[opam-devel] global installation with opam

[Louis Gesbert]

OPAMROOT has a few drawbacks:
* you want the switch root (eg ~/.opam/system) at /usr/local, not the global opamroot which would lead to /usr/local/system/lib. Unless you call your switch "local" and set OPAMROOT to /usr... (DON'T do that ;))
* it contains a lot of files you don't actually want in /usr/local (repo caches, all switches, etc.)
* even a single switch contains a few extra files we may not want in /usr/local (list of installed packages, pinned packages overlays, etc.)

On the bright side, all paths are defined cleanly using module OpamPath, and relocating some parts of a switch to an external directory should'nt be too problematic, as Thomas pointed out. Of course in the meantime, you could use OPAMROOT set as e.g. /shared/opam/ and then
```
for dir in sbin bin doc etc lib man share; do
  mv /shared/opam/system/$dir/* /usr/local/$dir
  rmdir /shared/opam/system/$dir
  ln -s /usr/local/$dir /shared/opam/system/$dir
done
```

Which is kind of what Daniel suggested for `opam link`, if I understood him correctly.
The relocation issue may cause some programs to look back to /shared, but that shouldn't be a problem.

Cheers,
Louis

> - Anil Madhavapeddy, 10/12/2014 23:18 -
> Thanks for the great writeup Simon!
> 
> I do wonder why Thomas thinks that OPAMROOT is a bad solution though.  It
> seems quite clean to me -- you can have an OPAM installation pointing to
> (e.g.) /usr/local/opam and either add that your global PATH or symlink binaries
> into /usr/local/bin.
> 
> This could be scripted up with a fairly trivial shell script (caveat: that I
> haven't actually written).
> 
> -anil
> 
> > On 10 Dec 2014, at 23:12, Thomas Gazagnaire <thomas at gazagnaire.org> wrote:
> > 
> > A (bad) solution is to set change OPAMROOT to an appropriate location.
> > 
> > Thanks for the write-up, this is very helpful to understand the use-cases. I've created https://github.com/ocaml/opam/issues/1895 to track that.
> > 
> > Best,
> > Thomas
> > 
> > 
> >> On 10 Dec 2014, at 13:16, Simon Cruanes <simon.cruanes.2007 at m4x.org> wrote:
> >> 
> >> Hello,
> >> 
> >> Is there a blessed way to install packages system-wide using Opam? I
> >> suspect there isn't, so I attached a document [1] that describes my
> >> use-cases and what I'm thinking of (of course I know you opam
> >> developers are busy).
> >> 
> >> Thanks!
> >> 
> >> Best,
> >> 
> > 
> > _______________________________________________
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> > opam-devel at lists.ocaml.org
> > http://lists.ocaml.org/listinfo/opam-devel
> > 
> 
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