GNU bug report logs - #76876
logname output is often wrong when linked with glibc

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Pádraig Brady <P <at> draigBrady.com>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#76876: closed (logname output is often wrong when linked with
 glibc)
Date: Sun, 09 Mar 2025 12:50:02 +0000

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Your message dated Sun, 9 Mar 2025 12:48:49 +0000
with message-id <aa363819-f9c0-4095-9a7c-ff9d29064104 <at> draigBrady.com>
and subject line Re: bug#76876: logname output is often wrong when linked with glibc
has caused the debbugs.gnu.org bug report #76876,
regarding logname output is often wrong when linked with glibc
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


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76876: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=76876
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From: Nicolas Boos <nicolas.boos <at> wanadoo.fr>
To: bug-coreutils <at> gnu.org
Subject: logname output is often wrong when linked with glibc
Date: Sat, 8 Mar 2025 17:46:22 +0100

First test case with logname 9.1 and glibc 2.36:
$ echo $LOGNAME
nicolas
$ logname
nicolas
$ su --login root
$ echo $LOGNAME
root
$ logname
nicolas
$ logname (musl)
root
$ logname (uclibc)
root

Second test case, with a minimal chroot, no /proc and busybox login:
$ echo $LOGNAME
nicolas
$ logname
logname: no login name
$ busybox logname
logname: getlogin: No such file or directory
$ logname (musl)
nicolas
$ logname (uclibc)
nicolas

It seems getlogin() is malfunctioning only with glibc.

The following patch with "equivalent code" fixes the issue:
--- logname.c.orig
+++ logname.c
@@ -71,7 +71,11 @@
 
   /* POSIX requires using getlogin (or equivalent code) and prohibits
      using a fallback technique.  */
-  cp = getlogin ();
+  #if __GLIBC__
+    cp = getenv ("LOGNAME");
+  #else
+    cp = getlogin ();
+  #endif
   if (! cp)
     error (EXIT_FAILURE, 0, _("no login name"));

Adding a permanent fix to gnulib/getlogin.c code might be a better solution.

NB

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From: Pádraig Brady <P <at> draigBrady.com>
To: Bruno Haible <bruno <at> clisp.org>, Nicolas Boos <nicolas.boos <at> wanadoo.fr>,
 bug-gnulib <at> gnu.org, Paul Eggert <eggert <at> cs.ucla.edu>
Cc: 76876-done <at> debbugs.gnu.org
Subject: Re: bug#76876: logname output is often wrong when linked with glibc
Date: Sun, 9 Mar 2025 12:48:49 +0000

On 09/03/2025 11:08, Bruno Haible via Gnulib discussion list wrote:
> I wrote:
>> With this, coreutils should be fine, since it already imports the 'getlogin'
>> module from gnulib.
> 
> Verified by comparing coreutils-9.5 with coreutils-HEAD on Alpine Linux 3.20:
> 
> With coreutils-9.5:
> 
> $ logname
> bruno
> $ su -
> Password:
> # logname
> root
> 
> Now:
> 
> $ logname
> bruno
> $ su -
> Password:
> # logname
> bruno
> 
> Paul, Pádraig: How about adding a coreutils/NEWS entry for this bug fix?

I pushed an update to coreutils NEWS mentioning the fix.
Marking this as done.

thanks!
Pádraig.

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