SSH

Reference Manual

Version 4.8.1

Table of Contents

ssh_sftp

Module

ssh_sftp

Module Summary

SFTP client.

Description

This module implements an SSH FTP (SFTP) client. SFTP is a secure, encrypted file transfer service available for SSH.

Data Types

sftp_option() =
    {timeout, timeout()} |
    {sftp_vsn, integer() >= 1} |
    {window_size, integer() >= 1} |
    {packet_size, integer() >= 1}

Error cause

reason() = atom() | string() | tuple()

A description of the reason why an operation failed.

The atom() value is formed from the sftp error codes in the protocol-level responses as defined in draft-ietf-secsh-filexfer-13 section 9.1. The codes are named as SSH_FX_* which are transformed into lowercase of the star-part. E.g. the error code SSH_FX_NO_SUCH_FILE will cause the reason() to be no_such_file.

The string() reason is the error information from the server in case of an exit-signal. If that information is empty, the reason is the exit signal name.

The tuple() reason are other errors like for example {exit_status,1}.

Crypto operations for open_tar

Specifies the encryption or decryption applied to tar files when using open_tar/3 or open_tar/4.

The encryption or decryption is applied to the generated stream of bytes prior to sending the resulting stream to the SFTP server.

For code examples see Section Example with encryption in the ssh Users Guide.

init_fun() =
    fun(() -> {ok, crypto_state()}) |
    fun(() -> {ok, crypto_state(), chunk_size()})

chunk_size() = undefined | integer() >= 1
crypto_state() = any()

The init_fun() in the tar_crypto_spec is applied once prior to any other crypto operation. The intention is that this function initiates the encryption or decryption for example by calling crypto:crypto_init/4 or similar. The crypto_state() is the state such a function may return.

If the selected cipher needs to have the input data partioned into blocks of a certain size, the init_fun() should return the second form of return value with the chunk_size() set to the block size. If the chunk_size() is undefined, the size of the PlainBins varies, because this is intended for stream crypto, whereas a fixed chunk_size() is intended for block crypto. A chunk_size() can be changed in the return from the crypto_fun(). The value can be changed between pos_integer() and undefined.

crypto_fun() =
    fun((TextIn :: binary(), crypto_state()) -> crypto_result())

crypto_result() =
    {ok, TextOut :: binary(), crypto_state()} |
    {ok, TextOut :: binary(), crypto_state(), chunk_size()}

The initial crypto_state() returned from the init_fun() is folded into repeated applications of the crypto_fun() in the tar_crypto_spec. The binary returned from that fun is sent to the remote SFTP server and the new crypto_state() is used in the next call of the crypto_fun().

If the crypto_fun() reurns a chunk_size(), that value is as block size for further blocks in calls to crypto_fun().

final_fun() =
    fun((FinalTextIn :: binary(), crypto_state()) ->
            {ok, FinalTextOut :: binary()})

If doing encryption, the final_fun() in the tar_crypto_spec is applied to the last piece of data. The final_fun() is responsible for padding (if needed) and encryption of that last piece.

Exports

apread(ChannelPid, Handle, Position, Len) -> {async, N} | Error

Types

ChannelPid = pid()
Handle = term()
Position = Len = integer()
Error = {error, reason()}
N = term()

The apread/4 function reads from a specified position, combining the position/3 and aread/3 functions.

apwrite(ChannelPid, Handle, Position, Data) -> {async, N} | Error

Types

ChannelPid = pid()
Handle = term()
Position = integer()
Data = binary()
Error = {error, reason()}
N = term()

The apwrite/4 function writes to a specified position, combining the position/3 and awrite/3 functions.

aread(ChannelPid, Handle, Len) -> {async, N} | Error

Types

ChannelPid = pid()
Handle = term()
Len = integer()
Error = {error, reason()}
N = term()

Reads from an open file, without waiting for the result. If the handle is valid, the function returns {async, N}, where N is a term guaranteed to be unique between calls of aread. The actual data is sent as a message to the calling process. This message has the form {async_reply, N, Result}, where Result is the result from the read, either {ok, Data}, eof, or {error, reason()}.

awrite(ChannelPid, Handle, Data) -> {async, N} | Error

Types

ChannelPid = pid()
Handle = term()
Data = binary()
Error = {error, reason()}
N = term()

Writes to an open file, without waiting for the result. If the handle is valid, the function returns {async, N}, where N is a term guaranteed to be unique between calls of awrite. The result of the write operation is sent as a message to the calling process. This message has the form {async_reply, N, Result}, where Result is the result from the write, either ok, or {error, reason()}.

close(ChannelPid, Handle) -> ok | Error
close(ChannelPid, Handle, Timeout) -> ok | Error

Types

ChannelPid = pid()
Handle = term()
Timeout = timeout()
Error = {error, reason()}

Closes a handle to an open file or directory on the server.

