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console_codes(4) — Linux manual page

console_codes(4) Kernel Interfaces Manual console_codes(4)

NAME top

 console_codes - Linux console escape and control sequences

DESCRIPTION top

 The Linux console implements a large subset of the VT102 and
 ECMA-48 / ISO/IEC 6429 / ANSI X3.64 terminal controls, plus
 certain private-mode sequences for changing the color palette,
 character-set mapping, and so on. 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 translation 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 simultaneously.
 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 movement or other control
 functions. See the Linux Console Controls section below for
 discussion.
 It is generally not good practice to hard-wire terminal controls
 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, possibly aborting a previous
 unfinished one, and CAN and SUB abort any escape sequence.) The
 recognized control characters 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 beginning 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)
 FF (0x0C, ^L)
 all give a linefeed, and if LF/NL (new-line mode) is set
 also a carriage return;
 CR (0x0D, ^M)
 gives a carriage return;
 SO (0x0E, ^N)
 activates the G1 character set;
 SI (0x0F, ^O)
 activates the G0 character set;
 CAN (0x18, ^X)
 SUB (0x1A, ^Z)
 abort escape sequences;
 ESC (0x1B, ^[)
 starts an escape sequence;
 DEL (0x7F)
 is ignored;
 CSI (0x9B)
 is equivalent to ESC [.
 ESC- but not CSI-sequences
 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 pointed at by G0,
 G1).
 ESC 8 DECRC Restore state most recently saved by ESC 7.
 ESC % Start sequence selecting character set
 ESC % @ Select default (ISO/IEC 646 / ISO/IEC 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 defining G0 character set
 (followed by one of B, 0, U, K, as below)
 ESC ( B Select default (ISO/IEC 8859-1 mapping).
 ESC ( 0 Select VT100 graphics mapping.
 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 (followed by one of
 B, 0, U, K, as above).
 ESC > DECPNM Set numeric keypad mode
 ESC = DECPAM Set application keypad mode
 ESC ] OSC Operating System Command prefix.
 ESC ] R Reset palette.
 ESC ] P Set palette, with parameter given in 7
 hexadecimal digits nrrggbb after the final P.
 Here n is the color (0–15), and rrggbb indicates
 the red/green/blue values (0–255).
 ECMA-48 CSI sequences
 CSI (or ESC [) is followed by a sequence of parameters, at most
 NPAR (16), that are decimal numbers separated by semicolons. 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.
 @ ICH Insert the indicated # of blank characters.
 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.
 ESC [ 3 J: erase whole display including scroll-back
 buffer (since Linux 3.0).
 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 current
 line.
 X ECH Erase the indicated # of characters on 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 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 Select Graphic Rendition
 The ECMA-48 SGR sequence ESC [ parameters m sets display
 attributes. Several attributes can be set in the same sequence,
 separated by semicolons. An empty parameter (between semicolons
 or string initiator or terminator) is interpreted as a zero.
 param result
 0 reset all attributes to their defaults
 1 set bold
 2 set half-bright (simulated with color on a color display)
 3 set italic (since Linux 2.6.22; 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
 (ECMA-48 says "primary font").
 11 select null mapping, set display control flag, reset toggle meta flag
 (ECMA-48 says "first alternate font").
 12 select null mapping, set display control flag, set toggle meta flag
 (ECMA-48 says "second alternate font"). The toggle meta flag causes the
 high bit of a byte to be toggled before the mapping table translation is
 done.
 21 set underline; before Linux 4.17, this value set normal intensity (as is
 done in many other terminals)
 22 set normal intensity
 23 italic off (since Linux 2.6.22)
 24 underline off
 25 blink off
 27 reverse video off
 30 set black foreground
 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
 38 256/24-bit foreground color follows, shoehorned into 16 basic colors
 (before Linux 3.16: set underscore on, set default foreground color)
 39 set default foreground color (before Linux 3.16: 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 background
 47 set white background
 48 256/24-bit background color follows, shoehorned into 8 basic colors
 49 set default background color
 90..97 set foreground to bright versions of 30..37
 100..107 set background, same as 40..47 (bright not supported)
 Commands 38 and 48 require further arguments:
 ;5;x 256 color: values 0..15 are IBGR (black, red, green,
 ... white), 16..231 a 6x6x6 color cube, 232..255 a
 grayscale ramp
 ;2;r;g;b 24-bit color, r/g/b components are in the range 0..255
 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 (Terminal
 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 replacing 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 autorepeat on.
 ESC [ ? 9 h
 X10 Mouse Reporting (default off): Set reporting mode to 1
 (or reset to 0)—see below.
 ESC [ ? 25 h
 DECTECM (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; 8–15 = bright versions of 0–7.
 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.
 ESC [ 15 ] Bring the previous console to the front (since
 Linux 2.6.0).
 ESC [ 16 ; n ] Set the cursor blink interval in milliseconds
 (since Linux 4.2).
 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
 make only 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 terminfo 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 bitmap 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(1)-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.
 The mouse tracking escape sequences generated by xterm(1) 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 button
 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(1) 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. Modifier
 information is also sent. It is enabled by sending ESC [ ? 1000 h
 and disabled with ESC [ ? 1000 l. On button press or release,
 xterm(1) 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 modifiers 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
 between the Linux console and 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 terminal
 driver.
 The xterm(1) 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 console:
 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 control 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(1) (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 ,円 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 character and line drawing
 set, UK, and US-ASCII, respectively.
 The user can configure xterm(1) to respond to VT220-specific
 control sequences, and it will identify itself as a VT52, VT100,
 and up depending on the way it is configured and initialized.
 It accepts ESC ] (OSC) for the setting of certain resources. In
 addition to the ECMA-48 string terminator (ST), xterm(1) accepts a
 BEL to terminate an OSC string. These are a few of the OSC
 control sequences recognized by xterm(1):
 ESC ] 0 ; txt ST Set icon name and window title
 to txt.
 ESC ] 1 ; txt ST Set icon name to txt.
 ESC ] 2 ; txt ST Set window title to txt.
 ESC ] 4 ; num; txt ST Set ANSI color num to txt.
 ESC ] 10 ; txt ST Set dynamic text color to txt.
 ESC ] 4 6 ; name ST Change log file to name
 (normally disabled by a
 compile-time option).
 ESC ] 5 0 ; fn ST Set font to fn.
 It recognizes the following with slightly modified meaning (saving
 more state, behaving closer to VT100/VT220):
 ESC 7 DECSC Save cursor
 ESC 8 DECRC Restore cursor
 It also recognizes
 ESC F Cursor to lower left corner of screen (if enabled
 by xterm(1)'s 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.
 ESC } LS2R Invoke the G2 character set as GR.
 ESC ~ LS1R Invoke the G1 character set as GR.
 It also recognizes ESC % and provides a more complete UTF-8
 implementation than Linux console.
 CSI Sequences
 Old versions of xterm(1), for example, from X11R5, interpret the
 blink SGR as a bold SGR. Later versions which implemented ANSI
 colors, for example, XFree86 3.1.2A in 1995, improved this by
 allowing the blink attribute to be displayed as a color. Modern
 versions of xterm implement blink SGR as blinking text and still
 allow colored text as an alternate rendering of SGRs. Stock X11R6
 versions did not recognize the color-setting SGRs until the
 X11R6.8 release, which incorporated XFree86 xterm. All ECMA-48
 CSI sequences recognized by Linux are also recognized by xterm,
 however xterm(1) implements several ECMA-48 and DEC control
 sequences not recognized by Linux.
 The xterm(1) program recognizes all of the DEC Private Mode
 sequences listed above, but none of the Linux private-mode
 sequences. For discussion of xterm(1)'s own private-mode
 sequences, refer to the Xterm Control Sequences document by Edward
 Moy, Stephen Gildea, and Thomas E. Dickey available with the X
 distribution. That document, though terse, is much longer than
 this manual page. For a chronological overview,
 ⟨http://invisible-island.net/xterm/xterm.log.html⟩
 details changes to xterm.
 The vttest program
 ⟨http://invisible-island.net/vttest/⟩
 demonstrates many of these control sequences. The xterm(1) source
 distribution also contains sample scripts which exercise other
 features.

