Tramp timeout for currently unreachable connections?

Tramp timeout for currently unreachable connections?

[Visuwesh]

Hello all,

I know that non-essential=t prevents Tramp from establishing new
connections but is there a way to make Tramp use a very short timeout
when trying to connect to a previously established connection that is
now unreachable?  What I mean is: if I am connected to a remote host via
a ssh connection /ssh:user@remote: and my internet connection goes down,
I do not want Tramp trying to fetch remote resources forever.  For
example, consider an abbreviate-file-name call when such a connection is
no longer reachable.  With M-x toggle-debug-on-quit,

    M-: (let ((non-essential t) (remote-file-name-access-timeout 1)) (abbreviate-file-name default-directory)) RET ... C-g

in a remote buffer yields the following backtrace:

Debugger entered--Lisp error: (quit "")
  signal(quit (""))
  tramp-signal-hook-function(quit nil)
  tramp-accept-process-output(#<process *tramp/ssh user@remote*>)
  tramp-wait-for-regexp(#<process *tramp/ssh user@remote*> nil "\\(?:^\\|\0\\)\\(?:[^\n#$]*///4a90d21f6648cee2bec7823f4b91fec3#\\$\\(?:\33\\[[0-?]*[ -/]*[@-~]\\)?\15?$\\)")
  tramp-wait-for-output(#<process *tramp/ssh user@remote*>)
  tramp-send-command((tramp-file-name "ssh" "user" nil "remote" nil "/home/user/tmp" nil) "test -e /home/user/tmp 2>/dev/null; echo tramp_exit_status $?")
  tramp-send-command-and-check((tramp-file-name "ssh" "user" nil "remote" nil "/home/user/tmp" nil) "test -e /home/user/tmp")
  tramp-sh-handle-file-exists-p("/ssh:user@remote:/home/user/tmp")
  apply(tramp-sh-handle-file-exists-p "/ssh:user@remote:/home/user/tmp")
  tramp-sh-file-name-handler(file-exists-p "/ssh:user@remote:/home/user/tmp")
  apply(tramp-sh-file-name-handler file-exists-p "/ssh:user@remote:/home/user/tmp")
  tramp-file-name-handler(file-exists-p "/ssh:user@remote:/home/user/tmp")
  file-exists-p("/ssh:user@remote:/home/user/tmp")
  tramp-handle-file-name-case-insensitive-p("/ssh:user@remote:/home/user/tmp/")
  apply(tramp-handle-file-name-case-insensitive-p "/ssh:user@remote:/home/user/tmp/")
  tramp-sh-file-name-handler(file-name-case-insensitive-p "/ssh:user@remote:/home/user/tmp/")
  apply(tramp-sh-file-name-handler file-name-case-insensitive-p "/ssh:user@remote:/home/user/tmp/")
  tramp-file-name-handler(file-name-case-insensitive-p "/ssh:user@remote:/home/user/tmp/")
  file-name-case-insensitive-p("/ssh:user@remote:/home/user/tmp/")
  tramp-handle-abbreviate-file-name("/ssh:user@remote:/home/user/tmp/")
  apply(tramp-handle-abbreviate-file-name "/ssh:user@remote:/home/user/tmp/")
  tramp-sh-file-name-handler(abbreviate-file-name "/ssh:user@remote:/home/user/tmp/")
  apply(tramp-sh-file-name-handler abbreviate-file-name "/ssh:user@remote:/home/user/tmp/")
  tramp-file-name-handler(abbreviate-file-name "/ssh:user@remote:/home/user/tmp/")
  abbreviate-file-name("/ssh:user@remote:/home/user/tmp/")
  (let ((non-essential t) (remote-file-name-access-timeout 1)) (abbreviate-file-name default-directory))
  eval((let ((non-essential t) (remote-file-name-access-timeout 1)) (abbreviate-file-name default-directory)) t)
  #f(compiled-function () #<bytecode -0x93fec5cef4eacc6>)()
  #f(compiled-function () #<bytecode -0x5db3e1955cb81d1>)()
  handler-bind-1(#f(compiled-function () #<bytecode -0x5db3e1955cb81d1>) (error) eval-expression--debug)
  eval-expression((let ((non-essential t) (remote-file-name-access-timeout 1)) (abbreviate-file-name default-directory)) nil nil 127)
  funcall-interactively(eval-expression (let ((non-essential t) (remote-file-name-access-timeout 1)) (abbreviate-file-name default-directory)) nil nil 127)
  call-interactively(eval-expression nil nil)
  command-execute(eval-expression)

