NAME
console_codes - Linux console escape and control sequences
DESCRIPTION
The Linux console implements a large subset of the VT102 and
ECMA-48/ISO 6429/ANSI X3.64 terminal controls, plus certain
private-mode sequences for changing the color palette,
character-set mapping, etc. In the tabular descriptions
below, the second column gives ECMA-48 or DEC mnemonics (the
latter if prefixed with DEC) for the given function.
Sequences without a mnemonic are neither ECMA-48 nor VT102.
After all the normal output processing has been done, and a
stream of characters arrives at the console driver for
actual printing, the first thing that happens is a transla-
tion from the code used for processing to the code used for
printing.
If the console is in UTF-8 mode, then the incoming bytes are
first assembled into 16-bit Unicode codes. Otherwise each
byte is transformed according to the current mapping table
(which translates it to a Unicode value). See the CHARACTER
SETS section below for discussion.
In the normal case, the Unicode value is converted to a font
index, and this is stored in video memory, so that the
corresponding glyph (as found in video ROM) appears on the
screen. Note that the use of Unicode (and the design of the
PC hardware) allows us to use 512 different glyphs simul-
taneously.
If the current Unicode value is a control character, or we
are currently processing an escape sequence, the value will
treated specially. Instead of being turned into a font
index and rendered as a glyph, it may trigger cursor move-
ment or other control functions. See the LINUX CONSOLE CON-
TROLS section below for discussion.
It is generally not good practice to hard-wire terminal con-
trols into programs. Linux supports a terminfo(5) database
of terminal capabilities. Rather than emitting console
escape sequences by hand, you will almost always want to use
a terminfo-aware screen library or utility such as
ncurses(3), tput(1), or reset(1).
LINUX CONSOLE CONTROLS
This section describes all the control characters and escape
sequences that invoke special functions (i.e. anything other
than writing a glyph at the current cursor location) on the
Linux console.
Control characters
A character is a control character if (before transformation
according to the mapping table) it has one of the 14 codes
00 (NUL), 07 (BEL), 08 (BS), 09 (HT), 0a (LF), 0b (VT), 0c
(FF), 0d (CR), 0e (SO), 0f (SI), 18 (CAN), 1a (SUB), 1b
(ESC), 7f (DEL). One can set a `display control characters'
mode (see below), and allow 07, 09, 0b, 18, 1a, 7f to be
displayed as glyphs. On the other hand, in UTF-8 mode all
codes 00-1f are regarded as control characters, regardless
of any `display control characters' mode.
If we have a control character, it is acted upon immediately
and then discarded (even in the middle of an escape
sequence) and the escape sequence continues with the next
character. (However, ESC starts a new escape sequence, pos-
sibly aborting a previous unfinished one, and CAN and SUB
abort any escape sequence.) The recognized control charac-
ters are BEL, BS, HT, LF, VT, FF, CR, SO, SI, CAN, SUB, ESC,
DEL, CSI. They do what one would expect:
BEL (0x07, ^G) beeps;
BS (0x08, ^H) backspaces one column (but not past the begin-
ning of the line);
HT (0x09, ^I) goes to the next tab stop or to the end of the
line if there is no earlier tab stop;
LF (0x0A, ^J), VT (0x0B, ^K) and FF (0x0C, ^L) all give a
linefeed;
CR (0x0D, ^M) gives a carriage return;
SO (0x0E, ^N) activates the G1 character set, and if LF/NL
(new line mode) is set also a carriage return;
SI (0x0F, ^O) activates the G0 character set;
CAN (0x18, ^X) and SUB (0x1A, ^Z) interrupt escape
sequences;
ESC (0x1B, ^[) starts an escape sequence;
DEL (0x7F) is ignored;
CSI (0x9B) is equivalent to ESC [.
ESC- but not CSI-sequences
l l l. ESC c RIS Reset. ESC D IND Linefeed. ESC
E NEL Newline. ESC H HTS Set tab stop at current
column. ESC M RI Reverse linefeed. ESC
Z DECID DEC private identification. The kernel
returns the string ESC [ ? 6 c, claiming
that it is a VT102. ESC 7 DECSC Save
current state (cursor coordinates, attributes,
character sets). ESC 8 DECRC Restore most recently
saved state. ESC [ CSI Control sequence introducer ESC
% Start sequence selecting character set ESC %
@ Select default (ISO 646 / ISO 8859-1) ESC %
G Select UTF-8 ESC % 8 Select UTF-8
(obsolete) ESC # 8 DECALN DEC screen alignment test -
fill screen with E's. ESC ( Start sequence defin-
ing G0 character set ESC ( B Select default (ISO
8859-1 mapping) ESC ( 0 Select vt100 graphics map-
ping ESC ( U Select null mapping - straight to
character ROM ESC ( K Select user mapping - the
map that is loaded by the utility mapscrn(8).
