apache/maven · warning

An I/O error occurred while checking if the packaged…

Error message

An I/O error occurred while checking if the packaged artifact is up-to-date against the build output directory. Continuing with the assumption that it is up-to-date.

What it means

Warning in ReactorReader (Maven 4's mechanism that resolves inter-module dependencies from the current reactor session): while comparing the packaged artifact file's timestamp against the build output directory to decide staleness, an IOException occurred. The code deliberately degrades gracefully, assumes the artifact IS up-to-date, and returns true. Risk: a genuinely stale packaged jar can be consumed as if fresh.

Solutions

1. Run the build with clean (mvn clean verify) so staleness is irrelevant and artifacts are repackaged.
2. Check permissions/ownership of the module's target/ directory and repair if unreadable.
3. Stop concurrent builds sharing one checkout, or use -Dmaven.repo.local / separate workspaces per job.
4. Exclude target/ from antivirus scanning; avoid placing builds on flaky network mounts.
5. If persistent, capture the IOException stack with -X to see which file operation failed.

Example fix

# before: incremental build consumes possibly stale artifact
mvn verify
# after: force repackaging when staleness warnings appear
mvn clean verify

# verify the reactor tree is clean and not shared before building
[ ! -e target ] || git clean -xdn target/ # inspect what would be removed

When it happens

Trigger: During a reactor build with the default workspace reader active, file attribute reads (Files.getLastModifiedTime / BasicFileAttributes walk of target/classes) throw IOException: unreadable target directory, permission changes, files deleted concurrently by another build/antivirus in the same tree, or exotic filesystems that fail attribute queries.

Common situations: Parallel builds sharing target/ directories; IDE and CLI builds racing on the same module; network file systems (NFS/SMB) with flaky attribute support; containers with read-only mounted target dirs.

Related errors

• Cannot read module information.
• Could not create resume.properties file.
• Could not find the selected project in the reactor
• Could not write fixed metadata to
• Edge between ' ' and ' ' introduces to cycle in the graph

AI-assisted analysis of apache/maven@e4093d4e12 (2026-08-21). Data as JSON: /api/errors/e7379193b78ac619. Report an issue: GitHub.

Appendix: source

Thrown at impl/maven-core/src/main/java/org/apache/maven/ReactorReader.java:272

                    LOGGER.warn(
                            "File '{}' is more recent than the packaged artifact for '{}', "
                                    + "please run a full `mvn package` build",
                            relativizeOutputFile(outputFile),
                            project.getArtifactId());
                    return false;
                } else if (LOGGER.isDebugEnabled()) {
                    LOGGER.debug(
                            "File '{}' timestamp {} vs artifact timestamp {} for '{}'",
                            relativizeOutputFile(outputFile),
                            outputFileLastModified,
                            artifactLastModified,
                            project.getArtifactId());
                }
            }

            return true;
        } catch (IOException e) {
            LOGGER.warn(
                    "An I/O error occurred while checking if the packaged artifact is up-to-date "
                            + "against the build output directory. "
                            + "Continuing with the assumption that it is up-to-date.",
                    e);
            return true;
        }
    }

    private boolean hasBeenPackagedDuringThisSession(MavenProject project) {
        boolean packaged = false;
        for (String phase : getLifecycles(project)) {
            switch (phase) {
                case "clean":
                    packaged = false;
                    break;
                case "package":
                case "install":
                case "deploy":

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