delete(ChannelPid, Name) -> ok | Error
delete(ChannelPid, Name, Timeout) -> ok | Error

Types

ChannelPid = pid()
Name = string()
Timeout = timeout()
Error = {error, reason()}

Deletes the file specified by Name.

del_dir(ChannelPid, Name) -> ok | Error
del_dir(ChannelPid, Name, Timeout) -> ok | Error

Types

ChannelPid = pid()
Name = string()
Timeout = timeout()
Error = {error, reason()}

Deletes a directory specified by Name. The directory must be empty before it can be successfully deleted.

list_dir(ChannelPid, Path) -> {ok, FileNames} | Error
list_dir(ChannelPid, Path, Timeout) -> {ok, FileNames} | Error

Types

ChannelPid = pid()
Path = string()
Timeout = timeout()
FileNames = [FileName]
FileName = string()
Error = {error, reason()}

Lists the given directory on the server, returning the filenames as a list of strings.

make_dir(ChannelPid, Name) -> ok | Error
make_dir(ChannelPid, Name, Timeout) -> ok | Error

Types

ChannelPid = pid()
Name = string()
Timeout = timeout()
Error = {error, reason()}

Creates a directory specified by Name. Name must be a full path to a new directory. The directory can only be created in an existing directory.

make_symlink(ChannelPid, Name, Target) -> ok | Error
make_symlink(ChannelPid, Name, Target, Timeout) -> ok | Error

Types

ChannelPid = pid()
Name = Target = string()
Timeout = timeout()
Error = {error, reason()}

Creates a symbolic link pointing to Target with the name Name.

open(ChannelPid, Name, Mode) -> {ok, Handle} | Error
open(ChannelPid, Name, Mode, Timeout) -> {ok, Handle} | Error

Types

ChannelPid = pid()
Name = string()
Mode = [read | write | append | binary | raw]
Timeout = timeout()
Handle = term()
Error = {error, reason()}

Opens a file on the server and returns a handle, which can be used for reading or writing.

opendir(ChannelPid, Path) -> {ok, Handle} | Error
opendir(ChannelPid, Path, Timeout) -> {ok, Handle} | Error

Types

ChannelPid = pid()
Path = string()
Timeout = timeout()
Handle = term()
Error = {error, reason()}

Opens a handle to a directory on the server. The handle can be used for reading directory contents.

open_tar(ChannelPid, Path, Mode) -> {ok, Handle} | Error
OTP 17.4
open_tar(ChannelPid, Path, Mode, Timeout) -> {ok, Handle} | Error
OTP 17.4

Types

ChannelPid = pid()
Path = string()
Mode = [read | write | {crypto, tar_crypto_spec()}]
Timeout = timeout()
Handle = term()
Error = {error, reason()}

Opens a handle to a tar file on the server, associated with ChannelPid. The handle can be used for remote tar creation and extraction. The actual writing and reading is performed by calls to erl_tar:add/3,4 and erl_tar:extract/2. Note: The erl_tar:init/3 function should not be called, that one is called by this open_tar function.

For code examples see Section SFTP Client with TAR Compression in the ssh Users Guide.

The crypto mode option is explained in the data types section above, see Crypto operations for open_tar. Encryption is assumed if the Mode contains write, and decryption if the Mode contains read.

position(ChannelPid, Handle, Location) ->
            {ok, NewPosition} | Error
position(ChannelPid, Handle, Location, Timeout) ->
            {ok, NewPosition} | Error

Types

ChannelPid = pid()
Handle = term()
Location =
    Offset |
    {bof, Offset} |
    {cur, Offset} |
    {eof, Offset} |
    bof | cur | eof
Timeout = timeout()
Offset = NewPosition = integer()
Error = {error, reason()}

Sets the file position of the file referenced by Handle. Returns {ok, NewPosition} (as an absolute offset) if successful, otherwise {error, reason()}. Location is one of the following:

Offset

The same as {bof, Offset}.

{bof, Offset}

Absolute offset.

{cur, Offset}

Offset from the current position.

{eof, Offset}

Offset from the end of file.

bof | cur | eof

The same as eariler with Offset 0, that is, {bof, 0} | {cur, 0} | {eof, 0}.

pread(ChannelPid, Handle, Position, Len) ->
         {ok, Data} | eof | Error
pread(ChannelPid, Handle, Position, Len, Timeout) ->
         {ok, Data} | eof | Error

Types

ChannelPid = pid()
Handle = term()
Position = Len = integer()
Timeout = timeout()
Data = string() | binary()
Error = {error, reason()}

The pread/3,4 function reads from a specified position, combining the position/3 and read/3,4 functions.

pwrite(ChannelPid, Handle, Position, Data) -> ok | Error
pwrite(ChannelPid, Handle, Position, Data, Timeout) -> ok | Error

Types

ChannelPid = pid()
Handle = term()
Position = integer()
Data = iolist()
Timeout = timeout()
Error = {error, reason()}

The pwrite/3,4 function writes to a specified position, combining the position/3 and write/3,4 functions.

read(ChannelPid, Handle, Len) -> {ok, Data} | eof | Error
read(ChannelPid, Handle, Len, Timeout) -> {ok, Data} | eof | Error

Types

ChannelPid = pid()
Handle = term()
Len = integer()
Timeout = timeout()
Data = string() | binary()
Error = {error, reason()}

Reads Len bytes from the file referenced by Handle. Returns {ok, Data}, eof, or {error, reason()}. If the file is opened with binary, Data is a binary, otherwise it is a string.