ESC ) Start sequence defining G1 (fol-
lowed by one of B, 0, U, K, as above). ESC
> DECPNM Set numeric keypad mode ESC
= DECPAM Set application keypad mode ESC
] OSC (Should be: Operating system command)
ESC ] P nrrggbb: set palette, with parameter
given in 7 hexadecimal digits after the final P
:-(. Here n is the color (0-16), and rrggbb indi-
cates the red/green/blue values (0-255).
ESC ] R: reset palette
ECMA-48 CSI sequences
CSI (or ESC [) is followed by a sequence of parameters, at
most NPAR (16), that are decimal numbers separated by semi-
colons. An empty or absent parameter is taken to be 0. The
sequence of parameters may be preceded by a single question
mark.
However, after CSI [ (or ESC [ [) a single character is read
and this entire sequence is ignored. (The idea is to ignore
an echoed function key.)
The action of a CSI sequence is determined by its final
character.
l l l. @ ICH Insert the indicated # of blank charac-
ters. A CUU Move cursor up the indicated # of rows.
B CUD Move cursor down the indicated # of rows.
C CUF Move cursor right the indicated # of columns.
D CUB Move cursor left the indicated # of columns.
E CNL Move cursor down the indicated # of rows, to
column 1. F CPL Move cursor up the indicated # of rows,
to column 1. G CHA Move cursor to indicated column in
current row. H CUP Move cursor to the indicated row,
column (origin at 1,1). J ED Erase display (default:
from cursor to end of display). ESC [ 1 J: erase
from start to cursor. ESC [ 2 J: erase whole
display. K EL Erase line (default: from cursor to end
of line). ESC [ 1 K: erase from start of line to
cursor. ESC [ 2 K: erase whole line.
L IL Insert the indicated # of blank lines.
M DL Delete the indicated # of lines. P DCH Delete
the indicated # of characters on the current line.
X ECH Erase the indicated # of characters on the current
line. a HPR Move cursor right the indicated # of
columns. c DA Answer ESC [ ? 6 c: `I am a VT102'.
d VPA Move cursor to the indicated row, current column.
e VPR Move cursor down the indicated # of rows.
f HVP Move cursor to the indicated row, column.
g TBC Without parameter: clear tab stop at the current
position. ESC [ 3 g: delete all tab stops.
h SM Set Mode (see below). l RM Reset Mode (see
below). m SGR Set attributes (see below).
n DSR Status report (see below). q DECLL Set
keyboard LEDs. ESC [ 0 q: clear all LEDs
ESC [ 1 q: set Scroll Lock LED ESC [ 2
q: set Num Lock LED ESC [ 3 q: set Caps Lock LED
r DECSTBM Set scrolling region; parameters are top and
bottom row. s ? Save cursor location.
u ? Restore cursor location. ` HPA Move cursor to
indicated column in current row.
ECMA-48 Set Graphics Rendition
The ECMA-48 SGR sequence ESC [ <parameters> m sets display
attributes. Several attributes can be set in the same
sequence.
l l. par result 0 reset all attributes to their
defaults 1 set bold 2 set half-bright (simulated with
color on a color display) 4 set underscore (simulated
with color on a color display) (the colors used to
simulate dim or underline are set using ESC ] ...)
5 set blink 7 set reverse video 10 reset selected
mapping, display control flag, and toggle meta flag.
11 select null mapping, set display control flag,
reset toggle meta flag. 12 select null mapping, set
display control flag, set toggle meta flag. (The toggle
meta flag causes the high bit of a byte to be toggled
before the mapping table translation is done.)
21 set normal intensity (this is not compatible with
ECMA-48) 22 set normal intensity 24 underline off
25 blink off 27 reverse video off 30 set black fore-
ground 31 set red foreground 32 set green foreground
33 set brown foreground 34 set blue foreground 35 set
magenta foreground 36 set cyan foreground 37 set white
foreground 38 set underscore on, set default foreground
color 39 set underscore off, set default foreground color
40 set black background 41 set red background 42 set
green background 43 set brown background 44 set blue
background 45 set magenta background 46 set cyan back-
ground 47 set white background 49 set default background
color
ECMA-48 Mode Switches
ESC [ 3 h
DECCRM (default off): Display control chars.
ESC [ 4 h
DECIM (default off): Set insert mode.
ESC [ 20 h
LF/NL (default off): Automatically follow echo of LF,
VT or FF with CR.
