systemd-pstore.service, systemd-pstore - A service to archive contents of pstore
/lib/systemd/systemd-pstore
systemd-pstore.service
systemd-pstore.service is a system service that archives the contents of the
Linux persistent storage filesystem, pstore, to other storage, thus preserving
the existing information contained in the pstore, and clearing pstore storage
for future error events.
Linux provides a persistent storage file system, pstore, that can store error
records when the kernel dies (or reboots or powers-off). These records in turn
can be referenced to debug kernel problems (currently the kernel stores the
tail of the kernel log, which also contains a stack backtrace, into pstore).
The pstore file system supports a variety of backends that map onto persistent
storage, such as the ACPI ERST and UEFI variables. The pstore backends
typically offer a relatively small amount of persistent storage, e.g. 64KiB,
which can quickly fill up and thus prevent subsequent kernel crashes from
recording errors. Thus there is a need to monitor and extract the pstore
contents so that future kernel problems can also record information in the
pstore.
The pstore service is independent of the kdump service. In cloud environments
specifically, host and guest filesystems are on remote filesystems (e.g. iSCSI
or NFS), thus kdump relies (implicitly and/or explicitly) upon proper
operation of networking software *and* hardware *and* infrastructure. Thus it
may not be possible to capture a kernel coredump to a file since writes over
the network may not be possible.
The pstore backend, on the other hand, is completely local and provides a path
to store error records which will survive a reboot and aid in post-mortem
debugging.
The
systemd-pstore executable does the actual work. Upon starting, the
pstore.conf file is read and the /sys/fs/pstore/ directory contents are
processed according to the options. Pstore files are written to the journal,
and optionally saved into /var/lib/systemd/pstore/.
The behavior of
systemd-pstore is configured through the configuration
file /etc/systemd/pstore.conf and corresponding snippets
/etc/systemd/pstore.conf.d/*.conf, see
pstore.conf(5).
To disable pstore processing by
systemd-pstore, set
in
pstore.conf(5).
The kernel has two parameters,
/sys/module/kernel/parameters/crash_kexec_post_notifiers and
/sys/module/printk/parameters/always_kmsg_dump, that control writes into
pstore. The first enables storing of the kernel log (including stack trace)
into pstore upon a panic or crash, and the second enables storing of the
kernel log upon a normal shutdown (shutdown, reboot, halt). These parameters
can be managed via the
tmpfiles.d(5) mechanism, specifically the file
/usr/lib/tmpfiles/systemd-pstore.conf.
Data stored in the journal can be viewed with
journalctl(1) as usual.
pstore.conf(5)