Project: Podman (App Definition and Development / Application Definition & Image Build)
File: volume.md

Create a bind mount. If `-v /HOST-DIR:/CONTAINER-DIR` is specified, Podman bind mounts `/HOST-DIR` from the host into `/CONTAINER-DIR` in the Podman container. Similarly, `-v SOURCE-VOLUME:/CONTAINER-DIR` mounts the named volume from the host into the container. If no such named volume exists, Podman creates one. If no source is given, the volume is created as an anonymously named volume with a randomly generated name, and is removed when the <<container|pod>> is removed via the `--rm` flag or the `podman rm --volumes` command. (Note when using the remote client, including Mac and Windows (excluding WSL2) machines, the volumes are mounted from the remote server, not necessarily the client machine.) The OPTIONS is a comma-separated list and can be one or more of: rw|ro* z|Z* [O*] [U*] [no]copy* [no]dev* [no]exec* [no]suid* [r]bind* </sup> idmap[=options*] The `CONTAINER-DIR` must be an absolute path such as `/src/docs`. The volume is mounted into the container at this directory. 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 returns an error. Users must pre-create the source files or directories. Any source that does not begin with a `.` or `/` is treated as the name of a named volume. If a volume with that name does not exist, it is created. Volumes created with names are not anonymous, and they are not removed by the `--rm` option and the `podman rm --volumes` command. Specify multiple -v options to mount one or more volumes into a <<container|pod>>. `Write Protected Volume Mounts` 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. `Chowning Volume Mounts` 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. 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. Chowning walks the file system under the volume and changes the UID/GID on each file. If the volume has thousands of inodes, this process takes a long time, delaying the start of the <<container|pod>>. Warning use with caution since this modifies the host filesystem. `Labeling Volume Mounts` 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. 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 or more <<containers|pods>> share the volume

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. Relabeling walks the file system under the volume and changes the label on each file, if the volume has thousands of inodes, this process takes a long time, delaying the start of the <<container|pod>>. If the volume was previously relabeled with the `z` option, Podman is optimized to not relabel a second time. If files are moved into the volume, then the labels can be manually change with the `chcon -Rt containerfilet PATH` command. Note: Do not relabel system files and directories. Relabeling system content might cause other confined services on the 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. $ podman <<fullsubcommand>> --security-opt label=disable -v $HOME:/home/user fedora touch /home/user/file `Overlay Volume Mounts` 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 is the lower, and the container storage directory is the upper. Modifications to the mount point are destroyed when the <<container|pod>> finishes executing, similar to a tmpfs mount point being unmounted. 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 does not remove it on lifecycle completion. Example :O,upperdir=/some/upper,workdir=/some/work Subsequent executions of the container sees the original source directory content, any changes from previous <<container|pod>> executions no longer exist. One use case of the overlay mount is sharing the package cache from the host into the container to allow speeding up builds. Note: 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 `containersharet` and can read/write `containerfilet`. If unable to change the labels on a source volume, SELinux container separation must be disabled for the <<|pod or infra>> container to work. Do not modify the source directory mounted into the <<container|pod>> with an overlay mount, it can cause unexpected failures. Only modify the directory after the container finishes running. `Mounts propagation` By default, bind-mounted volumes are `private`. That means any mounts done inside the <<container|pod>> are not visible on the host and vice versa. One can change this behavior by specifying a volume mount propagation property. When a volume is `shared`, mounts done under that volume inside the <<container|pod>> are visible on host and vice versa. Making a volume slave<sup></sup> enables only one-way mount propagation: mounts done on the host under that volume are visible inside the container but not the other way

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></sup> 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 is not mounted into the <<container|pod>>. Mounting the volume with a copy option tells podman to copy content from the underlying destination directory onto newly created internal volumes. The copy only happens on the initial creation of the volume. Content is not copied up when the volume is subsequently used on different containers. The copy option is ignored on bind mounts and has no effect. Mounting volumes with the nosuid options means that SUID executables on the volume can not be used by applications to change their privilege. By default volumes are mounted with nosuid. Mounting the volume with the noexec option means that no executables on the volume can be executed within the <<container|pod>>. Mounting the volume with the nodev option means that no devices on the volume can be used by processes within the <<container|pod>>. By default volumes are mounted with nodev. If the HOST-DIR is a mount point, then dev, suid, and exec options are ignored by the kernel. 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></sup> 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 converts /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. Note: if the user only has access rights via a group, accessing the volume from inside a rootless <<container|pod>> fails. `Idmapped mount` If `idmap` is specified, create an idmapped mount to the target user namespace in the container. The idmap option supports a custom mapping that can be different than the user namespace used by the container. The mapping can be specified after the idmap option like: `idmap=uids=0-1-10#10-11-10;gids=0-100-10`. For each triplet, the first value is the start of the backing file system IDs that are mapped to the second value on the host. The length of this mapping is given in the third value. Multiple ranges are separated with #.