Secure Shell Working Group J. Galbraith
Internet-Draft VanDyke Software
Expires: April 26, 2005 October 26, 2004
SSH File Transfer Protocol
draft-ietf-secsh-filexfer-06.txt
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Copyright Notice
Copyright (C) The Internet Society (2004).
Abstract
The SSH File Transfer Protocol provides secure file transfer
functionality over any 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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Use with the SSH Connection Protocol . . . . . . . . . . . . . 5
2.1 The Use of 'stderr' in the server . . . . . . . . . . . . 5
3. General Packet Format . . . . . . . . . . . . . . . . . . . . 6
3.1 Request Synchronization and Reordering . . . . . . . . . . 6
3.2 Packet Types . . . . . . . . . . . . . . . . . . . . . . . 7
4. Protocol Initialization . . . . . . . . . . . . . . . . . . . 9
4.1 Client Initialization . . . . . . . . . . . . . . . . . . 9
4.2 Server Initialization . . . . . . . . . . . . . . . . . . 9
4.3 Determining Server Newline Convention . . . . . . . . . . 10
4.4 Supported Features . . . . . . . . . . . . . . . . . . . . 11
4.5 Version re-negotiation . . . . . . . . . . . . . . . . . . 12
5. File Names . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6. File Attributes . . . . . . . . . . . . . . . . . . . . . . . 16
6.1 valid-attribute-flags . . . . . . . . . . . . . . . . . . 16
6.2 Type . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6.3 Size . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6.4 AllocationSize . . . . . . . . . . . . . . . . . . . . . . 18
6.5 Owner and Group . . . . . . . . . . . . . . . . . . . . . 19
6.6 Permissions . . . . . . . . . . . . . . . . . . . . . . . 19
6.7 Times . . . . . . . . . . . . . . . . . . . . . . . . . . 20
6.8 ACL . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
6.9 attrib-bits . . . . . . . . . . . . . . . . . . . . . . . 21
6.10 Text Hint . . . . . . . . . . . . . . . . . . . . . . . . 24
6.11 Mime type . . . . . . . . . . . . . . . . . . . . . . . . 24
6.12 Link Count . . . . . . . . . . . . . . . . . . . . . . . . 24
6.13 Extended Attributes . . . . . . . . . . . . . . . . . . . 24
7. Requests From the Client to the Server . . . . . . . . . . . . 26
7.1 Opening and Closing Files and Directories . . . . . . . . 26
7.1.1 Opening a File . . . . . . . . . . . . . . . . . . . . 26
7.1.2 Opening a Directory . . . . . . . . . . . . . . . . . 30
7.1.3 Closing Handles . . . . . . . . . . . . . . . . . . . 30
7.2 Reading and Writing . . . . . . . . . . . . . . . . . . . 31
7.2.1 Reading Files . . . . . . . . . . . . . . . . . . . . 31
7.2.2 Reading Directories . . . . . . . . . . . . . . . . . 31
7.2.3 Writing Files . . . . . . . . . . . . . . . . . . . . 32
7.3 Removing and Renaming Files . . . . . . . . . . . . . . . 32
7.4 Creating and Deleting Directories . . . . . . . . . . . . 34
7.5 Retrieving File Attributes . . . . . . . . . . . . . . . . 34
7.6 Setting File Attributes . . . . . . . . . . . . . . . . . 35
7.7 Dealing with Symbolic Links . . . . . . . . . . . . . . . 36
7.8 Canonicalizing the Server-Side Path Name . . . . . . . . . 37
7.8.1 Best Practice for Dealing with Paths . . . . . . . . . 37
8. Responses from the Server to the Client . . . . . . . . . . . 39
9. Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . 44
9.1 Checking File Contents . . . . . . . . . . . . . . . . . . 45
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9.2 Querying Available Space . . . . . . . . . . . . . . . . . 46
10. Implementation Considerations . . . . . . . . . . . . . . . 48
11. Security Considerations . . . . . . . . . . . . . . . . . . 49
12. Changes from Previous Protocol Versions . . . . . . . . . . 51
12.1 Changes Between Versions 6 and 5 . . . . . . . . . . . . . 51
12.2 Changes Between Versions 5 and 4 . . . . . . . . . . . . . 51
12.3 Changes Between Versions 4 and 3 . . . . . . . . . . . . . 52
12.4 Changes Between Versions 3 and 2 . . . . . . . . . . . . . 52
12.5 Changes Between Versions 2 and 1 . . . . . . . . . . . . . 52
12.6 Changes Between Versions 1 and 0 . . . . . . . . . . . . . 53
13. Trademark Issues . . . . . . . . . . . . . . . . . . . . . . 54
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 55
14.1 Normative References . . . . . . . . . . . . . . . . . . . . 55
14.2 Informative References . . . . . . . . . . . . . . . . . . . 55
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 56
Intellectual Property and Copyright Statements . . . . . . . . 57
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1. Introduction
This protocol provides secure file transfer (and more generally file
system access.) It 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, such as a
channel in the SSH2 protocol [1]. and that the server has already
authenticated the client, and that the identity of the client user is
available to the protocol.
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 the secsh architecture draft. [1]
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 RFC 2246 [7] and
transfer of management information in VPN applications.
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2. Use with the SSH Connection Protocol
When used with the SSH2 Protocol suite, this protocol is intended to
be used from the SSH Connection Protocol [3] as a subsystem, as
described in section ''Starting a Shell or a Command''. The
subsystem name used with this protocol is "sftp".
2.1 The Use of 'stderr' in the server
This protocol uses stdout and stdin to transmit binary protocol data.
The "session" channel SSH Connection Protocol [3], which is used by
the subsystem, also supports the use of stderr.
Data sent on stderr by the server SHOULD be considered free format
debug or supplemental error information, and MAY be displayed to the
user.
For example, during initialization, there is no client request
active, so errors or warning information cannot be sent to the client
as part of the SFTP protocol at this early stage. However, the
errors or warnings MAY be sent as stderr text.
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3. General Packet Format
All packets transmitted over the secure connection are of the
following format:
uint32 length
byte type
uint32 request-id
... type specific fields...
byte[length] data payload
'length' is the length of the entire packet, excluding the length
field itself, such that, for example, for a packet type containing no
type specific fields, the length field would be 5, and 9 bytes of
data would be sent on the wire. (This is the packet format used in
the secsh transport. [2]
All packet descriptions in this document omit the length field for
brevity; the length field MUST be included in any case.
Each request from the client contains a 'request-id' field. Each
response from the server includes that same 'request-id' from the
request that the server is responding to. One possible
implementation is for the client to us a monotonically increasing
request sequence number (modulo 2^32). There is, however, no
particular requirement the 'request-id' fields be unique.
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.
3.1 Request Synchronization and Reordering
The protocol and implementations 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
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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 in the sense that processing of no
request will be indefinitely delayed even if the client is sending
other requests so that there are multiple outstanding requests all
the time.
A client MUST be prepared to recieve responses to multiple overlapped
requests out of order.
This document defines one data type in addition to those defined in
secsh architecture draft. [1]
int64
Represents a 64-bit signed integer. Stored as eight bytes in the
order of decreasing significance (network byte order).
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.
3.2 Packet Types
The following values are defined for packet types.
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#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
RESERVED_FOR_EXTENSIONS 210-255
Additional packet types should only be defined if the protocol
version number (see Section ''Protocol Initialization'') 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 extensions, which can be vendor
specific. See Section ''Extensions'' for more details.
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4. Protocol Initialization
When the file transfer protocol starts, the client 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. Both parties
should from then on adhere to particular version of the protocol.
The version number of the protocol specified in this document is 6.
The version number should be incremented for each incompatible
revision of this protocol.
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4.1 Client Initialization
The SSH_FXP_INIT packet (from client to server) has the following
data:
uint32 version
Version 3 of this protocol allowed clients to include extensions in
the SSH_FXP_INIT packet; however, this can cause interoperability
problems with version 1 and version 2 servers because the client must
send this packet before knowing the servers version.
In this version of the protocol, clients MUST use the
SSH_FXP_EXTENDED packet to send extensions to the server after
version exchange has completed. Clients MUST NOT include extensions
in the version packet. This will prevent interoperability problems
with older servers
4.2 Server Initialization
The SSH_FXP_VERSION packet (from server to client) has the following
data:
uint32 version
<extension data>
'version' is the lower of the protocol version supported by the
server and the version number received from the client.
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The extension data 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.
