errno 20 (ENOTDIR): meaning and diagnosis

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: A path component needed as a directory is a nondirectory object, or an API received a non-directory dirfd.

Could be also:
Constant	Type	OS
ERROR_BAD_UNIT	Win32 error	Windows
KERN_INVALID_CAPABILITY	Kern return	Mac
ippStsNonIntelCpu	Intel Ipp Status	Any
CREATE_DELETE_LOCK_NOT_LOCKED	BugCheck Code	Windows

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ENODEV	EISDIR

ENOTDIR

Where path resolution stopped

ENOTDIR is more specific than “path not found.” During pathname resolution, a component before the final name must be a directory or resolve to one. If the process tries to continue through a regular file, device, or another nondirectory object, the operation fails with ENOTDIR. The same result can appear with *at-style APIs when a relative path is supplied with a descriptor that does not refer to a directory.

A trailing slash is another useful clue: it expresses an expectation that the final component is a directory. A file with that name can therefore produce ENOTDIR even though it exists.

How to investigate

Split the logged path into components and inspect the first component that is not a directory.
Check whether an environment variable, configuration key, or deployment substitution changed a directory path into a file path.
For openat(), renameat(), and similar calls, verify that the supplied dirfd is valid and refers to a directory.
Do not mask the condition by creating a missing directory until the expected object type is understood.

References

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