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<sect1 id="using-cygwinenv"><title>The <envar>CYGWIN</envar> environment
variable</title>

<sect2 id="cygwinenv-implemented-options">
<title>Implemented options</title>

<para>The <envar>CYGWIN</envar> 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 <literal>no</literal>.</para>

<itemizedlist mark="bullet">

<listitem>
<para><envar>(no)export</envar> - If set, the final values of these
settings are re-exported to the environment as <envar>CYGWIN</envar> again.
Defaults to off.</para>
</listitem>

<listitem>
<para>
<envar>error_start:Win32filepath</envar> - if set, runs
<filename>Win32filepath</filename> when cygwin encounters a fatal error, which
can be useful for debugging. Defaults to not set.
</para>
<para>
<filename>Win32filepath</filename> is typically set to <command>gdb</command> or
<command>dumper</command>.  If giving a path in
<filename>Win32filepath</filename>, note that it is a Windows-style path and not
a Cygwin path.
</para>
<para>
The filename of the executing program and it's Windows process id are appended
to the command as arguments.
</para>
<para>
  Note: This takes priority over writing core dump or .stackdump files, if
  enabled by <function>setrlimit(RLIMIT_CORE)</function> (e.g. via
  <command>ulimit -c</command>).
</para>
<para>
  Note: This has no effect if a debugger is already attached when the fatal
  error occurs.
</para>
<para>
  Note: The command invoked must either (i) attach to the errored process with
  <function>DebugActiveProcess()</function>, or (ii) forcibly terminate the
  errored process (with <function>TerminateProcess()</function> or similar), as
  otherwise the errored process will wait forever for a debugger to attach.
</para>
</listitem>

<listitem>
<para><envar>(no)glob[:ignorecase]</envar> - if set, command line arguments
containing UNIX-style file wildcard characters (brackets, braces, question mark,
asterisk, escaped with \) are expanded into lists of files that match 
those wildcards.
This is applicable only to programs run from non-Cygwin programs such as a CMD prompt.
That means that this setting does not affect globbing operations for shells such as
bash, sh, tcsh, zsh, etc.
Default is set.</para>
<para>This option also accepts an optional <literal>[no]ignorecase</literal> modifer.
If supplied, wildcard matching is case insensitive.  The default is <literal>noignorecase</literal></para>
</listitem>

<listitem>
<para><envar>(no)pipe_byte</envar> - if set, Cygwin opens pipes in byte mode rather than
message mode.  This is the default starting with Cygwin 3.4.0.
</para>
</listitem>

<listitem>
<para><envar>proc_retry:n</envar> - causes <function>fork()</function> and
<function>exec*()</function> 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.
</para>
</listitem>

<listitem>
<para><envar>(no)reset_com</envar> - 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.</para>
</listitem>

<listitem>
<para><envar>(no)wincmdln</envar> - if set, the windows complete command
line (truncated to ~32K) will be passed on any processes that it creates
in addition to the normal UNIX argv list.  Defaults to not set.</para>
</listitem>

<listitem>
<para><envar>(no)winjitdebug</envar> - if set, non-Cygwin executables
started from a Cygwin process will have their error mode reset to the
system default.  That means, if they don't call SetErrorMode()
explicitly, the OS will display error dialog boxes in the GUI if some
fatal error occurs.  Defaults to not set, so fatal errors in a
non-Cygwin child process will just result in an error code be propagated
back to the parent process.</para>
</listitem>

<listitem>
<para><envar>winsymlinks:{lnk,native,nativestrict,sys}</envar></para>

<itemizedlist mark="square">
<listitem>
<para>If set to just
<literal>winsymlinks</literal> or <literal>winsymlinks:lnk</literal>,
Cygwin creates symlinks as Windows shortcuts with a special header and
the R/O attribute set.</para>
</listitem>

<listitem>
<para>If set to <literal>winsymlinks:native</literal> or
<literal>winsymlinks:nativestrict</literal>, Cygwin creates symlinks as
native Windows symlinks on filesystems and OS versions supporting them.</para>

<para>The difference between <literal>winsymlinks:native</literal> and
<literal>winsymlinks:nativestrict</literal> is this:  If the filesystem
supports native symlinks and Cygwin fails to create a native symlink for
some reason, it will fall back to creating Cygwin default symlinks
with <literal>winsymlinks:native</literal>, while with
<literal>winsymlinks:nativestrict</literal> the <literal>symlink(2)</literal>
system call will immediately fail.</para>
</listitem>

<listitem>
<para>If set to <literal>winsymlinks:sys</literal>, Cygwin creates symlinks as
plain files with the <literal>system</literal> attribute, containing a magic
cookie followed by the path to which the link points.</para>
</listitem>
</itemizedlist>

