Re: Profile's LD_LIBRARY_PATH by default

[david larsson]

On 2020-10-29 10:07, Sébastien Lerique wrote:
> Hello!
>
> On 29 Oct 2020 at 10:10, david larsson <david.larsson@selfhosted.xyz> 
> wrote:
> > On 2020-10-28 13:49, Sébastien Lerique wrote:
> > > [snip]
> > > While running a racket program which uses OpenCV, I realised that my
> > > LD_LIBRARY_PATH does not contain my user's profile libs. I have
> > > `libopencv*.so` in `~/.guix-profile/lib/`, but running a racket
> > > program which needs that fails:
> > > ```
> > > $ racket capture.rkt
> > > ffi-lib: couldn't open "libopencv_core.so" (libopencv_core.so: cannot
> > > open shared object file: No such file or directory)
> > > ```
> > > While running
> > > ```
> > > env LD_LIBRARY_PATH=/home/sl/.guix-profile/lib/ racket capture.rkt
> > > ```
> > > works.
> > > (Also, this <http://0x0.st/ik3s.txt> is the output of `env
> > > LD_DEBUG=libs racket capture.rkt`.)
> > > Is this normal behaviour, i.e. that the path to dynamic libs 
> > > installed
> > > in my user profile should be manually configured in my shell startup
> > > scripts? Should this not be included in 
> > > `~/.guix-profile/etc/profile`?
>
> > I wondered the same, and got answer in the IRC #guix that setting
> > LD_LIBRARY_PATH is highly discouraged (unless you have a specific and
> > good reason to do so in a specific case - never globally). I a good 
> > explanation
> > about it here:
> > https://web.archive.org/web/20060719201954/http://www.visi.com/~barr/ldpath.html
> >
> > A good example of how it can go wrong:
> >
> > "In its startup script[a program called WidgetMan], it sets 
> > LD_LIBRARY_PATH to
> > point to its copy of Motif so it uses that one when it runs. As it 
> > happens,
> > WidgetMan is designed to launch other programs too. Unfortunately, 
> > when
> > WidgetMan launches other apps, they inherit the LD_LIBRARY_PATH 
> > setting and some
> > Motif based apps now break when run from WidgetMan because WidgetMan's 
> > Motif is
> > incompatible with (but the same library version as) the system Motif 
> > library.
> > Bummer!"
>
> Yes I see that makes sense. Does this mean that one shouldn't install
> libraries in user profiles?

Not necessarily - it shouldn't hurt anway IIUC. Though I assume it is 
more common to install libraries when you use guix environment or guix 
profile.

> Or maybe that, if I were to package this racket program, then it would
> depend on `opencv` and set its required lib paths properly in its
> package definition (so work no matter if it's system-wide or in a user
> profile)?

IIUC, yes, through package inputs and then the build-system usually 
finds the path for you.

> Then, for development, is setting LD_LIBRARY_PATH still the only way
> without installing the lib system-wide?

It is possibly the easiest way, but perhaps not the guix-iest way.

Please someone correct me if Im wrong here:

For development you can use guix environment or guix-profile and 
possibly even grafts if you want to develop against newer versions of 
opency.

Say you want to test updating the opency package in a profile created by 
guix package -m manifest.scm -p ~/guix-profiles/dev-profile; the new 
opency version can be grafted onto your racket package X (or all 
packages in the profile depending on opency) without rebuilding X, by 
adding "(replacement opency-fixed)" in the opency package definition in 
the profile manifest. On the next package update for the profile (i.e. 
guix package -m manifest-with-replacement.scm -p 
~/guix-profile/dev-profile) all dependencies of opency would be updated 
(such as your package X). The "manifest.scm" file is a package module 
that contains; the definition of opency with "(replacement 
opency-fixed)", the package definition for "opency-fixed", definition of 
X, and also any other packages you need to test.

see here: https://guix.gnu.org/manual/en/html_node/Security-Updates.html
and here: 
https://guix.gnu.org/manual/en/html_node/Invoking-guix-environment.html

> (that's a lot of questions, apologies!)

No problem :-)