rclone serve sftp

Serve the remote over SFTP.


rclone serve sftp implements an SFTP server to serve the remote over SFTP. This can be used with an SFTP client or you can make a remote of type sftp to use with it.

You can use the filter flags (eg --include, --exclude) to control what is served.

The server will log errors. Use -v to see access logs.

--bwlimit will be respected for file transfers. Use --stats to control the stats printing.

You must provide some means of authentication, either with --user/--pass, an authorized keys file (specify location with --authorized-keys - the default is the same as ssh), an --auth-proxy, or set the --no-auth flag for no authentication when logging in.

Note that this also implements a small number of shell commands so that it can provide md5sum/sha1sum/df information for the rclone sftp backend. This means that is can support SHA1SUMs, MD5SUMs and the about command when paired with the rclone sftp backend.

If you don't supply a --key then rclone will generate one and cache it for later use.

By default the server binds to localhost:2022 - if you want it to be reachable externally then supply "--addr :2022" for example.

Note that the default of "--vfs-cache-mode off" is fine for the rclone sftp backend, but it may not be with other SFTP clients.

Directory Cache

Using the --dir-cache-time flag, you can set how long a directory should be considered up to date and not refreshed from the backend. Changes made locally in the mount may appear immediately or invalidate the cache. However, changes done on the remote will only be picked up once the cache expires if the backend configured does not support polling for changes. If the backend supports polling, changes will be picked up on within the polling interval.

Alternatively, you can send a SIGHUP signal to rclone for it to flush all directory caches, regardless of how old they are. Assuming only one rclone instance is running, you can reset the cache like this:

kill -SIGHUP $(pidof rclone)

If you configure rclone with a remote control then you can use rclone rc to flush the whole directory cache:

rclone rc vfs/forget

Or individual files or directories:

rclone rc vfs/forget file=path/to/file dir=path/to/dir

File Buffering

The --buffer-size flag determines the amount of memory, that will be used to buffer data in advance.

Each open file descriptor will try to keep the specified amount of data in memory at all times. The buffered data is bound to one file descriptor and won't be shared between multiple open file descriptors of the same file.

This flag is a upper limit for the used memory per file descriptor. The buffer will only use memory for data that is downloaded but not not yet read. If the buffer is empty, only a small amount of memory will be used. The maximum memory used by rclone for buffering can be up to --buffer-size * open files.

File Caching

These flags control the VFS file caching options. The VFS layer is used by rclone mount to make a cloud storage system work more like a normal file system.

You'll need to enable VFS caching if you want, for example, to read and write simultaneously to a file. See below for more details.

Note that the VFS cache works in addition to the cache backend and you may find that you need one or the other or both.

--cache-dir string                   Directory rclone will use for caching.
--vfs-cache-max-age duration         Max age of objects in the cache. (default 1h0m0s)
--vfs-cache-mode string              Cache mode off|minimal|writes|full (default "off")
--vfs-cache-poll-interval duration   Interval to poll the cache for stale objects. (default 1m0s)
--vfs-cache-max-size int             Max total size of objects in the cache. (default off)

If run with -vv rclone will print the location of the file cache. The files are stored in the user cache file area which is OS dependent but can be controlled with --cache-dir or setting the appropriate environment variable.

The cache has 4 different modes selected by --vfs-cache-mode. The higher the cache mode the more compatible rclone becomes at the cost of using disk space.

Note that files are written back to the remote only when they are closed so if rclone is quit or dies with open files then these won't get written back to the remote. However they will still be in the on disk cache.

If using --vfs-cache-max-size note that the cache may exceed this size for two reasons. Firstly because it is only checked every --vfs-cache-poll-interval. Secondly because open files cannot be evicted from the cache.

--vfs-cache-mode off

In this mode the cache will read directly from the remote and write directly to the remote without caching anything on disk.

This will mean some operations are not possible

  • Files can't be opened for both read AND write
  • Files opened for write can't be seeked
  • Existing files opened for write must have O_TRUNC set
  • Files open for read with O_TRUNC will be opened write only
  • Files open for write only will behave as if O_TRUNC was supplied
  • Open modes O_APPEND, O_TRUNC are ignored
  • If an upload fails it can't be retried

--vfs-cache-mode minimal

This is very similar to "off" except that files opened for read AND write will be buffered to disks. This means that files opened for write will be a lot more compatible, but uses the minimal disk space.

These operations are not possible

  • Files opened for write only can't be seeked
  • Existing files opened for write must have O_TRUNC set
  • Files opened for write only will ignore O_APPEND, O_TRUNC
  • If an upload fails it can't be retried

--vfs-cache-mode writes

In this mode files opened for read only are still read directly from the remote, write only and read/write files are buffered to disk first.

This mode should support all normal file system operations.

If an upload fails it will be retried up to --low-level-retries times.

--vfs-cache-mode full

In this mode all reads and writes are buffered to and from disk. When a file is opened for read it will be downloaded in its entirety first.

This may be appropriate for your needs, or you may prefer to look at the cache backend which does a much more sophisticated job of caching, including caching directory hierarchies and chunks of files.

In this mode, unlike the others, when a file is written to the disk, it will be kept on the disk after it is written to the remote. It will be purged on a schedule according to --vfs-cache-max-age.

This mode should support all normal file system operations.

If an upload or download fails it will be retried up to --low-level-retries times.

Case Sensitivity

Linux file systems are case-sensitive: two files can differ only by case, and the exact case must be used when opening a file.

Windows is not like most other operating systems supported by rclone. File systems in modern Windows are case-insensitive but case-preserving: although existing files can be opened using any case, the exact case used to create the file is preserved and available for programs to query. It is not allowed for two files in the same directory to differ only by case.

