509 lines
21 KiB
XML
509 lines
21 KiB
XML
<?xml version="1.0" encoding='UTF-8'?>
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<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<sect1 id="using-specialnames"><title>Special filenames</title>
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<sect2 id="pathnames-etc"><title>Special files in /etc</title>
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<para>Certain files in Cygwin's <filename>/etc</filename> directory are
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read by Cygwin before the mount table has been established. The list
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of files is</para>
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<screen>
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/etc/fstab
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/etc/fstab.d/$USER
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/etc/passwd
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/etc/group
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</screen>
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<para>These file are read using native Windows NT functions which have
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no notion of Cygwin symlinks or POSIX paths. For that reason
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there are a few requirements as far as <filename>/etc</filename> is
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concerned.</para>
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<para>To access these files, the Cygwin DLL evaluates it's own full
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Windows path, strips off the innermost directory component and adds
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"\etc". Let's assume the Cygwin DLL is installed as
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<filename>C:\cygwin\bin\cygwin1.dll</filename>. First the DLL name as
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well as the innermost directory (<filename>bin</filename>) is stripped
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off: <filename>C:\cygwin\</filename>. Then "etc" and the filename to
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look for is attached: <filename>C:\cygwin\etc\fstab</filename>. So the
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/etc directory must be parallel to the directory in which the cygwin1.dll
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exists and <filename>/etc</filename> must not be a Cygwin symlink
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pointing to another directory. Consequentially none of the files from
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the above list, including the directory <filename>/etc/fstab.d</filename>
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is allowed to be a Cygwin symlink either.</para>
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<para>However, native NTFS symlinks and reparse points are transparent
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when accessing the above files so all these files as well as
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<filename>/etc</filename> itself may be NTFS symlinks or reparse
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points.</para>
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<para>Last but not least, make sure that these files are world-readable.
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Every process of any user account has to read these files potentially,
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so world-readability is essential. The only exception are the user
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specific files <filename>/etc/fstab.d/$USER</filename>, which only have
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to be readable by the $USER user account itself.</para>
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</sect2>
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<sect2 id="pathnames-dosdevices"><title>Invalid filenames</title>
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<para>Filenames invalid under Win32 are not necessarily invalid under Cygwin.
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There are a few rules which apply to Windows filenames. Most notably, DOS
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device names like <filename>AUX</filename>, <filename>COM1</filename>,
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<filename>LPT1</filename> or <filename>PRN</filename> (to name a few)
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cannot be used as filename or extension in a native Win32 application.
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So filenames like <filename>prn.txt</filename> or <filename>foo.aux</filename>
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are invalid filenames for native Win32 applications.</para>
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<para>This restriction doesn't apply to Cygwin applications. Cygwin
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can create and access files with such names just fine. Just don't try
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to use these files with native Win32 applications.</para>
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</sect2>
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<sect2 id="pathnames-specialchars">
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<title>Forbidden characters in filenames</title>
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<para>Some characters are disallowed in filenames on Windows filesystems.
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These forbidden characters are the ASCII control characters from ASCII
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value 1 to 31, plus the following characters which have a special meaning
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in the Win32 API:</para>
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<screen>
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" * : < > ? | \
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</screen>
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<para>Cygwin can't fix this, but it has a method to workaround this
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restriction. All of the above characters, except for the backslash,
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are converted to special UNICODE characters in the range 0xf000 to 0xf0ff
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(the "Private use area") when creating or accessing files by adding 0xf000
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to the forbidden characters' code points.</para>
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<para>The backslash has to be exempt from this conversion, because Cygwin
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accepts Win32 filenames including backslashes as path separators on input.
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Converting backslashes using the above method would make this impossible.</para>
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<para>Additionally Win32 filenames can't contain trailing dots and spaces
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for DOS backward compatibility. When trying to create files with trailing
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dots or spaces, all of them are removed before the file is created. This
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restriction only affects native Win32 applications. Cygwin applications
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can create and access files with trailing dots and spaces without problems.
