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Easy building and installing of Erlang/OTP instances.

kerl aims to be shell agnostic (it runs in a POSIX shell) and its only dependencies, excluding what's required to actually build Erlang/OTP, are curl and git.

All is done so that, once a specific release has been built, creating a new installation is as fast as possible.

Table of Contents

Installing kerl

If you are on macOS, and using homebrew, you can install kerl, along with shell completion, by running:

$ brew install kerl

Alternatively, you can download the script directly from GitHub:

$ curl -O https://raw.githubusercontent.com/kerl/kerl/master/kerl

Then ensure it is executable

$ chmod a+x kerl

and drop it in your $PATH.

Optionally, download and install kerl's bash_completion file from https://github.com/kerl/kerl/raw/master/bash_completion/kerl

Optionally, download and install kerl's zsh-completion file from https://github.com/kerl/kerl/raw/master/zsh_completion/_kerl

Updating kerl locally

Run:

$ kerl upgrade
Local kerl found (/usr/local/bin/kerl) at version 2.6.0.
Remote kerl found at version 3.0.0.
Versions are different. Upgrading to 3.0.0...
kerl 3.0.0 is now available at /usr/local/bin/kerl.
Updating list of available releases...
... done!

How kerl works

kerl keeps tracks of the releases it downloads, builds and installs, allowing easy installations to new destinations (without complete rebuilding) and easy switches between Erlang/OTP installations.

By default, kerl downloads source tarballs from the official Erlang/OTP repository but you can tell kerl to download from the official Erlang/OTP website by setting KERL_BUILD_BACKEND=tarball. However, this website does not use HTTPS and is down more often than GitHub.

You can also install directly from a raw Git repository by using the kerl build git <git_url> <git_version> <build_name> syntax.

Using kerl

List the available releases:

$ kerl list releases
17.5.6.10
18.3.4.11
19.3.6.13
20.3.8.26
21.3.8.24
22.3.4.26
23.3.4.19
24.3.4.16
25.3.2.9 *
26.2.2 *
27.0 *
Run './kerl update releases' to update this list.
Run './kerl list releases all' to view all available releases.
Note: * means "currently supported".

Pick your choice and build it:

$ kerl build 27.0 27.0
Downloading (from GitHub) Erlang/OTP 27.0 to /home/user/.kerl/archives...
...
Extracting source code for normal build...
Building (normal) Erlang/OTP 27.0 (27.0); please wait...
...
Erlang/OTP 27.0 (27.0) has been successfully built.

Note that named builds allow you to have different builds for the same Erlang/OTP release with different configure options:

$ KERL_BUILD_DOCS=yes kerl build 27.0 27.0-builtdocs
Extracting source code for normal build...
Building Erlang/OTP 27.0 (27.0-builtdocs); please wait...
...
Building docs...
Erlang/OTP 27.0 (27.0-builtdocs) has been successfully built.

You can verify your build has been registered:

$ kerl list builds
27.0,27.0
27.0,27.0-builtdocs

Now install a build to some location:

$ kerl install 27.0 /usr/local/lib/erlang/27.0
Installing Erlang/OTP 27.0 (27.0) in /usr/local/lib/erlang/27.0...
Building Dialyzer PLT...
Done building /usr/local/lib/erlang/27.0/dialyzer/plt.
You can activate this installation running the following command:
. /usr/local/lib/erlang/27.0/activate
Later on, you can leave the installation typing:
kerl_deactivate

Here again you can check the installation's been registered:

$ kerl list installations
27.0 /usr/local/lib/erlang/27.0

And at last activate it:

$ . /usr/local/lib/erlang/27.0/activate

Activation will backup your $PATH, and prepend it with the installation's bin/ directory. Thus it's only valid for the current shell session, and until you either activate another installation or call kerl_deactivate.

Note: alternatively you can use kerl build-install as a shortcut for the two previous actions to be played in sequence.

