Backblaze B2

B2 is Backblaze's cloud storage system.

Paths are specified as remote:bucket (or remote: for the lsd command.) You may put subdirectories in too, e.g. remote:bucket/path/to/dir.


Here is an example of making a b2 configuration. First run

rclone config

This will guide you through an interactive setup process. To authenticate you will either need your Account ID (a short hex number) and Master Application Key (a long hex number) OR an Application Key, which is the recommended method. See below for further details on generating and using an Application Key.

No remotes found, make a new one?
n) New remote
q) Quit config
n/q> n
name> remote
Type of storage to configure.
Choose a number from below, or type in your own value
XX / Backblaze B2
   \ "b2"
Storage> b2
Account ID or Application Key ID
account> 123456789abc
Application Key
key> 0123456789abcdef0123456789abcdef0123456789
Endpoint for the service - leave blank normally.
Remote config
account = 123456789abc
key = 0123456789abcdef0123456789abcdef0123456789
endpoint =
y) Yes this is OK
e) Edit this remote
d) Delete this remote
y/e/d> y

This remote is called remote and can now be used like this

See all buckets

rclone lsd remote:

Create a new bucket

rclone mkdir remote:bucket

List the contents of a bucket

rclone ls remote:bucket

Sync /home/local/directory to the remote bucket, deleting any excess files in the bucket.

rclone sync --interactive /home/local/directory remote:bucket

Application Keys

B2 supports multiple Application Keys for different access permission to B2 Buckets.

You can use these with rclone too; you will need to use rclone version 1.43 or later.

Follow Backblaze's docs to create an Application Key with the required permission and add the applicationKeyId as the account and the Application Key itself as the key.

Note that you must put the applicationKeyId as the account – you can't use the master Account ID. If you try then B2 will return 401 errors.


This remote supports --fast-list which allows you to use fewer transactions in exchange for more memory. See the rclone docs for more details.

Modification times

The modification time is stored as metadata on the object as X-Bz-Info-src_last_modified_millis as milliseconds since 1970-01-01 in the Backblaze standard. Other tools should be able to use this as a modified time.

Modified times are used in syncing and are fully supported. Note that if a modification time needs to be updated on an object then it will create a new version of the object.

Restricted filename characters

In addition to the default restricted characters set the following characters are also replaced:

Character Value Replacement
\ 0x5C

Invalid UTF-8 bytes will also be replaced, as they can't be used in JSON strings.

Note that in 2020-05 Backblaze started allowing \ characters in file names. Rclone hasn't changed its encoding as this could cause syncs to re-transfer files. If you want rclone not to replace \ then see the --b2-encoding flag below and remove the BackSlash from the string. This can be set in the config.

SHA1 checksums

The SHA1 checksums of the files are checked on upload and download and will be used in the syncing process.

Large files (bigger than the limit in --b2-upload-cutoff) which are uploaded in chunks will store their SHA1 on the object as X-Bz-Info-large_file_sha1 as recommended by Backblaze.

For a large file to be uploaded with an SHA1 checksum, the source needs to support SHA1 checksums. The local disk supports SHA1 checksums so large file transfers from local disk will have an SHA1. See the overview for exactly which remotes support SHA1.

Sources which don't support SHA1, in particular crypt will upload large files without SHA1 checksums. This may be fixed in the future (see #1767).

Files sizes below --b2-upload-cutoff will always have an SHA1 regardless of the source.


Backblaze recommends that you do lots of transfers simultaneously for maximum speed. In tests from my SSD equipped laptop the optimum setting is about --transfers 32 though higher numbers may be used for a slight speed improvement. The optimum number for you may vary depending on your hardware, how big the files are, how much you want to load your computer, etc. The default of --transfers 4 is definitely too low for Backblaze B2 though.

Note that uploading big files (bigger than 200 MiB by default) will use a 96 MiB RAM buffer by default. There can be at most --transfers of these in use at any moment, so this sets the upper limit on the memory used.


