What does cygwin do

Best of Techopedia weekly. News and Special Offers occasional. Techopedia Explains Cygwin. What Does Cygwin Mean? Share this Term. Unix Application Programming Interface. Tech moves fast! Stay ahead of the curve with Techopedia! You have to make certain settings in the OS depending on the Windows version to allow creating them as a non-privileged user. NTFS symlinks have a type. They are either a "file" or a "directory", depending on the target file type.

This information is utilized especially by Windows Explorer to show the correct file or directory icon in file listings without having to check on the target file and to know what actions are provided by clicking on the symlink. However, if a NTFS symlink points to a file "foo", and "foo" is deleted and replaced by a directory "foo", the symlink type of an NTFS symlink pointing to "foo" is unchanged and subsequently Windows Explorer will misbehave.

Consequentially, creating dangling NTFS symlinks is a nuisance, since the library does not know what type the still-to-be-created symlink target will be. Cygwin will not create dangling NTFS symlinks, but fallback to creating the default symlink type winsymlinks:native or just fail winsymlinks:nativestrict. Using this method, Cygwin generates symlinks by creating Windows shortcuts. When a user changes the shortcut, this will be detected by Cygwin and it will only use the Windows path then.

While Cygwin shortcuts are shown without the ". It guesses that files ending in. This guessing doesn't take place on filesystems providing real permission information NTFS, NFS , unless you switch the permission handling off using the mount flag "noacl" on these filesystems. As of version 1. However there is no guarantee that Cygwin is as secure as the Windows it runs on. Cygwin processes share some variables and are thus easier targets of denial of service type of attacks.

The select call in Winsock can only wait on sockets. If you are porting an application which already uses Winsock, then porting the application to Cygwin means to port the application to using the POSIX net functions.

You should never mix Cygwin net functions with direct calls to Winsock functions. You don't. Cross compilers packages to build Mingw-w64 targets are available in the Cygwin distro. Cygwin versioning is relatively complicated because of its status as a shared library. Additionally, there are DLL major and minor numbers that correspond to the name of the release, and a release number.

In other words, cygwin It's not actually part of the Cygwin DLL version number. The cygwin1. For example, the first major version 5 release, cygwin The minor version changes every time we make a new backward compatible Cygwin release available.

There is also a cygwin1. The release number is only incremented if we update an existing release in a way that does not effect the DLL like a missing header file. 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 compatibility version number. It is incremented when incompatible changes are made to the shared memory region or to any named shared mutexes, semaphores, etc.

Daylight saving Summer time and other time zone changes are decided on by politicians, and announced by government officials, sometimes with short or no notice, so time zone updates are released at least a few, and sometimes several, times a year. Details of changes are not known until they are announced publicly by officials, often in foreign languages. Those details then have to be noticed, possibly translated, passed to, picked up, and applied by the official tzdata source package maintainers.

That information has to be compiled, checked, and released publicly in an update to the official tzdata source package. Then those changes have to be picked up and applied to the Cygwin tzdata package, which has to be updated, built, tested, and released publicly. Time zone settings are updates to the daylight saving Summer time rules for dates of changes, hour offsets from UTC of time zones, and the geographic regions to which those rules and offsets apply, provided in the tzdata package included in all Cygwin installations.

Have you run the Cygwin Setup program recently to update at least the tzdata package? Are you developing applications using times which may be affected by time zones? Since the ctime , localtime , mktime , and strftime functions are required to set time zone information as if by calling tzset , there is no need for an explicit tzset call before using these functions. However, if none of the above functions are called first, applications should ensure tzset is called explicitly before using any other time functions, or checking or using time zone information.

In a Windows console window you can enable and capture mouse events using the xterm escape sequences for mouse events. If you are willing to be a package maintainer, great! We urgently need volunteers to prepare and maintain packages, because the priority of the Cygwin Team is Cygwin itself. You should also announce your intentions to the general cygwin list, in case others were thinking the same thing.

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. Or compile with the -s option to gcc. That means, in contrast to Windows, which uses an LLP64 data model, sizeof long! In the 32 bit Cygwin and Mingw-w64 environments, as well as in the 64 bit Mingw-w64 environment, it is no problem to substitute DWORD with unsigned long:.

Here are a few donts which should help porting applications from the known ILP32 data model of 32 bit Cygwin, to the LP64 data model of 64 bit Cygwin. Note that these are not Cygwin-only problems. Finding this kind of bug is very hard, because you will often see a problem which has no immediate connection to the actual bug.

Don't mix int and pointers at all! This will not work as expected anymore:. Along the same lines don't use the type int in pointer arithmetic. Don't cast pointers to int, don't cast pointer differences to int, and don't store pointer differences in an int type. Don't use functions returning pointers without declaration. For instance. This code will crash , unless you included string. The implicit rule in C is that an undeclared function is of type int. But int is 4 byte and pointers are 8 byte, so the string pointer given to printf is missing the upper 4 bytes.

