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Merge pull request containers#15706 from edsantiago/docs_dedup_volume
[CI:DOCS] Man pages: refactor common options: --volume
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| #### **--volume**, **-v**=*[[SOURCE-VOLUME|HOST-DIR:]CONTAINER-DIR[:OPTIONS]]* | ||
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| Create a bind mount. If `-v /HOST-DIR:/CONTAINER-DIR` is specified, Podman | ||
| bind mounts `/HOST-DIR` in the host to `/CONTAINER-DIR` in the Podman | ||
| container. Similarly, `-v SOURCE-VOLUME:/CONTAINER-DIR` will mount the named | ||
| volume from the host into the container. If no such named volume exists, Podman will | ||
| create one. (Note when using the remote client, including Mac and Windows (excluding WSL2) machines, the volumes will be mounted from the remote server, not necessarily the client machine.) | ||
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| The _OPTIONS_ is a comma-separated list and can be: <sup>[[1]](#Footnote1)</sup> | ||
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| * **rw**|**ro** | ||
| * **z**|**Z** | ||
| * [**O**] | ||
| * [**U**] | ||
| * [**no**]**copy** | ||
| * [**no**]**dev** | ||
| * [**no**]**exec** | ||
| * [**no**]**suid** | ||
| * [**r**]**bind** | ||
| * [**r**]**shared**|[**r**]**slave**|[**r**]**private**[**r**]**unbindable** | ||
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| The `CONTAINER-DIR` must be an absolute path such as `/src/docs`. The volume | ||
| will be mounted into the container at this directory. | ||
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| Volumes may specify a source as well, as either a directory on the host | ||
| or the name of a named volume. If no source is given, the volume will be created as an | ||
| anonymously named volume with a randomly generated name, and will be removed when | ||
| the <<container|pod>> is removed via the `--rm` flag or the `podman rm --volumes` command. | ||
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| If a volume source is specified, it must be a path on the host or the name of a | ||
| named volume. Host paths are allowed to be absolute or relative; relative paths | ||
| are resolved relative to the directory Podman is run in. If the source does not | ||
| exist, Podman will return an error. Users must pre-create the source files or | ||
| directories. | ||
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| Any source that does not begin with a `.` or `/` will be treated as the name of | ||
| a named volume. If a volume with that name does not exist, it will be created. | ||
| Volumes created with names are not anonymous, and they are not removed by the `--rm` | ||
| option and the `podman rm --volumes` command. | ||
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| Specify multiple **-v** options to mount one or more volumes into a | ||
| <<container|pod>>. | ||
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| `Write Protected Volume Mounts` | ||
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| Add **:ro** or **:rw** option to mount a volume in read-only or | ||
| read-write mode, respectively. By default, the volumes are mounted read-write. | ||
| See examples. | ||
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| `Chowning Volume Mounts` | ||
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| By default, Podman does not change the owner and group of source volume | ||
| directories mounted into containers. If a <<container|pod>> is created in a new user | ||
| namespace, the UID and GID in the container may correspond to another UID and | ||
| GID on the host. | ||
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| The `:U` suffix tells Podman to use the correct host UID and GID based on the | ||
| UID and GID within the <<container|pod>>, to change recursively the owner and group of | ||
| the source volume. | ||
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| **Warning** use with caution since this will modify the host filesystem. | ||
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| `Labeling Volume Mounts` | ||
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| Labeling systems like SELinux require that proper labels are placed on volume | ||
| content mounted into a <<container|pod>>. Without a label, the security system might | ||
| prevent the processes running inside the <<container|pod>> from using the content. By | ||
| default, Podman does not change the labels set by the OS. | ||
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| To change a label in the <<container|pod>> context, add either of two suffixes | ||
| **:z** or **:Z** to the volume mount. These suffixes tell Podman to relabel file | ||
| objects on the shared volumes. The **z** option tells Podman that two <<containers|pods>> | ||
| share the volume content. As a result, Podman labels the content with a shared | ||
| content label. Shared volume labels allow all containers to read/write content. | ||
| The **Z** option tells Podman to label the content with a private unshared label. | ||
| Only the current <<container|pod>> can use a private volume. | ||
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| Note: Do not relabel system files and directories. Relabeling system content | ||
| might cause other confined services on your machine to fail. For these types | ||
| of containers we recommend disabling SELinux separation. The option | ||
| **--security-opt label=disable** disables SELinux separation for the <<container|pod>>. | ||
| For example if a user wanted to volume mount their entire home directory into a | ||
| <<container|pod>>, they need to disable SELinux separation. | ||
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| $ podman <<fullsubcommand>> --security-opt label=disable -v $HOME:/home/user fedora touch /home/user/file | ||
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| `Overlay Volume Mounts` | ||
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| The `:O` flag tells Podman to mount the directory from the host as a | ||
| temporary storage using the `overlay file system`. The <<container|pod>> processes | ||
