cons man page on Plan9

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CONS(3)								       CONS(3)

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

       bind #c /dev


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

       Reading	the  cons file returns characters typed on the keyboard.  Nor‐
       mally, characters are buffered to enable erase and kill processing.   A
       control-U,  typed at the keyboard kills the current input line (removes
       all characters from the buffer of characters not yet  read  via	cons),
       and  a backspace erases the previous non-kill, non-erase character from
       the input buffer.  Killing and erasing only delete characters back  to,
       but  not including, the last newline.  Characters typed at the keyboard
       actually produce 21-bit runes (see utf(6)), but the  runes  are	trans‐
       lated into the variable-length UTF encoding (see utf(6)) before putting
       them into the buffer.  A read(2) of length greater than zero causes the
       process	to wait until a newline or a ends the buffer, and then returns
       as much of the buffer as the argument to read allows, but  only	up  to
       one  complete line.  A terminating is not put into the buffer.  If part
       of the line remains, the next read will return bytes from that  remain‐
       der and not part of any new line that has been typed since.

       If  the	string rawon has been written to the consctl file and the file
       is still open, cons is in raw mode: characters are not echoed  as  they
       are typed, backspace, and are not treated specially, and characters are
       available to read as soon as they are typed.  Ordinary  mode  is	 reen‐
       tered when rawoff is written to consctl or this file is closed.

       A  write	 (see  read(2)) to cons causes the characters to be printed on
       the console screen.

       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	processes  writing  to
       /dev/cons.   It	is  useful  for retrieving 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 advis‐
       able 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  con‐
       figured 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/hos‐
       towner may write this.

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

       Reads  from  random return a stream of random numbers.  The numbers are
       generated by a low priority kernel process that	loops  incrementing  a
       variable.   Each	 clock	tick  the  variable  is sampled and, if it has
       changed sufficiently, the last few bits are appended to a buffer.  This
       process	is  inefficient at best producing at most a few hundred 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.  Only  the
       host  owner has the ability to open this file.  The named kernel may be
       a Plan 9 executable or a 32-bit or  64-bit  ELF	executable.   On  some
       architectures (e.g., mips), it may also be a Plan 9 boot image.

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

   Statistics and Dynamic Status
       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  mil‐
       liseconds  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

       The time file holds one 32-bit number representing  the	seconds	 since
       start of epoch and three 64-bit numbers, representing 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,  TLB	 purges,  load
       average, idle time and time spent servicing interrupts.	The load aver‐
       age is in units of milli-CPUs and is decayed over time; idle  time  and
       interrupt  time	are percentage 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
	      n/m kernel malloc
	      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	 indi‐
       cates n used out of m available.	 These numbers are not blank padded.

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

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

       pgrpid	 process group number

       pid	 process number

       ppid	 parent's process number

       draw(3), keyboard(6), authsrv(6), utf(6), swap(8)


       For debugging, two control-T's followed by a  letter  generate  console
       output  and manage debugging: toggles whether the console debugger will
       be run if the system fails.  starts the console	debugger  immediately.
       kills the largest process; use with care.  prints data about processes.
       prints the run queue for processor 0.  prints the kernel stack.	prints
       data about kernel memory allocation.

       The system can be rebooted by typing

                             _         _         _ 
                            | |       | |       | |     
                            | |       | |       | |     
                         __ | | __ __ | | __ __ | | __  
                         \ \| |/ / \ \| |/ / \ \| |/ /  
                          \ \ / /   \ \ / /   \ \ / /   
                           \   /     \   /     \   /    
                            \_/       \_/       \_/ 
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