Can you describe your install method and environment? Is this a new installation or are you supporting a legacy installation? This matters since there are old Bash feed-sync scripts and new Python-based ones.
Also, if you are trying to run Greenbone with very thin resource (CPU/RAM) the feed-sync may not have enough resources to run. Maybe the process is killed by OOM killer but the lock is never released. See this thread
You can find out which one you are running by checking the script’s file path, and then checking the shebang header to determine which script is in use. To my knowledge, the new scripts only need to be run with sudo, you don’t need to set the user and group.
- Check the feed-sync executable path:
which <feed-sync-filename>
- Check the shebang line:
head -1 /path/to/feed-sync-filename
If you see #!/bin/bash, then you are using the old bash scripts. You should upgrade to the new Python-based greenbone-feed-sync.