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@section Cygwin API Questions
@subsection How does everything work?
There's a C library which provides a Unix-style API. The
applications are linked with it and voila - they run on Windows.
The aim is to add all the goop necessary to make your apps run on
Windows into the C library. Then your apps should run on Unix and
Windows with no changes at the source level.
The C library is in a DLL, which makes basic applications quite small.
And it allows relatively easy upgrades to the Win32/Unix translation
layer, providing that dll changes stay backward-compatible.
For a good overview of Cygwin, you may want to read the paper on Cygwin
published by the Usenix Association in conjunction with the 2d Usenix NT
Symposium in August 1998. It is available in html format on the project
WWW site.
@subsection Are development snapshots for the Cygwin library available?
Yes. They're made whenever anything interesting happens inside the
Cygwin library (usually roughly on a nightly basis, depending on how much
is going on). They are only intended for those people who wish to
contribute code to the project. If you aren't going to be happy
debugging problems in a buggy snapshot, avoid these and wait for a real
release. The snapshots are available from
http://sources.redhat.com/cygwin/snapshots/
@subsection How is the DOS/Unix CR/LF thing handled?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
Let's start with some background.
In UNIX, a file is a file and what the file contains is whatever the
program/programmer/user told it to put into it. In Windows, a file is
also a file and what the file contains depends not only on the
program/programmer/user but also the file processing mode.
When processing in text mode, certain values of data are treated
specially. A \n (new line) written to the file will prepend a \r
(carriage return) so that if you `printf("Hello\n") you in fact get
"Hello\r\n". Upon reading this combination, the \r is removed and the
number of bytes returned by the read is 1 less than was actually read.
This tends to confuse programs dependant on ftell() and fseek(). A
Ctrl-Z encountered while reading a file sets the End Of File flags even
though it truly isn't the end of file.
One of Cygwin's goals is to make it possible to easily mix Cygwin-ported
Unix programs with generic Windows programs. As a result, Cygwin opens
files in text mode as is normal under Windows. In the accompanying
tools, tools that deal with binaries (e.g. objdump) operate in unix
binary mode and tools that deal with text files (e.g. bash) operate in
text mode.
Some people push the notion of globally setting the default processing
mode to binary via mount point options or by setting the CYGWIN32
environment variable. But that creates a different problem. In
binary mode, the program receives all of the data in the file, including
a \r. Since the programs will no longer deal with these properly for
you, you would have to remove the \r from the relevant text files,
especially scripts and startup resource files. This is a porter "cop
out", forcing the user to deal with the \r for the porter.
It is rather easy for the porter to fix the source code by supplying the
appropriate file processing mode switches to the open/fopen functions.
Treat all text files as text and treat all binary files as binary.
To be specific, you can select binary mode by adding @code{O_BINARY} to
the second argument of an @code{open} call, or @code{"b"} to second
argument of an @code{fopen} call. You can also call @code{setmode (fd,
O_BINARY)}.
Note that because the open/fopen switches are defined by ANSI, they
exist under most flavors of Unix; open/fopen will just ignore the switch
since they have no meaning to UNIX.
Also note that @code{lseek} only works in binary mode.
Explanation adapted from mailing list email by Earnie Boyd
<earnie_boyd@@yahoo.com>.
@subsection Is the Cygwin library multi-thread-safe?
Multi-thread-safe support is turned on by default in 1.1.x releases
(i.e., in the latest net release). That does not mean that it is bug
free!
There is also limited support for 'POSIX threads', see the file
@code{cygwin.din} for the list of POSIX thread functions provided.
@subsection Why is some functionality only supported in Windows NT?
Windows 9x: n.
32 bit extensions and a graphical shell for a 16 bit patch to an
8 bit operating system originally coded for a 4 bit microprocessor,
written by a 2 bit company that can't stand 1 bit of competition.
But seriously, Windows 9x lacks most of the security-related calls and
has several other deficiencies with respect to its version of the Win32
API. See the calls.texinfo document for more information as to what
is not supported in Win 9x.
@subsection How is fork() implemented?
Cygwin fork() essentially works like a non-copy on write version
of fork() (like old Unix versions used to do). Because of this it
can be a little slow. In most cases, you are better off using the
spawn family of calls if possible.
Here's how it works:
Parent initializes a space in the Cygwin process table for child.
Parent creates child suspended using Win32 CreateProcess call, giving
the same path it was invoked with itself. Parent calls setjmp to save
its own context and then sets a pointer to this in the Cygwin shared
memory area (shared among all Cygwin tasks). Parent fills in the childs
.data and .bss subsections by copying from its own address space into
the suspended child's address space. Parent then starts the child.
Parent waits on mutex for child to get to safe point. Child starts and
discovers if has been forked and then longjumps using the saved jump
buffer. Child sets mutex parent is waiting on and then blocks on
another mutex waiting for parent to fill in its stack and heap. Parent
notices child is in safe area, copies stack and heap from itself into
child, releases the mutex the child is waiting on and returns from the
fork call. Child wakes from blocking on mutex, recreates any mmapped
areas passed to it via shared area and then returns from fork itself.
@subsection How does wildcarding (globbing) work?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
If an application using CYGWIN.DLL starts up, and can't find the
@code{PID} environment variable, it assumes that it has been started
from the a DOS style command prompt. This is pretty safe, since the
rest of the tools (including bash) set PID so that a new process knows
what PID it has when it starts up.
If the DLL thinks it has come from a DOS style prompt, it runs a
`globber' over the arguments provided on the command line. This means
that if you type @code{LS *.EXE} from DOS, it will do what you might
expect.
Beware: globbing uses @code{malloc}. If your application defines
@code{malloc}, that will get used. This may do horrible things to you.
@subsection How do symbolic links work?
Cygwin generates link files with a magic header. When
you open a file or directory that is a link to somewhere else, it
opens the file or directory listed in the magic header. Because we
don't want to have to open every referenced file to check symlink
status, Cygwin marks symlinks with the system attribute. Files
without the system attribute are not checked. Because remote samba
filesystems do not enable the system attribute by default, symlinks do
not work on network drives unless you explicitly enable this
attribute.
