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Early kdump inherits the settings of normal kdump, so any changes that caused normal kdump rebuilding also require rebuilding the system initramfs to make sure that the changes take effect for early kdump. Therefore, when the early kdump is enabled, provide a prompt message after the rebuilding of kdump initramfs is completed. Signed-off-by: Lianbo Jiang <lijiang@redhat.com> Acked-by: Dave Young <dyoung@redhat.com>
75 lines
2.8 KiB
Plaintext
75 lines
2.8 KiB
Plaintext
Early Kdump HOWTO
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Introduction
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------------
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Kdump service starts too late, so early crashes will have no chance to get
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kdump kernel booting, this will cause crash information to be lost. It is
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necessary to add a dracut module in order to load crash kernel and initramfs
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as early as possible. You can provide "rd.earlykdump" in grub commandline
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to enable, then the early kdump will load those files like the normal kdump,
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which is disabled by default.
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For the normal kdump service, it can check whether the early kdump has loaded
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the crash kernel and initramfs. It has no conflict with the early kdump.
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How to configure early kdump
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----------------------------
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We assume if you're reading this document, you should already have kexec-tools
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installed.
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You can rebuild the initramfs with earlykdump support with below steps:
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1. start kdump service to make sure kdump initramfs is created.
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# systemctl start kdump
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NOTE: If a crash occurs during boot process, early kdump captures a vmcore
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and reboot the system by default, so the system might go into crash loop.
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You can avoid such a crash loop by adding the following settings, which
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power off the system after dump capturing, to kdump.conf in advance:
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final_action poweroff
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failure_action poweroff
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For the failure_action, you can choose anything other than "reboot".
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2. rebuild system initramfs with earlykdump support.
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# dracut --add earlykdump
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3. add rd.earlykdump in grub kernel command line.
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Note:
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[1]. Early kdump initramfs size will be large because it includes vmlinuz and
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kdump initramfs. And for step 2 if you are sure to overwrite system initramfs
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you can backup the original initramfs and use "--force" option.
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[2]. Early kdump inherits the settings of normal kdump, so any changes that
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caused normal kdump rebuilding also require rebuilding the system initramfs
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to make sure that the changes take effect for early kdump. Therefore, after
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the rebuilding of kdump initramfs is completed, provide a prompt message to
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tell the fact.
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After making said changes, reboot your system to take effect. Of course, if you
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want to disable early kdump, you can simply remove "rd.earlykdump" from kernel
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boot parameters in grub, and reboot system like above.
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Once the boot is completed, you can check the status of the early kdump support
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on the command prompt:
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# journalctl -x|grep early-kdump
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Then, you will see some useful logs, for exapmle:
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1. if early kdump is successful.
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Mar 09 09:57:56 localhost.localdomain dracut-cmdline[190]: early-kdump is enabled.
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Mar 09 09:57:56 localhost.localdomain dracut-cmdline[190]: kexec: loaded early-
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kdump kernel
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2. if early kdump is disabled.
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Mar 09 10:02:47 localhost.localdomain dracut-cmdline[189]: early-kdump is disabled.
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Limitation
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----------
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At present, early kdump doesn't support fadump.
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