On 02/27/14 at 01:51pm, Hari Bathini wrote:
This patch adds fadump howto document to kexec-tools. The document
is prepared in reference to kexec-kdump-howto.txt document.
Signed-off-by: Mahesh Salgaonkar <mahesh(a)linux.vnet.ibm.com>
Signed-off-by: Hari Bathini <hbathini(a)linux.vnet.ibm.com>
---
fadump-howto.txt | 428 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 428 insertions(+)
create mode 100644 fadump-howto.txt
diff --git a/fadump-howto.txt b/fadump-howto.txt
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+Firmware assisted dump (fadump) HOWTO
+
+Introduction
+
+Firmware assisted dump is a new feature in the 3.4 mainline kernel supported
+only on powerpc architecture. The goal of firmware-assisted dump is to enable
+the dump of a crashed system, and to do so from a fully-reset system, and to
+minimize the total elapsed time until the system is back in production use. A
+complete documentation on implementation can be found at
+Documentation/powerpc/firmware-assisted-dump.txt in upstream linux kernel tree
+from 3.4 version and above.
+
+Please note that the firmware-assisted dump feature is only available on Power6
+and above systems with recent firmware versions.
+
+Overview
+
+Fadump
+
+Fadump is a robust kernel crash dumping mechanism to get reliable kernel crash
+dump with assistance from firmware. This approach does not use kexec, instead
+firmware assists in booting the kdump kernel while preserving memory contents.
+Unlike kdump, the system is fully reset, and loaded with a fresh copy of the
+kernel. In particular, PCI and I/O devices are reinitialized and are in a
+clean, consistent state. This second kernel, often called a capture kernel,
+boots with very little memory and captures the dump image.
+
+The first kernel registers the sections of memory with the Power firmware for
+dump preservation during OS initialization. These registered sections of memory
+are reserved by the first kernel during early boot. When a system crashes, the
+Power firmware fully resets the system, preserves all the system memory
+contents, save the the low memory (boot memory of size larger of 5% of system
s/the the/the
+RAM or 256MB) of RAM to the previous registered region. It will also
save
+system registers, and hardware PTE's.
+
+Fadump is supported only on ppc64 platform. The standard kernel and capture
+kernel are one and the same on ppc64.
+
+If you're reading this document, you should already have kexec-tools
+installed. If not, you install it via the following command:
+
+ # yum install kexec-tools
+
+Fadump Operational Flow:
+
+Like kdump, fadump also exports the ELF formatted kernel crash dump through
+/proc/vmcore. Hence existing kdump infrastructure can be used to capture fadump
+vmcore. The idea is to keep the functionality transparent to end user. From
+user perspective there is no change in the way kdump init script works.
+
+However, unlike kdump, fadump does not pre-load kdump kernel and initrd into
+reserved memory, instead it always uses default OS initrd during second boot
+after crash. Hence, for fadump, we rebuild the new kdump initrd and replace it
+with default initrd. Before replacing existing default initrd we take a backup
+of original default initrd which is restored back when user decides to switch
+to kdump. The dracut package has been enhanced to rebuild the default initrd
+with vmcore capture steps as per /etc/kdump.conf
+
+The control flow of fadump works as follows:
+01. System panics.
+02. At the crash, kernel informs power firmware that kernel has crashed.
+03. Firmware takes the control and reboots the entire system preserving
+ only the memory (resets all other devices).
+04. The reboot follows the normal booting process (non-kexec).
+05. The boot loader loads the default kernel and initrd from /boot
+06. The default initrd loads and runs /init
+07. dracut-kdump.sh script present in fadump aware default initrd checks if
+ '/proc/vmcore' file exists before executing steps to capture vmcore.
+ (This check will help to bypass the vmcore capture steps during normal boot
+ process.)
