backticks in rc.conf

[Giorgos Keramidas]

On Tue, 21 Jul 2009 11:29:20 +0200, Polytropon <freebsd at edvax.de> wrote:
> On Tue, 21 Jul 2009 09:46:47 +0100, chris scott <kraduk at googlemail.com> wrote:
>> can i use backticks in rc.conf?
>
> Basically, yes. The /etc/rc.conf file is run through sh, it is
> a shell script that assigns values to variables, but can (ab)use
> it to execute programs.
>
>> rsyncd_flags="--config=/etc/rsyncd.conf --address="` ifconfig bce1 | grep
>> inet | awk '{print $2}'`
>>
>> it works fine from the shell, however on reboot the address section doesnt
>> expand, or rather it goes blank
>
> You should use the full pathnames leading to ifconfig, grep, and awk.
> Make sure they are accessible when rc.conf is "executed".

There's a catch here that may go unnoticed for a while...

rc.conf may be sourced by /etc/rc *long* before filesystems are
mounted.  As a result grep or awk may be not be available and stop
rc.conf from loading.

It's probably a good idea to:

  * Add a special rsyncd_bind_address variable that is handled in
    `/usr/local/etc/rc.d/rsyncd' itself

  * Permit "AUTO" as the value of ${rsyncd_bind_address} and do the
    smart thing there.

  * Edit `/usr/local/etc/rc.d/rsyncd' to add a dependency for the
    "NETWORKING" and "FILESYSTEMS" special names, so that `rc.d/rsyncd'
    runs only after networking is up and /usr or other late-mounted
    filesystems have finished loading.