| Internet-Draft | SSH File Transfer Protocol | July 2025 |
| Nanni, et al. | Expires 2 January 2026 | [Page] |
The SSH File Transfer Protocol provides secure file transfer functionality over any secure and reliable data stream. It is the standard file transfer protocol for use with the SSH2 protocol. This document describes the file transfer protocol and its interface to the SSH2 protocol suite.¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.¶
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.¶
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."¶
This Internet-Draft will expire on 2 January 2026.¶
Copyright (c) 2025 IETF Trust and the persons identified as the document authors. All rights reserved.¶
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶
This protocol provides secure file transfer (and more generally file system access) functionality over a secure and reliable data stream, such as a channel in the SSH2 protocol [RFC4251].¶
This protocol is designed so that it could be used to implement a secure remote file system service, as well as a secure file transfer service.¶
This protocol assumes that it runs over a secure channel, and that the server has already authenticated the user at the client end, and that the identity of the client user is externally available to the server implementation.¶
In general, this protocol follows a simple request-response model. Each request and response contains a sequence number and multiple requests may be pending simultaneously. There are a relatively large number of different request messages, but a small number of possible response messages. Each request has one or more response messages that may be returned in result (e.g., a read either returns data or reports error status).¶
The packet format descriptions in this specification follow the notation presented in [RFC4251].¶
Even though this protocol is described in the context of the SSH2 protocol, this protocol is general and independent of the rest of the SSH2 protocol suite. It could be used in a number of different applications, such as secure file transfer over TLS [RFC8446] and transfer of management information in VPN applications.¶
When used with the SSH2 Protocol suite, this protocol is intended to be used from the SSH Connection Protocol as a subsystem, as described in Section 6.5 of [RFC4254] The subsystem name used with this protocol is "sftp".¶
All packets transmitted over the secure connection are of the following format:¶
uint32 length byte type byte[length - 1] data payload¶
That is, they are just data preceded by 32-bit length and 8-bit type fields.
The length field contains the length of the data area, and does not include the length field itself.
The format and interpretation of the data area depends on the packet type.¶
All packet descriptions below only specify the packet type and the data that goes into the data field.
Thus, they should be prefixed by the length and type fields.¶
The maximum size of a packet is in practice determined by the client (the maximum size of read or write requests that it sends, plus a few bytes of packet overhead). All servers SHOULD support packets of at least 34000 bytes (where the packet size refers to the full length, including the header above). This should allow for reads and writes of at most 32768 bytes.¶
There is no limit on the number of outstanding (non-acknowledged) requests that the client may send to the server. In practice this is limited by the buffering available on the data stream and the queuing performed by the server. If the server's queues are full, it should not read any more data from the stream, and flow control will prevent the client from sending more requests. Note, however, that while there is no restriction on the protocol level, the client's API may provide a limit in order to prevent infinite queuing of outgoing requests at the client.¶
The following values are defined for packet types.¶
#define SSH_FXP_INIT 1 #define SSH_FXP_VERSION 2 #define SSH_FXP_OPEN 3 #define SSH_FXP_CLOSE 4 #define SSH_FXP_READ 5 #define SSH_FXP_WRITE 6 #define SSH_FXP_LSTAT 7 #define SSH_FXP_FSTAT 8 #define SSH_FXP_SETSTAT 9 #define SSH_FXP_FSETSTAT 10 #define SSH_FXP_OPENDIR 11 #define SSH_FXP_READDIR 12 #define SSH_FXP_REMOVE 13 #define SSH_FXP_MKDIR 14 #define SSH_FXP_RMDIR 15 #define SSH_FXP_REALPATH 16 #define SSH_FXP_STAT 17 #define SSH_FXP_RENAME 18 #define SSH_FXP_READLINK 19 #define SSH_FXP_SYMLINK 20 #define SSH_FXP_STATUS 101 #define SSH_FXP_HANDLE 102 #define SSH_FXP_DATA 103 #define SSH_FXP_NAME 104 #define SSH_FXP_ATTRS 105 #define SSH_FXP_EXTENDED 200 #define SSH_FXP_EXTENDED_REPLY 201¶
Additional packet types should only be defined if the protocol version number (see Section 4) is incremented, and their use MUST be negotiated using the version number. However, the SSH_FXP_EXTENDED and SSH_FXP_EXTENDED_REPLY packets can be used to implement vendor-specific extensions. See Section 8 for more details.¶
When the file transfer protocol starts, it first sends a SSH_FXP_INIT (including its version number) packet to the server.
