Practical troubleshooting guides for npm, pip, Maven, and Docker errors.
Code: cannot_connect_to_daemon The Docker CLI cannot reach the Docker daemon, usually because the engine is stopped, the context is wrong, or the socket is unavailable.
Code: connect_no_route_to_host Docker cannot reach the registry host at the network level because the route is missing, blocked, or the destination is unreachable.
Code: daemon_sock_permission_denied Docker cannot access /var/run/docker.sock because your user lacks permission to the daemon socket or the socket ownership is wrong.
Code: denied_requested_access Docker denied access because the repository path is wrong, the image is private, or the provided credentials do not have permission.
Code: dial_tcp_connection_refused Docker reached the target host, but the TCP connection to the registry was refused, usually because nothing is listening or a firewall blocked it.
Code: exec_not_found Docker started the container, but the configured command or entrypoint was not found in the image PATH or at the specified path.
Code: exec_permission_denied The container entrypoint exists, but Docker cannot execute it because the file lacks execute permissions or the mount blocks execution.
Code: id_not_found Docker could not find the referenced container, image, network, or volume ID, usually because it was deleted, mistyped, or belongs to another context.
Code: invalid_reference_format Docker rejected the image name because the reference format is invalid, commonly due to uppercase letters, bad tagging, or malformed syntax.
Code: invalid_reference_lowercase Docker rejected the image reference because repository names must be lowercase, so uppercase letters or malformed syntax made it invalid.
Code: io_timeout Docker hit an i/o timeout while contacting the registry, usually because of DNS, proxy, firewall, or slow network connectivity.
Code: manifest_unknown Docker could not find the requested manifest for that image tag, which usually means the tag does not exist or the registry metadata is out of date.
Code: no_matching_manifest Docker found the image tag, but no manifest matches your OS or CPU architecture, so the image is not built for your platform.
Code: no_such_image Docker cannot find that image locally, so the image ID or tag is wrong, was removed, or was never pulled onto this machine.
Code: push_tag_not_exist Docker cannot push the image because the tag does not exist locally, so you need to tag the image correctly before pushing.
Code: registry_503_service_unavailable Docker reached the registry, but the registry returned HTTP 503 Service Unavailable, usually due to outage, overload, or proxy issues.
Code: repository_not_exist Docker cannot pull from that repository because the name is wrong, the repository does not exist, or your account lacks access.
Code: timeout_exceeded Docker timed out while waiting for the registry response, which usually points to slow network links, proxy issues, or an overloaded registry.
Code: too_many_requests Docker Hub rejected the pull because you hit its rate limit, often fixed by authenticating, waiting, or using a cached mirror.
Code: unable_to_remove_filesystem Docker cannot remove the container filesystem because the device is busy, usually due to running processes, mounts, or lingering references.
Code: unauthorized_authentication_required Docker registry authentication failed because no valid credentials were sent, so you need to log in or fix the token used for that registry.
Code: unauthorized_incorrect_password Docker login failed because the registry rejected the username or password, so the stored credentials or access token are wrong.
Code: volume_in_use Docker cannot remove the volume because a running or stopped container still references it, so you must detach or delete the dependent container first.
Code: CERT_HAS_EXPIRED npm rejected the HTTPS connection because the registry or proxy certificate is expired, so the TLS handshake can no longer be trusted.
Code: CERT_REVOKED npm rejected the HTTPS certificate because the registry or proxy certificate has been revoked and is no longer trusted.
Code: CERT_SIGNATURE_FAILURE npm rejected the registry TLS certificate because the certificate chain signature could not be verified by your local trust store.
Code: CERT_UNTRUSTED npm does not trust the registry certificate chain, usually because of a missing internal CA, corporate proxy, or intercepted HTTPS traffic.
Code: DEPTH_ZERO_SELF_SIGNED_CERT npm received a self-signed certificate at the top of the TLS chain, usually from a private registry or HTTPS-inspecting proxy.
Code: E401 npm received a 401 Unauthorized response from the registry because your token, password, or .npmrc authentication settings are missing or invalid.
Code: E403 npm was authenticated, but the registry returned 403 Forbidden because your account lacks permission for that package, scope, or action.
Code: E404 npm returned 404 because the package, version, scope, or registry URL does not exist at the registry you are using.
Code: E409 npm received HTTP 409 Conflict because that package version already exists or the registry state conflicts with the publish request.
