What is rebase and why did I need to run it on a fresh re-install?

[Peter Valdemar Mørch]

I was having no end of trouble after upgrading my cygwin installation...

So I wiped the entire
HKEY_LOCAL_MACHINE\SOFTWARE\Cygnus Solutions
registry key, and wiped C:\cygwin completely and reinstalled everything 
again. Still the same problems...

Finally, after fiddling with XWin.exe, I discovered this:
      31 [main] XWin 1604 fork_copy: linked dll data/bss pass 0 failed, 
0x84B000.
.0x84B050, done 0, windows pid 1632, Win32 error 87

Searching for this lead me to an often repeated suggestion: install 
rebase and run rebaseall. I ignored a HEAVY warning to only run this if 
I *really* know what I'm doing, and tried it anyway. It worked!

Now:
* What does rebase do?
* Why did I need to run it on my fresh cygwin install?
* Why does Larry Hall recommend to run it, when there is a prominent 
warning not to, unless I've "got a clue"?
* What did I do wrong when I upgraded my installation?

I suspect:

I had a previous Local Package Directory, that got trashed. When I 
upgraded, a new Local Package Directory got created containing the 
packages that got re-installed. Today, I wiped c:\cygwin completely, and 
re-used the new Local Package Directory, and more packages got 
downloaded into it. Is it the re-use of the Local Package Directory that 
is the root-cause of my problem? If so, what is the purpose of a Local 
Package Directory in the first place?

Also, during my upgrade yesterday, apparently I had some cygwin process 
running, because setup.exe couldn't run any of the postinst.sh scripts. 
"Entry point missing in cygwin.dll" or something like that. (Darn - I 
didn't write it down at the time). Is the Local Package Directory 
supposed to get modified by Post Install? And *that* trashed my Local 
Package Directory?

Confused,

Peter
-- 
Peter Valdemar Mørch
http://www.morch.com

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