rclone/docs/content/union.md

title	description
Union	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 mydrive2:/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 mydrive2:/backup/../desktop.

Behavior / Policies

The behavior of union backend is inspired by 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 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.

Setup

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>
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 = C:\dir1 C:\dir2 C:\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 C:\dir1, C:\dir2 and C:\dir3

rclone lsd remote:

List all the files in C:\dir1, C:\dir2 and C:\dir3

rclone ls remote:

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

rclone copy C:\source remote:source

{{< 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.

• Config: upstreams
• Env Var: RCLONE_UNION_UPSTREAMS
• Type: string
• Default: ""

--union-action-policy

Policy to choose upstream on ACTION category.

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

--union-create-policy

Policy to choose upstream on CREATE category.

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

--union-search-policy

Policy to choose upstream on SEARCH category.

• 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.

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

{{< rem autogenerated options stop >}}