klog(7)

NAME
     klog - kernel error logging interface

DESCRIPTION
     Minor device 0 of the klog driver is the interface between a process and
     the kernel's error logging mechanism.  When this device is open, messages
     printed by the kernel, which normally appear only in the system console
     window, also are buffered by the klog driver.  The data obtained by
     reading from this driver are the text of the kernel messages.  The driver
     may be opened only for reading by a single process.  Each read causes the
     requested number of bytes to be retrieved; the request is truncated if
     the read request is for more than the data currently available.

     Normally, this device is opened and read by syslogd(1M), the system
     logging daemon.

     This special device supports the following open(2) flags:

          O_NDELAY
               When set a read will not block if no data is present.  If not
               set, a read will block until information becomes available.

     Each ioctl(2) call that this special device supports has the form:

          ioctl(fd, cmd, arg)

     where the format and meaning of arg vary with the specified cmd as
     described below:

          FIONREAD
               Returns the number of bytes currently available to read to the
               area pointed to by arg, where arg is treated as a pointer to a
               variable of type size_t.

          FIONBIO
               Enables or disables non-blocking mode, according to the boolean
               value supplied as arg.  Enabling this mode has the same affect
               as the O_NDELAY flag for open(2).

          FIOASYNC
               Enables or disables asynchronous mode, according to the boolean
               value supplied as arg.  When asynchronous mode is enabled, the
               process group associated with the open of the special device
               receives a SIGIO signal when data is available to be read.

          TIOCSPGRP
               Set the process group for use with asynchronous I/O (FIOASYNC).
               For this command, arg should contain the process group id.

          TIOCGPGRP
               Returns the current process group to the area pointed to by
               arg, where arg is treated as a pointer to a variable of type
               int.

FILES
     /dev/klog special file

SEE ALSO
     open(2), ioctl(2), syslogd(1M)