4.3 Determining Server Newline Convention
In order to correctly process text files in a cross platform
compatible way, newline sequences must be converted between client
and server conventions.
The SSH_FXF_TEXT file open flag (Section 7.1.1) makes it possible to
request that the server translate a file to a 'canonical' wire
format. This format uses \r\n as the line separator.
Servers for systems using multiple newline characters (for example,
Mac OS X or VMS) or systems using counted records, MUST translate to
the canonical form.
However, to ease the burden of implementation on servers that use a
single, simple separator sequence, the following extension allows the
canonical format to be changed.
string "newline"
string new-canonical-separator (usually "\r" or "\n" or "\r\n")
All clients MUST support this extension.
When processing text files, clients SHOULD NOT translate any
character or sequence that is not an exact match of the server's
newline separator.
In particular, if the newline sequence being used is the canonical
"\r\n" sequence, a lone "\r" or a lone "\n" SHOULD be written through
without change.
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4.4 Supported Features
The sftp protocol has grown to be very rich, and now supports a
number of features that may not be available on all servers.
When a server receives a request for a feature it cannot support, it
MUST return a SSH_FX_OP_UNSUPPORTED status code, unless otherwise
specified. In order to facilitate clients being able to use the
maximum available feature set, and yet not be overly burdened by
dealing with SSH_FX_OP_UNSUPPORTED status codes, the following
extension is introduced.
string "supported"
string supported-structure
uint32 supported-attribute-mask
uint32 supported-attribute-bits
uint32 supported-open-flags
uint32 supported-access-mask
uint32 max-read-size
string extension-names[0..n]
supported-attribute-mask
This mask MAY by applied to the 'File Attributes'
valid-attribute-flags field (Section 6.1) to ensure that no
unsupported attributes are present during a operation which writes
attributes.
supported-attribute-bits
This mask MAY by applied to the 'File Attributes' attrib-bits
field (Section 6.9) to ensure that no unsupported attrib-bits are
present during a operation which writes attributes.
supported-open-flags
The supported-open-flags mask MAY be applied to the SSH_FXP_OPEN
(Section 7.1.1) flags field.
supported-access-mask
The supported-access-mask mask MAY be applied to the SSH_FXP_OPEN
(Section 7.1.1) desired-access field or the ace-mask field of an
ACL.
max-read-size
This is the maximum read size that the server gaurantees to
complete. For example, certain embedded server implementations
only complete the first 4K of a read, even if there is additional
data to be read from the file.
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If the server specifies a non-zero value, it MUST return at least
the max-read-size number of bytes for any read requesting
max-read-size bytes. Failure to return max-read-size bytes in
such a case indicates either EOF or another error condition
occurred.
extension names
The extension names may be empty (contains zero strings), or it
may contain any named extensions that the server wishes to
advertise.
The client must be able to differentiate between attribute
extensions (Section 6.13) and extended requests (Section 9) by the
extension name.
Naturally, if a given attribute field, attribute mask bit, open flag,
or extension is required for correct operation, the client MUST
either not allow the bit to be masked off, or MUST fail the operation
gracefully without sending the request to the server.
The client MAY send requests that are not supported by the server;
however, it is not normally expected to be productive to do so. The
client SHOULD apply the mask even to attrib structures received from
the server. The server MAY include attributes or attrib-bits that
are not included in the mask. Such attributes or attrib-bits are
effectively read-only.
4.5 Version re-negotiation
The version exchange during protocol startup forces an implementation
to support all versions up to it's highest supported version;
however, there have been a number of SFTP protocol versions deployed,
and it is supposed that more implementations will support the final
version of this protocol if they don't have to support all versions
between their currently deployed version and the final version.
Furthermore, only the current version of this protocol is documented,
so supporting earlier versions becomes problematic.
Therefore, the server SHOULD send the following extension as part of
it's INIT packet to inform the client of the versions it supports.
string "versions"
string comma-seperated-versions
'comma-seperated-versions' is a string of comma seperated version
numbers, for example, "3,6,7"
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A client wishing to support two non-continigous version of the
protocol must negotiate the lowest version for which it supports all
previous versions. When the client recieves the servers INIT packet,
if it includes the "versions" extension, it MAY send the following
extended request:
byte SSH_FXP_EXTENDED
uint32 request-id
string "version"
uint32 version-from-list
If the 'version-from-list' is one of the versions on the servers
list, the server MUST respond with SSH_FX_OK. If the server did not
send the "versions" extension, or the version-from-list was not
included, the server MAY send a status response describing the
failure, but MUST then close the channel.
Although this request does take a full round trip, no client need
wait for the response before continuing, because any valid request
MUST succeed.
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5. File Names
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 ".." (Section 11)as
referring to the parent directory, and "." as referring to the
current directory.
An empty path name is valid, and it refers to the user's default
directory (usually the user's home directory).
Otherwise, no syntax is defined for file names by this specification.
Clients should not make any other assumptions; however, they can
splice path name components returned by SSH_FXP_READDIR together
using a slash ('/') as the separator, and that will work as expected.
It is understood that the lack of well-defined semantics for file
names may cause interoperability problems between clients and servers
using radically different operating systems. However, this approach
is known to work acceptably with most systems, and alternative
approaches that e.g. treat file names as sequences of structured
components are quite complicated.
The prefered encoding for filenames is UTF-8. This is consistant
with IETF Policy on Character Sets and Languages [8] and it is
further supposed that the server is more likely to support any local
character set and be able to convert it to UTF-8.
The shortest valid UTF-8 encoding of the UNICODE data MUST be used.
The server is responsible for converting the UNICODE data to whatever
canonical form it requires. For example, if the server requires that
precomposed characters always be used, the server MUST NOT assume the
filename as sent by the client has this attribute, but must do this
normalization itself.
However, because the server does not always know the encoding of
filenames, it is not always possible for the server to preform a
valid translation to UTF-8. When an invalid translation to UTF-8 is
preformed, it becomes impossible to manipulate the file, because the
translation is not reversable. Therefore, the following extensions
are provided in order to make it possible for the server to
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communicate it's abilities to the client, and to allow the client to
control whether the server attempts the conversion.
A server MAY include the following extension with it's version
packet.
string "filename-charset"
string charset-name
A server that can always provide a valid UTF-8 translation for
filenames SHOULD NOT send this extension. Otherwise, the server
SHOULD this extension and include the encoding most likely to be used
for filenames. This value will most likely be derived from the
LC_CTYPE on most unix-like systems.
A server that does not send this extension MUST send all filenames
encoded in UTF-8. All clients MUST support UTF-8 filenames.
If the server included the 'filename-charset' extension with its
VERSION packet, a client MAY send the following extension to turn off
server translation to UTF-8.
string "filename-translation-control"
bool do-translate
If the client does not send this extension, the server MUST continue
to attempt translation to UTF-8. When a client sends this extension,
the server MUST enable or disable filename translation according to
the value of 'do-translate'
The server MUST respond with a STATUS response; if the server sent a
'filename-charset' extension, the status MUST be SUCCESS. Otherwise,
the status MUST be UNSUPPORTED.
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6. File Attributes
A new compound data type is defined for encoding file attributes.
The same encoding is used both when returning file attributes from
the server and when sending file attributes to the server.
uint32 valid-attribute-flags
byte type always present
uint64 size present only if flag SIZE
uint64 allocation-size present only if flag ALLOCATION_SIZE
string owner present only if flag OWNERGROUP
string group present only if flag OWNERGROUP
uint32 permissions present only if flag PERMISSIONS
int64 atime present only if flag ACCESSTIME
uint32 atime_nseconds present only if flag SUBSECOND_TIMES
int64 createtime present only if flag CREATETIME
uint32 createtime_nseconds present only if flag SUBSECOND_TIMES
int64 mtime present only if flag MODIFYTIME
uint32 mtime_nseconds present only if flag SUBSECOND_TIMES
string acl present only if flag ACL
uint32 attrib-bits present only if flag BITS
byte text-hint present only if flag TEXT_HINT
string mime-type present only if flag MIME_TYPE
uint32 link-count present only if flag LINK_COUNT
string untranslated-name present only if flag UNTRANSLATED_NAME
uint32 extended_count present only if flag EXTENDED
string extended_type
string extended_data
... more extended data (extended_type - extended_data pairs),
so that number of pairs equals extended_count
6.1 valid-attribute-flags
The 'valid-attribute-flags' specifies which of the fields are
present. Those fields for which the corresponding flag is not set
are not present (not included in the packet).
