opam-lint - Checks and validate package description ('opam') files.


opam lint [OPTION]⦠[FILES]â¦


Given an opam file, performs several quality checks on it and outputs recommendations, warnings or errors on stderr.



Name of the opam files to check, or directory containing them. Current directory if unspecified



Check upstream, archive availability and checksum(s)


Output a normalised version of the opam file to stdout


Lint the current definition of the given package instead of specifying an opam file directly.


Allow recursive lookups of *.opam files. Cf. --subpath also.

-s, --short

Only print the warning/error numbers, space-separated, if any


*.opam files are retrieved from the given sub directory instead of top directory. Sources are then taken from the targeted sub directory, internally only this subdirectory is copied/fetched. It can be combined with --recursive to have a recursive lookup on the subpath.

-W WARNS, --warnings=WARNS

Select the warnings to show or hide. WARNS should be a concatenation of +N, -N, @N, +N..M, -N..M, @N..M to respectively enable, disable or enable-as-error warning or error number N or all warnings with numbers between N and M inclusive. All warnings are enabled by default, unless WARNS starts with + or @, which disables all but the selected ones.


W20: Field 'opam-version' refers to the patch version of opam, it should be of the form MAJOR.MINOR

E21: Field 'opam-version' doesn't match the current version, validation may not be accurate

E22: Some fields are present but empty; remove or fill them

E23: Missing field 'maintainer'

E24: Field 'maintainer' has the old default value

W25: Missing field 'authors'

W26: No field 'install', but a field 'remove': install instructions probably part of 'build'. Use the 'install' field or a .install file

E28: Unknown package flags found

E29: Package dependencies or conflicts mention package variables

E31: Fields 'depends' and 'depopts' refer to the same package names

E32: Field 'ocaml-version:' and variable 'ocaml-version' are deprecated, use a dependency towards the 'ocaml' package instead for availability, and the 'ocaml:version' package variable for scripts

E33: Field 'os' is deprecated, use 'available' and the 'os' variable instead

E34: Field 'available:' contains references to package-local variables. It should only be determined from global configuration variables

W35: Missing field 'homepage'

W36: Missing field 'bug-reports'

W37: Missing field 'dev-repo'

E39: Command 'make' called directly, use the built-in variable instead

W41: Some packages are mentioned in package scripts or features, but there is no dependency or depopt toward them

E42: The 'dev-repo:' field doesn't use version control. You should use URLs of the form "git://", "git+https://", "hg+https://"...

E43: Conjunction used in 'conflicts:' field. Only '|' is allowed

W44: The 'plugin' package flag is set but the package name doesn't begin with 'opam-'

E45: Unclosed variable interpolations in strings

E46: Package is flagged "conf" but has source, install or remove instructions

W47: Synopsis should start with a capital and not end with a dot

W48: The fields 'build-test:' and 'build-doc:' are deprecated, and should be replaced by uses of the 'with-test' and 'with-doc' filter variables in the 'build:' and 'install:' fields, and by the newer 'run-test:' field

W49: The following URLs don't use version control but look like version control URLs

W50: The 'post' flag doesn't make sense with build or optional dependencies

E51: The behaviour for negated dependency flags 'build' or 'post' is unspecified

E52: Package is needlessly flagged "light-uninstall", since it has no remove instructions

E53: Mismatching 'extra-files:' field

W54: External dependencies should not contain spaces nor empty string

E55: Non-normalised OS or arch string being tested

E57: Synopsis must not be empty

W58: Found variable, predefined one

W59: url doesn't contain a checksum

E60: Upstream check failed

W61: ‘with-test‘ variable in ‘run-test‘ is out of scope, it will be ignored

W62: License doesn't adhere to the SPDX standard, see https://spdx.org/licenses/

E65: URLs must be absolute

W66: String that can't be resolved to bool in filtered package formula

E67: Checksum specified with a non archive url

W68: Missing field 'license'

W69: Package name in variable in string interpolation contains several '+', use


These options are common to all commands.

