Docker bind source path does not exist even though it does - linux

I have two ubuntu server VMs running on the same proxmox server. Both are running docker. I want to migrate one container from one of the VMs to the other. For that I need to attach a USB drive to the target VM which will be mounted inside the docker container. I mounted the drive exactly the same way in both VMs (the old one is shut down of course) and the mounting works, I can access the directory and see the contents of the drive. Now I want to run the container with the exact same command as I used on the old vm which looks something like this:
docker run -d --restart unless-stopped --stop-timeout 300 -p 8081:8081 --mount type=bind,source="/data",destination=/internal_data
This works in the old VM, but on the new one it says:
docker: Error response from daemon: invalid mount config for type "bind": bind source path does not exist: /data.
See 'docker run --help'.
I don't understand what's wrong. /data exists and is owned by root, the same as it is on the old VM. In fact, it's the same drive with the same contents. If I shut down the new VM and boot up the old one with the drive mounted in exactly the same way, it just works.
What can cause this error, if the source path does in fact exist?

I fixed it by mounting the drive in a mount point in /mnt/.
I changed nothing else and in the other VM it works when mounting on the root with the same user and permissions. No idea why that fixed it.

Related

mounting volume from inside the container in local directory [duplicate]

Assume that i have an application with this simple Dockerfile:
//...
RUN configure.sh --logmyfiles /var/lib/myapp
ENTRYPOINT ["starter.sh"]
CMD ["run"]
EXPOSE 8080
VOLUME ["/var/lib/myapp"]
And I run a container from that:
sudo docker run -d --name myapp -p 8080:8080 myapp:latest
So it works properly and stores some logs in /var/lib/myapp of docker container.
My question
I need these log files to automatically saved in host too, So how can i mount the /var/lib/myapp from the container to the /var/lib/myapp in host server (without removing current container) ?
Edit
I also see Docker - Mount Directory From Container to Host, but it doesn't solve my problem i need a way to backup my files from docker to host.
First, a little information about Docker volumes. Volume mounts occur only at container creation time. That means you cannot change volume mounts after you've started the container. Also, volume mounts are one-way only: From the host to the container, and not vice-versa. When you specify a host directory mounted as a volume in your container (for example something like: docker run -d --name="foo" -v "/path/on/host:/path/on/container" ubuntu), it is a "regular ole" linux mount --bind, which means that the host directory will temporarily "override" the container directory. Nothing is actually deleted or overwritten on the destination directory, but because of the nature of containers, that effectively means it will be overridden for the lifetime of the container.
So, you're left with two options (maybe three). You could mount a host directory into your container and then copy those files in your startup script (or if you bring cron into your container, you could use a cron to periodically copy those files to that host directory volume mount).
You could also use docker cp to move files from your container to your host. Now that is kinda hacky and definitely not something you should use in your infrastructure automation. But it does work very well for that exact purpose. One-off or debugging is a great situation for that.
You could also possibly set up a network transfer, but that's pretty involved for what you're doing. However, if you want to do this regularly for your log files (or whatever), you could look into using something like rsyslog to move those files off your container.
So how can i mount the /var/lib/myapp from the container to the /var/lib/myapp in host server
That is the opposite: you can mount an host folder to your container on docker run.
(without removing current container)
I don't think so.
Right now, you can check docker inspect <containername> and see if you see your log in the /var/lib/docker/volumes/... associated to the volume from your container.
Or you can redirect the result of docker logs <containername> to an host file.
For more example, see this gist.
The alternative would be to mount a host directory as the log folder and then access the log files directly on the host.
me#host~$ docker run -d -p 80:80 -v <sites-enabled-dir>:/etc/nginx/sites-enabled -v <certs-dir>:/etc/nginx/certs -v <log-dir>:/var/log/nginx dockerfile/nginx
me#host~$ ls <log-dir>
(again, that apply to a container that you start, not an existing running one)