Try to use only Windows datatypes in conjunction with Windows API function calls to avoid type problems. See the above ReadFile example.

Windows functions in printf calls should be treated carefully as well. This code is common for 32 bit code, but probably prints the wrong value on 64 bit:. Using gcc's -Wformat option would warn about this. Casting to the requested base type helps in this case:. This may hit a few projects which are around since before Y2K. The project maintainers took it for granted that Cygwin is running only on i CPUs and the code is making this assumption blindly. You have to check the code for such assumptions and fix them.

The project is using autotools, the config. Update the project configury cygport will do this by default and try again. The project uses Windows functions on Cygwin and it's suffering from the problems described in the preceeding FAQ entry. In all of this cases, please make sure to fix that upstream, or send your patches to the upstream maintainers, so the problems get fixed for the future. If your code depends on the CPU architecture, use the predefined compiler definition for the architecture, like this:.

This should only be used in the most desperate of occasions, though, and only if it's really about a difference in Windows API functionality! 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. To circumvent this, mount the path of the executable using the -X switch to enable cygexec for all executables in that folder; you will also need to exclude non-cygwin executables with the -x switch.

Enabling cygexec causes cygwin executables to talk directly to one another, which increases the command-line limit. If you have added other non-Cygwin programs to a path you want to mount cygexec, you can find them with a script like this:.

Try running cygserver. If you're using gcc , try adding an empty main function to one of your sources. Or, perhaps you have -lm too early in the link command line. It should be at the end:. 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 comdlg 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.

There are a few restrictions for calls to the Windows API. If your program uses the Cygwin API, then your executable cannot run without cygwin1. In particular, it is not possible to statically link with a Cygwin library to obtain an independent, self-contained executable. 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 command line.

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 2. 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 we can't agree to.

Fortunately, we have our own Windows API headers which are pretty complete. The short version is:. If you want to link statically from Visual Studio, to my knowledge none of the Cygwin developers have done this, but we have this report from the mailing list that it can be done this way:. Use the impdef program to generate a. Follow steps 1 and 2 to generate. Download crt0. Link your object files, cygwin1. Note that if you are using any other Cygwin based libraries that you will probably need to build them as DLLs using gcc and then generate import libraries for the MS VC linker.

If your. Otherwise, here are some steps:. 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. Maybe there is an option to force LINK. EXE to include an object file. Build a dummy C file referencing all the functions you need, either with a direct call or through an initialized function pointer. 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 Fetch the sources from the Cygwin GIT source repository.

If you change a certain core part of Cygwin, namely the layout of the Cygwin TLS area, you also have to install cocom.

Normally, building ignores any errors in building the documentation, which requires the dblatex , docbook2X , docbook-xml45 , docbook-xsl , and xmlto packages. This is the preferred method for acquiring the sources. Otherwise, if you are trying to duplicate a cygwin release then you should download the corresponding source package cygwin-x. If the build worked, you can install everything you like into the currently running system, except the Cygwin DLL cygwin1.

For installing the DLL, close down all Cygwin programs including bash windows, any servers like cygserver , etc. Then, for first testing, start up a Cygwin program from the Windows command prompt and see what happens. If you get a lengthy error messages like "user shared memory version mismatch detected" , it's very likely a Cygwin process still running using the old DLL.

Kill it in Windows' Task Manager or taskkill and try again. If it's still not working, and if you're sure there's no older Cygwin process still running, it's probably a bug you introduced with your changes.

From here on, you're on your own or discuss problems on the Cygwin-developers mailing list. Debugging symbols are stripped from distibuted Cygwin binaries, so to debug with gdb you will need to install the cygwin-debuginfo package to obtain the debug symbols for cygwin1. If your bug causes an exception inside cygwin1. You can also contact the mailing list for pointers a simple test case that demonstrates the bug is always welcome.

Unfortunately, this will be difficult. Exception handling and signals support semantics and args have been designed for x86 so you would need to write specific support for your platform. We don't know of any other incompatibilities. Please send us patches if you do this work! To create foo. This entrypoint address can be computed as the sum of the ImageBase and AddressOfEntryPoint values given by objdump -p. Note that the DllMain entrypoints for linked DLLs will have been executed before this breakpoint is hit.

You can debug your application using 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. You can use the strace. For information on using strace , see the Cygwin User's Guide. Other Windows exceptions are passed on to the handler if any , and reported as an unknown signal if an unhandled second chance exception occurs.

This currently has some known problems, for example, single-stepping from these signals may not work as expected. A common error is to put the library on the command line before the thing that needs things from it. This is right gcc hello. Note that this won't work if the linker flags --as-needed or --no-undefined are used, or if the library being linked with is a static library. See point 3 in Q: 6. This also has consequences for how weak symbols are resolved.

It's 64 bit aware. It exists, but you should rather include stdlib. 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 malloc before your main line is started. If you have written your own malloc to need some initialization to occur after main is called, then this will surely break. This re-entrant version of malloc will be called directly from within newlib , by-passing your custom version, and is probably incompatible with it.

