ONLINE BACKUP is not performed from the CRON Job on LINUX server (manually it works)
Chances are that the reason your script runs from the command line but fails from cron is that your DB2 environment is already initialized (i.e. via your .profile) for the interactive session, where it is not when called by cron.

Here's a suggested modification:

 #!/bin/bash
 #

 # Setup DB2 Environment
 . $HOME/sqllib/db2profile

 # Back up Database
 db2 -v "backup database maxdb71 online to /data/archiveBackup INCLUDE LOGS WITHOUT PROMPTING"


A few comments:


This will work if you're executing it via cron for the instance owner.  However, because it depends on the $HOME environment variable you would need to use the actual path to the instance owner's home directory if you wanted to run this via cron as a different user.
You should not reference binaries in /opt/ibm/db2/..., you should be using the binaries from the DB2 instance.  Because the script initializes the environment from the db2profile, the db2 command will be in the script's $PATH.
I removed some of the options from your backup command as these are not necessary.  DB2 is very intelligent when it comes to selecting run-time values for these, so you're likely to get worse backup performance if you override the defaults.
When you execute the script from cron, make sure you capture the output in a log file.  It will be very useful for debugging purposes. Example crontab:

00 23 * * * /path/to/script/backup.sh &gt; /path/to/script/backup.log 2&gt;&amp;1