Bind volumes that contains mount points mounted within docker container

I have a privileged docker container that will mount a custom File System with FUSE.
It is achieved by bind mounting /dev,/sys from the host to the container and running some custom software which accessed block device e.g. /dev/sdX inside the container to mount a custom FS on some mount point, let's say /mnt/some_mountpoint_inside_the_container (everything still happens inside the container).
Now, I would like to access this mount point that are mounted inside the docker container from the host but with no avail. So far, I have tried:
In my docker-compose.yaml, I defined a (binded) volume from host to container, e.g.:
...
volumes:
- /mnt/mountpoint_at_host:/mnt/some_mountpoint_inside_the_container
...
Then, I have FUSE mounted the custom FS inside the container on /mnt/some_mountpoint_inside_the_container. It seems that even I have added files in /mnt/mountpoint_at_host on my host, changes are not reflected within the container (i.e. ls -al /mnt/some_mountpoint_inside_the_container inside the container returns nothing). Only AFTER I have un-mounted /mnt/some_mountpoint_inside_the_container within the container, the created files on the host can now be found on the container.
I have also tried to bind mount a parent folder:
...
volumes:
- /mnt/mountpoint_at_host:/mnt/parent_folder
...
Then I created a folder on my host: mkdir -p /mnt/mountpoint_at_host/the_real_mntpt.
I have then again, FUSE mounted the custom FS in the docker container on:
/mnt/parent_folder/the_real_mntpt.
But still, changes on the host are not reflected on the container side, or the underlining block device.
Is there any way I can access to the mount point that are mounted within the container from the host? I have thought of methods like creating NFS service within the container after I have FUSE mounted the FS, and then exposing the NFS port to the host. But it seems a bit inefficient.
EDIT: I am using Ubuntu with docker.io/docker-compose from apt-get. The container itself is a CentOS 8.

Docker won't run a container after creating a symbolic link

I have access to a 10Gb virtual machine, which was already at 99% disk usage. In order to start a new container I moved my docker directory (previously at /var/snap/docker) to another disk where I have as much space as I need, and created a symbolic link at /var/snap called docker.
Now when I try to run a container it prints out:
Error response from daemon: OCI runtime create failed: /var/snap/docker/common/var-lib-docker/overlay2/833f49d424b2b1089aee6989bda609fa85d3a72540142c464e00e1fa4eec0a3b/merged is not an absolute path or is a symlink: unknown
Error: failed to start containers: ycsb
I don't know what I did wrong, or if this isn't supposed to work at all.
This used to work (to at least v19.03.1), but now does not.
However, you can explicitly change the Docker rootdir that the daemon uses, which is more secure.
From https://unix.stackexchange.com/questions/452368/change-docker-root-dir-on-red-hat-linux:
Edit (or create) the /etc/docker/daemon.json file so that it reads
{
"data-root": "/mnt/your-volume/var/snap/docker",
...other possible entries...
}
Restart the daemon with
sudo systemctl restart docker
And try your run.

How to mount a host directory into a running docker container

I want to mount my usb drive into a running docker instance for manually backup of some files.
I know of the -v feature of docker run, but this creates a new container.
Note: its a nextcloudpi container.
You can only change a very limited set of container options after a container starts up. Options like environment variables and container mounts can only be set during the initial docker run or docker create. If you want to change these, you need to stop and delete your existing container, and create a new one with the new mount option.
If there's data that you think you need to keep or back up, it should live in some sort of volume mount anyways. Delete and restart your container and use a -v option to mount a volume on where the data is kept. The Docker documentation has an example using named volumes with separate backup and restore containers; or you can directly use a host directory and your normal backup solution there. (Deleting and recreating a container as I suggested in the first paragraph is extremely routine, and this shouldn't involve explicit "backup" and "restore" steps.)
If you have data that's there right now that you can't afford to lose, you can docker cp it out of the container before setting up a more robust storage scheme.
As David Maze mentioned, it's almost impossible to change the volume location of an existing container by using normal docker commands.
I found an alternative way that works for me. The main idea is convert the existing container to a new docker image and initialize a new docker container on top of it. Hope works for you too.
# Create a new image from the container
docker commit CONTAINERID NEWIMAGENAME
# Create a new container on the top of the new image
docker run -v HOSTLOCATION:CONTAINERLOCATION NEWIMAGENAME
I know the question is from May, but for future searchers:
Create a mounting point on the host filesystem:
sudo mkdir /mnt/usb-drive
Run the docker container using the --mount option and set the "bind propagation" to "shared":
docker run --name mynextcloudpi -it --mount type=bind,source=/mnt/usb-drive,target=/mnt/disk,bind-propagation=shared nextcloudpi
Now you can mount your USB drive to the /mnt/usb-drive directory and it will be mounted to the /mnt/disk location inside the running container.
E.g: sudo mount /dev/sda1 /mnt/usb-drive
Change the /dev/sda1, of course.
More info about bind-propagation: https://docs.docker.com/storage/bind-mounts/#configure-bind-propagation

