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Introduced in 0.17.0

trace:on                                       # Enables trace mode
trace:off                                      # Disables trace mode

Trace Mode

By default, Dokku will constrain the amount of output displayed for any given command run. The verbosity of output can be increased by enabling trace mode. Trace mode will turn on the set -x flag for bash plugins, while other plugins are free to respect the environment variable DOKKU_TRACE and log differently as approprate. Trace mode can be useful to see where plugins are running commands that would otherwise be unexpected.

To enable trace mode, run trace:on

dokku trace:on
-----> Enabling trace mode

Trace mode can be disabled with trace:off

dokku trace:off
-----> Disabling trace mode

Common Problems

I deployed my app but I am getting the default nginx page

Most of the time it's caused by some defaults newer versions of nginx set. To make sure that's the issue you're having run the following:

nginx -t
## nginx: [emerg] could not build the server_names_hash, you should increase server_names_hash_bucket_size: 32

If you get a similar error just edit /etc/nginx/nginx.conf and add the following line to your http section:

http {
    (... existing content ...)
    server_names_hash_bucket_size 64;

Note that the server_names_hash_bucket_size setting defines the maximum domain name length. A value of 64 would allow domains with up to 64 characters. Set it to 128 if you need longer ones.

Save the file and try stopping nginx and starting it again:

dokku nginx:stop
dokku nginx:start

Using the EXPOSE directive in a Dockerfile may be another reason why you might see the default site. When the EXPOSE directive is in use and a proxy plugin is enabled (the default), the proxy plugin will listen to requests on the ports specified in the EXPOSE stanza.

For example, if you have an EXPOSE directive like so:


The port mapping will be http:8000:8000.

To avoid this issue, either of the following can be done:

  • Remove EXPOSE directive: This will require respecting the $PORT environment variable (automatically set by Dokku). Once that change is deployed, the port mapping should be cleared via the dokku ports:clear $APP command (where $APP is your app name).
  • Update the port mapping: Updating the port mapping to redirect port 80 to your app's exposed port via dokku ports:set $APP http:80:$EXPOSED_PORT can also fix the issue. This will also allow certificate management and the letsencrypt plugin to work correctly.

See the port management documentation for more information on how Dokku exposes ports for applications and how you can configure these for your app.

I want to deploy my app, but while pushing I get the following error

The following error may be emitted from a deploy:

! [remote rejected] master -> master (pre-receive hook declined)

The remote rejected error does not give enough information. Anything could have failed. Enable trace mode and begin debugging. If this does not help you, create a gist containing the full log, and create an issue.

One the reasons why you may get this error is because the command that is run in the container exited (without errors). For example, (in Procfile) when you define a new worker container to run Delayed Job and use the bin/delayed_job start command. This command deamonizes the process and exists. The container thinks it's done so it closes itself. The error you get is the one above. To fix the above problem for Delayed Job, you must define the worker to user rake jobs:work, which doesn't deamonize the process.

I get the aforementioned error in the build phase (after turning on Dokku tracing)

Most errors that happen in this phase are due to transient network issues (either locally or remotely) buildpack bugs.

Find the failed phase's container image (077581956a92 in this example).

docker ps -a  | grep build
## 94d9515e6d93        077581956a92                "/build"       29 minutes ago      Exited (0) 25 minutes ago                       cocky_bell

Start a new container with the failed image and poke around (i.e. ensure you can access the internet from within the container or attempt the failed command, if known).

docker run -ti 077581956a92 /bin/bash
curl -s -S
curl -o node-v0.10.30-linux-x64.tar.gz
tar tzf node-v0.10.30-linux-x64.tar.gz
## ...

Sometimes (especially on DigitalOcean) deploying again seems to get past these seemingly transient issues. Additionally we've seen issues if changing networks that have different DNS resolvers. In this case, you can run the following to update your resolv.conf.

resolvconf -u

Please see #841 and #649.

After adding an SSH key, I am told I cannot read from the remote repository on push

Connection closed by <host> port 22
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

Certain systems may have access to the dokku user via SSH disabled. Please check that the dokku user is allowed access to the system in the file /etc/security/access.conf. As Dokku does not manage this file, please consult your Operating System's documentation for more information.

I want to deploy my app but I am getting asked for the password of the Git user

Sometimes the following error message may be shown on push

fatal: 'NAME' does not appear to be a git repository
fatal: Could not read from remote repository.

