bug#53847: 28.0.91; Tramp SSHFS: incorrect remote home directory

bug#53847: 28.0.91; Tramp SSHFS: incorrect remote home directory

[Philipp Stephani]

To reproduce this, you need two GNU/Linux machines with the same user
name but different home directories.  Assume that on host 1 the user's
home directory is /home1/user, and that on host 2 the user's home
directory is /home2/user.  With the SSH protocol, home directory
expansion works as expected:

$ emacs -Q -batch -eval '(print (expand-file-name "/ssh:host-2:"))'
Tramp: Sending command ‘exec ssh -e none host-2’
Tramp: Found remote shell prompt on ‘host-2’
"/ssh:host-2:/home2/user/"

$ emacs -Q -batch -eval '(print (expand-file-name "/ssh:host-2:~"))'
Tramp: Sending command ‘exec ssh -e none host-2’
Tramp: Found remote shell prompt on ‘host-2’
"/ssh:host-2:/home2/user"

However, this fails with SSHFS:

$ emacs -Q -batch -eval '(print (expand-file-name "/sshfs:host-2:"))'
"/sshfs:host-2:/"

$ emacs -Q -batch -eval '(print (expand-file-name "/sshfs:host-2:~"))'
"/sshfs:host-2:/home1/user"


In GNU Emacs 28.0.91 (build 14, x86_64-pc-linux-gnu, GTK+ Version 3.24.31, cairo version 1.16.0)
 of 2022-02-07
Repository revision: 0d46ee2ddebb74a5a6e1d55da3641d1cd2ba5beb
Repository branch: emacs-28
Windowing system distributor 'The X.Org Foundation', version 11.0.12013000
System Description: Debian GNU/Linux rodete

Configured using:
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 'CFLAGS=-O0 -ggdb3''

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bug#53847: 28.0.91; Tramp SSHFS: incorrect remote home directory

[Michael Albinus]

Philipp Stephani <p.stephani2@gmail.com> writes:

Hi Philipp,

> To reproduce this, you need two GNU/Linux machines with the same user
> name but different home directories.  Assume that on host 1 the user's
> home directory is /home1/user, and that on host 2 the user's home
> directory is /home2/user.  With the SSH protocol, home directory
> expansion works as expected:
>
> However, this fails with SSHFS:

Tilde expansion is not possible for sshfs (and adb, rclone) methods of
Tramp. I've added a check, and Tramp raises an error now when it detects
a tilde. Pushed to master.

However, this breaks shell-command for these methods. In shell-mode,
comint-input-ring-file-name is set to something like
"/sshfs:user@host:~/.history". Expanding this file name raises the error
now. I have no idea how to fix this. Setting comint-input-ring-file-name
to "/sshfs:user@host:/dev/null"?

Best regards, Michael.

bug#53847: 28.0.91; Tramp SSHFS: incorrect remote home directory

[Michael Albinus]

Version: 28.2

Michael Albinus <michael.albinus@gmx.de> writes:

Hi Philipp,

>> To reproduce this, you need two GNU/Linux machines with the same user
>> name but different home directories.  Assume that on host 1 the user's
>> home directory is /home1/user, and that on host 2 the user's home
>> directory is /home2/user.  With the SSH protocol, home directory
>> expansion works as expected:
>>
>> However, this fails with SSHFS:
>
> Tilde expansion is not possible for sshfs (and adb, rclone) methods of
> Tramp. I've added a check, and Tramp raises an error now when it detects
> a tilde. Pushed to master.
>
> However, this breaks shell-command for these methods. In shell-mode,
> comint-input-ring-file-name is set to something like
> "/sshfs:user@host:~/.history". Expanding this file name raises the error
> now. I have no idea how to fix this. Setting comint-input-ring-file-name
> to "/sshfs:user@host:/dev/null"?

Should be fixed now, pushed to master. It will also be contained in the
upcoming Tramp 2.5.2.2 on GNU ELPA.

I'm closing the bug.

Best regards, Michael.

bug#53847: 28.0.91; Tramp SSHFS: incorrect remote home directory

[Philipp Stephani]

Am Mi., 9. Feb. 2022 um 17:10 Uhr schrieb Michael Albinus
<michael.albinus@gmx.de>:
>
> Philipp Stephani <p.stephani2@gmail.com> writes:
>
> Hi Philipp,
>
> > To reproduce this, you need two GNU/Linux machines with the same user
> > name but different home directories.  Assume that on host 1 the user's
> > home directory is /home1/user, and that on host 2 the user's home
> > directory is /home2/user.  With the SSH protocol, home directory
> > expansion works as expected:
> >
> > However, this fails with SSHFS:
>
> Tilde expansion is not possible for sshfs (and adb, rclone) methods of
> Tramp. I've added a check, and Tramp raises an error now when it detects
> a tilde. Pushed to master.
>

Thanks, but would it maybe be possible to find a better solution? I've
been using SSHFS for a while now, and this particular issue is pretty
annoying in practice. How about any of the following:
- When connecting over SSHFS, ask the remote host (via SSH) for the
home directory and cache the result.
- Allow the user to configure a per-host static home directory (i.e.
just a customizable mapping from hosts + users to home directories). I
regularly only connect to 2 hosts with known hostnames and home
directories, so at least for me maintaining such a mapping would be
feasible.
WDYT?

bug#53847: 28.0.91; Tramp SSHFS: incorrect remote home directory

[Michael Albinus]

Philipp Stephani <p.stephani2@gmail.com> writes:

Hi Philipp,

>> > To reproduce this, you need two GNU/Linux machines with the same user
>> > name but different home directories.  Assume that on host 1 the user's
>> > home directory is /home1/user, and that on host 2 the user's home
>> > directory is /home2/user.  With the SSH protocol, home directory
>> > expansion works as expected:
>> >
>> > However, this fails with SSHFS:
>>
>> Tilde expansion is not possible for sshfs (and adb, rclone) methods of
>> Tramp. I've added a check, and Tramp raises an error now when it detects
>> a tilde. Pushed to master.
>
> Thanks, but would it maybe be possible to find a better solution? I've
> been using SSHFS for a while now, and this particular issue is pretty
> annoying in practice. How about any of the following:
> - When connecting over SSHFS, ask the remote host (via SSH) for the
> home directory and cache the result.
> - Allow the user to configure a per-host static home directory (i.e.
> just a customizable mapping from hosts + users to home directories). I
> regularly only connect to 2 hosts with known hostnames and home
> directories, so at least for me maintaining such a mapping would be
> feasible.
> WDYT?

