Basta criar um arquivo bash:
#!/bin/bash
THEDBUSER="your_user"
THEDBPW="your_pass"
THEPATH="/opt/your/backups/path"
create_backup()
{
THEDATE=`date +%Y%m%d%H%M`
mysqldump
--skip-c omments
--routines
-u $THEDBUSER
-p${THEDBPW}
$1
| gzip > ${THEPATH}/dbbackup_${1}_${THEDATE}.bak.gz
}
create_backup "your_db"
create_backup "your_other_db"
create_backup "another_db"
find ${THEPATH}* -mtime +5 -delete
Em seguida, basta adicioná-lo aos trabalhos do cron crontab -e
0 12 * * * /opt/your/backups/path/make_backup.sh