Date: Fri, 13 Oct 2006 03:04:23 +0400 From: Yar Tikhiy <yar@comp.chem.msu.su> To: David Thompson <dat1965@yahoo.com> Cc: freebsd-rc@freebsd.org Subject: Re: Revised article on rc.d Message-ID: <20061012230423.GC72944@comp.chem.msu.su> In-Reply-To: <20061010015619.3492.qmail@web55109.mail.re4.yahoo.com> References: <20061009122342.GB2805@comp.chem.msu.su> <20061010015619.3492.qmail@web55109.mail.re4.yahoo.com>
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On Mon, Oct 09, 2006 at 06:56:19PM -0700, David Thompson wrote: > --- Yar Tikhiy <yar@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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