I would like to know if it is possible to make Tramp send non-nil
TIMEOUT argument to tramp-wait-for-output (maybe even higher up the
call chain).  I know of without-remote-files but is there a less heavier
hammer? Because I do _want_ Tramp to do its job when the connection is
still reachable.

Thank you.

P.S. Kindly keep me CC'd since I do not follow this list.

Re: Tramp timeout for currently unreachable connections?

[Michael Albinus]

Visuwesh <visuweshm@gmail.com> writes:

> Hello all,

Hi Visuwesh,

> I know that non-essential=t prevents Tramp from establishing new
> connections but is there a way to make Tramp use a very short timeout
> when trying to connect to a previously established connection that is
> now unreachable?  What I mean is: if I am connected to a remote host via
> a ssh connection /ssh:user@remote: and my internet connection goes down,
> I do not want Tramp trying to fetch remote resources forever.

Use 'M-x tramp-cleanup-connection'. Play with user option `tramp-connection-timeout'.

> Thank you.

Best regards, Michael.

Re: Tramp timeout for currently unreachable connections?

[Visuwesh]

[வியாழன் செப்டம்பர் 12, 2024] Michael Albinus wrote:

> Visuwesh <visuweshm@gmail.com> writes:
>
>> Hello all,
>
> Hi Visuwesh,

Hello Michael,

>> I know that non-essential=t prevents Tramp from establishing new
>> connections but is there a way to make Tramp use a very short timeout
>> when trying to connect to a previously established connection that is
>> now unreachable?  What I mean is: if I am connected to a remote host via
>> a ssh connection /ssh:user@remote: and my internet connection goes down,
>> I do not want Tramp trying to fetch remote resources forever.
>
> Use 'M-x tramp-cleanup-connection'.

I can always C-g and execute this command but I would like to do it
automagically in my lisp programs so, unfortunately, this isn't exactly
an option.  Half the time, I forget the freezes are due to Tramp
inability to speak with the remote machine too...

> Play with user option `tramp-connection-timeout'.

If I let-bind tramp-connection-timeout to 1 in the above example, Tramp
still tries to talk with the remote machine.  :-( Am I misunderstanding
your suggestion?  Should I be using with-(tramp-)timeout?

>> Thank you.
>
> Best regards, Michael.

Thank you for your answers.

Re: Tramp timeout for currently unreachable connections?

[Robert Pluim]

>>>>> On Thu, 12 Sep 2024 16:47:39 +0200, Michael Albinus <michael.albinus@gmx.de> said:

    Michael> Visuwesh <visuweshm@gmail.com> writes:
    >> Hello all,

    Michael> Hi Visuwesh,

    >> I know that non-essential=t prevents Tramp from establishing new
    >> connections but is there a way to make Tramp use a very short timeout
    >> when trying to connect to a previously established connection that is
    >> now unreachable?  What I mean is: if I am connected to a remote host via
    >> a ssh connection /ssh:user@remote: and my internet connection goes down,
    >> I do not want Tramp trying to fetch remote resources forever.

    Michael> Use 'M-x tramp-cleanup-connection'. Play with user option `tramp-connection-timeout'.

Idle thought: would enabling 'ServerAliveInterval' help at all here?
(my Tramp connections travel from one side of my desk to the other, so
I canʼt tell ☺️)

Robert
-- 

Re: Tramp timeout for currently unreachable connections?

