ssh - Main API of the ssh application
Please see following description for synopsis
ssh(3) Erlang Module Definition ssh(3)
NAME
ssh - Main API of the ssh application
DESCRIPTION
This is the interface module for the SSH application. The Secure Shell
(SSH) Protocol is a protocol for secure remote login and other secure
network services over an insecure network. See ssh(6) for details of
supported RFCs, versions, algorithms and unicode handling.
With the SSH application it is possible to start clients and to start
daemons (servers).
Clients are started with connect/2, connect/3 or connect/4. They open
an encrypted connection on top of TCP/IP. In that encrypted connection
one or more channels could be opened with ssh_connection:session_chan-
nel/2,4.
Each channel is an isolated "pipe" between a client-side process and a
server-side process. Those process pairs could handle for example file
transfers (sftp) or remote command execution (shell, exec and/or cli).
If a custom shell is implemented, the user of the client could execute
the special commands remotely. Note that the user is not necessarily a
human but probably a system interfacing the SSH app.
A server-side subssystem (channel) server is requested by the client
with ssh_connection:subsystem/4.
A server (daemon) is started with daemon/1, daemon/2 or daemon/3. Pos-
sible channel handlers (subsystems) are declared with the subsystem
option when the daemon is started.
To just run a shell on a remote machine, there are functions that bun-
dles the needed three steps needed into one: shell/1,2,3. Similarily,
to just open an sftp (file transfer) connection to a remote machine,
the simplest way is to use ssh_sftp:start_channel/1,2,3.
To write your own client channel handler, use the behaviour
ssh_client_channel. For server channel handlers use ssh_server_channel
behaviour (replaces ssh_daemon_channel).
Both clients and daemons accepts options that controls the exact behav-
iour. Some options are common to both. The three sets are called Client
Options, Daemon Options and Common Options.
The descriptions of the options uses the Erlang Type Language with
explaining text.
Note:
The User's Guide has examples and a Getting Started section.
KEYS AND FILES
A number of objects must be present for the SSH application to work.
Those objects are per default stored in files. The default names, paths
and file formats are the same as for OpenSSH. Keys could be generated
with the ssh-keygen program from OpenSSH. See the User's Guide.
The paths could easily be changed by options: user_dir and system_dir.
A completly different storage could be interfaced by writing call-back
modules using the behaviours ssh_client_key_api and/or
ssh_server_key_api. A callback module is installed with the option
key_cb to the client and/or the daemon.
Daemons
The keys are by default stored in files:
* Mandatory: one or more Host key(s) , both private and public.
Default is to store them in the directory /etc/ssh in the files
* ssh_host_dsa_key and ssh_host_dsa_key.pub
* ssh_host_rsa_key and ssh_host_rsa_key.pub
* ssh_host_ecdsa_key and ssh_host_ecdsa_key.pub
The host keys directory could be changed with the option sys-
tem_dir.
* Optional: one or more User's public key in case of publickey
authorization. Default is to store them concatenated in the file
.ssh/authorized_keys in the user's home directory.
The user keys directory could be changed with the option user_dir.
Clients
The keys and some other data are by default stored in files in the
directory .ssh in the user's home directory.
The directory could be changed with the option user_dir.
* Optional: a list of Host public key(s) for previously connected
hosts. This list is handled by the SSH application without any need
of user assistance. The default is to store them in the file
known_hosts.
The host_accepting_client_options() are associated with this list
of keys.
* Optional: one or more User's private key(s) in case of publickey
authorization. The default files are
* id_dsa and id_dsa.pub
* id_rsa and id_rsa.pub
* id_ecdsa and id_ecdsa.pub
DATA TYPES
Client Options
client_options() = [client_option()]
client_option() =
ssh_file:pubkey_passphrase_client_options() |
host_accepting_client_options() |
authentication_client_options() |
diffie_hellman_group_exchange_client_option() |
connect_timeout_client_option() |
recv_ext_info_client_option() |
opaque_client_options() |
gen_tcp:connect_option() |
common_option()
Options for clients. The individual options are further
explained below or by following the hyperlinks.
Note that not every gen_tcp:connect_option() is accepted. See
set_sock_opts/2 for a list of prohibited options.
Also note that setting a gen_tcp:connect_option() could change
the socket in a way that impacts the ssh client's behaviour neg-
atively. You use it on your own risk.
host_accepting_client_options() =
{silently_accept_hosts, accept_hosts()} |
{user_interaction, boolean()} |
{save_accepted_host, boolean()} |
{quiet_mode, boolean()}
accept_hosts() =
boolean() |
accept_callback() |
{HashAlgoSpec :: fp_digest_alg(), accept_callback()}
fp_digest_alg() = md5 | crypto:sha1() | crypto:sha2()
accept_callback() =
fun((PeerName :: string(), fingerprint()) -> boolean()) |
fun((PeerName :: string(),
Port :: inet:port_number(),
fingerprint()) ->
boolean())
fingerprint() = string() | [string()]
silently_accept_hosts:
This option guides the connect function on how to act when
the connected server presents a Host Key that the client has
not seen before. The default is to ask the user with a ques-
tion on stdio of whether to accept or reject the new Host
Key. See the option user_dir for specifying the path to the
file known_hosts where previously accepted Host Keys are
recorded. See also the option key_cb for the general way to
handle keys.
The option can be given in three different forms as seen
above:
* The value is a boolean(). The value true will make the
client accept any unknown Host Key without any user inter-
action. The value false preserves the default behaviour of
asking the user on stdio.
* An accept_callback() will be called and the boolean return
value true will make the client accept the Host Key. A
return value of false will make the client to reject the
Host Key and as a result the connection will be closed.
The arguments to the fun are:
* PeerName - a string with the name or address of the
remote host.