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</para>
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<para>An exception from this rule are some network filesystems (NetApp,
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NWFS) which choke on these filenames. They return with an error like
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"No such file or directory" when trying to create such files. Cygwin
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recognizes these filesystems and works around this problem by applying
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the same rule as for the other forbidden characters. Leading spaces and
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trailing dots and spaces will be converted to UNICODE characters in the
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private use area. This behaviour can be switched on explicitely for a
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filesystem or a directory tree by using the mount option
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<literal>dos</literal>.</para>
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</sect2>
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<sect2 id="pathnames-unusual">
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<title>Filenames with unusual (foreign) characters</title>
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<para> Windows filesystems use Unicode encoded as UTF-16
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to store filename information. If you don't use the UTF-8
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character set (see <xref linkend="setup-locale"></xref>) then there's a
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chance that a filename is using one or more characters which have no
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representation in the character set you're using.</para>
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<note><para>In the default "C" locale, Cygwin creates filenames using
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the UTF-8 charset. This will always result in some valid filename by
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default, but again might impose problems when switching to a non-"C"
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or non-"UTF-8" charset.</para></note>
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<note><para>To avoid this scenario altogether, always use UTF-8 as the
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character set.</para></note>
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<para>If you don't want or can't use UTF-8 as character set for whatever
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reason, you will nevertheless be able to access the file. How does that
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work? When Cygwin converts the filename from UTF-16 to your character
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set, it recognizes characters which can't be converted. If that occurs,
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Cygwin replaces the non-convertible character with a special character
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sequence. The sequence starts with an ASCII CAN character (hex code
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0x18, equivalent Control-X), followed by the UTF-8 representation of the
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character. The result is a filename containing some ugly looking
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characters. While it doesn't <emphasis role='bold'>look</emphasis> nice, it
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<emphasis role='bold'>is</emphasis> nice, because Cygwin knows how to convert
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this filename back to UTF-16. The filename will be converted using your
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usual character set. However, when Cygwin recognizes an ASCII CAN
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character, it skips over the ASCII CAN and handles the following bytes as
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a UTF-8 character. Thus, the filename is symmetrically converted back to
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UTF-16 and you can access the file.</para>
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<note><para>Please be aware that this method is not entirely foolproof.
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In some character set combinations it might not work for certain native
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characters.</para>
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<para>Only by using the UTF-8 charset you can avoid this problem safely.
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</para></note>
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</sect2>
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<sect2 id="pathnames-casesensitive">
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<title>Case sensitive filenames</title>
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<para>In the Win32 subsystem filenames are only case-preserved, but not
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case-sensitive. You can't access two files in the same directory which
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only differ by case, like <filename>Abc</filename> and
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<filename>aBc</filename>. While NTFS (and some remote filesystems)
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support case-sensitivity, the NT kernel does not support it by default.
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Rather, you have to tweak a registry setting and reboot. For that reason,
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case-sensitivity can not be supported by Cygwin, unless you change that
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registry value.</para>
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<para>If you really want case-sensitivity in Cygwin, you can switch it
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on by setting the registry value</para>
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<screen>
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HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\kernel\obcaseinsensitive
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</screen>
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<para>to 0 and reboot the machine.</para>
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<note>
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<para>
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When installing Microsoft's Services For Unix (SFU), you're asked if
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you want to use case-sensitive filenames. If you answer "yes" at this point,
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the installer will change the aforementioned registry value to 0, too. So, if
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you have SFU installed, there's some chance that the registry value is already
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set to case sensitivity.
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</para>
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</note>
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<para>After you set this registry value to 0, Cygwin will be case-sensitive
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by default on NTFS and NFS filesystems. However, there are limitations:
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while two <emphasis role='bold'>programs</emphasis> <filename>Abc.exe</filename>
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and <filename>aBc.exe</filename> can be created and accessed like other files,
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starting applications is still case-insensitive due to Windows limitations
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and so the program you try to launch may not be the one actually started. Also,
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be aware that using two filenames which only differ by case might
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result in some weird interoperability issues with native Win32 applications.
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You're using case-sensitivity at your own risk. You have been warned! </para>
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<para>Even if you use case-sensitivity, it might be feasible to switch to
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case-insensitivity for certain paths for better interoperability with
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native Win32 applications (even if it's just Windows Explorer). You can do
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this on a per-mount point base, by using the "posix=0" mount option in
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<filename>/etc/fstab</filename>, or your <filename>/etc/fstab.d/$USER</filename>
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file.</para>
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<para><filename>/cygdrive</filename> paths are case-insensitive by default.