Don't fail if all requested packages can't be installed: try to install as many as possible. Note that not all external solvers may support this option (recent versions of aspcud or mccs should). This is equivalent to setting $OPAMBESTEFFORT environment variable.

--cli=MAJOR.MINOR (absent=2.2)

Use the command-line interface syntax and semantics of MAJOR.MINOR. Intended for any persistent use of opam (scripts, blog posts, etc.), any version of opam in the same MAJOR series will behave as for the specified MINOR release. The flag was not available in opam 2.0, so to select the 2.0 CLI, set the OPAMCLI environment variable to 2.0 instead of using this parameter.


Colorize the output. WHEN must be one of always, never or auto.


Confirmation level, LEVEL must be one of ask, no, yes or unsafe-yes. Can be specified more than once. If --yes or --no are also given, the value of the last --confirm-level is taken into account. This is equivalent to setting $OPAMCONFIRMLEVEL‘.


Specify user preferences for dependency solving for this run. Overrides $OPAMCRITERIA, $OPAMFIXUPCRITERIA and $OPAMUPGRADECRITERIA. For details on the supported language, and the external solvers available, see http://opam.ocaml.org/doc/External_solvers.html. A general guide to using solver preferences can be found at http://www.dicosmo.org/Articles/usercriteria.pdf.


Debug option: Save the CUDF requests sent to the solver to FILENAME-<n>.cudf where <n> is the n-th call to the solver during the opam run.


Print debug message to stderr. This is equivalent to setting $OPAMDEBUG to "true".


Like --debug, but allows specifying the debug level (--debug sets it to 1). Equivalent to setting $OPAMDEBUG to a positive integer.


Print the git version of opam, if set (i.e. you are using a development version), and exit.

--help[=FMT] (default=auto)

Show this help in format FMT. The value FMT must be one of auto, pager, groff or plain. With auto, the format is pager or plain whenever the TERM env var is dumb or undefined.


Ignore extra pins required by packages that get pinned, either manually through opam pin or through opam install DIR. This is equivalent to setting IGNOREPINDEPENDS=true.


Save the results of the opam run in a computer-readable file. If the filename contains the character ‘%', it will be replaced by an index that doesn't overwrite an existing file. Similar to setting the $OPAMJSON variable.


Answer no to all opam yes/no questions without prompting. See also --confirm-level. This is equivalent to setting $OPAMNO to "true".


Removed in 2.1.


When configuring or updating a repository that is written for an earlier opam version (1.2), opam internally converts it to the current format. This disables this behaviour. Note that repositories should define their format version in a 'repo' file at their root, or they will be assumed to be in the older format. It is, in any case, preferable to upgrade the repositories manually using opam admin upgrade [--mirror URL] when possible.


Opam will replace itself with a newer binary found at OPAMROOT/opam if present. This disables this behaviour.

-q, --quiet

Disables --verbose.


Use ROOT as the current root path. This is equivalent to setting $OPAMROOT to ROOT.

--safe, --readonly

Make sure nothing will be automatically updated or rewritten. Useful for calling from completion scripts, for example. Will fail whenever such an operation is needed ; also avoids waiting for locks, skips interactive questions and overrides the $OPAMDEBUG variable. This is equivalent to set environment variable $OPAMSAFE.


Specify the CUDF solver to use for resolving package installation problems. This is either a predefined solver (this version of opam supports builtin-dummy-solver, builtin-dummy-z3-solver, builtin-0install, aspcud, mccs, aspcud-old, packup), or a custom command that should contain the variables %{input}%, %{output}%, %{criteria}%, and optionally %{timeout}%. This is equivalent to setting $OPAMEXTERNALSOLVER.


Fail whenever an error is found in a package definition or a configuration file. The default is to continue silently if possible.


Use SWITCH as the current compiler switch. This is equivalent to setting $OPAMSWITCH to SWITCH.


