`RuntimeException Backgroundjobs are using system cron! log error while they are not`

[TheWojtek]

⚠️ 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

After upgrading to 33, a new error starts popping up in the server:

RuntimeException Backgroundjobs are using system cron!

First of all, the "Basic" configuration page literally encourages to use system cron: "Use system cron service to call the cron.php file every 5 minutes." so it is kind of misleading.

My particular server does not use the system cron service (empty crontabs for all users), instead it uses the recommended timer/system service combination and according to the guide, it uses www-data as the service user.

Steps to reproduce

1. On a <33.0 instance, create timer and service accordingly, set up various background workers.
2. Upgrade to 33.0
3. Errors start popping up in the logs.

Expected behavior

No errors, as the server does not use system cron.

Nextcloud Server version

33

Operating system

Debian/Ubuntu

PHP engine version

PHP 8.3

Web server

Apache (supported)

Database engine version

MariaDB

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

Upgraded to a MAJOR version (ex. 31 to 32)

Are you using the Nextcloud Server Encryption module?

None

What user-backends are you using?

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

Configuration report

{
    "system": {
        "default_phone_region": "PL",
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "serverid": 0,
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "cloud.jakobczyk.org",
            "www.home102"
        ],
        "trusted_proxies": "***REMOVED SENSITIVE VALUE***",
        "push": "https:\/\/cloud.jakobczyk.org\/push",
        "forwarded_for_headers": [
            "HTTP_X_FORWARDED_FOR",
            "HTTP_X_REAL_IP"
        ],
        "allow_local_remote_servers": true,
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "skeletondirectory": "",
        "dbtype": "mysql",
        "version": "33.0.0.16",
        "overwrite.cli.url": "https:\/\/cloud.jakobczyk.org\/",
        "htaccess.RewriteBase": "\/",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "",
        "dbtableprefix": "oc_",
        "mysql.utf8mb4": true,
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "memcache.locking": "\\OC\\Memcache\\Redis",
        "memcache.local": "\\OC\\Memcache\\Redis",
        "memcache.distributed": "\\OC\\Memcache\\Redis",
        "redis": {
            "host": "***REMOVED SENSITIVE VALUE***",
            "port": 6379,
            "dbindex": 0,
            "timeout": 1.5
        },
        "maintenance": false,
        "theme": "",
        "maintenance_window_start": 1,
        "log_type": "file",
        "logfile": "\/var\/log\/nextcloud\/nextcloud.log",
        "loglevel": 3,
        "simpleSignUpLink.shown": false,
        "log_rotate_size": 10485760,
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpmode": "smtp",
        "mail_sendmailmode": "smtp",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpauthtype": "PLAIN",
        "mail_smtpauth": true,
        "mail_smtpport": "587",
        "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpname": "***REMOVED SENSITIVE VALUE***",
        "mail_smtppassword": "***REMOVED SENSITIVE VALUE***",
        "app.mail.imap.timeout": 10,
        "app.mail.smtp.timeout": 20,
        "app.mail.sieve.timeout": 15,
        "app.mail.verify-tls-peer": false,
        "app.mail.background-sync-interval": 600,
        "app_install_overwrite": [
            "occweb",
            "impersonate",
            "groupfolders"
        ],
        "memories.db.triggers.fcu": true,
        "memories.exiftool": "\/mnt\/www\/nextcloud\/apps\/memories\/bin-ext\/exiftool-amd64-glibc",
        "memories.vod.path": "\/mnt\/www\/nextcloud\/apps\/memories\/bin-ext\/go-vod-amd64",
        "memories.vod.ffmpeg": "\/usr\/bin\/ffmpeg",
        "memories.vod.ffprobe": "\/usr\/bin\/ffprobe",
        "enabledPreviewProviders": [
            "OC\\Preview\\Image",
            "OC\\Preview\\HEIC",
            "OC\\Preview\\Movie"
        ],
        "preview_max_x": 1024,
        "preview_max_y": 1024,
        "memories.gis_type": 1,
        "forbidden_filename_basenames": [
            "con",
            "prn",
            "aux",
            "nul",
            "com0",
            "com1",
            "com2",
            "com3",
            "com4",
            "com5",
            "com6",
            "com7",
            "com8",
            "com9",
            "com\u00b9",
            "com\u00b2",
            "com\u00b3",
            "lpt0",
            "lpt1",
            "lpt2",
            "lpt3",
            "lpt4",
            "lpt5",
            "lpt6",
            "lpt7",
            "lpt8",
            "lpt9",
            "lpt\u00b9",
            "lpt\u00b2",
            "lpt\u00b3"
        ],
        "forbidden_filename_characters": [
            "<",
            ">",
            ":",
            "\"",
            "|",
            "?",
            "*",
            "\\",
            "\/"
        ],
        "forbidden_filename_extensions": [
            " ",
            ".",
            ".filepart",
            ".part"
        ],
        "mail_smtpstreamoptions": {
            "ssl": {
                "allow_self_signed": false,
                "verify_peer": true,
                "verify_peer_name": true
            }
        }
    }
}

