Jan 14, 2016
blogd - boot logging on /dev/console
The blogd daemon determines the real underlying character device of /dev/console. blogd spawns a pty/tty pair to reconnect the current /dev/console with the slave of the pty/tty pair. During writing information from this slave to the real character device a ring buffer is used to hold the information for writing it to an existing logging file.
To fetch the real tty of /dev/console the program showconsole(8) can be used. This has the advantage that blogd will not hold the real character device of /dev/console as its controlling tty (would hangup any running getty on that character device).
|-f||This option is used at shutdown, that is reboot, halt, and poweroff but also for kexec.|
blogd knows a few signal to contol its behavior.
|SIGQUIT, SIGINT, and SIGTERM|
|will cause blogd tries to write out the ring buffer and to exit.|
|SIGIO||says blogd that now it is able to write on /var/log/boot.log which means that the file system is mounted read/write and the kernel messages are written to that file. After a reboot the file /var/log/boot.old may exists where the former messages can be found including the messages at shutdown upto the point where the file systems become unmounted.|
|SIGSYS||says blogd that it should stop writing to disk but continue to repeat messages to the old devices of the system console.|
blogd needs a mounted /proc and /dev/pts file system and tries to set the controlling tty to stdin if the real character device of /dev/console is not given. After reading /proc blogd tries to restore the status of the controlling tty to avoid problems with getty processes. This can fail because blogd forks to run in the background as a daemon.
|/proc/<pid of blogd>/stat|
|the stat file of the blogd process.|
|the system console.|
|logging file which is created by blogd(8)|
2000,2015 Werner Fink, 2000 SuSE GmbH Nuernberg, Germany, 2015 SuSE Linux GmbH.
Werner Fink <werner>