Code: E422 npm received HTTP 422 because the publish payload was semantically invalid, such as bad metadata, malformed tarball data, or invalid package state.
Code: EACCES npm hit EACCES because the current user does not have permission to read, write, or execute one of the required files or directories.
Code: EAI_AGAIN npm could not resolve the registry hostname because DNS returned EAI_AGAIN, a temporary lookup failure that usually clears on retry.
Code: EBADENGINE npm returned EBADENGINE because the package requires a different Node.js or npm version than the one running your install.
Code: EBADPLATFORM npm skipped or rejected the package because it does not support your current operating system or CPU architecture.
Code: EBUSY npm hit EBUSY because a file or directory was locked or still in use by another process, editor, antivirus tool, or sync service.
Code: ECONNABORTED npm aborted the network request before completion, often because the remote server closed the connection or a proxy interrupted it.
Code: ECONNREFUSED npm reached the registry host, but the TCP connection was refused, usually because the server, proxy, or mirror is not accepting connections.
Code: ECONNRESET npm lost the network connection because the peer reset the TCP session mid-request, often due to proxies, firewalls, or flaky networks.
Code: EEXIST npm hit EEXIST because it tried to create a file or directory that already exists where npm expected to create a new one.
Code: EINTEGRITY npm downloaded a package tarball whose checksum did not match the expected integrity value (lockfile/metadata mismatch).
Code: EINVALIDPACKAGENAME npm rejected the package name because it does not follow npm naming rules, such as invalid characters, uppercase letters, or reserved names.
Code: EINVALIDTAGNAME npm rejected the dist-tag because the tag name is invalid, reserved, or formatted in a way that conflicts with version parsing.
Code: EINVALIDVERSION npm rejected the version because the semver string is invalid or malformed in package metadata, tags, or your command.
Code: EISDIR npm hit EISDIR because it expected a file path, but the target resolved to a directory instead, so npm could not read or write it correctly.
Code: EJSONPARSE npm could not parse package.json because the JSON is invalid, such as trailing commas, mismatched quotes, or broken syntax.
Code: ELIFECYCLE npm returned ELIFECYCLE because a package lifecycle script like install, test, or build exited with a non-zero status.
Code: ELOCKVERIFY npm returned ELOCKVERIFY because the lockfile and installed dependency tree do not agree with what npm expected to verify.
Code: ELSPROBLEMS npm ls reported ELSPROBLEMS because the installed dependency tree contains missing, invalid, or extraneous packages.
Code: EMFILE npm hit EMFILE because the process opened too many files at once and exceeded the per-process file descriptor limit.
Code: ENAMETOOLONG npm hit ENAMETOOLONG because the generated file path exceeded your operating system path length limit during install or extract.
Code: ENEEDAUTH npm requires authentication for this registry or package, so you must log in or configure a valid auth token in .npmrc.
Code: ENFILE npm hit ENFILE because the whole system reached its open-file limit, so new files or sockets could not be opened.
Code: ENOENT npm hit ENOENT because a required file or directory was missing, often package.json, a lockfile path, or an extracted dependency.
Code: ENOSELF npm returned ENOSELF because the package name matches the project you are trying to install, creating a self-dependency.
Code: ENOSPC npm hit ENOSPC because the disk ran out of free space while extracting packages, writing cache data, or updating node_modules.
Code: ENOTDIR npm hit ENOTDIR because it expected a directory in the path, but a file exists there instead, breaking the package or cache lookup.
Code: ENOTEMPTY npm hit ENOTEMPTY because it tried to replace or remove a directory that still contains files, often during install, cleanup, or rename steps.
Code: ENOTFOUND npm could not resolve the registry hostname, so DNS lookup failed before npm could connect to the package registry.
Code: EOTP npm requires a one-time password for this publish or settings change because two-factor authentication is enabled on the account.
Code: EPERM npm hit EPERM because the operating system denied the filesystem operation, commonly due to permissions, locks, antivirus, or Windows file handling.
Code: EPIPE npm hit EPIPE because it tried to write output to a closed pipe or terminated process, often in CI logs or shell pipelines.
Code: EPUBLISHCONFLICT npm could not publish because that package version already exists in the registry, so you need a new version before publishing again.
Code: ERESOLVE npm failed with ERESOLVE because it could not build a dependency tree that satisfies the requested versions and peer dependency constraints.
