(topic-tljh-config)=

# Configuring TLJH with `tljh-config`

`tljh-config` is the commandline program used to make configuration
changes to TLJH.

## Running `tljh-config`

You can run `tljh-config` in two ways:

1. From inside a terminal in JupyterHub while logged in as an admin user.
   This method is recommended.
2. By directly calling `/opt/tljh/hub/bin/tljh-config` as root when
   logged in to the server via other means (such as SSH). This is an
   advanced use case, and not covered much in this guide.

(tljh-set)=

## Set / Unset a configuration property

TLJH's configuration is organized in a nested tree structure. You can
set a particular property with the following command:

```bash
sudo tljh-config set <property-path> <value>
```

where:

1. `<property-path>` is a dot-separated path to the property you want
   to set.
2. `<value>` is the value you want to set the property to.

For example, to set the password for the DummyAuthenticator, you
need to set the `auth.DummyAuthenticator.password` property. You would
do so with the following:

```bash
sudo tljh-config set auth.DummyAuthenticator.password mypassword
```

This can only set string and numerical properties, not lists.

To unset a configuration property you can use the following command:

```bash
sudo tljh-config unset <property-path>
```

Unsetting a configuration property removes the property from the configuration
file. If what you want is only to change the property's value, you should use
`set` and overwrite it with the desired value.

Some of the existing `<property-path>` are listed below by categories:

(tljh-base-url)=

### Base URL

Use `base_url` to determine the base URL used by JupyterHub. This parameter will
be passed straight to `c.JupyterHub.base_url`.

(tljh-set-auth)=

### Authentication

Use `auth.type` to determine authenticator to use. All parameters
in the config under `auth.{auth.type}` will be passed straight to the
authenticators themselves.

(tljh-set-ports)=

### Ports

Use `http.port` and `https.port` to set the ports that TLJH will listen on,
which are 80 and 443 by default. However, if you change these, note that
TLJH does a lot of other things to the system (with user accounts and sudo
rules primarily) that might break security assumptions your other
applications have, so use with extreme caution.

```bash
sudo tljh-config set http.port 8080
sudo tljh-config set https.port 8443
sudo tljh-config reload proxy
```

(tljh-set-listen-address)

### Listen address

Use `http.address` and `https.address` to set the addresses that TLJH will listen on,
which is an empty address by default (it means it listens on all interfaces by default).

```bash
sudo tljh-config set http.address 127.0.0.1
sudo tljh-config set https.address 127.0.0.1
sudo tljh-config reload proxy
```

(tljh-set-user-lists)=

### User Lists

- `users.allowed` takes in usernames to allow

- `users.banned` takes in usernames to ban

- `users.admin` takes in usernames to designate as admins

  ```bash
  sudo tljh-config add-item users.allowed good-user_1
  sudo tljh-config add-item users.allowed good-user_2
  sudo tljh-config add-item users.banned bad-user_6
  sudo tljh-config add-item users.admin admin-user_0
  sudo tljh-config remove-item users.allowed good-user_2
  ```

(tljh-set-user-limits)=

### User Server Limits

- `limits.memory` Specifies the maximum memory that can be used by each
  individual user. By default there is no memory limit. The limit can be
  specified as an absolute byte value. You can use
  the suffixes K, M, G or T to mean Kilobyte, Megabyte, Gigabyte or Terabyte
  respectively. Setting it to `None` disables memory limits.

  ```bash
  sudo tljh-config set limits.memory 4G
  ```

  Even if you want individual users to use as much memory as possible,
  it is still good practice to set a memory limit of 80-90% of total
  physical memory. This prevents one user from being able to single
  handedly take down the machine accidentally by OOMing it.

- `limits.cpu` A float representing the total CPU-cores each user can use.
  By default there is no CPU limit.
  1 represents one full CPU, 4 represents 4 full CPUs, 0.5 represents
  half of one CPU, etc. This value is ultimately converted to a percentage and
  rounded down to the nearest integer percentage,
  i.e. 1.5 is converted to 150%, 0.125 is converted to 12%, etc.
  Setting it to `None` disables CPU limits.

  ```bash
  sudo tljh-config set limits.cpu 2
  ```

(tljh-set-user-env)=

### User Environment

`user_environment.default_app` Set default application users are launched into.
Currently this can only be set to: `classic` and `jupyterlab`.

```bash
sudo tljh-config set user_environment.default_app jupyterlab
```

(tljh-set-extra-user-groups)=

## Extra User Groups

`users.extra_user_groups` is a configuration option that can be used
to automatically add a user to a specific group. By default, there are
no extra groups defined.

Users can be "paired" with the desired, **existing** groups using:

- `tljh-config set`, if only one user is to be added to the
  desired group:

```bash
tljh-config set users.extra_user_groups.group1 user1
```

- `tljh-config add-item`, if multiple users are to be added to
  the group:

```bash
tljh-config add-item users.extra_user_groups.group1 user1
tljh-config add-item users.extra_user_groups.group1 user2
```

(tljh-view-conf)=

## View current configuration

To see the current configuration, you can run the following command:

```bash
sudo tljh-config show
```

This will print the current configuration of your TLJH. This is very
useful when asking for support!

(tljh-reload-hub)=

## Reloading JupyterHub to apply configuration

After modifying the configuration, you need to reload JupyterHub for
it to take effect. You can do so with:

```bash
sudo tljh-config reload
```

This should not affect any running users. The JupyterHub will be
restarted and loaded with the new configuration.

(tljh-edit-yaml)=

## Advanced: `config.yaml`

`tljh-config` is a simple program that modifies the contents of the
`config.yaml` file located at `/opt/tljh/config/config.yaml`. `tljh-config`
is the recommended method of editing / viewing configuration since editing
YAML by hand in a terminal text editor is a large source of errors.

To learn more about the `tljh-config` usage, you can use the `--help` flag.
The `--help` flag can be used either directly, to get information about the
general usage of the command or after a positional argument. For example, using
it after an argument like `remove-item` gives information about this specific command.

```bash
sudo tljh-config --help

usage: tljh-config [-h] [--config-path CONFIG_PATH] {show,unset,set,add-item,remove-item,reload} ...

positional arguments:
  {show,unset,set,add-item,remove-item,reload}
    show                Show current configuration
    unset               Unset a configuration property
    set                 Set a configuration property
    add-item            Add a value to a list for a configuration property
    remove-item         Remove a value from a list for a configuration property
    reload              Reload a component to apply configuration change

optional arguments:
  -h, --help            show this help message and exit
  --config-path CONFIG_PATH
                        Path to TLJH config.yaml file
```

```bash
sudo tljh-config remove-item --help

usage: tljh-config remove-item [-h] key_path value

positional arguments:
  key_path    Dot separated path to configuration key to remove value from
  value       Value to remove from key_path

optional arguments:
  -h, --help  show this help message and exit
```
