21.2. Dumping a virtual machine core

To analyze why a virtual machine (VM) crashed or malfunctioned, you can dump the VM core to a file on disk for later analysis and diagnostics.

This section provides a brief introduction to core dumping and explains how you can dump a VM core to a specific file.

21.2.1. How virtual machine core dumping works

A virtual machine (VM) requires numerous running processes to work accurately and efficiently. In some cases, a running VM may terminate unexpectedly or malfunction while you are using it. Restarting the VM may cause the data to be reset or lost, which makes it difficult to diagnose the exact problem that caused the VM to crash.

In such cases, you can use the virsh dump utility to save (or dump) the core of a VM to a file before you reboot the VM. The core dump file contains a raw physical memory image of the VM which contains detailed information about the VM. This information can be used to diagnose VM problems, either manually, or by using a tool such as the crash utility.

Ressources supplémentaires

21.2.2. Creating a virtual machine core dump file

A virtual machine (VM) core dump contains detailed information about the state of a VM at any given time. This information, which is similar to a snapshot of the VM, can help you detect problems if a VM malfunctions or shuts down suddenly.

Conditions préalables

  • Make sure you have sufficient disk space to save the file. Note that the space occupied by the VM depends on the amount of RAM allocated to the VM.


  • Use the virsh dump utility.

    For example, the following command dumps the lander1 VM’s cores, its memory and the CPU common register file to gargantua.file in the /core/file directory.

    # virsh dump lander1 /core/file/gargantua.file --memory-only
    Domain 'lander1' dumped to /core/file/gargantua.file

The crash utility no longer supports the default file format of the virsh dump command. To analyze a core dump file using crash, you must create the file using the --memory-only option.

Additionally, you must use the --memory-only option when creating a core dump file to attach to a Red Hat Support Case.

Résolution de problèmes

If the virsh dump command fails with a System is deadlocked on memory error, ensure you are assigning sufficient memory for the core dump file. To do so, use the following crashkernel option value. Alternatively, do not use crashkernel at all, which assigns core dump memory automatically.


Ressources supplémentaires