1ssh(3) Erlang Module Definition ssh(3)
2
6 ssh - Main API of the ssh application
7
9 This is the interface module for the SSH application. The Secure Shell
10 (SSH) Protocol is a protocol for secure remote login and other secure
11 network services over an insecure network. See ssh(6) for details of
12 supported RFCs, versions, algorithms and unicode handling.
13 With the SSH application it is possible to start clients and to start
15 daemons (servers).
16 Clients are started with connect/2, connect/3 or connect/4. They open
18 an encrypted connection on top of TCP/IP. In that encrypted connection
19 one or more channels could be opened with ssh_connection:session_chan‐
20 nel/2,4.
21 Each channel is an isolated "pipe" between a client-side process and a
23 server-side process. Those process pairs could handle for example file
24 transfers (sftp) or remote command execution (shell, exec and/or cli).
25 If a custom shell is implemented, the user of the client could execute
26 the special commands remotely. Note that the user is not necessarily a
27 human but probably a system interfacing the SSH app.
28 A server-side subssystem (channel) server is requested by the client
30 with ssh_connection:subsystem/4.
31 A server (daemon) is started with daemon/1, daemon/2 or daemon/3. Pos‐
33 sible channel handlers (subsystems) are declared with the subsystem
34 option when the daemon is started.
35 To just run a shell on a remote machine, there are functions that bun‐
37 dles the needed three steps needed into one: shell/1,2,3. Similarily,
38 to just open an sftp (file transfer) connection to a remote machine,
39 the simplest way is to use ssh_sftp:start_channel/1,2,3.
40 To write your own client channel handler, use the behaviour
42 ssh_client_channel. For server channel handlers use ssh_server_channel
43 behaviour (replaces ssh_daemon_channel).
44 Both clients and daemons accepts options that controls the exact behav‐
46 iour. Some options are common to both. The three sets are called Client
47 Options, Daemon Options and Common Options.
48 The descriptions of the options uses the Erlang Type Language with
50 explaining text.
51 Note:
53 The User's Guide has examples and a Getting Started section.
54
57 A number of objects must be present for the SSH application to work.
58 Thoose objects are per default stored in files. The default names,
59 paths and file formats are the same as for OpenSSH. Keys could be gen‐
60 erated with the ssh-keygen program from OpenSSH. See the User's Guide.
61 The paths could easily be changed by options: user_dir and system_dir.
63 A completly different storage could be interfaced by writing call-back
65 modules using the behaviours ssh_client_key_api and/or
66 ssh_server_key_api. A callback module is installed with the option
67 key_cb to the client and/or the daemon.
68 Daemons
70 The keys are by default stored in files:
71 * Mandatory: one or more Host key(s) , both private and public.
73 Default is to store them in the directory /etc/ssh in the files
74 * ssh_host_dsa_key and ssh_host_dsa_key.pub
76 * ssh_host_rsa_key and ssh_host_rsa_key.pub
78 * ssh_host_ecdsa_key and ssh_host_ecdsa_key.pub
80 The host keys directory could be changed with the option sys‐
82 tem_dir.
83 * Optional: one or more User's public key in case of publickey
85 authorization. Default is to store them concatenated in the file
86 .ssh/authorized_keys in the user's home directory.
87 The user keys directory could be changed with the option user_dir.
89 Clients
91 The keys and some other data are by default stored in files in the
92 directory .ssh in the user's home directory.
93 The directory could be changed with the option user_dir.
95 * Optional: a list of Host public key(s) for previously connected
97 hosts. This list is handled by the SSH application without any need
98 of user assistance. The default is to store them in the file
99 known_hosts.
100 The host_accepting_client_options() are associated with this list
102 of keys.
103 * Optional: one or more User's private key(s) in case of publickey
105 authorization. The default files are
106 * id_dsa and id_dsa.pub
108 * id_rsa and id_rsa.pub
110 * id_ecdsa and id_ecdsa.pub
112
114 Client Options
115 client_options() = [client_option()]
116 client_option() =
118 ssh_file:pubkey_passphrase_client_options() |
119 host_accepting_client_options() |
120 authentication_client_options() |
121 diffie_hellman_group_exchange_client_option() |
122 connect_timeout_client_option() |
123 recv_ext_info_client_option() |
124 opaque_client_options() |
125 gen_tcp:connect_option() |
126 common_option()
127 Options for clients. The individual options are further
129 explained below or by following the hyperlinks.
130 host_accepting_client_options() =
132 {silently_accept_hosts, accept_hosts()} |
133 {user_interaction, boolean()} |
134 {save_accepted_host, boolean()} |
135 {quiet_mode, boolean()}
136 accept_hosts() =
138 boolean() |
139 accept_callback() |
140 {HashAlgoSpec :: fp_digest_alg(), accept_callback()}
141 fp_digest_alg() = md5 | crypto:sha1() | crypto:sha2()
143 accept_callback() =
145 fun((PeerName :: string(), fingerprint()) -> boolean())
146 fingerprint() = string() | [string()]
148 silently_accept_hosts:
150 This option guides the connect function on how to act when
151 the connected server presents a Host Key that the client has
152 not seen before. The default is to ask the user with a ques‐
153 tion on stdio of whether to accept or reject the new Host
154 Key. See the option user_dir for specifying the path to the
155 file known_hosts where previously accepted Host Keys are
156 recorded. See also the option key_cb for the general way to
157 handle keys.
