GETTYTAB(5)

GETTYTAB(5) · File Formats Manual — okay bestie, we’re about to read the terminal configuration data base page together, and it’s honestly giving vintage Unix main-character energy.

🌸 NAME 🌸

gettytab — terminal configuration data base.

💖 SYNOPSIS 💖

gettytab

✨ DESCRIPTION ✨

The gettytab file is a simplified version of the termcap(5) data base used to describe terminal lines. The initial terminal login process getty(8) reads the gettytab file every time it starts, which makes reconfiguring terminal characteristics simpler. Each entry in the data base describes one class of terminals.

There’s a default terminal class, default, that sets global defaults for all the other classes. (Like, the default entry gets read first, then the entry for the class you actually need is used to override particular settings. Slay.)

🎀 CAPABILITIES 🎀

Peep termcap(5) for a description of the file layout. The defaults listed below are what you get when there’s no entry in the table you looked up and no entry in the special default table either. Here’s the full roster: name · type · default · what it does.

• ac — str · default unused — expect-send chat script for modem answer.
• al — str · default unused — user to auto-login instead of prompting.
• ap — bool · default false — terminal uses any parity.
• bk — str · default 0377 — alternate end of line character (input break).
• c0 — num · default unused — tty control flags to write messages.
• c1 — num · default unused — tty control flags to read login name.
• c2 — num · default unused — tty control flags to leave terminal as.
• ce — bool · default false — use crt erase algorithm.
• ck — bool · default false — use crt kill algorithm.
• cl — str · default NULL.
• co — bool · default false — console — add \n after login prompt.
• ct — num · default 10 — chat timeout for ac and ic scripts.
• dc — num · default 0 — chat debug bitmask.
• de — num · default 0 — delay secs and flush input before writing first prompt.
• df — str · default %+ — the strftime(3) format used for %d in the banner message.
• ds — str · default ‘^Y’ — delayed suspend character.
• dx — bool · default false — set DECCTLQ.
• ec — bool · default false — leave echo OFF.
• ep — bool · default false — terminal uses even parity.
• er — str · default ‘^?’ — erase character.
• et — str · default ‘^D’ — end of text (EOF) character.
• ev — str · default NULL.
• fl — str · default ‘^O’ — output flush character.
• hc — bool · default false — do NOT hangup line on last close.
• he — str · default NULL.
• hn — str · default hostname — hostname.
• ht — bool · default false — terminal has real tabs.
• hw — bool · default false — do cts/rts hardware flow control.
• i0 — num · default unused — tty input flags to write messages.
• i1 — num · default unused — tty input flags to read login name.
• i2 — num · default unused — tty input flags to leave terminal as.
• ic — str · default unused — expect-send chat script for modem initialization.
• if — str · default unused — display named file before prompt, like /etc/issue.
• ig — bool · default false — ignore garbage characters in login name.
• im — str · default NULL.
• iM — str · default NULL.
• in — str · default ‘^C’ — interrupt character.
• is — num · default unused — input speed.
• kl — str · default ‘^U’ — kill character.
• l0 — num · default unused — tty local flags to write messages.
• l1 — num · default unused — tty local flags to read login name.
• l2 — num · default unused — tty local flags to leave terminal as.
• lm — str · default login: — login prompt.
• ln — str · default ‘^V’ — “literal next” character.
• lo — str · default /usr/bin/login.
• mb — bool · default false — do flow control based on carrier.
• nc — bool · default false — terminal does not supply carrier (set clocal).
• nl — bool · default false — terminal has (or might have) a newline character.
• np — bool · default false — terminal uses no parity (i.e., 8-bit characters).
• nx — str · default default — next table (for auto speed selection).
• o0 — num · default unused — tty output flags to write messages.
• o1 — num · default unused — tty output flags to read login name.
• o2 — num · default unused — tty output flags to leave terminal as.
• op — bool · default false — terminal uses odd parity.
• os — num · default unused — output speed.
• pc — str · default ‘\0’ — pad character.
• pe — bool · default false — use printer (hard copy) erase algorithm.
• pf — num · default 0 — delay between first prompt and following flush (seconds).
• pl — bool · default false — start PPP login program unconditionally if pp is specified.
• pp — str · default unused — PPP login program.
• ps — bool · default false — line connected to a MICOM port selector.
• qu — str · default ‘^\’ — quit character.
• rp — str · default ‘^R’ — line retype character.
• rt — num · default unused — ring timeout when using ac.
• rw — bool · default false — do NOT use raw for input, use cbreak.
• sp — num · default unused — line speed (input and output).
• su — str · default ‘^Z’ — suspend character.
• tc — str · default none — table continuation.
• to — num · default 0 — timeout (seconds).
• tt — str · default NULL.
• ub — bool · default false — do unbuffered output (of prompts etc).
• we — str · default ‘^W’ — word erase character.
• xc — bool · default false — do NOT echo control chars as ^X.
• xf — str · default ‘^S’ — XOFF (stop output) character.
• xn — str · default ‘^Q’ — XON (start output) character.
• Lo — str · default C — the locale name used for %d in the banner message.