[Visuwesh]

[வியாழன் செப்டம்பர் 12, 2024] Robert Pluim wrote:

>>>>>> On Thu, 12 Sep 2024 16:47:39 +0200, Michael Albinus <michael.albinus@gmx.de> said:
>
>     Michael> Visuwesh <visuweshm@gmail.com> writes:
>     >> Hello all,
>
>     Michael> Hi Visuwesh,
>
>     >> I know that non-essential=t prevents Tramp from establishing new
>     >> connections but is there a way to make Tramp use a very short timeout
>     >> when trying to connect to a previously established connection that is
>     >> now unreachable?  What I mean is: if I am connected to a remote host via
>     >> a ssh connection /ssh:user@remote: and my internet connection goes down,
>     >> I do not want Tramp trying to fetch remote resources forever.
>
>     Michael> Use 'M-x tramp-cleanup-connection'. Play with user option `tramp-connection-timeout'.
>
> Idle thought: would enabling 'ServerAliveInterval' help at all here?
> (my Tramp connections travel from one side of my desk to the other, so
> I canʼt tell ☺️)

I have it set to 100 but it doesn't help much.  I don't think I am
describing my problem well.  I have the following function

    (defun vz/stb--buffer-annotation (buffer)
      (let ((case-fold-search nil))
        (pcase (buffer-name buffer)
          ((rx bos (1+ anychar) "<" (+ (not ">")) ">")
              (let ((non-essential t))
                (vz/with-when (buffer-file-name buffer)
                  (abbreviate-file-name it)))
              ;; (let ((non-essential t))
              ;;   (vz/with-when (vz/file-visiting-buffer-p buffer)
              ;;     (abbreviate-file-name it)))
              )
          ((rx bos "*" (or "shell" "ssh") (? "-"))
              (let ((non-essential t))
                (abbreviate-file-name (buffer-local-value 'default-directory buffer))))
          (_ (vz/buffer-annotation buffer)))))

that returns an annotation string for my C-x b replacement.  If Tramp
already knows the connection is dead, non-essential=t signals Tramp to
not to bother to open a new connection.  I would like a similar variable
to make Tramp give up after a few seconds if it gets no reply from the
remote server in the case of connections that are no longer reachable.

Re: Tramp timeout for currently unreachable connections?

[Michael Albinus]

Robert Pluim <rpluim@gmail.com> writes:

Hi Robert,

>>>>>> On Thu, 12 Sep 2024 16:47:39 +0200, Michael Albinus <michael.albinus@gmx.de> said:
>
>     Michael> Visuwesh <visuweshm@gmail.com> writes:
>     >> Hello all,
>
>     Michael> Hi Visuwesh,
>
>     >> I know that non-essential=t prevents Tramp from establishing new
>     >> connections but is there a way to make Tramp use a very short timeout
>     >> when trying to connect to a previously established connection that is
>     >> now unreachable?  What I mean is: if I am connected to a remote host via
>     >> a ssh connection /ssh:user@remote: and my internet connection goes down,
>     >> I do not want Tramp trying to fetch remote resources forever.
>
>     Michael> Use 'M-x tramp-cleanup-connection'. Play with user option `tramp-connection-timeout'.
>
> Idle thought: would enabling 'ServerAliveInterval' help at all here?
> (my Tramp connections travel from one side of my desk to the other, so
> I canʼt tell ☺️)

Yes, even the Tramp manual speaks about:

--8<---------------cut here---------------start------------->8---
4.19.2 Detection of session hangouts
------------------------------------

‘ssh’ sessions on the local host hang when the network is down.  TRAMP
cannot safely detect such hangs.  OpenSSH can be configured to kill
such hangs with the following settings in ‘~/.ssh/config’:

     Host *
          ServerAliveInterval 5
          ServerAliveCountMax 2
--8<---------------cut here---------------end--------------->8---

But who reads manuals ...

> Robert

Best regards, Michael.

Re: Tramp timeout for currently unreachable connections?

