Am 30.07.2025 um 20:22 schrieb Jon Turney via Cygwin-apps:
On 28/07/2025 14:01, Matthew Sheets via Cygwin-apps wrote:
I've been poking around at what might be needed to facilitate a
portable Cygwin setup, and registry activity is one of the aspects
that would need to be addressed.
Are there any flags, options, special environment variables, etc.
that would prevent Cygwin from making any registry changes?
Cygwin FAQ 2.24 states the following:
"Cygwin doesn't store anything important in the registry anymore for
quite some time. There's no reason to save, restore or delete it."
- https://www.cygwin.com/faq.html#faq.setup.registry
After a fresh install to a clean system with a recent
CygwinSetup-x86_64.exe (June 30), registry entries like the following
can be found:
[HKEY_CURRENT_USER\SOFTWARE\Cygwin\Installations]
"e022582115c10879"="\\??\\C:\\cygwin64"
[HKEY_LOCAL_MACHINE\SOFTWARE\Cygwin\Installations]
"e022582115c10879"="\\??\\C:\\cygwin64"
These are records of the "installation key", a hash of the path Cygwin
is installed in (which is, um, added to the names of internal objects
to so that multiple cygwin installations are isolated from each other,
or something like that)
This is written to the registry by the DLL, purely for informational
purposes, I think.
> [HKEY_LOCAL_MACHINE\SOFTWARE\Cygwin\setup]
"rootdir"="C:\\cygwin64"
This last registry entry is written by setup.This is only used to
store the selected installation root directory, so that setup can
default to it, next time you run it.
It may also confuse setup as I reported some months ago. With two
installations (one for testing), setup was permantly switched to
proposing the test root, even after installing for the main working
installation again.
I'd suggest to drop this registry writing (i.e. make --no-write-registry
the default). Setup should check whether it's being called from within a
cygwin installation tree and use that, or fallback to the default.
You can prevent this with the '--no-write-registry' setup option.
This seems to be somewhat alluded to under FAQ 2.20.7, which covers
Cygwin uninstall:
"Finally, if you want to be thorough you can delete the registry tree
Software\Cygwin under HKEY_LOCAL_MACHINE and/or HKEY_CURRENT_USER.
However, if you followed the directions above you will have already
removed everything important. Typically only the installation
directory has been stored in the registry at all."
- https://www.cygwin.com/faq.html#faq.setup.uninstall-all
My initial thought was that these registry changes perhaps might be
made by the Setup executable, but in a search of the Setup source
code, nothing jumped out at me, but there were a few potential users
of reg_key::set_string() within the searchable repos on GitHub.
* https://cygwin.com/cgit/cygwin-apps/setup/tree/
See https://cygwin.com/cgit/cygwin-apps/setup/tree/mount.cc#n97
*
https://github.com/search?q=repo%3Acygwin%2Fcygwin+set_string&type=code
and
https://cygwin.com/cgit/newlib-cygwin/tree/winsup/cygwin/mm/cygheap.cc#n139