The server generally includes all attributes it knows about; however,
it may exclude attributes that are overly expensive to retrieve
unless the client explicitly requests them.
When writing attributes, the server SHOULD NOT modify attributes that
are not present in the structure. However, if necessary, the server
MAY use a default value for an absent attribute.
In general, unless otherwise specified, if a server cannot support
writing an attribute requested, it must fail the setstat operation.
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In this case, none of the attributes SHOULD be changed.
New fields can only be added by incrementing the protocol version
number (or by using the extension mechanism described below).
The following values are defined:
#define SSH_FILEXFER_ATTR_SIZE 0x00000001
#define SSH_FILEXFER_ATTR_PERMISSIONS 0x00000004
#define SSH_FILEXFER_ATTR_ACCESSTIME 0x00000008
#define SSH_FILEXFER_ATTR_CREATETIME 0x00000010
#define SSH_FILEXFER_ATTR_MODIFYTIME 0x00000020
#define SSH_FILEXFER_ATTR_ACL 0x00000040
#define SSH_FILEXFER_ATTR_OWNERGROUP 0x00000080
#define SSH_FILEXFER_ATTR_SUBSECOND_TIMES 0x00000100
#define SSH_FILEXFER_ATTR_BITS 0x00000200
#define SSH_FILEXFER_ATTR_ALLOCATION_SIZE 0x00000400
#define SSH_FILEXFER_ATTR_TEXT_HINT 0x00000800
#define SSH_FILEXFER_ATTR_MIME_TYPE 0x00001000
#define SSH_FILEXFER_ATTR_LINK_COUNT 0x00002000
#define SSH_FILEXFER_ATTR_UNTRANLATED_NAME 0x00004000
#define SSH_FILEXFER_ATTR_EXTENDED 0x80000000
0x00000002 was used in a previous version of this protocol. It is
now a reserved value and MUST NOT appear in the mask. Some future
version of this protocol may reuse this value.
6.2 Type
The type field is always present. The following types are defined:
#define SSH_FILEXFER_TYPE_REGULAR 1
#define SSH_FILEXFER_TYPE_DIRECTORY 2
#define SSH_FILEXFER_TYPE_SYMLINK 3
#define SSH_FILEXFER_TYPE_SPECIAL 4
#define SSH_FILEXFER_TYPE_UNKNOWN 5
#define SSH_FILEXFER_TYPE_SOCKET 6
#define SSH_FILEXFER_TYPE_CHAR_DEVICE 7
#define SSH_FILEXFER_TYPE_BLOCK_DEVICE 8
#define SSH_FILEXFER_TYPE_FIFO 9
On a POSIX system, these values would be derived from the mode field
of the stat structure. SPECIAL should be used for files that are of
a known type which cannot be expressed in the protocol. UNKNOWN
should be used if the type is not known.
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6.3 Size
The 'size' field specifies the number of bytes that can be read from
the file, or in other words, the location of the end-of-file. If it
is present during file creation, the file MUST be created and then
the EOF set to 'size'. A read from such a file SHOULD return nul
bytes, but this is not required if the underlying filesystem has
different characteristics.
If this field is present during a setstat operation, the file MUST be
extended or truncated to the specified size. Clients SHOULD
therefore be careful specifying size during a setstat operation.
Files opened with the SSH_FXF_TEXT flag may have a size that is
greater or less than the value of the size field.
6.4 AllocationSize
The 'allocation-size' field specifies the number of bytes that the
file consumes on disk. This is normally greater than or equal to the
'size' field. If it is present during file creation, it should be
treated as a hint as to the eventual file size. The server MAY
choose to preallocate the disk space to save the overhead of repeated
extends. However, the file size MUST NOT be set to this value. In
other words, a read from such a file MUST fail with an EOF error.
(Unless 'size' was also set.)
If the server is unable to honor this hint during create, the create
should succeed regardless. Because this field is a hint, the field
may be specified even if the server doesn't set the bit in it's
supported-attribute-mask.
If this field is present during a setstat operation, the file SHOULD
be extended or truncated to the specified size. Clients SHOULD
therefore be careful specifying size during a setstat operation.
If the file is extended by this operation, 'size' MUST not be
affected. If the file is truncated by this operation, 'size' will be
changed ot match the new file allocation.
If a server can not honor the setstat operation, it MUST NOT set
allocation-size in it's supported-attribute-mask, though it MAY still
send the allocation-size data if it can retrieve it. In addition,
such a server MUST fail a setstat operaiton that has the
allocation-size field present.
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6.5 Owner and Group
The 'owner' and 'group' fields are represented as UTF-8 strings; this
is the form used by NFS v4. See NFS version 4 Protocol [4]. The
following text is selected quotations from section 5.6.
To avoid a representation that is tied to a particular underlying
implementation at the client or server, the use of UTF-8 strings has
been chosen. The string should be of the form user@dns_domain".
This will allow for a client and server that do not use the same
local representation the ability to translate to a common syntax that
can be interpreted by both. In the case where there is no
translation available to the client or server, the attribute value
must be constructed without the "@". Therefore, the absence of the @
from the owner or owner_group attribute signifies that no translation
was available and the receiver of the attribute should not place any
special meaning with the attribute value. Even though the attribute
value cannot be translated, it may still be useful. In the case of a
client, the attribute string may be used for local display of
ownership.
user@localhost represents a user in the context of the server.
If either the owner or group field is zero length, the field should
be considered absent, and no change should be made to that specific
field.
6.6 Permissions
The 'permissions' field contains a bit mask specifying file
permissions. These permissions correspond to the st_mode field of
the stat structure defined by POSIX [5].
This protocol uses the following values for the symbols declared in
the posix standard.
#define S_IRUSR 0000400 (octal)
#define S_IWUSR 0000200
#define S_IXUSR 0000100
#define S_IRGRP 0000040
#define S_IWGRP 0000020
#define S_IXGRP 0000010
#define S_IROTH 0000004
#define S_IWOTH 0000002
#define S_IXOTH 0000001
#define S_ISUID 0004000
#define S_ISGID 0002000
#define S_ISVTX 0001000
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Implementations MUST NOT send bits that are not defined.
6.7 Times
The 'atime', 'createtime', and 'mtime' contain the accesses,
creation, and modification times of the files, respectively. They
are represented as seconds from Jan 1, 1970 in UTC.
A negative value indicates number of seconds before Jan 1, 1970. In
both cases, if the SSH_FILEXFER_ATTR_SUBSECOND_TIMES flag is set, the
nseconds field is to be added to the seconds field for the final time
representation. For example, if the time to be represented is
one-half second before 0 hour January 1, 1970, the seconds field
would have a value of negative one (-1) and the nseconds fields would
have a value of one-half second (500000000). Values greater than
999,999,999 for nseconds are considered invalid.
6.8 ACL
The 'ACL' field contains an ACL similar to that defined in section
5.9 of NFS version 4 Protocol [4].
uint32 ace-count
repeated ace-count time:
uint32 ace-type
uint32 ace-flag
uint32 ace-mask
string who [UTF-8]
ace-type is one of the following four values (taken from NFS Version
4 Protocol [4]:
#define ACE4_ACCESS_ALLOWED_ACE_TYPE 0x00000000;
#define ACE4_ACCESS_DENIED_ACE_TYPE 0x00000001;
#define ACE4_SYSTEM_AUDIT_ACE_TYPE 0x00000002;
#define ACE4_SYSTEM_ALARM_ACE_TYPE 0x00000003;
ace-flag is a combination of the following flag values. See NFS
Version 4 Protocol [4] section 5.9.2:
#define ACE4_FILE_INHERIT_ACE 0x00000001;
#define ACE4_DIRECTORY_INHERIT_ACE 0x00000002;
#define ACE4_NO_PROPAGATE_INHERIT_ACE 0x00000004;
#define ACE4_INHERIT_ONLY_ACE 0x00000008;
#define ACE4_SUCCESSFUL_ACCESS_ACE_FLAG 0x00000010;
#define ACE4_FAILED_ACCESS_ACE_FLAG 0x00000020;
#define ACE4_IDENTIFIER_GROUP 0x00000040;
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ace-mask is any combination of the following flags (taken from NFS
Version 4 Protocol [4] section 5.9.3:
#define ACE4_READ_DATA 0x00000001;
#define ACE4_LIST_DIRECTORY 0x00000001;
#define ACE4_WRITE_DATA 0x00000002;
#define ACE4_ADD_FILE 0x00000002;
#define ACE4_APPEND_DATA 0x00000004;
#define ACE4_ADD_SUBDIRECTORY 0x00000004;
#define ACE4_READ_NAMED_ATTRS 0x00000008;
#define ACE4_WRITE_NAMED_ATTRS 0x00000010;
#define ACE4_EXECUTE 0x00000020;
#define ACE4_DELETE_CHILD 0x00000040;
#define ACE4_READ_ATTRIBUTES 0x00000080;
#define ACE4_WRITE_ATTRIBUTES 0x00000100;
#define ACE4_DELETE 0x00010000;
#define ACE4_READ_ACL 0x00020000;
#define ACE4_WRITE_ACL 0x00040000;
#define ACE4_WRITE_OWNER 0x00080000;
#define ACE4_SYNCHRONIZE 0x00100000;
who is a UTF-8 string of the form described in 'Owner and Group'
(Section 6.5)
Also, as per '5.9.4 ACE who' [4] there are several identifiers that
need to be understood universally. Some of these identifiers cannot
be understood when an client access the server, but have meaning when
a local process accesses the file. The ability to display and modify
these permissions is permitted over SFTP.
