13.2. Version selection and bootup

Image mode for RHEL uses GRUB by default, with exception to IBM Z® architectures. Each version of image mode for RHEL currently available on a system has a menu entry.

The menu entry references an OSTree deployment, which consists of a Linux kernel, an initramfs and a hash linking to an OSTree commit, which you can pass by using the ostree=kernel argument.

During bootup, OSTree reads the kernel argument to determine which deployment to use as the root filesystem. Each update or change to the system, such as package installation, addition of kernel arguments, creates a new deployment.

This enables rolling back to a previous deployment if the update causes problems.