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The reason is that the native Windows %PATH% environment variable is not
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always using the correct case for all paths in it. As a result, if you use
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case-sensitivity on the <filename>/cygdrive</filename> prefix, your shell
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might claim that it can't find Windows commands like <command>attrib</command>
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or <command>net</command>. To ease the pain, the <filename>/cygdrive</filename>
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path is case-insensitive by default and you have to use the "posix=1" setting
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explicitly in <filename>/etc/fstab</filename> or
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<filename>/etc/fstab.d/$USER</filename> to switch it to case-sensitivity,
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or you have to make sure that the native Win32 %PATH% environment variable
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is using the correct case for all paths throughout.</para>
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<para>Note that mount points as well as device names and virtual
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paths like /proc are always case-sensitive! The only exception are
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the subdirectories and filenames under /proc/registry, /proc/registry32
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and /proc/registry64. Registry access is always case-insensitive.
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Read on for more information.</para>
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</sect2>
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<sect2 id="pathnames-posixdevices"> <title>POSIX devices</title>
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<para>While there is no need to create a POSIX <filename>/dev</filename>
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directory, the directory is automatically created as part of a Cygwin
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installation. It's existence is often a prerequisit to run certain
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applications which create symbolic links, fifos, or UNIX sockets in
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<filename>/dev</filename>. Also, the directories <filename>/dev/shm</filename>
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and <filename>/dev/mqueue</filename> are required to exist to use named POSIX
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semaphores, shared memory, and message queues, so a system without a real
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<filename>/dev</filename> directory is functionally crippled.
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</para>
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<para>Apart from that, Cygwin automatically simulates POSIX devices
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internally. The <filename>/dev</filename> directory is automagically
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populated with existing POSIX devices by Cygwin in a way comparable with a
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<ulink url="http://en.wikipedia.org/wiki/Udev">udev</ulink> based virtual
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<filename>/dev</filename> directory under Linux.</para>
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<para>
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Cygwin supports the following character devices commonly found on POSIX systems:
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</para>
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<screen>
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/dev/null
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/dev/zero
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/dev/full
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/dev/console Pseudo device name for the current console window of a session.
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Cygwin's /dev/console is not quite comparable with the console
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device on UNIX machines.
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/dev/cons0 Console sessions are numbered from /dev/cons0 upwards.
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/dev/cons1 Console device names are pseudo device names, only accessible
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... from processes within this very console session. This is due
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to a restriction in Windows.
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/dev/tty The current controlling tty of a session.
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/dev/ptmx Pseudo tty master device.
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/dev/pty0 Pseudo ttys are numbered from /dev/pty0 upwards as they are
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/dev/pty1 requested.
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...
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/dev/ttyS0 Serial communication devices. ttyS0 == Win32 COM1,
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/dev/ttyS1 ttyS1 == COM2, etc.
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...
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/dev/pipe
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/dev/fifo
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/dev/kmsg Kernel message pipe, for usage with sys logger services.
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/dev/random Random number generator.
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/dev/urandom
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/dev/dsp Default sound device of the system.
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</screen>
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<para>
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Cygwin also has several Windows-specific devices:
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</para>
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<screen>
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/dev/com1 The serial ports, starting with COM1 which is the same as ttyS0.
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/dev/com2 Please use /dev/ttySx instead.
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...
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/dev/conin Same as Windows CONIN$.
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/dev/conout Same as Windows CONOUT$.
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/dev/clipboard The Windows clipboard, text only
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/dev/windows The Windows message queue.
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</screen>
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<para>
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Block devices are accessible by Cygwin processes using fixed POSIX device
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names. These POSIX device names are generated using a direct conversion
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from the POSIX namespace to the internal NT namespace.
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E.g. the first harddisk is the NT internal device \device\harddisk0\partition0
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or the first partition on the third harddisk is \device\harddisk2\partition1.
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The first floppy in the system is \device\floppy0, the first CD-ROM is
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\device\cdrom0 and the first tape drive is \device\tape0.</para>
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<para>The mapping from physical device to the name of the device in the
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internal NT namespace can be found in various places. For hard disks and
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CD/DVD drives, the Windows "Disk Management" utility (part of the
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"Computer Management" console) shows that the mapping of "Disk 0" is
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\device\harddisk0. "CD-ROM 2" is \device\cdrom2. Another place to find
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this mapping is the "Device Management" console. Disks have a
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"Location" number, tapes have a "Tape Symbolic Name", etc.
