mirscreencast broke (moved socket) in #71

Status changed to 'Confirmed' because the bug affects multiple users.

This bug was fixed in the package phablet-tools - 1.0+14.10.20140616-0ubuntu1

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phablet-tools (1.0+14.10.20140616-0ubuntu1) utopic; urgency=low

  [ Oliver Grawert ]
  * phablet-screenshot: mirscreencast needs the socket location handed over now
    that the Mir socket moved to /run/mir_socket (LP: #1327139).
 -- Ubuntu daily release <email address hidden> Mon, 16 Jun 2014 19:16:47 +0000

Incomplete for Mir. Does anything-Mir need changing?

mirscreencast is shipped by mir-utils (which in turn comes from the mir source package) ...
the default for the mir socket in mirscreencast should be adjusted so the user is not forced to provide the argument, like it was before this regression showed up, the change to phablet-screenshot is just working around it.

Mir's default socket is $XDG_RUNTIME_DIR for reasons explained in LP #1236912. Mirscreencast reads the framebuffer contents from U-S-C, and currently U-S-C is hard-coded to override the default socket location with '/run/mir_socket'.

unity-system-compositor --spinner=/usr/bin/unity-system-compositor-spinner --file /run/mir_socket --from-dm-fd 9 --to-dm-fd 13 --vt 1

(Note that since '/var/run' is a symlink to ' /run' , '/run/mir_socket' == '/var/run/mir_socket'). So the right thing to do would be to change it in lightdm (responsible for launching the U-S-C) to not use an argument.

Or the easiest thing to do would be to not do anything and have mirscreencast continue providing the socket override.

iirc the move was a security team requirement, i assume the default socket should actually be moved to $XDG_RUNTIME_DIR and yes, then the lightdm startup should drop teh arg.

There are different sockets. Bug #1236912 was about the sockets apps in the user's session are supposed to be able to access, ie $XDG_RUNTIME_DIR/mir_socket. /run/mir_socket is AIUI different and not supposed to be accessed by apps.

Mir's default is already $XDG_RUNTIME_DIR/mir_socket. (Also, it's correct that /run/mir_socket is not for apps - it's only for unity8 to connect to u-s-c as a guest (nested) compositor. )

However, $XDG_RUNTIME_DIR cannot be used for the u-s-c, as it'd be against the XDG spec to have rw permissions for non-root on the directory, so phablet user (which unity8 runs as) would not be able to access it. I am guessing that's why lightdm is not using the default already.