how can I invoke zsh via screen when logged in via ssh?

how can I invoke zsh via screen when logged in via ssh?

[TJ Luoma]

I use zsh as my login shell for several accounts I connect to via ssh.


My connection to these accounts is often fragile, either because they
were initiated on an iOS device or behind a satellite internet
connection.


I had a thought today that perhaps one answer would be to use
'screen(1)' as my login shell for those accounts, but then I realized
that I didn't want that to be the shell I use for local logins, just
for SSH logins.


I wondered if anyone had already done this, so I didn't have to
re-invent the wheel, or might have some experience with potential
problems that I might run into when doing this.


1) Would 'zsh' function normally when in screen(1) ?


2) I've already noticed that emacs keys don't seem to work right, i.e.
control+a does not jump to the beginning of the line, although
control+e jumps to the end of the line. Should I make some adjustment
to `bindkeys` or anything else?


3) What's the 'best' way to invoke screen(1) from .zshenv ? I already have this:


PPID_NAME=$(command ps -o 'command=' -cp ${PPID} 2>/dev/null )


case "${PPID_NAME}" in

        sshd)

                        SSH=yes

        ;;


        launchd)

                        LAUNCHD=yes

        ;;


esac


So I was going to change it to:



PPID_NAME=$(command ps -o 'command=' -cp ${PPID} 2>/dev/null )


case "${PPID_NAME}" in

        sshd)

exec =screen -r || exec =screen

        ;;


        launchd)

                        LAUNCHD=yes

        ;;


esac


which would, I believe, resume an existing `screen` session if one
existed, but would otherwise just launch `screen` anew.


Is there a better way?


Thanks in advance,


TjL




ps - bonus question: anyone know how to tell screen(1) to _not_ show
its welcome message every time it launches?

Re: how can I invoke zsh via screen when logged in via ssh?

[Simon Ruderich]

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On Wed, Jan 22, 2014 at 02:54:02PM -0500, TJ Luoma wrote:
> 1) Would 'zsh' function normally when in screen(1) ?

Hello,

Of course. I use zsh almost exclusively from within GNU screen.

> 2) I've already noticed that emacs keys don't seem to work right, i.e.
> control+a does not jump to the beginning of the line, although
> control+e jumps to the end of the line. Should I make some adjustment
> to `bindkeys` or anything else?

GNU screen uses Ctrl-a as "prefix" for all its commands. To send
a "real" Ctrl-a to the process running in the screen window, use
Ctrl-a a.

> 3) What's the 'best' way to invoke screen(1) from .zshenv ? I
> already have this:
>
> [...]

This looks a little fragile. To check for a SSH session use one
of the SSH_* variables set by sshd, e.g. SSH_CONNECTION or
SSH_CLIENT.

    if [[ -n $SSH_CONNECTION ]]; then
        # inside a SSH session
    fi

> So I was going to change it to:
>
> [snip]
>
> which would, I believe, resume an existing `screen` session if one
> existed, but would otherwise just launch `screen` anew.

My current solution to automatically launch a GNU screen session
or connect to a running one looks like this:

    if [[ $TERM != dumb && $TERM != linux && -z $STY && -z $TMUX ]]; then
        # Get running detached sessions.
        session=$(screen -list | grep 'Detached' | awk '{ print $1; exit }')

        # Create a new session if none is running.
        if [[ -z $session ]]; then
            exec screen
        # Reattach to a running session.
        else
            exec screen -r $session
        fi
    fi

This must be added to the ~/.zshrc on the server.

You can easily adapt this for your setup. Just change the
condition inside [[ ... ]] to something like

    [[ -n $SSH_CONNECTION && -z $STY && -z $TMUX ]]

This condition is true if inside a ssh connection and neither GNU
screen nor tmux is already running.

> ps - bonus question: anyone know how to tell screen(1) to _not_ show
> its welcome message every time it launches?

man screen ;-)

Add "startup_message off" to your ~/.screenrc.

Regards
Simon
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Re: how can I invoke zsh via screen when logged in via ssh?

[TJ Luoma]

On Wed, Jan 22, 2014 at 4:22 PM, Simon Ruderich <simon@ruderich.org> wrote:
> man screen ;-)
>
> Add "startup_message off" to your ~/.screenrc.

