term - conventions for naming terminal types
The environment variable
TERM should normally contain the type name of
the terminal, console or display-device type you are using. This information
is critical for all screen-oriented programs, including your editor and
mailer.
A default
TERM value will be set on a per-line basis by either
/etc/inittab (e.g., System-V-like UNIXes) or
/etc/ttys (BSD
UNIXes). This will nearly always suffice for workstation and microcomputer
consoles.
If you use a dialup line, the type of device attached to it may vary. Older UNIX
systems pre-set a very dumb terminal type like “dumb” or
“dialup” on dialup lines. Newer ones may pre-set
“vt100”, reflecting the prevalence of DEC VT100-compatible
terminals and personal-computer emulators.
Modern telnets pass your
TERM environment variable from the local side to
the remote one. There can be problems if the remote terminfo or termcap entry
for your type is not compatible with yours, but this situation is rare and can
almost always be avoided by explicitly exporting “vt100”
(assuming you are in fact using a VT100-superset console, terminal, or
terminal emulator).
In any case, you are free to override the system
TERM setting to your
taste in your shell profile. The
tset(1) utility may be of assistance;
you can give it a set of rules for deducing or requesting a terminal type
based on the tty device and baud rate.
Setting your own
TERM value may also be useful if you have created a
custom entry incorporating options (such as visual bell or reverse-video)
which you wish to override the system default type for your line.
Terminal type descriptions are stored as files of capability data underneath
/etc/terminfo. To browse a list of all terminal names recognized by the
system, do
toe | more
from your shell. These capability files are in a binary format optimized for
retrieval speed (unlike the old text-based
termcap format they
replace); to examine an entry, you must use the
infocmp(1) command.
Invoke it as follows:
infocmp
entry_name
where
entry_name is the name of the type you wish to examine (and the
name of its capability file the subdirectory of /etc/terminfo named for its
first letter). This command dumps a capability file in the text format
described by
terminfo(5).
The first line of a
terminfo(5) description gives the names by which
terminfo knows a terminal, separated by “|” (pipe-bar)
characters with the last name field terminated by a comma. The first name
field is the type's
primary name, and is the one to use when setting
TERM. The last name field (if distinct from the first) is actually a
description of the terminal type (it may contain blanks; the others must be
single words). Name fields between the first and last (if present) are aliases
for the terminal, usually historical names retained for compatibility.
There are some conventions for how to choose terminal primary names that help
keep them informative and unique. Here is a step-by-step guide to naming
terminals that also explains how to parse them:
First, choose a root name. The root will consist of a lower-case letter followed
by up to seven lower-case letters or digits. You need to avoid using
punctuation characters in root names, because they are used and interpreted as
filenames and shell meta-characters (such as !, $, *, ?, etc.) embedded in
them may cause odd and unhelpful behavior. The slash (/), or any other
character that may be interpreted by anyone's file system (\, $, [, ]), is
especially dangerous (terminfo is platform-independent, and choosing names
with special characters could someday make life difficult for users of a
future port). The dot (.) character is relatively safe as long as there is at
most one per root name; some historical terminfo names use it.
The root name for a terminal or workstation console type should almost always
begin with a vendor prefix (such as
hp for Hewlett-Packard,
wy
for Wyse, or
att for AT&T terminals), or a common name of the
terminal line (
vt for the VT series of terminals from DEC, or
sun for Sun Microsystems workstation consoles, or
regent for the
ADDS Regent series. You can list the terminfo tree to see what prefixes are
already in common use. The root name prefix should be followed when
appropriate by a model number; thus
vt100,
hp2621,
wy50.
The root name for a PC-Unix console type should be the OS name, i.e.,
linux,
bsdos,
freebsd,
netbsd. It should
not be
console or any other generic that might cause confusion
in a multi-platform environment! If a model number follows, it should indicate
either the OS release level or the console driver release level.
The root name for a terminal emulator (assuming it does not fit one of the
standard ANSI or vt100 types) should be the program name or a readily
recognizable abbreviation of it (i.e.,
versaterm,
ctrm).
Following the root name, you may add any reasonable number of hyphen-separated
feature suffixes.
- 2p
- Has two pages of memory. Likewise 4p, 8p, etc.
- mc
- Magic-cookie. Some terminals (notably older Wyses) can only
support one attribute without magic-cookie lossage. Their base entry is
usually paired with another that has this suffix and uses magic cookies to
support multiple attributes.
- -am
- Enable auto-margin (right-margin wraparound).
- -m
- Mono mode - suppress color support.
- -na
- No arrow keys - termcap ignores arrow keys which are
actually there on the terminal, so the user can use the arrow keys
locally.
- -nam
- No auto-margin - suppress am capability.
- -nl
- No labels - suppress soft labels.
- -nsl
- No status line - suppress status line.
- -pp
- Has a printer port which is used.
- -rv
- Terminal in reverse video mode (black on white).
- -s
- Enable status line.
- -vb
- Use visible bell (flash) rather than beep.
- -w
- Wide; terminal is in 132-column mode.
Conventionally, if your terminal type is a variant intended to specify a line
height, that suffix should go first. So, for a hypothetical FuBarCo model 2317
terminal in 30-line mode with reverse video, best form would be
fubar-30-rv (rather than, say, “fubar-rv-30”).
Terminal types that are written not as standalone entries, but rather as
components to be plugged into other entries via
use capabilities, are
distinguished by using embedded plus signs rather than dashes.
Commands which use a terminal type to control display often accept a -T option
that accepts a terminal name argument. Such programs should fall back on the
TERM environment variable when no -T option is specified.
For maximum compatibility with older System V UNIXes, names and aliases should
be unique within the first 14 characters.
- /etc/terminfo/?/*
- compiled terminal capability database
- /etc/inittab
- tty line initialization (AT&T-like UNIXes)
- /etc/ttys
- tty line initialization (BSD-like UNIXes)
ncurses(3NCURSES),
terminfo(5),
term(5).