NOTES top

 ESC 8 (DECRC) is not able to restore the character set changed
 with ESC %.

BUGS top

 In Linux 2.0.23, CSI is broken, and NUL is not ignored inside
 escape sequences.
 Some older kernel versions (after Linux 2.0) interpret 8-bit
 control sequences. These "C1 controls" use codes between 128 and
 159 to replace ESC [, ESC ] and similar two-byte control sequence
 initiators. There are fragments of that in modern kernels (either
 overlooked or broken by changes to support UTF-8), but the
 implementation is incomplete and should be regarded as unreliable.
 Linux "private mode" sequences do not follow the rules in ECMA-48
 for private mode control sequences. In particular, those ending
 with ] do not use a standard terminating character. The OSC (set
 palette) sequence is a greater problem, since xterm(1) may
 interpret this as a control sequence which requires a string
 terminator (ST). Unlike the setterm(1) sequences which will be
 ignored (since they are invalid control sequences), the palette
 sequence will make xterm(1) appear to hang (though pressing the
 return-key will fix that). To accommodate applications which have
 been hardcoded to use Linux control sequences, set the xterm(1)
 resource brokenLinuxOSC to true.
 An older version of this document implied that Linux recognizes
 the ECMA-48 control sequence for invisible text. It is ignored.

SEE ALSO top

 ioctl_console(2), charsets(7)

COLOPHON top

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Pages that refer to this page: pv(1), quilt(1), ioctl_console(2), TIOCLINUX(2const)

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