Revised article on rc.d
Yar Tikhiy
yar at comp.chem.msu.su
Thu Oct 12 16:04:30 PDT 2006
On Mon, Oct 09, 2006 at 06:56:19PM -0700, David Thompson wrote:
> --- Yar Tikhiy <yar at comp.chem.msu.su> wrote:
> > After a long delay, I got down to my article on rc.d again. Many
> > thanks to Gary W. Swearingen for his valuable remarks. The new
> > version is available at http://people.freebsd.org/~yar/rcng/ . I
> > think this version can be added to our articles collection after a
> > few corrections that may be suggested by the readers. ;-)
>
> Regarding this paragraph,
>
> Note: An rc.d script must be written in the sh(1) language. It
> cannot be a binary executable because rc.d can opt to feed such
> scripts into a single instance of sh(1) instead of running each
> of them separately. This is controlled by an rc.conf(5) variable
> named rc_fast_and_loose. An rc.d script cannot be written in
> awk(1) or an interpreted language from ports for the same reason;
> in addition, it must be runnable early in the system startup
> sequence, before /usr has been mounted.
>
> This caveat is not really true in the strict technical sense.
> Consider if someone adds this line to their /etc/rc.d script,
>
> # KEYWORD: nostart
>
> then /etc/rc will not execute this script since rcorder is
> invoked with '-s nostart'. Thus the reasoning due to the
> $rc_fast_and_loose variable is not strictly accurate. That
> is, a script could technically be written in any interpreted
> language that happens to use '#' as its comment character;
> as long as the above comment line was added to the script.
> The problem is, of course, such scripts have to provide their
> own scaffolding, since rc.subr is written in sh(1); and the
> script cannot be run directly by /etc/rc due to the use of the
> sh(1) dot '.' operator (thus it needs 'KEYWORD: nostart' so
> that /etc/rc will skip it).
>
> Although not exactly clear in the above paragraph, the reason
> files in /etc/rc.d cannot be binary is because rc.d uses the
> sh(1) dot '.' operator *for all* invocations, like this,
>
> if [ -n "$rc_fast_and_loose" ]; then
> set $_arg; . $_file
> else
> ( trap "echo Script $_file interrupted; kill -QUIT $$" 3
> trap "echo Script $_file interrupted; exit 1" 2
> set $_arg; . $_file )
> fi
>
> But for '.', files in /etc/rc.d *could* be binary, but
> even then rcorder expects to process text files, not binary
> files. rcorder uses fparseln() to read each file, but this
> doesn't really affect reading a binary file. Thus rcorder
> processes binary files benignly, try 'rcorder /bin/*' and
> you'll see consistent output.
>
> Also in that paragraph, when I read this,
>
> ... a binary executable because rc.d can opt to feed ...
> ^^^^
> IMHO, it should probably say,
>
> ... a binary executable because /etc/rc can opt to feed ...
> ^^^^^^^
> though I understand you're referring to the rc.d system,
> some clarity is gained in that sentence by using /etc/rc.
I'd sum all the above up as follows: I went on slippery ground
when trying to give reasons for using sh(1) and only sh(1) :-)
How about the following paragraph as a replacement?
Note: The language of choice for rc.d scripting is sh(1).
The tight integration between all rc.d components effectively
prevents individual scripts from being written in a different
language.
--
Yar
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