Disable any external solver, and use the built-in one (this requires that opam has been compiled with a built-in solver). This is equivalent to setting $OPAMNOASPCUD or $OPAMUSEINTERNALSOLVER.

-v, --verbose

Be more verbose. One -v shows all package commands, repeat to also display commands called internally (e.g. tar, curl, patch etc.) Repeating n times is equivalent to setting $OPAMVERBOSE to "n".


Show version information.

-w, --working-dir

Whenever updating packages that are bound to a local, version-controlled directory, update to the current working state of their source instead of the last committed state, or the ref they are pointing to. As source directory is copied as it is, if it isn't clean it may result on a opam build failure. This only affects packages explicitly listed on the command-line. It can also be set with $OPAMWORKINGDIR.

-y, --yes

Answer yes to all opam yes/no questions without prompting. See also --confirm-level. This is equivalent to setting $OPAMYES to "true".


Opam makes use of the environment variables listed here. Boolean variables should be set to "0", "no", "false" or the empty string to disable, "1", "yes" or "true" to enable.

OPAMALLPARENS surround all filters with parenthesis.

OPAMASSUMEDEPEXTS see option ‘--assume-depexts'.

OPAMAUTOREMOVE see remove option ‘--auto-remove'.

OPAMBESTEFFORT see option ‘--best-effort'.

OPAMBESTEFFORTPREFIXCRITERIA sets the string that must be prepended to the criteria when the ‘--best-effort' option is set, and is expected to maximise the ‘opam-query' property in the solution.

OPAMBUILDDOC Removed in 2.1.

OPAMBUILDTEST Removed in 2.1.

OPAMCLI see option ‘--cli'.

OPAMCOLOR when set to always or never, sets a default value for the ‘--color' option.

OPAMCONFIRMLEVEL see option ‘--confirm-level‘. OPAMCONFIRMLEVEL has priority over OPAMYES and OPAMNO.

OPAMCRITERIA specifies user preferences for dependency solving. The default value depends on the solver version, use ‘config report' to know the current setting. See also option --criteria.

OPAMCUDFFILE save the cudf graph to file-actions-explicit.dot.

OPAMCUDFTRIM controls the filtering of unrelated packages during CUDF preprocessing.

OPAMCURL can be used to select a given 'curl' program. See OPAMFETCH for more options.

OPAMDEBUG see options ‘--debug' and ‘--debug-level'.

OPAMDEBUGSECTIONS if set, limits debug messages to the space-separated list of sections. Sections can optionally have a specific debug level (for example, CLIENT:2 or CLIENT CUDF:2), but otherwise use ‘--debug-level'.

OPAMDIGDEPTH defines how aggressive the lookup for conflicts during CUDF preprocessing is.

OPAMDOWNLOADJOBS sets the maximum number of simultaneous downloads.

OPAMDROPWORKINGDIR overrides packages previously updated with --working-dir on update. Without this variable set, opam would keep them unchanged unless explicitly named on the command-line.

OPAMDRYRUN see option ‘--dry-run'.

OPAMEDITOR sets the editor to use for opam file editing, overrides $EDITOR and $VISUAL.

OPAMERRLOGLEN sets the number of log lines printed when a sub-process fails. 0 to print all.

OPAMEXTERNALSOLVER see option ‘--solver'.

OPAMFAKE see option ‘--fake'.

OPAMFETCH specifies how to download files: either ‘wget', ‘curl' or a custom command where variables %{url}%, %{out}%, %{retry}%, %{compress}% and %{checksum}% will be replaced. Overrides the 'download-command' value from the main config file.

OPAMFIXUPCRITERIA same as OPAMUPGRADECRITERIA, but specific to fixup and reinstall.

OPAMIGNORECONSTRAINTS see install option ‘--ignore-constraints-on'.

OPAMIGNOREPINDEPENDS see option ‘--ignore-pin-depends'.

OPAMINPLACEBUILD see option ‘--inplace-build'.

OPAMJOBS sets the maximum number of parallel workers to run.

