When I created my installation like this:
sudo docker run -d --name myBlog -p 3001:2368 -e url=http://xxxx.com -v /var/www/myBlog/:/var/lib/ghost --restart always ghost
I was under the impression that I was defining that what ever is on /var/lib/ghost would be available in /var/www/myBlog/ but it seems that's not the case, when I check on /var/www/myBlog/ there is an empty folder. I created a new post so it can have some data but nothing is there.
Where exactly is the data being stored then? And is there a way I can access my current image that I'm using to see the files inside? I tried sudo docker run -it ghost but that gets me to the base image, not the one I'm using.
Please run the below command and you should be able to see files under target directory
docker run -d -e url=http://xxxx.com --name some-ghost -p 3001:2368 -v "$(pwd)/target":/var/lib/ghost/content ghost:1-alpine
Volumes work the other way around. The source is mapped into the container, mounted on top of whatever exists in that directory inside the container. When you mount over an existing directory in Linux, the parent filesystem at that location is no longer visible.
That means you'll see the host directory contents inside the container. Note this also includes filesystem permissions, and uid/gid ownership.
Named volumes (not the host volume used here) also feature an initialization step for an empty volume when the container is created, copying image contents to the volume before mounting it. It will not modify an existing volume.
Related
I am trying to run a docker container. This docker container contains a set of files inside a directory /mnt. I want this directory to be automatically copied to the host's machine /mnt directory, upon the creation of the container, and anything that will be changed in the container's /mnt directory should also be changed on the host's directory.
I am running this command:
docker run -d --restart always -v /mnt:/mnt <image name>
What is happening is that, instead of the container's directory being copied to the host, the opposite is happening. The host's empty /mnt directory is being copied and overriding the container's /mnt directory.
Why is this happening? And how can I solve it?
The correct way would be for you to design the container in a way that it did not create the data in the container, but used the mount /mnt instead.
But if you must, a standard volume may do what you want:
docker volume create hostmnt
docker run -d --restart always -v hostmnt:/mnt <image name>
After that you can do a shell script to copy or map the volume to wtv directory you want.
But my suggestion would be to docker cp the content, and redirect all data that need being saved to the host or to a data environment, if possible.
I'm learning docker and reading their chapter "Manage data in containers". In the "Mount a host directory as a data volume". They mentioned the following paragraph:
In addition to creating a volume using the -v flag you can also mount a directory from your Docker engine’s host into a container.
$ docker run -d -P --name web -v /src/webapp:/opt/webapp training/webapp python app.py
This command mounts the host directory, /src/webapp, into the container at /opt/webapp. If the path /opt/webapp already exists inside the container’s image, the /src/webapp mount overlays but does not remove the pre-existing content. Once the mount is removed, the content is accessible again. This is consistent with the expected behavior of the mount command.
Experiment 1
Then when I tried to run this command and try to inspect the container, I found that that actually container doesn't even run. Then I use docker logs web and find this error:
can't open file 'app.py': [Errno 2] No such file or directory
I assume that the /src/webapp mount overlays on the /opt/webapp, which there is no content.
Question 1
How can I remove this mount and check if the content is still there as the quote said?
Experiment 2
When I tried to run
$ docker run -d -P --name web2 -v newvolume:/opt/webapp training/webapp python app.py
I found that the container ran correctly. Then I use docker exec -it web2 /bin/bash and find that all of the existing content are still inside the /opt/webapp. I can also add more files inside here. So in this case, it looks like that the volume is not overlay but combined. If I use docker inspect web and check Mounts, then I'll see that the volume is created under /var/lib/docker/volumes/newvolume/_data
Question 2
If I give a name instead of a host-dir absolute path, then the volume will not overlay the container-dir /opt/webapp but connect the two dir together?
An alternative solution is to commit the container (or export it) using docker cli and re-create it without doing the mapping.
Question 1 How can I remove this mount and check if the content is still there as the quote said?
You would create a new container without the volume mount. E.g.
$ docker run -d -P --name web training/webapp python app.py
(Theoretically it's possible to perform some privileged operations to remove the mount on a running container, but inside the container you will not normally have this permission, and it's a good practice to get into the habit of treating containers as ephemeral.)