158 The option can be given in three different forms as seen
160 above:
161 * The value is a boolean(). The value true will make the
163 client accept any unknown Host Key without any user inter‐
164 action. The value false preserves the default behaviour of
165 asking the user on stdio.
166 * An accept_callback() will be called and the boolean return
168 value true will make the client accept the Host Key. A
169 return value of false will make the client to reject the
170 Host Key and as a result the connection will be closed.
171 The arguments to the fun are:
172 * PeerName - a string with the name or address of the
174 remote host.
175 * FingerPrint - the fingerprint of the Host Key as pub‐
177 lic_key:ssh_hostkey_fingerprint/1 calculates it.
178 * A tuple {HashAlgoSpec, accept_callback}. The HashAlgoSpec
180 specifies which hash algorithm shall be used to calculate
181 the fingerprint used in the call of the accept_callback().
182 The HashALgoSpec is either an atom or a list of atoms as
183 the first argument in public_key:ssh_hostkey_finger‐
184 print/2. If it is a list of hash algorithm names, the Fin‐
185 gerPrint argument in the accept_callback() will be a list
186 of fingerprints in the same order as the corresponding
187 name in the HashAlgoSpec list.
188 user_interaction:
190 If false, disables the client to connect to the server if
191 any user interaction is needed, such as accepting the server
192 to be added to the known_hosts file, or supplying a pass‐
193 word.
194 Even if user interaction is allowed it can be suppressed by
196 other options, such as silently_accept_hosts and password.
197 However, those options are not always desirable to use from
198 a security point of view.
199 Defaults to true.
201 save_accepted_host:
203 If true, the client saves an accepted host key to avoid the
204 accept question the next time the same host is connected. If
205 the option key_cb is not present, the key is saved in the
206 file "known_hosts". See option user_dir for the location of
207 that file.
208 If false, the key is not saved and the key will still be
210 unknown at the next access of the same host.
211 Defaults to true
213 quiet_mode:
215 If true, the client does not print anything on authoriza‐
216 tion.
217 Defaults to false
219 authentication_client_options() =
221 {user, string()} | {password, string()}
222 user:
224 Provides the username. If this option is not given, ssh
225 reads from the environment (LOGNAME or USER on UNIX, USER‐
226 NAME on Windows).
227 password:
229 Provides a password for password authentication. If this
230 option is not given, the user is asked for a password, if
231 the password authentication method is attempted.
232 diffie_hellman_group_exchange_client_option() =
234 {dh_gex_limits,
235 {Min :: integer() >= 1,
236 I :: integer() >= 1,
237 Max :: integer() >= 1}}
238 Sets the three diffie-hellman-group-exchange parameters that
240 guides the connected server in choosing a group. See RFC 4419
241 for the details. The default value is {1024, 6144, 8192}.
242 connect_timeout_client_option() = {connect_timeout, timeout()}
244 Sets a timeout on the transport layer connect time. For gen_tcp
246 the time is in milli-seconds and the default value is infinity.
247 See the parameter Timeout in connect/4 for a timeout of the
249 negotiation phase.
250 recv_ext_info_client_option() = {recv_ext_info, boolean()}
252 Make the client tell the server that the client accepts exten‐
254 sion negotiation, that is, include ext-info-c in the kexinit
255 message sent. See RFC 8308 for details and ssh(6) for a list of
256 currently implemented extensions.
257 Default value is true which is compatible with other implementa‐
259 tions not supporting ext-info.
260 Daemon Options (Server Options)
262 daemon_options() = [daemon_option()]
263 daemon_option() =
265 subsystem_daemon_option() |
266 shell_daemon_option() |
267 exec_daemon_option() |
268 ssh_cli_daemon_option() |
269 authentication_daemon_options() |
270 diffie_hellman_group_exchange_daemon_option() |
271 negotiation_timeout_daemon_option() |
272 hardening_daemon_options() |
273 callbacks_daemon_options() |
274 send_ext_info_daemon_option() |
275 opaque_daemon_options() |
276 gen_tcp:listen_option() |
277 common_option()
278 Options for daemons. The individual options are further
280 explained below or by following the hyperlinks.
281 subsystem_daemon_option() = {subsystems, subsystem_specs()}
283 subsystem_specs() = [subsystem_spec()]
285 subsystem_spec() = {Name :: string(), mod_args()}
287 Defines a subsystem in the daemon.
289 The subsystem_name is the name that a client requests to start
291 with for example ssh_connection:subsystem/4.
292 The channel_callback is the module that implements the
294 ssh_server_channel (replaces ssh_daemon_channel) behaviour in
295 the daemon. See the section Creating a Subsystem in the User's
296 Guide for more information and an example.
297 If the subsystems option is not present, the value of
299 ssh_sftpd:subsystem_spec([]) is used. This enables the sftp sub‐
300 system by default. The option can be set to the empty list if
301 you do not want the daemon to run any subsystems.