[Michael Albinus]

Visuwesh <visuweshm@gmail.com> writes:

> Hello Michael,

Hi Visuwesh,

>>> I know that non-essential=t prevents Tramp from establishing new
>>> connections but is there a way to make Tramp use a very short timeout
>>> when trying to connect to a previously established connection that is
>>> now unreachable?  What I mean is: if I am connected to a remote host via
>>> a ssh connection /ssh:user@remote: and my internet connection goes down,
>>> I do not want Tramp trying to fetch remote resources forever.
>>
>> Use 'M-x tramp-cleanup-connection'.
>
> I can always C-g and execute this command but I would like to do it
> automagically in my lisp programs so, unfortunately, this isn't exactly
> an option.  Half the time, I forget the freezes are due to Tramp
> inability to speak with the remote machine too...

Ah, I thought you're speaking about the interactive case.

>> Play with user option `tramp-connection-timeout'.
>
> If I let-bind tramp-connection-timeout to 1 in the above example, Tramp
> still tries to talk with the remote machine.  :-( Am I misunderstanding
> your suggestion?  Should I be using with-(tramp-)timeout?

tramp-connection-timeout is of help only for establishing a new
connection. That's why I've mentioned it, in conjuntion with
tramp-cleanup-connection.

> Thank you for your answers.

Best regards, Michael.

Re: Tramp timeout for currently unreachable connections?

[Visuwesh]

[வியாழன் செப்டம்பர் 12, 2024] Michael Albinus wrote:

> Robert Pluim <rpluim@gmail.com> writes:
>
> Hi Robert,
>
>>>>>>> On Thu, 12 Sep 2024 16:47:39 +0200, Michael Albinus <michael.albinus@gmx.de> said:
>>
>>     Michael> Visuwesh <visuweshm@gmail.com> writes:
>>     >> Hello all,
>>
>>     Michael> Hi Visuwesh,
>>
>>     >> I know that non-essential=t prevents Tramp from establishing new
>>     >> connections but is there a way to make Tramp use a very short timeout
>>     >> when trying to connect to a previously established connection that is
>>     >> now unreachable?  What I mean is: if I am connected to a remote host via
>>     >> a ssh connection /ssh:user@remote: and my internet connection goes down,
>>     >> I do not want Tramp trying to fetch remote resources forever.
>>
>>     Michael> Use 'M-x tramp-cleanup-connection'. Play with user option `tramp-connection-timeout'.
>>
>> Idle thought: would enabling 'ServerAliveInterval' help at all here?
>> (my Tramp connections travel from one side of my desk to the other, so
>> I canʼt tell ☺️)
>
> Yes, even the Tramp manual speaks about:
>
> 4.19.2 Detection of session hangouts
> ------------------------------------
>
> ‘ssh’ sessions on the local host hang when the network is down.  TRAMP
> cannot safely detect such hangs.  OpenSSH can be configured to kill
> such hangs with the following settings in ‘~/.ssh/config’:
>
>      Host *
>           ServerAliveInterval 5
>           ServerAliveCountMax 2
>
> But who reads manuals ...

Ahh!! It seems I completely misunderstood these two variables in my
initial reading of ssh_config(5) when I was initially reading through
the Tramp manual.  Thank you for pointing this out again.

>> Robert
>
> Best regards, Michael.

Re: Tramp timeout for currently unreachable connections?

[Michael Albinus]

Visuwesh <visuweshm@gmail.com> writes:

Hi Visuwesh,

>> Idle thought: would enabling 'ServerAliveInterval' help at all here?
>> (my Tramp connections travel from one side of my desk to the other, so
>> I canʼt tell ☺️)

