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Date:      Mon, 11 Jan 2021 13:21:07 +0100
From:      Polytropon <freebsd@edvax.de>
To:        Scott <freebsd-lists-5@thismonkey.com>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: Need help specifying args in rc.conf for a service
Message-ID:  <20210111132107.82de40d0.freebsd@edvax.de>
In-Reply-To: <X/w9IwVAFXyDr/ir@thismonkey.com>
References:  <X/w9IwVAFXyDr/ir@thismonkey.com>

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On Mon, 11 Jan 2021 22:57:23 +1100, Scott wrote:
> Hi all,
> 
> I posted this on the forums and was unsuccessful so I thought I'd try here:
> 
> I've been struggling to pass additional arguments to the Prometheus 
> node_exporter daemon in /etc/rc.conf.
> 
> The help for node_exporter provides an example argument (mount points to 
> ignore) as:
> 
> --collector.filesystem.ignored-mount-points="^/(dev)($|/)"
>                                 Regexp of mount points to ignore for filesystem collector.
> 
> The rc script says to use the _args variable to specify arguments to 
> node_exporter:
> # node_exporter_args (string):          Set extra arguments to pass to 
> # Default is "".
> 
> Adding the line:
> 
> node_exporter_args="--collector.filesystem.ignored-mount-points=\"^/(dev)($|/)\""
> 
> to /etc/rc.conf and running sh -x /usr/local/etc/rc.d/node_exporter start 
> results in:
> 
> + limits -C daemon su -m nobody -c 'sh -c "/usr/sbin/daemon  -f -p /var/run/node_exporter.pid -T node_exporter     /usr/bin/env /usr/local/bin/node_exporter     --web.listen-address=:9100     --collector.textfile.directory=/var/tmp/node_exporter     --collector.filesystem.ignored-mount-points="^/(dev)($|/)""'
> 
> Illegal variable name.
> 
> [...]
> 
> Can anyone please help?

If I see this correctly, the argument given to to the program's
option --collector.filesystem.ignored-mount-points= is to be a
regex, not the result of evaluating the regex (which the program
surely does internally). So my suggestion, without knowing any
further details, is to use this in /etc/rc.conf:

	node_exporter_args='--collector.filesystem.ignored-mount-points="^/(dev)($|/)"'

Always remember that /etc/rc.conf is, more or less, just a simple
shell script, so all rules applying to sh will apply to rc.conf
exactly. That's why 'single quotes' will stop any expansion and
transfer the value 1:1, which I think is what you are require to
do here. Characters such as $, " or ^ will be part of the string
handed over to the program, and will _not_ be interpreted by the
shell prior to assigning to the _args variable.

Within "double quotes", symbols such as $ have a specific meaning,
that's why you see the error ($ not properly quoted). So the
error message is completely valid and logical - and expected. ;-)




-- 
Polytropon
Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...



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