Docker For Mac Volume Mount Permission Denied 2018

Expected behavior In Container: A file created in a volume mount as root user. DanielSchwiperich opened this issue on Mar 3, 2018 2 comments. Readable by the host user running Docker (Note Docker runs as a regular user on the Mac,. It's more than just a Docker Volume Driver, but it provides storage persistence for running. The error was caused because Laravel tries to write something to the file system. Let me remind you here that file permissions on bind mounts are shared. I've never had a permission issue in MacOS, Docker for Mac tends to You.

Volumes are the preferred mechanism for persisting data generated by and usedby Docker containers. While bind mounts are dependent on thedirectory structure of the host machine, volumes are completely managed byDocker. Volumes have several advantages over bind mounts:

• Volumes are easier to back up or migrate than bind mounts.
• You can manage volumes using Docker CLI commands or the Docker API.
• Volumes work on both Linux and Windows containers.
• Volumes can be more safely shared among multiple containers.
• Volume drivers let you store volumes on remote hosts or cloud providers, toencrypt the contents of volumes, or to add other functionality.
• New volumes can have their content pre-populated by a container.

In addition, volumes are often a better choice than persisting data in acontainer’s writable layer, because a volume does not increase the size of thecontainers using it, and the volume’s contents exist outside the lifecycle of agiven container.

If your container generates non-persistent state data, consider using atmpfs mount to avoid storing the data anywhere permanently, and toincrease the container’s performance by avoiding writing into the container’swritable layer.

Volumes use rprivate bind propagation, and bind propagation is notconfigurable for volumes.

Choose the -v or --mount flag

Originally, the -v or --volume flag was used for standalone containers andthe --mount flag was used for swarm services. However, starting with Docker17.06, you can also use --mount with standalone containers. In general,--mount is more explicit and verbose. The biggest difference is that the -vsyntax combines all the options together in one field, while the --mountsyntax separates them. Here is a comparison of the syntax for each flag.

New users should try --mount syntax which is simpler than --volume syntax.

If you need to specify volume driver options, you must use --mount.

• -v or --volume: Consists of three fields, separated by colon characters(:). The fields must be in the correct order, and the meaning of each fieldis not immediately obvious.
  • In the case of named volumes, the first field is the name of the volume, and isunique on a given host machine. For anonymous volumes, the first field isomitted.
  • The second field is the path where the file or directory are mounted inthe container.
  • The third field is optional, and is a comma-separated list of options, suchas ro. These options are discussed below.
• --mount: Consists of multiple key-value pairs, separated by commas and eachconsisting of a <key>=<value> tuple. The --mount syntax is more verbosethan -v or --volume, but the order of the keys is not significant, andthe value of the flag is easier to understand.
  • The type of the mount, which can be bind, volume, ortmpfs. This topic discusses volumes, so the type is alwaysvolume.
  • The source of the mount. For named volumes, this is the name of the volume.For anonymous volumes, this field is omitted. May be specified as sourceor src.
  • The destination takes as its value the path where the file or directoryis mounted in the container. May be specified as destination, dst,or target.
  • The readonly option, if present, causes the bind mount to be mounted intothe container as read-only.
  • The volume-opt option, which can be specified more than once, takes akey-value pair consisting of the option name and its value.

Escape values from outer CSV parser

If your volume driver accepts a comma-separated list as an option,you must escape the value from the outer CSV parser. To escape a volume-opt,surround it with double quotes (') and surround the entire mount parameterwith single quotes (').

For example, the local driver accepts mount options as a comma-separatedlist in the o parameter. This example shows the correct way to escape the list.

The examples below show both the --mount and -v syntax where possible, and --mount is presented first.

Differences between -v and --mount behavior

As opposed to bind mounts, all options for volumes are available for both--mount and -v flags.

When using volumes with services, only --mount is supported.

Create and manage volumes

Unlike a bind mount, you can create and manage volumes outside the scope of anycontainer.

Create a volume:

List volumes:

Inspect a volume:

Remove a volume:

Start a container with a volume

If you start a container with a volume that does not yet exist, Docker createsthe volume for you. The following example mounts the volume myvol2 into/app/ in the container.

The -v and --mount examples below produce the same result. You can’t runthem both unless you remove the devtest container and the myvol2 volumeafter running the first one.

Use docker inspect devtest to verify that the volume was created and mountedcorrectly. Look for the Mounts section:

This shows that the mount is a volume, it shows the correct source anddestination, and that the mount is read-write.

Stop the container and remove the volume. Note volume removal is a separatestep.

Start a service with volumes

When you start a service and define a volume, each service container uses its ownlocal volume. None of the containers can share this data if you use the localvolume driver, but some volume drivers do support shared storage. Docker for AWS andDocker for Azure both support persistent storage using the Cloudstor plugin.