When rclone uploads a new version of a file it creates a new version of it. Likewise when you delete a file, the old version will be marked hidden and still be available. Conversely, you may opt in to a "hard delete" of files with the --b2-hard-delete flag which would permanently remove the file instead of hiding it.

Old versions of files, where available, are visible using the --b2-versions flag.

It is also possible to view a bucket as it was at a certain point in time, using the --b2-version-at flag. This will show the file versions as they were at that time, showing files that have been deleted afterwards, and hiding files that were created since.

If you wish to remove all the old versions, and unfinished large file uploads, then you can use the rclone cleanup remote:bucket command which will delete all the old versions of files, leaving the current ones intact. You can also supply a path and only old versions under that path will be deleted, e.g. rclone cleanup remote:bucket/path/to/stuff.

Note that cleanup will remove partially uploaded files from the bucket if they are more than a day old. If you want more control over the expiry date then run rclone backend cleanup b2:bucket -o max-age=1h to remove all unfinished large file uploads older than one hour, leaving old versions intact.

If you wish to remove all the old versions, leaving current files and unfinished large files intact, then you can use the rclone backend cleanup-hidden remote:bucket command. You can also supply a path and only old versions under that path will be deleted, e.g. rclone backend cleanup-hidden remote:bucket/path/to/stuff.

When you purge a bucket, the current and the old versions will be deleted then the bucket will be deleted.

However delete will cause the current versions of the files to become hidden old versions.

Here is a session showing the listing and retrieval of an old version followed by a cleanup of the old versions.

Show current version and all the versions with --b2-versions flag.

$ rclone -q ls b2:cleanup-test
        9 one.txt

$ rclone -q --b2-versions ls b2:cleanup-test
        9 one.txt
        8 one-v2016-07-04-141032-000.txt
       16 one-v2016-07-04-141003-000.txt
       15 one-v2016-07-02-155621-000.txt

Retrieve an old version

$ rclone -q --b2-versions copy b2:cleanup-test/one-v2016-07-04-141003-000.txt /tmp

$ ls -l /tmp/one-v2016-07-04-141003-000.txt
-rw-rw-r-- 1 ncw ncw 16 Jul  2 17:46 /tmp/one-v2016-07-04-141003-000.txt

Clean up all the old versions and show that they've gone.

$ rclone -q cleanup b2:cleanup-test

$ rclone -q ls b2:cleanup-test
        9 one.txt

$ rclone -q --b2-versions ls b2:cleanup-test
        9 one.txt

Versions naming caveat

When using --b2-versions flag rclone is relying on the file name to work out whether the objects are versions or not. Versions' names are created by inserting timestamp between file name and its extension.

        9 file.txt
        8 file-v2023-07-17-161032-000.txt
       16 file-v2023-06-15-141003-000.txt

If there are real files present with the same names as versions, then behaviour of --b2-versions can be unpredictable.

Data usage

It is useful to know how many requests are sent to the server in different scenarios.

All copy commands send the following 4 requests:


The b2_list_file_names request will be sent once for every 1k files in the remote path, providing the checksum and modification time of the listed files. As of version 1.33 issue #818 causes extra requests to be sent when using B2 with Crypt. When a copy operation does not require any files to be uploaded, no more requests will be sent.

Uploading files that do not require chunking, will send 2 requests per file upload:


Uploading files requiring chunking, will send 2 requests (one each to start and finish the upload) and another 2 requests for each chunk:



Versions can be viewed with the --b2-versions flag. When it is set rclone will show and act on older versions of files. For example

Listing without --b2-versions

$ rclone -q ls b2:cleanup-test
        9 one.txt

And with

$ rclone -q --b2-versions ls b2:cleanup-test
        9 one.txt
        8 one-v2016-07-04-141032-000.txt
       16 one-v2016-07-04-141003-000.txt
       15 one-v2016-07-02-155621-000.txt

Showing that the current version is unchanged but older versions can be seen. These have the UTC date that they were uploaded to the server to the nearest millisecond appended to them.

Note that when using --b2-versions no file write operations are permitted, so you can't upload files or delete them.

