Don't know if this is the best place to post, but my problem appears to be a desktop problem (and KWin has crashed, among other problems).

On Kubuntu 12.10 KDE Plasma startup, I'm now getting getting popup messages from "KDE Daemon", "Run Command Interface", and "Plasma Desktop Shell" ala "Could not find mimetype - inode/directory ... application/x-desktop ... application/octet-stream" and programs such as ksnapshot fail to work with similar messages. New logins appear problematical - sometimes I cannot change desktop, mouse does not work properly, etc. requiring a power-off/power-on to recover. Also, many icons now appear "broken".

Googling found only old (2009 and earlier) fixes which did not work for me, such as deleting "~/.kde/share/mimelnk/application/file-octet-stream.application" (which does not exist on my system). And searching this forum did not provide a match. I tried to open "File Associations" under "System Settings" but that crashed.

I have not been futzing with any settings myself which might have caused this. My suspicion is that the problem was caused by my installation of the open-source "calibre" Ebook reader on my machine, which I suspect has hosed my mime type associations. (I've now removed that software).

So the question is, how do I recover from this?

(PS: I should have nightly saves of all my system files, so could replace any now incorrect files with an earlier version if I knew which files)

You need to reinstall the shared-mime-info package. It is absolutely essential to the proper operation of KDE.

After even more googling, I finally came up with this URL http://www.mobileread.com/forums/archiv ... 03956.html which gave a clue as to the problem (the "error message" it gives is a translation of the german version which does not match the actual english error message, hence was not found by googling on that).

Short answer: I found _all_ files in /usr/share/mime/application/ were lacking "other" read permission! Also some other file/directories under /usr/share/mime/ had the same problem. Giving all files/directories under /usr/share/mime "r+o" permission got everything working again.

All those permission changes occurred upon installation of "calibre". In the cited post the "calibre" developer claims the problem lies in a problem with xde, not with calibre. Whatever. I no longer want to deal with trying to get open-source to work (this has already wasted 6 hours of my life) so have removed "calibre" and will do my eBook reading on a Windows box (which works just fine on installation). I've also restored all files under /usr/share/applications and /usr/share/mime/ to their pre-calibre-install versions.

I'm posting this solution/explanation so that someone else in a similar situation will hopefully find it by googling on "could not
find mimetype" and waste less of their life.

That is quite unusual - XDE should not be involved in changing permissions at all, especially in /usr/share/mime. Such behaviour would be a grave bug in XDE itself, or the distribution packages in question.