cons - console, clocks, process/process group ids, user, null, klog, stats, lights, noise,
sysstat, hz, swap, key, hostowner, hostdomain, authenticate, authcheck, authenticator
bind #c /dev
The console device serves a one-level directory giving access to the console and miscella-
Reading the cons file returns characters typed on the keyboard. Normally, 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 16-bit runes (see
utf(6)), but the runes are translated 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 buf-
fer 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 remainder 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 reentered 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 null file throws away anything written to it and always returns zero bytes when read.
The klog file contains the tail of messages written by kernel logging statements.
Writing a number (as plain text) to the lights device directs any lights that are avail-
able to turn on and off. The bits of the number are mapped to the lights in a processor-
Writing two blank- or tab-separated numbers to the noise device causes the machine to make
a tone, if possible. The first number is the frequency, in Hertz, and the second is the
duration, in milliseconds.
The hostdomain file contains the name of the authentication domain that this host belongs
to; see auth(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 permissions for any local devices.
The key file is used to set the DES key used for encryption. Each machine has one key.
Only the user named in /dev/hostowner may write this.
The authenticate file is used to authenticate new users to the kernel; see auth(6). After
an open, the first read returns a ticket request message of the following form:
Here num is 1, authid and hostid are the contents of hostowner, and authdom is the con-
tents of hostdomain. Chal is an 8 byte random challenge created by the kernel. A subse-
quent write of a valid ticket encrypted with the key contained in key changes the user
name of the writing process to the value of suid in the ticket. The ticket is of the
The ticket is valid if num is 64 and chal matches the challenge in the ticket request.
Writing an invalid ticket generates an error. A read following a successful write yields
an authenticator message of the form:
The authenticator is encrypted in noncekey from the ticket. Num is 66, id[0-4] are 0, and
chal matches the challenge in the original ticket request.
The authenticator file is used to generate an authenticator from a ticket. One writes a
ticket encrypted with the key contained in key, followed, optionally, by a 4-byte id; a
missing id defaults to zero. If the client uid matches the current user, a subsequent
read yields an authenticator for that ticket with the given id.
The authcheck file is used to match authenticators to tickets. A write of an authentica-
tor appended to the end of a ticket succeeds if the ticket is encrypted with the key con-
tained in key, the ticket's num is 65, the authenticator is encrypted with the ticket's
noncekey, the authenticator's and ticket's chal's match, the authenticator's num is 66,
and the authenticator's id is 0. Alternatively, the write may consist of ticket, authen-
ticator, chal, and id, in which case the given chal and id must match those of the authen-
The user file contains the name of the user associated with the current process. Any
process can change to user none by writing none to this file.
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 as an 11-digit number with leading blanks and
one trailing blank: twelve bytes total.
The cputime file holds 6 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
The clock file holds two numbers: the number of clock ticks since booting followed by the
number of clock ticks in a second.
The sysname file holds the textual name of the machine, e.g. kremvax, if known.
The sysstat file holds 8 numbers: processor number, context switches, interrupts, system
calls, page faults, tlb faults, tlb purges, and load average. The load average is in
units of milli-CPUs and is decayed over time; the others are total counts from boot time.
If the machine is a multiprocessor, sysstat holds one line per processor. Writing any-
thing to sysstat resets all of the counts on all processors.
The swap device holds a string of the form
m1/m2 memory s1/s2 swap
These give, for each of internal memory and the swapping area, the number of pages used
and the total 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
The other files served by the cons device are all single numbers:
hz frequency of the system clock
msec number of milliseconds since booting
pgrpid process group number
pid process number
ppid parent's process number
time number of seconds since the epoch 00:00:00 GMT, Jan. 1, 1970. (Can be written
once, to set at boot time.)
bit(3), keyboard(6), auth(6), utf(6), swap(8)
For debugging, two control-T's followed by a letter generate console output: prints data
about processes, prints data about streams, prints data about the mount device, prints
data about the bitblt device, and prints data about kernel memory allocation.
The system can be rebooted by typing