302 shell_daemon_option() =
304 {shell, mod_fun_args() | 'shell_fun/1'() | 'shell_fun/2'()}
305 'shell_fun/1'() = fun((User :: string()) -> pid())
307 'shell_fun/2'() =
309 fun((User :: string(), PeerAddr :: inet:ip_address()) -> pid())
310 Defines the read-eval-print loop used in a daemon when a shell
312 is requested by the client. The default is to use the Erlang
313 shell: {shell, start, []}
314 See the option exec for a description of how the daemon execute
316 exec-requests depending on the shell- and exec-options.
317 exec_daemon_option() = {exec, exec_spec()}
319 exec_spec() = {direct, exec_fun()}
321 exec_fun() = 'exec_fun/1'() | 'exec_fun/2'() | 'exec_fun/3'()
323 'exec_fun/1'() = fun((Cmd :: string()) -> exec_result())
325 'exec_fun/2'() =
327 fun((Cmd :: string(), User :: string()) -> exec_result())
328 'exec_fun/3'() =
330 fun((Cmd :: string(),
331 User :: string(),
332 ClientAddr :: ip_port()) ->
333 exec_result())
334 exec_result() =
336 {ok, Result :: term()} | {error, Reason :: term()}
337 This option changes how the daemon execute exec-requests from
339 clients. The term in the return value is formatted to a string
340 if it is a non-string type. No trailing newline is added in the
341 ok-case but in the error case.
342 Error texts are returned on channel-type 1 which usually is
344 piped to stderr on e.g Linux systems. Texts from a successful
345 execution will in similar manner be piped to stdout. The exit-
346 status code is set to 0 for success and -1 for errors. The exact
347 results presented on the client side depends on the client and
348 the client's operating system.
349 The option cooperates with the daemon-option shell in the fol‐
351 lowing way:
352 1. If the exec-option is present (the shell-option may or may
354 not be present)::
355 The exec-option fun is called with the same number of param‐
356 eters as the arity of the fun, and the result is returned to
357 the client.
358 2. If the exec-option is absent, but a shell-option is present
360 with the default Erlang shell::
361 The default Erlang evaluator is used and the result is
362 returned to the client.
363 3. If the exec-option is absent, but a shell-option is present
365 that is not the default Erlang shell::
366 The exec-request is not evaluated and an error message is
367 returned to the client.
368 4. If neither the exec-option nor the shell-option is
370 present::
371 The default Erlang evaluator is used and the result is
372 returned to the client.
373 If a custom CLI is installed (see the option ssh_cli) the rules
375 above are replaced by thoose implied by the custom CLI.
376 Note:
378 The exec-option has existed for a long time but has not previ‐
379 ously been documented. The old definition and behaviour are
380 retained but obey the rules 1-4 above if conflicting. The old
381 and undocumented style should not be used in new programs.
382 ssh_cli_daemon_option() = {ssh_cli, mod_args() | no_cli}
385 Provides your own CLI implementation in a daemon.
387 It is a channel callback module that implements a shell and com‐
389 mand execution. The shell's read-eval-print loop can be custom‐
390 ized, using the option shell. This means less work than imple‐
391 menting an own CLI channel. If ssh_cli is set to no_cli, the CLI
392 channels like shell and exec are disabled and only subsystem
393 channels are allowed.
394 authentication_daemon_options() =
396 ssh_file:system_dir_daemon_option() |
397 {auth_method_kb_interactive_data, prompt_texts()} |
398 {user_passwords, [{UserName :: string(), Pwd :: string()}]} |
399 {password, string()} |
400 {pwdfun, pwdfun_2() | pwdfun_4()}
401 prompt_texts() = kb_int_tuple() | kb_int_fun_3()
403 kb_int_tuple() =
405 {Name :: string(),
406 Instruction :: string(),
407 Prompt :: string(),
408 Echo :: boolean()}
409 kb_int_fun_3() =
411 fun((Peer :: ip_port(), User :: string(), Service :: string()) ->
412 kb_int_tuple())
413 pwdfun_2() =
415 fun((User :: string(), Password :: string()) -> boolean())
416 pwdfun_4() =
418 fun((User :: string(),
419 Password :: string(),
420 PeerAddress :: ip_port(),
421 State :: any()) ->
422 boolean() |
423 disconnect |
424 {boolean(), NewState :: any()})
425 auth_method_kb_interactive_data:
427 Sets the text strings that the daemon sends to the client
428 for presentation to the user when using keyboard-interactive
429 authentication.
430 If the fun/3 is used, it is called when the actual authenti‐
432 cation occurs and may therefore return dynamic data like
433 time, remote ip etc.
434 The parameter Echo guides the client about need to hide the
436 password.
437 The default value is: {auth_method_kb_interactive_data,
439 {"SSH server", "Enter password for \""++User++"\"", "pass‐
440 word: ", false}>
441 user_passwords:
443 Provides passwords for password authentication. The pass‐
444 words are used when someone tries to connect to the server
445 and public key user-authentication fails. The option pro‐
446 vides a list of valid usernames and the corresponding pass‐
447 words.
448 password:
450 Provides a global password that authenticates any user.
451 Warning:
453 Intended to facilitate testing.
454 From a security perspective this option makes the server very
456 vulnerable.
457 pwdfun with pwdfun_4():
460 Provides a function for password validation. This could used
461 for calling an external system or handeling passwords stored
462 as hash values.
