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FAQ
Q: How do you pronounce Leiningen?
A: It's LINE-ing-en. ['laɪnɪŋən]
Q: What's a group ID? How do snapshots work?
A: See the
tutorial
for background.
Q: How should I pick my version numbers?
A: Use semantic versioning.
Q: What if my project depends on jars that aren't in any repository?
A: You will need to get them in a repository. The
deploy guide
explains how to set up a private repository. In general it's easiest
to deploy them to a static HTTP server or a private S3 bucket. Once
the repo is set up, lein deploy private-repo com.mycorp/somejar 1.0.0 somejar.jar pom.xml
will push the artifacts out. If you don't
have a pom, you can create a dummy project with lein new
and
generate a pom from that. If you are just doing exploratory coding
you can deploy to file:///$HOME/.m2/repository
and the jars will
be available locally.
Q: I want to hack a project and one of its dependencies, but it's annoying to switch between them.
A: Leiningen provides a feature called checkout dependencies to
make this smoother. See the
tutorial
to learn more.
Q: Is it possible to exclude indirect dependencies?
A: Yes. Some libraries, such as log4j, depend on projects that are
not included in public repositories and unnecessary for basic
functionality. Projects listed as :dependencies
may exclude
any of their dependencies by using the :exclusions
key. See
lein help sample
for details.
Q: I specified a dependency on version X but am getting version Y; what's up?
A: One of your dependencies' dependencies has declared a
dependency on a hard version range, which overrides your "soft"
declaration. Running lein deps :tree
will identify which of your
dependencies are responsible for the version range. You can add an
:exclusions
clause to prevent that from affecting the rest of your
dependencies. See lein help sample
for how exclusions work. You
may also want to report a bug with the dependency that uses hard
version ranges as they cause all kinds of problems and exhibit
unintuitive behaviour.
Q: I have two dependencies, X and Y, which depends on Z. How is the version
of Z decided?
A: The decision depends on which depth and which order the dependencies come
in the :dependencies
vector: The dependency at the lowest depth will be
picked. If there are multiple versions of a single group/artifact at that
depth, the first of those will be picked. For instance, in the dependency
graph
[Z "1.0.9"]
[X "1.3.2"]
[Z "2.0.1"]
the direct dependency ([Z "1.0.9"]
) is picked, as it is closest to the root.
For the dependency graph
[X "1.3.2"]
[Z "2.0.1"]
[Y "1.0.5"]
[Z "2.1.3"]
the dependency X comes first, and therefore [Z "2.0.1"]
is picked. If we
place Y before X however, [Z "2.1.3"]
will be picked.
Note that this only applies to soft dependencies, and lein deps :tree
will
only warn if the latest version is not chosen.
Q: I'm behind an HTTP proxy; how can I fetch my dependencies?
A: Set the $http_proxy
environment variable in Leiningen 2.x. You can also
set $http_no_proxy
for a list of hosts that should be reached directly, bypassing
the proxy. This is a list of patterns separated by |
and may start or end with
a *
for wildcard, e.g. localhost|*.mydomain.com
.
For Leiningen 1.x versions, see the instructions for
configuring a Maven proxy
using ~/.m2/settings.xml
.
Q: What can be done to speed up launch?
A: The main delay involved in Leiningen comes from starting two
JVMs: one for your project and one for Leiningen itself. Most people
use a development cycle that involves keeping a single project REPL
process running for as long as they're working on that project.
Depending on your editor you may be able to do this via its Clojure
integration. (See nrepl.el or
fireplace, for example.)
Otherwise you can use the basic lein repl
.
Q: Still too slow; what else can make startup faster?
A: The wiki has a page covering
ways to improve startup time.
Q: What if I care more about long-term performance than startup time?
A: Leiningen 2.1.0 onward get a speed boost by disabling optimized
compilation (which only benefits long-running processes). This can
negatively affect performance in the long run, or lead to inaccurate
benchmarking results. If want the JVM to fully optimize, you can
you can switch profiles with lein with-profiles production run ...
.
Q: What does "Unrecognized VM option 'TieredStopAtLevel=1'" mean?
A: Old versions of the JVM do not support the directives Leiningen
uses for tiered compilation which allow the JVM to boot more
quickly. You can disable this behaviour with export LEIN_JVM_OPTS=
or upgrade your JVM to something more recent. (newer than b25 of Java 6)
Q: I'm attempting to run a project as a background process (lein run &
),
but the process suspends until it is in the foreground. How do I run a program
in the background?
