ssh keys and authorized_keys unprotected on FAT formatted partitions

When you mount a FAT partition in Linux, the Linux user, group, and others have full read, write, and execute permissions for that partition. This is because, unlike NTFS, FAT doesn’t support these permissions. Normally, you won’t notice much of a difference, as these are usually just USB drives for file transfers.

The situation changes if you permanently mount such a partition and then use a folder for a Docker container. In most Docker containers, root is also the primary user for all processes, so user permissions aren’t an issue.

That is, until you use ssh, which silently fails when you try to log in to the container with public key authorization. Root reads the keys and authorized_keys without any problems. But the ssh daemon refuses to work because group and others have read (and write) permissions, and you can’t change these permissions. The only real solution is to avoid using FAT, vFAT, or exFAT and format the partition with NTFS or ext4.