reason or another. These removed options are listed below. (no)binmode - This option has been removed because all file opens default to binary mode, unless the open mode has been specified explicitely in the open(2) call. check_case - This option has been removed in favor of real case sensitivity and the per-mount option "posix=[0|1]". For more information, read the documentation in and . codepage:[ansi|oem] - This option controled which character set is used for file and console operations. Since Cygwin is now doing all character conversion by itself, depending on the application call to the setlocale() function, and in turn by the setting of the environment variables $LANG, $LC_ALL, or $LC_CTYPE, this setting got useless. (no)ntea - This option has been removed since it only fakes security which is considered dangerous and useless. It also created an uncontrollably large file on FAT and was entirely useless on FAT32. (no)ntsec - This option has been removed in favor of the per-mount option "acl"/"noacl". For more information, read the documentation in . (no)server - Originally this option had to be enabled on the client side to use features only available when running cygserver. This option has been removed because Cygwin now always tries to contact cygserver if a function is called which requires cygserver being available. For more information, read the documentation in . (no)smbntsec - This option has been removed in favor of the per-mount option "acl"/"noacl". For more information, read the documentation in . (no)transparent_exe - This option has been removed because the behaviour it switched on is now the standard behaviour in Cygwin. (no)traverse - This option has been removed because traverse checking is not quite correctly implemented by Microsoft and it's behaviour is getting worse with each new OS version.