OWNER The owner of the file.
GROUP The group associated with the file.
EVERYONE The world.
INTERACTIVE Accessed from an interactive terminal.
NETWORK Accessed via the network.
DIALUP Accessed as a dialup user to the server.
BATCH Accessed from a batch job.
ANONYMOUS Accessed without any authentication.
AUTHENTICATED Any authenticated user (opposite of ANONYMOUS).
SERVICE Access from a system service.
To avoid conflict, these special identifiers are distinguish by an
appended "@". For example: ANONYMOUS@.
6.9 attrib-bits
These bits reflect various attributes of the file or directory on the
server.
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The following attrib-bits are defined:
#define SSH_FILEXFER_ATTR_FLAGS_READONLY 0x00000001
#define SSH_FILEXFER_ATTR_FLAGS_SYSTEM 0x00000002
#define SSH_FILEXFER_ATTR_FLAGS_HIDDEN 0x00000004
#define SSH_FILEXFER_ATTR_FLAGS_CASE_INSENSITIVE 0x00000008
#define SSH_FILEXFER_ATTR_FLAGS_ARCHIVE 0x00000010
#define SSH_FILEXFER_ATTR_FLAGS_ENCRYPTED 0x00000020
#define SSH_FILEXFER_ATTR_FLAGS_COMPRESSED 0x00000040
#define SSH_FILEXFER_ATTR_FLAGS_SPARSE 0x00000080
#define SSH_FILEXFER_ATTR_FLAGS_APPEND_ONLY 0x00000100
#define SSH_FILEXFER_ATTR_FLAGS_IMMUTABLE 0x00000200
#define SSH_FILEXFER_ATTR_FLAGS_SYNC 0x00000400
#define SSH_FILEXFER_ATTR_FLAGS_TRANSLATION_ERR 0x00000800
SSH_FILEXFER_ATTR_FLAGS_READONLY
Advisory, read-only bit. This bit is not part of the access
control information on the file, but is rather an advisory field
indicating that the file should not be written.
SSH_FILEXFER_ATTR_FLAGS_SYSTEM
The file is part of operating system.
SSH_FILEXFER_ATTR_FLAGS_HIDDEN
File SHOULD NOT be shown to user unless specifically requested.
For example, most UNIX systems SHOULD set this bit if the filename
begins with a 'period'. This bit may be read-only (Section 4.4).
Most UNIX systems will not allow this to be changed.
SSH_FILEXFER_ATTR_FLAGS_CASE_INSENSITIVE
This attribute can only apply to directories. This attribute is
always read-only, and cannot be modified. This attribute means
that files and directory names in this directory should be
compared without regard to case.
It is recommended that where possible, the server's filesystem be
allowed to do comparisons. For example, if a client wished to
prompt a user before overwriting a file, it should not compare the
new name with the previously retrieved list of names in the
directory. Rather, it should first try to create the new file by
specifying SSH_FXF_CREATE_NEW flag. Then, if this fails and
returns SSH_FX_FILE_ALREADY_EXISTS, it should prompt the user and
then retry the create specifying SSH_FXF_CREATE_TRUNCATE.
Unless otherwise specified, filenames are assumed to be case
sensitive.
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SSH_FILEXFER_ATTR_FLAGS_ARCHIVE
The file should be included in backup / archive operations.
SSH_FILEXFER_ATTR_FLAGS_ENCRYPTED
The file is stored on disk using file-system level transparent
encryption. This flag does not affect the file data on the wire
(for either READ or WRITE requests.)
SSH_FILEXFER_ATTR_FLAGS_COMPRESSED
The file is stored on disk using file-system level transparent
compression. This flag does not affect the file data on the wire.
SSH_FILEXFER_ATTR_FLAGS_SPARSE
The file is a sparse file; this means that file blocks that have
not been explicitly written are not stored on disk. For example,
if a client writes a buffer at 10 M from the beginning of the
file, the blocks between the previous EOF marker and the 10 M
offset would not consume physical disk space.
Some server may store all files as sparse files, in which case
this bit will be unconditionally set. Other servers may not have
a mechanism for determining if the file is sparse, and so the file
MAY be stored sparse even if this flag is not set.
SSH_FILEXFER_ATTR_FLAGS_APPEND_ONLY
The file can only be opened for writing in append mode.
SSH_FILEXFER_ATTR_FLAGS_IMMUTABLE
The file cannot be deleted or renamed, no hard link can be created
to this file and no data can be written to the file.
This bit implies a stronger level of protection than
SSH_FILEXFER_ATTR_FLAGS_READONLY, the file permission mask or
ACLs. Typically even the superuser cannot write to immutable
files, and only the superuser can set or remove the bit.
SSH_FILEXFER_ATTR_FLAGS_SYNC
When the file is modified, the changes are written synchronously
to the disk.
SSH_FILEXFER_ATTR_FLAGS_TRANSLATION_ERR
The server MAY include this bit in a directory listing or realpath
response. It indicates there was a failure in the translation to
UTF-8. If this flag is included, the server SHOULD also include
the UNTRANSLATED_NAME attribute.
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6.10 Text Hint
The value is one of the following enumerations, and indicates what
the server knows about the content of the file.
#define SSH_FILEXFER_ATTR_KNOWN_TEXT 0x01
#define SSH_FILEXFER_ATTR_GUESSED_TEXT 0x01
#define SSH_FILEXFER_ATTR_KNOWN_BINARY 0x01
#define SSH_FILEXFER_ATTR_GUESSED_BINARY 0x01
SSH_FILEXFER_ATTR_KNOWN_TEXT
The server knows the file is a text file, and should be opened
using the SSH_FXF_ACCESS_TEXT_MODE flag.
SSH_FILEXFER_ATTR_GUESSED_TEXT
The server has applied a hueristic or other mechanism and believes
that the file should be opened with the SSH_FXF_ACCESS_TEXT_MODE
flag.
SSH_FILEXFER_ATTR_KNOWN_BINARY
The server knows the file has binary content.
SSH_FILEXFER_ATTR_GUESSED_BINARY
The server has applied a hueristic or other mechanism and believes
has binary content, and should not be opened with the
SSH_FXF_ACCESS_TEXT_MODE flag.
This flag MUST NOT be present during a setstat operation. If this
flag is present during an fsetstat operation, the file handle is
converted to a text-mode handle, as if it had been opened with
SSH_FXF_ACCESS_TEXT_MODE.
6.11 Mime type
The 'mime-type' field contains the mime-type [9] string. Most
servers will not know this information and should not set the bit in
their supported-attribute-mask.
6.12 Link Count
The 'link-count' field contains the hard link count of the file.
This attribute MUST NOT be present during a setstat operation.
6.13 Extended Attributes
The SSH_FILEXFER_ATTR_EXTENDED flag provides a general extension
mechanism for the attrib structure. If the flag is specified, then
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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.
Additional fields can be added to the attributes by either defining
additional bits to the flags field to indicate their presence, or by
defining extended attributes for them. The extended attributes
mechanism is recommended for most purposes; additional flags bits
should only be defined by an IETF standards action that also
increments the protocol version number. The use of such new fields
MUST be negotiated by the version number in the protocol exchange.
It is a protocol error if a packet with unsupported protocol bits is
received.
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7. Requests From the Client to the Server
Requests from the client to the server represent the various file
system operations.
