I have bellow bash for full backup of MySQL database(Centos 7), And worked perfect.

MyBackupDb.sh file :

mysqldump -u root -pHERE THERE IS MY PASSWORD --all-databases > /opt/db_backups/database_`date +%d%m%y`.sql

When I execute /bin/bash /root/MyBackupDb.sh that work perfect.

But when I set bellow command in /etc/crontab :

# Example of job definition:
# .---------------- minute (0 - 59)
# |  .------------- hour (0 - 23)
# |  |  .---------- day of month (1 - 31)
# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# |  |  |  |  |
# *  *  *  *  * user-name command to be executed

  14 0  *  *  * /bin/bash /root/MyBackupDb.sh 

The crontab have erorr /bin/bash ERROR (getpwnam() failed) error.

Note : MyBackupDb.sh have 755 permission.