Source: ncurses
Version: 5.9+20140913-1
Control: affects -1 console-setup
Tags: patch
Severity: minor
As of the current version of the Terminfo database, the ‘linux’
terminal entry implies the use of the CP437 encoding for the
box-drawing characters and the like (also known as “alternate
character set”, or ACS):
$ nl -ba < misc/terminfo.src
…
1577 linux-basic|linux console,
1578 am, bce, eo, mir, msgr, xenl, xon,
1579 it#8, ncv#18, U8#1,
1580
acsc=+\020\,\021-\030.^Y0\333`\004a\261f\370g\361h\260i\316j\331k\277l\332m\300n\305o~p\304q\304r\304s_t\303u\264v\301w\302x\263y\363z\362{\343|\330}\234~\376,
(Read:
acsc=+\020\,\021-\030.^Y0█`\004a▒f°g±h░i╬j┘k┐l┌m└n┼o~p─q─r─s_t├u┤v┴w┬x│y≤z≥{π|╪}£~■.
And no, that’s /not/ line noise.)
This is hardly a safe assumption these days, especially taking
into account the widespread use of UTF-8, /including/ on ttys.
(Please also note that the console-setup Debconf scripts will
assume UTF-8 mode for ttys provided that the locale is a UTF-8
one, – which, I believe, are default with D-I installs.)
There’s a separate ‘linux-vt’ entry that’s intended to be used
when the terminal encoding is not known, or non-unibyte, and
which emits ACS characters using VT100 ESC sequences instead:
1678 # This uses graphics from VT codeset instead of from cp437.
1679 # reason: cp437 (aka "straight to font") is not functional under luit.
1680 # from: Andrey V Lukyanov <l...@long.yar.ru>.
1681 linux-vt|linux console using VT codes for graphics,
1682
acsc=++\,\,--..00``aaffgghhiijjkkllmmnnooppqqrrssttuuvvwwxxyyzz~~,
1683 rmacs=\E(K, rmpch@, sgr@, sgr0=\E[0m\E(K\017, smacs=\E(0,
1684 smpch@, use=linux,
Unfortunately, this entry misses the ‘enacs’ capability, so its
use doesn’t result in the proper ACS rendering, as in:
$ export TERM=linux-vt
$ tput enacs ; tput smacs ; printf %s\\n lk mj ; tput rmacs ;
lk
mj
Expected:
┌┐
└┘
The /minimal/ solution for the issue is to fix the linux-vt
entry by adding the missing ‘enacs’ capability:
linux-vt|linux console using VT codes for graphics,
acsc=++\,\,--..00``aaffgghhiijjkkllmmnnooppqqrrssttuuvvwwxxyyzz~~,
enacs=\E(B\E)0, rmacs=\E(K, rmpch@, sgr@, sgr0=\E[0m\E(K\017,
smacs=\E(0, smpch@, use=linux,
This could just as well be combined with explicitly passing
‘linux-vt’ to the getty(8) invocations in the default
/etc/inittab for the new GNU/Linux installations, – or similar
measures for the systems using different means to start up the
gettys.
The “proper” solution, in my opinion, is to:
• move the current variants of the ‘acsc’, ‘smacs’, ‘rmacs’
capabilities from linux-basic to a dedicated linux-cp437 entry
(following the suit of linux-koi8, linux-koi8r, linux-lat);
• replace them with the encoding-insensitive ‘acsc’, ‘smacs’,
‘rmacs’ variants from linux-vt, along with adding ‘enacs’ per
above;
• the linux-vt entry is then to be cut down to just ‘use=linux’
(and ‘sgr@’?), but otherwise retained for compatibility.
TIA.
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