| can modify content within the mountpoint which is stored in the | ||
| container storage in a separate directory. In overlay terms, the source | ||
| directory will be the lower, and the container storage directory will be the | ||
| upper. Modifications to the mount point are destroyed when the <<container|pod>> | ||
| finishes executing, similar to a tmpfs mount point being unmounted. | ||
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| For advanced users, the **overlay** option also supports custom non-volatile | ||
| **upperdir** and **workdir** for the overlay mount. Custom **upperdir** and | ||
| **workdir** can be fully managed by the users themselves, and Podman will not | ||
| remove it on lifecycle completion. | ||
| Example **:O,upperdir=/some/upper,workdir=/some/work** | ||
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| Subsequent executions of the container will see the original source directory | ||
| content, any changes from previous <<container|pod>> executions no longer exist. | ||
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| One use case of the overlay mount is sharing the package cache from the | ||
| host into the container to allow speeding up builds. | ||
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| Note: | ||
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| - The `O` flag conflicts with other options listed above. | ||
| Content mounted into the container is labeled with the private label. | ||
| On SELinux systems, labels in the source directory must be readable | ||
| by the <<|pod infra>> container label. Usually containers can read/execute `container_share_t` | ||
| and can read/write `container_file_t`. If unable to change the labels on a | ||
| source volume, SELinux container separation must be disabled for the <<|pod or infra>> container | ||
| to work. | ||
| - The source directory mounted into the <<container|pod>> with an overlay mount | ||
| should not be modified, it can cause unexpected failures. It is recommended | ||
| to not modify the directory until the container finishes running. | ||
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| `Mounts propagation` | ||
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| By default bind mounted volumes are `private`. That means any mounts done | ||
| inside the <<container|pod>> will not be visible on host and vice versa. One can change | ||
| this behavior by specifying a volume mount propagation property. Making a | ||
| volume shared mounts done under that volume inside the <<container|pod>> will be | ||
| visible on host and vice versa. Making a volume **slave** enables only one | ||
| way mount propagation and that is mounts done on host under that volume | ||
| will be visible inside container but not the other way around. <sup>[[1]](#Footnote1)</sup> | ||
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| To control mount propagation property of a volume one can use the [**r**]**shared**, | ||
| [**r**]**slave**, [**r**]**private** or the [**r**]**unbindable** propagation flag. | ||
| Propagation property can be specified only for bind mounted volumes and not for | ||
| internal volumes or named volumes. For mount propagation to work the source mount | ||
| point (the mount point where source dir is mounted on) has to have the right propagation | ||
| properties. For shared volumes, the source mount point has to be shared. And for | ||
| slave volumes, the source mount point has to be either shared or slave. | ||
| <sup>[[1]](#Footnote1)</sup> | ||
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| To recursively mount a volume and all of its submounts into a | ||
| <<container|pod>>, use the **rbind** option. By default the bind option is | ||
| used, and submounts of the source directory will not be mounted into the | ||
| <<container|pod>>. | ||
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| Mounting the volume with the **nosuid** options means that SUID applications on | ||
| the volume will not be able to change their privilege. By default volumes | ||
| are mounted with **nosuid**. | ||
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| Mounting the volume with the **noexec** option means that no executables on the | ||
| volume will be able to be executed within the <<container|pod>>. | ||
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| Mounting the volume with the **nodev** option means that no devices on the volume | ||
| will be able to be used by processes within the <<container|pod>>. By default volumes | ||
| are mounted with **nodev**. | ||
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| If the _HOST-DIR_ is a mount point, then **dev**, **suid**, and **exec** options are | ||
| ignored by the kernel. | ||
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| Use **df HOST-DIR** to figure out the source mount, then use | ||
| **findmnt -o TARGET,PROPAGATION _source-mount-dir_** to figure out propagation | ||
| properties of source mount. If **findmnt**(1) utility is not available, then one | ||
| can look at the mount entry for the source mount point in _/proc/self/mountinfo_. Look | ||
| at the "optional fields" and see if any propagation properties are specified. | ||
| In there, **shared:N** means the mount is shared, **master:N** means mount | ||
| is slave, and if nothing is there, the mount is private. <sup>[[1]](#Footnote1)</sup> | ||
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| To change propagation properties of a mount point, use **mount**(8) command. For | ||
| example, if one wants to bind mount source directory _/foo_, one can do | ||
| **mount --bind /foo /foo** and **mount --make-private --make-shared /foo**. This | ||
| will convert /foo into a shared mount point. Alternatively, one can directly | ||
| change propagation properties of source mount. Say _/_ is source mount for | ||
| _/foo_, then use **mount --make-shared /** to convert _/_ into a shared mount. | ||
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| Note: if the user only has access rights via a group, accessing the volume | ||
| from inside a rootless <<container|pod>> will fail. |
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