+09. Captures dump according to /etc/kdump.conf
+10. Is dump capture successful (yes goto 12, no goto 11)
+11. Perfom the default action specified in /etc/kdump.conf (Default action
+ is reboot, if unspecified)
+12. Reboot
+
+
+How to configure fadump:
+
+Again, we assume if you're reading this document, you should already have
+kexec-tools installed. If not, you install it via the following command:
+
+ # yum install kexec-tools
+
+To be able to do much of anything interesting in the way of debug analysis,
+you'll also need to install the kernel-debuginfo package, of the same arch
+as your running kernel, and the crash utility:
+
+ # yum --enablerepo=\*debuginfo install kernel-debuginfo.$(uname -m) crash
+
+Next up, we need to modify some boot parameters to enable firmware assisted
+dump. With the help of grubby, it's very easy to append "fadump=on" to the
end
+of your kernel boot parameters. Optionally, user can also append
+'fadump_reserve_mem=X' kernel cmdline to specify size of the memory to reserve
+for boot memory dump preservation.
+
+ # grubby --args="fadump=on" --update-kernel=/boot/vmlinuz-`uname -r`
+
+The term 'boot memory' means size of the low memory chunk that is required for
+a kernel to boot successfully when booted with restricted memory. By default,
+the boot memory size will be the larger of 5% of system RAM or 256MB.
+Alternatively, user can also specify boot memory size through boot parameter
+'fadump_reserve_mem=' which will override the default calculated size. Use this
+option if default boot memory size is not sufficient for second kernel to boot
+successfully.
+
+After making said changes, reboot your system, so that the specified memory is
+reserved and left untouched by the normal system. Take note that the output of
+'free -m' will show X MB less memory than without this parameter, which is
+expected. If you see OOM (Out Of Memory) error messages while loading capture
+kernel, then you should bump up the memory reservation size.
+
+Now that you've got that reserved memory region set up, you want to turn on
+the kdump init script:
+
+ # chkconfig kdump on
should be changed to systemctl enable kdump.service
+
+Then, start up kdump as well:
+
+ # systemctl start kdump.service
+
+This should turn on the firmware assisted functionality in kernel by
+echo'ing 1 to /sys/kernel/fadump_registered, leaving the system ready
+to capture a vmcore upon crashing. To test this out, you can force-crash
+your system by echo'ing a c into /proc/sysrq-trigger:
+
+ # echo c > /proc/sysrq-trigger
+
+You should see some panic output, followed by the system reset and booting into
+fresh copy of kernel. When default initrd loads and runs /init, vmcore should
+be copied out to disk (by default, in /var/crash/<YYYY-MM-DD-HH:MM>/vmcore),
The date format is date +%Y.%m.%d-%T which would be expanded to:
%Y.%m.%d-%H:%M:%S
+then the system rebooted back into your normal kernel.
+
+Once back to your normal kernel, you can use the previously installed crash
+kernel in conjunction with the previously installed kernel-debuginfo to
+perform postmortem analysis:
+
+ # crash /usr/lib/debug/lib/modules/2.6.17-1.2621.el5/vmlinux
+ /var/crash/2006-08-23-15:34/vmcore
+
+ crash> bt
+
+and so on...
+
+Saving vmcore-dmesg.txt
+----------------------
+Kernel log bufferes are one of the most important information available
+in vmcore. Now before saving vmcore, kernel log bufferes are extracted
+from /proc/vmcore and saved into a file vmcore-dmesg.txt. After
+vmcore-dmesg.txt, vmcore is saved. Destination disk and directory for
+vmcore-dmesg.txt is same as vmcore. Note that kernel log buffers will
+not be available if dump target is raw device.
+
+Dump Triggering methods:
+
+This section talks about the various ways, other than a Kernel Panic, in which
+fadump can be triggered. The following methods assume that fadump is configured
+on your system, with the scripts enabled as described in the section above.
+
+1) AltSysRq C
+
+FAdump can be triggered with the combination of the 'Alt','SysRq' and
'C'
+keyboard keys. Please refer to the following link for more details:
+
+http://kbase.redhat.com/faq/FAQ_43_5559.shtm
+
+In addition, on PowerPC boxes, fadump can also be triggered via Hardware
+Management Console(HMC) using 'Ctrl', 'O' and 'C' keyboard
keys.