@subsection Why do some files, which are not executables have the 'x' type.
When working out the unix-style attribute bits on a file, the library
has to fill out some information not provided by the WIN32 API.
It guesses that files ending in .exe and .bat are executable, as are
ones which have a "#!" as their first characters.
@subsection How secure is Cygwin in a multi-user environment?
Cygwin is not secure in a multi-user environment. For
example if you have a long running daemon such as "inetd"
running as admin while ordinary users are logged in, or if
you have a user logged in remotely while another user is logged
into the console, one cygwin client can trick another into
running code for it. In this way one user may gain the
priveledge of another cygwin program running on the machine.
This is because cygwin has shared state that is accessible by
all processes.
(Thanks to Tim Newsham (newsham@@lava.net) for this explanation).
@subsection How do the net-related functions work?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
The network support in Cygwin is supposed to provide the Unix API, not
the Winsock API.
There are differences between the semantics of functions with the same
name under the API.
E.g., the select system call on Unix can wait on a standard file handles
and handles to sockets. The select call in winsock can only wait on
sockets. Because of this, cygwin.dll does a lot of nasty stuff behind
the scenes, trying to persuade various winsock/win32 functions to do what
a Unix select would do.
If you are porting an application which already uses Winsock, then
using the net support in Cygwin is wrong.
But you can still use native Winsock, and use Cygwin. The functions
which cygwin.dll exports are called 'cygwin_<name>'. There
are a load of defines which map the standard Unix names to the names
exported by the dll -- check out include/netdb.h:
@example
..etc..
void cygwin_setprotoent (int);
void cygwin_setservent (int);
void cygwin_setrpcent (int);
..etc..
#ifndef __INSIDE_CYGWIN_NET__
#define endprotoent cygwin_endprotoent
#define endservent cygwin_endservent
#define endrpcent cygwin_endrpcent
..etc..
@end example
The idea is that you'll get the Unix->Cygwin mapping if you include
the standard Unix header files. If you use this, you won't need to
link with libwinsock.a - all the net stuff is inside the dll.
The mywinsock.h file is a standard winsock.h which has been hacked to
remove the bits which conflict with the standard Unix API, or are
defined in other headers. E.g., in mywinsock.h, the definition of
struct hostent is removed. This is because on a Unix box, it lives in
netdb. It isn't a good idea to use it in your applications.
As of the b19 release, this information may be slightly out of date.
@subsection I don't want Unix sockets, how do I use normal Win32 winsock?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
To use the vanilla Win32 winsock, you just need to #define Win32_Winsock
and #include "windows.h" at the top of your source file(s). You'll also
want to add -lwsock32 to the compiler's command line so you link against
libwsock32.a.
@subsection What version numbers are associated with Cygwin?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
There is a cygwin.dll major version number that gets incremented
every time we make a new Cygwin release available. This
corresponds to the name of the release (e.g. beta 19's major
number is "19"). There is also a cygwin.dll minor version number. If
we release an update of the library for an existing release, the minor
number would be incremented.
There are also Cygwin API major and minor numbers. The major number
tracks important non-backward-compatible interface changes to the API.
An executable linked with an earlier major number will not be compatible
with the latest DLL. The minor number tracks significant API additions
or changes that will not break older executables but may be required by
newly compiled ones.
Then there is a shared memory region compatibity version number. It is
incremented when incompatible changes are made to the shared memory
region or to any named shared mutexes, semaphores, etc.
Finally there is a mount point registry version number which keeps track
of non-backwards-compatible changes to the registry mount table layout.
This has been "B15.0" since the beta 15 release.
@subsection Why isn't _timezone set correctly?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
Did you explicitly call tzset() before checking the value of _timezone?
If not, you must do so.
@subsection Is there a mouse interface?
There is no way to capture mouse events from Cygwin. There are
currently no plans to add support for this.

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@section Programming Questions
@subsection Why are compiled executables so huge?!?
By default, gcc compiles in all symbols. You'll also find that gcc
creates large executables on UNIX.
If that bothers you, just use the 'strip' program, part of the binutils
package.
@subsection Where is glibc?
Cygwin does not provide glibc. It uses newlib instead, which provides
much (but not all) of the same functionality. Porting glibc to Cygwin
would be difficult.
@subsection Why is make behaving badly?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
Starting with the beta 19 release, make defaults to a win32 mode in
which backslashes in filenames are permitted and cmd.exe/command.com
is used as the sub-shell. In this mode, escape characters aren't
allowed among other restrictions. For this reason, you must set
the environment variable MAKE_MODE to UNIX to run make on ordinary Unix
Makefiles. Here is the full scoop:
MAKE_MODE selects between native Win32 make mode (the default) and
a Unix mode where it behaves like a Unix make. The Unix mode does
allow specifying Win32-style paths but only containing forward slashes
as the path separator. The path list separator character is a colon
in Unix mode.
Win32 mode expects path separators to be either / or \. Thus no
Unix-style \s as escape are allowed. Win32 mode also uses
cmd.exe/command.com as the subshell which means "copy" and "del"
(and other shell builtins) will work. The path list separator
character is semi-colon in Win32 mode. People who want an nmake-like
make might want to use this mode but no one should expect Unix
Makefiles to compile in this mode. That is why the default b19
install sets MAKE_MODE to UNIX.
@subsection Why the undefined reference to "WinMain@@16"?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
Try adding an empty main() function to one of your sources.
@subsection How do I use Win32 API calls?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
It's pretty simple actually. Cygwin tools require that you explicitly
link the import libraries for whatever Win32 API functions that you
are going to use, with the exception of kernel32, which is linked
automatically (because the startup and/or built-in code uses it).