OPAMJSON log json output to the given file (use character ‘%' to index the files).

OPAMKEEPBUILDDIR see install option ‘--keep-build-dir'.

OPAMKEEPLOGS tells opam to not remove some temporary command logs and some backups. This skips some finalisers and may also help to get more reliable backtraces.

OPAMLOCKED combination of ‘--locked' and ‘--lock-suffix' options.

OPAMLOGS logdir sets log directory, default is a temporary directory in /tmp

OPAMMAKECMD set the system make command to use.

OPAMMERGEOUT merge process outputs, stderr on stdout.

OPAMNO answer no to any question asked, see options ‘--no‘ and ‘--confirm-level‘. OPAMNO is ignored if either OPAMCONFIRMLEVEL or OPAMYES is set.

OPAMNOAGGREGATE with ‘opam admin check', don't aggregate packages.


OPAMNOAUTOUPGRADE disables automatic internal upgrade of repositories in an earlier format to the current one, on 'update' or 'init'.

OPAMNOCHECKSUMS enables option --no-checksums when available.

OPAMNODEPEXTS disables system dependencies handling, see option ‘--no-depexts'.


OPAMNOSELFUPGRADE see option ‘--no-self-upgrade'

OPAMPINKINDAUTO sets whether version control systems should be detected when pinning to a local path. Enabled by default since 1.3.0.

OPAMPRECISETRACKING fine grain tracking of directories.

OPAMPREPRO set this to false to disable CUDF preprocessing. Less efficient, but might help debugging solver issue.

OPAMREPOSITORYTARRING internally store the repositories as tar.gz files. This can be much faster on filesystems that don't cope well with scanning large trees but have good caching in /tmp. However this is slower in the general case.

OPAMREQUIRECHECKSUMS Enables option ‘--require-checksums' when available (e.g. for ‘opam install').

OPAMRETRIES sets the number of tries before failing downloads.

OPAMREUSEBUILDDIR see option ‘--reuse-build-dir'.

OPAMROOT see option ‘--root'. This is automatically set by ‘opam env --root=DIR --set-root'.

OPAMROOTISOK don't complain when running as root.

OPAMSAFE see option ‘--safe'.

OPAMSHOW see option ‘--show'.

OPAMSKIPUPDATE see option ‘--skip-updates'.

OPAMSKIPVERSIONCHECKS bypasses some version checks. Unsafe, for compatibility testing only.

OPAMSOLVERALLOWSUBOPTIMAL (default ‘true') allows some solvers to still return a solution when they reach timeout; while the solution remains assured to be consistent, there is no guarantee in this case that it fits the expected optimisation criteria. If ‘true', opam willcontinue with a warning, if ‘false' a timeout is an error. Currently only the builtin-z3 backend handles this degraded case.

OPAMSOLVERTIMEOUT change the time allowance of the solver. Default is 60.0, set to 0 for unlimited. Note that all solvers may not support this option.

OPAMSTATS display stats at the end of command.

OPAMSTATUSLINE display a dynamic status line showing what's currently going on on the terminal. (one of one of always, never or auto)

OPAMSTRICT fail on inconsistencies (file reading, switch import, etc.).

OPAMSWITCH see option ‘--switch'. Automatically set by ‘opam env --switch=SWITCH --set-switch'.

OPAMUNLOCKBASE see install option ‘--unlock-base'.

OPAMUPGRADECRITERIA specifies user preferences for dependency solving when performing an upgrade. Overrides OPAMCRITERIA in upgrades if both are set. See also option --criteria.

OPAMUSEINTERNALSOLVER see option ‘--use-internal-solver'.

OPAMUSEOPENSSL Removed in 2.2.

OPAMUTF8 use UTF8 characters in output (one of one of always, never or auto). By default ‘auto', which is determined from the locale).

OPAMUTF8MSGS use extended UTF8 characters (camels) in opam messages. Implies OPAMUTF8. This is set by default on macOS only.

