Mail Archives: cygwin/2002/01/29/21:35:28
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At 07:41 PM 1/23/02 +0100, Corinna Vinschen wrote:
>On Wed, Jan 23, 2002 at 01:22:29PM -0500, Pierre A. Humblet wrote:
>> OK, but can you give suggestions about how to debug processes
>> started under cygrunsrv? I tried to have cygrunsrv start a shell
>> and put strace in the shell script. However the problem does not
>> occur with this setup, only when the program is started directly.
>> Is there a way to produce Cygwin internal debug output without strace?
>
>Have a look into `how-to-debug-cygwin.txt' in the cygwin source
>directory. You can use the CYGWIN_SLEEP technique, for instance.
Corinna,
Sorry for the delay, I have been sidetracked. Here is an
explanation and a fix for the problem of incorrect uid
when the Cygwin and Windows usernames differ.
The passwd file is only scanned when starting a process from Windows,
or following seteuid().
When ntsec is not defined, internal_getlogin matches the
Windows username with the pw_name's in passwd to find the uid.
When ntsec is defined, internal_getlogin scans passwd by sid's.
Cygwin user names can then be different from Windows user names.
In my case the program was running as a service under cygrunsrv.
ntsec was not defined in the environment of the service manager,
but only as a -e CYGWIN= argument to cygrunsrv.
When cygrunsrv started it didn't find the Windows username in pw_name
and used the default uid. When the service application started, with
ntsec, it didn't scan the passwd file because cygrunsrv is a Cygwin
process. Thus the username and uid were incorrect under ntsec...
The same problem happens when a user with a Cygwin username
different from Windows starts without ntsec.
I saw 4 possible solutions.
1) Mandate ntsec if Cygwin and Windows user names differ.
Not so good. /etc/passwd is a shared resource and different users
may have different ntsec preferences. Unexpected situations can
occur.
2) Have the parent process notice that CYGWIN was changed and
force the child to rescan /etc/passwd
Complicated.
3) Rescan /etc/passwd if ntsec is defined and the uid is the
default (= administrator).
OK, but users running as administrator will be slowed down.
4) Always scan /etc/passwd for sid (on NT/2000/XP). If no success,
rescan based on Windows username.
A little inefficient at startup if ntsec is not enabled, but most
flexible [the two searches can also be combined, possible
optimization].
The attached uinfo.diff file implements solution 4.
It also does not set primary group in the token (useless).
I have also been burned by missing details in how-to-debug-cygwin.txt
and attach another diff file to improve it.
Pierre
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Content-Disposition: attachment; filename="uinfo.diff"
--- uinfo.cc.in Mon Nov 5 01:09:10 2001
+++ uinfo.cc Mon Jan 28 20:24:54 2002
@@ -127,13 +127,12 @@
NetApiBufferFree (ui);
}
- if (allow_ntsec)
- {
+
HANDLE ptok =3D user.token; /* Which is INVALID_HANDLE_VALUE if no
impersonation took place. */
DWORD siz;
cygsid tu;
- int ret =3D 0;
+ ret =3D 0;
/* Try to get the SID either from already impersonated token
or from current process first. To differ that two cases is
@@ -190,19 +189,13 @@
else
unsetenv ("USERPROFILE");
}
- }
/* If this process is started from a non Cygwin process,
- set token owner to the same value as token user and
- primary group to the group which is set as primary group
- in /etc/passwd. */
+ set token owner to the same value as token user */
if (ptok !=3D INVALID_HANDLE_VALUE && myself->ppid =3D=3D 1)
{
if (!SetTokenInformation (ptok, TokenOwner, &tu, sizeof tu))
debug_printf ("SetTokenInformation(TokenOwner): %E");
- if (gsid && !SetTokenInformation (ptok,=
TokenPrimaryGroup,
- &gsid, sizeof gsid))
- debug_printf ("SetTokenInformation(TokenPrimaryGroup): %E");
}
/* Close token only if it's a result from OpenProcessToken(). */
@@ -256,9 +249,9 @@
if ((p =3D internal_getlogin (cygheap->user)) !=3D NULL)
{
myself->uid =3D p->pw_uid;
- /* Set primary group only if ntsec is off or the process has been
+ /* Set primary group only if the process has been
started from a non cygwin process. */
- if (!allow_ntsec || myself->ppid =3D=3D 1)
+ if ( myself->ppid =3D=3D 1)
myself->gid =3D p->pw_gid;
}
else
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Content-Disposition: attachment; filename="how-to-debug-cygwin.diff"
--- how-to-debug-cygwin.txt.in Tue Jan 29 20:08:10 2002
+++ how-to-debug-cygwin.txt Tue Jan 29 20:17:50 2002
@@ -11,7 +11,9 @@
1. The first thing you'll need to do is to build cygwin1.dll and your=
crashed
application from sources. To debug them you'll need debug information,=
which
-is normally stripped from executables.
+is normally stripped from executables. You should also define the DEBUGGING=
+macro to enable some debug features. Debug from a console window (and=
not
+from windows such as rxvt), as some debugging messages go to the console.
2. Create known-working cygwin debugging environment.
- create a separate directory, say, c:\cygdeb, and put known-working
@@ -41,6 +43,8 @@
such situation: -b enables buffering of output and reduces additional
timeouts introduced by strace, and -m option allows you to mask certain
classes of *_printf() functions, reducing timeouts even more.
+ Programs started by strace are started as if directly from Windows, and
+ not as if from a Cygwin shell or program.
5. Problems at early startup.
Sometimes, something crashes at the very early stages of application
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