💀 the ones getty(8) no longer supports 💀

These capabilities are no longer supported by getty(8) — they’re still listed here, but bestie, do not expect them to be doing anything for you:

• bd — num · default 0 — backspace delay.
• cb — bool · default false — use crt backspace mode.
• cd — num · default 0 — carriage-return delay.
• f0 — num · default unused — tty mode flags to write messages.
• f1 — num · default unused — tty mode flags to read login name.
• f2 — num · default unused — tty mode flags to leave terminal as.
• fd — num · default 0 — form-feed (vertical motion) delay.
• lc — bool · default false — terminal has lower case.
• nd — num · default 0 — newline (line-feed) delay.
• uc — bool · default false — terminal is known upper case only.

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If no line speed is specified, speed will not be altered from that which prevails when getty is entered. Specifying an input or output speed will override line speed for the stated direction only.

The terminal modes used for outputting the message, for reading the login name, and for leaving the terminal set when it’s done are derived from the boolean flags you specify. If that derivation proves inadequate, any (or all) of these three can be overridden with one of the c0, c1, c2, i0, i1, i2, l0, l1, l2, o0, o1, or o2 numeric specifications. Those let you specify (usually in octal, with a leading '0') the exact values of the flags. These flags correspond to the termios c_cflag, c_iflag, c_lflag, and c_oflag fields, respectively. Each of these sets must be completely specified to be effective.

Should getty(8) receive a null character (presumed to indicate a line break), it will restart using the table indicated by the nx entry. If there is none, it will re-use its original table.

Delays are specified in milliseconds, and the nearest possible delay available in the tty driver will be used. If greater certainty is desired, delays with values 0, 1, 2, and 3 are interpreted as choosing that particular delay algorithm from the driver.

The cl screen clear string may be preceded by a (decimal) number of milliseconds of delay required (a la termcap). This delay is simulated by repeated use of the pad character pc.

The initial message, login message, and initial file — im, lm, and if — may include any of the following character sequences, which expand to information about the environment in which getty(8) is running:

• %d — the current date and time formatted according to the Lo and df strings.
• %h — the hostname of the machine, normally obtained from the system using gethostname(3), but also possibly overridden by the hn table entry. In either case it may be edited with the he POSIX “extended” regular expression, which is matched against the hostname. If there are no parenthesized subexpressions in the pattern, the entire matched string is used as the final hostname; otherwise, the first matched subexpression is used instead. If the pattern does not match, the original hostname is not modified.
• %t — the tty name.
• %m, %r, %s, %v — the type of machine, release of the operating system, name of the operating system, and version of the kernel, respectively, as returned by uname(3).
• %% — a “%” character.

When getty execs the login process, given in the lo string (usually /usr/bin/login), it will have set the environment to include the terminal type, as indicated by the tt string (if it exists). The ev string can be used to enter additional data into the environment. It is a list of comma separated strings, each of which will presumably be of the form name=value.

