Journald is a system service for collecting and storing log data, introduced with systemd. It tries to make it easier for system administrators to find interesting and relevant information among an ever-increasing amount of log messages.
To avoid excessive wear of the limited flash memory on Toradex modules, the journald data is stored in RAM only by default. To debug certain aspects such as unexpected reboots, it is handy to activate persistent journald logging, so the log messages of previous boot cycles can be reviewed.
Edit the file /etc/systemd/journald.conf
Modify the line
Edit the file /etc/tmpfiles.d/00-create-volatile.conf
delete the following line
d /var/volatile/log 1777 - -
Delete the symbolic link to the log folder
# rm /var/log
reboot the module twice
list all boot cycles, and display the detailed messages of the previous (not the current) boot cycle
# journalctl --list-boots # journalctl -b -1