The undefined symbol: _ZdlPvm error in Linux indicates a C++ ABI mismatch where the dynamic linker cannot find the operator delete(void*, unsigned long) symbol. This typically occurs when Qt5 libraries are compiled with a different GCC version than the application or system libraries. Resolving it requires aligning library versions, reinstalling packages via apt, and ensuring PyCharm uses a compatible Python environment.
Understanding the Root Cause
The symbol _ZdlPvm is a mangled C++ name for operator delete(void*, unsigned long). The "m" and "v" parameters refer to the size of the memory block and the alignment requirements. When you see this specific undefined symbol error, it means your executable was linked against a version of libstdc++.so (the standard C++ library) that expects certain symbols which are missing or incompatible in the currently loaded library instance.
This is most common in Ubuntu environments where multiple versions of GCC might be installed, or when mixing system-wide Qt5 libraries with user-compiled binaries. In PyCharm projects, this often happens if the IDE's Python interpreter is linked against system Qt libraries that were updated independently of the Python bindings like PyQt5 or PySide2. If the Qt libraries were upgraded via apt upgrade but the Python packages were not rebuilt or reinstalled, the ABI (Application Binary Interface) breaks.
Common Scenarios
- System Library Mismatch: You updated
libqt5core5aorlibstdc++6but did not restart services or rebuild dependent applications. - PyCharm Environment: The virtual environment’s Python binary was compiled against an older version of
libstdc++than the one currently provided by the OS. - Manual Compilation: You compiled a C++ extension module using a newer GCC than the system’s default Qt libraries.
Step-by-Step Resolution for Ubuntu
The first step is to ensure that all core system libraries are consistent. Ubuntu manages these dependencies through the Advanced Package Tool (APT). Start by updating your package list and checking for any broken dependencies. Open your terminal and run the following commands to repair any partially installed packages:
sudo apt update
sudo apt --fix-broken install
sudo dpkg --configure -aIf the error persists, you likely need to reinstall the specific Qt5 and C++ standard library packages. This forces APT to replace potentially corrupted or mismatched binaries with the correct versions from the repository. Run this command to force reinstall the core components:
sudo apt reinstall libqt5core5a libstdc++6After reinstalling, verify that the symbol is present in the current library. You can use the nm utility to check the dynamic symbol table of libstdc++.so.6. Look for the mangled name:
nm -D /usr/lib/x86_64-linux-gnu/libstdc++.so.6 | grep _ZdlPvmIf this returns no output, the library file itself is damaged or incorrect, and you may need to investigate deeper system issues. For related dependency problems, such as unmet dependencies that prevent proper installation, refer to our guide on Solving Ubuntu Unmet Dependencies Error.
Fixing the Issue in PyCharm
When working within PyCharm, the issue often stems from the Python interpreter’s linkage. PyCharm allows you to create virtual environments that isolate dependencies, but if you are using the system Python, it inherits the system’s library paths. To fix this, you should recreate your virtual environment to ensure it links against the correct, freshly installed libraries.
- Open PyCharm and go to File > Settings > Project > Python Interpreter.
- Select your current interpreter and click the gear icon to choose Remove.
- Add a new interpreter. Choose Venv Environment and select a new location for the virtual environment.
- Ensure the base interpreter is set to the latest available Python version in your Ubuntu distribution.
Once the new environment is created, reinstall your project dependencies using pip. This ensures that any C++ extensions (like PyQt5) are compiled against the current system headers and libraries. If you encounter signature verification errors during this process, check your repository configurations as described in Error Occurred: Signature Verification Failure in Ubuntu Repository.
Advanced Debugging with LD_DEBUG
If the standard fixes do not resolve the issue, you need to identify exactly which library is failing to load. Linux provides the LD_DEBUG environment variable to trace dynamic linking behavior. Run your application with the following command to get detailed logs:
LD_DEBUG=libs ./your_applicationLook for lines indicating "symbol lookup error" or "cannot open shared object file." This will tell you if the system is loading an old version of libstdc++ from a non-standard path, such as /usr/local/lib or a user-specific directory. If you find conflicting libraries, remove them or adjust your LD_LIBRARY_PATH to prioritize the system directories.
Preventing Future Occurrences
To avoid this error in the future, maintain consistency between your compiler and runtime libraries. Always use the same GCC version to compile C++ extensions as the one used to build the system’s libstdc++. In PyCharm, prefer using virtual environments over the global system Python for development projects. This isolation prevents accidental conflicts when the operating system updates its core libraries.
Additionally, regularly update your system packages. While rolling updates can sometimes introduce instability, staying on a supported LTS (Long Term Support) release of Ubuntu minimizes the risk of ABI mismatches. If you experience boot issues after major updates, such as volume full errors, consult resources on handling MokLinuxError: Volume Full; Not Bootable on Old ASUS Laptop scenarios to ensure your system remains stable.
Frequently Asked Questions
Why does this error happen only after an apt upgrade?
It happens because the upgrade replaced libstdc++ with a new version that has a different ABI or symbol layout, but your existing application or Python environment was not rebuilt to match. The old binary still expects the old symbols, leading to a lookup failure at runtime.
Can I fix this by changing my GCC version?
Yes, if you compiled your application yourself, switching to the exact GCC version used by the system’s Qt libraries can resolve the mismatch. However, for pre-built packages like those in PyCharm, you must rely on reinstalling the packages rather than changing the compiler.
How do I check which version of libstdc++ is being used?
You can use the ldd command on your executable. Run ldd ./your_app | grep stdc++ to see the path to the loaded library. Then use strings or nm on that specific file to verify if it contains the required symbol.
Is it safe to manually download and replace libstdc++.so.6?
No, it is highly risky. Manually replacing system libraries can break other applications and even the desktop environment. Always use apt to manage these files to ensure dependency tracking remains intact.
What if the symbol is missing from the library entirely?
If nm -D shows the symbol is missing, the library file is likely corrupted or from a completely different distribution. Reinstalling the libstdc++6 package via apt is the only reliable way to restore the correct file.