Mount SMB/CIFS share within a Docker container

I have a web application running in a Docker container. This application needs to access some files on our corporate file server (Windows Server with an Active Directory domain controller). The files I'm trying to access are image files created for our clients and the web application displays them as part of the client's portfolio.
On my development machine I have the appropriate folders mounted via entries in /etc/fstab and the host mount points are mounted in the Docker container via the --volume argument. This works perfectly.
Now I'm trying to put together a production container which will be run on a different server and which doesn't rely on the CIFS share being mounted on the host. So I tried to add the appropriate entries to the /etc/fstab file in the container & mounting them with mount -a. I get mount error(13): Permission denied.
A little research online led me to this article about Docker security. If I'm reading this correctly, it appears that Docker explicitly denies the ability to mount filesystems within a container. I tried mounting the shares read-only, but this (unsurprisingly) also failed.
So, I have two questions:
Am I correct in understanding that Docker prevents any use of mount inside containers?
Can anyone think of another way to accomplish this without mounting a CIFS share on the host and then mounting the host folder in the Docker container?
Yes, Docker is preventing you from mounting a remote volume inside the container as a security measure. If you trust your images and the people who run them, then you can use the --privileged flag with docker run to disable these security measures.
Further, you can combine --cap-add and --cap-drop to give the container only the capabilities that it actually needs. (See documentation) The SYS_ADMIN capability is the one that grants mount privileges.
yes
There is a closed issue mount.cifs within a container
https://github.com/docker/docker/issues/22197
according to which adding
--cap-add SYS_ADMIN --cap-add DAC_READ_SEARCH
to the run options will make mount -t cifs operational.
I tried it out and:
mount -t cifs //<host>/<path> /<localpath> -o user=<user>,password=<user>
within the container then works
You could use the smbclient command (part of the Samba package) to access the SMB/CIFS server from within the Docker container without mounting it, in the same way that you might use curl to download or upload a file.
There is a question on StackExchange Unix that deals with this, but in short:
smbclient //server/share -c 'cd /path/to/file; put myfile'
For multiple files there is the -T option which can create or extract .tar archives, however this looks like it would be a two step process (one to create the .tar and then another to extract it locally). I'm not sure whether you could use a pipe to do it in one step.
You can use a Netshare docker volume plugin which allows to mount remote CIFS/Samba as volumes.
Do not make your containers less secure by exposing many ports just to mount a share. Or by running it as --privileged
Here is how I solved this issue:
First mount the volume on the server that runs docker.
sudo mount -t cifs -o username=YourUserName,uid=$(id -u),gid=$(id -g) //SERVER/share ~/WinShare
Change the username, SERVER and WinShare here. This will ask your sudo password, then it will ask password for the remote share.
Let's assume you created WinShare folder inside your home folder. After running this command you should be able to see all the shared folders and files in WinShare folder. In addition to that since you use the uidand gid tags you will have write access without using sudo all the time.
Now you can run your container by using -v tag and share a volume between the server and the container.
Let's say you ran it like the following.
docker run -d --name mycontainer -v /home/WinShare:/home 2d244422164
You should be able to access the windows share and modify it from your container now.
To test it just do:
docker exec -it yourRunningContainer /bin/bash
cd /Home
touch testdocfromcontainer.txt
You should see testdocfromcontainer.txt in the windows share.

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