For example, to use graphics functions (GDI) you must link
with gdi32 like this:
gcc -o foo.exe foo.o bar.o -lgdi32
or (compiling and linking in one step):
gcc -o foo.exe foo.c bar.c -lgdi32
The following libraries are available for use in this way:
advapi32 largeint ole32 scrnsave vfw32
cap lz32 oleaut32 shell32 win32spl
comctl32 mapi32 oledlg snmp winmm
comdlg32 mfcuia32 olepro32 svrapi winserve
ctl3d32 mgmtapi opengl32 tapi32 winspool
dlcapi mpr penwin32 th32 winstrm
gdi32 msacm32 pkpd32 thunk32 wow32
glaux nddeapi rasapi32 url wsock32
glu32 netapi32 rpcdce4 user32 wst
icmp odbc32 rpcndr uuid
imm32 odbccp32 rpcns4 vdmdbg
kernel32 oldnames rpcrt4 version
The regular setup allows you to use the option -mwindows on the
command line to include a set of the basic libraries (and also
make your program a GUI program instead of a console program),
including user32, gdi32 and, IIRC, comdlg32.
Note that you should never include -lkernel32 on your link line
unless you are invoking ld directly. Do not include the same import
library twice on your link line. Finally, it is a good idea to
put import libraries last on your link line, or at least after
all the object files and static libraries that reference them.
The first two are related to problems the linker has (as of b18 at least)
when import libraries are referenced twice. Tables get messed up and
programs crash randomly. The last point has to do with the fact that
gcc processes the files listed on the command line in sequence and
will only resolve references to libraries if they are given after
the file that makes the reference.
@subsection How do I compile a Win32 executable that doesn't use Cygwin?
The -mno-cygwin flag to gcc makes gcc link against standard Microsoft
DLLs instead of Cygwin. This is desirable for native Windows programs
that don't need a UNIX emulation layer.
This is not to be confused with 'MinGW' (Minimalist GNU for Windows),
which is a completely separate effort. That project's home page is
@file{http://www.mingw.org/index.shtml}.
@subsection How do I make the console window go away?
The default during compilation is to produce a console application.
It you are writing a GUI program, you should either compile with
-mwindows as explained above, or add the string
"-Wl,--subsystem,windows" to the GCC commandline.
@subsection Why does make complain about a "missing separator"?
This problem usually occurs as a result of someone editing a Makefile
with a text editor that replaces tab characters with spaces. Command
lines must start with tabs. This is not specific to Cygwin.
@subsection Why can't we redistribute Microsoft's Win32 headers?
Subsection 2.d.f of the `Microsoft Open Tools License agreement' looks
like it says that one may not "permit further redistribution of the
Redistributables to their end users". We take this to mean that we can
give them to you, but you can't give them to anyone else, which is
something that Cygnus (err... Red Hat) can't agree to. Fortunately, we
have our own Win32 headers which are pretty complete.
@subsection How do I link against .lib files?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
1. Build a C file with a function table. Put all functions you intend
to use in that table. This forces the linker to include all the object
files from the .lib. Maybe there is an option to force LINK.EXE to
include an object file.
2. Build a dummy 'LibMain'.
3. Build a .def with all the exports you need.
4. Link with your .lib using link.exe.
or
1. Extract all the object files from the .lib using LIB.EXE.
2. Build a dummy C file referencing all the functions you need, either
with a direct call or through an initialized function pointer.
3. Build a dummy LibMain.
4. Link all the objects with this file+LibMain.
5. Write a .def.
6. Link.
You can use these methods to use MSVC (and many other runtime libs)
with Cygwin development tools.
Note that this is a lot of work (half a day or so), but much less than
rewriting the runtime library in question from specs...
(thanks to Jacob Navia (root@@jacob.remcomp.fr) for this explanation)
@subsection How do I rebuild the tools on my NT box?
@strong{Note:} You must build in a directory @emph{outside} the source
tree.
Assuming that you have the src installed as /src, will build in
the directory /obj, and want to install the tools in /install:
@example
bash
cd /obj
/src/configure --prefix=/install -v > configure.log 2>&1
make > make.log 2>&1
make install > install.log 2>&1
@end example
Normally, this will also attempt to build the documentation, which
additionally requires db2html, texi2html and possibly others.
These tools are not included in the Cygwin distribution, but are readily
obtainable:
@table @samp
@item db2html
Part of docbook, from @file{http://sources.redhat.com/docbook-tools/}.
@item texi2html
From @file{http://www.mathematik.uni-kl.de/~obachman/Texi2html/}.
@end table
To check a cygwin1.dll, run "make check" in the winsup/cygwin directory.
If that works, install everything @emph{except} the dll (if you can).
Then, close down all cygwin programs (including bash windows, inetd,
etc.), save your old dll, and copy the new dll to @emph{all} the
places where the old dll was (if there is more than one on your
machine). Then start up a bash window and see what happens. (Or better,
run a cygwin program from the Windows command prompt.)
If you get the error "shared region is corrupted" it means that two
different versions of cygwin1.dll are running on your machine at the
same time.
@subsection How can I compile a powerpc NT toolchain?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
Unfortunately, this will be difficult. It hasn't been built for
some time (late 1996) since Microsoft has dropped development of
powerpc NT. Exception handling/signals support semantics/args have been
changed for x86 and not updated for ppc so the ppc specific support would
have to be rewritten. We don't know of any other incompatibilities.
Please send us patches if you do this work!
@subsection How can I compile an Alpha NT toolchain?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
We have not ported the tools to Alpha NT and do not have plans to
do so at the present time. We would be happy to add support
for Alpha NT if someone contributes the changes to us.
@subsection How can I adjust the heap/stack size of an application?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
Pass heap/stack linker arguments to gcc. To create foo.exe with
a heap size of 1024 and a stack size of 4096, you would invoke
gcc as:
@code{gcc -Wl,--heap,1024,--stack,4096 -o foo foo.c}
@subsection How can I find out which dlls are needed by an executable?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
objdump -p provides this information.
@subsection How do I build a DLL?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
There's documentation that explains the process on the main Cygwin
project web page (http://sources.redhat.com/cygwin/).
