[PLUG] Mounting /usr/share vs symlinking

[Walt Mankowski via plug <plug@lists.phillylinux.org>]

Hi,

Last weekend, while updating Ubuntu to 21.04, I noticed that my /usr
partition was nearly full. It looked like the culprit was /usr/share,
so I moved it to a partition called /storage that had a lot of free
space, and symlinked /usr/share to /storage/usr_share.

That mostly worked. I noticed a few odd things, but there are always a
few odd things after an Ubuntu update and I didn't think much about
it. Then yesterday I discovered that both man(1) and file(1) were
broken. man reported a bizarre error:

$ man man
man: command exited with status 1: (cd /usr/share/man && /usr/lib/man-db/zsoelim) | (cd /usr/share/man && /usr/lib/man-db/manconv -f UTF-8:ISO-8859-1 -t UTF-8//IGNORE) | (cd /usr/share/man && preconv -e UTF-8) | (cd /usr/share/man && tbl) | (cd /usr/share/man && nroff -mandoc -rLL=218n -rLT=218n -Tutf8)

Whenever I ran file (e.g. to check if /usr/bin/man was actually a
shell script) it printed

/etc/magic, 4: Warning: using regular magic file `/usr/share/misc/magic'

and reported that everything I tried it on was either data or ASCII text.

I tried reinstalling man and file but that didn't help. After doing
some searching, I found a site that suggested I replace the symlink
with a mount. So I added this line to /etc/fstab:

/storage/usr_share /usr/share none bind 0 0

replaced the symlink with a directory, and mounted /usr/share.

It worked!

But *why* did it work? Why do man and file (and presumably other
commands I hadn't discovered yet) care if their data files are mounted
or symlinked?

Walt

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