I'm reluctant to repeat this again but it appeared that under a squeeze version of PPC Linux Linux imac 2.6.32-5-powerpc on a machine that had 512Mb of ram I ran: dd if=/dev/zero of=empty.dat bs=1024M count=66 Then it swelled so that it''s RES become around 900+Mb and I couldn't kill it. I tried by ^C, ^Z on the spawning terminal I tried by kill, kill -9 from another terminal, even as root! The box ran but was extremely slow with 90% iowait times. This appeared to be lasting indefinitely i.e. minutes so the only way I could recover it was to issue a reboot which worked! This surely is a DoS type issue as I only ran it as a normal user. I was just trying to fill up the spare disk space with zero blocks to I could create an easily compressed disk image. Anyway I don't recomend people try to repeat this unless they are happy to reboot to get out of it, it could just be I was unlucky or that PowerPC is vulnerable to this issue. If not I would suggest perhaps reporting it as a vulnerability to be fixed. Thanks in advance for any comments. Andrew