List of activated Apps

Enabled:
  - activity: 6.0.0-dev.0
  - app_api: 33.0.0
  - assistant: 3.3.0
  - bruteforcesettings: 6.0.0-dev.0
  - circles: 33.0.0
  - cloud_federation_api: 1.17.0
  - comments: 1.23.0
  - contactsinteraction: 1.14.1
  - context_chat: 5.3.1
  - dashboard: 7.13.0
  - dav: 1.36.0
  - federatedfilesharing: 1.23.0
  - federation: 1.23.0
  - files: 2.5.0
  - files_downloadlimit: 5.1.0-dev.0
  - files_external: 1.25.1
  - files_pdfviewer: 6.0.0-dev.0
  - files_reminders: 1.6.0
  - files_sharing: 1.25.2
  - files_trashbin: 1.23.0
  - files_versions: 1.26.0
  - groupfolders: 21.0.5
  - impersonate: 4.0.0
  - integration_openai: 4.2.0
  - logreader: 6.0.0
  - lookup_server_connector: 1.21.0
  - mail: 5.7.0
  - nextcloud_announcements: 5.0.0
  - notifications: 6.0.0
  - notify_push: 1.3.0
  - oauth2: 1.21.0
  - password_policy: 5.0.0-dev.0
  - photos: 6.0.0-dev.0
  - previewgenerator: 5.12.1
  - privacy: 5.0.0-dev.0
  - profile: 1.2.0
  - provisioning_api: 1.23.0
  - recognize: 11.0.1
  - recommendations: 6.0.0-dev.0
  - related_resources: 4.0.0-dev.0
  - serverinfo: 5.0.0-dev.0
  - settings: 1.16.0
  - sharebymail: 1.23.0
  - support: 5.0.0
  - survey_client: 5.0.0-dev.0
  - systemtags: 1.23.0
  - text: 7.0.0-dev.3
  - theming: 2.8.0
  - twofactor_backupcodes: 1.22.0
  - twofactor_totp: 15.0.0-dev.0
  - updatenotification: 1.23.0
  - user_status: 1.13.0
  - viewer: 6.0.0-dev.0
  - weather_status: 1.13.0
  - webhook_listeners: 1.5.0
  - workflowengine: 2.15.0

Nextcloud Signing status

No errors have been found.

Nextcloud Logs

{"reqId":"WYMqtSla42G05aaXqipM","level":3,"time":"2026-02-19T20:06:29+00:00","remoteAddr":"159.65.164.107","user":"--","app":"cron","method":"GET","url":"/cron.php","scriptName":"/cron.php","message":"Backgroundjobs are using system cron!","userAgent":"Cronless/2.0 (+http://cronless.com)","version":"33.0.0.16","exception":{"Exception":"RuntimeException","Message":"Backgroundjobs are using system cron!","Code":0,"Trace":[{"file":"/mnt/www/nextcloud/core/Service/CronService.php","line":100,"function":"runWeb","class":"OC\\Core\\Service\\CronService","type":"->"},{"file":"/mnt/www/nextcloud/cron.php","line":52,"function":"run","class":"OC\\Core\\Service\\CronService","type":"->"}],"File":"/mnt/www/nextcloud/core/Service/CronService.php","Line":229,"message":"Backgroundjobs are using system cron!","exception":"{\"class\":\"RuntimeException\",\"message\":\"Backgroundjobs are using system cron!\",\"code\":0,\"file\":\"/mnt/www/nextcloud/core/Service/CronService.php:229\",\"trace\":\"#0 /mnt/www/nextcloud/core/Service/CronService.php(100): OC\\Core\\Service\\CronService->runWeb()\\n#1 /mnt/www/nextcloud/cron.php(52): OC\\Core\\Service\\CronService->run()\\n#2 {main}\"}","CustomMessage":"Backgroundjobs are using system cron!"},"id":"6998c455b48c7"}

Additional info

No response

[solracsf]

1st of all, when calling cron.php from the system (crontab, systemd...) you're using the system cron. So, the message is good.

2nd, it seems that an external service (https://cronless.com) is calling https://yourinstance.tld/cron.php this is where this error is coming from.

3rd, I agree this should probably be logged at a lower level than the error level.

[joshtrichards]

Based on your log entry it's not a false positive; it's an accurate log entry as @solracsf described.

What did change in v33 from what I can tell, is that during a refactor (#55517), this error message was changed from only being sent (as web output) to the external caller (e.g. whatever this external service is that is calling your /cron.php URL via HTTP) to also being logged on the instance now.

Chances are, unless you recently configured that service, that it's been silently calling /cron.php remotely on your instance for who-knows-how-long. ;-)

Change pending in #58473 to continue to log albeit at a lower priority.

[TheWojtek]

Good, great insignts and a nice catch with cronless.

Funny thing is… this looks like a practical joke on me. I never used cronless, never had any need to as I own my servers and all my NC instances run very similar setups, including system (sic!) cron. I have never had any account on Cronless it seems. This cron error happens exactly every 12 hours, so it wouldn’t even make sense as a setup for an NC instance.

I can imagine how easy it would be to completely pollute someones log file now if a malicious actor called cron.php remotely every 5 seconds using an innocent free web service.

I will block the cronless IP on the firewall, but some followup may be needed due to this log pollution risk.