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b52fcb71a1
We always had 1G swap to work better with small memory setups, but this was omitted in the update to LinuxKit. Signed-off-by: Justin Cormack <justin.cormack@docker.com>
84 lines
3.9 KiB
Markdown
84 lines
3.9 KiB
Markdown
# LinuxKit Swap
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Image to enable creation of a swap file for a [linuxkit](https://github.com/linuxkit/linuxkit)-generated image.
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## Usage
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Normally, unless you are running explicitly in a desktop version, LinuxKit images do not have swap enabled. If you want swap, add the following to your `moby.yml`:
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```
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onboot:
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- name: swap
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image: linuxkit/swap:<hash>
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command: ["/swap.sh","--path","/var/external/swap","--size","2G"]
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```
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Note that you **must** mount the following:
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* `/var` to `/var` so it can place the swapfile in the right location.
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* `/dev` to `/dev` so it can do the right thing for devices
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### Options
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Options are passed to it via command-line options. The following are the options. Details follow.
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|Option|Parameter|Default|Required|Notes|
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|`--path`|Path to file as seen in the underlying OS||**Yes**||
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|`--size`|Target swapfile size||**Yes**||
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|`--condition`|_condition_||No|Condition that must be met to create a swapfile|
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|`--debug`|||No|Turns on verbose output from the command making the swap|
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|`--encrypt`|||No|Encrypts swapfile|
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#### File
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You can create a swapfile at the given path. You **must** provide exactly one swapfile path, or none will be created; there is no default. Passing fewer than or more than one `--path` option causes the container to exit with an error.
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The option `--path` takes a single argument _path_, path to the swapfile, e.g. `/var/mnt/swap2`.
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You **always** should put the swap file somewhere under `/var`, since that is where read-writable files and mounts exist in linuxkit images.
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#### Size
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`--size <size>` indicates the desired swapfile size, e.g. `2G` `100M` `5670K` `8765432`. There is no default. Acceptable size units are `G`, `M`, `K` and bytes of no unit provided.
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If disk space on the requested partition is insufficient to create the swapfile, the container exits with an error.
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#### Encryption
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If you want the swapfile to be encrypted, pass the `--encrypt` option. It will create an encrypted swapfile at the path you provide to `--path`, using devicemapper to map the clear device to `/dev/mapper/swapfile`.
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Encryption is performed using `cryptsetup` with `plain` encryption, using `/dev/urandom` to generate a random keyfile, key size of `256`, and cipher `aes-cbc-essiv:sha256`.
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#### Conditions
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You may want to create a swapfile only if certain conditions are met. Supported conditions are:
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* An external disk is available
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* Partition on which the swapfile will sit is of a minimum size.
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**All** conditions must be met. If a condition fails, the swapfile is not created, but the container exits with no error, unless you set the condition as `required`.
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Conditions are structured as follows: _type_:_parameter_:_required_
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In all cases, you may leave off _required_ if you wish to treat it as false, i.e. do not create swapfile but exit with no error if the condition is not met.
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##### Partition exists
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LinuxKit may be running from a small disk, and you only want to run if a particular large external disk is available. In that case, pass `--condition part:<path>:<required>` to indicate that swapfile is to be created only if _path_ already exists and is a mount point.
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Example: `--condition part:/var/mnt/external`
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##### Size
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You may set a minimum size for a partition (likely the one on which the swapfile will be created) using the `size` condition of the format `--condition size:<path>:<size>:<required>` to indicate that swapfile is to be created only if the partition on which _path_ exists is of minimum size _size_. Acceptable sizes are identical to those for the swapfile.
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Examples:
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* `--condition partsize:/var/mnt/external:100G:true`
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## Example
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An example yml file is included in [examples/swap.yml](../../examples/swap.yml). `swap.yml`. Note that you need to attach an external disk - trying to create a swapfile in tmpfs `/var` will fail.
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The sample command to run the enclosed is:
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```
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moby build swap.yml
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linuxkit run -disk size=4G swap
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```
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