Before you start

I suggest you are pepared for some addtional frustration, but it is moderate.
My assumption is at this point that you downloaded and unpacked the DB2 Software.

As on the MariaDB please see the Credits at the End. Some research was involved.1

Do this as root user

If root doesn't have a password yet, enter
sudo passwd
Start using root by entering
su

Install DB2

useradd -d /dbdata/db2inst1 db2inst1
useradd db2fenc1
passwd db2inst1
passwd db2fenc1

IMPORTANT! Check that the directory /dbdata/db2inst1 has been created or create it.
ls /dbdata/db2inst1
mkdir /dbdata/db2inst1

Change to the Install Directory

cd /opt/ibm/db2/<version>/instance

Create the Instance

./db2icrt db2fenc1 db2inst1

Connect to the Instance

su - db2inst1

Repeat the Steps for any other Instances you like to create.

Start the Database

db2start

If db2start fails with Error Message that a Library could not be found, IBM is a bit behind with Linux Verions.

Finding the missing Libraries2

sudo find / -name libaws-cpp-sdk-core.so

The Result might be

/opt/ibm/db2/V11.5.9fp0/lib64/awssdk/UBUNTU/20.04/libaws-cpp-sdk-core.so
/opt/ibm/db2/V11.5.9fp0/lib64/awssdk/UBUNTU/22.04/libaws-cpp-sdk-core.so
/opt/ibm/db2/V11.5.9fp0/lib64/awssdk/UBUNTU/18.04/libaws-cpp-sdk-core.so
/opt/ibm/db2/V11.5.9fp0/lib64/awssdk/RHEL/8.1/libaws-cpp-sdk-core.so
/opt/ibm/db2/V11.5.9fp0/lib64/awssdk/RHEL/9.2/libaws-cpp-sdk-core.so
/opt/ibm/db2/V11.5.9fp0/lib64/awssdk/RHEL/7.6/libaws-cpp-sdk-core.so
/opt/ibm/db2/V11.5.9fp0/lib64/awssdk/SLES/12.4/libaws-cpp-sdk-core.so
/opt/ibm/db2/V11.5.9fp0/lib64/awssdk/SLES/15.1/libaws-cpp-sdk-core.so<
/opt/ibm/db2/V11.5.9fp0/lib64/libaws-cpp-sdk-core.so

Based on your OS, create Symbolic Links

cd /opt/ibm/db2/V11.5.9fp0/lib64
sudo ln -s awssdk/RHEL/8.1/libaws-cpp-sdk-core.so libaws-cpp-sdk-core.so
sudo ln -s awssdk/RHEL/8.1/libaws-cpp-sdk-kinesis.so libaws-cpp-sdk-kinesis.so
sudo ln -s awssdk/RHEL/8.1/libaws-cpp-sdk-s3.so libaws-cpp-sdk-s3.so
sudo ln -s awssdk/RHEL/8.1/libaws-cpp-sdk-transfer.so libaws-cpp-sdk-transfer.so

Try staring the Database again

./db2start

Whops Banana: SQL10007N Message "-1390" could not be retrieved. Reason code: "3"4

That Points to the Environment Variable DB2INSTANCE not being set. Edit ./bashrc and add
export DB2INSTANCE=db2inst1
This is very IMPORTANT and I will elaborate on that more when it comes to Data Access

Try staring the Database again

./db2start

If you want to start DB2 via Systemd

Edit /etc/systemd/system/db2inst1.service
[Unit]
Description=DB2 start/stop script
After=rsyslog.service network.service sshd.service systemd-logind.service

[Service]
Type=forking
ExecStart=/bin/bash -c "/dbdata/db2inst1/sqllib/adm/db2start"
ExecStop=/bin/bash -c "/dbdata/db2inst1/sqllib/adm/db2stop force"
Environment="DB2INSTANCE=db2inst1"
User=db2inst1
Group=db2iadm1
RestartSec=30
Restart=always

[Install]
WantedBy=multi-user.target

Enable it with

systemctl enable db2inst1
systemctl start db2inst1

Check Status with

systemctl status db2 -l

How was the Beer consumption thus far? When it comes to Data Access Setup, you need stronger stuff!. If you want another Instance, repeat the Steps, but change 1 to 2 in the Groups and User Profiles, the Service File

Credits:
https://www.choudharysumit.com/2020/09/db2-instance-creation-on-linux.html

https://https://dba.stackexchange.com/questions/333207/db2-v11-5-9-0-installation-error-while-loading-shared-libraries-libaws-cpp-sdk

https://www.choudharysumit.com/2020/10/sql10007n-message-1390-could-not-be.html

https://superuser.com/questions/1462161/how-to-hide-an-account-on-kde-login-screen

Fatal error: Uncaught mysqli_sql_exception: Data too long for column 'agent' at row 1 in /var/www/html/MartinBrieger/visitor.php:180 Stack trace: #0 /var/www/html/MartinBrieger/visitor.php(180): mysqli->query() #1 /var/www/html/MartinBrieger/db2_multi.php(244): visitor() #2 {main} thrown in /var/www/html/MartinBrieger/visitor.php on line 180