463 This fun can also be used to make delays in authentication
465 tries for example by calling timer:sleep/1.
466 To facilitate for instance counting of failed tries, the
468 State variable could be used. This state is per connection
469 only. The first time the pwdfun is called for a connection,
470 the State variable has the value undefined.
471 The fun should return:
473 * true if the user and password is valid
475 * false if the user or password is invalid
477 * disconnect if a SSH_MSG_DISCONNECT message should be sent
479 immediately. It will be followed by a close of the under‐
480 lying tcp connection.
481 * {true, NewState:any()} if the user and password is valid
483 * {false, NewState:any()} if the user or password is invalid
485 A third usage is to block login attempts from a missbehaving
487 peer. The State described above can be used for this. The
488 return value disconnect is useful for this.
489 pwdfun with pwdfun_2():
491 Provides a function for password validation. This function
492 is called with user and password as strings, and returns:
493 * true if the user and password is valid
495 * false if the user or password is invalid
497 This variant is kept for compatibility.
499 diffie_hellman_group_exchange_daemon_option() =
501 {dh_gex_groups,
502 [explicit_group()] |
503 explicit_group_file() |
504 ssh_moduli_file()} |
505 {dh_gex_limits, {Min :: integer() >= 1, Max :: integer() >= 1}}
506 explicit_group() =
508 {Size :: integer() >= 1,
509 G :: integer() >= 1,
510 P :: integer() >= 1}
511 explicit_group_file() = {file, string()}
513 ssh_moduli_file() = {ssh_moduli_file, string()}
515 dh_gex_groups:
517 Defines the groups the server may choose among when diffie-
518 hellman-group-exchange is negotiated. See RFC 4419 for
519 details. The three variants of this option are:
520 {Size=integer(),G=integer(),P=integer()}:
522 The groups are given explicitly in this list. There may be
523 several elements with the same Size. In such a case, the
524 server will choose one randomly in the negotiated Size.
525 {file,filename()}:
527 The file must have one or more three-tuples {Size=inte‐
528 ger(),G=integer(),P=integer()} terminated by a dot. The
529 file is read when the daemon starts.
530 {ssh_moduli_file,filename()}:
532 The file must be in ssh-keygen moduli file format. The
533 file is read when the daemon starts.
534 The default list is fetched from the public_key application.
536 dh_gex_limits:
538 Limits what a client can ask for in diffie-hellman-group-
539 exchange. The limits will be {MaxUsed = min(MaxClient,Max),
540 MinUsed = max(MinClient,Min)} where MaxClient and MinClient
541 are the values proposed by a connecting client.
542 The default value is {0,infinity}.
544 If MaxUsed < MinUsed in a key exchange, it will fail with a
546 disconnect.
547 See RFC 4419 for the function of the Max and Min values.
549 negotiation_timeout_daemon_option() =
551 {negotiation_timeout, timeout()}
552 Maximum time in milliseconds for the authentication negotiation.
554 Defaults to 120000 ms (2 minutes). If the client fails to log in
555 within this time, the connection is closed.
556 hardening_daemon_options() =
558 {max_sessions, integer() >= 1} |
559 {max_channels, integer() >= 1} |
560 {parallel_login, boolean()} |
561 {minimal_remote_max_packet_size, integer() >= 1}
562 max_sessions:
564 The maximum number of simultaneous sessions that are
565 accepted at any time for this daemon. This includes sessions
566 that are being authorized. Thus, if set to N, and N clients
567 have connected but not started the login process, connection
568 attempt N+1 is aborted. If N connections are authenticated
569 and still logged in, no more logins are accepted until one
570 of the existing ones log out.
571 The counter is per listening port. Thus, if two daemons are
573 started, one with {max_sessions,N} and the other with
574 {max_sessions,M}, in total N+M connections are accepted for
575 the whole ssh application.
576 Notice that if parallel_login is false, only one client at a
578 time can be in the authentication phase.
579 By default, this option is not set. This means that the num‐
581 ber is not limited.
582 max_channels:
584 The maximum number of channels with active remote subsystem
585 that are accepted for each connection to this daemon
586 By default, this option is not set. This means that the num‐
588 ber is not limited.
589 parallel_login:
591 If set to false (the default value), only one login is han‐
592 dled at a time. If set to true, an unlimited number of login
593 attempts are allowed simultaneously.
594 If the max_sessions option is set to N and parallel_login is
596 set to true, the maximum number of simultaneous login
597 attempts at any time is limited to N-K, where K is the num‐
598 ber of authenticated connections present at this daemon.
599 Warning:
601 Do not enable parallel_logins without protecting the server by
602 other means, for example, by the max_sessions option or a
603 firewall configuration. If set to true, there is no protection
604 against DOS attacks.
605 minimal_remote_max_packet_size:
608 The least maximum packet size that the daemon will accept in
609 channel open requests from the client. The default value is
610 0.
611 callbacks_daemon_options() =
613 {failfun,
614 fun((User :: string(),
615 PeerAddress :: inet:ip_address(),
616 Reason :: term()) ->
617 term())} |
618 {connectfun,
619 fun((User :: string(),
620 PeerAddress :: inet:ip_address(),
621 Method :: string()) ->
622 term())}
623 connectfun:
625 Provides a fun to implement your own logging when a user
626 authenticates to the server.