The server responds with a SSH_FXP_VERSION packet, supplying the lowest of its own and the client's version number.
This is the negotiated protocol version number that both parties MUST adhere to.¶
The SSH_FXP_INIT packet (from client to server) has the following data:¶
uint32 version <extension data>¶
The SSH_FXP_VERSION packet (from server to client) has the following data:¶
uint32 version <extension data>¶
The version number of the protocol specified in this document is 3. The version number MUST be incremented for each incompatible revision of this protocol.¶
The extension data in the above packets MAY be empty, or MAY be a sequence of¶
string extension_name string extension_data¶
pairs (both strings MUST always be present if one is, but the extension_data string MAY be of zero length).
If present, these strings indicate extensions to the baseline protocol.
The extension_name field(s) identify the name of the extension.
The name SHOULD be of the form "name@domain", where the domain is the DNS domain name of the organization defining the extension.
Additional names that are not of this format may be defined later by the IETF.
Implementations MUST silently ignore any extensions whose name they do not recognize.¶
File attributes are encoded using the ATTRS compound data type:¶
uint32 flags
uint64 size present only if flag SSH_FILEXFER_ATTR_SIZE
uint32 uid present only if flag SSH_FILEXFER_ATTR_UIDGID
uint32 gid present only if flag SSH_FILEXFER_ATTR_UIDGID
uint32 permissions present only if flag SSH_FILEXFER_ATTR_PERMISSIONS
uint32 atime present only if flag SSH_FILEXFER_ACMODTIME
uint32 mtime present only if flag SSH_FILEXFER_ACMODTIME
uint32 extended_count present only if flag SSH_FILEXFER_ATTR_EXTENDED
string extended_type
string extended_data
... more extended data (extended_type - extended_data pairs),
so that number of pairs equals extended_count
¶
The flags specify which of the fields are present.
Those fields for which the corresponding flag is not set are not included in the packet.¶
The size field specifies the size of the file in bytes.¶
The uid and gid fields contain numeric Unix-like user and group identifiers, respectively.¶
The permissions field contains a bit mask of file permissions as defined by [POSIX].¶
The atime and mtime contain the access and modification times of the files, respectively.
They are represented as seconds from Jan 1, 1970 in UTC.¶
The SSH_FILEXFER_ATTR_EXTENDED flag provides a general extension mechanism for vendor-specific extensions.
If the flag is specified, then the extended_count field is present.
It specifies the number of extended_type-extended_data pairs that follow.
Each of these pairs specifies an extended attribute.
For each of the attributes, the extended_type field SHOULD be a string of the format "name@domain", where "domain" is a valid, registered domain name and "name" identifies the method.
The IETF may later standardize certain names that deviate from this format (e.g., that do not contain the "@" sign).
The interpretation of extended_data depends on the type.
Implementations SHOULD ignore extended data fields that they do not understand.¶
It is a protocol error if a packet with unsupported flags bits is received.¶
The flags bits are defined to have the following values:¶
#define SSH_FILEXFER_ATTR_SIZE 0x00000001 #define SSH_FILEXFER_ATTR_UIDGID 0x00000002 #define SSH_FILEXFER_ATTR_PERMISSIONS 0x00000004 #define SSH_FILEXFER_ATTR_ACMODTIME 0x00000008 #define SSH_FILEXFER_ATTR_EXTENDED 0x80000000¶
The ATTRS type is used when returning file attributes from the server and when sending file attributes to the server.
When sending it to the server, the flags field specifies which attributes are included.
For attributes that are not included the server MUST either use default values or not modify existing values.
When receiving attributes from the server, the flags specify which attributes are included in the returned data.
