---
title: "Union"
description: "Remote Unification"
---

# {{< icon "fa fa-link" >}} Union

The `union` remote provides a unification similar to UnionFS using other remotes.

Paths may be as deep as required or a local path, 
e.g. `remote:directory/subdirectory` or `/directory/subdirectory`.

During the initial setup with `rclone config` you will specify the upstream
remotes as a space separated list. The upstream remotes can either be a local paths or other remotes.

Attribute `:ro` and `:nc` can be attach to the end of path to tag the remote as **read only** or **no create**,
e.g. `remote:directory/subdirectory:ro` or `remote:directory/subdirectory:nc`.

Subfolders can be used in upstream remotes. Assume a union remote named `backup`
with the remotes `mydrive:private/backup`. Invoking `rclone mkdir backup:desktop`
is exactly the same as invoking `rclone mkdir mydrive:private/backup/desktop`.

There will be no special handling of paths containing `..` segments.
Invoking `rclone mkdir backup:../desktop` is exactly the same as invoking
`rclone mkdir mydrive:private/backup/../desktop`.

## Configuration

Here is an example of how to make a union called `remote` for local folders.
First run:

     rclone config

This will guide you through an interactive setup process:

```
No remotes found, make a new one?
n) New remote
s) Set configuration password
q) Quit config
n/s/q> n
name> remote
Type of storage to configure.
Choose a number from below, or type in your own value
[snip]
XX / Union merges the contents of several remotes
   \ "union"
[snip]
Storage> union
List of space separated upstreams.
Can be 'upstreama:test/dir upstreamb:', '\"upstreama:test/space:ro dir\" upstreamb:', etc.
Enter a string value. Press Enter for the default ("").
upstreams> remote1:dir1 remote2:dir2 remote3:dir3
Policy to choose upstream on ACTION class.
Enter a string value. Press Enter for the default ("epall").
action_policy>
Policy to choose upstream on CREATE class.
Enter a string value. Press Enter for the default ("epmfs").
create_policy>
Policy to choose upstream on SEARCH class.
Enter a string value. Press Enter for the default ("ff").
search_policy>
Cache time of usage and free space (in seconds). This option is only useful when a path preserving policy is used.
Enter a signed integer. Press Enter for the default ("120").
cache_time>
Remote config
--------------------
[remote]
type = union
upstreams = remote1:dir1 remote2:dir2 remote3:dir3
--------------------
y) Yes this is OK
e) Edit this remote
d) Delete this remote
y/e/d> y
Current remotes:

Name                 Type
====                 ====
remote               union

e) Edit existing remote
n) New remote
d) Delete remote
r) Rename remote
c) Copy remote
s) Set configuration password
q) Quit config
e/n/d/r/c/s/q> q
```

Once configured you can then use `rclone` like this,

List directories in top level in `remote1:dir1`, `remote2:dir2` and `remote3:dir3`

    rclone lsd remote:

List all the files in `remote1:dir1`, `remote2:dir2` and `remote3:dir3`

    rclone ls remote:

Copy another local directory to the union directory called source, which will be placed into `remote3:dir3`

    rclone copy C:\source remote:source

### Behavior / Policies

The behavior of union backend is inspired by [trapexit/mergerfs](https://github.com/trapexit/mergerfs). All functions are grouped into 3 categories: **action**, **create** and **search**. These functions and categories can be assigned a policy which dictates what file or directory is chosen when performing that behavior. Any policy can be assigned to a function or category though some may not be very useful in practice. For instance: **rand** (random) may be useful for file creation (create) but could lead to very odd behavior if used for `delete` if there were more than one copy of the file.

### Function / Category classifications

| Category | Description              | Functions                                                                           |
|----------|--------------------------|-------------------------------------------------------------------------------------|
| action   | Writing Existing file    | move, rmdir, rmdirs, delete, purge and copy, sync (as destination when file exist)  |
| create   | Create non-existing file | copy, sync (as destination when file not exist)                                     |
| search   | Reading and listing file | ls, lsd, lsl, cat, md5sum, sha1sum and copy, sync (as source)                       |
| N/A      |                          | size, about                                                                         |

### Path Preservation

Policies, as described below, are of two basic types. `path preserving` and `non-path preserving`.

All policies which start with `ep` (**epff**, **eplfs**, **eplus**, **epmfs**, **eprand**) are `path preserving`. `ep` stands for `existing path`.

A path preserving policy will only consider upstreams where the relative path being accessed already exists.

When using non-path preserving policies paths will be created in target upstreams as necessary.

