[Nix-dev] nix-multi-user installation script

[Andreas Herrmann]

Hi,

Thanks for having a look at this!


On Thursday 06 November 2014 13:17:57 Wout Mertens wrote:
> On Tue Oct 28 2014 at 10:15:03 PM Andreas Herrmann <andreash87 at gmx.ch>
> wrote:
> > I would like to ask you guys to have a look at this script and tell me
> > what you think of it. Do you think it could be valuable to add something
> > like this as an automated installer to the official Nix distribution
> > similar to the one for single-user mode?
>
> Definitely, although I think it would be best to have it as script to run
> after one already installed Nix. That way, existing installs can just be
> converted.

That is an interesting idea. The current single user install script installs
nix for a non-root user. How would you go about transforming such an
installation to a multi-user nix? Just chown it to root, or are there more
subtle issues to think about? (In particular the default-profile...)


> I did come up with a few specific questions during the course of this:
> >
> >  * The nix-daemon is not daemonizing itself. Why is that?
> >     On debian this is not a problem thanks to `start-stop-daemon`. On
> > CentOS I ended up writing a wrapper script.
> 
> Self-daemonizing daemons are not so wonderful. It's nicer to have a
> watchdog daemon doing the background running and logging, and it makes the
> program a little simpler.
> 
> Besides, you can daemonize anything from the shell simply by closing stdin
> and running in the background:
> 
> $ run_as_daemon >$LOGFILE 2>&1 <&- & echo $! > $PIDFILE
> 
> The shell does the right thing, disassociating the child when it exits etc.

Nice, I had forgotten about `<&-`. I should modify my wrapper accordingly.
The reason I chose a wrapper instead of doing the above right in the
init-script is, that CentOS offers a few standard shell functions which do
things like print that nice green `[  OK  ]` and such.


>  * The chroot build feature seems to require a statically linked bash.
> >     Compiling this (plus some dependencies) can take quite some time. Do
> > you think a static bash would be a
> >     viable addition to `nixpkgs`?
> 
> Not really - you just need to make sure all the libraries are in the
> chroot. I would think that it just works on Linux, where everything is
> linked only to /nix/store (unless the build got tainted). On Darwin the
> stdenv isn't pure yet but even then the required libraries can be copied.

On Thursday 06 November 2014 14:41:25 Peter Simons wrote:
> it "just works" on NixOS, because the system auto-generates an appropriate
> /etc/nix/nix.conf file that includes all bits required by "bash" into the
> chroot environment.
> [...]
> On other Linux systems, this needs to be configured manually.

So, coming back to this. Do you think the static bash would be a good package
to add?


On Thursday 06 November 2014 13:17:57 Wout Mertens wrote:
> Note that the chroot isn't really required to build things and in its
> current form it slows down builds. See
> https://github.com/NixOS/nix/issues/179 .

As I understand this the build seems to be slowed down by all the bind mounts.
But, shouldn't a non-trivial package spent far more time on actual building
than on bind mounting? I just think that the benefit in purity due to chroot
outweights the cost of the bind mount.


>  * Is there a way to add globally visible package overrides but still use
> > the nix-channel?
> 
> Absolutely, that's what packageOverrides in the nixpkgs configuration is
> for. If a binary build is available, it will be used, otherwise you'll do
> the build locally.

Thanks, then let me follow up on this: How can I configure global
packageOverrides that will be visible to all users; yet, still allow them to
add their own packageOverrides on top of that? I.e. where does the global
equivalent of `~/.nixpkgs/config.nix` go on a non-NixOS multi-user Nix?


Best, Andreas