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 op‐
34 tion 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 ex‐
50 plaining 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 Those objects are per default stored in files. The default names, paths
59 and file formats are the same as for OpenSSH. Keys could be generated
60 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. De‐
73 fault 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 au‐
85 thorization. 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 di‐
92 rectory .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 ex‐
129 plained below or by following the hyperlinks.
130 Note that not every gen_tcp:connect_option() is accepted. See
132 set_sock_opts/2 for a list of prohibited options.
133 Also note that setting a gen_tcp:connect_option() could change
135 the socket in a way that impacts the ssh client's behaviour neg‐
136 atively. You use it on your own risk.
137 host_accepting_client_options() =
139 {silently_accept_hosts, accept_hosts()} |
140 {user_interaction, boolean()} |
141 {save_accepted_host, boolean()} |
142 {quiet_mode, boolean()}
143 accept_hosts() =
145 boolean() |
146 accept_callback() |
147 {HashAlgoSpec :: fp_digest_alg(), accept_callback()}
148 fp_digest_alg() = md5 | crypto:sha1() | crypto:sha2()
150 accept_callback() =
152 fun((PeerName :: string(), fingerprint()) -> boolean()) |
153 fun((PeerName :: string(),
154 Port :: inet:port_number(),
155 fingerprint()) ->
156 boolean())
157 fingerprint() = string() | [string()]
159 silently_accept_hosts:
161 This option guides the connect function on how to act when
162 the connected server presents a Host Key that the client has
163 not seen before. The default is to ask the user with a ques‐
164 tion on stdio of whether to accept or reject the new Host
165 Key. See the option user_dir for specifying the path to the
166 file known_hosts where previously accepted Host Keys are
167 recorded. See also the option key_cb for the general way to
168 handle keys.
169 The option can be given in three different forms as seen
171 above:
172 * The value is a boolean(). The value true will make the
174 client accept any unknown Host Key without any user inter‐
175 action. The value false preserves the default behaviour of
176 asking the user on stdio.
177 * An accept_callback() will be called and the boolean return
179 value true will make the client accept the Host Key. A re‐
180 turn value of false will make the client to reject the
181 Host Key and as a result the connection will be closed.
182 The arguments to the fun are:
183 * PeerName - a string with the name or address of the re‐
185 mote host.
186 * FingerPrint - the fingerprint of the Host Key as pub‐
188 lic_key:ssh_hostkey_fingerprint/1 calculates it.
189 * A tuple {HashAlgoSpec, accept_callback}. The HashAlgoSpec
191 specifies which hash algorithm shall be used to calculate
192 the fingerprint used in the call of the accept_callback().
193 The HashALgoSpec is either an atom or a list of atoms as
194 the first argument in public_key:ssh_hostkey_finger‐
195 print/2. If it is a list of hash algorithm names, the Fin‐
196 gerPrint argument in the accept_callback() will be a list
197 of fingerprints in the same order as the corresponding
198 name in the HashAlgoSpec list.
199 user_interaction:
201 If false, disables the client to connect to the server if
202 any user interaction is needed, such as accepting the server
203 to be added to the known_hosts file, or supplying a pass‐
204 word.
205 Even if user interaction is allowed it can be suppressed by
207 other options, such as silently_accept_hosts and password.
208 However, those options are not always desirable to use from
209 a security point of view.
210 Defaults to true.
212 save_accepted_host:
214 If true, the client saves an accepted host key to avoid the
215 accept question the next time the same host is connected. If
216 the option key_cb is not present, the key is saved in the
217 file "known_hosts". See option user_dir for the location of
218 that file.
219 If false, the key is not saved and the key will still be un‐
221 known at the next access of the same host.
222 Defaults to true
224 quiet_mode:
226 If true, the client does not print anything on authoriza‐
227 tion.
228 Defaults to false
230 authentication_client_options() =
232 {user, string()} | {password, string()}
233 user:
235 Provides the username. If this option is not given, ssh
236 reads from the environment (LOGNAME or USER on UNIX, USER‐
237 NAME on Windows).
238 password:
240 Provides a password for password authentication. If this op‐
241 tion is not given, the user is asked for a password, if the
242 password authentication method is attempted.
