mfsroot starts sysinstall how?

Devin Teske devin.teske at
Wed Dec 12 18:22:43 UTC 2012

On Dec 12, 2012, at 7:50 AM, Rick Miller wrote:

> On Wed, Dec 12, 2012 at 10:44 AM, Rick Miller <vmiller at> wrote:
>> Hi All,
>> How is sysinstall invoked in a FreeBSD 8.x mfsroot.gz?

It's actually invoked in the place of init(8).

> To explain more, I would like to boot into a shell as opposed to
> sysinstall.  safe mode and single user don't seem to.

Safe mode and single user won't work because sysinstall is acting as init and it doesn't implement those functions.

To run a shell script in the place of init(8), you have to do some bootstrapping.

Enter DruidBSD  ( … not to be confused with previously discussed Druid [in another thread]).

DruidBSD is a ~24MB ISO (~32MB if you get the version that has the extra tools like memtest86, etc.):

Not only does it do what you're asking about … boot to a shell … but you can customize it.

It uses the same build framework as the Druid (requiring GNU make, mkisofs, and [optionally] perl -- only required if you want the ISO to work from both CD/DVD _and_ USB thumb drive). You can download the source code, make changes to the custom /etc/rc which does the bootstrapping for you, and more -- then when finished, simply say "gmake freebsd" to produce your new custom media.

It doesn't stop there… the /etc/rc that's in the mfsroot (link below):

Is designed to bust you out of the mfsroot and bootstrap you not into a derelict sh(1) prompt, but instead a [more] usable bash(1) prompt complete with hundreds of extra utilities.

PRO TIP: The Druid (which is the [much] larger ~500MB FreeBSD Installer that uses the same build framework) actually has a miniature version of DruidBSD tucked into its boot loader. That is to explain that when you use the FreeBSD Druid installer, the beastie boot menu has a fancy feature where you can select a different mfsroot from the menu (if you select the "rescue_mfsroot" then you're essentially invoking a custom version of DruidBSD, which we're talking about right now w/respect to replacing sysinstall(8) in an mfsroot with a bootstrap-to-interactive-shell).

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