Update docs for the new noauto dump target support
Signed-off-by: Kairui Song <kasong@redhat.com> Acked-by: Pingfan Liu <piliu@redhat.com>
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Kairui Song
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846e23a2d5
@ -283,11 +283,8 @@ to initate the dump and then click "Restart blade with NMI". This issues a
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system reset and invokes xmon debugger.
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Advanced Setups
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===============
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Dump targets
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------------
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============
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In addition to being able to capture a vmcore to your system's local file
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system, kdump can be configured to capture a vmcore to a number of other
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@ -295,7 +292,8 @@ locations, including a raw disk partition, a dedicated file system, an NFS
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mounted file system, or a remote system via ssh/scp. Additional options
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exist for specifying the relative path under which the dump is captured,
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what to do if the capture fails, and for compressing and filtering the dump
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(so as to produce smaller, more manageable, vmcore files).
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(so as to produce smaller, more manageable, vmcore files, see "Advanced Setups"
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for more detail on these options).
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In theory, dumping to a location other than the local file system should be
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safer than kdump's default setup, as its possible the default setup will try
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@ -308,31 +306,131 @@ as allowing for the centralization of vmcore files, should you have several
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systems from which you'd like to obtain vmcore files. Of course, note that
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these configurations could present problems if your network is unreliable.
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Advanced setups are configured via modifications to /etc/kdump.conf,
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which out of the box, is fairly well documented itself. Any alterations to
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/etc/kdump.conf should be followed by a restart of the kdump service, so
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the changes can be incorporated in the kdump initrd. Restarting the kdump
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service is as simple as '/sbin/systemctl restart kdump.service'.
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Kdump target and advanced setups are configured via modifications to
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/etc/kdump.conf, which out of the box, is fairly well documented itself.
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Any alterations to /etc/kdump.conf should be followed by a restart of the
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kdump service, so the changes can be incorporated in the kdump initrd.
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Restarting the kdump service is as simple as '/sbin/systemctl restart kdump.service'.
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Note that kdump.conf is used as a configuration mechanism for capturing dump
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files from the initramfs (in the interests of safety), the root file system is
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mounted, and the init process is started, only as a last resort if the
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initramfs fails to capture the vmcore. As such, configuration made in
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/etc/kdump.conf is only applicable to capture recorded in the initramfs. If
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for any reason the init process is started on the root file system, only a
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simple copying of the vmcore from /proc/vmcore to /var/crash/$DATE/vmcore will
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be preformed.
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There are two ways to config the dump target, config dump target only
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using "path", and config dump target explicitly. Interpretation of "path"
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also differs in two config styles.
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Config dump target only using "path"
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------------------------------------
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You can change the dump target by setting "path" to a mount point where
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dump target is mounted. When there is no explicitly configured dump target,
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"path" in kdump.conf represents the current file system path in which vmcore
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will be saved. Kdump will automatically detect the underlying device of
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"path" and use that as the dump target.
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In fact, upon dump, kdump creates a directory $hostip-$date with-in "path"
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and saves vmcore there. So practically dump is saved in $path/$hostip-$date/.
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Kdump will only check current mount status for mount entry corresponding to
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"path". So please ensure the dump target is mounted on "path" before kdump
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service starts.
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NOTES:
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- It's strongly recommanded to put an mount entry for "path" in /etc/fstab
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and have it auto mounted on boot. This make sure the dump target is
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reachable from the machine and kdump's configuration is stable.
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EXAMPLES:
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- path /var/crash/
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This is the default configuration. Assuming there is no disk mounted
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on /var/ or on /var/crash, dump will be saved on disk backing rootfs
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in directory /var/crash.
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- path /var/crash/ (A separate disk mounted on /var/crash)
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Say a disk /dev/sdb is mounted on /var. In this case dump target will
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become /dev/sdb and path will become "/" and dump will be saved
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on "sdb:/var/crash/" directory.
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- path /var/crash/ (NFS mounted on /var)
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Say foo.com:/export/tmp is mounted on /var. In this case dump target is
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nfs server and path will be adjusted to "/crash" and dump will be saved to
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foo.com:/export/tmp/crash/ directory.
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Config dump target explicitely
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------------------------------
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You can set the dump target explicitly in kdump.conf, and "path" will be
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the relative path in the specified dump target. For example, if dump
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target is "ext4 /dev/sda", then dump will be saved in "path" directory
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on /dev/sda.
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Same is the case for nfs dump. If user specified "nfs foo.com:/export/tmp/"
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as dump target, then dump will effectively be saved in
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"foo.com:/export/tmp/var/crash/" directory.