$ kerl build-install
usage: ./kerl build-install <release> [build_name] [directory]

$ kerl build-install git
usage: ./kerl build-install git <git_url> <git_version> <build_name> [directory]

You're now ready to work with your 27.0 installation:

$ erl -version
Erlang (SMP,ASYNC_THREADS) (BEAM) emulator version 13.2

When you're done just call the shell function:

$ kerl_deactivate

Anytime you can check which installation, if any, is currently active with:

$ kerl active
The current active installation is:
/usr/local/lib/erlang/27.0

You can get an overview of the current kerl state with:

$ kerl status
Available builds:
27.0,27.0
27.0,27.0-builtdocs
----------
Available installations:
27.0 /usr/local/lib/erlang/27.0
----------
The current active installation is:
/usr/local/lib/erlang/27.0
The Dialyzer PLT for the active installation is:
/usr/local/lib/erlang/27.0/dialyzer/plt
The build options for the active installation are:
...

You can delete builds and installations with the following commands:

$ kerl delete build 27.0-builtdocs
Build '27.0-builtdocs' has been deleted.

$ kerl delete installation 27.0
Installation '27.0' has been deleted.

You can easily deploy an installation to another host having ssh and rsync access with the following command:

$ kerl deploy anotherhost /usr/local/lib/erlang/27.0
Cloning Erlang/OTP 27.0 (/usr/local/lib/erlang/27.0) to anotherhost (/usr/local/lib/erlang/27.0)...

On anotherhost, you can activate this installation running the following command:

$ . /usr/local/lib/erlang/27.0/activate

Later on, you can leave the installation typing:

$ kerl_deactivate

Building Erlang/OTP from a GitHub fork

It is possible to build Erlang/OTP from a GitHub fork, by using the KERL_BUILD_BACKEND=git and setting OTP_GITHUB_URL to the URL of the fork. For example, to build <orgname>'s Erlang/OTP fork:

$ export KERL_BUILD_BACKEND=git
$ export OTP_GITHUB_URL='https://github.com/<orgname>/otp'
$ KERL_INCLUDE_RELEASE_CANDIDATES=yes kerl update releases
Getting releases from GitHub...
The available releases are:
...
24.0-rc3
24.0-rc3.1-orgname
24.3.4.16
24.3.4.16.1.1-orgname
25.0-rc3 *
25.0-rc3.1-orgname *
25.3.2.9 *
25.3.2.9.1-orgname *
26.0-rc3 *
26.0-rc3.1-orgname *
26.2.2 *
26.2.2.1-orgname *
27.0 *
27.0.1-orgname *

Note: this list, kept in a file managed by kerl, is different depending on the build backend you use.

From here (provided the KERL_BUILD_BACKEND and OTP_GITHUB_URL variables remain in place), it is possible to use kerl as before:

$ kerl build 27.0.1-orgname 27.0.1-orgname

Building Erlang/OTP from a Git source

You can build Erlang/OTP directly from a Git repository with a command of the form kerl build git <git_url> <git_version> <build_name> where <git_version> can be either a branch, a tag or a commit id that will be passed to git checkout:

$ kerl build git https://github.com/erlang/otp.git OTP-27.0 27.0
Checking out Erlang/OTP git repository from https://github.com/erlang/otp.git...
Building (git) Erlang/OTP OTP-27.0; please wait...
Erlang/OTP '27.0' (from git) has been successfully built.

Debugging kerl usage

If KERL_DEBUG is set to a value, then kerl will emit copious debug logging, including a best effort attempt at line numbers. The line numbers may or may not be accurate if kerl is run under the dash shell, as is commonly found in Alpine Linux/Docker images.

Configuring kerl

You can tune kerl using the .kerlrc file in your $HOME directory.

kerl and OpenSSL

If you're running kerl on macOS, it will try to guess the OpenSSL version to use if none is specified (e.g. via KERL_CONFIGURE_OPTIONS' --with-ssl).

