failed to start based on TERM

[szuecs]

% termshark
Error: terminal entry not found [TERM: screen.xterm-256color]
zsh: exit 1 termshark
% TERM=xterm-256color termshark
Packets read from interface eth0 have been saved in /$home/.cache/termshark/eth0-921608986.pcap

[pocc]

Please post tshark -v and any other relevant facts about your system.

[szuecs]

Relevant facts: I use screen

% tshark -v
TShark (Wireshark) 2.6.6 (Git v2.6.6 packaged as 2.6.6-1~ubuntu18.04.0)

Copyright 1998-2019 Gerald Combs <[email protected]> and contributors.
License GPLv2+: GNU GPL version 2 or later <http://www.gnu.org/licenses/old-licenses/gpl-2.0.html>
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Compiled (64-bit) with libpcap, with POSIX capabilities (Linux), with libnl 3,
with GLib 2.56.2, with zlib 1.2.11, with SMI 0.4.8, with c-ares 1.14.0, with Lua
5.2.4, with GnuTLS 3.5.18, with Gcrypt 1.8.1, with MIT Kerberos, with MaxMind DB
resolver, with nghttp2 1.30.0, with LZ4, with Snappy, with libxml2 2.9.4.

Running on Linux 4.15.0-47-generic, with Intel(R) Core(TM) i5-5300U CPU @
2.30GHz (with SSE4.2), with 15740 MB of physical memory, with locale
en_US.UTF-8, with libpcap version 1.8.1, with GnuTLS 3.5.18, with Gcrypt 1.8.1,
with zlib 1.2.11, binary plugins supported (13 loaded).

Built using gcc 7.3.0.

The same problem I had with some other Go tool, I don't remember which one it was. They fixed it by adding something to $TERM check if I recall correctly.

[pocc]

• Can you check whether updating tshark/Wireshark to v3.0.0 affects this problem?
• It's possible that there are builtin bash assumptions that shouldn't be there. If you have bash installed, can you check whether using that shell ameliorates this issue?
• Do you see this problem using a different terminal, not using screen?

[pocc]

@szuecs Do you have any updates? Were you able to find the $TERMINAL_VAR that fixed?

[pocc]

Noting this may be the same issue as #7.

[szuecs]

Sorry @pocc I did not see notifications.
It only happens if I use screen.
I did not tested a different tshark version.
As in #7 , I also use xfce4-terminal. So it might be a related problem.

The funny thing is that TERM=xterm-256color termshark starts, but does not show the cursor as in #7, too. Without screen (but with xfce4-terminal) everything works with cursor. I also had a problem in some other project with the TERM settings and a Go project. Maybe you use the same library and the problem is there.

[gcla]

Hi - I found an explanation for this TERM variable setting here in the screen manual:

https://www.gnu.org/software/screen/manual/screen.html#Window-Termcap

Here's a quick summary:

When screen tries to figure out a terminal name for itself, it first looks for an entry named screen.term, where term is the contents of your $TERM variable. If no such entry exists, screen tries ‘screen’ (or ‘screen-w’, if the terminal is wide (132 cols or more)). If even this entry cannot be found, ‘vt100’ is used as a substitute.

The idea is that if you have a terminal which doesn’t support an important feature (e.g. delete char or clear to EOS) you can build a new termcap/terminfo entry for screen (named ‘screen.dumbterm’) in which this capability has been disabled. If this entry is installed on your machines you are able to do a rlogin and still keep the correct termcap/terminfo entry. The terminal name is put in the $TERM variable of all new windows. screen also sets the $TERMCAP variable reflecting the capabilities of the virtual terminal emulated. Furthermore, the variable $WINDOW is set to the window number of each window.

I can reproduce this problem running screen on Ubuntu 18.10. In my shell, TERM=xterm-256color and when I start screen, TERM=screen.xterm-256color. Running screen with strace, I found a terminfo file at /lib/terminfo/s/screen.xterm-256color.

The reason termshark returns an error is that tcell has a compiled-in terminfo database, which is generated by running a small program that converts terminfo files into Go source code - for example

https://github.com/gdamore/tcell/blob/master/terminfo/term_xterm_256color.go

and that database does not contain an entry for screen.xterm-256color.

Having written all that, I'm not sure why tcell doesn't try to compile a terminfo file on-the-fly, on the machine on which it's running.

Setting TERM is fine, or I believe something like this in your ~/.screenrc will do it for new screen sessions

term screen-256color

[szuecs]

@gcla thanks for your investigation!
Do you want to file a bug to tcell or should I follow up?

[gcla]

Hi @szuecs - no prob, I'll add a tcell issue to figure this out.

[gcla]

I asked here:

gdamore/tcell#279

[gcla]

Hi @szuecs - @gdamore updated tcell so that it now builds a terminal description on-the-fly, if one is not found in tcell's database. I've updated termshark to depend on the latest tcell. This seems to fix this issue for me. Now if I launch screen, then run termshark, it runs correctly. If you want to try it out, here are build instructions:

git clone https://github.com/gcla/termshark
cd termshark
export GO111MODULE=on
go install ./...

Then termshark will be in ~/go/bin. Let me know!

[szuecs]

termshark starts successfully, now.
I have some problems seeing packets, but I will check it tomorrow again

[gcla]

ok, thank you

[szuecs]

The problem was that I ran it as root and not as user. If I run as normal user it works.
Thanks again for solving this issue!