Problems loading lantern.so when running R CMD check.

[ralmond]

I'm working on a package which uses torch. I installed torch by doing

install.package("cuda12.8",repos=...)
install.packge("torch")
torch::install_torch()

Which apparently ran without errors.

Things seem to be working properly when I run my testthat tests. However, when I run
R CMD check to thoroughly test my package, I'm consistently getting the following error:

Warning message:
ℹ torch failed to start, restart your R session to try again.
ℹ You might need to reinstall torch using `install_torch()`
✖ /home/ralmond/R/x86_64-pc-linux-gnu-library/4.5/torch/lib/liblantern.so -
  libcudart.so.12: cannot open shared object file: No such file or directory
Caused by error:
! /home/ralmond/R/x86_64-pc-linux-gnu-library/4.5/torch/lib/liblantern.so - libcudart.so.12: cannot open shared object file: No such file or directory 
Error : Lantern is not loaded. Please use `install_torch()` to install additional dependencies.
Error: unable to load R code in package ‘CPTtorch’
Execution halted
ERROR: lazy loading failed for package ‘CPTtorch’
* removing ‘/home/ralmond/ralmond1/Projects/CPTtorch.Rcheck/CPTtorch’

Checking in my torch directory, I see:

$ ls libcudart*
libcudart-256e6409.so.12  libcudart-c3a75b33.so.12

Is there a missing simlink?

[ralmond]

Manually adding symlinks to system.file("lib",package="torch"), for example adding

$ ln -s libcudart-c3a75b33.so.12 libcudart.so.12

and similar for other libs whi only have a libXXX-XXXXXXXX.so.N version, sort of works around the problem. R CMD check will now load the code and the rest of the run works pretty normally.

However, I still get the following warning:

W  checking whether the package can be loaded with stated dependencies (1.7s)
   Loading required package: methods
   Loading required package: torch
   Torch libraries are installed but loading them was unsuccessful. Please
   reinstall torch with `install_torch(reinstall = TRUE)` You can disable this
   check by setting `TORCH_VERIFY_LOAD` to "FALSE" Torch libraries installed in:
   '/home/ralmond/R/x86_64-pc-linux-gnu-library/4.5/torch'. Error: Lantern is not
   loaded. Please use `install_torch()` to install additional dependencies. In
   addition: Warning message: ℹ torch failed to start, restart your R session to
   try again. ℹ You might need to reinstall torch using `install_torch()` ✖ could
   not find function "packageName" Caused by error in `packageName()`: ! could not
   find function "packageName" Execution halted
   Torch libraries are installed but loading them was unsuccessful.
   Please reinstall torch with `install_torch(reinstall = TRUE)`
   You can disable this check by setting `TORCH_VERIFY_LOAD` to "FALSE"
   Torch libraries installed in:
   '/home/ralmond/R/x86_64-pc-linux-gnu-library/4.5/torch'.
   Error: Lantern is not loaded. Please use `install_torch()` to install
   additional dependencies. In addition: Warning message: ℹ torch failed to start,
   restart your R session to try again. ℹ You might need to reinstall torch using
   `install_torch()` ✖ could not find function "packageName" Caused by error in
   `packageName()`: ! could not find function "packageName" Execution halted
   Loading required package: R6
   Error: package or namespace load failed for ‘CPTtorch’:
    .onLoad failed in loadNamespace() for 'CPTtorch', details:
     call: NULL
     error: Lantern is not loaded. Please use `install_torch()` to install additional dependencies.
   Execution halted
   
   It looks like this package (or one of its dependent packages) has an
   unstated dependence on a standard package.  All dependencies must be
   declared in DESCRIPTION.
   See section ‘The DESCRIPTION file’ in the ‘Writing R Extensions’
   manual.
W  checking whether the package can be unloaded cleanly (1.8s)
   Error: package or namespace load failed for ‘CPTtorch’:
    .onLoad failed in loadNamespace() for 'CPTtorch', details:
     call: NULL
     error: Lantern is not loaded. Please use `install_torch()` to install additional dependencies.
   Execution halted
W  checking whether the namespace can be loaded with stated dependencies (1.7s)
   Error: .onLoad failed in loadNamespace() for 'CPTtorch', details:
     call: NULL
     error: Lantern is not loaded. Please use `install_torch()` to install additional dependencies.
   Execution halted
   
   A namespace must be able to be loaded with just the base namespace
   loaded: otherwise if the namespace gets loaded by a saved object, the
   session will be unable to start.
  

I think that torch is not properly initialized when it is loaded. There is a start_torch and latern_start function, but they are not exported.

[cregouby]

Hello @ralmond,

The way you install torch is quite unusual. You don't have to install dependant packages when you install torch. You don't have to symlink any file.
I would suggest to reinstall torch using the environment variables to control cuda version, debug, library locations etc :

??torch::install_torch

If anything fails, you may want to activate verbose installation through TORCH_INSTALL_DEBUG=1

If it is not enough, you may run the install_torch_sitrep() to get (and share ? ) a view on the state of your install.

Hope it helps.

[ralmond]

Thanks for the advice, but the problem is not loading torch. I've successfully loaded torch and the dependencies run when I load my package using library(CPTtorch).

> install_torch_sitrep()

── System Information ──────────────────────────────────────
• OS: "Linux" (Pop!_OS 24.04 LTS)
• R Version: "R version 4.5.3 (2026-03-11)"
• Platform: "x86_64-pc-linux-gnu"
• Architecture: "x86_64"

── Package Information ─────────────────────────────────────
[1] "2.8.0+cu128"

The problem comes when I run R CMD check CPTtorch. R CMD check tests loading the package in a number of ways (e.g., just attaching the package, and loading with the package being in the library). It is during those loads that I seem to be having the problem.

One problem which was causing R CMD check to abort is in my first post. That can be fixed (at least on *nix) by adding symlinks in the lib directory.

The second problem is the one in the second post, which at least only posts as a warning, letting R CMD check do its other checking.

My suspicion is that some initialization code is being called in torch:.onLoad() that needs to be called in torch:.onAttach() instead, but the initialization functions aren't exported, so I can't call them from my loading.

I suspect this is not unique to my package, but would be the case for any package that depends on torch.