7.1 Opening and Closing Files and Directories
Many operations in the protocol operate on open files. The
SSH_FXP_OPEN and SSH_FXP_OPENDIR requests return a handle (which is
an opaque, variable-length string) which may be used to access the
file or directory later. 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 should not modify or attempt to interpret the file handle
strings.
The file handle strings MUST NOT be longer than 256 bytes.
7.1.1 Opening a File
Files are opened and created using the SSH_FXP_OPEN message:
byte SSH_FXP_OPEN
uint32 request-id
string filename [UTF-8]
uint32 desired-access
uint32 flags
ATTRS attrs
The response to this message will be either SSH_FXP_HANDLE (if the
operation is successful) or SSH_FXP_STATUS (if the operation fails).
The 'request-id' field is the request identifier as for all requests.
The 'filename' field specifies the file name. See Section ''File
Names'' for more information.
The 'desired-access' field is a bitmask containing a combination of
values from the ace-mask flags from section 5.7.
The 'flags' field controls various aspects of the operation,
including whether or not the file is created and the kind of locking
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desired.
The following 'flags' are defined:
SSH_FXF_ACCESS_DISPOSITION = 0x00000007
SSH_FXF_CREATE_NEW = 0x00000000
SSH_FXF_CREATE_TRUNCATE = 0x00000001
SSH_FXF_OPEN_EXISTING = 0x00000002
SSH_FXF_OPEN_OR_CREATE = 0x00000003
SSH_FXF_TRUNCATE_EXISTING = 0x00000004
SSH_FXF_ACCESS_APPEND_DATA = 0x00000008
SSH_FXF_ACCESS_APPEND_DATA_ATOMIC = 0x00000010
SSH_FXF_ACCESS_TEXT_MODE = 0x00000020
SSH_FXF_ACCESS_READ_LOCK = 0x00000040
SSH_FXF_ACCESS_WRITE_LOCK = 0x00000080
SSH_FXF_ACCESS_DELETE_LOCK = 0x00000100
SSH_FXF_NOFOLLOW = 0x00000200
SSH_FXF_ACCESS_DISPOSITION
Disposition is a 3 bit field that controls how the file is opened.
The server MUST support these bits. Any one of the following
enumeration is allowed:
SSH_FXF_CREATE_NEW
A new file is created; if the file already exists, the server
MUST return status SSH_FX_FILE_ALREADY_EXISTS.
SSH_FXF_CREATE_TRUNCATE
A new file is created; if the file already exists, it is
truncated.
SSH_FXF_OPEN_EXISTING
An existing file is opened. If the file does not exist, the
server MUST return SSH_FX_NO_SUCH_FILE. If a directory in the
path does not exist, the server SHOULD return
SSH_FX_NO_SUCH_PATH. It is also acceptable if the server
returns SSH_FX_NO_SUCH_FILE in this case.
SSH_FXF_OPEN_OR_CREATE
If the file exists, it is opened. If the file does not exist,
it is created.
SSH_FXF_TRUNCATE_EXISTING
An existing file is opened and truncated. If the file does not
exist, the server MUST return the same error codes as defined
for SSH_FXF_OPEN_EXISTING.
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SSH_FXF_ACCESS_APPEND_DATA
Data is always written at the end of the file. The offset field
of the SSH_FXP_WRITE requests are ignored.
Data is not required to be appended atomically. This means that
if multiple writers attempt to append data simultaneously, data
from the first may be lost. However, data MAY be appended
atomically.
SSH_FXF_ACCESS_APPEND_DATA_ATOMIC
Data is always written at the end of the file. The offset field
of the SSH_FXP_WRITE requests are ignored.
Data MUST be written atomically so that there is no chance that
multiple appenders can collide and result in data being lost.
If both append flags are specified, the server SHOULD use atomic
append if it is available, but SHOULD use non-atomic appends
otherwise. The server SHOULD NOT fail the request in this case.
SSH_FXF_TEXT
Indicates that the server should treat the file as text and
convert it to the canonical newline convention in use. (See
Determining Server Newline Convention. (Section 4.3)
When a file is opened with the FXF_TEXT flag, the offset field in
both the read and write function are ignored.
Servers MUST correctly process multiple, parallel reads and writes
correctly in this mode. Naturally, it is permissible for them to
do this by serializing the requests.
Clients SHOULD use the SSH_FXF_ACCESS_APPEND_DATA flag to append
data to a text file rather then using write with a calculated
offset.
To support seeks on text files the following SSH_FXP_EXTENDED
packet is defined.
string "text-seek"
string file-handle
uint64 line-number
line-number is the index of the line number to seek to, where byte
0 in the file is line number 0, and the byte directly following
the first newline sequence in the file is line number 1 and so on.
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The response to a "text-seek" request is an SSH_FXP_STATUS
message.
An attempt to seek past the end-of-file should result in a
SSH_FX_EOF status.
Servers SHOULD support at least one "text-seek" in order to
support resume. However, a client MUST be prepared to receive
SSH_FX_OP_UNSUPPORTED when attempting a "text-seek" operation.
The client can then try a fall-back strategy, if it has one.
Clients MUST be prepared to handle SSH_FX_OP_UNSUPPORTED returned
for read or write operations that are not sequential.
SSH_FXF_ACCESS_READ_LOCK
The file should be opened with a read lock. The server MUST
gaurantee that the client will be the exclusive reader of the file
until the client closes the handle. If there is a conflicting
lock the server MUST return SSH_FX_LOCK_CONFlICT. If the server
cannot make the locking gaurantee, it MUST return
SSH_FX_OP_UNSUPPORTED.
SSH_FXF_ACCESS_WRITE_LOCK
The file should be opened with a write lock. The server MUST
gaurantee that the client will be the exclusive writer of the file
until the client closes the handle.
SSH_FXF_ACCESS_DELETE_LOCK
The file should be opened with a delete lock. The server MUST
gaurantee that the file will not be deleted until the client
closes the handle.
SSH_FXF_NOFOLLOW
If the final component of the path is a symlink, then the open
MUST fail, and the error SSH_FX_LINK_LOOP MUST be returned.
The 'attrs' field specifies the initial attributes for the file.
Default values MUST be supplied by the server for those attributes
that are not specified. See Section ''File Attributes'' for more
information.
The 'attrs' field is ignored if an exiting file is opened.
The following table is provided to assist in mapping posix semantics
to equivalent SFTP file open parameters:
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O_RDONLY
desired-access = READ_DATA|READ_ATTRIBUTES
O_WRONLY
desired-access = WRITE_DATA|WRITE_ATTRIBUTES
O_RDWR
desired-access =
READ_DATA|READ_ATTRIBUTES|WRITE_DATA|WRITE_ATTRIBUTES
O_APPEND
desired-access = WRITE_DATA|WRITE_ATTRIBUTES|APPEND_DATA
flags = SSH_FXF_ACCESS_APPEND_DATA and or
SSH_FXF_ACCESS_APPEND_DATA_ATOMIC
O_CREAT
flags = SSH_FXF_OPEN_OR_CREATE
O_TRUNC
flags = SSH_FXF_TRUNCATE_EXISTING
O_TRUNC|O_CREATE
flags = SSH_FXF_CREATE_TRUNCATE
7.1.2 Opening a Directory
To enumerate a directory, the client first obtains a handle and then
issues directory read requests. When enumeration is complete, the
handle MUST be closed.
byte SSH_FXP_OPENDIR
uint32 request-id
string path [UTF-8]
'request-id' is the request identifier.
'path' is the path name of the directory to be listed (without any
trailing slash). See Section 'File Names' for more information on
file names.
The response to this message will be either SSH_FXP_HANDLE (if the
operation is successful) or SSH_FXP_STATUS (if the operation fails).
7.1.3 Closing Handles
A handle is closed using the following request.
byte SSH_FXP_CLOSE
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uint32 request-id
string handle
'request-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 response to this request will be a SSH_FXP_STATUS message. Note
that on some server platforms even a close can fail. For example, if
the server operating system caches writes, and an error occurs while
flushing cached writes, the close operation may fail.
7.2 Reading and Writing
7.2.1 Reading Files
The following request can be used to read file data:
byte SSH_FXP_READ
uint32 request-id
string handle
uint64 offset
uint32 length
where 'request-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 'length' is the maximum number of bytes to read.
In response to this request, the server will read as many bytes as it
can from the file (up to 'length'), and return them in a SSH_FXP_DATA
message. If an error occurs or EOF is encountered before reading any
data, the server will respond with SSH_FXP_STATUS.
