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GETTYTAB(5) File Formats Manual GETTYTAB(5)

gettytab — terminal configuration data base

gettytab

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) accesses the gettytab file each time it starts, allowing simpler reconfiguration of terminal characteristics. Each entry in the data base is used to describe one class of terminals.

There is a default terminal class, default, that is used to set global defaults for all other classes. (That is, the default entry is read, then the entry for the class required is used to override particular settings.)

Refer to termcap(5) for a description of the file layout. The default column below lists defaults obtained if there is no entry in the table obtained, nor one in the special default table.

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

The following capabilities are no longer supported by getty(8):

bd num 0 backspace delay
cb bool false use crt backspace mode
cd num 0 carriage-return delay
fd num 0 form-feed (vertical motion) delay
lc bool false terminal has lower case
nd num 0 newline (line-feed) delay
uc bool false terminal is known upper case only

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 stated direction only.

Terminal modes to be used for the output of the message, for input of the login name, and to leave the terminal set as upon completion, are derived from the boolean flags specified. If the derivation should prove inadequate, any (or all) of these three may be overridden with one of the c0, c1, c2, i0, i1, i2, l0, l1, l2, o0, o1, or o2 numeric specifications, which can be used to 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.

The f0, f1, and f2 are excepted for backwards compatibility with a previous incarnation of the TTY sub-system. In these flags the bottom 16 bits of the (32 bits) value contain the sgttyb sg_flags field, while the top 16 bits represent the local mode word.

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, the nearest possible delay available in the tty driver will be used. Should greater certainty be 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, which is normally obtained from the system using gethostname(3), but may also be overridden by the hn table entry. In either case it may be edited with the he string. A '@' in the he string causes one character from the real hostname to be copied to the final hostname. A '#' in the he string causes the next character of the real hostname to be skipped. Each character that is neither '@' nor '#' is copied into the final hostname. Surplus '@' and '#' characters are ignored.
%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. The getty(8) utility 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.

login(1), gethostname(3), uname(3), termcap(5), getty(8), telnetd(8)

The gettytab file format appeared in 4.2BSD.

The special characters (erase, kill, etc.) are reset to system defaults by login(1). In 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.

February 26, 2018 macOS