* FingerPrint - the fingerprint of the Host Key as
hostkey_fingerprint/1 calculates it.
* A tuple {HashAlgoSpec, accept_callback}. The HashAlgoSpec
specifies which hash algorithm shall be used to calculate
the fingerprint used in the call of the accept_callback().
The HashALgoSpec is either an atom or a list of atoms as
the first argument in hostkey_fingerprint/2. If it is a
list of hash algorithm names, the FingerPrint argument in
the accept_callback() will be a list of fingerprints in
the same order as the corresponding name in the HashAlgo-
Spec list.
user_interaction:
If false, disables the client to connect to the server if
any user interaction is needed, such as accepting the server
to be added to the known_hosts file, or supplying a pass-
word.
Even if user interaction is allowed it can be suppressed by
other options, such as silently_accept_hosts and password.
However, those options are not always desirable to use from
a security point of view.
Defaults to true.
save_accepted_host:
If true, the client saves an accepted host key to avoid the
accept question the next time the same host is connected. If
the option key_cb is not present, the key is saved in the
file "known_hosts". See option user_dir for the location of
that file.
If false, the key is not saved and the key will still be
unknown at the next access of the same host.
Defaults to true
quiet_mode:
If true, the client does not print anything on authoriza-
tion.
Defaults to false
authentication_client_options() =
{user, string()} | {password, string()}
user:
Provides the username. If this option is not given, ssh
reads from the environment (LOGNAME or USER on UNIX, USER-
NAME on Windows).
password:
Provides a password for password authentication. If this
option is not given, the user is asked for a password, if
the password authentication method is attempted.
diffie_hellman_group_exchange_client_option() =
{dh_gex_limits,
{Min :: integer() >= 1,
I :: integer() >= 1,
Max :: integer() >= 1}}
Sets the three diffie-hellman-group-exchange parameters that
guides the connected server in choosing a group. See RFC 4419
for the details. The default value is {1024, 6144, 8192}.
connect_timeout_client_option() = {connect_timeout, timeout()}
Sets a timeout on the transport layer connect time. For gen_tcp
the time is in milli-seconds and the default value is infinity.
See the parameter Timeout in connect/4 for a timeout of the
negotiation phase.
recv_ext_info_client_option() = {recv_ext_info, boolean()}
Make the client tell the server that the client accepts exten-
sion negotiation, that is, include ext-info-c in the kexinit
message sent. See RFC 8308 for details and ssh(6) for a list of
currently implemented extensions.
Default value is true which is compatible with other implementa-
tions not supporting ext-info.
Daemon Options (Server Options)
daemon_options() = [daemon_option()]
daemon_option() =
subsystem_daemon_option() |
shell_daemon_option() |
exec_daemon_option() |
ssh_cli_daemon_option() |
tcpip_tunnel_out_daemon_option() |
tcpip_tunnel_in_daemon_option() |
authentication_daemon_options() |
diffie_hellman_group_exchange_daemon_option() |
negotiation_timeout_daemon_option() |
hello_timeout_daemon_option() |
hardening_daemon_options() |
callbacks_daemon_options() |
send_ext_info_daemon_option() |
opaque_daemon_options() |
gen_tcp:listen_option() |
common_option()
Options for daemons. The individual options are further
explained below or by following the hyperlinks.
Note that not every gen_tcp:listen_option() is accepted. See
set_sock_opts/2 for a list of prohibited options.
Also note that setting a gen_tcp:listen_option() could change
the socket in a way that impacts the ssh deamon's behaviour neg-
atively. You use it on your own risk.
subsystem_daemon_option() = {subsystems, subsystem_specs()}
subsystem_specs() = [subsystem_spec()]
subsystem_spec() = {Name :: string(), mod_args()}
Defines a subsystem in the daemon.
The subsystem_name is the name that a client requests to start
with for example ssh_connection:subsystem/4.
The channel_callback is the module that implements the
ssh_server_channel (replaces ssh_daemon_channel) behaviour in
the daemon. See the section Creating a Subsystem in the User's
Guide for more information and an example.
If the subsystems option is not present, the value of
ssh_sftpd:subsystem_spec([]) is used. This enables the sftp sub-
system by default. The option can be set to the empty list if
you do not want the daemon to run any subsystems.
shell_daemon_option() = {shell, shell_spec()}
shell_spec() = mod_fun_args() | shell_fun() | disabled
shell_fun() = 'shell_fun/1'() | 'shell_fun/2'()
'shell_fun/1'() = fun((User :: string()) -> pid())
'shell_fun/2'() =
fun((User :: string(), PeerAddr :: inet:ip_address()) -> pid())
Defines the read-eval-print loop used in a daemon when a shell
is requested by the client. The default is to use the Erlang
shell: {shell, start, []}
See the option exec-option for a description of how the daemon
executes shell-requests and exec-requests depending on the
shell- and exec-options.
exec_daemon_option() = {exec, exec_spec()}
exec_spec() =
{direct, exec_fun()} | disabled | deprecated_exec_opt()
exec_fun() = 'exec_fun/1'() | 'exec_fun/2'() | 'exec_fun/3'()
'exec_fun/1'() = fun((Cmd :: string()) -> exec_result())
'exec_fun/2'() =
fun((Cmd :: string(), User :: string()) -> exec_result())
'exec_fun/3'() =
fun((Cmd :: string(),
User :: string(),
ClientAddr :: ip_port()) ->
exec_result())
exec_result() =
{ok, Result :: term()} | {error, Reason :: term()}
This option changes how the daemon executes exec-requests from
clients. The term in the return value is formatted to a string
if it is a non-string type. No trailing newline is added in the
ok-case.
See the User's Guide section on One-Time Execution for examples.