For normal disk files, it is normally guaranteed that this will read
the specified number of bytes, or up to end of file. However, if the
read length is very long, the server may truncate it if it doesn't
support packets of that length. See General Packet Format (Section
3).
7.2.2 Reading Directories
In order to retrieve a directory listing, the client issues one or
more SSH_FXP_READDIR requests. In order to obtain a complete
directory listing, the client MUST issue repeated SSH_FXP_READDIR
requests until the server responds with an SSH_FXP_STATUS message.
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byte SSH_FXP_READDIR
uint32 request-id
string handle
where 'request-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 responds 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.
If there are no more names available to be read, the server MUST
respond with a SSH_FXP_STATUS message with error code of SSH_FX_EOF.
7.2.3 Writing Files
Writing to a file is achieved using the following message:
byte SSH_FXP_WRITE
uint32 request-id
string handle
uint64 offset
string data
where 'request-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 to an offset that extends 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 create a sparse
file.
The server responds to a write request with a SSH_FXP_STATUS message.
7.3 Removing and Renaming Files
The following request can be used to remove a file:
byte SSH_FXP_REMOVE
uint32 request-id
string filename [UTF-8]
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where 'request-id' is the request identifier and 'filename' is the
name of the file to be removed. See Section ''File Names'' for more
information. This request cannot be used to remove directories.
The server will respond to this request with a SSH_FXP_STATUS
message.
Files (and directories) can be renamed using the SSH_FXP_RENAME
message.
byte SSH_FXP_RENAME
uint32 request-id
string oldpath [UTF-8]
string newpath [UTF-8]
uint32 flags
where 'request-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.
'flags' is 0 or a combination of:
SSH_FXP_RENAME_OVERWRITE 0x00000001
SSH_FXP_RENAME_ATOMIC 0x00000002
SSH_FXP_RENAME_NATIVE 0x00000004
If flags does not include SSH_FXP_RENAME_OVERWRITE, and there already
exists a file with the name specified by newpath, the server MUST
respond with SSH_FX_FILE_ALREADY_EXISTS.
If flags includes SSH_FXP_RENAME_ATOMIC, and the destination file
already exists, it is replaced in an atomic fashion. I.e., there is
no observable instant in time where the name does not refer to either
the old or the new file. SSH_FXP_RENAME_ATOMIC implies
SSH_FXP_RENAME_OVERWRITE.
If flags includes SSH_FXP_RENAME_ATOMIC and the server cannot replace
the destination in an atomic fashion, then the server MUST respond
with SSH_FX_OP_UNSUPPORTED.
Because some servers cannot provide atomic rename, clients should
only specify atomic rename if correct operation requires it. If
SSH_FXP_RENAME_OVERWRITE is specified, the server MAY perform an
atomic rename even if it is not requested.
If flags includes SSH_FXP_RENAME_NATIVE, the server is free to do the
rename operation in whatever fashion it deems appropriate. Other
flag values are considered hints as to desired behavior, but not
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requirements.
The server will respond to this request with a SSH_FXP_STATUS
message.
7.4 Creating and Deleting Directories
New directories can be created using the SSH_FXP_MKDIR request. It
has the following format:
byte SSH_FXP_MKDIR
uint32 request-id
string path [UTF-8]
ATTRS attrs
where 'request-id' is the request identifier.
'path' specifies the directory to be created. See Section ''File
Names'' for more information on file names.
'attrs' specifies the attributes that should be applied to it upon
creation. Attributes are discussed in more detail in Section ''File
Attributes''.
The server will respond to this request with a SSH_FXP_STATUS
message. If a file or directory with the specified path already
exists, an error will be returned.
Directories can be removed using the SSH_FXP_RMDIR request, which has
the following format:
byte SSH_FXP_RMDIR
uint32 request-id
string path [UTF-8]
where 'request-id' is the request identifier, and 'path' specifies
the directory to be removed. See Section ''File Names'' for more
information on file names.
The server responds to this request with a SSH_FXP_STATUS message.
7.5 Retrieving File Attributes
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.
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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:
byte SSH_FXP_STAT or SSH_FXP_LSTAT
uint32 request-id
string path [UTF-8]
uint32 flags
where 'request-id' is the request identifier, and 'path' specifies
the file system object for which status is to be returned. The
server responds to this request with either SSH_FXP_ATTRS or
SSH_FXP_STATUS.
The flags field specify the attribute flags in which the client has
particular interest. This is a hint to the server. For example,
because retrieving owner / group and acl information can be an
expensive operation under some operating systems, the server may
choose not to retrieve this information unless the client expresses a
specific interest in it.
The client has no guarantee the server will provide all the fields
that it has expressed an interest in.
SSH_FXP_FSTAT differs from the others in that it returns status
information for an open file (identified by the file handle).
byte SSH_FXP_FSTAT
uint32 request-id
string handle
uint32 flags
where 'request-id' is the request identifier and 'handle' is a file
handle returned by SSH_FXP_OPEN. The server responds to this request
with SSH_FXP_ATTRS or SSH_FXP_STATUS.
7.6 Setting File Attributes
File attributes may be modified using the SSH_FXP_SETSTAT and
SSH_FXP_FSETSTAT requests.
byte SSH_FXP_SETSTAT
uint32 request-id
string path [UTF-8]
ATTRS attrs
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byte SSH_FXP_FSETSTAT
uint32 request-id
string handle
ATTRS attrs
request-id
The request identifier to be returned as part of the response.
path
The file system object (e.g. file or directory) whose attributes
are to be modified. If this object does not exist, or the user
does not have sufficient access to write the attributes, the
request MUST fail.
handle
The handle is a handle previously returned from a SSH_FXP_OPEN
request which identifies the file whose attributes are to be
modified. If the handle was not opened with sufficient access to
write the requested attributes, the request MUST fail.
attrs
Specifies the modified attributes to be applied. Attributes are
discussed in more detail in Section ''File Attributes''.
The server will respond with a SSH_FXP_STATUS message.
Because some systems must use separate system calls to set various
attributes, it is possible that a failure response will be returned,
but yet some of the attributes may be have been successfully
modified. If possible, servers SHOULD avoid this situation; however,
client MUST be aware that this is possible.
7.7 Dealing with Symbolic Links
The SSH_FXP_READLINK request reads the target of a symbolic link.
byte SSH_FXP_READLINK
uint32 request-id
string path [UTF-8]
where 'request-id' is the request identifier and 'path' specifies the
path name of the symlink to be read.
The server will 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. If an error occurs, the
server MAY respond with SSH_FXP_STATUS.
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The SSH_FXP_SYMLINK request creates a symbolic link on the server.
byte SSH_FXP_SYMLINK
uint32 request-id
string linkpath [UTF-8]
string targetpath [UTF-8]
where 'request-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 shall respond with a
SSH_FXP_STATUS.
7.8 Canonicalizing the Server-Side Path Name
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:
byte SSH_FXP_REALPATH
uint32 request-id
string path [UTF-8]
where 'request-id' is the request identifier and 'path' specifies the
path name to be canonicalized. The server will respond with a
SSH_FXP_NAME packet containing the name in canonical form and a dummy
attributes value. If an error occurs, the server may also respond
with SSH_FXP_STATUS.
The server SHOULD fail the request if the path is not present on the
server.
7.8.1 Best Practice for Dealing with Paths
The client SHOULD treat the results of SSH_FXP_REALPATH as a
canonical absolute path, even if the path does not appear to be
absolute. A client that use REALPATH(".") and treats the result as
absolute, even if there is no leading slash, will continue to
function correctly, even when talking to a Windows NT or VMS style
system, where absolute paths may not begin with a slash.
For example, if the client wishes to change directory up, and the
server has returned "c:/x/y/z" from REALPATH, the client SHOULD use
"c:/x/y/z/..".
As a second example, if the client wishes to open the file "x.txt" in
the current directory, and server has returned "dka100:/x/y/z" as the
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canonical path of the directory, the client SHOULD open
"dka100:/x/y/z/x.txt"
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8. Responses from the Server to the Client
The server responds to the client using one of a few response
packets. All requests can return a SSH_FXP_STATUS response upon
failure. When the operation is successful, and no data needs to be
returned, the SSH_FXP_STATUS response with SSH_FX_OK status is
appropriate.
Exactly one response will be returned for each request. Each
response packet contains a request identifier which can be used to
match each response with the corresponding request. Note that it is
legal to have several requests outstanding simultaneously, and the
server is allowed to send responses to them in a different order from
the order in which the requests were sent (the result of their
execution, however, is guaranteed to 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.
