313 lines
7.2 KiB
Text
313 lines
7.2 KiB
Text
.TH CONS 3
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.SH NAME
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cons \- console, clocks, process/process group ids, user, null, reboot, etc.
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.SH SYNOPSIS
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.nf
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.B bind #c /dev
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.B /dev/bintime
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.B /dev/config
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.B /dev/cons
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.B /dev/cputime
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.B /dev/drivers
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.B /dev/hostdomain
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.B /dev/hostowner
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.B /dev/kmesg
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.B /dev/kprint
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.B /dev/mordor
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.B /dev/null
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.B /dev/osversion
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.B /dev/pid
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.B /dev/ppid
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.B /dev/random
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.B /dev/reboot
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.B /dev/sysname
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.B /dev/sysstat
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.B /dev/time
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.B /dev/user
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.B /dev/zero
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.fi
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.SH DESCRIPTION
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The console device serves a one-level directory
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giving access to the console screen and
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miscellaneous information.
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.PP
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A
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.I write
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(see
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.IR read (2))
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to
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.B cons
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causes the characters to be printed on the console screen. Console
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input is handled by a different program (see
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.IR kbdfs (8)).
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.PP
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The
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.B osversion
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file contains a textual representation of the operating system's version and parameters.
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At the moment, it contains one field: the 9P protocol version, currently
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.BR 2000 .
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.PP
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The
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.B config
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file contains a copy of the kernel configuration file used to build the kernel.
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.PP
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The
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.B kmesg
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file holds the last 16 kilobytes of output written to the console
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by the kernel's print statements or by processes writing to
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.BR /dev/cons .
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It is useful for retrieving boot messages once the boot
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process is over.
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.PP
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The
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.B kprint
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file may be read to receive a copy of the data written
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to the console by the kernel's print statements or by processes
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writing to
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.BR /dev/cons .
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Only data written after the file is opened is available.
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If the machine's console is a serial line, the data is sent both to the
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console and to
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.BR kprint ;
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if its console is a graphics screen, the data is sent either to the
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display or to
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.BR kprint ,
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but not both.
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(It is advisable not to open
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.B kprint
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on terminals until you have started
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.IR rio (1).)
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.PP
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The
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.B null
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file throws away anything written to it
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and always returns zero when read.
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.PP
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The
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.B zero
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file is a read-only file that produces an infinite stream of zero-valued bytes when read.
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.PP
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The
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.B drivers
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file contains, one per line, a listing of available kernel drivers, in the format
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.IP
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.EX
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#c cons
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.EE
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.PP
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Each process name group (see
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.IR fork (2))
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maintains a mask of allowed drivers.
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A process can modify that mask through writes to the
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.B drivers
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file. Messages are in the format of:
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.IP
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.EX
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chdev \f2op\fP \f2devmask\fP
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.EE
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.PP
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.I Devmask
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is a string of driver characters.
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.I Op
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specifies how
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.I devmask
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is interpreted.
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.I Op
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is one of:
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.TP
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.B &
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Permit access to just the drivers specified in
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.IR devmask .
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.TP
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.B &~
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Permit access to all but the drivers specified in
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.IR devmask .
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.TP
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.B ~
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Remove access to all devices.
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.I Devmask
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is ignored.
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.PP
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Access may only be removed. No
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.I op
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permits a process to regain access to a driver
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once it has been removed.
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Removing access to
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.IR mnt (3)
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additionally prevents new mounts into the current namespace.
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The following removes access to all drivers except
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.IR draw (3),
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.IR cons (3),
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and
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.IR fs (3):
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.IP
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.EX
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chdev & ick
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.EE
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.PP
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The
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.B hostdomain
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file contains the name of the authentication domain that
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this host belongs to; see
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.IR authsrv (6).
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Only the user named in
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.B /dev/hostowner
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may write this.
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.PP
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The
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.B hostowner
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file contains the name of the user that owns the console device files.
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The hostowner also has group permissions for any local devices.
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.PP
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Reads from
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.B random
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return a stream of random bytes produced by the kernels cryptographic
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random number generator. The rate at which data can be read depends on
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the implementation and can vary from hundreds of megabytes to just
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a few hundred bits a second. Therefore,
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.B random
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should be treated as a seed to
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pseudo-random number generators which can produce a faster
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rate stream.