Since Erlang/OTP 25.1, OpenSSL 3.0 is supported, so the following applies

Erlang/OTP versionOpenSSL version
up until 25.11.1
after 25.13.0

kerl options

kerl options can be passed either via .kerlrc or environment variables, as shown below.

Color configuration

KERL_COLORIZE

Default: 1 (Enabled) Enable VT100 colorizing if tput available (provided by ncurses). Set to 0 to disable. Colorization will be disabled anyway if necessary requirements are missing.

Color for log levels can be overriden, by setting ANSI numerical color code to variables KERL_COLOR_* :

Locations on disk

KERL_BASE_DIR

Default: $HOME/.kerl Directory in which kerl will cache artifacts for building and installing.

KERL_CONFIG

Default: $HOME/.kerlrc File from which to source kerl configuration

KERL_DOWNLOAD_DIR

Default: ${KERL_BASE_DIR}/archives Directory in which to place downloaded artifacts

KERL_BUILD_DIR

Default: ${KERL_BASE_DIR}/builds Directory in which kerl will perform builds

KERL_GIT_DIR

Default: ${KERL_BASE_DIR}/gits Directory in which kerl will clone Git repositories for building.

Build configuration

KERL_CHECK_BUILD_PACKAGES

Default: yes (Enabled) kerl will try to probe your Linux distro for build-required packages logging where the probes fail. You can turn off this behaviour by setting the environment variable to something other than "yes".

KERL_AUTOCLEAN

Default: 1 (Enabled) Clean all build artifacts but the log file on failure. This allows safe build retries after failure while still keeping a log file with all attempted builds until success.

Set to 0 to keep build artifacts on failure.

KERL_CONFIGURE_OPTIONS

Space-separated options to pass to configure when building Erlang/OTP.

KERL_CONFIGURE_APPLICATIONS

Space-separated list of Erlang/OTP applications which should exclusively be built.

KERL_CONFIGURE_DISABLE_APPLICATIONS

Space-separated list of Erlang/OTP applications to disable during building.

KERL_BUILD_PLT

Create a PLT file alongside the built release.

KERL_USE_AUTOCONF

Use autoconf during build process.

Note: automatically enabled when using KERL_BUILD_BACKEND=git

KERL_BUILD_BACKEND

Default value: git Acceptable values: tarball, git

Note: docs are only fetched when this is set to tarball. To enable creation of docs when set to git, one must also set $KERL_BUILD_DOCS.

Note: this option has no effect when using kerl build git..., which invokes kerl to directly clone a Git repository and build from there.

KERL_RELEASE_TARGET

Allows building, alongside the regular VM, a list of various runtime types for debugging (such as cerl -debug or cerl -asan)

Note: enable this build using KERL_RELEASE_TARGET="debug asan"

Note: available types: opt, gcov, gprof, debug, valgrind, asan or lcnt

For more information: see "How to Build a Debug Enabled Erlang RunTime System" in https://www.erlang.org/doc/installation_guide/install.

OTP_GITHUB_URL

Default value: https://github.com/erlang/otp Acceptable value: any GitHub fork of Erlang/OTP

KERL_BUILD_DOCS

If $KERL_BUILD_DOCS is set, kerl will create docs from the built Erlang/OTP version regardless of origin (tarball backend from <erlang.org> or via kerl build git, or via git backend).

If $KERL_BUILD_DOCS is unset, kerl will only install docs when not installing a build created via kerl build git..., and according to KERL_INSTALL_HTMLDOCS and KERL_INSTALL_MANPAGES.

KERL_DOC_TARGETS

Default: chunks Available targets:

You can set multiple type of targets separated by space, example KERL_DOC_TARGETS="html chunks"

KERL_INSTALL_MANPAGES

Install man pages when not building from Git source.

It's noteworthy that when not using KERL_BUILD_DOCS=yes, the docset that may be downloaded can be up to 120 MB.