Question 2 If I give a name instead of a host-dir absolute path, then the volume will not overlay the container-dir /opt/webapp but connect the two dir together?
Almost. What's happening with named volumes is that docker provides an initialization step when the volume is empty and the container is created with that volume mount. The initialization step copies the contents of the image at that directory into the volume, including all files and directories recursively, ownership, and permissions. This is very useful to running containers as a non-root user with a volume directory that the user inside the container needs to be able to write into. After that initialization has happened, future containers with the same named volume will skip the initialization, even if the image content has changed, e.g. if you add new content into the image.
I know that, in some cases, mounting a named volume on a container can cause data from the container to be automatically copied to the volume, similar to what happens with anonymous volumes.
However, even after reading the docs, it's unclear to me what are the exact conditions that trigger the copy.
I created a test image with two files /root/a/a.txt and /root/b/b.txt and performed the following experiment:
$ docker volume create --name hello
hello
$ docker run -v hello:/root/a test /bin/true
$ docker run -v hello:/root/b test /bin/true
$ docker run -ti -v hello:/tmp/result test /bin/bash
(now inside the container)
# cd /tmp/result
# ls
a.txt
It seems that the data is copied into the volume after the first mount, and not afterwards (despite not having specified nocopy for the second mount).
Do named volumes have hidden state that tracks if they haven't been mounted yet? Or is the copy triggered just by the volume being empty? If copying only happens the first time, what is the purpose of the nocopy modifier to the -v option of docker run?
I'm using Docker version 1.11.1.
From my testing, it appears to trigger the copy when the volume is empty when you run the container.
I tested with a volume that was populated from a first mount point in one container. Using this named volume on a second mount point of another container showed the contents of the first mount point. I then deleted the contents but the container was still running and volume still mounted. Finally, I started a second container with a different mount point and the contents from the second mount point were then populated.
I was just going through this tutorial on Youtube, trying to understand the use of the -v command.
Why is the author using the -v command? He uses the command, like so:
docker run -v /var/lib/mysql --name=my_datastore -d busybox echo "my datastore"
Now I understand the above command to an extent:
--name=my_datastore gives the container a specific name.
-d busybox starts a container in detached mode, based on the busybox image.
After the command is executed the below line is echoed to the console.
my datastore
Now, the part I don't understand is the following:
-v /var/lib/mysql
Why is the -v command used here, and why the path /var/lib/mysql specified?
I am having difficulty understanding why the above line is used and in what context. Can anybody explain?
The -v (or --volume) argument to docker run is for creating storage space inside a container that is separate from the rest of the container filesystem. There are two forms of the command.
When given a single argument, like -v /var/lib/mysql, this allocates space from Docker and mounts it at the given location. This is primarily a way of allocating storage from Docker that is distinct from your service container. For example, you may want to run a newer version of a database application, which involves tearing down your existing MySQL container and starting a new one. You want your data to survive this process, so you store it in a volume that can be accessed by your database container.
When given two arguments (host_path:container_path), like -v /data/mysql:/var/lib/mysql, this mounts the specified directory on the host inside the container at the specified path (and, to be accurate, this can also be used to expose host files inside the container; for example -v /etc/localtime:/etc/localtime would make /etc/localtime on the host available as /etc/localtime inside the container). This is a way of either feeding information into your container, or providing a way for your container to make files accessible to the host.
If a container has volumes available, either through the use of the -v command line argument or via the VOLUME directive in a Dockerfile, these volumes can be accessed from another container using the --volumes-from option:
docker run --volumes-from my_datastore ...
This will make any volumes defined in the source container available in the container you're starting with --volumes-from.
This is discussed in more detail in the Docker Volumes documentation.
I have a Docker container which is running some code and creating some HTML reports. I want these reports to be published into a specific directory on the host machine, i.e. at /usr/share/nginx/reports
The way I have gone about doing this is to mount this host directory as a data volume, i.e. docker run -v /usr/share/nginx/reports --name my-container com.containers/my-container
However, when I ssh into the host machine, and check the contents of the directory /usr/share/nginx/reports, I don't see any of the report data there.