The server SHOULD return all attributes it knows about.¶
Requests from the client to the server represent the various file system operations.
Each request begins with an id field, which is a 32-bit identifier identifying the request (selected by the client).
The same identifier will be returned in the response to the request.
One possible implementation of it is a monotonically increasing request sequence number (modulo 2^32).¶
Many operations in the protocol operate on open files.
The SSH_FXP_OPEN request can return a file handle (which is an opaque variable-length string) which may be used to access the file later (e.g. in a read operation).
The client MUST NOT send requests to the server with bogus or closed handles.
However, the server MUST perform adequate checks on the handle in order to avoid security risks due to fabricated handles.¶
This design allows either stateful and stateless server implementation, as well as an implementation which caches state between requests but may also flush it. The contents of the file handle string are entirely up to the server and its design. The client MUST NOT modify or attempt to interpret the file handle strings.¶
The file handle strings MUST NOT be longer than 256 bytes.¶
The server MUST process requests relating to the same file in the order in which they are received. In other words, if an application submits multiple requests to the server, the results in the responses will be the same as if it had sent the requests one at a time and waited for the response in each case. For example, the server may process non-overlapping read/write requests to the same file in parallel, but overlapping reads and writes cannot be reordered or parallelized. However, there are no ordering restrictions on the server for processing requests from two different file transfer connections. The server may interleave and parallelize them at will.¶
There are no restrictions on the order in which responses to outstanding requests are delivered to the client, except that the server must ensure fairness. No request will be indefinitely delayed even if the client is sending other requests so that there are multiple outstanding requests all the time.¶
This protocol represents file names as strings. File names are assumed to use the slash ('/') character as a directory separator.¶
File names starting with a slash ('/') are "absolute", and are relative to the root of the file system. Names starting with any other character are relative to the user's default directory (home directory). Note that identifying the user is assumed to take place outside of this protocol.¶
Servers SHOULD interpret a path name component ".." as referring to the parent directory, and "." as referring to the current directory. Care must be taken that clients cannot use ".." to escape file system access limitations set by the server.¶
An empty path name is valid, and it refers to the user's default directory (usually the user's home directory).¶
Clients can splice path name components returned by SSH_FXP_READDIR together using a slash ('/') as the separator.¶
Otherwise, no syntax is defined for file names by this specification.¶
Files are opened and created using the SSH_FXP_OPEN message, whose data part is as follows:¶
uint32 id string filename uint32 pflags ATTRS attrs¶
The id field is the request identifier as for all requests.¶
The filename field specifies the file name.
See Section 6.2 for more information.¶
The pflags field is a bitmask.
The following bits have been defined.¶
#define SSH_FXF_READ 0x00000001 #define SSH_FXF_WRITE 0x00000002 #define SSH_FXF_APPEND 0x00000004 #define SSH_FXF_CREAT 0x00000008 #define SSH_FXF_TRUNC 0x00000010 #define SSH_FXF_EXCL 0x00000020¶
These have the following meanings:¶
SSH_FXF_CREAT MUST also be specified if this flag is used.¶
The attrs field specifies the initial attributes for the file.
Default values will be used for those attributes that are not specified.
See Section 5 for more information.¶
Regardless the server operating system, the file will always be opened in "binary" mode (i.e., no translations between different character sets and newline encodings).
If the operation is successful the server MUST respond with SSH_FXP_HANDLE.
If the operation failed the server MUST respond with SSH_FXP_STATUS.¶
A file is closed by using the SSH_FXP_CLOSE request.
Its data field has the following format:¶
uint32 id string handle¶
where id is the request identifier, and handle is a handle previously returned in the response to SSH_FXP_OPEN or SSH_FXP_OPENDIR.
The handle becomes invalid immediately after this request has been sent.¶
The server MUST respond with a SSH_FXP_STATUS message.
On some server platforms a close can fail.¶
Once a file has been opened, it can be read using the SSH_FXP_READ message, which has the following format:¶
uint32 id string handle uint64 offset uint32 len¶
where id is the request identifier, handle is an open file handle returned by SSH_FXP_OPEN, offset is the offset (in bytes) relative to the beginning of the file from where to start reading, and len is the maximum number of bytes to read.¶
In response to this request, the server MUST read as many bytes as it can from the file (up to len), and return them in a SSH_FXP_DATA message.