Code: EROFS npm hit EROFS because it tried to write cache or package files on a read-only filesystem, mount, or container layer.
Code: ERR_SOCKET_TIMEOUT npm hit a socket timeout while waiting for registry network I/O, usually because of slow connections, proxies, or an overloaded registry.
Code: ETARGET npm returned ETARGET because no published version matches the version range or dist-tag requested in your install command.
Code: ETIMEDOUT npm timed out while talking to the registry or downloading a package tarball, usually because of slow networks, proxies, or registry issues.
Code: EUSAGE npm returned EUSAGE because the command, flags, or configuration were invalid for that operation, so npm stopped before doing any work.
Code: HOSTNAME_MISMATCH npm connected over HTTPS, but the certificate presented by the server does not match the registry hostname you requested.
Code: SELF_SIGNED_CERT_IN_CHAIN npm rejected the TLS connection because a self-signed certificate appeared somewhere in the certificate chain to the registry.
Code: UNABLE_TO_GET_ISSUER_CERT npm could not build a trusted TLS chain because the issuer certificate for the registry was missing or unavailable.
Code: UNABLE_TO_GET_ISSUER_CERT_LOCALLY npm could not verify the registry TLS chain because the issuer certificate is missing from the local machine trust store.
Code: UNABLE_TO_VERIFY_LEAF_SIGNATURE npm could not verify the registry TLS certificate because the leaf certificate chain is incomplete or the required issuer is missing locally.
Code: DEPENDENCY_RESOLUTION_FAILURE Maven could not resolve one or more project dependencies, usually because of missing artifacts, bad repository settings, or network access problems.
Code: FAILED_TO_READ_ARTIFACT_DESCRIPTOR Maven could not download or parse the POM for a dependency/plugin, so it cannot resolve that artifact's transitive dependencies.
Code: FAILURE_TO_FIND_ARTIFACT Maven could not find an artifact in the configured repositories, and the missing result may be cached in the local repository.
Code: NON_RESOLVABLE_PARENT_POM Maven cannot resolve the `<parent>` POM for your project from the local filesystem or configured repositories.
Code: NO_POM_IN_DIRECTORY You ran a Maven goal that needs a `pom.xml`, but Maven cannot find one in the current directory (or via `-f`).
Code: COULD_NOT_TRANSFER_ARTIFACT Maven could not transfer the artifact from the repository, usually because of network failures, proxy issues, TLS problems, or bad credentials.
Code: PKIX_PATH_BUILDING_FAILED The JVM running Maven cannot validate the HTTPS certificate chain of the repository, so Maven refuses the connection.
Code: REPOSITORY_UNAUTHORIZED_401 The repository requires authentication, but Maven did not send valid credentials for the repository `<id>` being used.
Code: REPOSITORY_FORBIDDEN_403 The repository rejected the request (403). Your credentials may be valid, but you are not authorized for that repository/path or operation.
Code: PROXY_AUTH_REQUIRED_407 Maven is using an HTTP proxy to reach repositories, but the proxy requires authentication and Maven is not configured with valid proxy credentials.
Code: NO_PLUGIN_FOUND_FOR_PREFIX Maven cannot map that plugin prefix to a real plugin artifact, usually because the plugin is undeclared or missing from configured plugin repositories.
Code: PLUGIN_RESOLUTION_FAILURE Maven could not resolve the plugin or one of its dependencies, usually because plugin repositories, credentials, or network access are wrong.
Code: LOCAL_REPOSITORY_PERMISSION_DENIED Maven cannot write to the local repository directory (`~/.m2/repository` by default), usually due to permissions or a read-only filesystem.
Code: CHECKSUM_VALIDATION_FAILED Maven downloaded the artifact, but checksum verification failed, usually because the file is corrupted or a repository or proxy served different bytes.
Code: DEFAULT_HTTP_BLOCKER Maven 3.8.1 and newer refuse insecure HTTP repository URLs and route them through the built-in `maven-default-http-blocker` mirror.
Code: POM_MISSING Maven located a JAR coordinate, but could not download the corresponding POM, so it cannot determine transitive dependencies or metadata for that artifact.
Code: UNKNOWN_HOST_EXCEPTION The machine running Maven could not resolve the repository hostname via DNS, so Maven cannot download artifacts or metadata.
Code: SSL_HANDSHAKE_FAILURE The JVM running Maven could not complete the TLS handshake with the repository, so Maven cannot download artifacts over HTTPS.