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If the dump target is "raw", then "path" is ignored.
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If it's a filesystem target, kdump will need to know the right mount option.
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Kdump will check current mount status, and then /etc/fstab for mount options
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corresponding to the specified dump target and use it. If there are
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special mount option required for the dump target, it could be set by put
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an entry in fstab.
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If there are no related mount entry, mount option is set to "defaults".
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NOTES:
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- It's recommended to put an entry for the dump target in /etc/fstab
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and have it auto mounted on boot. This make sure the dump target is
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reachable from the machine and kdump won't fail.
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- Kdump ignores some mount options, including "noauto", "ro". This
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make it possible to keep the dump target unmounted or read-only
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when not used.
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EXAMPLES:
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- ext4 /dev/sda (mounted)
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path /var/crash/
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In this case dump target is set to /dev/sdb, path is the absolute path
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"/var/crash" in /dev/sda, vmcore path will saved on
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"sda:/var/crash" directory.
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- nfs foo.com:/export/tmp (mounted)
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path /var/crash/
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In this case dump target is nfs server, path is the absolute path
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"/var/crash", vmcore path will saved on "foo.com:/export/tmp/crash/" directory.
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- nfs foo.com:/export/tmp (not mounted)
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path /var/crash/
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Same with above case, kdump will use "defaults" as the mount option
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for the dump target.
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- nfs foo.com:/export/tmp (not mounted, entry with option "noauto,nolock" exists in /etc/fstab)
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path /var/crash/
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In this case dump target is nfs server, vmcore path will saved on
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"foo.com:/export/tmp/crash/" directory, and kdump will inherit "nolock" option.
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Dump target and mkdumprd
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------------------------
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MKdumprd is the tool used to create kdump initramfs, and it may change
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the mount status of the dump target in some condition.
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For both local filesystem and nfs dump the dump target must be mounted before
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building kdump initramfs. That means one needs to put an entry for the dump
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file system in /etc/fstab so that after reboot when kdump service starts,
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it can find the dump target and build initramfs instead of failing.
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Usually the dump target should be used only for kdump. If you worry about
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someone uses the filesystem for something else other than dumping vmcore
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you can mount it as read-only. Mkdumprd will still remount it as read-write
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for creating dump directory and will move it back to read-only afterwards.
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you can mount it as read-only or make it a noauto mount. Mkdumprd will
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mount/remount it as read-write for creating dump directory and will
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move it back to it's original state afterwards.
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Followings are the available config options for dump targets.
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Supported dump target types and requirements
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--------------------------------------------
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1) Raw partition
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@ -423,47 +521,8 @@ you've connected to it, and then input the target system user's password
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to send over the necessary ssh key file. Restart the kdump service via
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'/sbin/systemctl restart kdump.service' to commit this change to your kdump initrd.
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Path
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----
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"path" represents the file system path in which vmcore will be saved. In
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fact kdump creates a directory $hostip-$date with-in "path" and saves
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vmcore there. So practically dump is saved in $path/$hostip-$date/. To
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simplify discussion further, if we say dump will be saved in $path, it
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is implied that kdump will create another directory inside path and
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save vmcore there.
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If a dump target is specified in kdump.conf, then "path" is relative to the
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specified dump target. For example, if dump target is "ext4 /dev/sda", then
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dump will be saved in "$path" directory on /dev/sda.
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Same is the case for nfs dump. If user specified "nfs foo.com:/export/tmp/"
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as dump target, then dump will effectively be saved in
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"foo.com:/export/tmp/var/crash/" directory.
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Interpretation of path changes a bit if user has not specified a dump
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target explicitly in kdump.conf. In this case, "path" represents the
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absolute path from root. And dump target and adjusted path are arrived
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at automatically depending on what's mounted in the current system.
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Following are few examples.
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- path /var/crash/
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Assuming there is no disk mounted on /var/ or on /var/crash, dump will
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be saved on disk backing rootfs in directory /var/crash.
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- path /var/crash/ (A separate disk mounted on /var)
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Say a disk /dev/sdb is mouted on /var. In this case dump target will
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become /dev/sdb and path will become "/crash" and dump will be saved
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on "sdb:/crash/" directory.
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- path /var/crash/ (NFS mounted on /var)
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Say foo.com:/export/tmp is mounted on /var. In this case dump target is
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nfs server and path will be adjusted to "/crash" and dump will be saved to
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foo.com:/export/tmp/crash/ directory.
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Advanced Setups
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===============
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Kdump boot directory
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--------------------
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