If a non-zero timeout is specified, with to, then getty will exit within the indicated number of seconds, either having received a login name and passed control to login(1), or having received an alarm signal, and exited. This may be useful to hangup dial in lines.

Output from getty(8) is even parity unless op or np is specified. The op string may be specified with ap to allow any parity on input, but generate odd parity output. Note: this only applies while getty is being run — terminal driver limitations prevent a more complete implementation. getty(8) does not check parity of input characters in RAW mode. 🫶

If a pp string is specified and a PPP link bring-up sequence is recognized, getty will invoke the program referenced by the pp option. This can be used to handle incoming PPP calls. If the pl option is true as well, getty(8) will skip the user name prompt and the PPP detection phase, and will invoke the program specified by pp instantly. ✨

Getty provides some basic intelligent modem handling by providing a chat script feature available via two capabilities:

• ic — Chat script to initialize modem. 🎀
• ac — Chat script to answer a call. 🦋

A chat script is a set of expect/send string pairs. When a chat string starts, getty will wait for the first string, and if it finds it, will send the second, and so on. Strings specified are separated by one or more tabs or spaces. Strings may contain standard ASCII characters and special 'escapes', which consist of a backslash character followed by one or more characters which are interpreted as follows:

• \a — bell character. 🔔
• \b — backspace.
• \n — newline.
• \e — escape.
• \f — formfeed.
• \p — half-second pause.
• \r — carriage return.
• \S, \s — space character.
• \t — tab.
• \xNN — hexadecimal byte value.
• \0NNN — octal byte value.

Note that the \p sequence is only valid for send strings and causes a half-second pause between sending the previous and next characters. Hexadecimal values are, at most, 2 hex digits long, and octal values are a maximum of 3 octal digits. ⏳

The ic chat sequence is used to initialize a modem or similar device. A typical example of an init chat script for a modem with a hayes compatible command set might look like this:

:ic="" ATE0Q0V1\r OK\r ATS0=0\r OK\r:

This script waits for nothing (which always succeeds), sends a sequence to ensure that the modem is in the correct mode (suppress command echo, send responses in verbose mode), and then disables auto-answer. It waits for an "OK" response before it terminates. The init sequence is used to check modem responses to ensure that the modem is functioning correctly. If the init script fails to complete, getty considers this to be fatal, and results in an error logged via syslogd(8), and exiting. 😭

Similarly, an answer chat script is used to manually answer the phone in response to (usually) a "RING". When run with an answer script, getty opens the port in non-blocking mode, clears any extraneous input and waits for data on the port. As soon as any data is available, the answer chat script is started and scanned for a string, and responds according to the answer chat script. With a hayes compatible modem, this would normally look something like:

:ac=RING\r ATA\r CONNECT:

This causes the modem to answer the call via the "ATA" command, then scans input for a "CONNECT" string. If this is received before a ct timeout, then a normal login sequence commences. 🔥

The ct capability specifies a timeout for all send and expect strings. This timeout is set individually for each expect wait and send string and must be at least as long as the time it takes for a connection to be established between a remote and local modem (usually around 10 seconds). ⏱️

In most situations, you will want to flush any additional input after the connection has been detected, and the de capability may be used to do that, as well as delay for a short time after the connection has been established during which all of the connection data has been sent by the modem. 💜

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🌈 SEE ALSO 🌈

Your reference besties: login(1), gethostname(3), uname(3), termcap(5), getty(8). 💅

🦋 HISTORY 🦋

The gettytab file format appeared in 4.2BSD. ⭐

💀 BUGS 💀

The special characters (erase, kill, etc.) are reset to system defaults by login(1). In all cases, # or ^H typed in a login name will be treated as an erase character, and @ will be treated as a kill character. 🙈

The delay stuff is a real crock. Apart form its general lack of flexibility, some of the delay algorithms are not implemented. The terminal driver should support sane delay settings. 😭💀

The termcap(5) format is horrid, something more rational should have been chosen. 🍓

xoxo, bestie 💖 — this one's from Debian, dated September 29, 2022, and it's the GETTYTAB(5) page. 🎀