Oracle Instant Client enables development and deployment of applications that connect to Oracle Database, either on-premise or in the Cloud. The Instant Client libraries provide the necessary network connectivity and advanced data features to make full use of Oracle Database.
There have been a few changes in this release.
Since the packages comprise more than the Oracle Client Interface libraries, the installation documentation for 21c has moved from the OCI manual to the Database Client Installation Guide for Linux manual.
The other changes are with RPM packaging. The RPMs no longer have a version number in the package name (yes the version number is in the file name, but it's not in the package name itself). This aids in-place upgrades, letting each new available Oracle "Release Update" be automatically installed when you update your server. Also aiding upgrades is the way the packages now install into a directory with just the major version e.g. /usr/*/oracle/21/client64/... instead of the major number and release update number like /usr/*/oracle/19.9/client64/....
If you get the packages from yum.oracle.com, the channels have changed. Details are on the Instant Client for Oracle Linux page. Our Dockerfiles are also useful references. Get them here for OL8 and here for OL7. In summary:
On Oracle Linux 8:
sudo dnf install oracle-instantclient-release-el8 sudo dnf install oracle-instantclient-basic
On Oracle Linux 7:
sudo yum install oracle-instantclient-release-el7 sudo yum install oracle-instantclient-basic
If you don't want automatic upgrades to future new major releases, then use version lock.
For Oracle Linux 8:
sudo dnf install yum-plugin-versionlock sudo dnf versionlock oracle-instantclient-release-el8
For Oracle Linux 7:
sudo yum install yum-plugin-versionlock sudo yum versionlock oracle-instantclient-release-el7