message-ix on Windows server cannot find GAMS (show-versions fails)

[jiayl1202]

Code sample or context

import message_ix

Running this command in PowerShell works:
gams -> returns version and license info

But message-ix cannot detect GAMS:
message-ix show-versions

And when running:
scenario.solve()
it throws a java.lang.UnsatisfiedLinkError

ixmp:              3.11.1
message_ix:        0.0.0
message_ix_models: (not installed)
message_data:      (not installed)

click:             8.2.1
dask:              2025.7.0
genno:             1.28.2
graphviz:          (not installed)
ixmp4:             (not installed)
jpype:             1.6.0
     Java VM path: C:\Users\liujiayan\.conda\envs\messageix1\Library\lib\jvm\bin\server\jvm.dll
openpyxl:          3.1.5
pandas:            2.3.1
pint:              0.24.4
xarray:            2025.7.1
yaml:              6.0.2

iam_units:         2023.9.12
jupyter:           5.8.1
matplotlib:        3.10.3
plotnine:          0.15.0
pyam:              1.6.0

GAMS:              no 'gams' executable in IXMP_GAMS_PATH=(not set) or the system PATH
       system dir: C:\Users\Administrator

python:            3.13.5 | packaged by conda-forge | (main, Jun 16 2025, 08:20:19) [MSC v.1943 64 bit (AMD64)]
python-bits:       64
OS:                Windows
OS-release:        2019Server
machine:           AMD64
processor:         Intel64 Family 6 Model 143 Stepping 8, GenuineIntel
byteorder:         little
LC_ALL:            None
LANG:              None
LOCALE:            ('Chinese (Simplified)_China', '936')

I also tried the workaround from issue #523, modifying the gams.py file to explicitly locate the GAMS executable using shutil.which()`:

import os
from subprocess import check_output

gams_exec = os.getenv("GAMS_EXECUTABLE", "gams")
if os.name == "nt":
    import shutil
    found = shutil.which(gams_exec)
    if found:
        gams_exec = found
    else:
        gams_exec = "gams"
    cmd = f'{gams_exec} null.gms -LogOption=3'
else:
    cmd = [gams_exec, "null.gms", "-LogOption=3"]

output = check_output(
    cmd,
    shell=os.name == "nt",
    cwd=".",  # or temp_dir
    universal_newlines=True,
)
print(output)

The workaround above runs fine in isolation, but the original issues remain.

Expected result

message-ix show-versions should correctly detect the installed GAMS executable.
scenario.solve() should execute without throwing a Java `UnsatisfiedLinkError.
Problem description

I'm using message-ix on a Windows Server environment. GAMS is installed, added to the system PATH, and runs fine from PowerShell. However, when running message-ix show-versions, it reports that GAMS cannot be found. In addition, solving a scenario fails with:

java.lang.UnsatisfiedLinkError: java.lang.UnsatisfiedLinkError: no utiljni64 in java.library.path: D:\messageix\apifiles\Java\api;C:\Users\liujiayan\.conda\envs\messageix1\Lib\site-packages\ixmp\backend\jdbc\AMD64

Even though utiljni64.dll exists in D:\GAMS\48\apifiles\Java\api, and this path is included in the system environment variables (and verified via echo %PATH%).

I’ve restarted VS Code and the Conda environment, but the problem persists. Is this related to how Java resolves native libraries on Windows, or is there a specific way to configure ixmp or message-ix for Windows Server?

Versions

Output of ixmp show-versions

GAMS not found in PATH

Other relevant versions:

• Windows Server 2019
• Python 3.13.5 (Conda env: messageix1)
• ixmp:3.11.1
• message-ix: 0.0.0
• GAMS: 48.2
• Java: from GAMS installation
• VS Code + PowerShell terminal

[khaeru]

Hi there—thanks for a good amount of detail on this issue report. I've edited a bit to re-add the formatting from the template.

There are a few points to clarify and a few questions that could help diagnose.

• Is there a specific way to configure ixmp or message-ix for Windows Server?

  Every change to ixmp and message-ix is tested using GitHub Actions. See for example here. Our Windows tests run on the windows-latest runner image, which currently corresponds to Windows Server 2022. So, ixmp is known to work on at least this version of Windows Server with no special configuration. I don't believe the changes between Windows Server 2019 and 2022 are large enough such that there would be a difference in behaviour or in required configuration.

• When you say “I've restarted VS Code”—does this imply that you are using via PowerShell from within VS Code, i.e. the embedded terminal? If so, does that mean you run all the mentioned commands in this way? If not, then VS Code itself may not be relevant to the issue.

• “I also tried the workaround from GAMS is not registered correctly in show-versions #523 …”—to be clear, that issue was already marked as resolved via Use shutil.which() to locate gams #564 / in ixmp v3.11.0; see the What's New page in the docs. This means the issue should not persist/the fix should already be present in the version of ixmp you have installed (v3.11.1, according to the information you gave).

Some things that we can try to diagnose more precisely: run each of the following in the terminal and (Conda) environment you are using:

1. where gams
2. where ixmp
3. where message-ix
4. where python
5. python -c "import os; print(os.getenv('PATH'))"
6. python -c "import shutil; print(shutil.which('gams'))"
7. python -c "from ixmp.model.gams import GAMSInfo; print(GAMSInfo().__dict__)"