+
+2) Kernel OOPs
+
+If we want to generate a dump everytime the Kernel OOPses, we can achieve this
+by setting the 'Panic On OOPs' option as follows:
+
+ # echo 1 > /proc/sys/kernel/panic_on_oops
+
+3) PowerPC specific methods:
+
+On IBM PowerPC machines, issuing a soft reset invokes the XMON debugger(if
+XMON is configured). To configure XMON one needs to compile the kernel with
+the CONFIG_XMON and CONFIG_XMON_DEFAULT options, or by compiling with
+CONFIG_XMON and booting the kernel with xmon=on option.
+
+Following are the ways to remotely issue a soft reset on PowerPC boxes, which
+would drop you to XMON. Pressing a 'X' (capital alphabet X) followed by an
+'Enter' here will trigger the dump.
+
+3.1) HMC
+
+Hardware Management Console(HMC) available on Power4 and Power5 machines allow
+partitions to be reset remotely. This is specially useful in hang situations
+where the system is not accepting any keyboard inputs.
+
+Once you have HMC configured, the following steps will enable you to trigger
+fadump via a soft reset:
+
+On Power4
+ Using GUI
+
+ * In the right pane, right click on the partition you wish to dump.
+ * Select "Operating System->Reset".
+ * Select "Soft Reset".
+ * Select "Yes".
+
+ Using HMC Commandline
+
+ # reset_partition -m <machine> -p <partition> -t soft
+
+On Power5
+ Using GUI
+
+ * In the right pane, right click on the partition you wish to dump.
+ * Select "Restart Partition".
+ * Select "Dump".
+ * Select "OK".
+
+ Using HMC Commandline
+
+ # chsysstate -m <managed system name> -n <lpar name> -o dumprestart -r
lpar
+
+3.2) Blade Management Console for Blade Center
+
+To initiate a dump operation, go to Power/Restart option under "Blade Tasks"
in
+the Blade Management Console. Select the corresponding blade for which you want
+to initate the dump and then click "Restart blade with NMI". This issues a
+system reset and invokes xmon debugger.
+
+
+Advanced Setups:
Is these duplicate chunks really necessary, I would suggest change this file
for fadump only, and keep the general part in original howto so we only need
update one file when we need update it in the future. I means but not limited
to below sections about kdump configuration related stuff..
+
+In addition to being able to capture a vmcore to your system's local file
+system, fadump can be configured to capture a vmcore to a number of other
+locations, including a raw disk partition, a dedicated file system, an NFS
+mounted file system, or a remote system via ssh/scp. Additional options
+exist for specifying the relative path under which the dump is captured,
+what to do if the capture fails, and for compressing and filtering the dump
+(so as to produce smaller, more manageable, vmcore files).
+
+In theory, dumping to a location other than the local file system should be
+safer than fadump's default setup, as its possible the default setup will try
+dumping to a file system that has become corrupted. The raw disk partition and
+dedicated file system options allow you to still dump to the local system,
+but without having to remount your possibly corrupted file system(s),
+thereby decreasing the chance a vmcore won't be captured. Dumping to an
+NFS server or remote system via ssh/scp also has this advantage, as well
+as allowing for the centralization of vmcore files, should you have several
+systems from which you'd like to obtain vmcore files. Of course, note that
+these configurations could present problems if your network is unreliable.
+
+Advanced setups are configured via modifications to /etc/kdump.conf,
+which out of the box, is fairly well documented itself. Any alterations to
+/etc/kdump.conf should be followed by a restart of the kdump service, so
+the changes can be incorporated in the fadump aware default initrd. Restarting
+the kdump service is as simple as '/sbin/systemctl restart kdump.service'.
