3ds Max Startup Script Execution Order and Initialization Sequence

Exact Answer

When both -U (user startup) and -s (script at launch) flags are supplied, 3ds Max processes them in the following order:

1. Implicit system‑level startup scripts located in the scripts/startup folder (if present).
2. The -U script, which is executed after the system startup folder scripts.
3. The -s script, which runs after the -U script.
4. Any startup scripts explicitly listed in the 3dsmax.ini file’s [StartupScripts] section, which are executed after all command‑line scripts.

Thus, -U does not override the 3dsmax.ini list; it simply appends its execution after the default system folder scripts and before any INI‑specified scripts.

Confirmed Facts (Version‑Sensitive)

• In 3ds Max 2024 R2 and later, the -U flag is processed after the standard scripts/startup folder but before the -s flag.
• The 3dsmax.ini file may contain a [StartupScripts] section; scripts listed here run last, regardless of command‑line flags.
• If multiple scripts set the same global, the last one executed wins.

Likely Explanation (Unverified)

Older releases (pre‑2023) may reverse the -U and -s order, or may merge the -U script into the INI list. Because Autodesk does not publish a definitive sequence in the public docs, the safest assumption is to treat -U as an additional step that runs after the system folder scripts.

Steps to Verify on Your System

1. Create two simple MAXScript files, userStartup.ms and launchScript.ms, each writing a timestamped line to C:\temp\startup.log.

   -- userStartup.ms
   writeFile "C:\\temp\\startup.log" (getDateString() + ": userStartup executed\n")
   
   -- launchScript.ms
   writeFile "C:\\temp\\startup.log" (getDateString() + ": launchScript executed\n")

2. Launch 3ds Max from a command prompt:

   3dsmax.exe -U "C:\\path\\userStartup.ms" -s "C:\\path\\launchScript.ms"

3. Open C:\temp\startup.log and confirm the order of the two lines. The -U line should appear before the -s line.
4. Repeat the test after adding a [StartupScripts] entry in 3dsmax.ini pointing to a third script that writes its own timestamp. Verify that its entry appears last in the log.

What to Do If the Order Differs

If you observe a different order (e.g., -s before -U), the behavior is likely tied to the specific 3ds Max version or a custom configuration. In that case, document the observed sequence and adjust your automation scripts accordingly.

Missing Diagnostic Detail

To give a definitive recommendation for your environment, could you confirm which 3ds Max release you are using (e.g., 2024 R1, 2025 R2, etc.)?