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Unfortunately, the places where this information is found is not very
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well-defined.</para>
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<para>
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For external disks (USB-drives, CF-cards in a cardreader, etc) you can use
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Cygwin to show the mapping. <filename>/proc/partitions</filename>
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contains a list of raw drives known to Cygwin. The <command>df</command>
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command shows a list of drives and their respective sizes. If you match
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the information between <filename>/proc/partitions</filename> and the
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<command>df</command> output, you should be able to figure out which
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external drive corresponds to which raw disk device name.</para>
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<note><para>Apart from tape devices which are not block devices and are
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by default accessed directly, accessing mass storage devices raw
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is something you should only do if you know what you're doing and know how to
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handle the information. <emphasis role='bold'>Writing</emphasis> to a raw
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mass storage device you should only do if you
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<emphasis role='bold'>really</emphasis> know what you're doing and are aware
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of the fact that any mistake can destroy important information, for the
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device, and for you. So, please, handle this ability with care.
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<emphasis role='bold'>You have been warned.</emphasis></para></note>
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<para>
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Last but not least, the mapping from POSIX /dev namespace to internal
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NT namespace is as follows:
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</para>
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<screen>
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POSIX device name Internal NT device name
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/dev/st0 \device\tape0, rewind
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/dev/nst0 \device\tape0, no-rewind
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/dev/st1 \device\tape1
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/dev/nst1 \device\tape1
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...
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/dev/st15
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/dev/nst15
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/dev/fd0 \device\floppy0
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/dev/fd1 \device\floppy1
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...
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/dev/fd15
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/dev/sr0 \device\cdrom0
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/dev/sr1 \device\cdrom1
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...
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/dev/sr15
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/dev/scd0 \device\cdrom0
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/dev/scd1 \device\cdrom1
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...
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/dev/scd15
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/dev/sda \device\harddisk0\partition0 (whole disk)
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/dev/sda1 \device\harddisk0\partition1 (first partition)
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...
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/dev/sda15 \device\harddisk0\partition15 (fifteenth partition)
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/dev/sdb \device\harddisk1\partition0
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/dev/sdb1 \device\harddisk1\partition1
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[up to]
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/dev/sddx \device\harddisk127\partition0
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/dev/sddx1 \device\harddisk127\partition1
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...
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/dev/sddx15 \device\harddisk127\partition15
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</screen>
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<para>
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if you don't like these device names, feel free to create symbolic
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links as they are created on Linux systems for convenience:
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</para>
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<screen>
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ln -s /dev/sr0 /dev/cdrom
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ln -s /dev/nst0 /dev/tape
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...
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</screen>
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</sect2>
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<sect2 id="pathnames-exe"><title>The .exe extension</title>
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<para>Win32 executable filenames end with <filename>.exe</filename>
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but the <filename>.exe</filename> need not be included in the command,
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so that traditional UNIX names can be used. However, for programs that
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end in <filename>.bat</filename> and <filename>.com</filename>, you
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cannot omit the extension. </para>
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<para>As a side effect, the <command> ls filename</command> gives
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information about <filename>filename.exe</filename> if
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<filename>filename.exe</filename> exists and <filename>filename</filename>
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does not. In the same situation the function call
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<function>stat("filename",..)</function> gives information about
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<filename>filename.exe</filename>. The two files can be distinguished
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by examining their inodes, as demonstrated below.
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<screen>
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<prompt>bash$</prompt> <userinput>ls * </userinput>
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a a.exe b.exe
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<prompt>bash$</prompt> <userinput>ls -i a a.exe</userinput>
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445885548 a 435996602 a.exe
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<prompt>bash$</prompt> <userinput>ls -i b b.exe</userinput>
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432961010 b 432961010 b.exe
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</screen>
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If a shell script <filename>myprog</filename> and a program
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<filename>myprog.exe</filename> coexist in a directory, the shell
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script has precedence and is selected for execution of
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<command>myprog</command>. Note that this was quite the reverse up to
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Cygwin 1.5.19. It has been changed for consistency with the rest of Cygwin.
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</para>
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<para>The <command>gcc</command> compiler produces an executable named
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<filename>filename.exe</filename> when asked to produce
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<filename>filename</filename>. This allows many makefiles written
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for UNIX systems to work well under Cygwin.</para>
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</sect2>
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<sect2 id="pathnames-proc"><title>The /proc filesystem</title>
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<para>
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Cygwin, like Linux and other similar operating systems, supports the
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<filename>/proc</filename> virtual filesystem. The files in this
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directory are representations of various aspects of your system,
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for example the command <userinput>cat /proc/cpuinfo</userinput>
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displays information such as what model and speed processor you have.
