docker/cli · error
got a device
Error message
got a device
What it means
Returned by ValidateOutputPathFileMode, used by `docker cp` output-path validation, when the destination file mode has os.ModeDevice set. Copying onto a device node (block or character device like /dev/sda or /dev/null) is refused because docker cp only supports directories and regular files as destinations; the message is wrapped into "invalid output path: %q must be a directory or a regular file".
Source
Thrown at cli/command/utils.go:92
}
if fileInfo.Mode().IsDir() || fileInfo.Mode().IsRegular() {
return nil
}
if err := ValidateOutputPathFileMode(fileInfo.Mode()); err != nil {
return fmt.Errorf("invalid output path: %q must be a directory or a regular file: %w", path, err)
}
}
return nil
}
// ValidateOutputPathFileMode validates the output paths of the "docker cp" command
// and serves as a helper to [ValidateOutputPath]
func ValidateOutputPathFileMode(fileMode os.FileMode) error {
switch {
case fileMode&os.ModeDevice != 0:
return errors.New("got a device")
case fileMode&os.ModeIrregular != 0:
return errors.New("got an irregular file")
}
return nil
}
func invalidParameter(err error) error {
return invalidParameterErr{err}
}
type invalidParameterErr struct{ error }
func (invalidParameterErr) InvalidParameter() {}
func notFound(err error) error {
return notFoundErr{err}
}
View on GitHub (pinned to e9452d6e78)
Solutions
- Copy to a regular file or directory instead: `docker cp ctr:/file ./file`.
- If you want the content on stdout, use `docker cp ctr:/file -` (streams a tar) or `docker exec ctr cat /file > out`.
- Check and fix the destination path your script computes so it doesn't point into /dev.
Example fix
# before docker cp mycontainer:/etc/hosts /dev/sda # after docker cp mycontainer:/etc/hosts ./hosts
When it happens
Trigger: `docker cp container:/path /dev/<something>` or any cp invocation whose local destination resolves to an existing device file; ValidateOutputPath stats the path and its mode has ModeDevice set at cli/command/utils.go:92.
Common situations: Attempting `docker cp ctr:/file /dev/stdout`-style tricks with real device nodes; scripts that computed a wrong destination path landing in /dev; destination path collisions with device files in containers/chroots.
Related errors
- got an irregular file
- plugin candidate path cannot be empty
- plugin SchemaVersion version cannot be empty
- config file is required
- source can not be empty
AI-assisted analysis of docker/cli@e9452d6e78 (2026-08-01).
Data as JSON: /data/errors/5dfb12356a7092d8.json.
Report an issue: GitHub.