I have just one partition.
After some days I've found the solution to this problem.
I run out of disk space due to log files size. In /var/log I found 3 big log files that had filled up my disk (syslog, kern.log and messages). I explored through them and realized what caused the massive logs. Finally, I removed them and reboot.
F. System Size Used Availa Use% Mounted
/dev/hda6 7,0G 6,3G 356M 95% /
tmpfs 122M 4,0K 122M 1% /dev/shm
tmpfs 10M 740K 9,3M 8% /dev