Tramp uses already a cached value for the home directory, under the key
"~". You could try the following:

--8<---------------cut here---------------start------------->8---
(add-to-list 'tramp-connection-properties
             (list (regexp-quote "/sshfs:user@randomhost.your.domain:")
                   "~" "/home/user"))
--8<---------------cut here---------------end--------------->8---

It is untested, and you need a fresh git checkout of master. Please
report whether it works; I would add the recipe to the manual then.

Best regards, Michael.

bug#53847: 28.0.91; Tramp SSHFS: incorrect remote home directory

[Michael Albinus]

Michael Albinus <michael.albinus@gmx.de> writes:

Hi Philipp,

>> Thanks, but would it maybe be possible to find a better solution? I've
>> been using SSHFS for a while now, and this particular issue is pretty
>> annoying in practice. How about any of the following:
>> - When connecting over SSHFS, ask the remote host (via SSH) for the
>> home directory and cache the result.
>> - Allow the user to configure a per-host static home directory (i.e.
>> just a customizable mapping from hosts + users to home directories). I
>> regularly only connect to 2 hosts with known hostnames and home
>> directories, so at least for me maintaining such a mapping would be
>> feasible.
>> WDYT?
>
> Tramp uses already a cached value for the home directory, under the key
> "~". You could try the following:
>
> (add-to-list 'tramp-connection-properties
>              (list (regexp-quote "/sshfs:user@randomhost.your.domain:")
>                    "~" "/home/user"))
>
> It is untested, and you need a fresh git checkout of master. Please
> report whether it works; I would add the recipe to the manual then.

Well, it didn't work out of the box. So I've pushed a fix to the master
branch in order to support this. Note, that you need the connection
property "~user", with "user" being your remote user name.

The Tramp manual has been enhanced with this new section:

--8<---------------cut here---------------start------------->8---
5.5 Expanding ‘~’ to home directory
===================================

Home directories on remote hosts can be typed as tilde ‘~’.  If
possible, they are expanded to the remote user’s home directory on the
remote host.  Example:

     /ssh:user@host:~
     ⇒ /ssh:user@host:/home/user

   This works in general for ‘ssh’-like methods, and for ‘sudoedit’.
These methods allow also the home directory expansion for another
user, like

     /sudoedit::~otheruser
     ⇒ /sudoedit:root@localhost:/home/otheruser

   For other methods, a home directory can be expanded only if
supported.  This happens for example for the ‘sftp’ method.  Methods,
which require a share directory in the remote file name (‘afp’,
‘smb’), use the value of this share directory as home directory:

     /smb:user@host:~
     ⇒ /smb:user@host:/share

   Since Tramp cannot know in advance which share directory is
intended to use, this expansion can be applied only when a share
directory has been used already.

   The methods ‘adb’, ‘rclone’ and ‘sshfs’ do not support home
directory expansion at all.  However, TRAMP keeps the home directory
in the cache.  Therefore, those methods could be configured to expand
a home directory via a connection property, *Note Predefined
connection information::.  Example:

     (add-to-list 'tramp-connection-properties
                  (list (regexp-quote "/sshfs:user@randomhost.your.domain:")
                        "~user" "/home/user"))

   When your remote file name does not contain a ‘user’ part, the
connection property "~" must be used instead.
--8<---------------cut here---------------end--------------->8---

Best regards, Michael.

bug#53847: 28.0.91; Tramp SSHFS: incorrect remote home directory

[Philipp Stephani]

Am Do., 10. März 2022 um 12:37 Uhr schrieb Michael Albinus
<michael.albinus@gmx.de>:
>
> Michael Albinus <michael.albinus@gmx.de> writes:
>
> Hi Philipp,
>
> >> Thanks, but would it maybe be possible to find a better solution? I've
> >> been using SSHFS for a while now, and this particular issue is pretty
> >> annoying in practice. How about any of the following:
> >> - When connecting over SSHFS, ask the remote host (via SSH) for the
> >> home directory and cache the result.
> >> - Allow the user to configure a per-host static home directory (i.e.
> >> just a customizable mapping from hosts + users to home directories). I
> >> regularly only connect to 2 hosts with known hostnames and home
> >> directories, so at least for me maintaining such a mapping would be
> >> feasible.
> >> WDYT?
> >
> > Tramp uses already a cached value for the home directory, under the key
> > "~". You could try the following:
> >
> > (add-to-list 'tramp-connection-properties
> >              (list (regexp-quote "/sshfs:user@randomhost.your.domain:")
> >                    "~" "/home/user"))
> >
> > It is untested, and you need a fresh git checkout of master. Please
> > report whether it works; I would add the recipe to the manual then.
>
> Well, it didn't work out of the box. So I've pushed a fix to the master
> branch in order to support this. Note, that you need the connection
> property "~user", with "user" being your remote user name.

Thanks, I'll try this out for a while to see whether it works for me.