Code: OFFLINE_MODE Maven is running with offline mode enabled (`-o` / `--offline`), so it will not contact remote repositories to download missing artifacts.
Code: COMMAND_NOT_FOUND Your shell can't find a `pip` executable on `PATH` (or you're using an environment where `pip` is intentionally not installed).
Code: WINDOWS_NOT_RECOGNIZED Windows cannot find the pip command because Python or its Scripts directory is missing from PATH, or pip was not installed correctly.
Code: EXTERNALLY_MANAGED_ENVIRONMENT Your OS Python is marked as "externally managed" (PEP 668), so pip refuses to modify the system environment outside a virtual environment.
Code: NO_MODULE_NAMED_PIP Python cannot import pip because pip is not installed in that interpreter, the environment is broken, or you are using the wrong Python executable.
Code: UNKNOWN_COMMAND pip does not have `update` or `upgrade` subcommands. Upgrading packages is done with `pip install --upgrade ...`.
Code: NO_REQUIREMENT_GIVEN pip install failed because no package, requirements file, wheel, or local path was provided, so pip had nothing to install.
Code: OLD_SCRIPT_WRAPPER You're running pip through an outdated entrypoint script. It still works today, but it can break after pip upgrades.
Code: REQUIREMENTS_FILE_NOT_FOUND pip was asked to install from a requirements file path that does not exist (wrong filename, wrong directory, or missing checkout).
Code: INVALID_REQUIREMENT pip could not parse a requirement specifier (malformed version constraint, quotes/smart-quotes, comments, or an invalid line in a requirements file).
Code: DIRECTORY_NOT_INSTALLABLE You asked pip to install from a local directory or sdist, but it doesn't contain standard Python packaging metadata (`pyproject.toml` or `setup.py`).
Code: NO_MATCHING_DISTRIBUTION pip could not find any installable release that matches your requirement and your environment (Python version, OS/architecture, and index configuration).
Code: REQUIRES_PYTHON_MISMATCH The package (or one of its dependencies) declares a `Requires-Python` range that excludes the Python interpreter you're using.
Code: DEPENDENCY_CONFLICT pip found conflicting dependency constraints and could not choose a set of package versions that satisfies every requirement.
Code: INSTALLED_PACKAGES_CONFLICT Your environment is already inconsistent. pip installed or upgraded something, but the full installed set now contains version conflicts.
Code: SUBPROCESS_EXITED_WITH_ERROR pip delegated part of the install to an external build step (PEP 517 backend or legacy `setup.py`) and that subprocess failed.
Code: FAILED_TO_BUILD_WHEELS pip attempted to build a wheel from a PEP 517 project, but the wheel build failed and pip cannot install it without a wheel.
Code: BUILD_TOOLCHAIN_MISSING pip is building a package from source, but your system is missing a required toolchain (C/C++ compiler, Python headers, MSVC Build Tools, or Rust).
Code: PERMISSION_DENIED pip tried to write into a directory you don't have permission to modify (often system site-packages or a protected install directory).
Code: NO_SPACE_LEFT_ON_DEVICE The machine ran out of disk space while pip was downloading/building/installing packages (often in the temp directory or cache).
Code: CACHE_DIR_NOT_OWNED pip detected that its cache directory is owned by a different user (often because pip was previously run with `sudo`), so it disables caching for safety.
Code: SSL_MODULE_NOT_AVAILABLE Your Python was built or installed without SSL support, so pip cannot make HTTPS requests to package indexes like PyPI.
Code: NETWORK_RETRIES_TIMEOUTS pip is repeatedly failing to reach the package index due to network timeouts, proxy issues, or TLS incompatibilities, and it is retrying until it gives up.
Code: HASH_MISMATCH You are using hash-checking mode (`--require-hashes`), but the downloaded file's hash doesn't match, or some requirements are missing hashes.
Code: RECORD_FILE_NOT_FOUND pip cannot uninstall a package because it cannot find the installed-files manifest (`RECORD`) in the package metadata.
Code: DISTUTILS_UNINSTALL_BLOCKED pip will not uninstall the package because distutils or OS packaging installed it without metadata that safely maps files to remove.
Code: CACHE_DESERIALIZATION_FAILED pip detected a corrupted or incompatible cache entry and ignored it. Installs may be slower or may fail if corruption is widespread.