The following example starts a nginx service with four replicas, each of whichuses a local volume called myvol2.

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Use docker service ps devtest-service to verify that the service is running:

Remove the service, which stops all its tasks:

Removing the service does not remove any volumes created by the service.Volume removal is a separate step.

Syntax differences for services

The docker service create command does not support the -v or --volume flag.When mounting a volume into a service’s containers, you must use the --mountflag.

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Populate a volume using a container

If you start a container which creates a new volume, as above, and the containerhas files or directories in the directory to be mounted (such as /app/ above),the directory’s contents are copied into the volume. The container thenmounts and uses the volume, and other containers which use the volume alsohave access to the pre-populated content.

To illustrate this, this example starts an nginx container and populates thenew volume nginx-vol with the contents of the container’s/usr/share/nginx/html directory, which is where Nginx stores its default HTMLcontent.

The --mount and -v examples have the same end result.

After running either of these examples, run the following commands to clean upthe containers and volumes. Note volume removal is a separate step.

Use a read-only volume

For some development applications, the container needs to write into the bindmount so that changes are propagated back to the Docker host. At other times,the container only needs read access to the data. Remember that multiplecontainers can mount the same volume, and it can be mounted read-write for someof them and read-only for others, at the same time.

This example modifies the one above but mounts the directory as a read-onlyvolume, by adding ro to the (empty by default) list of options, after themount point within the container. Where multiple options are present, separatethem by commas.

The --mount and -v examples have the same result.

Use docker inspect nginxtest to verify that the readonly mount was createdcorrectly. Look for the Mounts section:

Stop and remove the container, and remove the volume. Volume removal is aseparate step.

Share data among machines

When building fault-tolerant applications, you might need to configure multiplereplicas of the same service to have access to the same files.

There are several ways to achieve this when developing your applications.One is to add logic to your application to store files on a cloud objectstorage system like Amazon S3. Another is to create volumes with a driver thatsupports writing files to an external storage system like NFS or Amazon S3.

Volume drivers allow you to abstract the underlying storage system from theapplication logic. For example, if your services use a volume with an NFSdriver, you can update the services to use a different driver, as an example tostore data in the cloud, without changing the application logic.

Use a volume driver

When you create a volume using docker volume create, or when you start acontainer which uses a not-yet-created volume, you can specify a volume driver.The following examples use the vieux/sshfs volume driver, first when creatinga standalone volume, and then when starting a container which creates a newvolume.

Initial set-up

This example assumes that you have two nodes, the first of which is a Dockerhost and can connect to the second using SSH.

On the Docker host, install the vieux/sshfs plugin:

Create a volume using a volume driver

This example specifies a SSH password, but if the two hosts have shared keysconfigured, you can omit the password. Each volume driver may have zero or moreconfigurable options, each of which is specified using an -o flag.

Start a container which creates a volume using a volume driver

This example specifies a SSH password, but if the two hosts have shared keysconfigured, you can omit the password. Each volume driver may have zero or moreconfigurable options. If the volume driver requires you to pass options, youmust use the --mount flag to mount the volume, rather than -v.

Create a service which creates an NFS volume

This example shows how you can create an NFS volume when creating a service. This example uses 10.0.0.10 as the NFS server and /var/docker-nfs as the exported directory on the NFS server. Note that the volume driver specified is local.

NFSv3

NFSv4

Backup, restore, or migrate data volumes

Volumes are useful for backups, restores, and migrations. Use the--volumes-from flag to create a new container that mounts that volume.

Backup a container

For example, create a new container named dbstore:

Then in the next command, we:

• Launch a new container and mount the volume from the dbstore container
• Mount a local host directory as /backup
• Pass a command that tars the contents of the dbdata volume to a backup.tar file inside our /backup directory.

When the command completes and the container stops, we are left with a backup ofour dbdata volume.

Restore container from backup

With the backup just created, you can restore it to the same container, oranother that you made elsewhere.

For example, create a new container named dbstore2:

Then un-tar the backup file in the new container`s data volume:

You can use the techniques above to automate backup, migration and restoretesting using your preferred tools.

Remove volumes

A Docker data volume persists after a container is deleted. There are two typesof volumes to consider:

• Named volumes have a specific source from outside the container, for example awesome:/bar.
• Anonymous volumes have no specific source so when the container is deleted, instruct the Docker Engine daemon to remove them.

Remove anonymous volumes

To automatically remove anonymous volumes, use the --rm option. For example,this command creates an anonymous /foo volume. When the container is removed,the Docker Engine removes the /foo volume but not the awesome volume.

Remove all volumes

To remove all unused volumes and free up space:

Next steps

• Learn about bind mounts.
• Learn about tmpfs mounts.
• Learn about storage drivers.
• Learn about third-party volume driver plugins.