Linux – SSH garbling characters in vim/nano on remote server

linuxsshterminal

… and it's driving me insane.

Basically (this has been happening over the past couple months), I log into a few different CentOS servers (one Linode, another VPS, and a shared host to which I have shell access), running 5.5, 5.7, and 6, from my Mac running OS X Lion, using Terminal.

Basically:

$ ssh username@example.com

[remote-host] $ nano somefile.txt

Once I start editing the file, if I use the arrow keys to move around the cursor, or start deleting, then typing again, the cursor jumps around a bit, and if I save the file and reopen it, it's obvious that the cursor was, in fact, jumping all over the place on a line for no apparent reason.

I end up getting things like "This is a neof text." When I had typed in (to the cursor-crazy editor) "This is a line of text."

It's a big problem when it comes to editing configuration files, because I often have to edit one line, save and close, then reopen just to make sure that line is right… then edit another line… and it's getting quite annoying.

I found Linode Lish Shell Vim and Nano rendering troubles: lines not appearing / cursor positions wrong, but I don't know if that relates much, since that's specifically referring to lish.

Best Answer

[Update: As of Mac OS X Mountain Lion 10.8, Terminal supports the Backtab escape sequence, eliminating this issue.]

The version(s?) of nano on those servers sometimes sends a Backtab (ESC [ Z) sequence when moving the cursor left by one character, but Terminal doesn't support this sequence, so nano thinks the cursor has moved when it hasn't and its idea about the current position of the cursor is out of synch with the terminal.

For reasons I can't fathom, nano sends a Backtab when moving to the left and the cursor is one character to the right of a tab stop. Similarly, IIRC, it sends a Tab (Control-I) when moving to the right and the cursor is one character to the left of a tab stop. I don't know why it does this around tab stops instead of always moving left/right using the same character sequences. The version of nano shipped with Mac OS X Lion 10.7 doesn't do this.

Nano only does this when the terminfo says the cbt capability is supported. The default terminfo for Terminal is xterm-256color, which declares this capability and maps it to the Backtab sequence. A workaround is to set the TERM environment variable to something that doesn't declare this capability. You can do this on the local machine before invoking ssh or in the shell startup file on the remote host. Setting it to xterm-color will do in a pinch, though it is not recommended, as it disables other important behaviors (e.g. 256 colors, BCE, alternate screen content preservation). (A more heavyweight approach is to customize your xterm-256color (or xterm) terminfo file on the remote host to remove cbt.)

Customizing the remote host (one way or another) is recommended, so the customizations don't apply locally or to other remote hosts, but the simplest workaround is to change a Terminal preference setting to use xterm-color instead of xterm-256color:

Terminal > Preferences > Settings > [profile] > Advanced > Declare terminal as:

I recommend duplicating an existing settings profile, customizing it and only using it when you're connecting to those remote hosts.

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