Well i found out what went wrong in my case. I had mounted a partition over an older folder. Then i started downloading something into that folder. It worked ok until i got a disk full error. I checked with df but the new partition was reported empty. But the root partition was reported as full. I checked with du -sh all the folders in / but if I summed up all except /proc I couldn't make up the space on the root partition. Anyhow, after a reboot (without mounting the additional partition) the df reported the space correctly and I have seen that /var had the rest of the space. The mount point was /var/srv/Indexes and somehow the data got downloaded onto the root partition instead of the new partition mounted there. In fact after i got the disk full error that folder was behaving strange. If i issued a ls i got the right listing. but if i tried to do a cd in one of the new downloaded folders i would get not found error (even if ls reprted them there...). I suppose it had something to do with rights over the mount point or something. Regarding the /proc/kcore it was the only thing i could find to blame at that point. Now i know that doesn't use any space on the disk.