# Contacts / CardDAV

Nextcloud ships a CardDAV backend for users to store and share their address books and contacts.

## System Address Book

Changed in version 27: The system address book is now accessible to all Nextcloud users

Nextcloud maintains a read-only address book containing contact information of all users of the instance.

Disabled users are removed from this address book.

You can disable access to the system address book by using the app config value `system_addressbook_exposed`.

Run `occ config:app:set dav system_addressbook_exposed --value="no"` to disable access to the system address book for all users. Please note that this does not influence Federated sharing.

Warning

If clients have already connected to the CalDAV endpoint, the clients might experience sync issues after system address book access was disabled. This can often be remedied by choosing a different default address book on the client and forcing a resync.

### Privacy and User Property Scopes

Contact information in the system address book is taken from users’ profile information. Profile properties are only written to the system contact if the scope is set to Local or higher.

Users who set all their property scopes to Private are removed from the system address book and therefore not seen by other users.

File sharing settings controls the enumeration of other users.

- If username autocompletion is not allowed, the system address book will only show user’s own system contact but no other contacts.

- If username autocompletion is allowed, users will see contact cards for all other users.

  - If autocompletion is limited to users within the same groups, users will see contact cards for other users in shared groups.

  - If autocompletion is limited to matching phone numbers, the system address book will only show user’s own system contact but no other contacts.

  - If autocompletion is limited to users within the same groups and matching phone numbers, users will see contact cards for other users in shared groups.

### Address Book Sync

The address book is updated automatically with every added, modified, disabled or removed user. Admins can also trigger a full rewrite of the address book with occ.

## Shared items

Added in version 5.5.0.

For this feature, the shipped related resources app needs to be enabled.

## Rate limits

Nextcloud rate limits the creation of address books and how many can be created in a short period of time. The default is 10 address books per hour. This can be customized as follows:

    # Set limit to 15 items per 30 minutes
    php occ config:app:set dav rateLimitAddressBookCreation --type=integer --value=15
    php occ config:app:set dav rateLimitPeriodAddressBookCreation --type=integer --value=1800

Additionally, the maximum number of address books a user may create is limited to 10 items. This can be customized too:

    # Allow users to create 50 addressbooks
    php occ config:app:set dav maximumAdressbooks --type=integer --value=50

or:

    # Allow users to create address books without restriction
    php occ config:app:set dav maximumAdressbooks --type=integer --value=-1

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