all messages for Emacs-related lists mirrored at yhetil.org
 help / color / mirror / code / Atom feed
* bug#39399: tramp depends on unstable details of shell command line processing
@ 2020-02-02 21:28 John F Carr
  2020-02-03  8:58 ` Michael Albinus
  2020-07-27  4:12 ` 内藤 祐一郎
  0 siblings, 2 replies; 9+ messages in thread
From: John F Carr @ 2020-02-02 21:28 UTC (permalink / raw)
  To: 39399

I use emacs tramp mode for remote editing.  It stopped working on my FreeBSD systems when I upgraded to a development version.  The cause appears to be due to /bin/sh reprinting the entire line when a backspace is sent rather than sending only a backspace-space-backspace sequence.  The failure follows a change in the line editing library (shared with NetBSD) rather than the shell itself.

Environment is emacs 24.5 or 26.3 running on Mac OS Catalina.  The remote system is FreeBSD 13.0 development.  Tramp works with Linux or FreeBSD 12.1 as the remote system.

Here's what happens.

I load tramp and open a file like /ssh:user@host:/.  Emacs spawns ssh to connect.  The first thing tramp does is send

stty -inlcr -onlcr -echo kill '^U' erase '^H'

But this doesn't do much because the tty is in raw mode rather than cooked due to the shell's line editor.  So tramp falls back to a hack to detect echoed input.  It sends "_echo" followed by a string of backspace characters.  "_echo" is unlikely to appear in program output.

Here is the next command after the initial stty:

_echo^H^H^H^H^Hstty icanon erase ^H cols 32767_echo^H^H^H^H^H

The groups of 5 ^H represent 5 backspace characters and the lone ^H in the middle is a two character sequence for stty.

The terminal output from a 12.1 system is

_echo^H ^H^H ^H^H ^H^H ^H^H ^Hstty icanon erase ^H cols 32767_echo^H ^H^H ^H^H ^H^H ^H^H ^H
#$ 

where again the middle ^H is a two character sequence and the others are backspace characters. There is a carriage return between the two lines.  "#$ " is the shell prompt set by tramp.

The terminal output from a FreeBSD 13.0 development branch system is

_echo
#$ _ech ^H
#$ _ec ^H
#$ _e ^H
#$ _ ^H
#$  ^Hstty icanon erase ^H cols 32767_echo
#$ stty icanon erase ^H cols 32767_ech ^H
#$ stty icanon erase ^H cols 32767_ec ^H
#$ stty icanon erase ^H cols 32767_e ^H
#$ stty icanon erase ^H cols 32767_ ^H
#$ stty icanon erase ^H cols 32767 ^H
#$ 

with carriage returns between lines.  This does not make sense to emacs, which hangs waiting for something it recognizes.  I can recover by hitting control-G which aborts the tramp connection.

This issue is also reported to FreeBSD at https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=243807.




^ permalink raw reply	[flat|nested] 9+ messages in thread

end of thread, other threads:[~2020-07-28  7:34 UTC | newest]

Thread overview: 9+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2020-02-02 21:28 bug#39399: tramp depends on unstable details of shell command line processing John F Carr
2020-02-03  8:58 ` Michael Albinus
2020-02-04  8:34   ` Michael Albinus
2020-02-05 23:42     ` John F Carr
2020-02-06  9:13       ` Michael Albinus
2020-07-27  4:12 ` 内藤 祐一郎
2020-07-27 18:01   ` Michael Albinus
2020-07-28  2:51     ` 内藤 祐一郎
2020-07-28  7:34       ` Michael Albinus

Code repositories for project(s) associated with this external index

	https://git.savannah.gnu.org/cgit/emacs.git
	https://git.savannah.gnu.org/cgit/emacs/org-mode.git

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.