Manual rootful app backup run fails for Popen.__init__() unexpected keyword argument 'check'

[DavidePrincipi]

Running a manual backup from the Backup and Restore page (Scheduled Backups > Run backup now) fails with Core 3.20.0 when the backup includes a rootful app.

Steps to reproduce

• Install Core 3.20.0 and Dnsmasq
• Schedule a backup that includes Dnsmasq
• Run the backup from the UI

Expected behavior

The backup completes successfully.

Actual behavior

The task fails with the following error:

<6>run-backup --backup=1
...
dnsmasq1: starting backup 1 at Thu Jul  2 12:27:25 2026
...
[ERROR] restic backup failed: Popen.__init__() got an unexpected keyword argument 'check'
Ignoring "latest": no snapshot matched given filter (Paths:[] Tags:[] Hosts:[])
dnsmasq1: backup 1 failed (exit code 1)
Backup 1 finished with failures: dnsmasq1

Components

• Core 3.20.0

See also

• https://community.nethserver.org/t/backup-error-dnsmasq-to-smb-share/27976

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Thanks to Pagaille and Maddin for reporting.