The format of the data portion of the SSH_FXP_STATUS response is as
follows:
byte SSH_FXP_STATUS
uint32 request-id
uint32 error/status code
string error message (ISO-10646 UTF-8 [RFC-2279])
string language tag (as defined in [RFC-1766])
<error-specific data>
request-id
The 'request-id' specified by the client in the request the server
is responding to.
error/status code
Machine readable status code indicating the result of the request.
Error code values are defined below. The value SSH_FX_OK
indicates success, and all other values indicate failure.
error message
Human readable description of the error. 'language tag' specifies
the language the error is in.
<error-specific data>
The error-specific data may be empty, or may contain additional
information about the error. For error codes that send
error-specific data, the format of the data is defined below.
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Error codes:
#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
#define SSH_FX_INVALID_HANDLE 9
#define SSH_FX_NO_SUCH_PATH 10
#define SSH_FX_FILE_ALREADY_EXISTS 11
#define SSH_FX_WRITE_PROTECT 12
#define SSH_FX_NO_MEDIA 13
#define SSH_FX_NO_SPACE_ON_FILESYSTEM 14
#define SSH_FX_QUOTA_EXCEEDED 15
#define SSH_FX_UNKNOWN_PRINCIPLE 16
#define SSH_FX_LOCK_CONFlICT 17
#define SSH_FX_DIR_NOT_EMPTY 18
#define SSH_FX_NOT_A_DIRECTORY 19
#define SSH_FX_INVALID_FILENAME 20
#define SSH_FX_LINK_LOOP 21
SSH_FX_OK
Indicates successful completion of the operation.
SSH_FX_EOF
An attempt to read past the end-of-file was made; or, there are no
more directory entries to return.
SSH_FX_NO_SUCH_FILE
A reference was made to a file which does not exist.
SSH_FX_PERMISSION_DENIED
The user does not have sufficient permissions to perform the
operation.
SSH_FX_FAILURE
An error occured, but no specific error code exists to describe
the failure.
This error message SHOULD always have meaningful text in the the
'error message' field.
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SSH_FX_BAD_MESSAGE
A badly formatted packet or other SFTP protocol incompatibility
was detected.
SSH_FX_NO_CONNECTION
There is no connection to the server. This error can only be
generated locally, and MUST NOT be return by a server.
SSH_FX_CONNECTION_LOST
The connection to the server was lost. This error can only be
generated locally, and MUST NOT be return by a server.
SSH_FX_OP_UNSUPPORTED
An attempted operation could not be completed by the server
because the server does not support the operation.
This error MAY be generated locally by the client if e.g. the
version number exchange indicates that a required feature is not
supported by the server, or it may be returned by the server if
the server does not implement an operation).
SSH_FX_INVALID_HANDLE
The handle value was invalid.
SSH_FX_NO_SUCH_PATH
The file path does not exist or is invalid.
SSH_FX_FILE_ALREADY_EXISTS
The file already exists.
SSH_FX_WRITE_PROTECT
The file is on read-only media, or the media is write protected.
SSH_FX_NO_MEDIA
The requested operation cannot be completed because there is no
media available in the drive.
SSH_FX_NO_SPACE_ON_FILESYSTEM
The requested operation cannot be completed because there is no
free space on the filesystem.
SSH_FX_QUOTA_EXCEEDED
The operation cannot be completed because the it would exceed the
users storage quota.
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SSH_FX_UNKNOWN_PRINCIPLE
A principle referenced by the request (either the 'owner',
'group', or 'who' field of an ACL), was unknown. The error
specific data contains the problematic names. The format is one
or more:
string unknown-name
Each string contains the name of a principle that was unknown.
SSH_FX_LOCK_CONFLICT
The file could not be opened because it is locked by another
process.
SSH_FX_DIR_NOT_EMPTY
The directory is not empty.
SSH_FX_NOT_A_DIRECTORY
The specified file is not a directory.
SSH_FX_INVALID_FILENAME
The filename is not valid.
SSH_FX_LINK_LOOP
Too many symbolic links encountered.
The SSH_FXP_HANDLE response has the following format:
byte SSH_FXP_HANDLE
uint32 request-id
string handle
where 'request-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:
byte SSH_FXP_DATA
uint32 request-id
string data
where 'request-id' is the request identifier, and 'data' is an
arbitrary byte string containing the requested data. The data string
may 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
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read is from something other than a regular file.
The SSH_FXP_NAME response has the following format:
byte SSH_FXP_NAME
uint32 request-id
uint32 count
repeats count times:
string filename [UTF-8]
ATTRS attrs
where 'request-id' is the request identifier, 'count' is the number
of names returned in this response, and the remaining fields repeat
'count' times. 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), and 'attrs' is the attributes of the file
as described in Section ''File Attributes''.
The SSH_FXP_ATTRS response has the following format:
byte SSH_FXP_ATTRS
uint32 request-id
ATTRS attrs
where 'request-id' is the request identifier, and 'attrs' is the
returned file attributes as described in Section ''File Attributes''.
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9. Extensions
The SSH_FXP_EXTENDED request provides a generic extension mechanism
for adding additional commands.
byte SSH_FXP_EXTENDED
uint32 request-id
string extended-request
... any request-specific data ...
request-id
Identifier to be returned from the server with the response.
extended-request
A string naming the extension. Vendor-specific extensions have
use the "name@domain" syntax, where domain is an internet domain
name of the vendor defining the request.
The IETF may also define extensions to the protocol. These
extension names will not have an '@' in them.
request-specific data
The rest of the request is defined by the extension, 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 ''Responses from the Server to the
Client''. Additionally, the server may also 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:
byte SSH_FXP_EXTENDED_REPLY
uint32 request-id
... any request-specific data ...
There is a range of packet types reserved for use by extensions. In
order to avoid collision, extensions that that use additional packet
types should determine those numbers dynamically.
The suggested way of doing this is have an extension request from the
client to the server that enables the extension; the extension
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response from the server to the client would specify the actual type
values to use, in additional to any other data.
Extension authors should be mindful of the limited range of packet
types available (there are only 45 values available) and avoid
requiring a new packet type where possible.
9.1 Checking File Contents
This extension allows a client to easily check if a file (or portion
thereof) that it already has matches what is on the server.
byte SSH_FXP_EXTENDED
uint32 request-id
string "md5-hash" / "md5-hash-handle"
string filename / file-handle
uint64 start-offset
uint64 length
string quick-check-hash
filename
Used if "md5-hash" is specified; indicates the name of the file to
use. The has will be of the file contents as it would appear on
the wire if the file were opened with no special flags.
file-handle
Used if "md5-hash-handle" is specified; specifies a file handle to
read the data from. The handle MUST be a file handle, and
ACE4_READ_DATA MUST have been included in the desired-access when
the file was opened.
If this file handle was opened in TEXT mode, the md5-hash must be
made of the data as it would be sent on the wire.
start-offset
The starting offset of the data to hash.
length
The length of data to include in the hash. If both start-offset
and length are zero, the entire file should be included.
quick-check-hash
The hash over the first 2048 bytes of the data range as the client
knows it, or the entire range, if it is less than 2048 bytes.
This allows the server to quickly check if it is worth the
resources to hash a big file.
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If this is a zero length string, the client does not have the
data, and is requesting the hash for reasons other than comparing
with a local file. The server MAY return SSH_FX_OP_UNSUPPORTED in
this case.
The response is either a SSH_FXP_STATUS packet, indicating an error,
or the following extended reply packet:
byte SSH_FXP_EXTENDED_REPLY
uint32 request-id
string "md5-hash"
string hash
If 'hash' is zero length, then the 'quick-check-hash' did not match,
and no hash operation was preformed. Otherwise, 'hash' contains the
hash of the entire data range (including the first 2048 bytes that
were included in the 'quick-check-hash'.)
9.2 Querying Available Space
The following extension provides a way to discover the available
space for an arbitrary path.
byte SSH_FXP_EXTENDED
uint32 request-id
string "space-available"
string path [UTF-8]
path
'path' for which the available space should be reported. This
'path' is not required to be the mount point path, but MAY be a
directory or file contained within the mount.
byte SSH_FXP_EXTENDED_REPLY
uint32 request-id
uint64 total-space-on-device
uint64 unused-on-device
uint64 total-space-available-to-user
uint64 unused-space-available-to-user
total-space-on-device
The total amount of storage space on the device which stores
'path', both used and unused, or 0 if unknown.