ECMA-48 Status Report Commands
ESC [ 5 n
Device status report (DSR): Answer is ESC [ 0 n (Termi-
nal OK).
ESC [ 6 n
Cursor position report (CPR): Answer is ESC [ y ; x R,
where x,y is the cursor location.
DEC Private Mode (DECSET/DECRST) sequences.
These are not described in ECMA-48. We list the Set Mode
sequences; the Reset Mode sequences are obtained by replac-
ing the final `h' by `l'.
ESC [ ? 1 h
DECCKM (default off): When set, the cursor keys send an
ESC O prefix, rather than ESC [.
ESC [ ? 3 h
DECCOLM (default off = 80 columns): 80/132 col mode
switch. The driver sources note that this alone does
not suffice; some user-mode utility such as
resizecons(8) has to change the hardware registers on
the console video card.
ESC [ ? 5 h
DECSCNM (default off): Set reverse-video mode.
ESC [ ? 6 h
DECOM (default off): When set, cursor addressing is
relative to the upper left corner of the scrolling
region.
ESC [ ? 7 h
DECAWM (default on): Set autowrap on. In this mode, a
graphic character emitted after column 80 (or column
132 of DECCOLM is on) forces a wrap to the beginning of
the following line first.
ESC [ ? 8 h
DECARM (default on): Set keyboard autorepreat on.
ESC [ ? 9 h
X10 Mouse Reporting (default off): Set reporting mode
to 1 (or reset to 0) - see below.
ESC [ ? 25 h
DECCM (default on): Make cursor visible.
ESC [ ? 1000 h
X11 Mouse Reporting (default off): Set reporting mode
to 2 (or reset to 0) - see below.
Linux Console Private CSI Sequences
The following sequences are neither ECMA-48 nor native
VT102. They are native to the Linux console driver. Colors
are in SGR parameters: 0 = black, 1 = red, 2 = green, 3 =
brown, 4 = blue, 5 = magenta, 6 = cyan, 7 = white.
l l. ESC [ 1 ; n ] Set color n as the underline color
ESC [ 2 ; n ] Set color n as the dim color
ESC [ 8 ] Make the current color pair the default attributes.
ESC [ 9 ; n ] Set screen blank timeout to n minutes.
ESC [ 10 ; n ] Set bell frequency in Hz.
ESC [ 11 ; n ] Set bell duration in msec.
ESC [ 12 ; n ] Bring specified console to the front.
ESC [ 13 ] Unblank the screen.
ESC [ 14 ; n ] Set the VESA powerdown interval in minutes.
CHARACTER SETS
The kernel knows about 4 translations of bytes into
console-screen symbols. The four tables are: a) Latin1 ->
PC, b) VT100 graphics -> PC, c) PC -> PC, d) user-defined.
There are two character sets, called G0 and G1, and one of
them is the current character set. (Initially G0.) Typing
^N causes G1 to become current, ^O causes G0 to become
current.
These variables G0 and G1 point at a translation table, and
can be changed by the user. Initially they point at tables
a) and b), respectively. The sequences ESC ( B and ESC ( 0
and ESC ( U and ESC ( K cause G0 to point at translation
table a), b), c) and d), respectively. The sequences ESC )
B and ESC ) 0 and ESC ) U and ESC ) K cause G1 to point at
translation table a), b), c) and d), respectively.
The sequence ESC c causes a terminal reset, which is what
you want if the screen is all garbled. The oft-advised "echo
^V^O" will only make G0 current, but there is no guarantee
that G0 points at table a). In some distributions there is
a program reset(1) that just does "echo ^[c". If your ter-
minfo entry for the console is correct (and has an entry
rs1=\Ec), then "tput reset" will also work.
The user-defined mapping table can be set using mapscrn(8).
The result of the mapping is that if a symbol c is printed,
the symbol s = map[c] is sent to the video memory. The bit-
map that corresponds to s is found in the character ROM, and
can be changed using setfont(8).
MOUSE TRACKING
The mouse tracking facility is intended to return xterm-
compatible mouse status reports. Because the console driver
has no way to know the device or type of the mouse, these
reports are returned in the console input stream only when
the virtual terminal driver receives a mouse update ioctl.
These ioctls must be generated by a mouse-aware user-mode
application such as the gpm(8) daemon.
Parameters for all mouse tracking escape sequences generated
by xterm encode numeric parameters in a single character as
value+040. For example, `!' is 1. The screen coordinate
system is 1-based.