627 failfun:
629 Provides a fun to implement your own logging when a user
630 fails to authenticate.
631 send_ext_info_daemon_option() = {send_ext_info, boolean()}
633 Make the server (daemon) tell the client that the server accepts
635 extension negotiation, that is, include ext-info-s in the kex‐
636 init message sent. See RFC 8308 for details and ssh(6) for a
637 list of currently implemented extensions.
638 Default value is true which is compatible with other implementa‐
640 tions not supporting ext-info.
641 Options common to clients and daemons
643 common_options() = [common_option()]
644 common_option() =
646 ssh_file:user_dir_common_option() |
647 profile_common_option() |
648 max_idle_time_common_option() |
649 key_cb_common_option() |
650 disconnectfun_common_option() |
651 unexpectedfun_common_option() |
652 ssh_msg_debug_fun_common_option() |
653 rekey_limit_common_option() |
654 id_string_common_option() |
655 pref_public_key_algs_common_option() |
656 preferred_algorithms_common_option() |
657 modify_algorithms_common_option() |
658 auth_methods_common_option() |
659 inet_common_option() |
660 fd_common_option()
661 The options above can be used both in clients and in daemons
663 (servers). They are further explained below.
664 profile_common_option() = {profile, atom()}
666 Used together with ip-address and port to uniquely identify a
668 ssh daemon. This can be useful in a virtualized environment,
669 where there can be more that one server that has the same ip-
670 address and port. If this property is not explicitly set, it is
671 assumed that the the ip-address and port uniquely identifies the
672 SSH daemon.
673 max_idle_time_common_option() = {idle_time, timeout()}
675 Sets a time-out on a connection when no channels are active.
677 Defaults to infinity.
678 rekey_limit_common_option() =
680 {rekey_limit,
681 Bytes ::
682 limit_bytes() |
683 {Minutes :: limit_time(), Bytes :: limit_bytes()}}
684 limit_bytes() = integer() >= 0 | infinity
686 limit_time() = integer() >= 1 | infinity
688 Sets the limit when rekeying is to be initiated. Both the max
690 time and max amount of data could be configured:
691 * {Minutes, Bytes} initiate rekeying when any of the limits
693 are reached.
694 * Bytes initiate rekeying when Bytes number of bytes are
696 transferred, or at latest after one hour.
697 When a rekeying is done, both the timer and the byte counter are
699 restarted. Defaults to one hour and one GByte.
700 If Minutes is set to infinity, no rekeying will ever occur due
702 to that max time has passed. Setting Bytes to infinity will
703 inhibit rekeying after a certain amount of data has been trans‐
704 ferred. If the option value is set to {infinity, infinity}, no
705 rekeying will be initiated. Note that rekeying initiated by the
706 peer will still be performed.
707 key_cb_common_option() =
709 {key_cb,
710 Module :: atom() | {Module :: atom(), Opts :: [term()]}}
711 Module implementing the behaviour ssh_client_key_api and/or
713 ssh_server_key_api. Can be used to customize the handling of
714 public keys. If callback options are provided along with the
715 module name, they are made available to the callback module via
716 the options passed to it under the key 'key_cb_private'.
717 The Opts defaults to [] when only the Module is specified.
719 The default value of this option is {ssh_file, []}. See also the
721 manpage of ssh_file.
722 A call to the call-back function F will be
724 Module:F(..., [{key_cb_private,Opts}|UserOptions])
726 where ... are arguments to F as in ssh_client_key_api and/or
729 ssh_server_key_api. The UserOptions are the options given to
730 ssh:connect, ssh:shell or ssh:daemon.
731 pref_public_key_algs_common_option() =
733 {pref_public_key_algs, [pubkey_alg()]}
734 List of user (client) public key algorithms to try to use.
736 The default value is the public_key entry in the list returned
738 by ssh:default_algorithms/0.
739 If there is no public key of a specified type available, the
741 corresponding entry is ignored. Note that the available set is
742 dependent on the underlying cryptolib and current user's public
743 keys.
744 See also the option user_dir for specifying the path to the
746 user's keys.
747 disconnectfun_common_option() =
749 {disconnectfun, fun((Reason :: term()) -> void | any())}
750 Provides a fun to implement your own logging when the peer dis‐
752 connects.
753 unexpectedfun_common_option() =
755 {unexpectedfun,
756 fun((Message :: term(), {Host :: term(), Port :: term()}) ->
757 report | skip)}
758 Provides a fun to implement your own logging or other action
760 when an unexpected message arrives. If the fun returns report
761 the usual info report is issued but if skip is returned no
762 report is generated.
763 ssh_msg_debug_fun_common_option() =
765 {ssh_msg_debug_fun,
766 fun((ssh:connection_ref(),
767 AlwaysDisplay :: boolean(),
768 Msg :: binary(),
769 LanguageTag :: binary()) ->
770 any())}
771 Provide a fun to implement your own logging of the SSH message
773 SSH_MSG_DEBUG. The last three parameters are from the message,
774 see RFC 4253, section 11.3. The connection_ref() is the refer‐
775 ence to the connection on which the message arrived. The return
776 value from the fun is not checked.