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unused-space-on-device
The total amount of unused storage availabe on the device which
stores 'path', or 0 if unknown.
total-space-available-to-user
The total amount of storage space, both used and unused, available
to the authenticated user on the device which stores 'path', or 0
if unknown.
unused-space-on-device
The total amount of unused storage available to the authenticated
user on the device which stores 'path', or 0 if unknown.
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10. Implementation Considerations
In order for this protocol to perform well, especially over high
latency networks, multiple read and write requests should be queued
to the server.
The data size of requests should match the maximum packet size for
the next layer up in the protocol chain.
When implemented over ssh, the best performance should be achieved
when the data size matches the channels max packet, and the channel
window is a multiple of the channel packet size.
Implementations MUST be aware that requests do not have to be
satisfied in the order issued. (See Request Synchronization and
Reordering (Section 3.1).)
Implemenations MUST also be aware that read requests may not return
all the requested data, even if the data is available.
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11. Security Considerations
It is assumed that both ends of the connection have been
authenticated and that the connection has privacy and integrity
features. Such security issues are left to the underlying transport
protocol, except to note that if this is not the case, an attacker
could manipulate files on the server at will and thus wholly
compromise the server.
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 [6].
Extreme care must be used when interpreting file handle strings. In
particular, care must be taken that a file handle string is valid in
the context of a given SFTP session. For example, the sftp server
daemon may have files which it has opened for its own purposes, and
the client must not be able to access these files by specifying an
arbitrary file handle string.
The permission field of the attrib structure (Section 6.6) may
include the SUID, SGID, and SVTX (sticky) bits. Clients should use
extreme caution when setting these bits on either remote or local
files. (I.e., just because a file was SUID on the remote system does
not necessarily imply that it should be SUID on the local system.)
Filesystems often contain entries for objects that are not files at
all, but are rather devices. For example, it may be possible to
access serial ports, tape devices, or named pipes using this
protocol. Servers should exercise caution when granting access to
such resources. In addition to the dangers inherent in allowing
access to such a device, some devices may be 'slow', and could cause
denial of service by causing the server to block for a long period of
time while I/O is performed to such a device.
Servers should take care that file-system quotas are respected for
users. In addition, implementations should be aware that attacks may
be possible, or facilitated, by filling a filesystem. For example,
filling the filesystem where event logging and auditing occurs may,
at best, cause the system to crash, or at worst, allow the attacker
to take untraceable actions in the future.
Servers should take care that filenames are in their appropriate
canonical form, and to insure that filenames not in canonical form
cannot be used to bypass access checks or controls.
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If the server implementation limits access to certain parts of the
file system, extra care must be taken in parsing file names which
contain the '..' path element, and when following symbolic links,
shortcuts, or other filesystem objects which might transpose the path
to refer to an object outside of the restricted area. There have
been numerous reported security bugs where a ".." in a path name has
allowed access outside the intended area.
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12. Changes from Previous Protocol Versions
The SSH File Transfer Protocol has changed over time, before its
standardization. The following is a description of the incompatible
changes between different versions.
12.1 Changes Between Versions 6 and 5
********************* DO NOT IMPLEMENT ***********************
********************* DO NOT IMPLEMENT ***********************
***** *****
***** There will be more edits after IETF 61. *****
***** *****
********************* DO NOT IMPLEMENT ***********************
********************* DO NOT IMPLEMENT ***********************
o Add ability to negotiate version when client supports discontigous
ranges of protocol version.
o Add 'filename-charset' and the 'filename-translation-control'
extensions to allow better support of servers that can't reliably
translate to UTF-8.
o Add DIR_NOT_EMPTY, NOT_A_DIRECTORY, INVALID_FILENAME and LINK_LOOP
error codes.
o Added space-available extension.
o Added NOFOLLOW flag to open flags.
o Added allocation-size, text-hint, link-count, mime-type, and
untranslated-name fields to attrib structure. Add
ATTR_FLAGS_TRANSLATION_ERR to the attrib-bits.
12.2 Changes Between Versions 5 and 4
Many of the changes between version 5 and version 4 are to better
support the changes in version 4, and to better specify error
conditions.
o Add "supported" extension to communicate features supported.
o Clarify error handling when client requests unsupported feature.
(For example, attempts to write an unsupported attribute.)
o Add attrib-bits field to the attribute structure, which specifies
a number of boolean attributes related to files and directories,
including advisory read-only and case-sensitivity bits.
o Clarify the actual bit values to be used for the permissions field
(since posix doesn't define values) and correct the value of
ATTR_PERMISSIONS flag.
o Some reordering of sections to attempt to get a better grouping of
related functionality.
o Open request explicitly specifies the access desired for the file.
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o Add support for explicitly requesting file locking.
o Add support for better control of the rename operation.
o Add SSH_FX_NO_SPACE_ON_FILESYSTEM, SSH_FX_QUOTA_EXCEEDED, and
SSH_FX_UNKNOWN_PRINCIPLE error codes.
o Add support for error specific data. This is used by a new
SSH_FX_UNKNOWN_PRINCIPLE error to communicate which principles are
unknown.
o Add support for retrieving md5-hash of file contents.
o Update security section.
12.3 Changes Between Versions 4 and 3
Many of the changes between version 4 and version 3 are to the
attribute structure to make it more flexible for non-unix platforms.
o Clarify the use of stderr by the server.
o Clarify handling of very large read requests by the server.
o Make all filenames UTF-8.
o Added 'newline' extension.
o Made time fields 64 bit, and optionally have nanosecond
resolution.
o Made file attribute owner and group strings so they can actually
be used on disparate systems.
o Added createtime field, and added separate flags for atime,
createtime, and mtime so they can be set separately.
o Split the file type out of the permissions field and into its own
field (which is always present.)
o Added acl attribute.
o Added SSH_FXF_TEXT file open flag.
o Added flags field to the get stat commands so that the client can
specifically request information the server might not normally
included for performance reasons.
o Removed the long filename from the names structure-- it can now be
built from information available in the attrs structure.
o Added reserved range of packet numbers for extensions.
o Added several additional error codes.
12.4 Changes Between Versions 3 and 2
o The SSH_FXP_READLINK and SSH_FXP_SYMLINK messages were added.
o The SSH_FXP_EXTENDED and SSH_FXP_EXTENDED_REPLY messages were
added.
o The SSH_FXP_STATUS message was changed to include fields 'error
message' and 'language tag'.
12.5 Changes Between Versions 2 and 1
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o The SSH_FXP_RENAME message was added.
12.6 Changes Between Versions 1 and 0
o Implementation changes, no actual protocol changes.
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13. Trademark Issues
"ssh" is a registered trademark of SSH Communications Security Corp
in the United States and/or other countries.
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14. References
14.1 Normative References
[1] Ylonen, T. and C. Lonvick, "SSH Protocol Architecture",
draft-ietf-secsh-architecture-16 (work in progress), June 2004.
[2] Ylonen, T. and C. Lonvick, "SSH Transport Layer Protocol",
draft-ietf-secsh-transport-18 (work in progress), June 2004.
[3] Ylonen, T., Kivinen, T., Rinne, T. and S. Lehtinen, "SSH
Connection Protocol", draft-ietf-secsh-connect-19 (work in
progress), June 2004.
[4] Shepler, S., Callaghan, B., Robinson, D., Thurlow, R., Beame,
C., Eisler, M. and D. Noveck, "NFS version 4 Protocol", RFC
3010, December 2000.
[5] Institute of Electrical and Electronics Engineers, "Information
Technology - Portable Operating System Interface (POSIX) - Part
1: System Application Program Interface (API) [C Language]",
IEEE Standard 1003.2, 1996.
14.2 Informative References
[6] Ylonen, T. and C. Lonvick, "SSH Authentication Protocol",
draft-ietf-secsh-userauth-21 (work in progress), June 2004.
[7] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC
2246, January 1999.
[8] Alvestrand, H., "IETF Policy on Character Sets and Languages",
BCP 18, RFC 2277, January 1998.
[9] Borenstein, N. and N. Freed, "MIME (Multipurpose Internet Mail
Extensions) Part One: Mechanisms for Specifying and Describing
the Format of Internet Message Bodies", RFC 1521, September
1993.
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Author's Address
Joseph Galbraith
VanDyke Software
4848 Tramway Ridge Blvd
Suite 101
Albuquerque, NM 87111
US
Phone: +1 505 332 5700
EMail: galb-list@vandyke.com
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