+
+
+Note that kdump.conf is used as a configuration mechanism for capturing dump
+files from the initramfs (in the interests of safety), the root file system is
+mounted, and the init process is started, only as a last resort if the
+initramfs fails to capture the vmcore. As such, configuration made in
+/etc/kdump.conf is only applicable to capture recorded in the initramfs. If
+for any reason the init process is started on the root file system, only a
+simple copying of the vmcore from /proc/vmcore to /var/crash/$DATE/vmcore will
+be performed.
+
+For both local filesystem and nfs dump the dump target must be mounted before
+building fadump aware initramfs. That means one needs to put an entry for the
+dump file system in /etc/fstab so that after reboot when kdump service starts,
+it can find the dump target and build initramfs instead of failing.
+Usually the dump target should be used only for fadump. If you worry about
+someone uses the filesystem for something else other than dumping vmcore
+you can mount it as read-only. Mkdumprd will still remount it as read-write
+for creating dump directory and will move it back to read-only afterwards.
+
+Raw partition
+
+Raw partition dumping requires that a disk partition in the system, at least
+as large as the amount of memory in the system, be left unformatted. Assuming
+/dev/vg/lv_kdump is left unformatted, kdump.conf can be configured with
+'raw /dev/vg/lv_kdump', and the vmcore file will be copied via dd directly
+onto partition /dev/vg/lv_kdump. Restart the kdump service via
+'/sbin/systemctl restart kdump.service' to commit this change to your fadump
+aware default initrd. Dump target should be persistent device name, such as lvm
+or device mapper canonical name.
+
+Dedicated file system
+
+Similar to raw partition dumping, you can format a partition with the file
+system of your choice, Again, it should be at least as large as the amount
+of memory in the system. Assuming it should be at least as large as the
+amount of memory in the system. Assuming /dev/vg/lv_kdump has been
+formatted ext4, specify 'ext4 /dev/vg/lv_kdump' in kdump.conf, and a
+vmcore file will be copied onto the file system after it has been mounted.
+Dumping to a dedicated partition has the advantage that you can dump multiple
+vmcores to the file system, space permitting, without overwriting previous ones,
+as would be the case in a raw partition setup. Restart the kdump service via
+'/sbin/systemctl restart kdump.service' to commit this change to
+your fadump aware default initrd. Note that for local file systems ext4 and
+ext2 are supported as dumpable targets. Kdump will not prevent you from
+specifying other filesystems, and they will most likely work, but their
+operation cannot be guaranteed. For instance specifying a vfat filesystem or
+msdos filesystem will result in a successful load of the kdump service, but
+during crash recovery, the dump will fail if the system has more than 2GB of
+memory (since vfat and msdos filesystems do not support more than 2GB files).
+Be careful of your filesystem selection when using this target.
+
+It is recommended to use persistent device names or UUID/LABEL for file system
+dumps. One example of persistent device is /dev/vg/<devname>.
+
+NFS mount
+
+Dumping over NFS requires an NFS server configured to export a file system
+with full read/write access for the root user. All operations done within
+the fadump aware default initrd are done as root, and to write out a vmcore
+file, we obviously must be able to write to the NFS mount. Configuring an NFS
+server is outside the scope of this document, but either the no_root_squash
+or anonuid options on the NFS server side are likely of interest to permit
+the fadump aware default initrd operations write to the NFS mount as root.
+
+Assuming your're exporting /dump on the machine
nfs-server.example.com,
+once the mount is properly configured, specify it in kdump.conf, via
+'nfs nfs-server.example.com:/dump'. The server portion can be specified either
+by host name or IP address. Following a system crash, the fadump aware default
+initrd will mount the NFS mount and copy out the vmcore to your NFS server.
+Restart the kdump service via '/sbin/systemctl restart kdump.service' to commit
+this change to your fadump aware initrd.
+
+Remote system via ssh/scp
+
+Dumping over ssh/scp requires setting up passwordless ssh keys for every
+machine you wish to have dump via this method. First up, configure kdump.conf
+for ssh/scp dumping, adding a config line of 'ssh user@server', where
'user'
+can be any user on the target system you choose, and 'server' is the host
+name or IP address of the target system. Using a dedicated, restricted user
+account on the target system is recommended, as there will be keyless ssh
+access to this account.
