Maven build invalid POM

Question

I am using Spring Boot 1.5.8 as parent POM for my project. While building, it keeps on giving warnings for some POMs. They are not errors, but I am uncomfortable with warnings as they might cause a problem in future that is difficult to trace.

Maven version: 3.5.0

Here is part of POM:

  <parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>1.5.8.RELEASE</version>
  </parent>

Entire POM can be found at: https://paste.ubuntu.com/25828364/

Here is command used to create effective POM:

mvn -X help:effective-pom

Relevant part of the log

[DEBUG] =======================================================================
[INFO] 
[INFO] --- maven-help-plugin:2.2:effective-pom (default-cli) @ Apeiron ---
[DEBUG] Using mirror mavenrepo (http://artifactory.zendu.com/mavenrepo) for snapshots (http://snapshots.maven.codehaus.org/maven2).
[WARNING] The POM for org.apache.maven:maven-plugin-api:jar:2.2.1 is invalid, transitive dependencies (if any) will not be available: 3 problems were encountered while building the effective model for org.apache.maven:maven-plugin-api:[unknown-version]
[ERROR] Invalid packaging for parent POM org.apache.maven:maven-plugin-api:[unknown-version], must be "pom" but is "jar" @ 
[ERROR] Invalid packaging for parent POM org.apache.maven:maven-plugin-api:[unknown-version], must be "pom" but is "jar" @ 
[FATAL] The parents form a cycle: org.apache.maven:maven-plugin-api:2.2.1 -> org.apache.maven:maven-plugin-api:2.2.1 @ 

[WARNING] The POM for org.apache.maven:maven-project:jar:2.0.6 is invalid, transitive dependencies (if any) will not be available: 3 problems were encountered while building the effective model for org.apache.maven:maven-project:[unknown-version]
[ERROR] Invalid packaging for parent POM org.apache.maven:maven-project:[unknown-version], must be "pom" but is "jar" @ 
[ERROR] Invalid packaging for parent POM org.apache.maven:maven-project:[unknown-version], must be "pom" but is "jar" @ 
[FATAL] The parents form a cycle: org.apache.maven:maven-project:2.0.6 -> org.apache.maven:maven-project:2.0.6 @ 

[WARNING] The POM for org.apache.maven:maven-model:jar:2.0.6 is invalid, transitive dependencies (if any) will not be available: 3 problems were encountered while building the effective model for org.apache.maven:maven-model:[unknown-version]
[ERROR] Invalid packaging for parent POM org.apache.maven:maven-model:[unknown-version], must be "pom" but is "jar" @ 
[ERROR] Invalid packaging for parent POM org.apache.maven:maven-model:[unknown-version], must be "pom" but is "jar" @ 
[FATAL] The parents form a cycle: org.apache.maven:maven-model:2.0.6 -> org.apache.maven:maven-model:2.0.6 @ 

[WARNING] The POM for org.apache.maven:maven-artifact:jar:2.0.6 is invalid, transitive dependencies (if any) will not be available: 3 problems were encountered while building the effective model for org.apache.maven:maven-artifact:[unknown-version]
[ERROR] Invalid packaging for parent POM org.apache.maven:maven-artifact:[unknown-version], must be "pom" but is "jar" @ 
[ERROR] Invalid packaging for parent POM org.apache.maven:maven-artifact:[unknown-version], must be "pom" but is "jar" @ 
[FATAL] The parents form a cycle: org.apache.maven:maven-artifact:2.0.6 -> org.apache.maven:maven-artifact:2.0.6 @ 

[DEBUG] Dependency collection stats: {ConflictMarker.analyzeTime=2, ConflictMarker.markTime=1, ConflictMarker.nodeCount=112, ConflictIdSorter.graphTime=2, ConflictIdSorter.topsortTime=0, ConflictIdSorter.conflictIdCount=39, ConflictIdSorter.conflictIdCycleCount=0, ConflictResolver.totalTime=13, ConflictResolver.conflictItemCount=95, DefaultDependencyCollector.collectTime=821, DefaultDependencyCollector.transformTime=24}

Answer 1

Considering the 1.5.8-RELEASE version of that artifact is indeed of pom packaging, it is possible that you have a network issue.

That would prevent the artifact to be properly downloaded in your maven cached repository, and explain the "unknown version"