Dear ubuntuforum users,

I get the "The system is running in low-graphics mode" error.

Before the error occured I (stupidly) messed around with permission in the tmp folder: I opened Nautilus (with root rights) and set the permission so that all processes are allowed to write to that folder.

After the reboot the system now displays the error message. I opened a terminal, logged in, and tried to analyse the error:

Code:
df -h
reveals that my /dev/sda6 partition is almost completetly full:
Filesystem: /dev/sda6 Size: 7.4G Used: 7.1G Avail: 0 Use%: 100% Mounted on /
Another suggestion was to run
Code:
sudo du -kxa / | sort -nr | head
with the result of
sort: write failed: /tmp/sort[6 random letters, e.g. SFyDay]: No space left on device.
I read that full disc space may result in this error so I guess that a process (after I changed permissions) filled my tmp folder. I am not able to enter any graphical interface, only have the terminal. I am not a really advanced user so please bear with me. My questions are: How do I navigate to that full tmp folder and delete content? And how do I set the permissions to the previous state?