<para>Note that this setting has no effect where Cygwin knows that the
filesystem only supports a creating symlinks in a specific way.</para>

<para>For more information on symbolic links, see
<xref linkend="pathnames-symlinks"></xref>.</para>

</listitem>

<listitem>
<para><envar>disable_pcon</envar> - if set, pseudo console support in
pty will be disabled.  This is for programs which do not work properly
under pty with pseudo console enabled.  Defaults to not set.</para>
</listitem>

</itemizedlist>

</sect2>

<sect2 id="cygwinenv-removed-options">
<title>Obsolete options</title>

<para>
Certain CYGWIN options available in past releases have been removed over
time for one reason or another.  These obsolete options are listed
below.</para>

<itemizedlist mark="bullet">

<listitem>
<para><envar>(no)binmode</envar> - This option has been removed because
all file opens default to binary mode, unless the open mode has been specified
explicitly in the open(2) call.
</para>
</listitem>

<listitem>
<para><envar>(no)detect_bloda</envar> - No case of a BLODA found by this
option has been reported in years.</para>
</listitem>

<listitem>
<para><envar>(no)dosfilewarning</envar> - This option had been disabled for
quite some time and nobody missed it.</para>
</listitem>

<listitem>
<para><envar>check_case</envar> - 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 <xref linkend="mount-table"></xref> and
<xref linkend="pathnames-casesensitive"></xref>.</para>
</listitem>

<listitem>
<para><envar>codepage:[ansi|oem]</envar> - This option controlled
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 <function>setlocale()</function> function, and in
turn by the setting of the environment variables <envar>$LANG</envar>,
<envar>$LC_ALL</envar>, or <envar>$LC_CTYPE</envar>, this setting
became superfluous.</para>
</listitem>

<listitem>
<para><envar>(no)envcache</envar> - Originally, <envar>envcache</envar>
controlled caching of environment variable conversion between Win32 and
POSIX.  The default setting works fine, the option was just useless.</para>
</listitem>

<listitem>
<para><envar>forkchunk:[intval]</envar> - This option allowed to influence
the <function>fork()</function> function in the way the memory of the
parent process gets copied to the child process.  This functionality was
only useful for Windows 95/98/Me.
</para>
</listitem>

<listitem>
<para><envar>(no)ntea</envar> -  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.</para>
</listitem>

<listitem>
<para><envar>(no)ntsec</envar> - This option has been removed in favor of
the per-mount option "acl"/"noacl".  For more information, read the
documentation in <xref linkend="mount-table"></xref>.</para>
</listitem>

<listitem>
<para><envar>(no)server</envar> - Originally this option had to be
enabled on the client side to use features only available when running
<command>cygserver</command>.  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 <xref linkend="using-cygserver"></xref>.</para>
</listitem>

<listitem>
<para><envar>(no)smbntsec</envar> - This option has been removed in favor of
the per-mount option "acl"/"noacl".  For more information, read the
documentation in <xref linkend="mount-table"></xref>.</para>
</listitem>

<listitem>
<para><envar>(no)strip_title</envar> - Removed because setting the Window title
can be controlled by the application via Escape sequences.</para>
</listitem>

<listitem>
<para><envar>(no)title</envar> - Removed because setting the Window title
can be controlled by the application via Escape sequences.</para>
</listitem>

<listitem>
<para><envar>(no)transparent_exe</envar> - This option has been removed
because the behaviour it switched on is now the standard behaviour in
Cygwin.</para>
</listitem>

<listitem>
<para><envar>(no)traverse</envar> - This option has been removed because
traverse checking is not quite correctly implemented by Microsoft and
it's behaviour has been getting worse with each new OS version.  This
complicates its usage so the option has been removed for now.</para>
</listitem>

<listitem>
<para><envar>(no)tty</envar> - If set, Cygwin enabled extra support
(i.e., termios) for UNIX-like ttys in the Windows console. This option
has been removed because it can be easily replaced by using a terminal
like <command>mintty</command>, and it does not work well with some
Windows programs.</para>
</listitem>

<listitem>
<para><envar>(no)upcaseenv</envar> - This option could be used to convert
all environment variables to uppercase.  This was the default behavior in
older releases of Cygwin.  Since keeping the case of environment variables
intact is POSIXly correct, Cygwin now does not change the case
of environment variables, except for a restricted set to maintain minimal
backward compatibility.  The current list of always uppercased variables is:
</para>
<screen>
  COMMONPROGRAMFILES
  COMSPEC
  PATH
  SYSTEMDRIVE
  SYSTEMROOT
  TEMP
  TMP
  WINDIR
</screen>
</listitem>

</itemizedlist>

</sect2>

</sect1>