@subsection How can I set a breakpoint at MainCRTStartup?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
Set a breakpoint at *0x401000 in gdb and then run the program in
question.
@subsection How can I build a relocatable dll?
@strong{(Please note: This section has not yet been updated for the
latest net release. However, there was a discussion on the cygwin
mailing list recently that addresses this issue. Read
@file{http://sources.redhat.com/ml/cygwin/2000-06/msg00688.html} and
related messages.)}
You must execute the following sequence of five commands, in this
order:
@example
$(LD) -s --base-file BASEFILE --dll -o DLLNAME OBJS LIBS -e ENTRY
$(DLLTOOL) --as=$(AS) --dllname DLLNAME --def DEFFILE \
--base-file BASEFILE --output-exp EXPFILE
$(LD) -s --base-file BASEFILE EXPFILE -dll -o DLLNAME OBJS LIBS -e ENTRY
$(DLLTOOL) --as=$(AS) --dllname DLLNAME --def DEFFILE \
--base-file BASEFILE --output-exp EXPFILE
$(LD) EXPFILE --dll -o DLLNAME OBJS LIBS -e ENTRY
@end example
In this example, $(LD) is the linker, ld.
$(DLLTOOL) is dlltool.
$(AS) is the assembler, as.
DLLNAME is the name of the DLL you want to create, e.g., tcl80.dll.
OBJS is the list of object files you want to put into the DLL.
LIBS is the list of libraries you want to link the DLL against. For
example, you may or may not want -lcygwin. You may want -lkernel32.
Tcl links against -lcygwin -ladvapi32 -luser32 -lgdi32 -lcomdlg32
-lkernel32.
DEFFILE is the name of your definitions file. A simple DEFFILE would
consist of ``EXPORTS'' followed by a list of all symbols which should
be exported from the DLL. Each symbol should be on a line by itself.
Other programs will only be able to access the listed symbols.
BASEFILE is a temporary file that is used during this five stage
process, e.g., tcl.base.
EXPFILE is another temporary file, e.g., tcl.exp.
ENTRY is the name of the function which you want to use as the entry
point. This function should be defined using the WINAPI attribute,
and should take three arguments:
int WINAPI startup (HINSTANCE, DWORD, LPVOID)
This means that the actual symbol name will have an appended @@12, so if
your entry point really is named @samp{startup}, the string you should
use for ENTRY in the above examples would be @samp{startup@@12}.
If your DLL calls any Cygwin API functions, the entry function will need
to initialize the Cygwin impure pointer. You can do that by declaring
a global variable @samp{_impure_ptr}, and then initializing it in the
entry function. Be careful not to export the global variable
@samp{_impure_ptr} from your DLL; that is, do not put it in DEFFILE.
@example
/* This is a global variable. */
struct _reent *_impure_ptr;
extern struct _reent *__imp_reent_data;
int entry (HINSTANT hinst, DWORD reason, LPVOID reserved)
@{
_impure_ptr = __imp_reent_data;
/* Whatever else you want to do. */
@}
@end example
You may put an optional `--subsystem windows' on the $(LD) lines. The
Tcl build does this, but I admit that I no longer remember whether
this is important. Note that if you specify a --subsytem <x> flag to ld,
the -e entry must come after the subsystem flag, since the subsystem flag
sets a different default entry point.
You may put an optional `--image-base BASEADDR' on the $(LD) lines.
This will set the default image base. Programs using this DLL will
start up a bit faster if each DLL occupies a different portion of the
address space. Each DLL starts at the image base, and continues for
whatever size it occupies.
Now that you've built your DLL, you may want to build a library so
that other programs can link against it. This is not required: you
could always use the DLL via LoadLibrary. However, if you want to be
able to link directly against the DLL, you need to create a library.
Do that like this:
$(DLLTOOL) --as=$(AS) --dllname DLLNAME --def DEFFILE --output-lib LIBFILE
$(DLLTOOL), $(AS), DLLNAME, and DEFFILE are the same as above. Make
sure you use the same DLLNAME and DEFFILE, or things won't work right.
LIBFILE is the name of the library you want to create, e.g.,
libtcl80.a. You can then link against that library using something
like -ltcl80 in your linker command.
@subsection How can I debug what's going on?
You can debug your application using @code{gdb}. Make sure you
compile it with the -g flag! If your application calls functions in
MS dlls, gdb will complain about not being able to load debug information
for them when you run your program. This is normal since these dlls
don't contain debugging information (and even if they did, that debug
info would not be compatible with gdb).
@subsection Can I use a system trace mechanism instead?
Yes. You can use the @code{strace.exe} utility to run other cygwin
programs with various debug and trace messages enabled. For information
on using @code{strace}, see the Cygwin User's Guide or the file
@code{winsup/utils/utils.sgml}.
Alternatively, you can set the @code{STRACE} environment variable to
@code{1}, and get a whole load of debug information on your screen
whenever a Cygwin app runs. This is an especially useful tool to use
when tracking bugs down inside the Cygwin library. @code{STRACE} can be
set to different values to achieve different amounts of granularity.
You can set it to @code{0x10} for information about syscalls or
@code{0x800} for signal/process handling-related info, to name two. The
strace mechanism is well documented in the Cygwin library sources in the
file @code{winsup/cygwin/include/sys/strace.h}.
@subsection Why doesn't gdb handle signals?
Unfortunately, there is only minimal signal handling support in gdb
currently. Signal handling only works with Windows-type signals.
SIGINT may work, SIGFPE may work, SIGSEGV definitely does. You cannot
'stop', 'print' or 'nopass' signals like SIGUSR1 or SIGHUP to the
process being debugged.
@subsection The linker complains that it can't find something.
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
A common error is to put the library on the command line before
the thing that needs things from it.
This is wrong @code{gcc -lstdc++ hello.cc}.
This is right @code{gcc hello.cc -lstdc++}.
