[pacman-dev] [RFC] adding a --sysroot option

[Andrew Gregory]

On 11/30/16 at 11:51am, Allan McRae wrote:
> On 30/11/16 01:58, Andrew Gregory wrote:
> > pacman's --root option is regularly (mis)used to use pacman to manage
> > a mounted guest system, typically one whose pacman installation is
> > currently broken.  We have a few configuration defaults in place to
> > make this sort of work, but support is incomplete.  Those defaults
> > only actually take effect if the settings haven't been set in
> > a configuration file, several options still default to the host system
> > resources, and using the guest's pacman configuration requires
> > updating all configured paths to the new mounted location.
> 
> What use would the current --root option be after this is implemented?
> Is this just a bug that --root should already be working exactly like
> proposed new option?

The --root option merely specifies where package files are installed.
That is not necessarily the root directory of a system. --root can't
work like the new option because other configured paths can be outside
it and it can't affect which configuration files are read because it
can be specified in a configuration file.  --sysroot would be
a command-line-only option and all paths would have to exist under it.

> > Adding a --sysroot/--chroot option would allow pacman to properly
> > operate in a mounted guest system.  At the moment, there are two ways
> > we could accomplish this:  prefix all paths with the sysroot or just
> > call chroot(2).  Obviously, the problem with chroot(2) is that it
> > requires special privileges.  Unfortunately, I think my symbolic
> > user/group patch (https://patchwork.archlinux.org/patch/3694/) will
> > require chroot to work properly as I can't find any other way to look
> > up users/groups in a mounted guest.  So, we may have to implement both
> > approaches so that regular users can perform queries but privileged
> > users can perform transactions with proper symbolic name support.
> 
> Don't we already chroot when running the install scripts?  Is this just
> a case of extending that chroot to the entire operation?

We do chroot for scripts and hooks, but we chroot to --root, which
could be a subdirectory inside --sysroot.

apg