243 diffie_hellman_group_exchange_client_option() =
245 {dh_gex_limits,
246 {Min :: integer() >= 1,
247 I :: integer() >= 1,
248 Max :: integer() >= 1}}
249 Sets the three diffie-hellman-group-exchange parameters that
251 guides the connected server in choosing a group. See RFC 4419
252 for the details. The default value is {1024, 6144, 8192}.
253 connect_timeout_client_option() = {connect_timeout, timeout()}
255 Sets a timeout on the transport layer connect time. For gen_tcp
257 the time is in milli-seconds and the default value is infinity.
258 See the parameter Timeout in connect/4 for a timeout of the ne‐
260 gotiation phase.
261 recv_ext_info_client_option() = {recv_ext_info, boolean()}
263 Make the client tell the server that the client accepts exten‐
265 sion negotiation, that is, include ext-info-c in the kexinit
266 message sent. See RFC 8308 for details and ssh(6) for a list of
267 currently implemented extensions.
268 Default value is true which is compatible with other implementa‐
270 tions not supporting ext-info.
271 Daemon Options (Server Options)
273 daemon_options() = [daemon_option()]
274 daemon_option() =
276 subsystem_daemon_option() |
277 shell_daemon_option() |
278 exec_daemon_option() |
279 ssh_cli_daemon_option() |
280 tcpip_tunnel_out_daemon_option() |
281 tcpip_tunnel_in_daemon_option() |
282 authentication_daemon_options() |
283 diffie_hellman_group_exchange_daemon_option() |
284 negotiation_timeout_daemon_option() |
285 hello_timeout_daemon_option() |
286 hardening_daemon_options() |
287 callbacks_daemon_options() |
288 send_ext_info_daemon_option() |
289 opaque_daemon_options() |
290 gen_tcp:listen_option() |
291 common_option()
292 Options for daemons. The individual options are further ex‐
294 plained below or by following the hyperlinks.
295 Note that not every gen_tcp:listen_option() is accepted. See
297 set_sock_opts/2 for a list of prohibited options.
298 Also note that setting a gen_tcp:listen_option() could change
300 the socket in a way that impacts the ssh deamon's behaviour neg‐
301 atively. You use it on your own risk.
302 subsystem_daemon_option() = {subsystems, subsystem_specs()}
304 subsystem_specs() = [subsystem_spec()]
306 subsystem_spec() = {Name :: string(), mod_args()}
308 Defines a subsystem in the daemon.
310 The subsystem_name is the name that a client requests to start
312 with for example ssh_connection:subsystem/4.
313 The channel_callback is the module that implements the
315 ssh_server_channel (replaces ssh_daemon_channel) behaviour in
316 the daemon. See the section Creating a Subsystem in the User's
317 Guide for more information and an example.
318 If the subsystems option is not present, the value of
320 ssh_sftpd:subsystem_spec([]) is used. This enables the sftp sub‐
321 system by default. The option can be set to the empty list if
322 you do not want the daemon to run any subsystems.
323 shell_daemon_option() = {shell, shell_spec()}
325 shell_spec() = mod_fun_args() | shell_fun() | disabled
327 shell_fun() = 'shell_fun/1'() | 'shell_fun/2'()
329 'shell_fun/1'() = fun((User :: string()) -> pid())
331 'shell_fun/2'() =
333 fun((User :: string(), PeerAddr :: inet:ip_address()) -> pid())
334 Defines the read-eval-print loop used in a daemon when a shell
336 is requested by the client. The default is to use the Erlang
337 shell: {shell, start, []}
338 See the option exec-option for a description of how the daemon
340 executes shell-requests and exec-requests depending on the
341 shell- and exec-options.