@subsection I use a function I know is in the API, but I still get a link error.
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
The function probably isn't declared in the header files, or
the UNICODE stuff for it isn't filled in.
@subsection Can you make DLLs that are linked against libc ?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
Yes.
@subsection Where is malloc.h?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
Include stdlib.h instead of malloc.h.
@subsection Can I use my own malloc?
If you define a function called @code{malloc} in your own code, and link
with the DLL, the DLL @emph{will} call your @code{malloc}. Needless to
say, you will run into serious problems if your malloc is buggy.
If you run any programs from the DOS command prompt, rather than from in
bash, the DLL will try and expand the wildcards on the command line.
This process uses @code{malloc} @emph{before} your main line is started.
If you have written your own @code{malloc} to need some initialization
to occur after @code{main} is called, then this will surely break.
Moreover, there is an outstanding issue with @code{_malloc_r} in
@code{newlib}. This re-entrant version of @code{malloc} will be called
directly from within @code{newlib}, by-passing your custom version, and
is probably incompatible with it. But it may not be possible to replace
@code{_malloc_r} too, because @code{cygwin1.dll} does not export it and
Cygwin does not expect your program to replace it. This is really a
newlib issue, but we are open to suggestions on how to deal with it.
@subsection Can I mix objects compiled with msvc++ and gcc?
Yes, but only if you are combining C object files. MSVC C++ uses a
different mangling scheme than GNU C++, so you will have difficulties
combining C++ objects.
@subsection Can I use the gdb debugger to debug programs built by VC++?
No, not for full (high level source language) debugging.
The Microsoft compilers generate a different type of debugging
symbol information, which gdb does not understand.
However, the low-level (assembly-type) symbols generated by
Microsoft compilers are coff, which gdb DOES understand.
Therefore you should at least be able to see all of your
global symbols; you just won't have any information about
data types, line numbers, local variables etc.
@subsection Where can I find info on x86 assembly?
CPU reference manuals for Intel's current chips are available in
downloadable PDF form on Intel's web site:
@file{http://developer.intel.com/design/pro/manuals/}
@subsection Shell scripts aren't running properly from my makefiles?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
You need to have . (dot) in your $PATH. You should NOT need to add
/bin/sh in front of each and every shell script invoked in your
Makefiles.
@subsection What preprocessor do I need to know about?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
We use _WIN32 to signify access to the Win32 API and __CYGWIN__ for
access to the Cygwin environment provided by the dll.
We chose _WIN32 because this is what Microsoft defines in VC++ and
we thought it would be a good idea for compatibility with VC++ code
to follow their example. We use _MFC_VER to indicate code that should
be compiled with VC++.
@subsection Where can I get f77 and objc components for B20 EGCS 1.1?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
B20-compatible versions of the f77 and objc components are available
from @file{http://www.xraylith.wisc.edu/~khan/software/gnu-win32/}.
@subsection How should I port my Unix GUI to Windows?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
There are two basic strategies for porting Unix GUIs to Windows.
The first is to use a portable graphics library such as tcl/tk, X11, or
V (and others?). Typically, you will end up with a GUI on Windows that
requires some runtime support. With tcl/tk, you'll want to include the
necessary library files and the tcl/tk DLLs. In the case of X11, you'll
need everyone using your program to have an X11 server installed.
The second method is to rewrite your GUI using Win32 API calls (or MFC
with VC++). If your program is written in a fairly modular fashion, you
may still want to use Cygwin if your program contains a lot of shared
(non-GUI-related) code. That way you still gain some of the portability
advantages inherent in using Cygwin.
@subsection Why not use DJGPP ?
DJGPP is a similar idea, but for DOS instead of Win32. DJGPP uses a
"DOS extender" to provide a more reasonable operating interface for its
applications. The Cygwin toolset doesn't have to do this since all of
the applications are native WIN32. Applications compiled with the
Cygwin tools can access the Win32 API functions, so you can write
programs which use the Windows GUI.
You can get more info on DJGPP by following
@file{http://www.delorie.com/}.

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@section Where can I get more information?
@subsection Where's the documentation?
There are links to quite a lot of it on the main Cygwin project web
page: @file{http://sources.redhat.com/cygwin/}. Be sure to at least
read any 'Release Notes' or 'Readme' or 'read this' links on the main
web page, if there are any.
There is a comprehensive Cygwin User's Guide at
@file{http://sources.redhat.com/cygwin/cygwin-ug-net/cygwin-ug-net.html}
and an API Reference at
@file{http://sources.redhat.com/cygwin/cygwin-api/cygwin-api.html}.
There is an interesting paper about Cygwin from the 1998 USENIX Windows
NT Workshop Proceedings at
@file{http://sources.redhat.com/cygwin/usenix-98/cygwin.html}.
You can find documentation for the individual GNU tools at
@file{http://www.fsf.org/manual/}. (You should read GNU manuals from a
local mirror, check @file{http://www.fsf.org/server/list-mirrors.html}
for a list of them.)
@subsection What Cygwin mailing lists can I join?
Comprehensive information about the Cygwin mailing lists can be found at
@file{http://sources.redhat.com/cygwin/lists.html}.
To subscribe to the main list, send a message to
cygwin-subscribe@@sources.redhat.com. To unsubscribe from the
main list, send a message to cygwin-unsubscribe@@sources.redhat.com.
In both cases, the subject and body of the message are ignored.
Similarly, to subscribe to the Cygwin annoucements list, send a message
to cygwin-announce-subscribe@@sources.redhat.com. To unsubscribe,
send a message to cygwin-announce-unsubscribe@@sources.redhat.com.
If you are going to help develop the Cygwin library by volunteering for
the project, you will want to subscribe to the Cygwin developers list,
called cygwin-developers. If you are contributing to Cygwin tools &
applications, rather than the library itself, then you should subscribe
to cygwin-apps. The same mechanism as described for the first two lists
works for these as well. Both cygwin-developers and cygwin-apps are
by-approval lists.
