"Cinnamon has crashed. Cinnamon in fallbackmode." - why?

[roadam]

Hi,
Cinnamon 17.1 reinstalled 2 days ago after problem with sound devices - suddenly disapeared.
Today I left Cinnamon for couple of hours (forgot turn comp off).
Then I saw "Cinnamon has crashed. Cinnamon is running in fallbackmode."
Rebooting didn't help. Crashed immediately after reboot.
The only way of recovery was running in text mode (without X):

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sudo apt-get --purge autoremove cinnamon

and then:

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sudo apt-get install cinnamon

and

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sudo reboot

System is fully restored.
How can I find a reason of crash?

[austin.texas]

You can open the log file viewer (Menu > Administration > Log File Viewer) and see if there are any error messages in there.

[roadam]

I could, but I have SSD so set log files (ex. syslog, auth.log, dpkg.log, Xorg.0.log) to RAM => actual session logs are only accessible.
In fstab:

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# Modification for SSD
tmpfs      /var/log        tmpfs      defaults,noatime        0    0
tmpfs      /tmp          tmpfs      defaults,noatime,mode=1777    0    0

Did anybody have such or similar accident?
Any tips are welcome.

PS.Forgot to mention I had to configure Xorg too.
I've done this by installing new Nvidia driver accordingly.

[MellowTigger]

I did my first reboot after a few days of usage. I'm now having the same problem. I'll try roadam's previously mentioned solution to get a working Cinnamon back. Meanwhile, I'm still in the fallback mode.

I did use Applications / System Tools / Log File Viewer. It does show a prominent error that "/var/log/mail.log" does not exist, but it doesn't seem particularly relevant. The only other odd messages are these, which also don't seem relevant to Cinnamon not working.

mdm[1741]: PAM unable to dlopen(pam_kwallet.so): /lib/security/pam_kwallet.so: cannot open shared object file: No such file or directory
kernel: [ 1321.865069] systemd-hostnamed[3677]: Warning: nss-myhostname is not installed. Changing the local hostname might make it unresolveable. Please install nss-myhostname!

p.s. I tried the earlier commands to reinstall cinnamon then reboot. It did not solve my problem. I still have to use Fallback Mode. And this time, I do not get any menu system at all, just desktop icons and a right-click menu.
p.p.s. One other oddity. When first launching Firefox, I get a window that says, "Firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart your system."

[MellowTigger]

For what it's worth, I was also unable to switch back to Nouveau drivers during this escapade. Thankfully, other people are having this same issue this morning, and I was able to get back my Nvidia-331 drivers (and a working Cinnamon) with help in this thread.