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<html><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968"><title>Environment Variables</title><link rel="stylesheet" type="text/css" href="docbook.css"><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot"><link rel="home" href="cygwin-ug-net.html" title="Cygwin User's Guide"><link rel="up" href="setup-net.html" title="Chapter 2. Setting Up Cygwin"><link rel="prev" href="setup-net.html" title="Chapter 2. Setting Up Cygwin"><link rel="next" href="setup-maxmem.html" title="Changing Cygwin's Maximum Memory"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Environment Variables</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="setup-net.html">Prev</a> </td><th width="60%" align="center">Chapter 2. Setting Up Cygwin</th><td width="20%" align="right"> <a accesskey="n" href="setup-maxmem.html">Next</a></td></tr></table><hr></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="setup-env"></a>Environment Variables</h2></div></div></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a name="setup-env-ov"></a>Overview</h3></div></div></div><p>
All Windows environment variables are imported when Cygwin starts.
Apart from that, you may wish to specify settings of several important
environment variables that affect Cygwin's operation.</p><p>
The <code class="envar">CYGWIN</code> variable is used to configure a few global
settings for the Cygwin runtime system. Typically you can leave
<code class="envar">CYGWIN</code> unset, but if you want to set one ore more
options, you can set it using a syntax like this, depending on the shell
in which you're setting it. Here is an example in CMD syntax:</p><pre class="screen">
<code class="prompt">C:\></code> <strong class="userinput"><code>set CYGWIN=error_start:C:\cygwin\bin\gdb.exe glob</code></strong>
</pre><p>
This is, of course, just an example. For the recognized settings of the
<code class="envar">CYGWIN</code> environment variable, see
<a class="xref" href="using-cygwinenv.html" title="The CYGWIN environment variable">the section called “The <code class="envar">CYGWIN</code> environment
variable”</a>.
</p><p>
Locale support is controlled by the <code class="envar">LANG</code> and
<code class="envar">LC_xxx</code> environment variables. For a more detailed description
see <a class="xref" href="setup-locale.html" title="Internationalization">the section called “Internationalization”</a>.
</p><p>
The <code class="envar">PATH</code> environment variable is used by Cygwin
applications as a list of directories to search for executable files
to run. This environment variable is converted from Windows format
(e.g. <code class="filename">C:\Windows\system32;C:\Windows</code>) to UNIX format
(e.g., <code class="filename">/cygdrive/c/Windows/system32:/cygdrive/c/Windows</code>)
when a Cygwin process first starts.
Set it so that it contains at least the <code class="filename">x:\cygwin\bin</code>
directory where "<code class="filename">x:\cygwin</code> is the "root" of your
cygwin installation if you wish to use cygwin tools outside of bash.
This is usually done by the batch file you're starting your shell with.
</p><p>
The <code class="envar">HOME</code> environment variable is used by many programs to
determine the location of your home directory. This environment variable,
if it exists, is converted from Windows format when a Cygwin process first
starts. However, it's usually set in the shell profile scripts in the /etc
directory, and it's <span class="bold"><strong>not</strong></span> recommended to set
the variable in your Windows environment.
</p><p>
The <code class="envar">TERM</code> environment variable specifies your terminal
type. It is automatically set to <code class="literal">cygwin</code> if you have
not set it to something else.
</p><p>The <code class="envar">LD_LIBRARY_PATH</code> environment variable is used by
the Cygwin function <code class="function">dlopen ()</code> as a list of
directories to search for .dll files to load. This environment variable
is converted from Windows format to UNIX format when a Cygwin process
first starts. Most Cygwin applications do not make use of the
<code class="function">dlopen ()</code> call and do not need this variable.
</p><p>The <code class="envar">GMON_OUT_PREFIX</code> environment variable is helpful
in some situations when profiling Cygwin programs. For more information,
see <a class="xref" href="gprof.html#gprof-fork" title="Profiling programs that fork">the section called “Profiling programs that fork”</a>. Only software developers with a
need to profile their programs have a use for this variable.
</p><p>
In addition to <code class="envar">PATH</code>, <code class="envar">HOME</code>,
<code class="envar">LD_LIBRARY_PATH</code>, and <code class="envar">GMON_OUT_PREFIX</code>,
there are three other environment
variables which, if they exist in the Windows environment, are
converted to UNIX format: <code class="envar">TMPDIR</code>, <code class="envar">TMP</code>,
and <code class="envar">TEMP</code>. The first is not set by default in the
Windows environment but the other two are, and they point to the
default Windows temporary directory. If set, these variables will be
used by some Cygwin applications, possibly with unexpected results.
You may therefore want to unset them by adding the following two lines
to your <code class="filename">~/.bashrc</code> file:
</p><pre class="screen">
unset TMP
unset TEMP
</pre><p>
This is done in the default <code class="filename">~/.bashrc</code> file.
Alternatively, you could set <code class="envar">TMP</code>
and <code class="envar">TEMP</code> to point to <code class="filename">/tmp</code> or to
any other temporary directory of your choice. For example:
</p><pre class="screen">
export TMP=/tmp
export TEMP=/tmp
</pre><p>
</p></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a name="setup-env-win32"></a>Restricted Win32 environment</h3></div></div></div><p>There is a restriction when calling Win32 API functions which
require a fully set up application environment. Cygwin maintains its own
environment in POSIX style. The Win32 environment is usually stripped
to a bare minimum and not at all kept in sync with the Cygwin POSIX
environment.</p><p>If you need the full Win32 environment set up in a Cygwin process,
you have to call</p><pre class="screen">
#include <sys/cygwin.h>
cygwin_internal (CW_SYNC_WINENV);
</pre><p>to synchronize the Win32 environment with the Cygwin environment.
Note that this only synchronizes the Win32 environment once with the
Cygwin environment. Later changes using the <code class="function">setenv</code>
or <code class="function">putenv</code> calls are not reflected in the Win32
environment. In these cases, you have to call the aforementioned
<code class="function">cygwin_internal</code> call again.</p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="setup-net.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="setup-net.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="setup-maxmem.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 2. Setting Up Cygwin </td><td width="20%" align="center"><a accesskey="h" href="cygwin-ug-net.html">Home</a></td><td width="40%" align="right" valign="top"> Changing Cygwin's Maximum Memory</td></tr></table></div></body></html>