[Bug]: Not able to change key dbhost with occ config:system:set to value 'db', all other values are possible

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

Not able to change key dbhost with occ config:system:set to value 'db', all other values are possible for example:

• abc
• ab
• dbb
• etc.

Steps to reproduce

1. Spin up nextcloud:28.0.2-fpm
2. Run docker exec -it -u 502 nextcloud-app-1 php /var/www/html/occ config:system:set "dbhost" --value="db"
3. No change
4. Run docker exec -it -u 502 nextcloud-app-1 php /var/www/html/occ config:system:set "dbhost" --value="ab"
5. Changed in config.php

Expected behavior

Change value in config.php

Installation method

Community Docker image

Nextcloud Server version

28

Operating system

Other

PHP engine version

Other

Web server

Nginx

Database engine version

MariaDB

Is this bug present after an update or on a fresh install?

None

Are you using the Nextcloud Server Encryption module?

Encryption is Disabled

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

{
    "system": {
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "***"
        ],
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "mysql",
        "version": "28.0.2.5",
        "overwrite.cli.url": "https:\/\/***",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "",
        "dbtableprefix": "oc_",
        "mysql.utf8mb4": true,
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "maintenance": true,
        "maintenance_window_start": 1,
        "theme": "",
        "loglevel": 0,
        "updater.release.channel": "stable",
        "default_phone_region": "DE",
        "preview_max_x": "2048",
        "preview_max_y": "2048",
        "jpeg_quality": "60",
        "mail_smtpmode": "smtp",
        "mail_smtpsecure": "ssl",
        "mail_sendmailmode": "smtp",
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpauthtype": "LOGIN",
        "mail_smtpauth": 1,
        "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpport": "465",
        "mail_smtpname": "***REMOVED SENSITIVE VALUE***",
        "mail_smtppassword": "***REMOVED SENSITIVE VALUE***"
    }
}

List of activated Apps

No response

Nextcloud Signing status

No response

Nextcloud Logs

No response

Additional info

No response

Start by reproducing the occ config:system:set command in the Nextcloud 28.0.2-fpm Docker setup and trace how the CLI handles the dbhost value before writing config.php. Compare the failed value db with a working value such as ab; done means setting dbhost to db updates config.php as expected.