/flags /maven/mvn-u-update-snapshots

mvn -U: force Maven to re-check snapshots and missing artifacts

updated 2026-10-24

tool: Maven
command: mvn
flag: -U, --update-snapshots
default: off (remote checks follow each repository's updatePolicy, daily by default)

mvn -U clean install (long form --update-snapshots) forces Maven to check the remote repositories for newer SNAPSHOT versions and to retry artifacts that previously failed to download, ignoring the update interval. Without it, Maven checks a snapshot at most once a day by default and remembers failed downloads, which produces the familiar "was cached in the local repository, resolution will not be reattempted until the update interval of central has elapsed or updates are forced" error. "Updates are forced" means exactly -U.

When you need it

A teammate deployed a new 1.4.0-SNAPSHOT of a library, but your build keeps using yesterday's copy.
A dependency failed to download once (network problem, wrong repository, missing credentials) and every later build fails immediately with the cached-failure message, even after the cause was fixed.
A plugin or dependency was published to a repository after Maven first looked for it.

bash

mvn -U clean install            # check snapshots and retry failed downloads
mvn -U dependency:tree          # see what versions resolve now
mvn -nsu clean install          # the opposite: never update snapshots in this build

Option	Effect
-U, --update-snapshots	Check for updated snapshots and missing releases now
-nsu, --no-snapshot-updates	Do not update snapshots at all during this build
-UM, --update-metadata	Force updates of repository metadata (plugin prefixes, version ranges); newer Maven releases
-UA, --update-artifacts	Retry cached artifact retrieval errors; newer Maven releases
-o, --offline	No remote access at all
updatePolicy in settings.xml	always, daily (default), interval:MINUTES or never per repository

What -U does not do

-U does not delete or re-download released versions such as guava:33.0.0-jre: releases are immutable and stay in ~/.m2/repository. If a released artifact in the local repository is corrupt (for example a truncated jar), delete that version's folder and build again, or use mvn dependency:purge-local-repository.

It also does not change which version is chosen. If the POM asks for 1.3.0, -U will never pick 1.4.0; for newer releases see mvn versions:display-dependency-updates.

Pitfalls

Using -U on every local build slows it down, because every snapshot is checked against every repository. Keep it for CI or for the moment you need it.
The cached-failure message can hide the real cause. Run once with -U -e to see the actual download error (proxy, 401 Unauthorized, wrong URL in settings.xml).
Plugin prefix resolution uses repository metadata; a stale prefix cache is one reason for No plugin found for prefix, and -U refreshes it.
Gradle's counterpart is --refresh-dependencies.

FAQ

Does mvn -U re-download every dependency?

No. Released versions that are already in the local repository are never downloaded again. -U only makes Maven check remote repositories for newer SNAPSHOT builds and retry artifacts whose earlier download failed.

What does 'resolution will not be reattempted until the update interval has elapsed' mean?

An earlier build could not download the artifact, and Maven cached that failure in the local repository. Until the repository's update interval passes (daily by default) it will not try again; -U forces an immediate retry.

How do I make Maven always check for new snapshots?

Set <updatePolicy>always</updatePolicy> for snapshots on the repository in settings.xml or the POM. That costs a remote check on every build, so many teams prefer -U in CI only.

Sources

flags · mavenmvn -o (--offline): build without accessing remote repositoriesmvn -o builds with the local repository only and never contacts remote repositories. Preparing with dependency:go-offline, settings.xml offline mode, pitfalls.commands · mavenmvn dependency:tree: show the Maven dependency tree and find conflictsmvn dependency:tree prints every direct and transitive dependency of a Maven project. Filter it with -Dincludes, show conflicts with -Dverbose, save to a file.errors · mavenNo plugin found for prefix 'spring-boot' in the current project and in the plugin groupsmvn spring-boot:run fails with No plugin found for prefix when pom.xml does not declare the plugin or mvn runs in the wrong folder. Add it or use full names.flags · gradlegradle build --refresh-dependencies: ignore the dependency cache--refresh-dependencies makes Gradle re-check every dependency against the repositories instead of trusting its cache. When to use it, and lighter fixes.