Error texts are returned on channel-type 1 which usually is
piped to stderr on e.g Linux systems. Texts from a successful
execution are returned on channel-type 0 and will in similar
manner be piped to stdout. The exit-status code is set to 0 for
success and 255 for errors. The exact results presented on the
client side depends on the client and the client's operating
system.
In case of the {direct, exec_fun()} variant or no exec-option at
all, all reads from standard_input will be from the received
data-events of type 0. Those are sent by the client. Similarily
all writes to standard_output will be sent as data-events to the
client. An OS shell client like the command 'ssh' will usally
use stdin and stdout for the user interface.
The option cooperates with the daemon-option shell in the fol-
lowing way:
1. If neither the exec-option nor the shell-option is
present::
The default Erlang evaluator is used both for exec and shell
requests. The result is returned to the client.
2. If the exec_spec's value is disabled (the shell-option may
or may not be present)::
No exec-requests are executed but shell-requests are not
affected, they follow the shell_spec's value.
3. If the exec-option is present and the exec_spec value =/=
disabled (the shell-option may or may not be present)::
The exec_spec fun() is called with the same number of param-
eters as the arity of the fun, and the result is returned to
the client. Shell-requests are not affected, they follow the
shell_spec's value.
4. If the exec-option is absent, and the shell-option is
present with the default Erlang shell as the shell_spec's
value::
The default Erlang evaluator is used both for exec and shell
requests. The result is returned to the client.
5. If the exec-option is absent, and the shell-option is
present with a value that is neither the default Erlang shell
nor the value disabled::
The exec-request is not evaluated and an error message is
returned to the client. Shell-requests are executed accord-
ing to the value of the shell_spec.
6. If the exec-option is absent, and the shell_spec's value is
disabled::
Exec requests are executed by the default shell, but shell-
requests are not executed.
If a custom CLI is installed (see the option ssh_cli) the rules
above are replaced by thoose implied by the custom CLI.
Note:
The exec-option has existed for a long time but has not previ-
ously been documented. The old definition and behaviour are
retained but obey the rules 1-6 above if conflicting. The old
and undocumented style should not be used in new programs.
deprecated_exec_opt() = function() | mod_fun_args()
Old-style exec specification that are kept for compatibility,
but should not be used in new programs
ssh_cli_daemon_option() = {ssh_cli, mod_args() | no_cli}
Provides your own CLI implementation in a daemon.
It is a channel callback module that implements a shell and com-
mand execution. The shell's read-eval-print loop can be custom-
ized, using the option shell. This means less work than imple-
menting an own CLI channel. If ssh_cli is set to no_cli, the CLI
channels like shell and exec are disabled and only subsystem
channels are allowed.
authentication_daemon_options() =
ssh_file:system_dir_daemon_option() |
{auth_method_kb_interactive_data, prompt_texts()} |
{user_passwords, [{UserName :: string(), Pwd :: string()}]} |
{pk_check_user, boolean()} |
{password, string()} |
{pwdfun, pwdfun_2() | pwdfun_4()}
prompt_texts() =
kb_int_tuple() | kb_int_fun_3() | kb_int_fun_4()
kb_int_tuple() =
{Name :: string(),
Instruction :: string(),
Prompt :: string(),
Echo :: boolean()}
kb_int_fun_3() =
fun((Peer :: ip_port(), User :: string(), Service :: string()) ->
kb_int_tuple())
kb_int_fun_4() =
fun((Peer :: ip_port(),
User :: string(),
Service :: string(),
State :: any()) ->
kb_int_tuple())
pwdfun_2() =
fun((User :: string(), Password :: string() | pubkey) ->
boolean())
pwdfun_4() =
fun((User :: string(),
Password :: string() | pubkey,
PeerAddress :: ip_port(),
State :: any()) ->
boolean() |
disconnect |
{boolean(), NewState :: any()})
auth_method_kb_interactive_data:
Sets the text strings that the daemon sends to the client
for presentation to the user when using keyboard-interactive
authentication.
If the fun/3 or fun/4 is used, it is called when the actual
authentication occurs and may therefore return dynamic data
like time, remote ip etc.
The parameter Echo guides the client about need to hide the
password.
The default value is: {auth_method_kb_interactive_data,
{"SSH server", "Enter password for \""++User++"\"", "pass-
word: ", false}>
user_passwords:
Provides passwords for password authentication. The pass-
words are used when someone tries to connect to the server
and public key user-authentication fails. The option pro-
vides a list of valid usernames and the corresponding pass-
words.
Warning:
Note that this is very insecure due to the plain-text pass-
words; it is intended for test purposes. Use the pwdfun option
to handle the password checking instead.
pk_check_user:
Enables checking of the client's user name in the server
when doing public key authentication. It is disabled by
default.
The term "user" is used differently in OpenSSH and SSH in
Erlang/OTP: see more in the User's Guide.
If the option is enabled, and no pwdfun is present, the user
name must present in the user_passwords for the check to
succeed but the value of the password is not checked.
In case of a pwdfun checking the user, the atom pubkey is
put in the password argument.
password:
Provides a global password that authenticates any user.
Warning:
Intended to facilitate testing.
From a security perspective this option makes the server very
vulnerable.
pwdfun with pwdfun_4():
Provides a function for password validation. This could used
for calling an external system or handeling passwords stored
as hash values.
This fun can also be used to make delays in authentication
tries for example by calling timer:sleep/1.
To facilitate for instance counting of failed tries, the
State variable could be used. This state is per connection
only. The first time the pwdfun is called for a connection,
the State variable has the value undefined.
The fun should return:
* true if the user and password is valid
* false if the user or password is invalid
* disconnect if a SSH_MSG_DISCONNECT message should be sent
immediately. It will be followed by a close of the under-
lying tcp connection.