> I have it set to 100 but it doesn't help much.  I don't think I am
> describing my problem well.  I have the following function
>
>     (defun vz/stb--buffer-annotation (buffer)
>       (let ((case-fold-search nil))
>         (pcase (buffer-name buffer)
>           ((rx bos (1+ anychar) "<" (+ (not ">")) ">")
>               (let ((non-essential t))
>                 (vz/with-when (buffer-file-name buffer)
>                   (abbreviate-file-name it)))
>               ;; (let ((non-essential t))
>               ;;   (vz/with-when (vz/file-visiting-buffer-p buffer)
>               ;;     (abbreviate-file-name it)))
>               )
>           ((rx bos "*" (or "shell" "ssh") (? "-"))
>               (let ((non-essential t))
>                 (abbreviate-file-name (buffer-local-value 'default-directory buffer))))
>           (_ (vz/buffer-annotation buffer)))))
>
> that returns an annotation string for my C-x b replacement.  If Tramp
> already knows the connection is dead, non-essential=t signals Tramp to
> not to bother to open a new connection.  I would like a similar variable
> to make Tramp give up after a few seconds if it gets no reply from the
> remote server in the case of connections that are no longer reachable.

I've quoted the Tramp manual in my answer to Robert: "‘ssh’ sessions on
the local host hang when the network is down.  TRAMP cannot safely
detect such hangs."

The reason is, that Tramp just sees a server, which doesn't respond to a
request. It doesn't know the reason for that non-responsiveness. The
request could be, for example, to copy a file of dozens or hundreds MBs
(yes, I've seen this in the wild). This can take a long time, and it
would be intended by the user. There is no good timeout value to stop
waiting the the response.

Best regards, Michael.

Re: Tramp timeout for currently unreachable connections?

[Visuwesh]

[வியாழன் செப்டம்பர் 12, 2024] Michael Albinus wrote:

> Visuwesh <visuweshm@gmail.com> writes:
>
> Hi Visuwesh,
>
>>> Idle thought: would enabling 'ServerAliveInterval' help at all here?
>>> (my Tramp connections travel from one side of my desk to the other, so
>>> I canʼt tell ☺️)
>
>> I have it set to 100 but it doesn't help much.  I don't think I am
>> describing my problem well.  I have the following function
>>
>>     (defun vz/stb--buffer-annotation (buffer)
>>       (let ((case-fold-search nil))
>>         (pcase (buffer-name buffer)
>>           ((rx bos (1+ anychar) "<" (+ (not ">")) ">")
>>               (let ((non-essential t))
>>                 (vz/with-when (buffer-file-name buffer)
>>                   (abbreviate-file-name it)))
>>               ;; (let ((non-essential t))
>>               ;;   (vz/with-when (vz/file-visiting-buffer-p buffer)
>>               ;;     (abbreviate-file-name it)))
>>               )
>>           ((rx bos "*" (or "shell" "ssh") (? "-"))
>>               (let ((non-essential t))
>>                 (abbreviate-file-name (buffer-local-value 'default-directory buffer))))
>>           (_ (vz/buffer-annotation buffer)))))
>>
>> that returns an annotation string for my C-x b replacement.  If Tramp
>> already knows the connection is dead, non-essential=t signals Tramp to
>> not to bother to open a new connection.  I would like a similar variable
>> to make Tramp give up after a few seconds if it gets no reply from the
>> remote server in the case of connections that are no longer reachable.
>
> I've quoted the Tramp manual in my answer to Robert: "‘ssh’ sessions on
> the local host hang when the network is down.  TRAMP cannot safely
> detect such hangs."
>
> The reason is, that Tramp just sees a server, which doesn't respond to a
> request. It doesn't know the reason for that non-responsiveness. The
> request could be, for example, to copy a file of dozens or hundreds MBs
> (yes, I've seen this in the wild). This can take a long time, and it
> would be intended by the user. There is no good timeout value to stop
> waiting the the response.

Thanks, so the only realistic option is to adjust those ssh variables to
a sensible value then.  I was under the impression that there existed a
variable or function that would force Tramp to use a specific timeout
value but in retrospect, I see that it would be unreliable.  Thank you
once again for pointing to the manual making me realise my initial
misunderstanding of the ssh variables.

> Best regards, Michael.

Thank you for your patience in answering my questions!