342 exec_daemon_option() = {exec, exec_spec()}
344 exec_spec() =
346 {direct, exec_fun()} | disabled | deprecated_exec_opt()
347 exec_fun() = 'exec_fun/1'() | 'exec_fun/2'() | 'exec_fun/3'()
349 'exec_fun/1'() = fun((Cmd :: string()) -> exec_result())
351 'exec_fun/2'() =
353 fun((Cmd :: string(), User :: string()) -> exec_result())
354 'exec_fun/3'() =
356 fun((Cmd :: string(),
357 User :: string(),
358 ClientAddr :: ip_port()) ->
359 exec_result())
360 exec_result() =
362 {ok, Result :: term()} | {error, Reason :: term()}
363 This option changes how the daemon executes exec-requests from
365 clients. The term in the return value is formatted to a string
366 if it is a non-string type. No trailing newline is added in the
367 ok-case.
368 See the User's Guide section on One-Time Execution for examples.
370 Error texts are returned on channel-type 1 which usually is
372 piped to stderr on e.g Linux systems. Texts from a successful
373 execution are returned on channel-type 0 and will in similar
374 manner be piped to stdout. The exit-status code is set to 0 for
375 success and 255 for errors. The exact results presented on the
376 client side depends on the client and the client's operating
377 system.
378 In case of the {direct, exec_fun()} variant or no exec-option at
380 all, all reads from standard_input will be from the received
381 data-events of type 0. Those are sent by the client. Similarily
382 all writes to standard_output will be sent as data-events to the
383 client. An OS shell client like the command 'ssh' will usally
384 use stdin and stdout for the user interface.
385 The option cooperates with the daemon-option shell in the fol‐
387 lowing way:
388 1. If neither the exec-option nor the shell-option is
390 present::
391 The default Erlang evaluator is used both for exec and shell
392 requests. The result is returned to the client.
393 2. If the exec_spec's value is disabled (the shell-option may
395 or may not be present)::
396 No exec-requests are executed but shell-requests are not af‐
397 fected, they follow the shell_spec's value.
398 3. If the exec-option is present and the exec_spec value =/=
400 disabled (the shell-option may or may not be present)::
401 The exec_spec fun() is called with the same number of param‐
402 eters as the arity of the fun, and the result is returned to
403 the client. Shell-requests are not affected, they follow the
404 shell_spec's value.
405 4. If the exec-option is absent, and the shell-option is
407 present with the default Erlang shell as the shell_spec's
408 value::
409 The default Erlang evaluator is used both for exec and shell
410 requests. The result is returned to the client.
411 5. If the exec-option is absent, and the shell-option is
413 present with a value that is neither the default Erlang shell
414 nor the value disabled::
415 The exec-request is not evaluated and an error message is
416 returned to the client. Shell-requests are executed accord‐
417 ing to the value of the shell_spec.
418 6. If the exec-option is absent, and the shell_spec's value is
420 disabled::
421 Exec requests are executed by the default shell, but shell-
422 requests are not executed.
423 If a custom CLI is installed (see the option ssh_cli) the rules
425 above are replaced by thoose implied by the custom CLI.
426 Note:
428 The exec-option has existed for a long time but has not previ‐
429 ously been documented. The old definition and behaviour are re‐
430 tained but obey the rules 1-6 above if conflicting. The old and
431 undocumented style should not be used in new programs.
432 deprecated_exec_opt() = function() | mod_fun_args()
435 Old-style exec specification that are kept for compatibility,
437 but should not be used in new programs
438 ssh_cli_daemon_option() = {ssh_cli, mod_args() | no_cli}
440 Provides your own CLI implementation in a daemon.
442 It is a channel callback module that implements a shell and com‐
444 mand execution. The shell's read-eval-print loop can be custom‐
445 ized, using the option shell. This means less work than imple‐
446 menting an own CLI channel. If ssh_cli is set to no_cli, the CLI
447 channels like shell and exec are disabled and only subsystem
448 channels are allowed.
