apache/maven · warning

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

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.

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":

View on GitHub (pinned to e4093d4e12)

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

• Unable to prompt
• Error copying POM to the local repository.
• The super POM {resource} is damaged, please verify the integ
• Two or more projects in the reactor have the same identifier
• Could not create resume.properties file.

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