title: docker exec and mysqldump in cronjob problem
body: <p>I found some problem when I used docker exec and mysqldump in cronjob</p>
  <p>I wanted to  backup my database in  container and tried this and it worked well</p>
  <pre><code>sudo docker exec -it --user root lemp_mariadb mysqldump -uroot -pxxxxxxx iot  &gt;/home/backup/backup_data.gz
  </code></pre>
  <p>But when I used this in crontab I got file output without anything and the file size is 0 byte</p>
  <p><code>0 24 * * * docker exec -it --user root lemp_mariadb mysqldump -uroot -pxxxxxxx iot  &gt;/home/backup/backup_data.gz</code></p>
  <p>What did I do wrong?</p>