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Version 2.12
Jan 14, 2016


Boot logging


blogd - boot logging on /dev/console


/sbin/blogd [-f]


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.
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.
/var/log/boot.log, /var/log/boot.old
logging file which is created by blogd(8)


2000,2015 Werner Fink, 2000 SuSE GmbH Nuernberg, Germany, 2015 SuSE Linux GmbH.


Werner Fink <>
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