I don't know what's going on. The last evening I left my computer with about 700MB of free space on the system partition and today there is no free space on disk, moreover a lot of files containing data is, according to system, 0 bytes, but actually files are full of right data like text (and they have the icon of blank document). After deleting some files I can see no changes - still no free space. These files were deleted permanently and were not used during deleting.Yesterday I did command sync once and for the first time ever. Today I also did following as root: sync; sudo sh -c 'echo 3 > /proc/sys/vm/drop_caches'.It looks like it's something wrong with partition or actually file system.There was no rebooting the system for a long time and this is in my case the last thing I would like to do now.Moreover, I noticed that I've got no command history in terminal - the file .bash_history is empty. Is this because of dropping cache or my disk is broken down? If the first, what else was cleared among noticeable things like the bash history?Yesterday I used to make the disk working hard due to some actions like file serching and things alike but after that untill the evening everything was fine.One more annoying thing I noticed was working process called update-apt-xapian-index-dbus which is still in background but it's sleeping now (I couldn't kill it, it comes back everytime I try so).I see no other errors - the system is still working and it's stable.I'd like to know what is happening with my system... Do you have any suggestion? How to diagnose it? How to display real free space and sizes of files? Is a reboot necessary?Edit: One thing else is that key strokes like Shift+Del are not working.And I was trying to find files created during the night, but find / -ctime=0 shows then also older files, same for -mtime.I frgot to mention that I use Ubuntu.**EDIT: I just found the file called .xsession-errors and it's about 650MB, so maybe it's the space I lost (it maches), it's accessed and modified today one hour ago, but I can't say (and check) when it's created. How about this? Next to that file is .xsession-errors.old modified in the day of last reboot and it's under 0,5MB. Did I just find my free space?And command sync can be a cause of problem with partition? I read so somewhere, but really can it?**Edit: I opened the file .xsession-errors and what can I  see inside is some true errors with description about displaying windows and thousands of lines with Illegal character <2e> in hex string and millions lines with Write error: Unknow error. I guess it was writing till free space on disk was available.  The character is not always <2e> but it repeats the most often.
Free space: 0 bytes and files full of data shown as empty
disk