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</para>
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<para>
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One unique aspect of the Cygwin <filename>/proc</filename> filesystem
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is <filename>/proc/registry</filename>, see next section.
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</para>
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<para>
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The Cygwin <filename>/proc</filename> is not as complete as the
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one in Linux, but it provides significant capabilities. The
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<systemitem>procps</systemitem> package contains several utilities
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that use it.
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</para>
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</sect2>
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<sect2 id="pathnames-proc-registry"><title>The /proc/registry filesystem</title>
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<para>
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The <filename>/proc/registry</filename> filesystem provides read-only
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access to the Windows registry. It displays each <literal>KEY</literal>
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as a directory and each <literal>VALUE</literal> as a file. As anytime
|
|
you deal with the Windows registry, use caution since changes may result
|
|
in an unstable or broken system. There are additionally subdirectories called
|
|
<filename>/proc/registry32</filename> and <filename>/proc/registry64</filename>.
|
|
They are identical to <filename>/proc/registry</filename> on 32 bit
|
|
host OSes. On 64 bit host OSes, <filename>/proc/registry32</filename>
|
|
opens the 32 bit processes view on the registry, while
|
|
<filename>/proc/registry64</filename> opens the 64 bit processes view.
|
|
</para>
|
|
<para>
|
|
Reserved characters ('/', '\', ':', and '%') or reserved names
|
|
(<filename>.</filename> and <filename>..</filename>) are converted by
|
|
percent-encoding:
|
|
<screen>
|
|
<prompt>bash$</prompt> <userinput>regtool list -v '\HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices'</userinput>
|
|
...
|
|
\DosDevices\C: (REG_BINARY) = cf a8 97 e8 00 08 fe f7
|
|
...
|
|
<prompt>bash$</prompt> <userinput>cd /proc/registry/HKEY_LOCAL_MACHINE/SYSTEM</userinput>
|
|
<prompt>bash$</prompt> <userinput>ls -l MountedDevices</userinput>
|
|
...
|
|
-r--r----- 1 Admin SYSTEM 12 Dec 10 11:20 %5CDosDevices%5CC%3A
|
|
...
|
|
<prompt>bash$</prompt> <userinput>od -t x1 MountedDevices/%5CDosDevices%5CC%3A</userinput>
|
|
0000000 cf a8 97 e8 00 08 fe f7 01 00 00 00
|
|
</screen>
|
|
The unnamed (default) value of a key can be accessed using the filename
|
|
<filename>@</filename>.
|
|
</para>
|
|
<para>
|
|
If a registry key contains a subkey and a value with the same name
|
|
<filename>foo</filename>, Cygwin displays the subkey as
|
|
<filename>foo</filename> and the value as <filename>foo%val</filename>.
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2 id="pathnames-at"><title>The @pathnames</title>
|
|
<para>To circumvent the limitations on shell line length in the native
|
|
Windows command shells, Cygwin programs, when invoked by non-Cygwin processes, expand their arguments
|
|
starting with "@" in a special way. If a file
|
|
<filename>pathname</filename> exists, the argument
|
|
<filename>@pathname</filename> expands recursively to the content of
|
|
<filename>pathname</filename>. Double quotes can be used inside the
|
|
file to delimit strings containing blank space.
|
|
In the following example compare the behaviors
|
|
<command>/bin/echo</command> when run from bash and from the Windows command prompt.</para>
|
|
|
|
<example id="pathnames-at-ex"><title> Using @pathname</title>
|
|
<screen>
|
|
<prompt>bash$</prompt> <userinput>/bin/echo 'This is "a long" line' > mylist</userinput>
|
|
<prompt>bash$</prompt> <userinput>/bin/echo @mylist</userinput>
|
|
@mylist
|
|
<prompt>bash$</prompt> <userinput>cmd</userinput>
|
|
<prompt>c:\></prompt> <userinput>c:\cygwin\bin\echo @mylist</userinput>
|
|
This is a long line
|
|
</screen>
|
|
</example>
|
|
</sect2>
|
|
</sect1>
|