Cannot allocate memory

The Cannot allocate memory error indicates that the operating system or runtime failed to allocate the requested memory to a process. This occurs when a program asks for memory and the system cannot fulfill the request due to exhausted RAM, insufficient swap space, strict resource limits, or kernel-level allocation constraints. The error commonly appears on Linux and Windows systems, Java and Spring Boot applications, Docker containers, databases, and server processes.

When does this error occur?

  • Starting applications on systems with low available memory
  • Processes requesting large memory blocks
  • Systems running out of RAM and swap space
  • Containers with restrictive memory limits
  • Applications affected by memory fragmentation or leaks

Root cause of Cannot allocate memory

This error occurs at the OS memory management level when the kernel cannot allocate memory for a process request. Causes include depleted physical RAM, exhausted swap space, low virtual memory limits, restrictive container or process limits, or fragmented memory that prevents allocating a contiguous block. The operating system enforces these limits to maintain system stability.

How to fix the error (step-by-step)

Linux / macOS

Check current memory and swap availability. 

free -m

swapon --show

If swap is insufficient, increase or add swap space. 

sudo fallocate -l 2G /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile

Windows

Review system memory usage and virtual memory settings. 

taskmgr

Ensure the system page file is enabled and sized appropriately.

Java / Spring Boot

Reduce memory pressure or adjust JVM heap allocation. 

-Xms512m -Xmx2048m

Avoid allocating excessively large objects in application code.

Docker / containers

Inspect container memory limits. 

docker inspect <container-name>

Increase memory allocation if required. 

docker run --memory=2g <image>

Database / network services

Review service memory configuration such as caches, buffers, and connection limits to prevent excessive allocation requests.

Verify the fix

Restart the affected application or service and monitor memory usage. The system should successfully allocate memory, and the Cannot allocate memory error should no longer appear during normal operation.

Common mistakes to avoid

  • Adding swap without investigating memory usage patterns
  • Allocating large memory blocks unnecessarily
  • Ignoring container or process memory limits
  • Running memory-heavy workloads on undersized systems
  • Failing to monitor memory consumption over time

Quick tip

Always size system memory and swap based on peak workload, not average usage.

FAQ

Q: Is Cannot allocate memory the same as Out of memory?

A: They are related but not identical. This error occurs at allocation time, while Out of memory often appears after memory has already been exhausted.

Q: Can adding swap always fix this error?

A: Not always. Swap helps, but applications with high memory demands may still require more physical RAM.

Conclusion

The Cannot allocate memory error indicates that the system cannot fulfill a memory allocation request. Proper memory sizing, limit configuration, and monitoring resolve the issue. Refer to related root error references on ErrorFixHub for deeper system-level diagnostics.

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