Bug#324900: nscd: umount /var fails (unclean shutdowns)

[GOTO Masanori <gotom@debian.or.jp>]

At Wed, 31 Aug 2005 17:48:20 +0200,
Gabor Gombas wrote:
> Well, if /bin/sh is bash, then it is not weird at all, it is the same
> "bash vs. NSS" problem that came up several times in the past (last time
> quite recently on debian-devel). Previously it only happened with NSS
> modules that link to libraries under /usr, now it also affects nscd.

Thanks for your detailed explanation.

> - by calling /etc/init.d/rc, bash is executed
> - bash unconditionally does some NSS calls during startup (getpwuid
>   etc.); this in turn
> - loads all NSS modules that serve passwd maps -> if a module uses
>   libraries from /usr, now you have a live memory mapping under /usr so
>   you cannot unmount it during shutdown

Why is this "unconditionally" happenned?  What setting does this cause
this problem?

> - bash (libc) connects to nscd
> - nscd sends a file descriptor of /var/db/nscd/passwd to bash, and bash
>   does an mmap(2) on the received fd -> now you have a live memory
>   mapping under /var thus you cannot unmount it during shutdown
> - /etc/init.d/rc eventually kills nscd but that does not help, since the
>   bash process executing /etc/init.d/rc still has the cache file mapped
>   (deleting the cache file also doesn't help since unlink(2) only
>   operates on the directory and does not invalidate the memory mapping)

Zlatko, could you confirm what process actually has this mapping using
lsof?

Regards,
-- gotom