449 authentication_daemon_options() =
451 ssh_file:system_dir_daemon_option() |
452 {auth_method_kb_interactive_data, prompt_texts()} |
453 {user_passwords, [{UserName :: string(), Pwd :: string()}]} |
454 {pk_check_user, boolean()} |
455 {password, string()} |
456 {pwdfun, pwdfun_2() | pwdfun_4()}
457 prompt_texts() =
459 kb_int_tuple() | kb_int_fun_3() | kb_int_fun_4()
460 kb_int_tuple() =
462 {Name :: string(),
463 Instruction :: string(),
464 Prompt :: string(),
465 Echo :: boolean()}
466 kb_int_fun_3() =
468 fun((Peer :: ip_port(), User :: string(), Service :: string()) ->
469 kb_int_tuple())
470 kb_int_fun_4() =
472 fun((Peer :: ip_port(),
473 User :: string(),
474 Service :: string(),
475 State :: any()) ->
476 kb_int_tuple())
477 pwdfun_2() =
479 fun((User :: string(), Password :: string() | pubkey) ->
480 boolean())
481 pwdfun_4() =
483 fun((User :: string(),
484 Password :: string() | pubkey,
485 PeerAddress :: ip_port(),
486 State :: any()) ->
487 boolean() |
488 disconnect |
489 {boolean(), NewState :: any()})
490 auth_method_kb_interactive_data:
492 Sets the text strings that the daemon sends to the client
493 for presentation to the user when using keyboard-interactive
494 authentication.
495 If the fun/3 or fun/4 is used, it is called when the actual
497 authentication occurs and may therefore return dynamic data
498 like time, remote ip etc.
499 The parameter Echo guides the client about need to hide the
501 password.
502 The default value is: {auth_method_kb_interactive_data,
504 {"SSH server", "Enter password for \""++User++"\"", "pass‐
505 word: ", false}>
506 user_passwords:
508 Provides passwords for password authentication. The pass‐
509 words are used when someone tries to connect to the server
510 and public key user-authentication fails. The option pro‐
511 vides a list of valid usernames and the corresponding pass‐
512 words.
513 pk_check_user:
515 Enables checking of the client's user name in the server
516 when doing public key authentication. It is disabled by de‐
517 fault.
518 The term "user" is used differently in OpenSSH and SSH in
520 Erlang/OTP: see more in the User's Guide.
521 If the option is enabled, and no pwdfun is present, the user
523 name must present in the user_passwords for the check to
524 succeed but the value of the password is not checked.
525 In case of a pwdfun checking the user, the atom pubkey is
527 put in the password argument.
528 password:
530 Provides a global password that authenticates any user.
531 Warning:
533 Intended to facilitate testing.
534 From a security perspective this option makes the server very
536 vulnerable.
537 pwdfun with pwdfun_4():
540 Provides a function for password validation. This could used
541 for calling an external system or handeling passwords stored
542 as hash values.
543 This fun can also be used to make delays in authentication
545 tries for example by calling timer:sleep/1.
546 To facilitate for instance counting of failed tries, the
548 State variable could be used. This state is per connection
549 only. The first time the pwdfun is called for a connection,
550 the State variable has the value undefined.
551 The fun should return:
553 * true if the user and password is valid
555 * false if the user or password is invalid
557 * disconnect if a SSH_MSG_DISCONNECT message should be sent
559 immediately. It will be followed by a close of the under‐
560 lying tcp connection.
561 * {true, NewState:any()} if the user and password is valid
563 * {false, NewState:any()} if the user or password is invalid
565 A third usage is to block login attempts from a missbehaving
567 peer. The State described above can be used for this. The
568 return value disconnect is useful for this.
569 In case of the pk_check_user is set, the atom pubkey is put
571 in the password argument when validating a public key login.
572 The pwdfun is then responsible to check that the user name
573 is valid.
574 pwdfun with pwdfun_2():
576 Provides a function for password validation. This function
577 is called with user and password as strings, and returns:
578 * true if the user and password is valid
580 * false if the user or password is invalid
582 In case of the pk_check_user is set, the atom pubkey is put
584 in the password argument when validating a public key login.
585 The pwdfun is then responsible to check that the user name
586 is valid.