OPAMVALIDATIONHOOK if set, uses the ‘%{hook%}' command to validate an opam repository update.

OPAMVERBOSE see option ‘--verbose'.


OPAMWITHDEVSETUP see install option ‘--with-dev-setup'.

OPAMWITHDOC see install option ‘--with-doc'.

OPAMWITHTEST see install option ‘--with-test.

OPAMWORKINGDIR see option ‘--working-dir'.

OPAMYES see options ‘--yes' and ‘--confirm-level‘. OPAMYES has priority over OPAMNO and is ignored if OPAMCONFIRMLEVEL is set.

OPAMVAR_var overrides the contents of the variable var when substituting ‘%{var}%‘ strings in ‘opam‘ files.

OPAMVAR_package_var overrides the contents of the variable package:var when substituting ‘%{package:var}%‘ strings in ‘opam‘ files.


All scripts and programmatic invocations of opam should use ‘--cli' in order to ensure that they work seamlessly with future versions of the opam client. Additionally, blog posts or other documentation can benefit, as it prevents information from becoming stale.

Although opam only supports roots (~/.opam/) for the current version, it does provide backwards compatibility for its command-line interface.

Since CLI version support was only added in opam 2.1, use OPAMCLI to select 2.0 support (as opam 2.0 will just ignore it), and ‘--cli=2.1' for 2.1 (or later) versions, since an environment variable controlling the parsing of syntax is brittle. To this end, opam displays a warning if OPAMCLI specifies a valid version other than 2.0, and also if ‘--cli=2.0' is specified.

The command-line version is selected by using the ‘--cli' option or the OPAMCLI environment variable. ‘--cli' may be specified morethan once, where the last instance takes precedence. OPAMCLI is only inspected if ‘--cli' is not given.


As an exception to the following, the ‘exec' command returns 127 if the command was not found or couldn't be executed, and the command's exit value otherwise.


Success, or true for boolean queries.


False. Returned when a boolean return value is expected, e.g. when running with --check, or for queries like opam lint.


Bad command-line arguments, or command-line arguments pointing to an invalid context (e.g. file not following the expected format).


Not found. You requested something (package, version, repository, etc.) that couldn't be found.


Aborted. The operation required confirmation, which wasn't given.


Could not acquire the locks required for the operation.


There is no solution to the user request. This can be caused by asking to install two incompatible packages, for example.


Error in package definition, or other metadata files. Using --strict raises this error more often.


Package script error. Some package operations were unsuccessful. This may be an error in the packages or an incompatibility with your system. This can be a partial error.


Sync error. Could not fetch some remotes from the network. This can be a partial error.


Configuration error. Opam or system configuration doesn't allow operation, and needs fixing.


Solver failure. The solver failed to return a sound answer. It can be due to a broken external solver, or an error in solver configuration.


Internal error. Something went wrong, likely due to a bug in opam itself.


User interrupt. SIGINT was received, generally due to the user pressing Ctrl-C.


on success.


on indiscriminate errors reported on standard error.


on command line parsing errors.


on unexpected internal errors (bugs).


See https://opam.ocaml.org/doc.


David Allsopp <david@tarides.com>
Vincent Bernardoff <vb@luminar.eu.org>
Raja Boujbel <raja.boujbel@ocamlpro.com>
Kate Deplaix <kit-ty-kate@outlook.com>
Roberto Di Cosmo <roberto@dicosmo.org>
Thomas Gazagnaire <thomas@gazagnaire.org>
Louis Gesbert <louis.gesbert@ocamlpro.com>
Fabrice Le Fessant <Fabrice.Le_fessant@inria.fr>
Anil Madhavapeddy <anil@recoil.org>
Guillem Rieu <guillem.rieu@ocamlpro.com>
Ralf Treinen <ralf.treinen@pps.jussieu.fr>
Frederic Tuong <tuong@users.gforge.inria.fr>




Check bug reports at https://github.com/ocaml/opam/issues.