This is really a newlib issue, but we are open to suggestions on how to deal with it. Yes, but only if you are combining C object files. 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.

If your scripts are in the current directory, you must have. It is not normally there by default. Many programs which rely on these toolkits will work with little, if any, porting work if they are otherwise portable. However, there are a few things to look out for:. Some packages written for both Windows and X11 incorrectly treat Cygwin as a Windows platform rather than a Unix variant.

In order for this to work, the program must be linked with the -Wl,--export-all-symbols linker flag. Programs which include their own loadable modules plugins often must have its modules linked against the symbols in the program. The most portable solution is for such programs to provide all its symbols except for main in a shared library, against which the plugins can be linked. Otherwise, the symbols from the executable itself must be exported.

Symbols must be exported from the executable with a -Wl,--export-all-symbols,--out-implib,libfoo. Cygwin FAQ. About Cygwin 1. What is it? What versions of Windows are supported? Where can I get it? Is it free software? What version of Cygwin is this, anyway? Who's behind the project? Setting up Cygwin 2. What is the recommended installation procedure? What about an automated Cygwin installation? Does the Cygwin Setup program accept command-line arguments? Can I install Cygwin without administrator rights?

Can I use the Cygwin Setup program to get old versions of packages like gcc How does Cygwin secure the installation and update process? What else can I do to ensure that my installation and updates are secure?

Is the Cygwin Setup program, or one of the packages, infected with a virus? My computer hangs when I run Cygwin Setup! What packages should I download? Where are 'make', 'gcc', 'vi', etc? How do I just get everything? How much disk space does Cygwin require? How do I know which version I upgraded from? What if the Cygwin Setup program fails? My Windows logon name has a space in it, will this cause problems? How do I uninstall individual packages? How do I uninstall a Cygwin service?

How do I uninstall all of Cygwin? How do I install snapshots? How can I make my own portable Cygwin on CD? How do I save, restore, delete, or modify the Cygwin information stored in the registry? Further Resources 3. Where's the documentation? What Cygwin mailing lists can I join? What if I have a problem? Using Cygwin 4. Starting a new terminal window is slow. What's going on? Why is Cygwin suddenly so slow? Why can't my services access network shares? Bash or another shell says "command not found", but it's right there!

Why doesn't bash read my. How can I get bash filename completion to be case insensitive? Why can't I cd into a shortcut to a directory? I'm having basic problems with find. Why doesn't su work? Why doesn't man -k, apropos or whatis work? Why doesn't chmod work? Why doesn't my shell script work? How do I print under Cygwin? Why don't international Unicode characters work?

My application prints international characters but I only see gray boxes 4. Can I bundle Cygwin with my product for free? Why isn't package XYZ available in Cygwin? Why is the Cygwin package of XYZ so out of date? How can I access other drives? How can I copy and paste into Cygwin console windows?

What firewall should I use with Cygwin? How can I share files between Unix and Windows? Is Cygwin case-sensitive?? What about DOS special filenames? When it hangs, how do I get it back? Why the weird directory structure?

How do anti-virus programs like Cygwin? Is there a Cygwin port of XEmacs? Why don't some of my old symlinks work anymore? Why don't symlinks work on Samba-mounted filesystems? Why does public key authentication with ssh fail after updating to Cygwin 1.

Why is my. Why do my files have extra permissions after updating to Cygwin 1. Why do my Tk programs not work anymore? What applications have been found to interfere with Cygwin? How do I fix fork failures? Cygwin API Questions 5. How does everything work? Are development snapshots for the Cygwin library available? Is the Cygwin library multi-thread-safe?

How is fork implemented? How does wildcarding globbing work? How do symbolic links work? Why do some files, which are not executables have the 'x' type.

How secure is Cygwin in a multi-user environment? How do the net-related functions work? I don't want Unix sockets, how do I use normal Windows winsock? What version numbers are associated with Cygwin? Why isn't my time or zone set correctly? Is there a mouse interface? Programming Questions 6. How do I contribute a package? How do I contribute to Cygwin? Why are compiled executables so huge?!? What do I have to look out for when porting applications to 64 bit Cygwin?

My project doesn't build at all on 64 bit Cygwin. What's up? Where is glibc? Where is Objective C? Why does my make fail on Cygwin with an execvp error? Active 7 years, 7 months ago. Viewed 25k times. Paul R k 33 33 gold badges silver badges bronze badges. Ario Ario 2 2 gold badges 3 3 silver badges 11 11 bronze badges. It does what it says on the tin: gives you a Unix-like environment on Windows.

It's easy enough to install it and try it out - it works pretty well and does not disrupt your Windows environment. Ario, more like the opposite It compiles code which is written for Windows, to run on Windows. Show 1 more comment. Active Oldest Votes. Because it keeps confusing people: Cygwin: think of it as an OS.

Would you say Cygwin is like terminal emulator or like a shell on the windows kernel or none of the above? MSYS 2 is more the shell-like thing. JFA the userspace libraries and utilities. The shell is part of the latter.