587 This variant is kept for compatibility.
589 diffie_hellman_group_exchange_daemon_option() =
591 {dh_gex_groups,
592 [explicit_group()] |
593 explicit_group_file() |
594 ssh_moduli_file()} |
595 {dh_gex_limits, {Min :: integer() >= 1, Max :: integer() >= 1}}
596 explicit_group() =
598 {Size :: integer() >= 1,
599 G :: integer() >= 1,
600 P :: integer() >= 1}
601 explicit_group_file() = {file, string()}
603 ssh_moduli_file() = {ssh_moduli_file, string()}
605 dh_gex_groups:
607 Defines the groups the server may choose among when diffie-
608 hellman-group-exchange is negotiated. See RFC 4419 for de‐
609 tails. The three variants of this option are:
610 {Size=integer(),G=integer(),P=integer()}:
612 The groups are given explicitly in this list. There may be
613 several elements with the same Size. In such a case, the
614 server will choose one randomly in the negotiated Size.
615 {file,filename()}:
617 The file must have one or more three-tuples {Size=inte‐
618 ger(),G=integer(),P=integer()} terminated by a dot. The
619 file is read when the daemon starts.
620 {ssh_moduli_file,filename()}:
622 The file must be in ssh-keygen moduli file format. The
623 file is read when the daemon starts.
624 The default list is fetched from the public_key application.
626 dh_gex_limits:
628 Limits what a client can ask for in diffie-hellman-group-ex‐
629 change. The limits will be {MaxUsed = min(MaxClient,Max),
630 MinUsed = max(MinClient,Min)} where MaxClient and MinClient
631 are the values proposed by a connecting client.
632 The default value is {0,infinity}.
634 If MaxUsed < MinUsed in a key exchange, it will fail with a
636 disconnect.
637 See RFC 4419 for the function of the Max and Min values.
639 hello_timeout_daemon_option() = {hello_timeout, timeout()}
641 Maximum time in milliseconds for the first part of the ssh ses‐
643 sion setup, the hello message exchange. Defaults to 30000 ms (30
644 seconds). If the client fails to send the first message within
645 this time, the connection is closed.
646 negotiation_timeout_daemon_option() =
648 {negotiation_timeout, timeout()}
649 Maximum time in milliseconds for the authentication negotiation.
651 Defaults to 120000 ms (2 minutes). If the client fails to log in
652 within this time, the connection is closed.
653 hardening_daemon_options() =
655 {max_sessions, integer() >= 1} |
656 {max_channels, integer() >= 1} |
657 {parallel_login, boolean()} |
658 {minimal_remote_max_packet_size, integer() >= 1}
659 max_sessions:
661 The maximum number of simultaneous sessions that are ac‐
662 cepted at any time for this daemon. This includes sessions
663 that are being authorized. Thus, if set to N, and N clients
664 have connected but not started the login process, connection
665 attempt N+1 is aborted. If N connections are authenticated
666 and still logged in, no more logins are accepted until one
667 of the existing ones log out.
668 The counter is per listening port. Thus, if two daemons are
670 started, one with {max_sessions,N} and the other with
671 {max_sessions,M}, in total N+M connections are accepted for
672 the whole ssh application.
673 Notice that if parallel_login is false, only one client at a
675 time can be in the authentication phase.
676 By default, this option is not set. This means that the num‐
678 ber is not limited.
679 max_channels:
681 The maximum number of channels with active remote subsystem
682 that are accepted for each connection to this daemon
683 By default, this option is not set. This means that the num‐
685 ber is not limited.
686 parallel_login:
688 If set to false (the default value), only one login is han‐
689 dled at a time. If set to true, an unlimited number of login
690 attempts are allowed simultaneously.
691 If the max_sessions option is set to N and parallel_login is
693 set to true, the maximum number of simultaneous login at‐
694 tempts at any time is limited to N-K, where K is the number
695 of authenticated connections present at this daemon.
696 Warning:
698 Do not enable parallel_logins without protecting the server by
699 other means, for example, by the max_sessions option or a
700 firewall configuration. If set to true, there is no protection
701 against DOS attacks.
