Gradle is only able to detect the OpenJDK I have manually downloaded from AdoptOpenJDK, and unpacked under /usr/java/.
https://docs.gradle.org/current/userguide/toolchains.html#sec:auto_detection
These OpenJDK I have unpacked are listed as
+ AdoptOpenJDK 11.0.11
| Location: /usr/java/jdk-11.0.11+9
| Language Version: 11
| Vendor: AdoptOpenJDK
| Is JDK: true
| Detected by: Current JVM
+ AdoptOpenJDK 11.0.9.1
| Location: /usr/java/jdk-11.0.9.1+1
| Language Version: 11
| Vendor: AdoptOpenJDK
| Is JDK: true
| Detected by: Common Linux Locations
+ AdoptOpenJDK 14.0.2
| Location: /usr/java/jdk-14.0.2+12
| Language Version: 14
| Vendor: AdoptOpenJDK
| Is JDK: true
| Detected by: Common Linux Locations
+ AdoptOpenJDK 15.0.1
| Location: /usr/java/jdk-15.0.1+9
| Language Version: 15
| Vendor: AdoptOpenJDK
| Is JDK: true
| Detected by: Common Linux Locations
+ AdoptOpenJDK 16
| Location: /usr/java/jdk-16+36
| Language Version: 16
| Vendor: AdoptOpenJDK
| Is JDK: true
| Detected by: Common Linux Locations
+ Oracle JDK 1.8.0_221
| Location: /usr/java/jdk1.8.0_221
| Language Version: 8
| Vendor: Oracle
| Is JDK: true
| Detected by: Common Linux Locations
+ Oracle JDK 1.8.0_181
| Location: /usr/java/jdk1.8.0_181
| Language Version: 8
| Vendor: Oracle
| Is JDK: true
| Detected by: Common Linux Locations
Gradle does not detect the OpenJDK I have installed through the Linux package manager, and those are installed under /usr/lib64/jvm/.
What are these Common Linux Locations?
The /usr/lib64/jvm/ should be a part of these locations.
I have been digging around in the Gradle Code.
These are the Linux locations
this(factory, OperatingSystem.current(), "/usr/lib/jvm", "/usr/java");
Defined in LinuxInstallationSupplier.java.
A fix should be done there, to use /usr/lib64/jvm instead of /usr/lib/jvm, or in addition to.
A Pull Request have been made for this.