Re: Profile's LD_LIBRARY_PATH by default

[david larsson <david.larsson@selfhosted.xyz>]

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 :-)