Red Hat Summit14.3. Known limitations of soft reboots
A soft reboot running in image mode has specific limitations because it is designed to update the userspace while leaving the kernel untouched. The known limitations are:
-
Kernel and hardware remain unchanged: Any changes to the kernel, hardware drivers, or low-level kernel parameters are not applied during a soft reboot. For these updates to take effect, a full system reboot is necessary. Also , kernel settings, for example, those configured by using
sysctl, are not reset during a soft reboot. The system continues to use the same settings from before the reboot. -
Firmware initialization: During a soft reboot, the operating system (OS) skips the firmware initialization. This is because the OS retains control and directly restarts the kernel using a system call, instead of fully relinquishing control to the hardware. The
kexec system callmanages this process. - User responsibility for kernel module alignment with userspace changes: Even in image mode for RHEL, the user remains responsible for rebuilding and aligning custom kernel modules with userspace changes and a soft reboot does not bypass this. In fact, a soft reboot specifically keeps the running kernel, which can introduce compatibility issues if the userspace has been updated to expect a different kernel version or set of modules.
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