Revised article on rc.d

[David Thompson]

--- 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.

--
David

__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com