If the file is read past eof, only the remaining bytes are read and returned. If no bytes are read, eof is returned.

read_file(ChannelPid, File) -> {ok, Data} | Error
read_file(ChannelPid, File, Timeout) -> {ok, Data} | Error

Types

ChannelPid = pid()
File = string()
Data = binary()
Timeout = timeout()
Error = {error, reason()}

Reads a file from the server, and returns the data in a binary.

read_file_info(ChannelPid, Name) -> {ok, FileInfo} | Error
read_file_info(ChannelPid, Name, Timeout) ->
                  {ok, FileInfo} | Error

Types

ChannelPid = pid()
Name = string()
Timeout = timeout()
FileInfo = file:file_info()
Error = {error, reason()}

Returns a file_info record from the file system object specified by Name or Handle. See file:read_file_info/2 for information about the record.

Depending on the underlying OS:es links might be followed and info on the final file, directory etc is returned. See read_link_info/2 on how to get information on links instead.

read_link(ChannelPid, Name) -> {ok, Target} | Error
read_link(ChannelPid, Name, Timeout) -> {ok, Target} | Error

Types

ChannelPid = pid()
Name = Target = string()
Timeout = timeout()
Error = {error, reason()}

Reads the link target from the symbolic link specified by name.

read_link_info(ChannelPid, Name) -> {ok, FileInfo} | Error
read_link_info(ChannelPid, Name, Timeout) ->
                  {ok, FileInfo} | Error

Types

ChannelPid = pid()
Name = string()
FileInfo = file:file_info()
Timeout = timeout()
Error = {error, reason()}

Returns a file_info record from the symbolic link specified by Name or Handle. See file:read_link_info/2 for information about the record.

rename(ChannelPid, OldName, NewName) -> ok | Error
rename(ChannelPid, OldName, NewName, Timeout) -> ok | Error

Types

ChannelPid = pid()
OldName = NewName = string()
Timeout = timeout()
Error = {error, reason()}

Renames a file named OldName and gives it the name NewName.

Types

Host = ssh:host()
TcpSocket = ssh:open_socket()
SftpOptions = [ sftp_option() ]
ChannelPid = pid()
ConnectionRef = ssh:connection_ref()
Error = {error, reason()}

If no connection reference is provided, a connection is set up, and the new connection is returned. An SSH channel process is started to handle the communication with the SFTP server. The returned pid for this process is to be used as input to all other API functions in this module.

Options:

{timeout, timeout()}

There are two ways to set a timeout for the underlying ssh connection:

  • If the connection timeout option connect_timeout is set, that value is used also for the negotiation timeout and this option (timeout) is ignored.
  • Otherwise, this option (timeout) is used as the negotiation timeout only and there is no connection timeout set

The value defaults to infinity.

{sftp_vsn, integer()}

Desired SFTP protocol version. The actual version is the minimum of the desired version and the maximum supported versions by the SFTP server.

All other options are directly passed to ssh:connect/3 or ignored if a connection is already provided.

stop_channel(ChannelPid) -> ok

Types

ChannelPid = pid()

Stops an SFTP channel. Does not close the SSH connection. Use ssh:close/1 to close it.

write(ChannelPid, Handle, Data) -> ok | Error
write(ChannelPid, Handle, Data, Timeout) -> ok | Error

Types

ChannelPid = pid()
Handle = term()
Data = iodata()
Timeout = timeout()
Error = {error, reason()}

Writes data to the file referenced by Handle. The file is to be opened with write or append flag. Returns ok if successful or {error, reason()} otherwise.

write_file(ChannelPid, File, Data) -> ok | Error
write_file(ChannelPid, File, Data, Timeout) -> ok | Error

Types

ChannelPid = pid()
File = string()
Data = iodata()
Timeout = timeout()
Error = {error, reason()}

Writes a file to the server. The file is created if it does not exist but overwritten if it exists.

write_file_info(ChannelPid, Name, FileInfo) -> ok | Error
write_file_info(ChannelPid, Name, FileInfo, Timeout) -> ok | Error

Types

ChannelPid = pid()
Name = string()
FileInfo = file:file_info()
Timeout = timeout()
Error = {error, reason()}

Writes file information from a file_info record to the file specified by Name. See file:write_file_info/[2,3] for information about the record.