DB2 Express-C on Mac OS X

You do not want to change DBINSTANCE. All that does is change what instance is the "main" one for your OS. And you only have one instance from what I understand (named db2 I believe). I'm betting this has more to do with permissions as you are attempting to run db2sampl, which I believe creates the sample database if I remember correctly. Instance owner should be able to run this without any issues.

If I were you, I would run db2sampl as instance owner and then perform your necessary GRANTs for db2-user once the database is there.

First of all you need to edit/create the /etc/sysctl.conf and insert the following:

 kern.sysv.shmmax=1073741824                                                                                                                                                 
 kern.sysv.shmmin=1
 kern.sysv.shmmni=4096
 kern.sysv.shmseg=32
 kern.sysv.shmall=1179648
 kern.maxfilesperproc=65536
 kern.maxfiles=65536

reboot. Then google db2 express c mac osx and download db2 express c 9.5.2 for mac osx. Once downloaded uncompress the file

tar -xzvf db2exc_952_MAC_x86_64.tar.gz

enter the exp directory and start the installation wizard as root

cd exp
sudo ./db2setup

before continuing you need to create 2 users, one for administration purposes and another one as instance owner. For the second user name use no more than 8 characters and use just letters, otherwise the node name won't be accepted later on. Follow the installation wizard steps: enter the username for the DAS and for the instance owner. Once the installation is complete, you need to switch to the instance owner (dbuser in our case):

su dbuser

add the following line to your .bashrc file:

. ~/sqllib/db2profile

exit and relogin. If everything went well you should be able to start db2 (as a root) and create the SAMPLE database

sudo db2start
db2sampl 
db2

That's it!