Am I doing something wrong?
The host machine is an Ubuntu server, and the Docker container is also Ubuntu, no boot2docker weirdness going on here.
From "Managing data in containers", mounting a host folder to a container would be:
docker run -v /Users/<path>:/<container path>
(see "Use volume")
Using only -v /usr/share/nginx/reports would declare the internal container path /usr/share/nginx/reports as a volume, but would have nothing to do with the host folder.
This is one of the type of mounts available:
The answer to this question is problematic because it varies depending on your operating system and your full requirements. The answer by VonC makes some assumptions that should be addressed and is therefore only correct in some contexts. Other answers on this topic generally ignore the fact that some people are running linux, others windows, and still others are on OSX or other weird OS's.
As VonC mentioned in his answer, in a lot of cases it is possible to bind-mount a host directory straight into the container, using a -v host-path:container-path argument to the docker command (you can also use --volume for added readability or --mount for rocket-science).
One of the biggest problems (in 2020) is the use of the Windows Subsystem for Linux (WSL), where bind-mounting a host volume is fraught with error and may or may not work as expected depending on whether the path mounted is in the linux filesystem or the windows filesystem. VonC's answer was written before WSL became a big problem, but it still makes assumptions about the local filesystem being real rather than mounted into a virtual-machine of some kind.
I have found that a lot of engineers prefer to bypass this unnecessary confusion through the use of docker volumes. A docker volume can be created with the command:
docker volume create <name>
Listed with
docker volume ls
and removed with
docker volume rm <name>
You can mount this by specifying the name of the volume on the left-hand-side of the --volume argument. If your volume was called, for example, 'logs', you could use something like --volume logs:/usr/share/nginx/reports to bind it to the log dir you're interested in. You can view the contents of the directory with something like this:
docker run -it --rm --volume logs:/logs alpine ls -AlF /logs/
This should list the files in that directory. If you have a file called 'nginx.log' for example, you could view it like this:
docker run -it --rm --volume logs:/logs alpine less /logs/nginx.log
And the contents would be paged to your terminal.
You can bind this volume to multiple containers simultaneously if needed. This is useful if, for example, you're writing to your logs with one container, and paging them to a console with another.
If you want to copy the example log file from above into a tmp directory on your local filesystem you can achieve that with:
docker run -it --rm --volume logs:/logs --volume /tmp:/local_tmp alpine cp /logs/nginx.log /local_tmp/
I am using Docker toolbox on windows. I am Working on a Spring Boot Application using Docker. My application writes logs to
users/path/service.log
So when i started my application from host terminal the Log file was successfully updated.
But the same when i did on docker no file was created and neither updated.
So i changed my log file location to match with the Container's Directories
var/log/service.log
I started my container again and my file was updated again.
You can choose any location as long as it matches with the container Directory. Just bash into the container and see what suits you.
Next step is to copy log files from container to host.
So in order to copy those logs to your host. You can use one of two ways i know of-
1- use Volumes in docker
2- use following Docker command to copy file from docker container to host-:
docker cp <containerId>:/file/path/within/container /host/path/target
First, you need to create a directory where you want to share the data
mkdir -p /abc/def/
Now, you need to create a docker volume using the below command. As we see here, we are specifying device as '/abc/def/'
docker volume create --driver local \
--opt type=none \
--opt device=/abc/def/ \
--opt o=bind \
spark-volume
Now, start your container with below command..
docker run -d \
--mount type=volume,dst=/abc/def/,volume-driver=local,volume-opt=type=none,volume-opt=o=bind,volume-opt=device=/opt/spark/ \
--network host \
img:tag
Now, docker container will use /abc/def/ in local Filesystem as its storage and you will have all contents of /abc/def/ in docker container available in Local Filesystem
In your application, if you set a working directory for your php code (report path), the path must be the one on the container. Then docker will copie automaticly copy to your host directory. It wasn't docker mis-configuration, but my application that was writing to the wrong place. Weird at first, but did work in my case.