If an error occurs or EOF is encountered before reading any data, the server MUST respond with SSH_FXP_STATUS.¶
The client SHOULD then close the handle using the SSH_FXP_CLOSE request when it is done.¶
Writing to a file is achieved using the SSH_FXP_WRITE message, which has the following format:¶
uint32 id string handle uint64 offset string data¶
where id is a request identifier, handle is a file handle returned by SSH_FXP_OPEN, offset is the offset (in bytes) from the beginning of the file where to start writing, and data is the data to be written.¶
The write will extend the file if writing beyond the end of the file. It is legal to write way beyond the end of the file; the semantics are to write zeroes from the end of the file to the specified offset and then the data. On most operating systems, such writes do not allocate disk space but instead leave "holes" in the file.¶
The server MUST respond to a write request with a SSH_FXP_STATUS message.¶
The client SHOULD then close the handle using the SSH_FXP_CLOSE request when it is done.¶
Files can be removed using the SSH_FXP_REMOVE message.
It has the following format:¶
uint32 id string filename¶
where id is the request identifier and filename is the name of the file to be removed.
See Section 6.2 for more information.
This request cannot be used to remove directories.¶
The server MUST respond to this request with a SSH_FXP_STATUS message.¶
Files (and directories) can be renamed using the SSH_FXP_RENAME message.
Its data is as follows:¶
uint32 id string oldpath string newpath¶
where id is the request identifier, oldpath is the name of an existing file or directory, and newpath is the new name for the file or directory.
It is an error if there already exists a file with the name specified by newpath.
The server may also fail rename requests in other situations, for example if oldpath and newpath point to different file systems on the server.¶
The server MUST respond to this request with a SSH_FXP_STATUS message.¶
New directories can be created using the SSH_FXP_MKDIR request.
It has the following format:¶
uint32 id string path ATTRS attrs¶
where id is the request identifier, path and attrs specifies the modifications to be made to its attributes.
See Section 6.2 for more information on file names.
Attributes are discussed in more detail in Section 5.
path specifies the directory to be created.
The server MUST respond to this request with a SSH_FXP_STATUS message.
The server MUST return an error if a file or directory with the specified path already exists.¶
Directories can be removed using the SSH_FXP_RMDIR request, which has the following format:¶
uint32 id string path¶
where id is the request identifier, and path specifies the directory to be removed.
See Section 6.2 for more information on file names.
The server MUST respond to this request with a SSH_FXP_STATUS message.
The server MUST return an error if no directory with the specified path exists, or if the specified directory is not empty, or if the path specified a file system object other than a directory.¶
The files in a directory can be listed using the SSH_FXP_OPENDIR and SSH_FXP_READDIR requests.
Each SSH_FXP_READDIR request returns one or more file names with full file attributes for each file.
The client should call SSH_FXP_READDIR repeatedly until it has found the file it is looking for or until the server responds with a SSH_FXP_STATUS message indicating an error (normally SSH_FX_EOF if there are no more files in the directory).
The client SHOULD then close the handle using the SSH_FXP_CLOSE request.¶
The SSH_FXP_OPENDIR request opens a directory for reading.
It has the following format:¶
uint32 id string path¶
where id is the request identifier and path is the path name of the directory to be listed (without any trailing slash).
See Section 6.2 for more information on file names.
The server MUST respond to this request with either a SSH_FXP_HANDLE or a SSH_FXP_STATUS message.
The server MUST return an error if the path does not specify a directory or if the directory is not readable.¶
Once the directory has been successfully opened, files (and directories) contained in it can be listed using SSH_FXP_READDIR requests.
These are of the following format:¶
uint32 id string handle¶
where id is the request identifier, and handle is a handle returned by SSH_FXP_OPENDIR.