* {true, NewState:any()} if the user and password is valid
* {false, NewState:any()} if the user or password is invalid
A third usage is to block login attempts from a missbehaving
peer. The State described above can be used for this. The
return value disconnect is useful for this.
In case of the pk_check_user is set, the atom pubkey is put
in the password argument when validating a public key login.
The pwdfun is then responsible to check that the user name
is valid.
pwdfun with pwdfun_2():
Provides a function for password validation. This function
is called with user and password as strings, and returns:
* true if the user and password is valid
* false if the user or password is invalid
In case of the pk_check_user is set, the atom pubkey is put
in the password argument when validating a public key login.
The pwdfun is then responsible to check that the user name
is valid.
This variant is kept for compatibility.
diffie_hellman_group_exchange_daemon_option() =
{dh_gex_groups,
[explicit_group()] |
explicit_group_file() |
ssh_moduli_file()} |
{dh_gex_limits, {Min :: integer() >= 1, Max :: integer() >= 1}}
explicit_group() =
{Size :: integer() >= 1,
G :: integer() >= 1,
P :: integer() >= 1}
explicit_group_file() = {file, string()}
ssh_moduli_file() = {ssh_moduli_file, string()}
dh_gex_groups:
Defines the groups the server may choose among when diffie-
hellman-group-exchange is negotiated. See RFC 4419 for
details. The three variants of this option are:
{Size=integer(),G=integer(),P=integer()}:
The groups are given explicitly in this list. There may be
several elements with the same Size. In such a case, the
server will choose one randomly in the negotiated Size.
{file,filename()}:
The file must have one or more three-tuples {Size=inte-
ger(),G=integer(),P=integer()} terminated by a dot. The
file is read when the daemon starts.
{ssh_moduli_file,filename()}:
The file must be in ssh-keygen moduli file format. The
file is read when the daemon starts.
The default list is fetched from the public_key application.
dh_gex_limits:
Limits what a client can ask for in diffie-hellman-group-
exchange. The limits will be {MaxUsed = min(MaxClient,Max),
MinUsed = max(MinClient,Min)} where MaxClient and MinClient
are the values proposed by a connecting client.
The default value is {0,infinity}.
If MaxUsed < MinUsed in a key exchange, it will fail with a
disconnect.
See RFC 4419 for the function of the Max and Min values.
hello_timeout_daemon_option() = {hello_timeout, timeout()}
Maximum time in milliseconds for the first part of the ssh ses-
sion setup, the hello message exchange. Defaults to 30000 ms (30
seconds). If the client fails to send the first message within
this time, the connection is closed.
negotiation_timeout_daemon_option() =
{negotiation_timeout, timeout()}
Maximum time in milliseconds for the authentication negotiation.
Defaults to 120000 ms (2 minutes). If the client fails to log in
within this time, the connection is closed.
hardening_daemon_options() =
{max_sessions, integer() >= 1} |
{max_channels, integer() >= 1} |
{parallel_login, boolean()} |
{minimal_remote_max_packet_size, integer() >= 1}
max_sessions:
The maximum number of simultaneous sessions that are
accepted at any time for this daemon. This includes sessions
that are being authorized. Thus, if set to N, and N clients
have connected but not started the login process, connection
attempt N+1 is aborted. If N connections are authenticated
and still logged in, no more logins are accepted until one
of the existing ones log out.
The counter is per listening port. Thus, if two daemons are
started, one with {max_sessions,N} and the other with
{max_sessions,M}, in total N+M connections are accepted for
the whole ssh application.
Notice that if parallel_login is false, only one client at a
time can be in the authentication phase.
By default, this option is not set. This means that the num-
ber is not limited.
max_channels:
The maximum number of channels with active remote subsystem
that are accepted for each connection to this daemon
By default, this option is not set. This means that the num-
ber is not limited.
parallel_login:
If set to false (the default value), only one login is han-
dled at a time. If set to true, an unlimited number of login
attempts are allowed simultaneously.
If the max_sessions option is set to N and parallel_login is
set to true, the maximum number of simultaneous login
attempts at any time is limited to N-K, where K is the num-
ber of authenticated connections present at this daemon.
Warning:
Do not enable parallel_logins without protecting the server by
other means, for example, by the max_sessions option or a
firewall configuration. If set to true, there is no protection
against DOS attacks.
minimal_remote_max_packet_size:
The least maximum packet size that the daemon will accept in
channel open requests from the client. The default value is
0.
callbacks_daemon_options() =
{failfun,
fun((User :: string(),
PeerAddress :: inet:ip_address(),
Reason :: term()) ->
term())} |
{connectfun,
fun((User :: string(),
PeerAddress :: inet:ip_address(),
Method :: string()) ->
term())}
connectfun:
Provides a fun to implement your own logging when a user
authenticates to the server.
failfun:
Provides a fun to implement your own logging when a user
fails to authenticate.
send_ext_info_daemon_option() = {send_ext_info, boolean()}
Make the server (daemon) tell the client that the server accepts
extension negotiation, that is, include ext-info-s in the kex-
init message sent. See RFC 8308 for details and ssh(6) for a
list of currently implemented extensions.
Default value is true which is compatible with other implementa-
tions not supporting ext-info.
tcpip_tunnel_in_daemon_option() = {tcpip_tunnel_in, boolean()}
Enables (true) or disables (false) the possibility to tunnel a
TCP/IP connection in to a server. Disabled per default.
tcpip_tunnel_out_daemon_option() =
{tcpip_tunnel_out, boolean()}
Enables (true) or disables (false) the possibility to tunnel a
TCP/IP connection out of a server. Disabled per default.