Rclone supports generating file share links for private B2 buckets. They can either be for a file for example:

./rclone link B2:bucket/path/to/file.txt

or if run on a directory you will get:

./rclone link B2:bucket/path

you can then use the authorization token (the part of the url from the ?Authorization= on) on any file path under that directory. For example:


Standard options

Here are the Standard options specific to b2 (Backblaze B2).


Account ID or Application Key ID.


  • Config: account
  • Type: string
  • Required: true


Application Key.


  • Config: key
  • Env Var: RCLONE_B2_KEY
  • Type: string
  • Required: true


Permanently delete files on remote removal, otherwise hide files.


  • Config: hard_delete
  • Type: bool
  • Default: false

Advanced options

Here are the Advanced options specific to b2 (Backblaze B2).


Endpoint for the service.

Leave blank normally.


  • Config: endpoint
  • Type: string
  • Required: false


A flag string for X-Bz-Test-Mode header for debugging.

This is for debugging purposes only. Setting it to one of the strings below will cause b2 to return specific errors:

  • "fail_some_uploads"
  • "expire_some_account_authorization_tokens"
  • "force_cap_exceeded"

These will be set in the "X-Bz-Test-Mode" header which is documented in the b2 integrations checklist.


  • Config: test_mode
  • Type: string
  • Required: false


Include old versions in directory listings.

Note that when using this no file write operations are permitted, so you can't upload files or delete them.


  • Config: versions
  • Type: bool
  • Default: false


Show file versions as they were at the specified time.

Note that when using this no file write operations are permitted, so you can't upload files or delete them.


  • Config: version_at
  • Type: Time
  • Default: off


Cutoff for switching to chunked upload.

Files above this size will be uploaded in chunks of "--b2-chunk-size".

This value should be set no larger than 4.657 GiB (== 5 GB).


  • Config: upload_cutoff
  • Type: SizeSuffix
  • Default: 200Mi


Cutoff for switching to multipart copy.

Any files larger than this that need to be server-side copied will be copied in chunks of this size.

The minimum is 0 and the maximum is 4.6 GiB.


  • Config: copy_cutoff
  • Type: SizeSuffix
  • Default: 4Gi


Upload chunk size.

When uploading large files, chunk the file into this size.

Must fit in memory. These chunks are buffered in memory and there might a maximum of "--transfers" chunks in progress at once.

5,000,000 Bytes is the minimum size.


  • Config: chunk_size
  • Type: SizeSuffix
  • Default: 96Mi


Concurrency for multipart uploads.

This is the number of chunks of the same file that are uploaded concurrently.

Note that chunks are stored in memory and there may be up to "--transfers" * "--b2-upload-concurrency" chunks stored at once in memory.


  • Config: upload_concurrency
  • Type: int
  • Default: 4


Disable checksums for large (> upload cutoff) files.

Normally rclone will calculate the SHA1 checksum of the input before uploading it so it can add it to metadata on the object. This is great for data integrity checking but can cause long delays for large files to start uploading.


  • Config: disable_checksum
  • Type: bool
  • Default: false


Custom endpoint for downloads.

This is usually set to a Cloudflare CDN URL as Backblaze offers free egress for data downloaded through the Cloudflare network. Rclone works with private buckets by sending an "Authorization" header. If the custom endpoint rewrites the requests for authentication, e.g., in Cloudflare Workers, this header needs to be handled properly. Leave blank if you want to use the endpoint provided by Backblaze.

The URL provided here SHOULD have the protocol and SHOULD NOT have a trailing slash or specify the /file/bucket subpath as rclone will request files with "{download_url}/file/{bucket_name}/{path}".


https://mysubdomain.mydomain.tld (No trailing "/", "file" or "bucket")


  • Config: download_url
  • Type: string
  • Required: false


Time before the public link authorization token will expire in s or suffix ms|s|m|h|d.

This is used in combination with "rclone link" for making files accessible to the public and sets the duration before the download authorization token will expire.

The minimum value is 1 second. The maximum value is one week.


