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Issue Description

While trying to access an OpenVZ container using the following command:

vzctl enter 10524

you may encounter this error:

Unable to fork: Cannot allocate memory

Here, 10524 refers to the container ID.

Step 1: Check Node Memory Availability

First, verify whether the host node is running out of memory:

free -m

If the system shows sufficient free memory, the issue is likely not at the node level.

Step 2: Check Resource Limits (privvmpages)

If memory is not the issue, the problem is usually related to OpenVZ memory limits, especially privvmpages.

Check current resource usage:

cat /proc/user_beancounters

This file contains resource usage and limits for all containers.

Step 3: Identify the Problem Container

Locate the entry for container 10524 and check the privvmpages values:

• If failcnt is high or non-zero
• And memory is marked as exhausted

Then the container has hit its memory limit.

Step 4: Increase privvmpages Limit

Edit the container configuration file:

vim /etc/sysconfig/vz-scripts/10524.conf

Find the privvmpages parameter and increase its value.

Example:

PRIVVMPAGES="unlimited:unlimited"

or set a higher limit based on server capacity.

Step 5: Restart the Container

Apply the changes by restarting the container:

vzctl restart 10524

Conclusion

The “Unable to fork: Cannot allocate memory” error in OpenVZ is typically caused by exhausted privvmpages limits, not always system-wide memory issues. Increasing the container’s memory allocation resolves the issue in most cases.

If you require help, contact SupportPRO Server Admin