There is a searchable archive of the main mailing list at
@file{http://sources.redhat.com/ml/cygwin/}. There is an alternate
archive, also searchable, at @file{http://www.delorie.com/archives/}.
Cygwin mailing lists are not gatewayed to USENET, so anti-spam measures
in your email address are neither required nor appreciated. Also, avoid
sending HTML content to Cygwin mailing lists.
@subsection Posting Guidelines (Or: Why won't you/the mailing list answer my questions?)
If you follow these guidelines, you are much more likely to get a
helpful response from the Cygwin developers and/or the Cygwin community at
large:
@itemize @bullet
@item Read the User's Guide and the FAQ first.
@item Check the mailing list archives. Your topic may have come up
before. (It may even have been answered!) Use the search facilities
at the links above. Try the alternate site if the main archive is not
producing search results.
@item Explain your problem carefully and completely. "I installed Blah
and it doesn't work!" wastes everybody's time. It provides no
information for anyone to help you with your problem. You should
provide:
@itemize @bullet
@item A problem statement: How does it behave, how do you think it
should behave, and what makes you think it's broken? (Oh yeah, and what
is @emph{"it"}?)
@item Information about your Windows OS ("Win95 OSR2" or "NT4/SP3" or
"Win2K" or "Win98 SE" or ...).
@item Details about your installation process, or attempts at same. (Internet or
Directory install? If the former, exactly when and from what mirror?
If the latter, which packages did you download? Which version of
setup.exe? Any subsequent updates?)
@item Details about your Cygwin setup, accomplished by @emph{pasting}
the output of 'cygcheck -s -v -r' into your message. (Do not send the
output as a file attachment.)
@item A valid return address, so that a reply doesn't require manual editing of
the 'To:' header.
@end itemize
@item Your message must be relevant to the list. Messages that are
@emph{not} directly related to Cygwin are considered off-topic and are
unwelcome. For example, the following are off-topic:
@itemize @bullet
@item General programming language questions
@item General Windows programming questions
@item General UNIX shell programming questions
@item General application usage questions
@item How to make millions by working at home
@item Announcements from LaserJet toner cartridge suppliers
@end itemize
@end itemize
If you do not follow the above guidelines, you may still elicit a
response, but you may not appreciate it!
Inquiries about support contracts and commercial licensing should go to
info@@cygnus.com. If you want to purchase the Cygwin 1.0 CD-ROM, visit
@file{http://www.cygnus.com/cygwin/} or write to
cygwin-info@@cygnus.com. While not strictly @emph{unappreciated} in the
main cygwin list, you'll get the information you need more quickly if
you write to the correct address in the first place.
Beyond that, perhaps nobody has time to answer your question. Perhaps
nobody knows the answer.

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@section Using Cygwin
@subsection How should I set my PATH?
If you look at the "Cygwin 1.1.0" (or similar) shortcut created in the
"Cygnus Solutions" programs folder, you'll see that it runs
@code{C:\cygwin\bin\cygwin.bat} (assuming your root is
@code{C:\cygwin}). The contents should look something like this:
@example
@@echo off
SET MAKE_MODE=unix
SET PATH=C:\cygwin\bin;C:\cygwin\usr\local\bin;%PATH%
bash
@end example
Effectively, this @strong{prepends} /usr/bin and /usr/local/bin to your
Windows system path. If you choose to reset your PATH, say in
$HOME/.bashrc, then you should follow this rule. You @strong{must} have
@code{/usr/bin} in your PATH @strong{before} any Windows system
directories. (And you must not omit the Windows system directories!)
Otherwise you will likely encounter all sorts of problems
running Cygwin applications.
If you haven't messed up the default mounts, then @code{/bin} and
@code{/usr/bin} are the same location, so you only need one of them in
your PATH. You should use @code{/usr/local/bin} for installing
additional Cygwin applications that are not part of the core net
release. (That is, anything not found in an ftp mirror of @code{latest}
and installed by @code{setup.exe}.)
@subsection How do I convert between Windows and UNIX paths?
Use the 'cygpath' utility. Type '@code{cygpath}' with no arguments to
get usage information. For example (on my installation):
@example
bash$ cygpath --windows ~/.bashrc
D:\starksb\.bashrc
bash$ cygpath --unix C:/cygwin/bin/cygwin.bat
/usr/bin/cygwin.bat
bash$ cygpath --unix C:\\cygwin\\bin\\cygwin.bat
/usr/bin/cygwin.bat
@end example
Note that bash interprets the backslash '\' as an escape character, so
you must type it twice in the bash shell if you want it to be recognised
as such.
@subsection How do I set /etc up?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
If you want a valid /etc set up (so "ls -l" will display correct
user information for example) and if you are running NT (preferably
with an NTFS file system), you should just need to create the /etc
directory on the filesystem mounted as / and then use mkpasswd and
mkgroup to create /etc/passwd and /etc/group respectively. Since
Windows 95/98's Win32 API is less complete, you're out of luck if
you're running Windows 95/98.
@subsection Why doesn't bash read my .bashrc file on startup?
Your .bashrc is read from your home directory specified by the HOME
environment variable. It uses /.bashrc if HOME is not set. So you need
to set HOME correctly, or move your .bashrc to the top of the drive
mounted as / in Cygwin.
@subsection How can I get bash filename completion to be case insensitive?
"shopt -s nocaseglob" should do the trick.
@subsection Can I use paths/filenames containing spaces in them?
Cygwin does support spaces in filenames and paths. That said, some
utilities that use the library may not, since files don't typically
contain spaces in Unix. If you stumble into problems with this, you
will need to either fix the utilities or stop using spaces in filenames
used by Cygwin tools.
In particular, bash interprets space as a word separator. You would have
to quote a filename containing spaces, or escape the space character.
For example:
@example
bash-2.03$ cd '/cygdrive/c/Program Files'
@end example
or
@example
bash-2.03$ cd /cygdrive/c/Program\ Files
@end example
@subsection Why can't I cd into a shortcut to a directory?
