.. SPDX-License-Identifier: GPL-2.0 Debugging Kernel Shutdown Hangs with pstore+++++++++++++++++++++++++++++++++++++++++++ Overview========If the system hangs while shutting down, the kernel logs may need to beretrieved to debug the issue. On systems that have a UART available, it is best to configure the kernel to usethis UART for kernel console output. If a UART isn't available, the ``pstore`` subsystem provides a mechanism topersist this data across a system reset, allowing it to be retrieved on the nextboot. Kernel Configuration====================To enable ``pstore`` and enable saving kernel ring buffer logs, set thefollowing kernel configuration options: * ``CONFIG_PSTORE=y``* ``CONFIG_PSTORE_CONSOLE=y`` Additionally, enable a backend to store the data. Depending upon your platformsome potential options include: * ``CONFIG_EFI_VARS_PSTORE=y``* ``CONFIG_PSTORE_RAM=y``* ``CONFIG_CHROMEOS_PSTORE=y``* ``CONFIG_PSTORE_BLK=y`` Kernel Command-line Parameters==============================Add these parameters to your kernel command line: * ``printk.always_kmsg_dump=Y``	* Forces the kernel to dump the entire message buffer to pstore during		shutdown* ``efi_pstore.pstore_disable=N``	* For EFI-based systems, ensures the EFI backend is active Userspace Interaction and Log Retrieval=======================================On the next boot after a hang, pstore logs will be available in the pstorefilesystem (``/sys/fs/pstore``) and can be retrieved by userspace. On systemd systems, the ``systemd-pstore`` service will help do the following: #. Locate pstore data in ``/sys/fs/pstore``#. Read and save it to ``/var/lib/systemd/pstore``#. Clear pstore data for the next event