I'm trying to understand when containers copy preexisting files into a mounted volume on the same directory. For example
FROM ubuntu
RUN mkdir /testdir
RUN echo "Hello world" > /testdir/file.txt
running:
#docker create volume vol
#docker run -dit -v vol:/testdir myimage
#docker exec -it 900444b7ab86 ls -la /testdir
drwxr-xr-x 2 root root 4096 May 11 18:43 .
drwxr-xr-x 1 root root 4096 May 11 18:43 ..
-rw-r--r-- 1 root root 6 May 11 17:53 file.txt
The image for example also has files in:
# docker exec -it 900444b7ab86 ls -la /etc/cron.daily
total 20
drwxr-xr-x 2 root root 4096 Apr 26 21:17 .
drwxr-xr-x 1 root root 4096 May 11 18:43 ..
-rwxr-xr-x 1 root root 1478 Apr 20 10:08 apt-compat
-rwxr-xr-x 1 root root 1176 Nov 2 2017 dpkg
-rwxr-xr-x 1 root root 249 Jan 25 15:09 passwd
But for example when I run it with
docker run -it 900444b7ab81 -v vol:/etc/cron.daily
The directory is now empty..
Why don't the files get copied this time?
#docker run -dit -v vol:/testdir
That is not a valid docker command, there's no image reference included, so there's nothing for docker to run.
docker run -it 900444b7ab81 -v vol:/etc/cron.daily
This will attempt to run the image 900444b7ab81 with the command -v vol:/etc/cron.daily. Before you had a container id with a very similar id, so it's not clear that you aren't trying to do a run with a container id instead of an image id. And the command -v likely doesn't exist inside the container.
The order of these arguments is important, the first thing after the run that isn't an option or arg to the previous option is treated as the image reference. After that reference, anything else passed is a command to run in the container. So if you wanted to mount the volume, you need to move that option before the image id.
I'm trying to understand when containers copy preexisting files into a mounted volume on the same directory.
With named volumes, docker initializes an empty named volume upon creation of the container with the contents of the image at that location. Once the volume has files in it, it will be mapped as is into the container on any subsequent usage, so changes to the image at the same location will not be seen.
Related
Docker version 20.10.2
I'm just starting out on Docker and following training guides - but something hasn't been mentioned so far (that I have discovered) - when I run a container to write some data out to Docker volume, if I run that container again and attach to the same volume, the newly named data will not append into it ?
Here is my rather basic Dockerfile
FROM ubuntu
RUN mkdir applocal
RUN touch applocal/applocalfile."$(date --iso-8601=seconds)"
RUN ls -la applocal
I run this sequence of commands...
docker build Dockerfile -t mine/applocal-persist
Sending build context to Docker daemon 2.048kB
Step 1/4 : FROM ubuntu
---> c29284518f49
Step 2/4 : RUN mkdir applocal
---> Running in 9f796f4d988a
Removing intermediate container 9f796f4d988a
---> 99005a7ffed1
Step 3/4 : RUN touch applocal/applocalfile."$(date --iso-8601=seconds)"
---> Running in ffbf2f4c636a
Removing intermediate container ffbf2f4c636a
---> 199bc706dcc6
Step 4/4 : RUN ls -la applocal
---> Running in 7da02faa9fba
total 8
drwxr-xr-x 1 root root 4096 Jul 16 13:52 .
drwxr-xr-x 1 root root 4096 Jul 16 13:52 ..
-rw-r--r-- 1 root root 0 Jul 16 13:52 applocalfile.2021-07-16T13:52:00+00:00
Removing intermediate container 7da02faa9fba
---> 7387c521d82b
Successfully built 7387c521d82b
Successfully tagged mine/applocal-persist:latest
Then run the command...
docker run -v applocalsaved:/applocal mine/applocal-persist
Looking at the Volume data it has worked
ls -la /var/lib/docker/volumes/applocalsaved/_data/
total 8
drwxr-xr-x 2 root root 4096 Jul 16 14:55 .
drwxr-xr-x 3 root root 4096 Jul 16 14:55 ..
-rw-r--r-- 1 root root 0 Jul 16 14:52 applocalfile.2021-07-16T13:52:00+00:00
If I wait a few minutes later and re-run docker run -v applocalsaved:/applocal mine/applocal-persist
...and check the volume data again, no new file exists
ls -la /var/lib/docker/volumes/applocalsaved/_data/
total 8
drwxr-xr-x 2 root root 4096 Jul 16 14:55 .
drwxr-xr-x 3 root root 4096 Jul 16 14:55 ..