Bah! *kicks self*

I _had_ read (well, "visually scanned") `man screen` but had been
looking for things like 'hushlogin' or 'suppress' not something as
straightforward as "startup".

Thanks for the tips, I'll definitely give them a try!

(Thanks also to nyuszika7h who replied off-list).

TjL

Re: how can I invoke zsh via screen when logged in via ssh?

[Dirk Heinrichs]

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Am 22.01.2014 22:22, schrieb Simon Ruderich:

>> 2) I've already noticed that emacs keys don't seem to work right, i.e.
>> > control+a does not jump to the beginning of the line, although
>> > control+e jumps to the end of the line. Should I make some adjustment
>> > to `bindkeys` or anything else?
> GNU screen uses Ctrl-a as "prefix" for all its commands. To send
> a "real" Ctrl-a to the process running in the screen window, use
> Ctrl-a a.

I've remapped this to Ctrl-o in .screenrc:

escape ^Oo

Bye...

    Dirk
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Re: how can I invoke zsh via screen when logged in via ssh?

[nyuszika7h]

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I replied off-list? Fail. >_>

Re: how can I invoke zsh via screen when logged in via ssh?

[Kurtis Rader]

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I strongly recommend using tmux rather than screen. It has a much saner
configuration language and is more powerful. It also correctly handles
terminals which support 256 colors. I wrote a pair of scripts for work that
wraps around ssh and tmux (and iTerm2 for Mac OS X). This allows me to type

    work attach

to create iTerm2 windows appropriately sized and positioned and attach each
to its corresponding tmux session on the remote host. If the tmux session
isn't already running one is created. It also takes care of ensuring the
DISPLAY environment variable is set appropriately to allow X11 based apps
to display on my local system.

It also supports a bunch of other commands, For example, "work list" to
enumerate existing tmux sessions. Or "work ssh" to get a raw ssh session.

If there's interest I can work on removing my employer specific bits (which
deal with managing a VPN tunnel).



On Wed, Jan 22, 2014 at 11:54 AM, TJ Luoma <luomat@gmail.com> wrote:

> I use zsh as my login shell for several accounts I connect to via ssh.
>
>
> My connection to these accounts is often fragile, either because they
> were initiated on an iOS device or behind a satellite internet
> connection.
>
>
> I had a thought today that perhaps one answer would be to use
> 'screen(1)' as my login shell for those accounts, but then I realized
> that I didn't want that to be the shell I use for local logins, just
> for SSH logins.
>
>
> I wondered if anyone had already done this, so I didn't have to
> re-invent the wheel, or might have some experience with potential
> problems that I might run into when doing this.
>
>
> 1) Would 'zsh' function normally when in screen(1) ?
>
>
> 2) I've already noticed that emacs keys don't seem to work right, i.e.
> control+a does not jump to the beginning of the line, although
> control+e jumps to the end of the line. Should I make some adjustment
> to `bindkeys` or anything else?
>
>
> 3) What's the 'best' way to invoke screen(1) from .zshenv ? I already have
> this:
>
>
> PPID_NAME=$(command ps -o 'command=' -cp ${PPID} 2>/dev/null )
>
>
> case "${PPID_NAME}" in
>
>         sshd)
>
>                         SSH=yes
>
>         ;;
>
>
>         launchd)
>
>                         LAUNCHD=yes
>
>         ;;
>
>
> esac
>
>
> So I was going to change it to:
>
>
>
> PPID_NAME=$(command ps -o 'command=' -cp ${PPID} 2>/dev/null )
>
>
> case "${PPID_NAME}" in
>
>         sshd)
>
> exec =screen -r || exec =screen
>
>         ;;
>
>
>         launchd)
>
>                         LAUNCHD=yes
>
>         ;;
>
>
> esac
>
>
> which would, I believe, resume an existing `screen` session if one
> existed, but would otherwise just launch `screen` anew.
>
>
> Is there a better way?
>
>
> Thanks in advance,
>
>
> TjL
>
>
>
>
> ps - bonus question: anyone know how to tell screen(1) to _not_ show
> its welcome message every time it launches?
>



-- 
Kurtis Rader
Caretaker of the exceptional canines Junior and Hank

Re: how can I invoke zsh via screen when logged in via ssh?