The X10 compatibility mode sends an escape sequence on but-
ton press encoding the location and the mouse button
pressed. It is enabled by sending ESC [ ? 9 h and disabled
with ESC [ ? 9 l. On button press, xterm sends ESC [ M bxy
(6 characters). Here b is button-1, and x and y are the x
and y coordinates of the mouse when the button was pressed.
This is the same code the kernel also produces.
Normal tracking mode (not implemented in Linux 2.0.24) sends
an escape sequence on both button press and release. Modif-
ier information is also sent. It is enabled by sending ESC
[ ? 1000 h and disabled with ESC [ 1000 l. On button press
or release, xterm sends ESC [ M bxy. The low two bits of b
encode button information: 0=MB1 pressed, 1=MB2 pressed,
2=MB3 pressed, 3=release. The upper bits encode what modif-
iers were down when the button was pressed and are added
together: 4=Shift, 8=Meta, 16=Control. Again x and y are
the x and y coordinates of the mouse event. The upper left
corner is (1,1).
COMPARISONS WITH OTHER TERMINALS
Many different terminal types are described, like the Linux
console, as being `VT100-compatible'. Here we discuss
differences vbetween the Linux console an the two most
important others, the DEC VT102 and xterm(1).
Control-character handling
The vt102 also recognized the following control characters:
NUL (0x00) was ignored;
ENQ (0x05) triggered an answerback message;
DC1 (0x11, ^Q, XON) resumed transmission;
DC3 (0x13, ^S, XOFF) caused vt100 to ignore (and stop
transmitting) all codes except XOFF and XON.
VT100-like DC1/DC3 processing may be enabled by the tty
driver.
The xterm program (in vt100 mode) recognizes the control
characters BEL, BS, HT, LF, VT, FF, CR, SO, SI, ESC.
Escape sequences
VT100 console sequences not implemented on the Linux con-
sole:
l l l. ESC N SS2 Single shift 2. (Select G2 character
set for the next character only.) ESC
O SS3 Single shift 3. (Select G3 character set for the
next character only.) ESC P DCS Device con-
trol string (ended by ESC \) ESC X SOS Start of string.
ESC ^ PM Privacy message (ended by ESC \) ESC
\ ST String terminator ESC * ... Designate G2
character set ESC + ... Designate G3 character set
The program xterm (in vt100 mode) recognizes ESC c, ESC # 8,
ESC >, ESC =, ESC D, ESC E, ESC H, ESC M, ESC N, ESC O, ESC
P ... ESC , ESC Z (it answers ESC [ ? 1 ; 2 c, `I am a vt100
with advanced video option') and ESC ^ ... ESC with the
same meanings as indicated above. It accepts ESC (, ESC ),
ESC *, ESC + followed by 0, A, B for the DEC special char-
acter and line drawing set, UK, and USASCII, respectively.
It accepts ESC ] for the setting of certain resources:
l l. ESC ] 0 ; txt BEL Set icon name and window title to
txt. ESC ] 1 ; txt BEL Set icon name to txt. ESC ] 2 ;
txt BEL Set window title to txt. ESC ] 4 6 ; name
BEL Change log file to name (normally disabled by a
compile-time option) ESC ] 5 0 ; fn BEL Set font to fn.
It recognizes the following with slightly modified meaning:
l l l. ESC 7 DECSC Save cursor ESC 8 DECRC Restore
cursor
It also recognizes
l l l. ESC F Cursor to lower left corner of screen
(if enabled by the hpLowerleftBugCompat resource)
ESC l Memory lock (per HP terminals).
Locks memory above the cursor. ESC
m Memory unlock (per HP terminals). ESC
n LS2 Invoke the G2 character set. ESC
o LS3 Invoke the G3 character set. ESC
| LS3R Invoke the G3 character set as GR. Has
no visible effect in xterm. ESC } LS2R Invoke the G2
character set as GR. Has no visible effect in
xterm. ESC ~ LS1R Invoke the G1 character set as GR.
Has no visible effect in xterm.
It does not recognize ESC % ...
CSI Sequences
The xterm program (as of XFree86 3.1.2G) does not recognize
the blink or invisible-mode SGRs. Stock X11R6 versions do
not recognize the color-setting SGRs. All other ECMA-48 CSI
sequences recognized by Linux are also recognized by xterm,
and vice-versa.
The xterm program will recognize all of the DEC Private Mode
sequences listed above, but none of the Linux private-mode
sequences. For discussion of xterm's own private-mode
sequences, refer to the Xterm Control Sequences document by
Edward Moy and Stephen Gildea, available with the X distri-
bution.
BUGS
In 2.0.23, CSI is broken, and NUL is not ignored inside
escape sequences.
SEE ALSO
console(4), console_ioctl(4), charsets(4)