Persistent Log Support

By default, system logs generated by the Linux® microPlatform (LmP) are stored in a tmpfs mount point (/var/volatile), without persistent support across reboots.

This is done to minimize both the number of write operations to the disk (stored in memory), and the amount of disk space used.

While storing the system log in memory can reduce the load on the disk, this may not always be desired. Especially during development, being able to restore the log from previous boots can provide useful information.

Follow the instructions below to enable persistent logging support.

Disable OpenEmbedded VOLATILE_LOG_DIR

OpenEmbedded controls the /var/log behavior via the variable VOLATILE_LOG_DIR, which is enabled by default. This links /var/log to /var/volatile/log (/var/volatile is a tmpfs mount point). When disabled, /var/log is set as a normal directory, making it persistent.

Add the following to meta-subscriber-overrides/conf/machine/include/lmp-factory-custom.inc to disable VOLATILE_LOG_DIR:

VOLATILE_LOG_DIR = "no"

Add systemd-journald-persistent to Your Image

The recipe systemd-journald-persistent (in meta-updater) provides a default configuration file for systemd-journald. This enables persistent logging support. The default limit is set at 64M, which is safe for most deployments.

Add systemd-journald-persistent to meta-subscriber-overrides/recipes-samples/images/lmp-factory-image.bb (or any other image used by your meta-subscriber-overrides layer), as described in Adding Packages to the Image.

Optional: Customize systemd-journald Options

Note

Special attention is required when defining your own systemd-journald configuration file. A high SystemMaxUse value may cause the logging to consume a substantial amount of disk space.

Create your own systemd-journald configuration file by overriding 10-persistent-journal.conf. This is used by the systemd-journald-persistent recipe. Within your meta-subscriber-overrides layer:

$ cat recipes-support/systemd-journald-persistent/systemd-journald-persistent.bbappend
FILESEXTRAPATHS:prepend := "${THISDIR}/files:"

And:

$ cat recipes-support/systemd-journald-persistent/files/10-persistent-journal.conf
[Journal]
Storage=persistent
SystemMaxUse=32M
SystemMaxFiles=10
SyncIntervalSec=60

For the complete list of options supported by journald please check the journald.conf manual.