[Richard Hartmann]

If you have a flakey connection, have a look at mosh[1]; using this
instead of ssh on my laptop has been nothing but great.


Richard


[1] http://mosh.mit.edu/

Re: how can I invoke zsh via screen when logged in via ssh?

[Axel Beckert]

Hi,

On Fri, Jan 24, 2014 at 01:40:52PM +0100, Richard Hartmann wrote:
> If you have a flakey connection, have a look at mosh[1]; using this
> instead of ssh on my laptop has been nothing but great.

Besides Mosh there's also AutoSSH[2] in case you need port forwarding
and other stuff in combination with automatic SSH reconnects.

  [2] http://www.harding.motd.ca/autossh/

But both are not available for iOS AFAIK.

On Thu, Jan 23, 2014 at 10:12:29PM -0800, Kurtis Rader wrote:
> I strongly recommend using tmux rather than screen.

I don't. (SCNR)

> It also correctly handles terminals which support 256 colors.

GNU Screen works fine for me with 256 colors for many years now.
(Other people claim they're getting eye-cancer from my 256-color mutt
running inside my main Screen session. :-)

		Kind regards, Axel
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Re: how can I invoke zsh via screen when logged in via ssh?

[Christoph (Stucki) von Stuckrad]

On Fri, 24 Jan 2014, Richard Hartmann wrote:

> If you have a flakey connection, have a look at mosh[1]; using this
> instead of ssh on my laptop has been nothing but great.
...
> [1] http://mosh.mit.edu/

Definitely right! Since 'mosh' exists, working with a laptop
from different places on the same surviving connection (on
screen of course) is a lot easier than before. :-)
Except if the laptop reboots, for which you still ned screen.

But, may be the answer to the original Subject, is as simple as:

If you have the wrong login-shell and can not change it,
you eighter set the SHELL Variable in your startup files,
or you put 'shell /usr/bin/zsh' into your '~/.screenrc'.
In both cases all Screen-Windows run with 'zsh'.

Stucki

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Re: how can I invoke zsh via screen when logged in via ssh?

[lilydjwg]

On Wed, Jan 22, 2014 at 02:54:02PM -0500, TJ Luoma wrote:
> I use zsh as my login shell for several accounts I connect to via ssh.
>
>
> My connection to these accounts is often fragile, either because they
> were initiated on an iOS device or behind a satellite internet
> connection.
>
>
> I had a thought today that perhaps one answer would be to use
> 'screen(1)' as my login shell for those accounts, but then I realized
> that I didn't want that to be the shell I use for local logins, just
> for SSH logins.
>
>
> I wondered if anyone had already done this, so I didn't have to
> re-invent the wheel, or might have some experience with potential
> problems that I might run into when doing this.

So you might be interested in mosh[1] (the mobile shell), which I find
is great for slow unstable connections.

[1]: http://mosh.mit.edu/

> [...]

-- 
Best regards,
lilydjwg

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http://lilydjwg.is-programmer.com/
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Re: how can I invoke zsh via screen when logged in via ssh?

[Thorsten Kampe]

* TJ Luoma (Wed, 22 Jan 2014 14:54:02 -0500)
> I had a thought today that perhaps one answer would be to use
> 'screen(1)' as my login shell for those accounts, but then I realized
> that I didn't want that to be the shell I use for local logins, just
> for SSH logins.

That's pretty much the same way I use it.
 
> I wondered if anyone had already done this, so I didn't have to
> re-invent the wheel, or might have some experience with potential
> problems that I might run into when doing this.
> 
> 
> 3) What's the 'best' way to invoke screen(1) from .zshenv ? I
> already have this:
> [...]
> 
> which would, I believe, resume an existing `screen` session if one
> existed, but would otherwise just launch `screen` anew.

Why don't you simply read the man page and invoke screen with the 
right options?! Would have saved you tons of time...

I suggest you replace all your ssh calls like "ssh user@host" with
"ssh -t user@host screen -xRR ssh". That creates a session with name 
"ssh" or connect to an already running session with that name.

Thorsten