Temporary workaround for SIGSEGV problem of gnome-shell of debian sid.

After upgrading on debian sid, I found gnome-shell was always killed by SIGSEGV. This SIGSEGV was emerged from libcogl9.However I couldn't purge libcogl9 on debian sid ,because libcogl9 and many other packages depended to libcogl9 are released to repository of debian sid.There are no easy options to purge libcogl9.

According to a report (Bug#666889: Problem with this transition, leading to gnome-shell segfault on login), I downgraded to libclutter-1.0-0-1.8.4-1 which came from testing repository and also purged libcogl9.After that, gnome-shell of sid is successfuly worked again.

I memorized how-to below,

Step 1. Add testing(wheezy) repository to /etc/apt/sources.list,shown as below,

...snip...
deb http://ftp.debian.or.jp/debian/ wheezy main contrib non-free
deb-src http://ftp.debian.or.jp/debian/ wheezy main contrib non-free

Step 2. Set priority of testing(wheezy) lower than sid.

$ cat /etc/apt/preferences.d/testing
Package: *
Pin: release wheezy
Pin-Priority: 150
$ cat /etc/apt/preferences.d/unstable
Package: *
Pin: relase unstable
Pin-Priority: 500

Step 3. Get repository information of testing(wheezy),

env LANG=C sudo aptitude update

Step 4. Purge libcogl9 like this,

$ env LANG=C sudo aptitude purge libcogl9
...snip...
Accept this solution? [Y/n/q/?] e 
...After visual menu was invoked,choose 'Downgrade libclutter-1.0-0 to XXXX 
(unstable) to XXX(testing)' and choose 'Remove libcogl9'. After '.' key pressed,
confirm summary about downgrading of packages. After press 'g' twice,removing
and downgrade procedures are started.

Step 5. Try to restart gdm3 and login. Check gnome-shell works properly.

$ sudo /etc/init.d/gdm3 restart
...Login to your account....

Step 6. If gnome-shell works fine, put additionary pin settings preventing from accidentialy installing libcogl9.

$ cat /etc/apt/preferences.d/experimental
Package: libcogl9
Pin: release experimental
Pin-Priority: -100

Package: *
Pin: release experimental
Pin-Priority: 150
$ cat /etc/apt/preferences.d/unstable
Package: libcogl9
Pin: release unstable
Pin-Priority: -100

Package: *
Pin: release unstable
Pin-Priority: 500