[Koha] crontab not working

hi to all i'm using cron tab to abort indexing with zebra .. i installed koha 3.04 on ubuntu 9.10 and when running the below command in crontab not working i don't know why .. any helo ? : ) PERL5LIB=/usr/share/koha/lib/ KOHA_CONF=/etc/koha/koha-conf.xml ## rebuild zebra */1 * * * * KOHA_CONF=/etc/koha/koha-conf.xml PERL5LIB=/usr/share/koha/lib/ /usr/share/koha/bin/migration_tools/rebuild_zebra.pl -b -a -z >/dev/null