Sticky‑Bit Directories and ACLs: Why “Permission denied” Still Happens
When you try to move a file into a directory that has the sticky bit set, the kernel first checks the directory’s owner and the user’s write permission. If the directory is owned by someone else, the sticky bit forces it to also check the file’s owner. ACLs can grant write access to a group or user, but the sticky‑bit logic still requires the file’s owner to match the directory’s owner unless the moving user has the write permission on the file itself. That subtle rule is the source of a lot of “Permission denied” errors that only surface when ACLs are involved.
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