3.1. Configuration

3.1.1. Overview

The global configuration file for cabal-install is ~/.cabal/config. If you do not have this file, cabal will create it for you on the first call to cabal update. Alternatively, you can explicitly ask cabal to create it for you using

$ cabal user-config update

You can change the location of the global configuration file by specifying either --config-file=FILE on the command line or by setting the CABAL_CONFIG environment variable.

Most of the options in this configuration file are also available as command line arguments, and the corresponding documentation can be used to lookup their meaning. The created configuration file only specifies values for a handful of options. Most options are left at their default value, which it documents; for instance,

-- executable-stripping: True

means that the configuration file currently does not specify a value for the executable-stripping option (the line is commented out), and that the default is True; if you wanted to disable stripping of executables by default, you would change this line to

executable-stripping: False

You can also use cabal user-config update to migrate configuration files created by older versions of cabal.

3.1.2. Environment variables

Various environment variables affect cabal-install.

CABAL_CONFIG
The variable to find global configuration file.
CABAL_DIR

Default content directory for cabal-install files. Default value is getAppUserDataDirectory "cabal", which is $HOME/.cabal on unix systems and %APPDATA%\cabal in Windows.

Note

The CABAL_DIR might be dropped in the future, when cabal-install starts to use XDG Directory specification.

CABAL_BUILDDIR
The override for default dist build directory. Note, the nix-style builds build directory (dist-newstyle) is not affected by this environment variable.

3.1.2.1. Configuration file discovery

  1. If $CABAL_CONFIG is set use it,
  2. otherwise if $CABAL_DIR is set use $CABAL_DIR/config
  3. otherwise use getAppUserDirectory "cabal"

If the configuration file doesn’t exist cabal-install will generate the default one, with directories based on $CABAL_DIR (if set) or getAppUserDirectory "cabal" prefix.

3.1.3. Repository specification

An important part of the configuration is the specification of the repository. When cabal creates a default config file, it configures the repository to be the central Hackage server:

repository hackage.haskell.org
  url: http://hackage.haskell.org/

The name of the repository is given on the first line, and can be anything; packages downloaded from this repository will be cached under ~/.cabal/packages/hackage.haskell.org (or whatever name you specify; you can change the prefix by changing the value of remote-repo-cache). If you want, you can configure multiple repositories, and cabal will combine them and be able to download packages from any of them.

3.1.3.1. Using secure repositories

For repositories that support the TUF security infrastructure (this includes Hackage), you can enable secure access to the repository by specifying:

repository hackage.haskell.org
  url: http://hackage.haskell.org/
  secure: True
  root-keys: <root-key-IDs>
  key-threshold: <key-threshold>

The <root-key-IDs> and <key-threshold> values are used for bootstrapping. As part of the TUF infrastructure the repository will contain a file root.json (for instance, http://hackage.haskell.org/root.json) which the client needs to do verification. However, how can cabal verify the root.json file itself? This is known as bootstrapping: if you specify a list of root key IDs and a corresponding threshold, cabal will verify that the downloaded root.json file has been signed with at least <key-threshold> keys from your set of <root-key-IDs>.

You can, but are not recommended to, omit these two fields. In that case cabal will download the root.json field and use it without verification. Although this bootstrapping step is then unsafe, all subsequent access is secure (provided that the downloaded root.json was not tampered with). Of course, adding root-keys and key-threshold to your repository specification only shifts the problem, because now you somehow need to make sure that the key IDs you received were the right ones. How that is done is however outside the scope of cabal proper.

More information about the security infrastructure can be found at https://github.com/haskell/hackage-security.

3.1.3.2. Local no-index repositories

It’s possible to use a directory of .tar.gz package files as a local package repository.

repository my-local-repository
  url: file+noindex:///absolute/path/to/directory

cabal will construct the index automatically from the package-name-version.tar.gz files in the directory, and will use optional corresponding package-name-version.cabal files as new revisions.

For example, if /absolute/path/to/directory looks like

/absolute/path/to/directory/
    foo-0.1.0.0.tar.gz
    bar-0.2.0.0.tar.gz
    bar-0.2.0.0.cabal

then cabal will create an index with two packages:

  • foo-0.1.0.0 using the source and .cabal file inside foo-0.1.0.0.tar.gz
  • bar-0.2.0.0 using the source inside bar-0.2.0.0.tar.gz and bar-0.2.0.0.cabal

The index is cached inside the given directory. If the directory is not writable, you can append #shared-cache fragment to the URI, then the cache will be stored inside the remote-repo-cache directory. The part of the path will be used to determine the cache key part.

Note

cabal-install creates a .cache file, and will aggressively use its contents if it exists. Therefore if you change the contents of the directory, remember to wipe the cache too.

Note

The URI scheme file: is interpreted as a remote repository, as described in the previous sections, thus requiring manual construction of 01-index.tar file.

3.1.3.3. Legacy repositories

Currently cabal supports single kind of “legacy” repositories. It is specified using

remote-repo: hackage.haskell.org:http://hackage.haskell.org/packages/archive

This is just syntactic sugar for

repository hackage.haskell.org
  url: http://hackage.haskell.org/packages/archive

although, in (and only in) the specific case of Hackage, the URL http://hackage.haskell.org/packages/archive will be silently translated to http://hackage.haskell.org/.

3.1.3.4. Secure local repositories

If you want to use repositories on your local file system, it is recommended instead to use a secure local repository:

repository my-local-repo
  url: file:/path/to/local/repo
  secure: True
  root-keys: <root-key-IDs>
  key-threshold: <key-threshold>

The layout of these secure local repos matches the layout of remote repositories exactly; the hackage-repo-tool can be used to create and manage such repositories.

3.2. Building and installing packages

To be written

3.2.1. Installing packages from Hackage

The cabal tool also can download, configure, build and install a Hackage_ package and all of its dependencies in a single step. To do this, run:

$ cabal install [PACKAGE...]

To browse the list of available packages, visit the Hackage_ web site.