I have been using the bpgetconfig command to query our client version.

We are in the mist of upgrading to version 5.1.

The query shows that the clients are  5.1,  How do I verify that mp4 has
been applied ? 

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As Wayne had stated, the only way to find out the client version is to
check the /usr/openv/netbackup/bin/version file on the client.

When you are looking at "Client Properties" with the java gui/admin
console or using the equivalent command line arguments (bpgetconfig),
you are only seeing the bpcd daemon version. The bpcd daemon (listening
on port 13782) has the Netbackup version build into the source code and
you will only get the GA version from it.

Hope this helps.