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This page helps you to solve a few common issues with IHP. In the long term, we should find solutions for these issues so that they don’t appear every again. Until then, we have this page so that you can find a solution when you paste the error message into Google.
In case your problem cannot be solved with the steps on this page, join our Slack community. We’re happy to help!

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Auto Troubleshooting

Run this to automatically check for the most common IHP issues: 
curl --silent https://raw.githubusercontent.com/digitallyinduced/ihp/master/Troubleshoot/ihp-troubleshoot | python3
It will tell you what is wrong and the steps you need to do to fix it.

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Common Issues

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Makefile:7: /../lib/IHP/Makefile.dist: No such file or directory

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Running ihp-new builds a lot of Haskell packages and takes hours to complete

Problem:When you try to start a new IHP project by running ihp-new someproject, nix seems to start compiling a lot of Haskell packages with GHC.Solution:This is most likely caused by a change we did to our binary cache. Run cachix use digitallyinduced to fix this.

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warning: substituter ‘https://digitallyinduced.cachix.org’ does not have a valid signature for path …

Problem:When running ihp-new someproject to create a new project, nix seems to not use the binary cache with the above warning. Instead, it tries to build all the packages itself, which takes hours.Solution:This is caused by a change we did to our binary cache. Open ~/.config/nix/nix.conf. There take a look at the trusted-public-keys = property. You should have two entries there (the public key of our old binary cache, and the new one). Remove the old one digitallyinduced.cachix.org-1:3mGU1b6u5obFp2VUfI55Xe8/+mawl7y9Eztu3rb94PI= (should be first of the two digitallyinduced keys). Then save the file and the problem is fixed.

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error: file ‘/build/db/.s.PGSQL.5432’ has an unsupported type

Problem:When you try to start a nix-shell, an error like this happens:
$ devenv up
error: file '/build/db/.s.PGSQL.5432' has an unsupported type
Solution:This happens because nix cannot use the Postgres Unix socket which is in build/db. Usually, this happens when the development server of IHP is still running. Stop your IHP development server and then try again.When the development server is not running, check that you have no Postgres processes belonging to this Unix socket running anymore. In case there are no more processes running, try to remove the file via rm -f.

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Unbound implicit parameter (?modelContext::ModelContext)

The full error message looks like this:
MyModule.hs:7:29: error:
    * Unbound implicit parameter (?modelContext::ModelContext)
        arising from a use of `fetch'
    * In the second argument of `(|>)', namely `fetch'
      In a stmt of a 'do' block: users <- query @User |> fetch
      In the expression:
        do users <- query @User |> fetch
           return users
  |
7 |     users <- query @User |> fetch
Problem:IHP uses an implicit parameter called ?modelContext to pass around the database connection. The ? question mark is part of the variable name. When you do a database query from a helper function outside of your controller actions the database connection needs to be passed to your function. This works automatically because it’s an implicit parameter but needs to be specified inside your type signature.Solution:Add (?modelContext :: ModelContext) => to the start of your type signature.
-- OLD:
fetchUser :: Text -> IO [User]
fetchUser name = do
    users <- query @User |> fetch
    return users

-- NEW:
fetchUser :: (?modelContext :: ModelContext) => Text -> IO [User]
fetchUser name = do
    users <- query @User |> fetch
    return users

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Creating a new IHP project with ihp-new yields git error

When you followed the steps as described on the getting started page (i.e. installing Nix and IHP) but one of the steps erred during installation (e.g. connection issues, privileges not set correctly) the cache utilized by nix might not be properly initialized. This can manifest itself as a git error (output below) when running ihp-new <project-name>.
We will now create your project. This may take up to 30 seconds.
fatal: not a git repository (or any of the parent directories): .git
fatal: not a git repository (or any of the parent directories): .git
error: program 'git' failed with exit code 128
If you have a “fresh” nix install, this can be solved by removing your ~/.cache/nix directory completely.
rm -rf ~/.cache/nix
After removing your nix cache, running ihp-new <project-name> will remain silent for a while since it will re-cache a substantial number of nix dependencies.

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Ubuntu on Windows Subsystem for Linux (WSL): ghc-pkg: Couldn't open database...

Problem:When you run ihp-new blog to create a new project on a system using Ubuntu running on Windows Subsystem for Linux 1, you get an error like:
ghc-pkg: Couldn't open database /nix/store/...-ghc-8.10.3-with-packages/lib/ghc-8.10.3/package.conf.d for modification: {handle: ...}: hLock: invalid argument (Invalid argument)
Solution:Switch to WSL 2.

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Slow Compilation of Generated Types

Problem:Your project has a large database schema and Generated.Types takes a long time to compile. This is especially noticeable when the schema has many tables with foreign key relationships.Cause:For each foreign key relationship, IHP generates type parameters on record types, QueryBuilder fields for has-many relationships, Include type family instances, and complex UpdateField instances. These are expensive for GHC’s type checker, and the cost grows with the number of tables and relationships.Solution:If your project does not use fetchRelated or Include types, you can disable this machinery to speed up compilation. Set ihp.relationSupport = false; in your flake.nix:
ihp = {
    enable = true;
    relationSupport = false;
};
This applies to both the dev shell and production builds.Alternatively, set the environment variable manually:
export IHP_RELATION_SUPPORT=0
See Relationships: Disabling Relation Support for Faster Compilation for details on what changes and what stops working.

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OAuth/HTTPS in Docker fails: certificate has unknown CA

Problem:Inside a container built with Nix dockerTools.buildImage, HTTPS requests fail with:
HttpExceptionRequest ... (InternalException (HandshakeFailed (Error_Protocol "certificate has unknown CA" UnknownCa)))
This can affect Google OAuth, GitHub API calls, S3 uploads, etc.Cause:Minimal images produced by dockerTools.buildImage do not include a root CA bundle at /etc/ssl/certs by default, and SSL libraries cannot validate certificates.Solution:Override the IHP Docker image to include CA certificates and set SSL env vars. See the detailed snippet and explanation in Deployment → Deploying with Docker → “TLS certificates in Nix-built Docker images”.

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