CONS(3)                                                   CONS(3)

     NAME
          cons - console, clocks, process/process group ids, user,
          null, reboot, etc.

     SYNOPSIS
          bind #c /dev

          /dev/bintime
          /dev/config
          /dev/cons
          /dev/cputime
          /dev/drivers
          /dev/hostdomain
          /dev/hostowner
          /dev/kmesg
          /dev/kprint
          /dev/mordor
          /dev/null
          /dev/osversion
          /dev/pgrpid
          /dev/pid
          /dev/ppid
          /dev/random
          /dev/reboot
          /dev/swap
          /dev/sysname
          /dev/sysstat
          /dev/time
          /dev/user
          /dev/zero

     DESCRIPTION
          The console device serves a one-level directory giving
          access to the console screen and miscellaneous information.

          A write (see read(2)) to cons causes the characters to be
          printed on the console screen. Console input is handled by a
          different program (see kbdfs(8)).

          The osversion file contains a textual representation of the
          operating system's version and parameters.  At the moment,
          it contains one field: the 9P protocol version, currently
          2000.

          The config file contains a copy of the kernel configuration
          file used to build the kernel.

          The kmesg file holds the last 16 kilobytes of output written
          to the console by the kernel's print statements or by pro-
          cesses writing to /dev/cons.  It is useful for retrieving

     CONS(3)                                                   CONS(3)

          boot messages once the boot process is over.

          The kprint file may be read to receive a copy of the data
          written to the console by the kernel's print statements or
          by processes writing to /dev/cons.  Only data written after
          the file is opened is available.  If the machine's console
          is a serial line, the data is sent both to the console and
          to kprint; if its console is a graphics screen, the data is
          sent either to the display or to kprint, but not both.  (It
          is advisable not to open kprint on terminals until you have
          started rio(1).)

          The null file throws away anything written to it and always
          returns zero when read.

          The zero file is a read-only file that produces an infinite
          stream of zero-valued bytes when read.

          The drivers file contains, one per line, a listing of the
          drivers configured in the kernel, in the format

               #c cons

          The hostdomain file contains the name of the authentication
          domain that this host belongs to; see authsrv(6). Only the
          user named in /dev/hostowner may write this.

          The hostowner file contains the name of the user that owns
          the console device files.  The hostowner also has group per-
          missions for any local devices.

          Reads from random return a stream of random bytes produced
          by the kernels cryptographic random number generator. The
          rate at which data can be read depends on the implementation
          and can vary from hundreds of megabytes to just a few hun-
          dred bits a second. Therefore, random should be treated as a
          seed to pseudo-random number generators which can produce a
          faster rate stream.

          Writing the string reboot to reboot causes the system to
          shutdown and, if possible, restart.  Writing the string
          reboot kernelpath loads the named kernel image and restarts,
          preserving the kernel configuration in #ec, except that the
          bootfile variable is set to kernelpath. Writing the string
          rdb activates the remote kernel debugger (see rdbfs(4)).
          Only the host owner has the ability to open this file.

          Bintime is a binary interface that provides the same infor-
          mation as time (q.v.), in binary form, and also controls
          clock frequency and clock trim.  All integers read or writ-
          ten from bintime are in big endian order.  Unlike the other
          files, reads and writes do not affect the offset.

     CONS(3)                                                   CONS(3)

          Therefore, there is no need for a seek back to zero between
          subsequent accesses.  A read of bintime returns 24 bytes,
          three 8 byte numbers, representing nanoseconds since start
          of epoch, clock ticks, and clock frequency.

          A write to bintime is a message with one of 3 formats:

          n<8-byte time>
                      set the nanoseconds since epoch to the given
                      time.

          d<8-byte delta><4-byte period>
                      trim the nanoseconds since epoch by delta over
                      the next period seconds.

          f<8-byte freq>
                      Set the frequency for interpreting clock ticks
                      to be freq ticks per second.

          The rest of the files contain (mostly) read-only strings.
          Each string has a fixed length: a read(2) of more than that
          gives a result of that fixed length (the result does not
          include a terminating zero byte); a read of less than that
          length leaves the file offset so the rest of the string (but
          no more) will be read the next time.  To reread the file
          without closing it, seek must be used to reset the offset.
          When the file contains numeric data each number is formatted
          in decimal.  If the binary number fits in 32 bits, it is
          formatted as an 11 digit decimal number with leading blanks
          and one trailing blank; totaling 12 bytes.  Otherwise, it is
          formatted as 21 digit decimal numbers with leading blanks
          and one trailing blank; totaling 22 bytes.

          The cputime file holds six 32-bit numbers, containing the
          time in milliseconds that the current process has spent in
          user mode, system calls, real elapsed time, and then the
          time spent, by exited children and their descendants, in
          user mode, system calls, and real elapsed time.

          The time file holds one 32-bit number representing the sec-
          onds since start of epoch and three 64-bit numbers, repre-
          senting nanoseconds since start of epoch, clock ticks, and
          clock frequency.

          A write of a decimal number to time will set the seconds
          since epoch.

          The sysname file holds the textual name of the machine, e.g.
          kremvax, if known.

          The sysstat file holds 10 numbers: processor number, context
          switches, interrupts, system calls, page faults, TLB faults,

     CONS(3)                                                   CONS(3)

          TLB purges, load average, idle time and time spent servicing
          interrupts.  The load average is in units of milli-CPUs and
          is decayed over time; idle time and interrupt time are per-
          centage units; the others are total counts from boot time.
          If the machine is a multiprocessor, sysstat holds one line
          per processor.  Writing anything to sysstat resets all of
          the counts on all processors.

          The swap device holds a text block giving memory usage
          statistics:

               n memory
               n pagesize
               n kernel
               n/m user
               n/m swap
               a/n/m kernel malloc
               a/n/m kernel draw

          These are total memory (bytes), system page size (bytes),
          kernel memory (pages), user memory (pages), swap space
          (pages), kernel malloced data (bytes), and kernel graphics
          data (bytes).  The expression n/m indicates n used out of m
          available.  For kernel malloc and kernel draw, a indicates
          the current allocation in bytes.  These numbers are not
          blank padded.

          To turn on swapping, write to swap the textual file descrip-
          tor number of a file or device on which to swap.  See
          swap(8).

          Reads and writes to mordor will inevitably cause the front
          to fall off.

          The other files served by the cons device are all single
          numbers:

          pgrpid    process group number

          pid       process number

          ppid      parent's process number

     SEE ALSO
          draw(3), kbd(3), kbdfs(8), keyboard(6), authsrv(6), utf(6),
          swap(8)

     SOURCE
          /sys/src/9/port/devcons.c