Options common to clients and daemons
common_options() = [common_option()]
common_option() =
ssh_file:user_dir_common_option() |
profile_common_option() |
max_idle_time_common_option() |
key_cb_common_option() |
disconnectfun_common_option() |
unexpectedfun_common_option() |
ssh_msg_debug_fun_common_option() |
rekey_limit_common_option() |
id_string_common_option() |
pref_public_key_algs_common_option() |
preferred_algorithms_common_option() |
modify_algorithms_common_option() |
auth_methods_common_option() |
inet_common_option() |
fd_common_option()
The options above can be used both in clients and in daemons
(servers). They are further explained below.
profile_common_option() = {profile, atom()}
Used together with ip-address and port to uniquely identify a
ssh daemon. This can be useful in a virtualized environment,
where there can be more that one server that has the same ip-
address and port. If this property is not explicitly set, it is
assumed that the the ip-address and port uniquely identifies the
SSH daemon.
max_idle_time_common_option() = {idle_time, timeout()}
Sets a time-out on a connection when no channels are open.
Defaults to infinity. The unit is milliseconds.
The timeout is not active until channels are started, so it does
not limit the time from the connection creation to the first
channel opening.
rekey_limit_common_option() =
{rekey_limit,
Bytes ::
limit_bytes() |
{Minutes :: limit_time(), Bytes :: limit_bytes()}}
limit_bytes() = integer() >= 0 | infinity
limit_time() = integer() >= 1 | infinity
Sets the limit when rekeying is to be initiated. Both the max
time and max amount of data could be configured:
* {Minutes, Bytes} initiate rekeying when any of the limits
are reached.
* Bytes initiate rekeying when Bytes number of bytes are
transferred, or at latest after one hour.
When a rekeying is done, both the timer and the byte counter are
restarted. Defaults to one hour and one GByte.
If Minutes is set to infinity, no rekeying will ever occur due
to that max time has passed. Setting Bytes to infinity will
inhibit rekeying after a certain amount of data has been trans-
ferred. If the option value is set to {infinity, infinity}, no
rekeying will be initiated. Note that rekeying initiated by the
peer will still be performed.
key_cb_common_option() =
{key_cb,
Module :: atom() | {Module :: atom(), Opts :: [term()]}}
Module implementing the behaviour ssh_client_key_api and/or
ssh_server_key_api. Can be used to customize the handling of
public keys. If callback options are provided along with the
module name, they are made available to the callback module via
the options passed to it under the key 'key_cb_private'.
The Opts defaults to [] when only the Module is specified.
The default value of this option is {ssh_file, []}. See also the
manpage of ssh_file.
A call to the call-back function F will be
Module:F(..., [{key_cb_private,Opts}|UserOptions])
where ... are arguments to F as in ssh_client_key_api and/or
ssh_server_key_api. The UserOptions are the options given to
ssh:connect, ssh:shell or ssh:daemon.
pref_public_key_algs_common_option() =
{pref_public_key_algs, [pubkey_alg()]}
List of user (client) public key algorithms to try to use.
The default value is the public_key entry in the list returned
by ssh:default_algorithms/0.
If there is no public key of a specified type available, the
corresponding entry is ignored. Note that the available set is
dependent on the underlying cryptolib and current user's public
keys.
See also the option user_dir for specifying the path to the
user's keys.
disconnectfun_common_option() =
{disconnectfun, fun((Reason :: term()) -> void | any())}
Provides a fun to implement your own logging or other handling
at disconnects.
unexpectedfun_common_option() =
{unexpectedfun,
fun((Message :: term(), {Host :: term(), Port :: term()}) ->
report | skip)}
Provides a fun to implement your own logging or other action
when an unexpected message arrives. If the fun returns report
the usual info report is issued but if skip is returned no
report is generated.
ssh_msg_debug_fun_common_option() =
{ssh_msg_debug_fun,
fun((ssh:connection_ref(),
AlwaysDisplay :: boolean(),
Msg :: binary(),
LanguageTag :: binary()) ->
any())}
Provide a fun to implement your own logging of the SSH message
SSH_MSG_DEBUG. The last three parameters are from the message,
see RFC 4253, section 11.3. The connection_ref() is the refer-
ence to the connection on which the message arrived. The return
value from the fun is not checked.
The default behaviour is ignore the message. To get a printout
for each message with AlwaysDisplay = true, use for example
{ssh_msg_debug_fun, fun(_,true,M,_)-> io:format("DEBUG: ~p~n",
[M]) end}
id_string_common_option() =
{id_string,
string() |
random |
{random, Nmin :: integer() >= 1, Nmax :: integer() >= 1}}
The string the daemon will present to a connecting peer ini-
tially. The default value is "Erlang/VSN" where VSN is the ssh
application version number.
The value random will cause a random string to be created at
each connection attempt. This is to make it a bit more difficult
for a malicious peer to find the ssh software brand and version.
The value {random, Nmin, Nmax} will make a random string with at
least Nmin characters and at most Nmax characters.
