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Copy and mount folders in a pot

In this section we explore all features available to mount a folder or a ZFS dataset or to copy files or directories from the host to a pot

Copy in a pot

pot supports a command to copy directories or files inside a pot

The copy happens when the command is executed and only at that time. copy-in is not a configuration parameter of a pot, it's just a command that copy things over.

Copy a file

Copying a single file in a pot is very straightforward: 

# pot copy-in -p casserole -s myfile -d /var/tmp

With this command, the file myfile is copied in /var/tmp of the pot casserole.

Note

This command supports single file only. No glob or regular expression can be used

Copy a directory

Copying a directory is also very straightforward: 

# pot copy-in -p casserole -s mydir -d /var/tmp
With this command, the directory mydir (and all its content) is copied in /var/tmp, creating the directory /var/tmp/mydir.

Mount in a pot

pot supports several mount options. In particular, three different types of things can be mounted:

  • a generic directory
  • a ZFS dataset
  • a fscomp

pot provides the mount-in command to specify what has to be mounted, how and where.

If the pot is already running, the mount will occur on the fly. If the pot is not running, the element will be mounted at start.

The mount-in command will change the pot configuration. Every time the pot start, the element will be mounted at start and unmounted at stop.

To check what will be mounted in a pot, the following command will show: 

# pot info -v -p casserole
The -v flag is relevant to show the dataset section, where the mounts are listed.

Generic directory

A directory can be mounted in an existing pot via the command: 

# pot mount-in -p casserole -m /mnt -d mydir
where:

  • -p casserole : the name of the pot
  • -m /mnt : the mountpoint inside the pot
  • -d mydir : the directory to be mounted

By default, the mount is implemented via nullfs(5) and in read/write mode.

To mount in read-only mode, the flag -r can be used.

ZFS dataset

A ZFS dataset can be mounted in an existing pot via the command: 

# pot mount-in -p casserole -m /mnt -z zroot/mydataset
where:

  • -p casserole : the name of the pot
  • -m /mnt : the mountpoint inside the pot
  • -z zroot/mydataset : the ZFS dataset to be mounted

By default, the mount is implemented via nullfs(5) and in read/write mode.

To mount in read-only mode, the flag -r can be used.

If the ZFS dataset is used only by one pot and the performance penalty introduced by nullfs(5) is undesired, the flag -w can be used. This flag will change the mountpoint of the ZFS dataset to be inside the pot.

fscomp

To support users managing additional ZFS datasets for pot, the concept of fscomp (AKA file system component) has been introduced.

A fscomp is just a ZFS dataset, but it can be convenient to use for users that are not familiar with ZFS, because pot already provides some commands (snapshot, rollback, clone) to manage those ZFS dataset. However, an experienced user would probably prefer to manage ZFS datasets independently.

To use a fscomp, it has first to be created: 

# pot create-fscomp -f myfscomp
This command creates an empty ZFS dataset, a volume, that can be attached to one or more pots.

The list of available fscomps can be obtained with the command: 

# pot ls -f

Finally, a fscomp can be mounted in a pot with the command: 

# pot mount-in -p casserole -f myfscomp -m /mnt
where:

  • -p casserole : the name of the pot
  • -m /mnt : the mountpoint inside the pot
  • -f myfscomp : the fscomp to be mounted

By default, the mount is implemented via nullfs(5) and in read/write mode.

To mount in read-only mode, the flag -r can be used.

The fscomp is a ZFS dataset, hence the -w flag can be used to avoid nullfs(5) overhead, by changing the mountpoint of the dataset. This feature, however, make sense if the fscomp is used only by one pot at a time.

Last update: 2020-03-05