702 minimal_remote_max_packet_size:
705 The least maximum packet size that the daemon will accept in
706 channel open requests from the client. The default value is
707 0.
708 callbacks_daemon_options() =
710 {failfun,
711 fun((User :: string(),
712 PeerAddress :: inet:ip_address(),
713 Reason :: term()) ->
714 term())} |
715 {connectfun,
716 fun((User :: string(),
717 PeerAddress :: inet:ip_address(),
718 Method :: string()) ->
719 term())}
720 connectfun:
722 Provides a fun to implement your own logging when a user au‐
723 thenticates to the server.
724 failfun:
726 Provides a fun to implement your own logging when a user
727 fails to authenticate.
728 send_ext_info_daemon_option() = {send_ext_info, boolean()}
730 Make the server (daemon) tell the client that the server accepts
732 extension negotiation, that is, include ext-info-s in the kex‐
733 init message sent. See RFC 8308 for details and ssh(6) for a
734 list of currently implemented extensions.
735 Default value is true which is compatible with other implementa‐
737 tions not supporting ext-info.
738 tcpip_tunnel_in_daemon_option() = {tcpip_tunnel_in, boolean()}
740 Enables (true) or disables (false) the possibility to tunnel a
742 TCP/IP connection in to a server. Disabled per default.
743 tcpip_tunnel_out_daemon_option() =
745 {tcpip_tunnel_out, boolean()}
746 Enables (true) or disables (false) the possibility to tunnel a
748 TCP/IP connection out of a server. Disabled per default.
749 Options common to clients and daemons
751 common_options() = [common_option()]
752 common_option() =
754 ssh_file:user_dir_common_option() |
755 profile_common_option() |
756 max_idle_time_common_option() |
757 key_cb_common_option() |
758 disconnectfun_common_option() |
759 unexpectedfun_common_option() |
760 ssh_msg_debug_fun_common_option() |
761 rekey_limit_common_option() |
762 id_string_common_option() |
763 pref_public_key_algs_common_option() |
764 preferred_algorithms_common_option() |
765 modify_algorithms_common_option() |
766 auth_methods_common_option() |
767 inet_common_option() |
768 fd_common_option()
769 The options above can be used both in clients and in daemons
771 (servers). They are further explained below.
772 profile_common_option() = {profile, atom()}
774 Used together with ip-address and port to uniquely identify a
776 ssh daemon. This can be useful in a virtualized environment,
777 where there can be more that one server that has the same ip-ad‐
778 dress and port. If this property is not explicitly set, it is
779 assumed that the the ip-address and port uniquely identifies the
780 SSH daemon.
781 max_idle_time_common_option() = {idle_time, timeout()}
783 Sets a time-out on a connection when no channels are open. De‐
785 faults to infinity. The unit is milliseconds.
786 The timeout is not active until channels are started, so it does
788 not limit the time from the connection creation to the first
789 channel opening.
790 rekey_limit_common_option() =
792 {rekey_limit,
793 Bytes ::
794 limit_bytes() |
795 {Minutes :: limit_time(), Bytes :: limit_bytes()}}
796 limit_bytes() = integer() >= 0 | infinity
798 limit_time() = integer() >= 1 | infinity
800 Sets the limit when rekeying is to be initiated. Both the max
802 time and max amount of data could be configured:
803 * {Minutes, Bytes} initiate rekeying when any of the limits
805 are reached.
806 * Bytes initiate rekeying when Bytes number of bytes are
808 transferred, or at latest after one hour.
809 When a rekeying is done, both the timer and the byte counter are
811 restarted. Defaults to one hour and one GByte.
812 If Minutes is set to infinity, no rekeying will ever occur due
814 to that max time has passed. Setting Bytes to infinity will in‐
815 hibit rekeying after a certain amount of data has been trans‐
816 ferred. If the option value is set to {infinity, infinity}, no
817 rekeying will be initiated. Note that rekeying initiated by the
818 peer will still be performed.