(It is a protocol error to attempt to use an ordinary file handle returned by SSH_FXP_OPEN.)¶
The server MUST respond to this request with either a SSH_FXP_NAME or a SSH_FXP_STATUS message.
One or more names MAY be returned at a time.
Full status information is returned for each name in order to speed up typical directory listings.¶
When the client no longer wishes to read more names from the directory, it SHOULD call SSH_FXP_CLOSE for the handle.
The handle SHOULD be closed regardless of whether an error has occurred or not.¶
Very often, file attributes are automatically returned by SSH_FXP_READDIR.
However, sometimes there is need to specifically retrieve the attributes for a named file.
This can be done using the SSH_FXP_STAT, SSH_FXP_LSTAT and SSH_FXP_FSTAT requests.¶
SSH_FXP_STAT and SSH_FXP_LSTAT only differ in that SSH_FXP_STAT follows symbolic links on the server, whereas SSH_FXP_LSTAT does not follow symbolic links.
Both have the same format:¶
uint32 id string path¶
where id is the request identifier, and path specifies the file system object for which status is to be returned.
The server MUST respond to this request with either SSH_FXP_ATTRS or SSH_FXP_STATUS.¶
SSH_FXP_FSTAT differs from the others in that it returns status information for an open file (identified by the file handle).
Its format is as follows:¶
uint32 id string handle¶
where id is the request identifier and handle is a file handle returned by SSH_FXP_OPEN.
The server MUST respond to this request with SSH_FXP_ATTRS or SSH_FXP_STATUS.¶
File attributes may be modified using the SSH_FXP_SETSTAT and SSH_FXP_FSETSTAT requests.
These requests are used for operations such as changing the ownership, permissions or access times, as well as for truncating a file.¶
The SSH_FXP_SETSTAT request is of the following format:¶
uint32 id string path ATTRS attrs¶
where id is the request identifier, path specifies the file system object (e.g. file or directory) whose attributes are to be modified, and attrs specifies the modifications to be made to its attributes.
Attributes are discussed in more detail in Section 5.¶
The server MUST respond to this request with a SSH_FXP_STATUS message.
The server MUST return an error if the specified file system object does not exist or the user does not have sufficient rights to modify the specified attributes.¶
The SSH_FXP_FSETSTAT request modifies the attributes of a file which is already open.
It has the following format:¶
uint32 id string handle ATTRS attrs¶
where id is the request identifier, handle is a file handle returned by SSH_FXP_OPEN identifying the file whose attributes are to be modified, and attrs specifies the modifications to be made to its attributes.
Attributes are discussed in more detail in Section 5.
The server MUST respond to this request with SSH_FXP_STATUS.
The server MUST return an error if the user does not have sufficient rights to modify the specified attributes.¶
The SSH_FXP_READLINK request may be used to read the target of a symbolic link.
It would have a data part as follows:¶
uint32 id string path¶
where id is the request identifier and path specifies the path name of the symlink to be read.¶
If an error occurs, the server MUST respond with SSH_FXP_STATUS.
Otherwise, the server MUST respond with a SSH_FXP_NAME packet containing only one name and a dummy attributes value.
The name in the returned packet contains the target of the link.¶
The SSH_FXP_SYMLINK request will create a symbolic link on the server.
It is of the following format:¶
uint32 id string linkpath string targetpath¶
where id is the request identifier, linkpath specifies the path name of the symlink to be created and targetpath specifies the target of the symlink.
The server MUST respond with a SSH_FXP_STATUS indicating either success (SSH_FX_OK) or an error condition.¶
The SSH_FXP_REALPATH request can be used to have the server canonicalize any given path name to an absolute path.
This is useful for converting path names containing ".." components or relative pathnames without a leading slash into absolute paths.
The format of the request is as follows:¶
uint32 id string path¶
where id is the request identifier and path specifies the path name to be canonicalized.
If an error occurs, the server MUST respond with SSH_FXP_STATUS.
Otherwise, the server MUST respond with a SSH_FXP_NAME packet containing only one name and a dummy attributes value.