777 The default behaviour is ignore the message. To get a printout
779 for each message with AlwaysDisplay = true, use for example
780 {ssh_msg_debug_fun, fun(_,true,M,_)-> io:format("DEBUG: ~p~n",
781 [M]) end}
782 id_string_common_option() =
784 {id_string,
785 string() |
786 random |
787 {random, Nmin :: integer() >= 1, Nmax :: integer() >= 1}}
788 The string the daemon will present to a connecting peer ini‐
790 tially. The default value is "Erlang/VSN" where VSN is the ssh
791 application version number.
792 The value random will cause a random string to be created at
794 each connection attempt. This is to make it a bit more difficult
795 for a malicious peer to find the ssh software brand and version.
796 The value {random, Nmin, Nmax} will make a random string with at
798 least Nmin characters and at most Nmax characters.
799 preferred_algorithms_common_option() =
801 {preferred_algorithms, algs_list()}
802 algs_list() = [alg_entry()]
804 alg_entry() =
806 {kex, [kex_alg()]} |
807 {public_key, [pubkey_alg()]} |
808 {cipher, double_algs(cipher_alg())} |
809 {mac, double_algs(mac_alg())} |
810 {compression, double_algs(compression_alg())}
811 kex_alg() =
813 'diffie-hellman-group-exchange-sha1' |
814 'diffie-hellman-group-exchange-sha256' |
815 'diffie-hellman-group1-sha1' | 'diffie-hellman-group14-sha1' |
816 'diffie-hellman-group14-sha256' |
817 'diffie-hellman-group16-sha512' |
818 'diffie-hellman-group18-sha512' | 'curve25519-sha256' |
819 'curve25519-sha256@libssh.org' | 'curve448-sha512' |
820 'ecdh-sha2-nistp256' | 'ecdh-sha2-nistp384' |
821 'ecdh-sha2-nistp521'
822 pubkey_alg() =
824 'ecdsa-sha2-nistp256' | 'ecdsa-sha2-nistp384' |
825 'ecdsa-sha2-nistp521' | 'ssh-ed25519' | 'ssh-ed448' |
826 'rsa-sha2-256' | 'rsa-sha2-512' | 'ssh-dss' | 'ssh-rsa'
827 cipher_alg() =
829 '3des-cbc' | 'AEAD_AES_128_GCM' | 'AEAD_AES_256_GCM' |
830 'aes128-cbc' | 'aes128-ctr' | 'aes128-gcm@openssh.com' |
831 'aes192-ctr' | 'aes256-ctr' | 'aes256-gcm@openssh.com' |
832 'chacha20-poly1305@openssh.com'
833 mac_alg() =
835 'AEAD_AES_128_GCM' | 'AEAD_AES_256_GCM' | 'hmac-sha1' |
836 'hmac-sha2-256' | 'hmac-sha2-512'
837 compression_alg() = none | zlib | 'zlib@openssh.com'
839 double_algs(AlgType) =
841 [{client2server, [AlgType]} | {server2client, [AlgType]}] |
842 [AlgType]
843 List of algorithms to use in the algorithm negotiation. The
845 default algs_list() can be obtained from default_algorithms/0.
846 If an alg_entry() is missing in the algs_list(), the default
848 value is used for that entry.
849 Here is an example of this option:
851 {preferred_algorithms,
853 [{public_key,['ssh-rsa','ssh-dss']},
854 {cipher,[{client2server,['aes128-ctr']},
855 {server2client,['aes128-cbc','3des-cbc']}]},
856 {mac,['hmac-sha2-256','hmac-sha1']},
857 {compression,[none,zlib]}
858 ]
859 }
860 The example specifies different algorithms in the two directions
863 (client2server and server2client), for cipher but specifies the
864 same algorithms for mac and compression in both directions. The
865 kex (key exchange) is implicit but public_key is set explicitly.
866 For background and more examples see the User's Guide.
868 If an algorithm name occurs more than once in a list, the behav‐
870 iour is undefined. The tags in the property lists are also
871 assumed to occur at most one time.
872 Warning:
874 Changing the values can make a connection less secure. Do not
875 change unless you know exactly what you are doing. If you do not
876 understand the values then you are not supposed to change them.
877 modify_algorithms_common_option() =
880 {modify_algorithms, modify_algs_list()}
881 modify_algs_list() =
883 [{append, algs_list()} |
884 {prepend, algs_list()} |
885 {rm, algs_list()}]
886 Modifies the list of algorithms to use in the algorithm negotia‐
888 tion. The modifications are applied after the option pre‐
889 ferred_algorithms (if existing) is applied.
890 The algoritm for modifications works like this:
892 * Input is the modify_algs_list() and a set of algorithms A
894 obtained from the preferred_algorithms option if existing,
895 or else from the ssh:default_algorithms/0.
896 * The head of the modify_algs_list() modifies A giving the
898 result A'.
899 The possible modifications are:
901 * Append or prepend supported but not enabled algorithm(s)
903 to the list of algorithms. If the wanted algorithms
904 already are in A they will first be removed and then
905 appended or prepended,
906 * Remove (rm) one or more algorithms from A.
908 * Repeat the modification step with the tail of mod‐
910 ify_algs_list() and the resulting A'.
