chkrootkit throws Signal 13 when searching through /var/tmp

On my debian squeeze server in the chkrootkit log I get loads of these errors: /usr/bin/find: Prozeß "head" wurde durch das Signal 13 abgebrochen. /usr/bin/find: Prozeß "head" wurde durch das Signal 13 abgebrochen. which means head terminated by signal 13 A google search gives a lot of same problems, but no solution. It comes from these lines in /usr/sbin/chkrootkit: if [ echo abc | head -n 1 = "abc" ]; then fileshead="${find} ${ROOTDIR}tmp ${ROOTDIR}var/tmp ${findargs} -type f -exec head -n 1 {} \; | $egrep '#!.*php' 2> /dev/null" else fileshead="${find} ${ROOTDIR}tmp ${ROOTDIR}var/tmp ${findargs} -type f -exec head -1 {} \; | grep '#!.*php' 2> /dev/null" fi when I enter directly as root: /usr/bin/find /var/tmp -type f -exec head -1 {} \; | grep php 2> /dev/null;date I get the same errors. egrep instead makes no difference.