preferred_algorithms_common_option() =
{preferred_algorithms, algs_list()}
algs_list() = [alg_entry()]
alg_entry() =
{kex, [kex_alg()]} |
{public_key, [pubkey_alg()]} |
{cipher, double_algs(cipher_alg())} |
{mac, double_algs(mac_alg())} |
{compression, double_algs(compression_alg())}
kex_alg() =
'diffie-hellman-group-exchange-sha1' |
'diffie-hellman-group-exchange-sha256' |
'diffie-hellman-group1-sha1' | 'diffie-hellman-group14-sha1' |
'diffie-hellman-group14-sha256' |
'diffie-hellman-group16-sha512' |
'diffie-hellman-group18-sha512' | 'curve25519-sha256' |
'curve25519-sha256@libssh.org' | 'curve448-sha512' |
'ecdh-sha2-nistp256' | 'ecdh-sha2-nistp384' |
'ecdh-sha2-nistp521'
pubkey_alg() =
'ecdsa-sha2-nistp256' | 'ecdsa-sha2-nistp384' |
'ecdsa-sha2-nistp521' | 'ssh-ed25519' | 'ssh-ed448' |
'rsa-sha2-256' | 'rsa-sha2-512' | 'ssh-dss' | 'ssh-rsa'
cipher_alg() =
'3des-cbc' | 'AEAD_AES_128_GCM' | 'AEAD_AES_256_GCM' |
'aes128-cbc' | 'aes128-ctr' | 'aes128-gcm@openssh.com' |
'aes192-ctr' | 'aes192-cbc' | 'aes256-cbc' | 'aes256-ctr' |
'aes256-gcm@openssh.com' | 'chacha20-poly1305@openssh.com'
mac_alg() =
'AEAD_AES_128_GCM' | 'AEAD_AES_256_GCM' | 'hmac-sha1' |
'hmac-sha1-etm@openssh.com' | 'hmac-sha1-96' |
'hmac-sha2-256' | 'hmac-sha2-512' |
'hmac-sha2-256-etm@openssh.com' |
'hmac-sha2-512-etm@openssh.com'
compression_alg() = none | zlib | 'zlib@openssh.com'
double_algs(AlgType) =
[{client2server, [AlgType]} | {server2client, [AlgType]}] |
[AlgType]
List of algorithms to use in the algorithm negotiation. The
default algs_list() can be obtained from default_algorithms/0.
If an alg_entry() is missing in the algs_list(), the default
value is used for that entry.
Here is an example of this option:
{preferred_algorithms,
[{public_key,['ssh-rsa','ssh-dss']},
{cipher,[{client2server,['aes128-ctr']},
{server2client,['aes128-cbc','3des-cbc']}]},
{mac,['hmac-sha2-256','hmac-sha1']},
{compression,[none,zlib]}
]
}
The example specifies different algorithms in the two directions
(client2server and server2client), for cipher but specifies the
same algorithms for mac and compression in both directions. The
kex (key exchange) is implicit but public_key is set explicitly.
For background and more examples see the User's Guide.
If an algorithm name occurs more than once in a list, the behav-
iour is undefined. The tags in the property lists are also
assumed to occur at most one time.
Warning:
Changing the values can make a connection less secure. Do not
change unless you know exactly what you are doing. If you do not
understand the values then you are not supposed to change them.
modify_algorithms_common_option() =
{modify_algorithms, modify_algs_list()}
modify_algs_list() =
[{append, algs_list()} |
{prepend, algs_list()} |
{rm, algs_list()}]
Modifies the list of algorithms to use in the algorithm negotia-
tion. The modifications are applied after the option pre-
ferred_algorithms (if existing) is applied.
The algoritm for modifications works like this:
* Input is the modify_algs_list() and a set of algorithms A
obtained from the preferred_algorithms option if existing,
or else from the ssh:default_algorithms/0.
* The head of the modify_algs_list() modifies A giving the
result A'.
The possible modifications are:
* Append or prepend supported but not enabled algorithm(s)
to the list of algorithms. If the wanted algorithms
already are in A they will first be removed and then
appended or prepended,
* Remove (rm) one or more algorithms from A.
* Repeat the modification step with the tail of mod-
ify_algs_list() and the resulting A'.
If an unsupported algorithm is in the modify_algs_list(), it
will be silently ignored
If there are more than one modify_algorithms options, the result
is undefined.
Here is an example of this option:
{modify_algorithms,
[{prepend, [{kex, ['diffie-hellman-group1-sha1']}],
{rm, [{compression, [none]}]}
]
}
The example specifies that:
* the old key exchange algorithm 'diffie-hellman-group1-sha1'
should be the main alternative. It will be the main alterna-
tive since it is prepened to the list
* The compression algorithm none (= no compression) is removed
so compression is enforced
For background and more examples see the User's Guide.
inet_common_option() = {inet, inet | inet6}
IP version to use when the host address is specified as any.
auth_methods_common_option() = {auth_methods, string()}
Comma-separated string that determines which authentication
methods that the client shall support and in which order they
are tried. Defaults to "publickey,keyboard-interactive,password"
Note that the client is free to use any order and to exclude
methods.
fd_common_option() = {fd, gen_tcp:socket()}
Allows an existing file-descriptor to be used (passed on to the
transport protocol).
Other data types
host() = string() | inet:ip_address() | loopback
ip_port() = {inet:ip_address(), inet:port_number()}
mod_args() = {Module :: atom(), Args :: list()}
mod_fun_args() =
{Module :: atom(), Function :: atom(), Args :: list()}
open_socket() = gen_tcp:socket()
The socket is supposed to be result of a gen_tcp:connect or a
gen_tcp:accept. The socket must be in passive mode (that is,
opened with the option {active,false}).
daemon_ref()
Opaque data type representing a daemon.
Returned by the functions daemon/1,2,3.
connection_ref()
Opaque data type representing a connection between a client and
a server (daemon).
Returned by the functions connect/2,3,4 and ssh_sftp:start_chan-
nel/2,3.
channel_id()
Opaque data type representing a channel inside a connection.
Returned by the functions ssh_connection:session_channel/2,4.
connection_info_tuple() =
{client_version, version()} |
{server_version, version()} |
{user, string()} |
{peer, {inet:hostname(), ip_port()}} |
{sockname, ip_port()} |
{options, client_options()} |
{algorithms, conn_info_algs()} |
{channels, conn_info_channels()}
version() = {protocol_version(), software_version()}
protocol_version() =
{Major :: integer() >= 1, Minor :: integer() >= 0}
software_version() = string()
conn_info_algs() =
[{kex, kex_alg()} |
{hkey, pubkey_alg()} |
{encrypt, cipher_alg()} |
{decrypt, cipher_alg()} |
{send_mac, mac_alg()} |
{recv_mac, mac_alg()} |
{compress, compression_alg()} |
{decompress, compression_alg()} |
{send_ext_info, boolean()} |
{recv_ext_info, boolean()}]
conn_info_channels() = [proplists:proplist()]
Return values from the connection_info/1 and connection_info/2
functions.