KERL_INSTALL_HTMLDOCS

Install HTML documentation when not building from Git source.

It's noteworthy that when not using KERL_BUILD_DOCS=yes, the docset that may be downloaded can be up to 120 MB.

KERL_SASL_STARTUP

Build Erlang/OTP to use SASL startup instead of minimal (default, when var is unset).

Activation configuration

The following applies when activating an installation (i.e. . ${KERL_DEFAULT_INSTALL_DIR}/19.2/activate).

KERL_ENABLE_PROMPT

When set, automatically prefix the shell prompt with a section containing the Erlang/OTP version (see $KERL_PROMPT_FORMAT ).

KERL_PROMPT_FORMAT

Default: (%BUILDNAME%) Available variables:

The format of the prompt section to add.

KERL_GIT_CLONE_DEPTH

Default: not set Value passed to git clone --depth= when using kerl build git ....

Note: this doesn't always result in smaller clones.

Installation configuration

KERL_DEFAULT_INSTALL_DIR

Effective when calling kerl install <build> with no installation location argument.

If unset, $PWD is used.

If set, install the build under $KERL_DEFAULT_INSTALL_DIR/${buildname}.

KERL_APP_INSTALL_DIR

Effective when calling kerl upgrade. This is the folder where the kerl application resides.

If unset, $PWD is used.

If set, kerl is installed at $KERL_APP_INSTALL_DIR/kerl.

KERL_DEPLOY_SSH_OPTIONS + KERL_DEPLOY_RSYNC_OPTIONS

Options passed to ssh and rsync during kerl deploy tasks.

Command reference

You can also get information on the following by executing kerl (no parameters) on your shell.

build

$ kerl build <release> [build_name]
$ # or
$ kerl build git <git_url> <git_version> <build_name>

Creates a named build either from an official Erlang/OTP release or from a git repository.

$ kerl build 27.0 27.0
$ #or
$ kerl build git https://github.com/erlang/otp.git OTP-27.0 27.0

Tuning

Configure options

You can specify the configure options to use when building Erlang/OTP with the KERL_CONFIGURE_OPTIONS variable, either in your $HOME/.kerlrc file or prepending it to the command line. A full list of all options can be found the in Erlang/OTP documentation.

Configure applications

If non-empty, you can specify the subset of applications to use when building (and subsequent installing) Erlang/OTP with the KERL_CONFIGURE_APPLICATIONS variable, either in your $HOME/.kerlrc file or prepending it to the command line.

$ KERL_CONFIGURE_APPLICATIONS="kernel stdlib sasl" kerl build 27.0 27.0-minimal
Configure disable applications

If non-empty, you can specify the subset of applications to disable when building (and subsequent installing) Erlang/OTP with the KERL_CONFIGURE_DISABLE_APPLICATIONS variable, either in your $HOME/.kerlrc file or prepending it to the command line.

$ KERL_CONFIGURE_DISABLE_APPLICATIONS="odbc" kerl build 27.0 27.0-no-odbc
Enable autoconf

You can enable the use of autoconf in the build process setting KERL_USE_AUTOCONF=yes in your $HOME/.kerlrc file.

Note: autoconf is always enabled for Git builds.

Using shell export command in .kerlrc

Configure variables which includes spaces such as those in CFLAGS cannot be passed on with KERL_CONFIGURE_OPTIONS. In such a case you can use shell export command to define the environment variables for ./configure. Note well: this method has a side effect to change your shell execution environment after activating a kerl installation of Erlang/OTP. Here is an example of .kerlrc for building Erlang/OTP for FreeBSD with clang compiler:

<!-- markdownlint-disable MD007 # line-length --> 
$ # for clang
$ export CC=clang CXX=clang CFLAGS="-g -O3 -fstack-protector" LDFLAGS="-fstack-protector"
$ # compilation options
$ KERL_CONFIGURE_OPTIONS="--disable-native-libs --enable-vm-probes --with-dynamic-trace=dtrace --with-ssl=/usr/local --with-javac --enable-hipe --enable-kernel-poll --with-wx-config=/usr/local/bin/wxgtk2u-2.8-config --without-odbc --enable-threads --enable-sctp --enable-smp-support"
<!-- markdownlint-enable MD007 # line-length -->

In case you cannot access the default directory for temporary files (/tmp) or simply want them somewhere else, you can also provide your own directory with the variable TMP_DIR.

