wsltty closes immediately when using a non-default mount path

[pd93]

In the latest Windows Insider Build 17093 there is a new WSL configuration file at /etc/wsl.conf. This file allows you (among other things) to specify the mount point for your windows drives (defaults to /mnt/).

My motivation for changing the mount point is that I want to use Docker via the WSL and this doesn't currently work because of an issue with volumes being mounted to the wrong location. Mounting your Windows drives to / via the /etc/wsl.conf file solves this problem, but breaks wsltty.

Once the mount point is changed, wsltty closes immediately when started. I wasn't sure if this was a wsltty or wslbridge issue, so I opened it here first.

Starting up the Ubuntu app works as expected.

[mintty]

First, try to get hold of any error message by adding -h alw to the mintty invocation (or Hold=always to the config file). Also, it would be useful to separate the test cases and invoke wslbridge explicitly, either from a cygwin installation (with wslbridge and wslbridge-backend in /usr/bin, can be copied from the wsltty installation), or by running /bin/wslbridge from a minimal wsltty-based Cygwin shell: %LOCALAPPDATA%/wsltty/bin/mintty /bin/dash.

[pd93]

So adding Hold=always in the config file allowed me to grab the error that prints to the console:

wslbridge error: failed to start backend process
note: backend error output: /bin/bash: /mnt/c/Users/pete/AppData/Local/wsltty/bin/wslbridge-backend: No such file or directory

Running wslbridge from dash just returns wslbridge: not found, What exactly should I be typing to invoke it explicitly? (I don't have cygwin installed currently, but am happy to if needed)

[mintty]

/bin/wslbridge

[mintty]

backend error output: /bin/bash: /mnt/c/Users/pete/AppData/Local/wsltty/bin/wslbridge-backend: ...

Apparently wslbridge tries to convert the path to find its backend in %LOCALAPPDATA% (or actually /bin from the cygwin point of view), based on WSL default assumption. @rprichard: so this is a wslbridge issue...

[pd93]

When running /bin/wslbridge, I get the same error as I get when launching wsltty. I will open an issue with wslbridge and link it back to here.

[mintty]

Apart from the startup problem, changing the mount point would actually also spoil the mintty path conversion, for Ctrl+click file opening and pathname pasting. Is the information also available in the registry? How does it look like in the wsl.conf file?

[mintty]

If you want to try patching wslbridge, you'd need a Cygwin installation, with packages gcc-core and make, download wsltty and run make wslbridge-frontend.

[pd93]

I'm happy to help contribute to this as not many are running the latest Windows builds. I shall get an instance of Cygwin installed again today and have a look at wslbridge in more detail.

The wsl.conf file uses the .ini format. The file does not exist unless the user creates it and the only thing required to change the mount point is the following:

[automount]
root = /

More details on the file in the link in the OP.

I'm not sure if there is an 'official' way to obtain the root mount point in WSL, but if not, you could either parse the .ini file or run something like mount | grep C: | awk '{ print $3 }' to get the mount point for the C drive.

I mentioned this in the wslbridge issue, but it's worth mentioning here too that in the latest builds, there is a tool called wslpath which performs WSL -> Windows path conversion and back natively. (I've tested this and it complies with non-default mount points).

[mintty]

It's best to acquire the information from the file (or registry, if available, if you could have a look) so mintty can set it up without starting another instance of WSL in advance.

[pd93]

I can't see that there is anything in the registry after a quick search, but tbh, I'm not 100% sure where I'd be looking anyway. From the documentation, it sounds like the wsl.conf file is read directly on launch.

I think reading from the file is going to be the easiest solution here.. Is there a problem accessing the file in /etc/wsl.conf before starting an instance of WSL? - I know there can be problems when opening a file on the Linux filesystem in Windows.

[mintty]

Is the "root" the mount point or the mount prefix? The examples show it always with trailing slash; if you drop that, like "/drive", will mounts be "/drive/c" or "/drivec"?

[pd93]

Just tested this and it's a prefix. The trailing slash seems to make no difference to the resulting mount point. If a value of /drive is given, all the drives will be mounted to /drive/x (where x is a drive letter). The directory /drive must exist before the wsl starts or the drives are not mounted.

[pd93]

@mintty I was thinking about this today, and it occurred to me that any user that is willing to go through the effort of creating a config file in the WSL probably doesn't mind editing the wsltty config as well. So why not just add a setting to the config file which stores the root mount point. If this setting is absent then we just use the wsl defualt: /mnt/

[mintty]

Possible. But it's also fairly feasible to do that implicitly in mintty, I just haven't had the time to do it yet. However, that's only the smaller part of the issue, applicable to filename copy/paste. The major problem is that wslbridge will not find its backend, so we'll have to patch it...

[pd93]

Hey @mintty Now that the wslbridge issue is closed, what needs to be done here to close the wsltty issue?

[mintty]

I need to find the time to check out the wslbridge update, integrate it, and adapt mintty to also consider the mount path for its drag-and-drop and click-open features. Also I'm currently concerned with a stalling condition related to sixel graphics display. Although that problem has been in the code for 2 years already, I'm not feeling too comfortable to make another release without fixing it first...

[mintty]

Support for WSL mount point configuration is now available in mintty (for open/paste path conversion) and wsltty (building with the wslbridge 'wslpath' version). There will be a release soon. However, I'm not really comfortable with releasing with a branch version; maybe we can ask @rprichard to merge or even release it.

[rprichard]

The wslpath change is already merged into wslbridge master, but I haven't made a release containing it yet.

[mintty]

Released 1.8.5 which supports WSL mount path configuration (both /etc/wsl.conf and /etc/fstab) when starting and with path name conversion (for click-open and drag-and-drop paste).

[pd93]

@mintty Amazing. Thanks for the support. I'll give this a go first thing when I get home today. Just in time for the Windows 10 1803 release that includes the wslpath features

[pd93]

Everything works as expected 👍 Thanks again