In the option info tuple are only the options included that dif-
fers from the default values.
daemon_info_tuple() =
{port, inet:port_number()} |
{ip, inet:ip_address()} |
{profile, atom()} |
{options, daemon_options()}
Return values from the daemon_info/1 and daemon_info/2 func-
tions.
In the option info tuple are only the options included that dif-
fers from the default values.
opaque_client_options()
opaque_daemon_options()
opaque_common_options()
Opaque types that define experimental options that are not to be
used in products.
EXPORTS
close(ConnectionRef) -> ok | {error, term()}
Types:
ConnectionRef = connection_ref()
Closes an SSH connection.
connect(Host, Port, Options) -> Result
connect(Host, Port, Options, NegotiationTimeout) -> Result
connect(TcpSocket, Options) -> Result
connect(TcpSocket, Options, NegotiationTimeout) -> Result
Types:
Host = host()
Port = inet:port_number()
Options = client_options()
TcpSocket = open_socket()
NegotiationTimeout = timeout()
Result = {ok, connection_ref()} | {error, term()}
Connects to an SSH server at the Host on Port.
As an alternative, an already open TCP socket could be passed to
the function in TcpSocket. The SSH initiation and negotiation
will be initiated on that one with the SSH that should be at the
other end.
No channel is started. This is done by calling ssh_connec-
tion:session_channel/[2, 4].
The NegotiationTimeout is in milli-seconds. The default value is
infinity or the value of the connect_timeout option, if present.
For connection timeout, use the option connect_timeout.
connection_info(ConnectionRef) -> InfoTupleList
connection_info(ConnectionRef, Key :: ItemList | Item) ->
InfoTupleList | InfoTuple
Types:
ConnectionRef = connection_ref()
ItemList = [Item]
Item =
client_version | server_version | user | peer | sockname
|
options | algorithms | sockname
InfoTupleList = [InfoTuple]
InfoTuple = connection_info_tuple()
Returns information about a connection intended for e.g debug-
ging or logging.
When the Key is a single Item, the result is a single InfoTuple
set_sock_opts(ConnectionRef, SocketOptions) ->
ok | {error, inet:posix()}
Types:
ConnectionRef = connection_ref()
SocketOptions = [gen_tcp:option()]
Sets tcp socket options on the tcp-socket below an ssh connec-
tion.
This function calls the inet:setopts/2, read that documentation
and for gen_tcp:option().
All gen_tcp socket options except
* active
* deliver
* mode and
* packet
are allowed. The excluded options are reserved by the SSH appli-
cation.
Warning:
This is an extremly dangerous function. You use it on your own
risk.
Some options are OS and OS version dependent. Do not use it
unless you know what effect your option values will have on an
TCP stream.
Some values may destroy the functionality of the SSH protocol.
get_sock_opts(ConnectionRef, SocketGetOptions) ->
ok | {error, inet:posix()}
Types:
ConnectionRef = connection_ref()
SocketGetOptions = [gen_tcp:option_name()]
Get tcp socket option values of the tcp-socket below an ssh con-
nection.
This function calls the inet:getopts/2, read that documentation.
daemon(Port | TcpSocket) -> Result
daemon(Port | TcpSocket, Options) -> Result
daemon(HostAddress, Port, Options) -> Result
Types:
Port = integer()
TcpSocket = open_socket()
Options = daemon_options()
HostAddress = host() | any
Result = {ok, daemon_ref()} | {error, atom()}
Starts a server listening for SSH connections on the given port.
If the Port is 0, a random free port is selected. See dae-
mon_info/1 about how to find the selected port number.
As an alternative, an already open TCP socket could be passed to
the function in TcpSocket. The SSH initiation and negotiation
will be initiated on that one when an SSH starts at the other
end of the TCP socket.
For a description of the options, see Daemon Options.
Please note that by historical reasons both the HostAddress
argument and the gen_tcp connect_option() {ip,Address} set the
listening address. This is a source of possible inconsistent
settings.
The rules for handling the two address passing options are:
* if HostAddress is an IP-address, that IP-address is the lis-
tening address. An 'ip'-option will be discarded if present.
* if HostAddress is the atom loopback, the listening address
is loopback and an loopback address will be choosen by the
underlying layers. An 'ip'-option will be discarded if
present.
* if HostAddress is the atom any and no 'ip'-option is
present, the listening address is any and the socket will
listen to all addresses
* if HostAddress is any and an 'ip'-option is present, the
listening address is set to the value of the 'ip'-option
daemon_info(DaemonRef) ->
{ok, InfoTupleList} | {error, bad_daemon_ref}
daemon_info(DaemonRef, Key :: ItemList | Item) ->
InfoTupleList | InfoTuple | {error, bad_daemon_ref}
Types:
DaemonRef = daemon_ref()
ItemList = [Item]
Item = ip | port | profile | options
InfoTupleList = [InfoTuple]
InfoTuple = daemon_info_tuple()
Returns information about a daemon intended for e.g debugging or
logging.
When the Key is a single Item, the result is a single InfoTuple
Note that daemon_info/1 and daemon_info/2 returns different
types due to compatibility reasons.
default_algorithms() -> algs_list()
Returns a key-value list, where the keys are the different types
of algorithms and the values are the algorithms themselves.