-rw-r--r-- 1 root root 0 Jul 16 14:52 applocalfile.2021-07-16T13:52:00+00:00
Run history...
docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
6d16e9aa495e mine/applocal-persist "bash" 57 seconds ago Exited (0) 55 seconds ago distracted_cohen
69ff06d9c886 mine/applocal-persist "bash" 2 minutes ago Exited (0) 2 minutes ago affectionate_lehmann
I've listed the Volume Inspect here...
docker volume inspect applocalsaved
[
{
"CreatedAt": "2021-07-16T14:55:24+01:00",
"Driver": "local",
"Labels": null,
"Mountpoint": "/var/lib/docker/volumes/applocalsaved/_data",
"Name": "applocalsaved",
"Options": null,
"Scope": "local"
}
]
I'm obviously missing a trick here - or misunderstanding what is going on or the design around this.
Thanks in advance
For info: I'm using Windows running Virtual Box and running Ubuntu 21.04 as a VM
Those commands run once when the image is built.
If you want something to run on container startup, you can use CMD or ENTRYPOINT
https://docs.docker.com/engine/reference/builder/#cmd
https://docs.docker.com/engine/reference/builder/#entrypoint
The commands in the Dockerfile only run once, when the image is originally built. You can verify this for example by just running the image without a volume mount:
docker build -t mine/applocal-persist .
docker run --rm mine/applocal-persist \
ls -l ./applocal
sleep 60
docker run --rm mine/applocal-persist \
ls -l ./applocal
If you start the container with a named volume mounted, only if the volume is a Docker named volume and only if the volume is empty, the contents of the image will be copied into the volume. (This doesn't happen on Docker bind mounts, Kubernetes volumes, or if the image has changed; I would not rely on this for any sort of data sharing since it works in so few contexts.)
Conversely, if you start the container with any sort of volume mounted, whatever content is in the volume completely replaces what's in the image. You can see this with some more experimentation:
# Build the image
docker build -t mine/applocal-persist
# Start the container with a new named volume mounted; see what's there.
docker volume rm applocalsaved
docker run --rm -v applocalsaved:/applocal mine/applocal-persist \
ls -l /applocal
# Edit a file in the volume and see that it gets persisted across restarts
docker run --rm -v applocalsaved:/applocal mine/applocal-persist \
touch /applocal/foo
docker run --rm -v applocalsaved:/applocal mine/applocal-persist \
ls -l /applocal
# But it is not included in the image without the bind mount
docker run --rm mine/applocal-persist \
ls -l /applocal
sleep 60
# Rebuild the image
docker build -t mine/applocal-persist
# In the base image, you will see the updated timestamp
docker run --rm mine/applocal-persist \
ls -l /applocal
# But if you mount the volume, the old volume contents replace the
# image contents and you will only see the old timestamp
docker run --rm -v applocalsaved:/applocal mine/applocal-persist \
ls -l /applocal
I am on a remote server where I am a user in the group docker. I created two volumes:
docker create volume conan && docker create volume code`
I am using the docker image called conanio/gcc10, so I run:
docker run --rm \
-v code:/home/conan/.code \
-v conan:/home/conan/.conan \
-it conanio/gcc10 /bin/bash
Then in the container environment I have:
drwxr-xr-x 2 conan 1001 4096 Jun 23 01:58 .conan/
drwxr-xr-x 2 root root 4096 Jun 23 01:58 .code/
why they have different owner? .code's owner is root and .conan's owner is conan?
I tried different names and all are the same, only .conan's owner is conan.
I also tried other images as well. Is that because the conan volume matches the user name in the container???
is there a way to use conan for other mounted volume as well?
I am trying to learn Docker volumes, and I am using centos:latest as my base image. When I try to run a Docker command, I am unable to access the attached volume inside the container:
Command:
sudo docker run -it --name test -v /home/user/Myhostdir:/mydata centos:latest /bin/bash
Error:
[user#0bd1bb78b1a5 mydata]$ ls
ls: cannot open directory .: Permission denied
When I try to ls to find the folder permission, it says 1001. What's happening, and how can to solve this?
drwxrwxr-x. 2 1001 1001 38 Jun 2 23:12 mydata
My local machine:
[user#xxx07012 Myhostdir]$ pwd
/home/user/Myhostdir
[user#swathi07012 Myhostdir]$ ls -al
total 12
drwxrwxr-x. 2 user user 38 Jun 2 23:12 .
drwx------. 18 user user 4096 Jun 2 23:11 ..
-rw-rw-r--. 1 user user 15 Jun 2 23:12 text.2.txt
-rw-rw-r--. 1 user user 25 Jun 2 23:12 text.txt
This is partially a Docker issue, but mostly an SELinux issue. I am assuming you are running an old 1.x version of Docker.
You have a couple of options. First, you could take a look at this blog post to understand the issue a bit more and possibly use the fix mentioned there.
