Enable cgroup v2 on RHEL8

Environment

• Red Hat Enterprise Linux 8

Issue

• How to enable cgroup v2 on RHEL8?
• Is cgroup v2 supported on RHEL 8?

Resolution

By default RHEL8 runs on cgroup-v1. You can switch to using cgroup-v2 by adding systemd.unified_cgroup_hierarchy=1 parameter on the kernel command line and reboot.

Using grubby tool

To modify the kernel command line, you can use the grubby tool:

# grubby --update-kernel=ALL --args="systemd.unified_cgroup_hierarchy=1"

Using grub2-mkconfig

Alternatively, you can use the the grub2-mkconfig method:

1. Edit the /etc/default/grub file.

2. This file contains multiple GRUB2 options. Kernel boot parameters are specified by the line that contains GRUB_CMDLINE_LINUX.
   Add the parameter systemd.unified_cgroup_hierarchy=1 at the end of GRUB_CMDLINE_LINUX line within the quotes.

3. Once the file is edited, save it and execute the command specified below to generate a new grub.cfg file:

  For an MBR (BIOS-based) system
  # grub2-mkconfig -o /boot/grub2/grub.cfg

  For a GPT (UEFI-based) system:
  # grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg

4. Now, reboot the system to apply the changes.

5. Execute the following command to validate.

# mount -l|grep cgroup
cgroup2 on /sys/fs/cgroup type cgroup2 (rw,nosuid,nodev,noexec,relatime,nsdelegate)

The following Red Hat documentation has more details about updating grub command line parameters:

• How to manually modify the boot parameter in grub before the system boots
• Mounting cgroups-v2

Diagnostic Steps

# mount -l|grep cgroup
cgroup2 on /sys/fs/cgroup type cgroup2 (rw,nosuid,nodev,noexec,relatime,nsdelegate)

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