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README: Update documentation

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Documentation now mentions the new name of the tool (kdumpst)
and the support of both initcpio/dracut; also updated the pstore
instructions - users might need to reserve some memory for that,
not all HWs are like the Steam Deck, which contains some pre-reserved
region of memory. Improved the TODO section a bit too.

Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
This commit is contained in:
Guilherme G. Piccoli
2023-03-24 18:55:49 -03:00
parent 4b5746a60e
commit e8b70ac199
1 changed files with 45 additions and 33 deletions
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78
README.md
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@ -1,13 +1,16 @@
```
# ###########################################################################
# ########################## Arch Kdump / Pstore ###########################
# ##################### kdumpst: pstore + kdump tooling #####################
# ###########################################################################
#
#
# This is the Arch Kdump/Pstore infrastructure; the goal is to collect
# data whenever a kernel crash is detected. There is a lightweight
# collection, that only grabs dmesg, and a more complete setting to grab the
# whole (compressed) vmcore. See the DETAILS section below for more info.
# This is the kdumpst infrastructure; the goal is to collect data whenever
# a kernel crash/panic is detected. There is a lightweight collection, that
# only grabs dmesg, and a more complete setting to grab the whole (compressed)
# vmcore. It supports both pstore (for the lightweight collection) and kdump
# for both collecting dmesg or even the full vmcore. In kdump "mode", both
# initcpio and dracut initramfs images are supported. The focus is Arch Linux
# (and spin-off distros), but should work in most systemd-based distros.
#
#
# ############################ HOW-TO USE IT ##############################
@ -15,19 +18,25 @@
# 1. Install the package with pacman if not available in your system; to check
# if it's already installed look the pacman installed package list. Also, be
# sure the systemd service was properly loaded by checking
# 'systemctl status kdump-init.service'.
# 'systemctl status kdumpst-init.service'.
#
# 2. In a crash event, the dmesg log is collected, and by default this happens
# via the Pstore mechanism, i.e., no extra memory should be reserved and no
# GRUB change is required. If 'lsmod' shows "ramoops", then Pstore is in use.
# Some extra files are collected besides dmesg, like dmidecode output and the
# "/etc/os-release" file.
# via the pstore mechanism, i.e., no crashkernel memory needs to be reserved
# and no GRUB change is required. If 'lsmod' shows "ramoops", then pstore is
# likely in use (check dmesg for "ramoops" to be sure). Some extra files are
# collected besides dmesg, like dmidecode output and "/etc/os-release".
#
# 3. The logs are stored in a ZIP file in the folder at "$MOUNT_FOLDER/logs"
# (see the config file); this file is named as: "kdump-TIMESTAMP.zip",
# where TIMESTAMP is the current timestamp (tz is UTC).
# 3. It might be necessary to reserve a bit of memory for pstore in the general
# case, if not pre-reserved due to kernel alignment or through the device-tree;
# check the output of "grep buffer /proc/iomem" - if empty or too small buffer,
# one could save PSTORE_MEM_AMOUNT bytes (see the config file) from kernel use
# with the "mem=" parameter (requires bootloader configuration).
#
# 4. (IMPORTANT) Please, test the infrastructure in order to see if a dummy
# 4. The logs are stored in a ZIP file in the folder at "$MOUNT_FOLDER/logs"
# (see the config file); this file is named as: "kdumpst-TIMESTAMP.zip",
# where TIMESTAMP is the current timestamp (UTC timezone).
#
# 5. (IMPORTANT) Please, test the infrastructure in order to see if a dummy
# crash log is collected before using it to try debugging complex issues.
# In order to do that, login to a shell and execute, as root user:
# 'echo 1 > /proc/sys/kernel/sysrq ; echo c > /proc/sysrq-trigger'
@ -35,44 +44,47 @@
# This action will trigger a dummy crash and reboot the system; check if
# there is a ZIP file with the crash logs in the directory described in (3).
#
# 5. Various tunings are available at "/usr/share/kdump.d/*" files; for
# example, the users can choose Kdump instead of Pstore (USE_PSTORE_RAM),
# and if using Kdump, collect the full vmcore (FULL_COREDUMP). The vmcore is
# not stored in the ZIP file, but it's saved in "$MOUNT_FOLDER/crash".
# NOTICE that, if Kdump is used instead of Pstore (either per user's choice
# or due to some failure in Pstore), a reboot is necessary before kdump is
# 6. Various tunings are available at "/usr/share/kdumpst.d/*" files; for
# example, the users can choose kdump instead of pstore (USE_PSTORE_RAM),
# and if using Kdump, collect the full vmcore (FULL_COREDUMP) or not.
# The vmcore is not stored in the ZIP file, but it's saved in the folder
# "$MOUNT_FOLDER/crash".
# NOTICE that, if kdump is used instead of pstore (either per user's choice
# or due to some failure in pstore), a reboot is necessary before kdump is
# usable, in order to effectively reserve crashkernel memory.
#
# 6. Error and succeeding messages are sent to systemd journal, so running
# 'journalctl -b | grep kdump' would hopefully bring some information.
# 7. Error and succeeding messages are sent to systemd journal, so running
# 'journalctl -b | grep kdumpst' would hopefully bring some information.
#
#
# ############################## DETAILS ##################################
# CAVEATS / INSTRUCTIONS
# ###########################################################################
# (a) We automatically edit GRUB config in case Pstore fails or if the user's
# choice is to use Kdump. But it requires one reboot in order the crashkernel
# (a) We automatically edit GRUB config in case pstore fails or if the user's
# choice is to use kdump. But it requires one reboot in order the crashkernel
# memory is effectively reserved by kernel.
#
# In case Kdump is used, the crashkernel necessary memory was empirically
# determined; setting 144M wasn't enough, 160M is unstable, so 192M seems
# good enough. This amount might change in future kernel versions, requiring
# tests using the approach suggested in the step (4) above.
# determined; setting 192M wasn't enough always, so 256M seems good enough.
# This amount might change in future kernel versions, requiring tests using
# the approach suggested in the step (5) above.
#
#
# TODOs
# ###########################################################################
# * The package currently doesn't uninstall the dracut/initcpio hooks, this
# is something to be implemented soon, either in the install script or as an
# option of kdumpst-load script.
#
# * We should explore /etc/grub.d/ instead of messing with the general grub
# config file directly to add the "crashkernel" kernel parameter.
#
# * Would be interesting to have a clean-up mechanism, to keep up to N most
# recent ZIP log files, instead of keeping all of them forever.
#
# * Pstore ramoops back-end has some limitations that we're discussing with
# the kernel community - right now we can only collect ONE dmesg and its
# size is truncated on "record_size" bytes, not allowing a file split like
# efi-pstore; thankfully we still can collect 2MiB dmesg, but hopefully we can
# improve that upstream.
#
# * Add a more reliable reboot mechanism - we had seen issues in the past
# with "reboot -f", and relying in sysrq reboot as a quirk managed to be a safe
# option, so this is something to think about. Should be easy to implement.
# efi-pstore; thankfully we can still save a 2MiB dmesg, which seems enough.
#
```