You get asked for a password because your SSH secret key can't be found. This may happen if the private key corresponding to the public key you added with sshcommand acl-add is not located in the default location ~/.ssh/id_rsa.

You have to point SSH to the correct secret key for your domain name. Add the following to your ~/.ssh/config:

  IdentityFile "~/.ssh/KEYNAME"

Also see issue #116.

I successfully deployed my application with no deployment errors and receiving Bad Gateway when attempting to access the application

In many cases the application will require the a process.env.PORT port opposed to a specified port.

When specifying your port you may want to use something similar to:

var port = process.env.PORT || 3000

Please see #282.

Additionally, your application should listen/bind to all interfaces ( Many frameworks default to listening on

Please see #5798.

Deployment fails because of slow internet connection, messages shows gzip: stdin: unexpected end of file

If you see output similar this when deploying:

 Command: 'set -o pipefail; curl --fail --retry 3 --retry-delay 1 --connect-timeout 3 --max-time 30 -s -o - | tar zxf -' failed unexpectedly:
 !     gzip: stdin: unexpected end of file
 !     tar: Unexpected EOF in archive
 !     tar: Unexpected EOF in archive
 !     tar: Error is not recoverable: exiting now

it might that the cURL command that is supposed to fetch the buildpack (anything in the low megabyte file size range) takes too long to finish, due to slowish connection. To overwrite the default values (connection timeout: 90 seconds, total maximum time for operation: 600 seconds), set the following environment variables:

dokku config:set --global CURL_TIMEOUT=1200
dokku config:set --global CURL_CONNECT_TIMEOUT=180

Please see #509.

Another reason for this error (although it may respond immediately ruling out a timeout issue) may be because you've set the config setting SSL_CERT_FILE. Using a config setting with this key interferes with the buildpack's ability to download its dependencies, so you must rename the config setting to something else, e.g. MY_APP_SSL_CERT_FILE.

Build fails with Killed message

This generally occurs when the server runs out of memory. You can either add more RAM to your server or setup swap space. The follow script will create 2 GB of swap space.

sudo install -o root -g root -m 0600 /dev/null /swapfile
dd if=/dev/zero of=/swapfile bs=1k count=2048k
mkswap /swapfile
swapon /swapfile
echo "/swapfile       swap    swap    auto      0       0" | sudo tee -a /etc/fstab
sudo sysctl -w vm.swappiness=10
echo vm.swappiness = 10 | sudo tee -a /etc/sysctl.conf

I successfully deployed my application with no deployment errors but I'm receiving Connection Timeout when attempting to access the application

This can occur if Dokku is running on a system with a firewall like UFW enabled (some OS versions like Ubuntu have this enabled by default). You can check if this is your case by running the following script:

sudo ufw status

If the previous script returned Status: active and a list of ports, UFW is enabled and is probably the cause of the symptom described above. To disable it, run:

sudo ufw disable

I can't connect to my application because the server is sending an invalid response, or can't provide a secure connection

This isn't usually an issue with Dokku, but rather an app config problem. This can happen when your application is configured to enforce secure connections/HSTS, but you don't have SSL set up for the app.

In Rails at least, if your application.rb or environmnents/production.rb include the line configure.force_ssl = true which includes HSTS, try commenting that out and redeploying.

If this solves the issue temporarily, longer term you should consider configuring SSL.

My application deploys properly, but won't load in browser "connection refused"

This could be a result of a bad proxy configuration (http:5000:5000 may be incorrect). Run dokku ports:report node-js-app to check if your app has the correct proxy configuration. It should show something like the following.

=====> node-js-app ports information
       Port map:                http:80:5000 https:443:5000

Set dokku ports:set node-js-app http:80:5000 to get proxy correctly configured for http endpoint.

I deployed a new app but now subdomains are miss-routed

Sometimes nginx does something funky and cant actually reload for whatever reason.

# Validate the configuration
$ sudo nginx -t
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful

$ sudo service nginx restart

# Re-enable Letsencrypt

Example: existing AppA (https) and AppB(https), deployed NEW (non-https) then noticed right away NEW's subdomain showed AppB's content and cert but under its own subdomain (cert miss-match of course). AppB still works. AppA also changed to show AppB content and cert.. Other apps were unaffected.

Consider caddy and traefik support via docker containers if this continues to be an issue.