A: For long-lasting processes, it's better to create an uberjar
and run that or use lein trampoline run &
. For short-lived ones,
both lein run <&- &
and bash -c "lein run &"
will work fine.
Q: I'm getting "could not transfer artifact ... peer not authenticated"
A: This means that either your JVM is not configured with the
correct certificate authorities, or you're experiencing a
man-in-the-middle attack
on your SSL connection. Leiningen ships with the current Clojars
public certificate at the time of this writing, so you should be
able to work around problems with your CA by putting :certificates ["clojars.pem"]
in your :user
profile, assuming the certificate
that ships with Leiningen hasn't expired.
Q: How do I determine my project's version at runtime?
A: Leiningen writes a file called pom.properties
into
target/classes
which contains a the version number and current git
revision of the project. In previous versions of Leiningen this was
only available when running from jar files, but as of 2.4.1 it's
available during lein run ...
, etc. You can read it by running
this code (replace "group" and "artifact" with values appropriate to
your project):
(with-open [pom-properties-reader (io/reader (io/resource "META-INF/maven/group/artifact/pom.properties"))]
(doto (java.util.Properties.)
(.load pom-properties-reader)))
Q: How can I read my project map at runtime?
A: Usually you do not need the complete project map, only a specific subset
of some values. If you want different configuration based on different tasks,
then environ is probably a good fit.
If you want information like the project's version number or git revision,
read the question and answer above.
Generally those solutions are sufficient, but if you need more than this, you
should rather read the project.clj
yourself. The project map changes based
on the task you use, and so different tasks (repl, jar, uberjar to name a few)
will make it hard to make the testing- and production project map identical.
To add project.clj
to your classpath, you can add in
lein-shell and prepend :prep-tasks
with ["shell" "cp" "project.clj" "resources/project.clj"]
and read it
through e.g.
(read-string (slurp (io/resource "project.clj")))
Q: I need to do AOT for an uberjar; can I avoid it during development?
A: A reasonable request. Leiningen supports isolating different
profiles by their target directory. Simply specify :target-path "target/%s"
in order to have each profile set use a different
directory for generated files. Then you can put your :aot
settings in the :uberjar
profile, and the .class files created
from the AOT process will not affect normal development use. You can
specify the profile-isolated :target-path
in your :user
profile if
you want it applied across all the projects you work on.
Q: Is there a way to use an uberjar without AOT?
A: As of Leiningen 2.4.0, if you omit :main
in project.clj
,
your uberjars will use clojure.main
as their entry point. You can
launch with java -jar my-app-standalone.jar -m my.entry.namespace arg1 arg2 [...]
without any AOT, but it will take longer to launch.
Q: Why does lein jar
package some namespaces from dependencies into my jar?
A: This is likely because you want to AOT-compile namespaces. Any
AOT-compiled namespace can only depend on AOT-compiled namespaces. Therefore,
if you depend on a namespace in a dependency that is not AOT-compiled, it will
be AOT-compiled and bundled with the jar.
Q: I'd like to have certain config active only on a certain OS.
A: You can do this by using unquote in the :dev
profile:
:profiles {:dev [:dev/all ~(leiningen.core.utils/get-os)]
:dev/all {...}
:linux {...}
:windows {...}
:macosx {...}}
You can also check things like (System/getProperty "java.specification.version")
to use the JVM version or any other
property.
Q: I get a java.security.KeyException
or sun.security.provider.certpath.SunCertPathBuilderException
when running lein
A: The java.security.KeyException
indicates an ssl error when trying to communicate with the HTTPS server via Java. This could be because you need to update the JDK, or some other package (e.g. with old versions of the nss package).
- On Fedora, you might just try running a
sudo yum update
to update all of your packages orsudo yum update nss
. - On Debian/Ubuntu,
sudo update-ca-certificates -f
might help, orsudo /var/lib/dpkg/info/ca-certificates-java.postinst configure
- You should also check your system clock and make sure the time is accurate; it's possible to run into SSL connection failures if your clock is way out of sync.
- If it still doesn't work, please see if any of these 'ssl' labelled issues might help
Q: lein
/lein.bat
won't download leiningen-x.y.z-SNAPSHOT.jar
A: You probably downloaded lein
/lein.bat
from the master branch. Unless you plan to build leiningen yourself or help develop it, we suggest you use the latest stable version: lein/lein.bat