ack outputs nothing using crontab in linux. In the crontab file (edited with sudo crontab -e): And cat /ext/test110.sh will show After cron, there are 1.t and 2.t in /ext cat 2.t will output /usr/bin/ack; However, nothing in 1.t. If I run ack “localhost” /etc/hosts > /ext/3.t in bash (4.3.30) or sh directly, it will output: 127.0.0.1 localhost It seems