911 If an unsupported algorithm is in the modify_algs_list(), it
913 will be silently ignored
914 If there are more than one modify_algorithms options, the result
916 is undefined.
917 Here is an example of this option:
919 {modify_algorithms,
921 [{prepend, [{kex, ['diffie-hellman-group1-sha1']}],
922 {rm, [{compression, [none]}]}
923 ]
924 }
925 The example specifies that:
928 * the old key exchange algorithm 'diffie-hellman-group1-sha1'
930 should be the main alternative. It will be the main alterna‐
931 tive since it is prepened to the list
932 * The compression algorithm none (= no compression) is removed
934 so compression is enforced
935 For background and more examples see the User's Guide.
937 inet_common_option() = {inet, inet | inet6}
939 IP version to use when the host address is specified as any.
941 auth_methods_common_option() = {auth_methods, string()}
943 Comma-separated string that determines which authentication
945 methods that the client shall support and in which order they
946 are tried. Defaults to "publickey,keyboard-interactive,password"
947 Note that the client is free to use any order and to exclude
949 methods.
950 fd_common_option() = {fd, gen_tcp:socket()}
952 Allows an existing file-descriptor to be used (passed on to the
954 transport protocol).
955 Other data types
957 host() = string() | inet:ip_address() | loopback
958 ip_port() = {inet:ip_address(), inet:port_number()}
960 mod_args() = {Module :: atom(), Args :: list()}
962 mod_fun_args() =
964 {Module :: atom(), Function :: atom(), Args :: list()}
965 open_socket() = gen_tcp:socket()
967 The socket is supposed to be result of a gen_tcp:connect or a
969 gen_tcp:accept. The socket must be in passive mode (that is,
970 opened with the option {active,false}).
971 daemon_ref()
973 Opaque data type representing a daemon.
975 Returned by the functions daemon/1,2,3.
977 connection_ref()
979 Opaque data type representing a connection between a client and
981 a server (daemon).
982 Returned by the functions connect/2,3,4 and ssh_sftp:start_chan‐
984 nel/2,3.
985 channel_id()
987 Opaque data type representing a channel inside a connection.
989 Returned by the functions ssh_connection:session_channel/2,4.
991 connection_info_tuple() =
993 {client_version, version()} |
994 {server_version, version()} |
995 {user, string()} |
996 {peer, {inet:hostname(), ip_port()}} |
997 {sockname, ip_port()} |
998 {options, client_options()} |
999 {algorithms, conn_info_algs()} |
1000 {channels, conn_info_channels()}
1001 version() = {protocol_version(), software_version()}
1003 protocol_version() =
1005 {Major :: integer() >= 1, Minor :: integer() >= 0}
1006 software_version() = string()
1008 conn_info_algs() =
1010 [{kex, kex_alg()} |
1011 {hkey, pubkey_alg()} |
1012 {encrypt, cipher_alg()} |
1013 {decrypt, cipher_alg()} |
1014 {send_mac, mac_alg()} |
1015 {recv_mac, mac_alg()} |
1016 {compress, compression_alg()} |
1017 {decompress, compression_alg()} |
1018 {send_ext_info, boolean()} |
1019 {recv_ext_info, boolean()}]
1020 conn_info_channels() = [proplists:proplist()]
1022 Return values from the connection_info/1 and connection_info/2
1024 functions.
1025 In the option info tuple are only the options included that dif‐
1027 fers from the default values.
1028 daemon_info_tuple() =
1030 {port, inet:port_number()} |
1031 {ip, inet:ip_address()} |
1032 {profile, atom()} |
1033 {options, daemon_options()}
1034 Return values from the daemon_info/1 and daemon_info/2 func‐
1036 tions.
1037 In the option info tuple are only the options included that dif‐
1039 fers from the default values.
1040 opaque_client_options
1042 opaque_daemon_options
1044 opaque_common_options
1046 Opaque types that define experimental options that are not to be
1048 used in products.
1049
1051 close(ConnectionRef) -> ok | {error, term()}
1052 Types:
1054 ConnectionRef = connection_ref()
1056 Closes an SSH connection.
1058 connect(Host, Port, Options) -> Result
1060 connect(Host, Port, Options, NegotiationTimeout) -> Result
1061 connect(TcpSocket, Options) -> Result
1062 connect(TcpSocket, Options, NegotiationTimeout) -> Result
1063 Types:
1065 Host = host()
1067 Port = inet:port_number()
1068 Options = client_options()
1069 TcpSocket = open_socket()
1070 NegotiationTimeout = timeout()
1071 Result = {ok, connection_ref()} | {error, term()}
1072 Connects to an SSH server at the Host on Port.
1074 As an alternative, an already open TCP socket could be passed to
1076 the function in TcpSocket. The SSH initiation and negotiation
1077 will be initiated on that one with the SSH that should be at the
1078 other end.
1079 No channel is started. This is done by calling ssh_connec‐
1081 tion:session_channel/[2, 4].
1082 The NegotiationTimeout is in milli-seconds. The default value is
1084 infinity. For connection timeout, use the option connect_time‐
1085 out.