Cygwin does not follow MS Windows Explorer Shortcuts (*.lnk files). It
sees a shortcut as a regular file and this you cannot "cd" into it.
Some people have suggested replacing the current symbolic link scheme
with shortcuts. The major problem with this is that .LNK files would
then be used to symlink Cygwin paths that may or may not be valid
under native Win32 non-Cygwin applications such as Explorer.
@subsection I'm having basic problems with find. Why?
Make sure you are using the find that came with Cygwin and that you
aren't picking up the Win32 find command instead. You can verify that
you are getting the right one by doing a "type find" in bash.
@subsection Why don't cursor keys work under Win95/Win98?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
Careful examination shows that they not just non-functional, but
rather behave strangely, for example, with NumLock off, keys on numeric
keyboard work, until you press usual cursor keys, when even numeric
stop working, but they start working again after hitting alphanumeric
key, etc. This reported to happen on localized versions of Win98 and
Win95, and not specific to Cygwin (there're known cases of Alt+Enter
(fullscreen/windowed toggle) not working and shifts sticking with
other programs). The cause of this problem is Microsoft keyboard
localizer which by default installed in 'autoexec.bat'. Corresponding
line looks like:
@example
keyb ru,,C:\WINDOWS\COMMAND\keybrd3.sys
@end example
(That's for russian locale.) You should comment that line if you want
your keys working properly. Of course, this will deprive you of your
local alphabet keyboard support, so you should think about
another localizer. exUSSR users are of course knowledgable of Keyrus
localizer, and it might work for other locales too, since it has keyboard
layout editor. But it has russian messages and documentation ;-(
Reference URL is http://www.hnet.ru/software/contrib/Utils/KeyRus/
(note the you may need to turn off Windows logo for Keyrus to operate
properly).
@subsection Is it OK to have multiple copies of the DLL?
You should only have one copy of the Cygwin DLL on your system. If you
have multiple versions, they will conflict and cause problems.
If you get the error "shared region is corrupted" it means you have
multiple versions of cygwin1.dll running at the same time. This could
happen, for example, if you update cygwin1.dll without exiting @emph{all}
Cygwin apps (including inetd) beforehand.
@subsection Where can I find "more"?
If you are looking for the "more" pager, you should use the "less" pager
instead.
@subsection Where can I find "which"?
There is no "which" command with Cygwin. However, you can use the bash
shell builtin "type" which does something similar.
@subsection How can I access other drives?
You have some flexibility here.
Cygwin has a builtin "cygdrive prefix" for drives that are not mounted.
You can access any drive, say Z:, as '/cygdrive/z/'.
In some applications (notably bash), you can use the familiar windows
<drive>:/path/, using posix forward-slashes ('/') instead of Windows
backward-slashes ('\'). (But see the warning below!) This maps in the
obvious way to the Windows path, but will be converted internally to use
the Cygwin path, following mounts (default or explicit). For example:
@example
bash-2.03$ cd C:/Windows
bash-2.03$ pwd
/cygdrive/c/Windows
@end example
and
@example
bash-2.03$ cd C:/cygwin
bash-2.03$ pwd
/
@end example
for a default setup. (You could also use backward-slashes in the
Windows path, but these would have to be escaped from the shell.)
@strong{Warning:} There is some ambiguity in going from a Windows path
to the posix path, because different posix paths, through different
mount points, could map to the same Windows directory. This matters
because different mount points may be binmode or textmode, so the
behaviour of Cygwin apps will vary depending on the posix path used to
get there.
You can avoid the ambiguity of Windows paths, and avoid typing
"/cygdrive", by explicitly mounting drives to posix paths. For example:
@example
bash$ mkdir /c
bash$ mount c:/ /c
bash$ ls /c
@end example
Note that you only need to mount drives once. The mapping is kept
in the registry so mounts stay valid pretty much indefinitely.
You can only get rid of them with umount (or the registry editor).
The '-b' option to mount mounts the mountpoint in binary mode
("binmode") where text and binary files are treated equivalently. This
should only be necessary for badly ported Unix programs where binary
flags are missing from open calls. It is also the setting for /,
/usr/bin and /usr/lib in a default Cygwin installation. The default for
new mounts is text mode ("textmode"), which is also the mode for all
"cygdrive" mounts.
@subsection How can I copy and paste into Cygwin console windows?
Under Windows NT, open the properties dialog of the console window.
The options contain a toggle button, named "Quick edit mode". It must
be ON. Save the properties.
Under Windows 9x, open the properties dialog of the console window.
Select the Misc tab. Uncheck Fast Pasting. Check QuickEdit.
@subsection What does "mount failed: Device or resource busy" mean?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
This usually means that you are trying to mount to a location
already in use by mount. For example, if c: is mounted as '/'
and you try to mount d: there as well, you will get this error
message. First "umount" the old location, then "mount" the new one and
you should have better luck.
If you are trying to umount '/' and are getting this message, you may
need to run @code{regedit.exe} and change the "native" key for the '/'
mount in one of the mount points kept under
HKEY_CURRENT_USER/Software/Cygnus Solutions/CYGWIN.DLL setup/<version>
where <version> is the latest registry version associated with the
Cygwin library.
@subsection How can I share files between Unix and Windows?
During development, we have both Unix boxes running Samba and
NT/Windows 95/98 machines. We often build with cross-compilers
under Unix and copy binaries and source to the Windows system
or just toy with them directly off the Samba-mounted partition.
On dual-boot NT/Windows 9x machines, we usually use the FAT
filesystem so we can also access the files under Windows 9x.
@subsection Are mixed-case filenames possible with Cygwin?
Several Unix programs expect to be able to use to filenames
spelled the same way, but with different case. A prime example
of this is perl's configuration script, which wants @code{Makefile} and
@code{makefile}. WIN32 can't tell the difference between files with
just different case, so the configuration fails.
