Moby: docker-commit and ADD/COPY truncate file and directory modification times

[gg7]

Steps to reproduce:

COPY:

gg7@gg7:~$ mkdir docker-mtime-test
gg7@gg7:~$ cd docker-mtime-test

gg7@gg7:~/docker-mtime-test$ touch example-file
gg7@gg7:~/docker-mtime-test$ stat example-file
  File: ‘example-file’
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: fc01h/64513d    Inode: 7602338     Links: 1
Access: (0664/-rw-rw-r--)  Uid: ( 1001/  gg7)   Gid: ( 1001/  gg7)
Access: 2015-10-19 14:13:28.441785563 +0100
Modify: 2015-10-19 14:13:28.441785563 +0100
Change: 2015-10-19 14:13:28.441785563 +0100
 Birth: -

gg7@gg7:~/docker-mtime-test$ cat > Dockerfile <<EOF
FROM ubuntu:14.04
COPY example-file /example-file
RUN stat /example-file
EOF

gg7@gg7:~/docker-mtime-test$ docker build --no-cache -t docker-mtime-test .
Sending build context to Docker daemon  2.56 kB
Step 0 : FROM ubuntu:14.04
 ---> fa81ed084842
Step 1 : COPY example-file /example-file
 ---> 8212ccaf4c14
Removing intermediate container cece2b393603
Step 2 : RUN stat /example-file
 ---> Running in 86bd29f2fa49
  File: '/example-file'
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 6ch/108d        Inode: 43          Links: 1
Access: (0664/-rw-rw-r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2015-10-19 13:15:27.415707557 +0000
Modify: 2015-10-19 13:13:28.000000000 +0000
Change: 2015-10-19 13:15:27.415707557 +0000
 Birth: -
 ---> cb0e1fdb58bd
Removing intermediate container 86bd29f2fa49
Successfully built cb0e1fdb58bd

Actual results: the modification time of /example-file is reported to be 2015-10-19 13:13:28.000000000 +0000.

Expected results: the modification time of /example-file should be 2015-10-19 13:13:28.441785563 +0000.

docker-commit:

gg7@gg7:~$  docker run -it --name mtime-test ubuntu:14.04 /bin/bash
root@613e6c0fe6ac:/# touch /example-file
root@613e6c0fe6ac:/# stat /example-file
  File: '/example-file'
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 66h/102d        Inode: 72          Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2015-10-19 13:36:29.888088708 +0000
Modify: 2015-10-19 13:36:29.888088708 +0000
Change: 2015-10-19 13:36:29.888088708 +0000
 Birth: -
root@613e6c0fe6ac:/# exit
exit
gg7@gg7:~$ docker commit mtime-test mtime-test-image
b67d16fcb577fb3ece29cf007f1cef2ebc4a6351bc3e3a3e77eab5648461095c
gg7@gg7:~$ docker run -it --name mtime-test-2 mtime-test-image /bin/bash
root@1a5e038e6a2c:/# stat /example-file
  File: '/example-file'
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 66h/102d        Inode: 75          Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2015-10-19 13:36:55.572503813 +0000
Modify: 2015-10-19 13:36:29.000000000 +0000
Change: 2015-10-19 13:36:55.572503813 +0000
 Birth: -
root@1a5e038e6a2c:/#

Why is this important?

Some build systems rely on modification timestamps to detect file updates.

Environment details:

cat /etc/lsb-release:

DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=14.04
DISTRIB_CODENAME=trusty
DISTRIB_DESCRIPTION="Ubuntu 14.04.3 LTS"

uname -a:

Linux gg7 3.13.0-51-generic #84-Ubuntu SMP Wed Apr 15 12:08:34 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

docker version:

Client:
 Version:      1.8.3
 API version:  1.20
 Go version:   go1.4.2
 Git commit:   f4bf5c7
 Built:        Mon Oct 12 05:37:18 UTC 2015
 OS/Arch:      linux/amd64

Server:
 Version:      1.8.3
 API version:  1.20
 Go version:   go1.4.2
 Git commit:   f4bf5c7
 Built:        Mon Oct 12 05:37:18 UTC 2015
 OS/Arch:      linux/amd64

docker info:

Containers: 8
Images: 632
Storage Driver: aufs
 Root Dir: /var/lib/docker/aufs
 Backing Filesystem: extfs
 Dirs: 656
 Dirperm1 Supported: false
Execution Driver: native-0.2
Logging Driver: json-file
Kernel Version: 3.13.0-51-generic
Operating System: Ubuntu 14.04.3 LTS
CPUs: 8
Total Memory: 15.66 GiB
Name: gg7
ID: ACSH:EYI5:G36O:2SRA:FWLH:U4GF:VMJM:C4KF:73MH:L273:TCCO:GW3K
WARNING: No swap limit support

[schnittchen]

Just ran into this today.

The only conceivable workaround is taring files up, COPYing them and extracting again...

UPDATE the additional tar operations made things overall slower.

[zyxue]

Given this issue has been open for so long, I assume it can be hard to fix in Docker. I'm curious why it would be hard to preserve the timestamp during COPY?

[daym]

This bug makes it basically impossible to select only parts you need from an existing stage using "COPY --from"--because every time you do, it messes something up in the subset.

Since usually if you compose things you do NOT want to have tools like tar and co available (except when you are the author of tar, I guess), the tar workaround is a hack, too.

Also, let's say you use something else to either preserve or fix up the timestamp inside the docker image, now your docker image is twice the size.

Therefore, the feature of preserving timestamps is necessary.