console_codes(4) — Linux manual page

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CONSOLE_CODES(4)        Linux Programmer's 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 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), and 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) and 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 [     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 defining G0 character set
                          (followed by one of B, 0, U, K, as below)
       ESC ( B            Select default (ISO 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      (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 (0–15), and rrggbb
                          indicates 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 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)
       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
       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 \, 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 2.0.23, CSI is broken, and NUL is not ignored inside escape
       sequences.

       Some older kernel versions (after 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

       This page is part of release 5.12 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

Linux                          2021-03-22               CONSOLE_CODES(4)

Pages that refer to this page: ioctl_console(2)