getpwnam(3) issues

[Alejandro Colomar]

> Date: 2026-09-17 19:08:56+0200
> From: Alejandro Colomar <alx@kernel.org>
>
> Hi!
> 
> I've noticed a few issues related to getpwnam(3).
> 
> 1)
> 
> The glibc manual says 'getpwname' once to (presumably) refer to
> getpwnam(3) --note no trailing 'e'--.
> 
> I checked the source code, and there seems to also be a source-
> code comment and a README comment with the same issues.
> 
> 	alx@devuan:~/src/gnu/glibc/master$ grep -rn getpwname
> 	nss/bug17079.c:120:  /* Test getpwname_r.  */
> 	hesiod/README.hesiod:20:  * getpwname(), getpwuid()
> 	manual/pattern.texi:2127:uses @code{getpwname} to look up that user in the user database, and
> 	alx@devuan:~/src/gnu/glibc/master$ find | grep getpwname
> 	alx@devuan:~/src/gnu/glibc/master$ 
> 
> 2)
> 
> getpwnam(3) sets errno=0 if no entry was found.  However, it should
> preserve the errno set by the user (this is what musl does --at least,
> that's what I've been told--, and what POSIX requires).
> 
> 	alx@devuan:~/tmp$ cat getpwnam.c 
> 	#include <errno.h>
> 	#include <pwd.h>
> 	#include <stdio.h>
> 
> 	int
> 	main(void)
> 	{
> 		errno = 42;
> 		if (getpwnam("nonexistent!!!") == NULL)
> 			printf("%d\n", errno);
> 	}
> 	alx@devuan:~/tmp$ gcc -Wall -Wextra getpwnam.c 
> 	alx@devuan:~/tmp$ ./a.out 
> 	0
> 
> The glibc manual doesn't document this weirdness (or I couldn't fint
> it), so it seems it could be unintentional.  But even if it were
> intentional, it's not good behavior.
> 
> I didn't find any promise in the glibc manual that errno is never
> cleared, but this is assumed to hold everywhere.

POSIX indeed requires it:

	No function in this volume of POSIX.1-2024 shall set errno to 0.


Cheers,
Alex

> 
> 
> Have a lovely day!
> Alex
> 
> -- 
> <https://www.alejandro-colomar.es>



-- 
<https://www.alejandro-colomar.es>
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