The name in the returned packet MUST be in canonical form.¶
Exactly one response MUST be returned by the server for each request from the client. Each response packet MUST contain a request identifier which MUST be used to match the response with the corresponding request. Note that it is legal to have several requests outstanding simultaneously, and the server MAY send responses for them in a different order from the order in which the requests were sent. The result of their execution, however, MUST be as if they had been processed one at a time in the order in which the requests were sent.¶
Response packets are of the same general format as request packets. Each response packet begins with the request identifier.¶
In case a request fails, the server MUST return a SSH_FXP_STATUS message.
When the operation is successful, the response message type depends on the request.
If no data needs to be returned to the client, the server MUST respond with a SSH_FXP_STATUS message and the status MUST be SSH_FX_OK.
Otherwise, the SSH_FXP_HANDLE message is used to return a file handle for SSH_FXP_OPEN or SSH_FXP_OPENDIR requests, SSH_FXP_DATA is used to return data for SSH_FXP_READ requests, SSH_FXP_NAME is used to return one or more file names for SSH_FXP_READDIR or SSH_FXP_REALPATH requests, and SSH_FXP_ATTRS is used to return file attributes for SSH_FXP_STAT, SSH_FXP_LSTAT, or SSH_FXP_FSTAT requests.¶
The format of the data portion of the SSH_FXP_STATUS response is as follows:¶
uint32 id uint32 error/status code string error message string language tag¶
where id is the request identifier, and error/status code indicates the result of the requested operation.
The value SSH_FX_OK indicates success, and all other values indicate failure.
The error message field contains a UTF-8 [RFC3629] encoded human readable message, and language tag identifies the language [RFC5646] of the message.¶
The following error/status code values are defined:¶
#define SSH_FX_OK 0 #define SSH_FX_EOF 1 #define SSH_FX_NO_SUCH_FILE 2 #define SSH_FX_PERMISSION_DENIED 3 #define SSH_FX_FAILURE 4 #define SSH_FX_BAD_MESSAGE 5 #define SSH_FX_NO_CONNECTION 6 #define SSH_FX_CONNECTION_LOST 7 #define SSH_FX_OP_UNSUPPORTED 8¶
SSH_FX_READ it MUST be returned when no more data is available in the file, and for SSH_FX_READDIR it MUST be returned when no more files are contained in the directory.¶
The SSH_FXP_HANDLE response has the following format:¶
uint32 id string handle¶
where id is the request identifier, and handle is an arbitrary string that identifies an open file or directory on the server.
The handle is opaque to the client; the client MUST NOT attempt to interpret or modify it in any way.
The length of the handle string MUST NOT exceed 256 data bytes.¶
The SSH_FXP_DATA response has the following format:¶
uint32 id string data¶
where id is the request identifier, and data is an arbitrary byte string containing the requested data.
The data string MUST be at most the number of bytes requested in a SSH_FXP_READ request, but MAY also be shorter if end of file is reached or if the read is from something other than a regular file.¶
The SSH_FXP_NAME response has the following format:¶
uint32 id
uint32 count
repeats count times:
string filename
string longname
ATTRS attrs
¶
where id is the request identifier, count is the number of names returned in this response, and the remaining fields repeat count times (so that all three fields are first included for the first file, then for the second file, etc).
In the repeated part, filename is a file name being returned (for SSH_FXP_READDIR, it will be a relative name within the directory, without any path components; for SSH_FXP_REALPATH it will be an absolute path name), longname is an expanded format for the file name, similar to what is returned by ls -l on Unix-like systems, and attrs is the attributes of the file as described in Section 5.¶
The format of the longname field is unspecified by this protocol.
It MUST be suitable for use in the output of a directory listing command (in fact, the recommended operation for a directory listing command is to simply display this data).
