Mounting file that was previously non-existent fails with: [8] System error: not a directory

[goneflyin]

To preface, this issue may be specific to boot2docker and/or VirtualBox.

version details:

bash-3.2$ docker version
Client:
 Version:      1.9.1
 API version:  1.21
 Go version:   go1.5.1
 Git commit:   a34a1d5
 Built:        Sat Nov 21 00:48:57 UTC 2015
 OS/Arch:      darwin/amd64

Server:
 Version:      1.9.1
 API version:  1.21
 Go version:   go1.4.3
 Git commit:   a34a1d5
 Built:        Fri Nov 20 17:56:04 UTC 2015
 OS/Arch:      linux/amd64

bash-3.2$ docker info
Containers: 25
Images: 355
Server Version: 1.9.1
Storage Driver: aufs
 Root Dir: /mnt/sda1/var/lib/docker/aufs
 Backing Filesystem: extfs
 Dirs: 405
 Dirperm1 Supported: true
Execution Driver: native-0.2
Logging Driver: json-file
Kernel Version: 4.1.13-boot2docker
Operating System: Boot2Docker 1.9.1 (TCL 6.4.1); master : cef800b - Fri Nov 20 19:33:59 UTC 2015
CPUs: 2
Total Memory: 7.79 GiB
Name: ndev
ID: 7FPV:3H7E:T5XH:4DOS:DJ3O:D4SA:F7FR:7RHG:2LYQ:JZ2I:XXB5:JR3M
Debug mode (server): true
 File Descriptors: 150
 Goroutines: 349
 System Time: 2016-01-13T15:51:46.916222527Z
 EventsListeners: 2
 Init SHA1:
 Init Path: /usr/local/bin/docker
 Docker Root Dir: /mnt/sda1/var/lib/docker
Labels:
 provider=virtualbox

Also, running OS X v10.10 with VirtualBox:

bash-3.2$ VBoxManage -v
5.0.12r104815

bash-3.2$ uname -a
Darwin <elided>.local 14.5.0 Darwin Kernel Version 14.5.0: Tue Sep  1 21:23:09 PDT 2015; root:xnu-2782.50.1~1/RELEASE_X86_64 x86_64

Because boot2docker automounts /Users, this reproduction must be done in your home directory or at a lower level.

1. Mount a plain image (I used ubuntu) and mount a non-existent file when running the image. Note that in the local filesystem a nested directory was created when an existent file or directory could not be found.
2. Subsequently, delete the auto-created innermost directory and replace it with a normal file.
3. Re-run your docker image with the same volume mounting info.

bash-3.2$ pwd
/Users/scott/docker-issue

bash-3.2$ ls -al
total 0
drwxr-xr-x    2 scott  wheel    68 Jan 13 10:16 .
drwxr-xr-x+ 138 scott  staff  4692 Jan 13 10:05 ..

bash-3.2$ docker run --rm -i -t -v $(pwd)/a/nested/file.out:/file.out ubuntu /bin/bash

root@e6e3ac91631c:/# ls -al file.out
total 4
drwxr-xr-x  1 1000 staff   68 Jan 13  2016 .
drwxr-xr-x 33 root root  4096 Jan 13 16:00 ..

root@e6e3ac91631c:/# exit

bash-3.2$ ls -al
total 0
drwxr-xr-x    3 scott  wheel   102 Jan 13 10:16 .
drwxr-xr-x+ 138 scott  staff  4692 Jan 13 10:05 ..
drwxr-xr-x    3 scott  wheel   102 Jan 13 10:16 a

bash-3.2$ ls -al a/nested
total 0
drwxr-xr-x  3 scott  wheel  102 Jan 13 10:16 .
drwxr-xr-x  3 scott  wheel  102 Jan 13 10:16 ..
drwxr-xr-x  2 scott  wheel   68 Jan 13 10:16 file.out

bash-3.2$ ls -al a/nested/file.out
total 0
drwxr-xr-x  2 scott  wheel   68 Jan 13 10:16 .
drwxr-xr-x  3 scott  wheel  102 Jan 13 10:16 ..

bash-3.2$ rmdir a/nested/file.out

bash-3.2$ echo "now this is a file" > a/nested/file.out

bash-3.2$ docker run --rm -i -t -v $(pwd)/a/nested/file.out:/file.out ubuntu /bin/bash
Timestamp: 2016-01-13 16:00:53.095601395 +0000 UTC
Code: System error

Message: not a directory

Frames:

---
0: setupRootfs
Package: github.com/opencontainers/runc/libcontainer
File: rootfs_linux.go@40

---
1: Init
Package: github.com/opencontainers/runc/libcontainer.(*linuxStandardInit)
File: standard_init_linux.go@57

---
2: StartInitialization
Package: github.com/opencontainers/runc/libcontainer.(*LinuxFactory)
File: factory_linux.go@242

---
3: initializer
Package: github.com/docker/docker/daemon/execdriver/native
File: init.go@35

---
4: Init
Package: github.com/docker/docker/pkg/reexec
File: reexec.go@26

---
5: main
Package: main
File: docker.go@18

---
6: main
Package: runtime
File: proc.go@63

---
7: goexit
Package: runtime
File: asm_amd64.s@2232
Error response from daemon: Cannot start container 12112c4bab1d924a10ebe1e46ea1446cf6f1131d7595287681b624a047237c18: [8] System error: not a directory

bash-3.2$

[cpuguy83]

This is because when the file doesn't exist, docker creates a dir (note that this functionality is deprecated and will be removed in 1.11). If in the container there exists a file at the path you specified, you'll get the error since you can't mount a dir onto a file.

For example: -v /foo:/bar.
If /foo doesn't exist docker creates a dir called /foo
If /bar does exist, and /bar is a file, this will cause a conflict when trying to mount the new /foo dir onto the file /bar in the container.