$ export TMP_DIR=/your/custom/temporary/dir

Building documentation

Prior to kerl 1.0, kerl always downloaded prepared documentation from erlang.org. Now if KERL_BUILD_DOCS=yes is set, kerl will build the man pages and HTML documentation from the source repository in which it is working.

Note: this variable takes precedent over the other documentation parameters.

install

Installing a build

$ kerl install <build_name> [directory]

Installs a named build to the specified filesystem location.

$ kerl install 27.0 /usr/local/lib/erlang/27.0

If path is omitted the current working directory will be used. However, if KERL_DEFAULT_INSTALL_DIR is defined in $HOME/.kerlrc, KERL_DEFAULT_INSTALL_DIR/<build-name> will be used instead.

Install location restrictions

Warning: kerl assumes the given installation directory is for its sole use. If you later delete it with the kerl delete command, the whole directory will be deleted, along with anything you may have added to it!

So only install kerl in an empty (or non-existant) directory.

If you attempt to install kerl in $HOME or .erlang or $KERL_BASE_DIR, then kerl will give you an error and refuse to proceed. If you try to install kerl in a directory that exists and is not empty, kerl will give you an error.

Tuning
SASL startup

You can have SASL started automatically setting KERL_SASL_STARTUP=yes in your $HOME/.kerlrc file or prepending it to the command line.

Manpages installation

You can have manpages installed automatically setting KERL_INSTALL_MANPAGES=yes in your $HOME/.kerlrc file or prepending it to the command line.

Note: for Git-based builds, you want to set KERL_BUILD_DOCS=yes

HTML docs installation

You can have HTML docs installed automatically setting KERL_INSTALL_HTMLDOCS=yes in your $HOME/.kerlrc file or prepending it to the command line.

Note: for Git-based builds, you want to set KERL_BUILD_DOCS=yes

Documentation installation

Man pages will be installed to [path]/man and HTML docs will be installed in [path]/html. The kerl activate script manipulates the MANPATH of the current shell such that man 3 gen_server or erl -man gen_server should work perfectly.

Do not fret - kerl_deactivate restores your shell's MANPATH to whatever its original value was.

deploy

$ kerl deploy <[user@]host> [directory] [remote_directory]

Deploys the specified installation to the given host and location.

$ kerl deploy anotherhost /path/to/install/dir

If [remote_directory] is omitted the specified [directory] will be used.

If both [directory] and [remote_directory] are omitted the current working directory will be used.

NOTE: kerl assumes the specified host is accessible via ssh and rsync.

Tuning

Additional SSH options

You can have additional options given to ssh by setting them in the KERL_DEPLOY_SSH_OPTIONS variable in your $HOME/.kerlrc file or on the command line, e.g. KERL_DEPLOY_SSH_OPTIONS='-qx -o PasswordAuthentication=no'.

Additional RSYNC options

You can have additional options given to rsync by setting them in the KERL_DEPLOY_RSYNC_OPTIONS variable in your $HOME/.kerlrc file or on the command line, e.g. KERL_DEPLOY_RSYNC_OPTIONS='--delete'.

update

$ kerl update releases

If KERL_BUILD_BACKEND=tarball this command fetches the up-to-date list of Erlang/OTP releases from erlang.org.

If it is set to KERL_BUILD_BACKEND=git this command fetches an up-to-date list of Erlang/OTP tags from the official Erlang/OTP GitHub repository.

