Anatomy of the Docker for Mac virtual disk

VM session.sh

# Show some info about the virtual disk
mymac> qemu-img check ~/Library/Containers/com.docker.docker/Data/com.docker.driver.amd64-linux/Docker.qcow2                                                                                                       ✓  10118
    No errors were found on the image.
    54968/1048576 = 5.24% allocated, 0.95% fragmented, 0.00% compressed clusters
    Image end offset: 3606183936
mymac> qemu-img info ~/Library/Containers/com.docker.docker/Data/com.docker.driver.amd64-linux/Docker.qcow2                                                                                                        ✓  10138
    image: ~/Library/Containers/com.docker.docker/Data/com.docker.driver.amd64-linux/Docker.qcow2
    file format: qcow2
    virtual size: 64G (68719476736 bytes)
    disk size: 3.4G
    cluster_size: 65536
    Format specific information:
        compat: 1.1
        lazy refcounts: true
        refcount bits: 16
        corrupt: false

# Copy and compress virtual disk to Linux VM folder
qemu-img convert -c -O qcow2 ~/Library/Containers/com.docker.docker/Data/com.docker.driver.amd64-linux/Docker.qcow2 dockermac.qcow2

# Login into Linux VM
mymac>vagrant ssh
[vagrant@centos7-adb ~]$ ll /vagrant
    total 1065220
    -rw-r--r--. 1 qemu    qemu    1090781184 Jun 10 12:33 dockermac.qcow2
    -rw-r--r--. 1 vagrant vagrant       2137 Jun 10 12:08 Vagrantfile

# Install libguestfs
[vagrant@centos7-adb ~]$ sudo yum install  libguestfs-tools

# Start libguestfs shell
[vagrant@centos7-adb ~]$ sudo guestfish
><fs> add /vagrant/dockermac.qcow2             # add a copy of Docker for Mac virtual disk
><fs> run
 100% ⟦▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒⟧ 00:00
><fs> list-filesystems
    /dev/sda1: swap
    /dev/sda2: ext4
><fs>  mount /dev/sda2 /                       # mount virtual disk under Linux VM
><fs> ll /
    total 52
    drwxr-xr-x 10 root root  4096 Jun  9 13:29 .
    drwxr-xr-x 19 root root  4096 Jun 10 16:17 ..
    drwxr-xr-x  4 root root  4096 May 20 20:54 cache
    drwxr-xr-x  2 root root  4096 May  6 06:00 empty
    drwxr-xr-x  2 root root  4096 May 20 20:54 git
    drwxr-xr-x  8 root root  4096 Jun  9 13:29 lib
    lrwxrwxrwx  1 root root     9 Jun  9 13:29 lock -> /run/lock
    drwxr-xr-x  3 root root  4096 Jun  9 13:29 log
    drwx------  2 root root 16384 Jun  9 13:29 lost+found
    lrwxrwxrwx  1 root root     4 Jun  9 13:29 run -> /run
    drwxr-xr-x  3 root root  4096 May  6 06:00 spool
    drwxrwxrwt  2 root root  4096 May  6 06:00 tmp
    ----------  1 root root     0 Jun  9 13:29 transfused_start.log

# found a container running in Mac
><fs> ll /lib/docker/containers/45a946cb64d29f7aea8789c710093d494ae07d6bb9dc256ddb5e70e1992be95d/
    total 1016
    drwx------ 3 root root    4096 Jun  9 14:14 .
    drwx------ 3 root root    4096 Jun 10 09:46 ..
    -rw-r----- 1 root root 1000621 Jun 10 10:06 45a946cb64d29f7aea8789c710093d494ae07d6bb9dc256ddb5e70e1992be95d-json.log
    -rw-r--r-- 1 root root    3337 Jun  9 14:14 config.v2.json
    -rw-r--r-- 1 root root    1101 Jun  9 14:14 hostconfig.json
    -rw-r--r-- 1 root root      13 Jun  9 14:14 hostname
    -rw-r--r-- 1 root root     174 Jun  9 14:14 hosts
    -rw-r--r-- 1 root root      37 Jun  9 14:14 resolv.conf
    -rw------- 1 root root      71 Jun  9 14:14 resolv.conf.hash
    drwx------ 2 root root    4096 Jun  9 14:14 shm 
[vagrant@centos7-adb ~]$ exit

# Now if you want to shrink virtual disk to save space (e.g. after you cleaned up obsolete images and containers)
# Stop running Docker daemon
mymac> cd ~/Library/Containers/com.docker.docker/Data/com.docker.driver.amd64-linux/ 
mymac> mv Docker.qcow2 Docker.qcow2.backup
mymac> qemu-img convert -O qcow2 Docker.qcow2.backup Docker.qcow2
mymac> qemu-img check Docker.qcow2.backup                                                                                                                   ✓  10162
    No errors were found on the image.
    54969/1048576 = 5.24% allocated, 0.96% fragmented, 0.00% compressed clusters
    Image end offset: 3606249472
mymac> qemu-img check Docker.qcow2                                                                                                                          ✓  10163
    No errors were found on the image.
    39636/1048576 = 3.78% allocated, 0.01% fragmented, 0.00% compressed clusters
    Image end offset: 2601385984
# Start your Docker for mac
mymac> /Applications/Docker.app/Contents/Resources/bin/docker-diagnose                                                                                      ✓  10165
    OS X: version 10.11.5 (build: 15F34)
    Docker.app: version: v1.11.1-beta14.5.m
    Running diagnostic tests:
    [OK]      docker-cli
    [OK]      Moby booted
    [OK]      driver.amd64-linux
    [OK]      vmnetd
    [OK]      osxfs
    [OK]      db
    [OK]      slirp
    [OK]      menubar
    [OK]      environment
    [OK]      Docker
    [OK]      VT-x
    Docker logs are being collected into /tmp/20160610-205107.tar.gz
    Most specific failure is: No error was detected
# All good!