### Quota Relevant Policies

Some policies rely on quota information. These policies should be used only if your upstreams support the respective quota fields.

| Policy     | Required Field |
|------------|----------------|
| lfs, eplfs | Free           |
| mfs, epmfs | Free           |
| lus, eplus | Used           |
| lno, eplno | Objects        |

To check if your upstream supports the field, run `rclone about remote: [flags]` and see if the required field exists.

### Filters

Policies basically search upstream remotes and create a list of files / paths for functions to work on. The policy is responsible for filtering and sorting. The policy type defines the sorting but filtering is mostly uniform as described below.

* No **search** policies filter.
* All **action** policies will filter out remotes which are tagged as **read-only**.
* All **create** policies will filter out remotes which are tagged **read-only** or **no-create**.

If all remotes are filtered an error will be returned.

### Policy descriptions

The policies definition are inspired by [trapexit/mergerfs](https://github.com/trapexit/mergerfs) but not exactly the same. Some policy definition could be different due to the much larger latency of remote file systems.

| Policy           | Description                                                |
|------------------|------------------------------------------------------------|
| all | Search category: same as **epall**. Action category: same as **epall**. Create category: act on all upstreams. |
| epall (existing path, all) | Search category: Given this order configured, act on the first one found where the relative path exists. Action category: apply to all found. Create category: act on all upstreams where the relative path exists. |
| epff (existing path, first found) | Act on the first one found, by the time upstreams reply, where the relative path exists. |
| eplfs (existing path, least free space) | Of all the upstreams on which the relative path exists choose the one with the least free space. |
| eplus (existing path, least used space) | Of all the upstreams on which the relative path exists choose the one with the least used space. |
| eplno (existing path, least number of objects) | Of all the upstreams on which the relative path exists choose the one with the least number of objects. |
| epmfs (existing path, most free space) | Of all the upstreams on which the relative path exists choose the one with the most free space. |
| eprand (existing path, random) | Calls **epall** and then randomizes. Returns only one upstream. |
| ff (first found) | Search category: same as **epff**. Action category: same as **epff**. Create category: Act on the first one found by the time upstreams reply. |
| lfs (least free space) | Search category: same as **eplfs**. Action category: same as **eplfs**. Create category: Pick the upstream with the least available free space. |
| lus (least used space) | Search category: same as **eplus**. Action category: same as **eplus**. Create category: Pick the upstream with the least used space. |
| lno (least number of objects) | Search category: same as **eplno**. Action category: same as **eplno**. Create category: Pick the upstream with the least number of objects. |
| mfs (most free space) | Search category: same as **epmfs**. Action category: same as **epmfs**. Create category: Pick the upstream with the most available free space. |
| newest | Pick the file / directory with the largest mtime. |
| rand (random) | Calls **all** and then randomizes. Returns only one upstream. |

{{< rem autogenerated options start" - DO NOT EDIT - instead edit fs.RegInfo in backend/union/union.go then run make backenddocs" >}}
### Standard options

Here are the Standard options specific to union (Union merges the contents of several upstream fs).

#### --union-upstreams

List of space separated upstreams.

Can be 'upstreama:test/dir upstreamb:', '"upstreama:test/space:ro dir" upstreamb:', etc.

Properties:

- Config:      upstreams
- Env Var:     RCLONE_UNION_UPSTREAMS
- Type:        string
- Required:    true

#### --union-action-policy

Policy to choose upstream on ACTION category.

Properties:

- Config:      action_policy
- Env Var:     RCLONE_UNION_ACTION_POLICY
- Type:        string
- Default:     "epall"

#### --union-create-policy

Policy to choose upstream on CREATE category.

Properties:

- Config:      create_policy
- Env Var:     RCLONE_UNION_CREATE_POLICY
- Type:        string
- Default:     "epmfs"

#### --union-search-policy

Policy to choose upstream on SEARCH category.

Properties:

- Config:      search_policy
- Env Var:     RCLONE_UNION_SEARCH_POLICY
- Type:        string
- Default:     "ff"

#### --union-cache-time

Cache time of usage and free space (in seconds).

This option is only useful when a path preserving policy is used.

Properties:

- Config:      cache_time
- Env Var:     RCLONE_UNION_CACHE_TIME
- Type:        int
- Default:     120

### Advanced options

Here are the Advanced options specific to union (Union merges the contents of several upstream fs).

#### --union-min-free-space

Minimum viable free space for lfs/eplfs policies.

If a remote has less than this much free space then it won't be
considered for use in lfs or eplfs policies.

Properties:

- Config:      min_free_space
- Env Var:     RCLONE_UNION_MIN_FREE_SPACE
- Type:        SizeSuffix
- Default:     1Gi

### Metadata

Any metadata supported by the underlying remote is read and written.

See the [metadata](/docs/#metadata) docs for more info.

{{< rem autogenerated options stop >}}