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.PP
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Writing the string
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.B reboot
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to
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.B reboot
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causes the system to shutdown and, if
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possible, restart.
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Writing the string
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.B reboot
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.I kernelpath
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loads the named kernel image and restarts,
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preserving the kernel configuration in
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.BR #ec ,
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except that the
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.B bootfile
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variable is set to
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.IR kernelpath .
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Writing the string
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.B rdb
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activates the remote kernel debugger (see
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.IR rdbfs (4)).
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Only the host
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owner has the ability to open this file.
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.PP
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.B Bintime
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is a binary interface that provides
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the same information as
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.B time
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.RI ( q.v. ),
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in binary form,
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and also controls clock frequency and clock trim.
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All integers read or written from
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.B bintime
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are in big endian order.
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Unlike the other files, reads and writes do not affect
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the offset. Therefore, there is no need for a seek
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back to zero between subsequent accesses.
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A read of
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.B bintime
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returns 24 bytes, three 8 byte numbers, representing nanoseconds
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since start of epoch, clock ticks, and clock frequency.
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.PP
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A write to
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.B bintime
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is a message with one of 3 formats:
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.IP "\f5n\fP<8-byte \f2time\fP>" 1.2i
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set the nanoseconds since epoch to the given
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.IR time .
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.IP "\f5d\fP<8-byte \f2delta\fP><4-byte \f2period\fP>" 1.2i
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trim the nanoseconds since epoch by
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.I delta
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over the next
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.I period
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seconds.
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.IP "\f5f\fP<8-byte \f2freq\fP>" 1.2i
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Set the frequency for interpreting clock ticks to be
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.I freq
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ticks per second.
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.PP
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The rest of the files contain (mostly) read-only strings.
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Each string has a fixed length: a
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.IR read (2)
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of more than that gives a result of that fixed length (the result does not
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include a terminating zero byte);
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a
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.I read
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of less than that length leaves the file offset so the
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rest of the string (but no more) will be read the next time.
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To reread the file without closing it,
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.I seek
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must be used to reset the offset.
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When the file contains numeric data
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each number is formatted in decimal.
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If the binary number fits in 32 bits, it is formatted as an
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11 digit decimal number with
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leading blanks and one trailing blank; totaling 12 bytes.
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Otherwise, it
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is formatted as 21 digit decimal numbers with leading blanks and one
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trailing blank; totaling 22 bytes.
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.PP
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The
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.B cputime
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file holds six 32-bit numbers, containing the time in milliseconds
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that the current process has spent in user mode, system calls,
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real elapsed time, and then the time spent, by exited children and their descendants,
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in user mode, system calls, and real elapsed time.
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.PP
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The
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.B time
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file holds one 32-bit number representing the seconds since start of epoch
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and three 64-bit numbers, representing nanoseconds since
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start of epoch, clock ticks, and clock frequency.
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.PP
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A write of a decimal number to
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.B time
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will set the seconds since epoch.
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.PP
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The
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.B sysname
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file holds the textual name of the machine, e.g.
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.BR kremvax ,
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if known.
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.PP
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The
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.B sysstat
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file holds 10 numbers:
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processor number, context switches, interrupts, system calls, page faults,
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TLB faults, TLB purges, load average, idle time and time spent servicing interrupts.
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The load average is in units of milli-CPUs and is decayed over time;
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idle time and interrupt time are percentage units;
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the others are total counts from boot time.
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If the machine is a multiprocessor,
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.B sysstat
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holds one line per processor.
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Writing anything to
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.B sysstat
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resets all of the counts on all processors.
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.PP
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Reads and writes to
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.IR mordor
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will inevitably cause the front to fall off.
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.PP
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The other files served by the
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.I cons
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device are all single numbers:
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.TP 10
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.B pid
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process number
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.TP
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.B ppid
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parent's process number
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.SH SEE ALSO
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.IR draw (3),
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.IR kbd (3),
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.IR kbdfs (8),
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.IR keyboard (6),
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.IR authsrv (6),
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.IR utf (6),
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.IR swap (8)
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.SH SOURCE
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.B /sys/src/9/port/devcons.c
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