Note: the output of this function can be tweaked with KERL_INCLUDE_RELEASE_CANDIDATES=yes to print release candidates.

list

$ kerl list <releases|builds|installations> [all]

Lists the releases, builds or installations available.

When listing releases (without option all), the following applies:

Note: using all means all available releases are shown without filters.

delete

$ kerl delete build <build_name>
$ # or
$ kerl delete installation <build_name|directory>

Deletes the specified build or installation.

$ kerl delete build 27.0
The 27.0 build has been deleted

$ kerl delete installation /usr/local/lib/erlang/27.0
The installation in /usr/local/lib/erlang/27.0 has been deleted

active

$ kerl active

Prints the path of the currently active installation, if any.

$ kerl active
The current active installation is:
/usr/local/lib/erlang/27.0

status

$ kerl status

Prints the available builds and installations as well as the currently active installation.

$ kerl status
Available builds:
27.0,27.0
27.0,27.0-builtdocs
----------
Available installations:
27.0 /usr/local/lib/erlang/27.0
----------
The current active installation is:
/usr/local/lib/erlang/27.0
Dialyzer PLT for the active installation is:
/usr/local/lib/erlang/27.0/dialyzer/plt
The build options for the active installation are:
...

path

$ kerl path [installation]

Prints the path of the currently active installation if one is active. When given an installation name, it will return the path to that installation location on disk. This makes it useful for automation without having to run kerl's output through other tools to extract to path information.

$ kerl path
No active kerl-managed erlang installation

$ kerl path 27.0
/usr/local/lib/erlang/27.0

build-install

$ kerl build-install <release> [build_name] [directory]
kerl build-install git <git_url> <git_version> <build_name> [directory]

Combines kerl build and kerl install into a single command.

plt

Prints Dialyzer PLT path for the active installation.

prompt

Prints a string suitable for insertion in prompt.

cleanup

$ kerl cleanup <build_name|all>

Remove compilation artifacts (use after installation), for a given build or for "all".

emit-activate

$ kerl emit-activate <release> <build_name> <directory> [sh|bash|fish|csh]

Print the activate script, as generated by kerl.

Note: the output defaults to shell sh (also bash), as per file activate. To emit activate.fish, or activate.csh, set the last argument to fish or csh, respectively.

version

Prints current version.

Important notes

Note on .kerlrc

Since .kerlrc is a dot file for /bin/sh, running shell commands inside the .kerlrc will affect the shell and environment variables for the commands being executed later. For example, the shell export commands in .kerlrc will affect your login shell environment when activating curl. Use with care.

Shell support

fish

kerl has basic support for the fish shell.

To activate an installation:

$ source /path/to/install/dir/activate.fish

Deactivation is the same as in other shells:

$ kerl_deactivate

C

kerl has basic support for the C shells (csh, tcsh, etc.).

To activate an installation:

$ source /path/to/install/dir/activate.csh

The activation script sources file .kerlrc.csh instead of .kerlrc.

Deactivation is the same as in other shells:

$ kerl_deactivate

Command-line completion

Optionally, download and install kerl's:

depending on your preferred shell.

The kerl glossary

Here are the abstractions kerl is handling:

The kerl project

Erlang/OTP support policy

As of September 2021, we are supporting the current Erlang/OTP release version and 2 prior release versions (same as upstream Erlang/OTP). Older Erlang/OTP releases may or may not work. We will advance release support as new releases of Erlang/OTP become available.

Code of conduct

You can read more about our code of conduct at CODE_OF_CONDUCT.md.

Contributing to kerl

Contributions are welcome! Be sure to read and follow the general guidelines made explicit in CONTRIBUTING.md.

License

kerl is MIT-licensed, as per LICENSE.md. You'll also find the same license notice inside the distributable shell script.

Changelog

Check CHANGELOG.md and also GitHub releases.