Errno Libretto

By Hal Stern, Unix Insider |  Operating Systems

huey% df `dirname /usr/lib/gfx/config.common`
Filesystem                 kbytes    used   avail capacity  Mounted on
bigboy:/export/home/stern 1952573  944377  812946    54%   /home/stern

Watch where you drop direct maps for the automounter, and where you
use hierarchical maps that may deposit NFS mounts in the middle of
someone's home directory. Applications that rely on making backup
copies or renaming input data sets using
hard links
will fail if an NFS mount is introduced into the middle. For example,
assume you are mounting home directories using the following
hierarchical automounter map:

* \
	/	homeserv:/export/home/&
	/fxdata	dataserv:/export/datasets/fxdata

When /home/stern is mounted, /home/stern/fxdata is picked
up from the machine dataserv. So far, so good. But an
application may assume that it can create a hard link between files in
/home/stern/fxdata and /home/stern/backup, since they
appear to be on the same filesystem. The link() system
call fails, however, with EXDEV because the hard link would cross
volume boundaries.

Trail of stale crumbs

NFS errors tend to be hard to resolve because you're assigning blame
in more than one operating system and host environment. Here are some of
the common pitfalls:

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