1086 connection_info(ConnectionRef) -> InfoTupleList
1088 connection_info(ConnectionRef, Key :: ItemList | Item) ->
1090 InfoTupleList | InfoTuple
1091 Types:
1093 ConnectionRef = connection_ref()
1095 ItemList = [Item]
1096 Item =
1097 client_version | server_version | user | peer | sockname
1098 |
1099 options | algorithms | sockname
1100 InfoTupleList = [InfoTuple]
1101 InfoTuple = connection_info_tuple()
1102 Returns information about a connection intended for e.g debug‐
1104 ging or logging.
1105 When the Key is a single Item, the result is a single InfoTuple
1107 daemon(Port | TcpSocket) -> Result
1109 daemon(Port | TcpSocket, Options) -> Result
1110 daemon(HostAddress, Port, Options) -> Result
1111 Types:
1113 Port = integer()
1115 TcpSocket = open_socket()
1116 Options = daemon_options()
1117 HostAddress = host() | any
1118 Result = {ok, daemon_ref()} | {error, atom()}
1119 Starts a server listening for SSH connections on the given port.
1121 If the Port is 0, a random free port is selected. See dae‐
1122 mon_info/1 about how to find the selected port number.
1123 As an alternative, an already open TCP socket could be passed to
1125 the function in TcpSocket. The SSH initiation and negotiation
1126 will be initiated on that one when an SSH starts at the other
1127 end of the TCP socket.
1128 For a description of the options, see Daemon Options.
1130 Please note that by historical reasons both the HostAddress
1132 argument and the gen_tcp connect_option() {ip,Address} set the
1133 listening address. This is a source of possible inconsistent
1134 settings.
1135 The rules for handling the two address passing options are:
1137 * if HostAddress is an IP-address, that IP-address is the lis‐
1139 tening address. An 'ip'-option will be discarded if present.
1140 * if HostAddress is the atom loopback, the listening address
1142 is loopback and an loopback address will be choosen by the
1143 underlying layers. An 'ip'-option will be discarded if
1144 present.
1145 * if HostAddress is the atom any and no 'ip'-option is
1147 present, the listening address is any and the socket will
1148 listen to all addresses
1149 * if HostAddress is any and an 'ip'-option is present, the
1151 listening address is set to the value of the 'ip'-option
1152 daemon_info(DaemonRef) ->
1154 {ok, InfoTupleList} | {error, bad_daemon_ref}
1155 daemon_info(DaemonRef, Key :: ItemList | Item) ->
1157 InfoTupleList | InfoTuple | {error, bad_daemon_ref}
1158 Types:
1160 DaemonRef = daemon_ref()
1162 ItemList = [Item]
1163 Item = ip | port | profile | options
1164 InfoTupleList = [InfoTuple]
1165 InfoTuple = daemon_info_tuple()
1166 Returns information about a daemon intended for e.g debugging or
1168 logging.
1169 When the Key is a single Item, the result is a single InfoTuple
1171 Note that daemon_info/1 and daemon_info/2 returns different
1173 types due to compatibility reasons.
1174 default_algorithms() -> algs_list()
1176 Returns a key-value list, where the keys are the different types
1178 of algorithms and the values are the algorithms themselves.
1179 See the User's Guide for an example.
1181 shell(Host | TcpSocket) -> Result
1183 shell(Host | TcpSocket, Options) -> Result
1184 shell(Host, Port, Options) -> Result
1185 Types:
1187 Host = host()
1189 TcpSocket = open_socket()
1190 Port = inet:port_number()
1191 Options = client_options()
1192 Result = ok | {error, Reason::term()}
1193 Connects to an SSH server at Host and Port (defaults to 22) and
1195 starts an interactive shell on that remote host.
1196 As an alternative, an already open TCP socket could be passed to
1198 the function in TcpSocket. The SSH initiation and negotiation
1199 will be initiated on that one and finaly a shell will be started
1200 on the host at the other end of the TCP socket.
1201 For a description of the options, see Client Options.
1203 The function waits for user input, and does not return until the
1205 remote shell is ended (that is, exit from the shell).
1206 start() -> ok | {error, term()}
1208 start(Type) -> ok | {error, term()}
1210 Types:
1212 Type = permanent | transient | temporary
1214 Utility function that starts the applications crypto, pub‐
1216 lic_key, and ssh. Default type is temporary. For more informa‐
1217 tion, see the application(3) manual page in Kernel.
1218 stop() -> ok | {error, term()}
1220 Stops the ssh application. For more information, see the appli‐
1222 cation(3) manual page in Kernel.
1223 stop_daemon(DaemonRef :: daemon_ref()) -> ok
1225 stop_daemon(Address :: inet:ip_address(),
1227 Port :: inet:port_number()) ->
1228 ok
1229 stop_daemon(Address :: any | inet:ip_address(),
1231 Port :: inet:port_number(),
1232 Profile :: atom()) ->
1233 ok
1234 Stops the listener and all connections started by the listener.
1236 stop_listener(SysSup :: daemon_ref()) -> ok
1238 stop_listener(Address :: inet:ip_address(),
1240 Port :: inet:port_number()) ->
1241 ok
1242 stop_listener(Address :: any | inet:ip_address(),
1244 Port :: inet:port_number(),
1245 Profile :: term()) ->
1246 ok
1247 Stops the listener, but leaves existing connections started by
1249 the listener operational.
1250Ericsson AB ssh 4.8 ssh(3)