Using screen on Synology (DSM6): "Cannot find termcap entry for 'xterm-256color"

Question

Using screen on Synology (DSM6) I get the error

Cannot find termcap entry for 'xterm-256color'

when I type screen .

I am aware of the quick fix from this question Unix screen utility error: Cannot find termcap entry for 'xterm-256color' .
So TERM=xterm screen does work and launches screen .

But I would like to set TERM to a different value on my machine, so I could just type screen instead.
Can I choose the color mode screen uses and set it somewhere?

Answer 1

Using.bashrc you can set the TERM back to a working version. My issue was the screen.xterm-256color did not exist.

# ~/.screenrc
# Fix screen and vim
# "E437: terminal capability "cm" required"
if [[ $TERM = 'screen.xterm-256color' ]]; then
  export TERM=xterm-256color
fi

For the.bashrc changes to take effect in screen you need to tell screen to treat each terminal as a new shell

#~/.screenrc
# Treat all new screen tabs as new shells
shell -$SHELL

Answer 2

screen filters out escape sequences which it does not support. It doesn't support the xterm-style escape sequence which changes color values, but uses only the predefined color palette of your terminal.

If you do

infocmp screen-256color xterm-256color

you'll probably notice several differences. The one dealing with changing color values is initc . (Choosing a given color from the palette is done with setaf and setab ).

The warning message is because (apparently) your machine does not have a terminal description for xterm-256color installed, eg, if you ssh to the machine and it gets TERM from your local machine. screen wants to know what TERM applies to outside , to help it convert to its inside ( TERM=screen ). A quick read of the documentation and source code shows that while it has several features for amending the conversion between in/out TERM , and for choosing a particular inside-TERM, there is no .screenrc setting for overriding the environment variable TERM .

Here's a pointer to the relevant chunk of code in screen :

    if ((attach_term = getenv("TERM")) == 0 || *attach_term == 0)
        Panic(0, "Please set a terminal type.");
    if (strlen(attach_term) > MAXTERMLEN)
        Panic(0, "$TERM too long - sorry.");
    GetTTY(0, &attach_Mode);

where it ensures that TERM is set, and a pointer to (a couple of levels down) where it checks if TERM corresponds to an actual terminal description :

if (*D_termname == 0 || e_tgetent(tbuf, D_termname) != 1) {
    Msg(0, "Cannot find terminfo entry for '%s'.", D_termname);
    return -1;
}

So... if you want to just run "screen", you could make a shell alias, or simple script which sets TERM as you are doing now.