+
+Once kdump.conf is appropriately configured, issue the command
+'kdumpctl propagate' to automatically set up the ssh host keys and transmit
+the necessary bits to the target server. You'll have to type in 'yes'
+to accept the host key for your targer server if this is the first time
+you've connected to it, and then input the target system user's password
+to send over the necessary ssh key file. Restart the kdump service via
+'/sbin/systemctl restart kdump.service' to commit this change to the fadump
+aware default initrd.
+
+Path
+
+By default, local file system vmcore files are written to /var/crash/%DATE
+on the local system, ssh/scp dumps to /var/crash/%HOST-%DATE on the target
+system, dedicated file system partition dumps to ./var/crash/%DATE, and
+NFS dumps to ./var/crash/%HOST-%DATE, the latter two both relative to
+their respective mount points within the fadump initrd (usually /mnt). The
+'/var/crash' portion of the path can be overridden using kdump.conf's
'path'
+variable, should you wish to write the vmcore out to a different location. For
+example, 'path /data/coredumps' would lead to vmcore files being written to
+/data/coredumps/%DATE if you were dumping to your local file system. Note
+that the path option is ignored if your kdump configuration results in the
+core being saved from the initscripts in the root filesystem.
+
+Kdump Post-Capture Executable
+
+It is possible to specify a custom script or binary you wish to run following
+an attempt to capture a vmcore. The executable is passed an exit code from
+the capture process, which can be used to trigger different actions from
+within your post-capture executable.
+
+Kdump Pre-Capture Executable
+
+It is possible to specify a custom script or binary you wish to run before
+capturing a vmcore. Exit status of this binary is interpreted:
+0 - continue with dump process as usual
+non 0 - reboot the system
+
+Extra Binaries
+
+If you have specific binaries or scripts you want to have made available
+within your fadump aware default initrd, you can specify them by their full
+path, and they will be included in your initrd, along with all dependent
+libraries. This may be particularly useful for those running post-capture
+scripts that rely on other binaries.
+
+Extra Modules
+
+By default, only the bare minimum of kernel modules will be included in your
+fadump aware default initrd. Should you wish to capture your vmcore files to a
+non-boot-path storage device, such as an iscsi target disk or clustered file
+system, you may need to manually specify additional kernel modules to load into
+your fadump aware default initrd.
+
+Default action
+==============
+Default action specifies what to do when dump to configured dump target
+fails. By default, default action is "reboot" and that is system reboots
+if attempt to save dump to dump target fails.
+
+There are other default actions available though.
+
+- dump_to_rootfs
+ This option tries to mount root and save dump on root filesystem
+ in a path specified by "path". This option will generally make
+ sense when dump target is not root filesystem. For example, if
+ dump is being saved over network using "ssh" then one can specify
+ default to "dump_to_rootfs" to try saving dump to root filesystem
+ if dump over network fails.
+
+- shell
+ Drop into a shell session inside initramfs.
+- halt
+ Halt system after failure
+- poweroff
+ Poweroff system after failure.
+
+Compression and filtering
+
+Refer "Compression and filtering" section in "kexec-kdump-howto.txt"
document.
+Compression and filtering are same for kdump & fadump.
+
+
+Notes on rootfs mount:
+Dracut is designed to mount rootfs by default. If rootfs mounting fails it
+will refuse to go on. So fadump leaves rootfs mounting to dracut currently.
+We make the assumtion that proper root= cmdline is being passed to dracut
+initramfs for the time being. If you need modify "KDUMP_COMMANDLINE=" in
+/etc/sysconfig/kdump, you will need to make sure that appropriate root=
+options are copied from /proc/cmdline. In general it is best to append
+command line options using "KDUMP_COMMANDLINE_APPEND=" instead of replacing
+the original command line completely.
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