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CompTIA Linux+ XK0-005 - 4.3 - Out of Memory (OOM): Process Killer

In Linux environments, managing memory is crucial for maintaining system stability. However, under certain conditions, when available memory is exhausted, the Out of Memory (OOM) killer is invoked to prevent system crashes. This guide focuses on understanding the OOM killer, its role in handling memory issues, and common sysctl settings to configure its behavior.

What is the OOM Process Killer?

The OOM killer is a mechanism in the Linux kernel designed to handle out of memory situations. When the available memory is insufficient to satisfy the memory requests of all running processes, the OOM killer identifies and terminates specific processes to free up memory and prevent system instability.

The OOM killer uses a scoring algorithm to assess the "badness" of a process. The badness score is determined based on factors like memory usage, process priority, and time since the last OOM event. The OOM killer selects the process with the highest badness score and terminates it to reclaim memory.

Configuring the OOM Killer

You can configure the behavior of the OOM killer by adjusting various sysctl settings. Here are some common sysctl settings related to the OOM killer and their functions:

  • vm.oom_kill_allocating_task: When set to 0, the OOM killer will not kill the process that triggered the out of memory condition. Instead, it will select another process to terminate.
  • vm.overcommit_memory: This setting determines the memory overcommit behavior. Setting it to 0 enables a conservative overcommit policy, while setting it to 1 or 2 allows more aggressive memory overcommitment.
  • vm.panic_on_oom: When set to 1, the system will initiate a kernel panic in an out of memory situation, causing a system reboot.
  • vm.oom_dump_tasks: When set to 1, the system will generate a detailed oom-kill trace in the kernel log, providing information about the killed processes.

To modify these sysctl settings, open the /etc/sysctl.conf configuration file using a text editor and add or modify the desired settings, saving the changes.

Then, apply the new sysctl settings using the following command:

sysctl -p


The OOM killer is an important component in Linux systems that helps manage memory-related issues. By understanding its role and configuring its behavior through sysctl settings, you can adjust how the OOM killer selects and terminates processes in an out of memory scenario.

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