Usually file systems on macOS are case-insensitive. It is possible to make macOS file systems case-sensitive but that is not the default

The "--vfs-case-insensitive" mount flag controls how rclone handles these two cases. If its value is "false", rclone passes file names to the mounted file system as is. If the flag is "true" (or appears without a value on command line), rclone may perform a "fixup" as explained below.

The user may specify a file name to open/delete/rename/etc with a case different than what is stored on mounted file system. If an argument refers to an existing file with exactly the same name, then the case of the existing file on the disk will be used. However, if a file name with exactly the same name is not found but a name differing only by case exists, rclone will transparently fixup the name. This fixup happens only when an existing file is requested. Case sensitivity of file names created anew by rclone is controlled by an underlying mounted file system.

Note that case sensitivity of the operating system running rclone (the target) may differ from case sensitivity of a file system mounted by rclone (the source). The flag controls whether "fixup" is performed to satisfy the target.

If the flag is not provided on command line, then its default value depends on the operating system where rclone runs: "true" on Windows and macOS, "false" otherwise. If the flag is provided without a value, then it is "true".

Auth Proxy

If you supply the parameter --auth-proxy /path/to/program then rclone will use that program to generate backends on the fly which then are used to authenticate incoming requests. This uses a simple JSON based protocl with input on STDIN and output on STDOUT.

PLEASE NOTE: --auth-proxy and --authorized-keys cannot be used together, if --auth-proxy is set the authorized keys option will be ignored.

There is an example program bin/test_proxy.py in the rclone source code.

The program's job is to take a user and pass on the input and turn those into the config for a backend on STDOUT in JSON format. This config will have any default parameters for the backend added, but it won't use configuration from environment variables or command line options - it is the job of the proxy program to make a complete config.

This config generated must have this extra parameter

  • _root - root to use for the backend

And it may have this parameter

  • _obscure - comma separated strings for parameters to obscure

If password authentication was used by the client, input to the proxy process (on STDIN) would look similar to this:

	"user": "me",
	"pass": "mypassword"

If public-key authentication was used by the client, input to the proxy process (on STDIN) would look similar to this:

	"user": "me",
	"public_key": "AAAAB3NzaC1yc2EAAAADAQABAAABAQDuwESFdAe14hVS6omeyX7edc...JQdf"

And as an example return this on STDOUT

	"type": "sftp",
	"_root": "",
	"_obscure": "pass",
	"user": "me",
	"pass": "mypassword",
	"host": "sftp.example.com"

This would mean that an SFTP backend would be created on the fly for the user and pass/public_key returned in the output to the host given. Note that since _obscure is set to pass, rclone will obscure the pass parameter before creating the backend (which is required for sftp backends).

The program can manipulate the supplied user in any way, for example to make proxy to many different sftp backends, you could make the user be user@example.com and then set the host to example.com in the output and the user to user. For security you'd probably want to restrict the host to a limited list.

Note that an internal cache is keyed on user so only use that for configuration, don't use pass or public_key. This also means that if a user's password or public-key is changed the cache will need to expire (which takes 5 mins) before it takes effect.

This can be used to build general purpose proxies to any kind of backend that rclone supports.

rclone serve sftp remote:path [flags]


      --addr string                            IPaddress:Port or :Port to bind server to. (default "localhost:2022")
      --auth-proxy string                      A program to use to create the backend from the auth.
      --authorized-keys string                 Authorized keys file (default "~/.ssh/authorized_keys")
      --dir-cache-time duration                Time to cache directory entries for. (default 5m0s)
      --dir-perms FileMode                     Directory permissions (default 0777)
      --file-perms FileMode                    File permissions (default 0666)
      --gid uint32                             Override the gid field set by the filesystem. (default 1001)
  -h, --help                                   help for sftp
      --key stringArray                        SSH private host key file (Can be multi-valued, leave blank to auto generate)
      --no-auth                                Allow connections with no authentication if set.
      --no-checksum                            Don't compare checksums on up/download.
      --no-modtime                             Don't read/write the modification time (can speed things up).
      --no-seek                                Don't allow seeking in files.
      --pass string                            Password for authentication.
      --poll-interval duration                 Time to wait between polling for changes. Must be smaller than dir-cache-time. Only on supported remotes. Set to 0 to disable. (default 1m0s)
      --read-only                              Mount read-only.
      --uid uint32                             Override the uid field set by the filesystem. (default 1001)
      --umask int                              Override the permission bits set by the filesystem. (default 2)
      --user string                            User name for authentication.
      --vfs-cache-max-age duration             Max age of objects in the cache. (default 1h0m0s)
      --vfs-cache-max-size SizeSuffix          Max total size of objects in the cache. (default off)
      --vfs-cache-mode CacheMode               Cache mode off|minimal|writes|full (default off)
      --vfs-cache-poll-interval duration       Interval to poll the cache for stale objects. (default 1m0s)
      --vfs-case-insensitive                   If a file name not found, find a case insensitive match.
      --vfs-read-chunk-size SizeSuffix         Read the source objects in chunks. (default 128M)
      --vfs-read-chunk-size-limit SizeSuffix   If greater than --vfs-read-chunk-size, double the chunk size after each chunk read, until the limit is reached. 'off' is unlimited. (default off)
      --vfs-read-wait duration                 Time to wait for in-sequence read before seeking. (default 20ms)
      --vfs-write-wait duration                Time to wait for in-sequence write before giving error. (default 1s)

See the global flags page for global options not listed here.