Tarsnap config files are ignored

[Chris <chris@the-study.net>]

I have just installed the Tarsnap client on two different setups,
one being Cygwin, and the other a Trisquel Linux virtual
machine. I compiled and installed both of them into the default
location (/usr/local), generated the key file into a /root folder,
and copied the example config file to /usr/local/etc/tarsnap.conf,
without making any changes to it.

When I run tarsnap commands that require parameters that are
available in the config files, namely keyfile and cachedir,
tarsnap tells me that I need to include them, suggesting that it
can't find them, like so:

    $ sudo tarsnap --list-archives
    tarsnap: Keys must be provided via --keyfile option

I've tried this with multiple different commands, all with the same
effect. It seems that tarsnap simply can't see the config file.

I tried setting up a .tarsnaprc file with cachedir and keyfile
entries, in case there was a permissions issue with the
default config file, but this made no difference.

Because I get the same result on two different systems, and I
can't find any mention anywhere of other people having this
problem, I can only assume that at some point I've done something
wrong -- I just can't work out what it can be.

Does anybody know what the problem could be, or can suggest some
things to try?

-- Chris
chris@the-study.net