By john The container cannot write to the mounted folder. Or the container wrote files and now you cannot delete them from the host, even as an administrator. Both are the same problem wearing different clothes, https://saborcitosrestaurant.com/ and the explanation is short: Linux does not recognise usernames, only numbers.
The shared number space
A container and its host share a kernel, which means they share the same numeric UID and GID space. Nothing reconciles those numbers between them by default.
The container has its own /etc/passwd. It may contain a user called appuser or www-data. The host has its own, with entirely different names. Neither file matters at the boundary. When a process writes a file, the kernel records a number. When the host later checks permissions, it compares numbers.
So a container running as UID 0 writing into a bind mount produces files owned by UID 0 on the host — root-owned files in your home directory. And a container running as UID 1001 trying to write into a directory owned by host UID 1000 with restrictive permissions gets refused, because 1001 is not 1000, is not in the group, and “others” have no write access.
This is why bind mounts bite hardest. Files keep their host UID and GID, host permissions apply directly, and there is no translation layer doing anything helpful in the background.
Diagnosing it in about a minute
Three pieces of information settle almost every case. Look at the numeric ownership of the files on the host — not the names, the numbers, since names are what mislead you here. Ask the container what identity it is actually running as. Then compare the two.
If the numbers differ and the permissions do not grant access to “others,” you have found your answer. There is nothing subtle left to investigate.
The fixes, in rough order of preference
The cleanest option is often to avoid the problem: use a named volume instead of a bind mount where the host does not need direct access. On first mount of an empty volume, the container directory’s contents are copied in with ownership intact, and new files follow the container’s effective UID.
Where a bind mount is genuinely required, run the container as the UID and GID that owns the host directory. This aligns the numbers rather than working around them.
Alternatively, change the host directory’s ownership to match the container’s user. This works, with the trade-off that you may then need elevated privileges to edit those files yourself.
The fix to refuse
Making everything world-writable makes files writable by any user and any process on the system. It reliably silences the error, which is exactly why it spreads. On anything reachable from a network it is a serious weakness, and it is chosen overwhelmingly often by people who never revisit it.
Two numbers do not match. Make them match, or stop making the host responsible for the file.