Or you could just upgrade to a newer version of Docker. I tested mounting a simple volume on Docker version 18.03.1-ce:
docker run -it --name test -v /home/chris/test:/mydata centos:latest /bin/bash
[root#bfec7af20b99 /]# cd mydata/
[root#bfec7af20b99 mydata]# ls
test.txt.txt
[root#bfec7af20b99 mydata]# ls -l
total 0
-rwxr-xr-x 1 root root 0 Jun 3 00:40 test.txt.txt
When mounting a volume with the following command:
docker run -t -i --volumes-from FOO BAR
the volumes from FOO are mounted with root as owner. I can't read and write to that without running as root as far as I know. Must I run as root or is there some other way?
I have tried by creating the folder with other owner before mounting but the mounting seems to overwrite that.
Edit: A chown would work if it could be done automatically after the mounting somehow.
I'm not sure why you aren't able to change your folder permissions in your source image. This works without issue in my lab:
$ cat df.vf-uid
FROM busybox
RUN mkdir -p /data && echo "hello world" > /data/hello && chown -R 1000 /data
$ docker build -f df.vf-uid -t test-vf-uid .
...
Successfully built 41390b132940
$ docker create --name test-vf-uid -v /data test-vf-uid
e12df8f84a3b1f113ad5440b62552b40c4fd86f99eec44698af9163a7b960727
$ docker run --volumes-from test-vf-uid -u 1000 -it --rm busybox /bin/sh
/ $ ls -al /data
total 12
drwxr-xr-x 2 1000 root 4096 Aug 22 11:44 .
drwxr-xr-x 19 root root 4096 Aug 22 11:45 ..
-rw-r--r-- 1 1000 root 12 Aug 22 11:43 hello
/ $ echo "success" >/data/world
/ $ ls -al /data
total 16
drwxr-xr-x 2 1000 root 4096 Aug 22 11:46 .
drwxr-xr-x 19 root root 4096 Aug 22 11:45 ..
-rw-r--r-- 1 1000 root 12 Aug 22 11:43 hello
-rw-r--r-- 1 1000 root 8 Aug 22 11:46 world
/ $ cat /data/hello /data/world
hello world
success
/ $ exit
So, what I ended up doing was mounting the volume to another container and change the owner (using uid of the owner I wanted in the final setup) from that container. Apparently uid's are uid's regardless. This means that I can run without being root in the final container. Perhaps there are easier ways to do it but this seems to work at least. Something like this: (untested code clip from my final solution)
docker run -v /opt/app --name Foo ubuntu /bin/bash
docker run --rm --volumes-from Foo -v $(pwd):/FOO ubuntu bash -c "chown -R 9999 /opt/app"
docker run -t -i --volumes-from FOO BAR
I have created a new docker image. It creates a new folder /hello.
When I run this image as a container, I can access the container by the docker exec -it .. bash command and when I perform ls I see the /hello folder.
This /hello folder is also saved in a Docker volume container.
So I have linked the container with an existing Docker volume. So it's persistent.
Now is my question: Is it possible to perform the following in a Dockerfile?
A new image wants to use the same volume as the previous container, and copying the /hello file to its own container.
Is this possible to perform in a docker file?
No, this is not possible in your Dockerfile.
You may use a running containers volumes by using the --volumes-from argument when you run another container with docker run.
Example:
Dockerfile
FROM ubuntu:14.04
VOLUME /hello
Then:
$ docker build -t test-image-with-volume .
$ docker run -ti --name test-image-with-volume test-image-with-volume bash
/# cd /hello
/# ls -la
total 8
drwxr-xr-x 2 root root 4096 Jan 18 14:59 ./
drwxr-xr-x 22 root root 4096 Jan 18 14:59 ../
Then in another terminal (while above container is still running):
Dockerfile
FROM ubuntu:14.04
Then:
$ docker build -t test-image-without-volume .
$ docker run -ti test-image-without-volume bash
/# cd /hello
bash: cd: /hello: No such file or directory
/# exit
$ docker run -ti --volumes-from test-image-with-volume test-image-without-volume bash
/# cd /hello
total 8
drwxr-xr-x 2 root root 4096 Jan 18 14:59 ./
drwxr-xr-x 22 root root 4096 Jan 18 14:59 ../
/# touch test
Then in your original terminal:
/# ls -la /hello
total 8
drwxr-xr-x 2 root root 4096 Jan 18 15:04 .
drwxr-xr-x 22 root root 4096 Jan 18 15:03 ..
-rw-r--r-- 1 root root 0 Jan 18 15:04 test
And in your new terminal:
/# ls -la /hello
total 8
drwxr-xr-x 2 root root 4096 Jan 18 15:04 .
drwxr-xr-x 22 root root 4096 Jan 18 15:03 ..
-rw-r--r-- 1 root root 0 Jan 18 15:04 test
You can only link volumes from one container to another while the container with the volumes is still running.