.CU file extension
To open .CU files on Windows, right-click the .cu file → Open with → choose a text/code editor (for example, an editor you already trust) to view it as plain text.
To open a .cu file, use a code editor or IDE (it is usually CUDA source code). If your system labels it as “CU-SeeMe” (application/cu-seeme), open it as plain text in a trusted editor rather than looking for a video app.
Last updated: April 30, 2026 · Reviewed by Julian Stricker
Open on your device
Choose your operating system for a dedicated step-by-step opening guide.
How to open .CU files
Use these platform-specific instructions to open .CU files safely.
Windows
- Right-click the .cu file → Open with → choose a text/code editor (for example, an editor you already trust) to view it as plain text.
- If you need to build/run it, open the containing project in your CUDA development environment and compile with the CUDA toolchain (not by double-clicking the file).
Mac
- Control-click the .cu file → Open With → choose a code editor to open it as plain text.
- For compiling, use a CUDA-capable development setup for your project; .cu files are normally compiled as part of a build, not opened as a standalone document.
Linux
- Open the .cu file with a code editor (or any text editor) to inspect it as source code.
- If your desktop shows it as “CU-SeeMe” due to MIME mapping, explicitly choose “Open With Text Editor” (the content is what matters, not the label).
- To compile, use your project’s build process with the CUDA toolchain.
iOS
- Open the .cu file in the Files app with a text/code viewer app; if it won’t preview well, transfer it to a desktop editor for proper viewing and building.
Android
- Open the .cu file using a text/code editor app; for compiling/building CUDA code, move it to a desktop CUDA development environment.
Security notes
- .cu files are usually plain-text source code, but they can still be risky: building or running code from untrusted sources can execute malicious behavior during compilation scripts or when you run the resulting program.
- Be cautious with .cu files received via email or downloads: confirm the origin and inspect the code before compiling, especially if the project includes build scripts or dependencies.
- MIME misclassification (application/cu-seeme) can cause unexpected apps to be suggested; prefer opening unknown .cu files in a text editor first to avoid triggering vulnerable or inappropriate parsers.
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Can't open this file?
These are the most common causes and fixes when .CU files fail to open.
Common reasons
- The file is identified as “CU-SeeMe” or opens in the wrong app
- Double-clicking doesn’t “run” the file
- The .cu file looks unreadable or binary
Fix steps
- Ignore the label and open the file with a plain text/code editor to confirm whether it contains CUDA C/C++ source.
- On Linux desktops, consider adjusting file associations so .cu opens in your editor by default (association changes affect convenience, not the file format).
OS-specific troubleshooting
What is a .CU file?
A .cu file is most often a CUDA source file containing C/C++ code plus CUDA extensions (e.g., GPU kernel functions) intended to be compiled with NVIDIA’s CUDA toolchain. Some desktop MIME databases map .cu to application/cu-seeme (from the older CU-SeeMe ecosystem), which is a file association/mime-label issue rather than a guarantee of actual file contents.
Background
In real-world development workflows, .cu is widely used for CUDA programming: developers write GPU-accelerated code in .cu files and compile it as part of a C/C++ project using CUDA tooling. Because it is source code, it is typically opened and edited with text editors and IDEs, and version-controlled like other code files.
Separately, many Linux distributions and applications ship a mime.types mapping that associates the extension .cu with the MIME type application/cu-seeme. That MIME label references CU-SeeMe, an early videoconferencing system, and it can cause desktops or mail clients to misclassify .cu attachments.
Practically, treat unknown .cu files as text first: open in a code editor to inspect content. If it contains readable C/C++-like code, it is almost certainly a CUDA source file; if it looks binary/garbled or does not resemble source, confirm its origin with the sender or the project it belongs to.
Common MIME types: application/cu-seeme
Further reading
Authoritative resources for more details on the .CU format.
Common .CU issues
The file is identified as “CU-SeeMe” or opens in the wrong app
Some systems map .cu to the MIME type application/cu-seeme, which can lead to misleading “Open with” suggestions and icons.
- Ignore the label and open the file with a plain text/code editor to confirm whether it contains CUDA C/C++ source.
- On Linux desktops, consider adjusting file associations so .cu opens in your editor by default (association changes affect convenience, not the file format).
Double-clicking doesn’t “run” the file
.cu is typically source code, not an executable document; it must be compiled (usually as part of a project).
- Open the file in a code editor/IDE and locate the project/build instructions (README, build scripts, or IDE configuration).
- Compile using the CUDA toolchain as intended by the project rather than trying to execute the .cu file directly.
The .cu file looks unreadable or binary
Not every file named .cu is guaranteed to be CUDA source; it may be misnamed, corrupted, or from another workflow.
- Verify the source of the file (project repository, sender, or download) and re-download if it may be incomplete.
- Check whether the content is plain text; if it is not, ask for the correct file or documentation describing what the file should contain.
FAQ
Is a .cu file the same as a C or C++ file?
It is usually CUDA C/C++ source: largely C/C++ syntax plus CUDA-specific constructs intended for GPU programming and compilation with CUDA tooling.
Why does my Linux system call it application/cu-seeme?
Some widely distributed mime.types lists map the .cu extension to application/cu-seeme. That mapping comes from the CU-SeeMe name and can be unrelated to CUDA source files.
Can I convert a .cu file by renaming it to .txt or .cpp?
Renaming doesn’t convert content. If it is plain-text CUDA code, you can open it as text regardless of the extension, but building it as CUDA code still typically expects .cu and the CUDA toolchain.
What should I do on mobile if I only need to read it?
Use a text/code viewer app to read it as plain text. For compiling or running CUDA code, transfer it to a desktop environment with CUDA tooling.
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