In releases prior to beta 16, mount had a special mixed case option
which renamed files in such a way as to allow mixed case filenames. We
chose to remove the support when we rewrote the path handling code for
beta 16. The standard Windows apps -- explorer.exe,
cmd.exe/command.com, etc. -- do not distinguish filenames that differed
only in case, resulting in some (very) undesirable behavior.
Sergey Okhapkin had maintained a mixed-case patch ('coolview') until
about B20.1, but this has not been updated to recent versions of Cygwin.
@subsection What about DOS special filenames?
Files cannot be named com1, lpt1, or aux (to name a few); either as
the root filename or as the extension part. If you do, you'll have
trouble. Unix programs don't avoid these names which can make things
interesting. E.g., the perl distribution has a file called
@code{aux.sh}. The perl configuration tries to make sure that
@code{aux.sh} is there, but an operation on a file with the magic
letters 'aux' in it will hang.
@subsection When it hangs, how do I get it back?
If something goes wrong and the tools hang on you for some reason (easy
to do if you try and read a file called aux.sh), first try hitting ^C to
return to bash or the cmd prompt.
If you start up another shell, and applications don't run, it's a good
bet that the hung process is still running somewhere. Use the Task
Manager, pview, or a similar utility to kill the process.
And, if all else fails, there's always the reset button/power switch.
This should never be necessary under Windows NT.
@subsection Why the weird directory structure?
Why do /lib and /usr/lib (and /bin, /usr/bin) point to the same thing?
Why use mounts instead of symbolic links?
Can I use a disk root (e.g., C:\) as Cygwin root? Why is this discouraged?
After a new installation in the default location, your mount points will
look something like this:
@example
Device Directory Type Flags
C:\cygwin\bin /usr/bin user binmode
C:\cygwin\lib /usr/lib user binmode
C:\cygwin / user binmode
@end example
Note that /bin and /usr/bin point to the same location, as do /lib and
/usr/lib. This is intentional, and you should not undo these mounts
unless you @emph{really} know what you are doing.
Various applications and packages may expect to be installed in /lib or
/usr/lib (similarly /bin or /usr/bin). Rather than distinguish between
them and try to keep track of them (possibly requiring the occasional
duplication or symbolic link), it was decided to maintain only one
actual directory, with equivalent ways to access it.
Symbolic links had been considered for this purpose, but were dismissed
because they do not always work on Samba drives. Also, mounts are
faster to process because no disk access is required to resolve them.
Note that non-cygwin applications will not observe Cygwin mounts (or
symlinks for that matter). For example, if you use WinZip to unpack the
tar distribution of a Cygwin package, it may not get installed to the
correct Cygwin path. @emph{So don't do this!}
It is strongly recommended not to make the Cygwin root directory the
same as your drive's root directory, unless you know what you are doing
and are prepared to deal with the consequences. It is generally easier
to maintain the Cygwin hierarchy if it is isolated from, say, C:\. For
one thing, you avoid possible collisions with other (non-cygwin)
applications that may create (for example) \bin and \lib directories.
(Maybe you have nothing like that installed now, but who knows about
things you might add in the future?)
@subsection How do anti-virus programs like Cygwin?
Users have reported that McAfee (now NAI) VirusScan for NT (and others?) is
incompatible with Cygwin. This is because it tries to scan the
newly loaded shared memory in the cygwin.dll, which can cause fork()s
to fail, wreaking havoc on many of the tools.
There are also reports of NAI VirusScan causing the system to hang when
unpacking tar.gz archives. This is surely a bug in VirusScan, and
should be reported to NAI. The only workaround is to disable VirusScan
when accessing these files. This can be an issue during setup, and is
discussed in that FAQ entry.
@subsection Why can't I run bash as a shell under NT Emacs?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
Place the following code in your startup file and try again:
@smallexample
(load "comint")
(fset 'original-comint-exec-1 (symbol-function 'comint-exec-1))
(defun comint-exec-1 (name buffer command switches)
(let ((binary-process-input t)
(binary-process-output nil))
(original-comint-exec-1 name buffer command switches)))
@end smallexample
@subsection info error "dir: No such file or directory"
Cygwin packages install their info documentation in the /usr/info
directory. But you need to create a @code{dir} file there before the
standalone info program (probably @code{/usr/bin/info}) can be used to
read those info files. This is how you do it:
@example
bash$ cd /usr/info
bash$ for f in *.info ; do install-info $f dir ; done
@end example
This may generate warnings:
@example
install-info: warning: no info dir entry in `gzip.info'
install-info: warning: no info dir entry in `time.info'
@end example
The @code{install-info} command cannot parse these files, so you will
have to add their entries to @code{/usr/info/dir} by hand.
@subsection Why do I get a message saying Out of Queue slots?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
"Out of queue slots!" generally occurs when you're trying to remove
many files that you do not have permission to remove (either because
you don't have permission, they are opened exclusively, etc). What
happens is Cygwin queues up these files with the supposition that it
will be possible to delete these files in the future. Assuming that
the permission of an affected file does change later on, the file will
be deleted as requested. However, if too many requests come in to
delete inaccessible files, the queue overflows and you get the message
you're asking about. Usually you can remedy this with a quick chmod,
close of a file, or other such thing. (Thanks to Larry Hall for
this explanation).
@subsection Why don't symlinks work on samba-mounted filesystems?
Symlinks are marked with "system" file attribute. Samba does not
enable this attribute by default. To enable it, consult your Samba
documentation and then add these lines to your samba configuration
file:
@smallexample
map system = yes
create mask = 0775
@end smallexample
Note that the 0775 can be anything as long as the 0010 bit is set.
@subsection Why does df report sizes incorrectly.
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
There is a bug in the Win32 API function GetFreeDiskSpace that
makes it return incorrect values for disks larger than 2 GB in size.
Perhaps that may be your problem?
@subsection Has the screen program been ported yet?
@strong{(Please note: This section has not yet been updated for the latest
net release.)}
Screen requires either unix domain sockets or fifoes. Neither of
them have been implemented in Cygwin yet.