screen and $TERM and misformatted vi

jernst · 2017-10-04 18:46:26

For complicated reasons, I'm ssh'ing from my Mac (Terminal.app) into an Arch Linux box, where I need to run ckermit or screen over USB to have a console on a second Linux box.

This works, but somewhere in between information about terminal size and and some other things get lost, so I cannot really run an interactive editor such as vi on the second Linux box: the display is completely misformatted, making editing impossible. E.g. "vi foo" shows:

line 1
      line 2
            line 3

I assume this can be made to work somehow, and I'm hoping to learn how.

All three (Mac, Linux 1, Linux 2) have "export TERM=vt100". I run screen as "screen /dev/ttyUSB0 115200". Everything is fine between the Mac and the first Linux box.

Slithery · 2017-10-04 19:12:04

jernst wrote:

All three (Mac, Linux 1, Linux 2) have "export TERM=vt100".

You shouldn't be exporting TERM anywhere, it's known to cause issues.

jernst · 2017-10-04 19:17:47

slithery wrote:

You shouldn't be exporting TERM anywhere, it's known to cause issues.

Without, the Mac and first Linux box have TERM=vt100 and the second Linux box has TERM=vt220. I figured that could cause problems. But setting all of them to vt100 or vt220 causes no change in behavior. (As I write this, I realize that I might not understand how $TERM actually works.)

Trilby · 2017-10-04 19:23:08

jernst wrote:

But setting all of them to vt100 or vt220 causes no change in behavior.

He said don't set them at all. Get rid of any "TERM=..." anywhere in any of your shellrc or related files. That should only be set by the terminal itself, and ideally would be a read-only setting, but environment variables can't be made read-only. When you change the setting of TERM, you are interrupting normal communication channels and effectively lying to client programs - so it's no surprise if they don't work right.

Last edited by Trilby (2017-10-04 19:24:25)

jernst · 2017-10-04 19:42:14

I have restarted everything without any manual settings of TERM, also checked "grep TERM ~/.??*". No change in behavior.

My guess would be that the $TERM info does not make it across the serial/USB/screen connection? Or do I need to do something with stty?

On the Mac "stty -a" says:

speed 9600 baud; 35 rows; 155 columns;
lflags: icanon isig iexten echo echoe -echok echoke -echonl echoctl
	-echoprt -altwerase -noflsh -tostop -flusho pendin -nokerninfo
	-extproc
iflags: -istrip icrnl -inlcr -igncr ixon -ixoff ixany imaxbel iutf8
	-ignbrk brkint -inpck -ignpar -parmrk
oflags: opost onlcr -oxtabs -onocr -onlret
cflags: cread cs8 -parenb -parodd hupcl -clocal -cstopb -crtscts -dsrflow
	-dtrflow -mdmbuf
cchars: discard = ^O; dsusp = ^Y; eof = ^D; eol = <undef>;
	eol2 = <undef>; erase = ^?; intr = ^C; kill = ^U; lnext = ^V;
	min = 1; quit = ^\; reprint = ^R; start = ^Q; status = ^T;
	stop = ^S; susp = ^Z; time = 0; werase = ^W;

On Linux 1:

speed 9600 baud; rows 35; columns 155; line = 0;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = M-^?; eol2 = M-^?; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W;
lnext = ^V; discard = ^O; min = 1; time = 0;
-parenb -parodd -cmspar cs8 -hupcl -cstopb cread -clocal -crtscts
-ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl ixon -ixoff -iuclc ixany imaxbel -iutf8
opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0
isig icanon iexten echo echoe -echok -echonl -noflsh -xcase -tostop -echoprt echoctl echoke -flusho -extproc

On Linux 2:

speed 0 baud; rows 0; columns 0; line = 0;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>;
eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R;
werase = ^W; lnext = ^V; discard = ^O; min = 1; time = 0;
-parenb -parodd -cmspar cs5 hupcl -cstopb cread clocal -crtscts
-ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl ixon ixoff
-iuclc -ixany -imaxbel iutf8
opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0
isig icanon -iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt
-echoctl echoke -flusho -extproc

I do not know what all these things mean, but there clearly are differences, like "cs5" vs "cs8" (which apparently means character size). Unfortunately "stty cs8" on Linux 2 says "stty: 'standard input': unable to perform all requested operations" -- whatever that means.

BTW, what does "M-^?" mean? I tried to set it, but it says I need an integer argument.

seth · 2017-10-04 20:48:27

My guess is that screen is messing up the TERM variable (again)
https://bbs.archlinux.org/viewtopic.php?id=230308

echo $TERM

jernst · 2017-10-04 20:56:33

seth wrote:

My guess is that screen is messing up the TERM variable (again)

Given the above values for $TERM, what would you suggest I should try?

seth · 2017-10-04 21:18:18

This is only a problem when using screen.
First check the actual values of $TERM

If it's vt100 (and you really don't cause this by exporting the value somewhere), run "toe | grep Terminal.app" and pick one that looks reasonable. Export that and see what happens.

jernst · 2017-10-04 21:47:04

Here's what I did. On the Mac:

$ toe | grep Terminal.app
nsterm    	AppKit Terminal.app
nsterm+7  	AppKit Terminal.app v41+ basic capabilities w/ASCII charset
...

and lots of variations. On the Mac:

export TERM=nsterm

Then I ssh into Linux box 1, and see that $TERM=nsterm. So far so good.

Now I do my "screen /dev/ttyUSB0" and on Linux box 2, I'm back at "TERM=vt220" so it did not propagate. Now I tried both leaving this value, and setting it to nsterm, but in both cases, I get the same corrupted vi output as always. I tried some other values for TERM, but same behavior.

jernst · 2017-10-04 22:02:21

Just noticed that vim works, but vi still does not -- both regardless of various values of $TERM in various places.

So my immediate problem (editing remote files) seems to be solved.... but I'd still like to know how to solve this properly.

Add-on: well, "works" is relative. It allows me to edit the files I need to edit, but it thinks the terminal has a different size than it does, as does "more" and other tools. So I'm hobbled although not fatally so any more.

Last edited by jernst (2017-10-04 23:11:57)

Arch Linux

#1 2017-10-04 18:46:26

screen and $TERM and misformatted vi

#2 2017-10-04 19:12:04

Re: screen and $TERM and misformatted vi

#3 2017-10-04 19:17:47

Re: screen and $TERM and misformatted vi

#4 2017-10-04 19:23:08

Re: screen and $TERM and misformatted vi

#5 2017-10-04 19:42:14

Re: screen and $TERM and misformatted vi

#6 2017-10-04 20:48:27

Re: screen and $TERM and misformatted vi

#7 2017-10-04 20:56:33

Re: screen and $TERM and misformatted vi

#8 2017-10-04 21:18:18

Re: screen and $TERM and misformatted vi

#9 2017-10-04 21:47:04

Re: screen and $TERM and misformatted vi

#10 2017-10-04 22:02:21

Re: screen and $TERM and misformatted vi

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