Debian allows you to record boot messages by means of the bootlogd daemon. According to man pages:
Bootlogd runs in the background and copies all strings sent to the /dev/console device to a logfile. If the logfile is not accessible, the messages will be kept in memory until it is.
This feature is not enabled by default. Edit /etc/default/bootlogd and modify it to enable recording of boot messages:
# Run bootlogd at startup ?
BOOTLOGD_ENABLE=Yes
Now bootlogd will start sending boot messages to /var/log/boot.
Tags: Linux