See the User's Guide for an example.
shell(Host | TcpSocket) -> Result
shell(Host | TcpSocket, Options) -> Result
shell(Host, Port, Options) -> Result
Types:
Host = host()
TcpSocket = open_socket()
Port = inet:port_number()
Options = client_options()
Result = ok | {error, Reason::term()}
Connects to an SSH server at Host and Port (defaults to 22) and
starts an interactive shell on that remote host.
As an alternative, an already open TCP socket could be passed to
the function in TcpSocket. The SSH initiation and negotiation
will be initiated on that one and finaly a shell will be started
on the host at the other end of the TCP socket.
For a description of the options, see Client Options.
The function waits for user input, and does not return until the
remote shell is ended (that is, exit from the shell).
start() -> ok | {error, term()}
start(Type) -> ok | {error, term()}
Types:
Type = permanent | transient | temporary
Utility function that starts the applications crypto, pub-
lic_key, and ssh. Default type is temporary. For more informa-
tion, see the application(3) manual page in Kernel.
stop() -> ok | {error, term()}
Stops the ssh application. For more information, see the appli-
cation(3) manual page in Kernel.
stop_daemon(DaemonRef :: daemon_ref()) -> ok
stop_daemon(Address :: inet:ip_address(),
Port :: inet:port_number()) ->
ok
stop_daemon(Address :: any | inet:ip_address(),
Port :: inet:port_number(),
Profile :: atom()) ->
ok
Stops the listener and all connections started by the listener.
stop_listener(SysSup :: daemon_ref()) -> ok
stop_listener(Address :: inet:ip_address(),
Port :: inet:port_number()) ->
ok
stop_listener(Address :: any | inet:ip_address(),
Port :: inet:port_number(),
Profile :: term()) ->
ok
Stops the listener, but leaves existing connections started by
the listener operational.
tcpip_tunnel_from_server(ConnectionRef, ListenHost, ListenPort,
ConnectToHost, ConnectToPort) ->
{ok, TrueListenPort} | {error, term()}
tcpip_tunnel_from_server(ConnectionRef, ListenHost, ListenPort,
ConnectToHost, ConnectToPort, Timeout) ->
{ok, TrueListenPort} | {error, term()}
Types:
ConnectionRef = connection_ref()
ListenHost = host()
ListenPort = inet:port_number()
ConnectToHost = host()
ConnectToPort = inet:port_number()
Timeout = timeout()
TrueListenPort = inet:port_number()
Asks the remote server of ConnectionRef to listen to Listen-
Host:ListenPort. When someone connects that address, the connec-
tion is forwarded in an encrypted channel from the server to the
client. The client (that is, at the node that calls this func-
tion) then connects to ConnectToHost:ConnectToPort.
The returned TrueListenPort is the port that is listened to. It
is the same as ListenPort, except when ListenPort = 0. In that
case a free port is selected by the underlying OS.
Note that in case of an Erlang/OTP SSH server (daemon) as peer,
that server must have been started with the option tcpip_tun-
nel_out to allow the connection.
tcpip_tunnel_to_server(ConnectionRef, ListenHost, ListenPort,
ConnectToHost, ConnectToPort) ->
{ok, TrueListenPort} | {error, term()}
tcpip_tunnel_to_server(ConnectionRef, ListenHost, ListenPort,
ConnectToHost, ConnectToPort, Timeout) ->
{ok, TrueListenPort} | {error, term()}
Types:
ConnectionRef = connection_ref()
ListenHost = host()
ListenPort = inet:port_number()
ConnectToHost = host()
ConnectToPort = inet:port_number()
Timeout = timeout()
TrueListenPort = inet:port_number()
Tells the local client to listen to ListenHost:ListenPort. When
someone connects to that address, the connection is forwarded in
an encrypted channel to the peer server of ConnectionRef. That
server then connects to ConnectToHost:ConnectToPort.
The returned TrueListenPort is the port that is listened to. It
is the same as ListenPort, except when ListenPort = 0. In that
case a free port is selected by the underlying OS.
Note that in case of an Erlang/OTP SSH server (daemon) as peer,
that server must have been started with the option tcpip_tun-
nel_in to allow the connection.
hostkey_fingerprint(HostKey) -> string()
hostkey_fingerprint(DigestType, HostKey) -> string()
hostkey_fingerprint([DigestType], HostKey) -> [string()]
Types:
HostKey = public_key:public_key()
DigestType = public_key:digest_type()
Calculates a ssh fingerprint from a public host key as openssh
does.
The algorithm in hostkey_fingerprint/1 is md5 to be compatible
with older ssh-keygen commands. The string from the second vari-
ant is prepended by the algorithm name in uppercase as in newer
ssh-keygen commands.
Examples:
2> ssh:hostkey_fingerprint(Key).
"f5:64:a6:c1:5a:cb:9f:0a:10:46:a2:5c:3e:2f:57:84"
3> ssh:hostkey_fingerprint(md5,Key).
"MD5:f5:64:a6:c1:5a:cb:9f:0a:10:46:a2:5c:3e:2f:57:84"
4> ssh:hostkey_fingerprint(sha,Key).
"SHA1:bSLY/C4QXLDL/Iwmhyg0PGW9UbY"
5> ssh:hostkey_fingerprint(sha256,Key).
"SHA256:aZGXhabfbf4oxglxltItWeHU7ub3Dc31NcNw2cMJePQ"
6> ssh:hostkey_fingerprint([sha,sha256],Key).
["SHA1:bSLY/C4QXLDL/Iwmhyg0PGW9UbY",
"SHA256:aZGXhabfbf4oxglxltItWeHU7ub3Dc31NcNw2cMJePQ"]
Ericsson AB ssh 4.13 ssh(3)