However, clients SHOULD NOT attempt to parse the longname field for file attributes; they SHOULD use the attrs field instead.¶
The RECOMMENDED format for the longname field is as follows:¶
-rwxr-xr-x 1 mjos staff 348911 Mar 25 14:29 t-filexfer 1234567890 123 12345678 12345678 12345678 123456789012¶
Here, the first line is sample output, and the second field indicates widths of the various fields. Fields are separated by spaces. The first field lists file permissions for user, group, and others; the second field is link count; the third field is the name of the user who owns the file; the fourth field is the name of the group that owns the file; the fifth field is the size of the file in bytes; the sixth field (which actually may contain spaces, but is fixed to 12 characters) is the file modification time, and the seventh field is the file name. Each field is specified to be a minimum of certain number of character positions (indicated by the second line above), but may also be longer if the data does not fit in the specified length.¶
The SSH_FXP_ATTRS response has the following format:¶
uint32 id ATTRS attrs¶
where id is the request identifier, and attrs is the returned file attributes as described in Section 5.¶
The SSH_FXP_EXTENDED request provides a generic extension mechanism for adding vendor-specific commands.
The request has the following format:¶
uint32 id string extended-request ... any request-specific data ...¶
where id is the request identifier, and extended-request SHOULD be a string of the format "name@domain", where domain is an internet domain name of the vendor defining the request.
The rest of the request is completely vendor-specific, and servers SHOULD only attempt to interpret it if they recognize the extended-request name.¶
The server MAY respond to such requests using any of the response packets defined in Section 7.
The server MAY alternatively respond with a SSH_FXP_EXTENDED_REPLY packet, as defined below.
If the server does not recognize the extended-request name, then the server MUST respond with SSH_FXP_STATUS with error/status set to SSH_FX_OP_UNSUPPORTED.¶
The SSH_FXP_EXTENDED_REPLY packet can be used to carry arbitrary extension-specific data from the server to the client.
It is of the following format:¶
uint32 id ... any request-specific data ...¶
This protocol assumes that it is run over a secure channel and that the endpoints of the channel have been authenticated. Thus, this protocol assumes that it is externally protected from network-level attacks.¶
This protocol provides file system access to arbitrary files on the server (only constrained by the server implementation). It is the responsibility of the server implementation to enforce any access controls that may be required to limit the access allowed for any particular user (the user being authenticated externally to this protocol, typically using the SSH User Authentication Protocol [RFC4252].¶
Care must be taken in the server implementation to check the validity of received file handle strings. The server should not rely on them directly; it MUST check the validity of each handle before relying on it.¶
This document has no IANA actions.¶
The following people authored the 2001 version (draft-ietf-secsh-filexfer-02.txt) of this document.
Rights as specified in RFC 5738 were granted to the IETF Trust in December 2024.¶
Tatu Ylonen Email: ylo@clausal.com Sami Lehtinen EMail: sjl@iki.fi¶
This section is to be removed before publication.¶
The SSH_FXP_SYMLINK in Section 6.10 is specified as¶
uint32 id string linkpath string targetpath¶
The wildly deployed OpenSSH implementation deviates from that¶
https://cvsweb.openbsd.org/cgi-bin/cvsweb/~checkout~/src/usr.bin/ssh/PROTOCOL¶
4.1. sftp: Reversal of arguments to SSH_FXP_SYMLINK When OpenSSH's sftp-server was implemented, the order of the arguments to the SSH_FXP_SYMLINK method was inadvertently reversed. Unfortunately, the reversal was not noticed until the server was widely deployed. Since fixing this to follow the specification would cause incompatibility, the current order was retained. For correct operation, clients should send SSH_FXP_SYMLINK as follows:¶
uint32 id string targetpath string linkpath¶
Should we instead fix the draft? AsyncSSH implements both versions and matches on the client or server version string:¶
https://github.com/ronf/asyncssh/blob/76c14dd0034d33773e2f50f91d167bfd22c3e021/asyncssh/sftp.py#L3182 https://github.com/ronf/asyncssh/blob/76c14dd0034d33773e2f50f91d167bfd22c3e021/asyncssh/sftp.py#L2854¶
SSH_FX_NO_CONNECTION and SSH_FX_CONNECTION_LOST are specified in Section 7.
They are "pseudo-error" codes and MUST NOT be returned by the server.
Can we remove them, they do not serve any purpose.
Or is this too confusing because it creates a gap in the status / error code list?¶
While we have the hood open, do we want to direct the IANA to create a registry for extensions?¶