  • Config: download_auth_duration
  • Type: Duration
  • Default: 1w


How often internal memory buffer pools will be flushed. (no longer used)


  • Config: memory_pool_flush_time
  • Type: Duration
  • Default: 1m0s


Whether to use mmap buffers in internal memory pool. (no longer used)


  • Config: memory_pool_use_mmap
  • Type: bool
  • Default: false


Set the number of days deleted files should be kept when creating a bucket.

On bucket creation, this parameter is used to create a lifecycle rule for the entire bucket.

If lifecycle is 0 (the default) it does not create a lifecycle rule so the default B2 behaviour applies. This is to create versions of files on delete and overwrite and to keep them indefinitely.

If lifecycle is >0 then it creates a single rule setting the number of days before a file that is deleted or overwritten is deleted permanently. This is known as daysFromHidingToDeleting in the b2 docs.

The minimum value for this parameter is 1 day.

You can also enable hard_delete in the config also which will mean deletions won't cause versions but overwrites will still cause versions to be made.

See: rclone backend lifecycle for setting lifecycles after bucket creation.


  • Config: lifecycle
  • Type: int
  • Default: 0


The encoding for the backend.

See the encoding section in the overview for more info.


  • Config: encoding
  • Type: Encoding
  • Default: Slash,BackSlash,Del,Ctl,InvalidUtf8,Dot


Description of the remote.


  • Config: description
  • Type: string
  • Required: false

Backend commands

Here are the commands specific to the b2 backend.

Run them with

rclone backend COMMAND remote:

The help below will explain what arguments each command takes.

See the backend command for more info on how to pass options and arguments.

These can be run on a running backend using the rc command backend/command.


Read or set the lifecycle for a bucket

rclone backend lifecycle remote: [options] [<arguments>+]

This command can be used to read or set the lifecycle for a bucket.

Usage Examples:

To show the current lifecycle rules:

rclone backend lifecycle b2:bucket

This will dump something like this showing the lifecycle rules.

        "daysFromHidingToDeleting": 1,
        "daysFromUploadingToHiding": null,
        "fileNamePrefix": ""

If there are no lifecycle rules (the default) then it will just return [].

To reset the current lifecycle rules:

rclone backend lifecycle b2:bucket -o daysFromHidingToDeleting=30
rclone backend lifecycle b2:bucket -o daysFromUploadingToHiding=5 -o daysFromHidingToDeleting=1

This will run and then print the new lifecycle rules as above.

Rclone only lets you set lifecycles for the whole bucket with the fileNamePrefix = "".

You can't disable versioning with B2. The best you can do is to set the daysFromHidingToDeleting to 1 day. You can enable hard_delete in the config also which will mean deletions won't cause versions but overwrites will still cause versions to be made.

rclone backend lifecycle b2:bucket -o daysFromHidingToDeleting=1

See: https://www.backblaze.com/docs/cloud-storage-lifecycle-rules


  • "daysFromHidingToDeleting": After a file has been hidden for this many days it is deleted. 0 is off.
  • "daysFromUploadingToHiding": This many days after uploading a file is hidden


Remove unfinished large file uploads.

rclone backend cleanup remote: [options] [<arguments>+]

This command removes unfinished large file uploads of age greater than max-age, which defaults to 24 hours.

Note that you can use --interactive/-i or --dry-run with this command to see what it would do.

rclone backend cleanup b2:bucket/path/to/object
rclone backend cleanup -o max-age=7w b2:bucket/path/to/object

Durations are parsed as per the rest of rclone, 2h, 7d, 7w etc.


  • "max-age": Max age of upload to delete


Remove old versions of files.

rclone backend cleanup-hidden remote: [options] [<arguments>+]

This command removes any old hidden versions of files.

Note that you can use --interactive/-i or --dry-run with this command to see what it would do.

rclone backend cleanup-hidden b2:bucket/path/to/dir


rclone about is not supported by the B2 backend. Backends without this capability cannot determine free space for an rclone mount or use policy mfs (most free space) as a member of an rclone union remote.

See List of backends that do not support rclone about and rclone about