819 key_cb_common_option() =
821 {key_cb,
822 Module :: atom() | {Module :: atom(), Opts :: [term()]}}
823 Module implementing the behaviour ssh_client_key_api and/or
825 ssh_server_key_api. Can be used to customize the handling of
826 public keys. If callback options are provided along with the
827 module name, they are made available to the callback module via
828 the options passed to it under the key 'key_cb_private'.
829 The Opts defaults to [] when only the Module is specified.
831 The default value of this option is {ssh_file, []}. See also the
833 manpage of ssh_file.
834 A call to the call-back function F will be
836 Module:F(..., [{key_cb_private,Opts}|UserOptions])
838 where ... are arguments to F as in ssh_client_key_api and/or
841 ssh_server_key_api. The UserOptions are the options given to
842 ssh:connect, ssh:shell or ssh:daemon.
843 pref_public_key_algs_common_option() =
845 {pref_public_key_algs, [pubkey_alg()]}
846 List of user (client) public key algorithms to try to use.
848 The default value is the public_key entry in the list returned
850 by ssh:default_algorithms/0.
851 If there is no public key of a specified type available, the
853 corresponding entry is ignored. Note that the available set is
854 dependent on the underlying cryptolib and current user's public
855 keys.
856 See also the option user_dir for specifying the path to the
858 user's keys.
859 disconnectfun_common_option() =
861 {disconnectfun, fun((Reason :: term()) -> void | any())}
862 Provides a fun to implement your own logging or other handling
864 at disconnects.
865 unexpectedfun_common_option() =
867 {unexpectedfun,
868 fun((Message :: term(), {Host :: term(), Port :: term()}) ->
869 report | skip)}
870 Provides a fun to implement your own logging or other action
872 when an unexpected message arrives. If the fun returns report
873 the usual info report is issued but if skip is returned no re‐
874 port is generated.
875 ssh_msg_debug_fun_common_option() =
877 {ssh_msg_debug_fun,
878 fun((ssh:connection_ref(),
879 AlwaysDisplay :: boolean(),
880 Msg :: binary(),
881 LanguageTag :: binary()) ->
882 any())}
883 Provide a fun to implement your own logging of the SSH message
885 SSH_MSG_DEBUG. The last three parameters are from the message,
886 see RFC 4253, section 11.3. The connection_ref() is the refer‐
887 ence to the connection on which the message arrived. The return
888 value from the fun is not checked.
889 The default behaviour is ignore the message. To get a printout
891 for each message with AlwaysDisplay = true, use for example
892 {ssh_msg_debug_fun, fun(_,true,M,_)-> io:format("DEBUG: ~p~n",
893 [M]) end}
894 id_string_common_option() =
896 {id_string,
897 string() |
898 random |
899 {random, Nmin :: integer() >= 1, Nmax :: integer() >= 1}}
900 The string the daemon will present to a connecting peer ini‐
902 tially. The default value is "Erlang/VSN" where VSN is the ssh
903 application version number.
904 The value random will cause a random string to be created at
906 each connection attempt. This is to make it a bit more difficult
907 for a malicious peer to find the ssh software brand and version.
908 The value {random, Nmin, Nmax} will make a random string with at
910 least Nmin characters and at most Nmax characters.
911 preferred_algorithms_common_option() =
913 {preferred_algorithms, algs_list()}
914 algs_list() = [alg_entry()]
916 alg_entry() =
918 {kex, [kex_alg()]} |
919 {public_key, [pubkey_alg()]} |
920 {cipher, double_algs(cipher_alg())} |
921 {mac, double_algs(mac_alg())} |
922 {compression, double_algs(compression_alg())}
923 kex_alg() =
925 'diffie-hellman-group-exchange-sha1' |
926 'diffie-hellman-group-exchange-sha256' |
927 'diffie-hellman-group1-sha1' | 'diffie-hellman-group14-sha1' |
928 'diffie-hellman-group14-sha256' |
929 'diffie-hellman-group16-sha512' |
930 'diffie-hellman-group18-sha512' | 'curve25519-sha256' |
931 'curve25519-sha256@libssh.org' | 'curve448-sha512' |
932 'ecdh-sha2-nistp256' | 'ecdh-sha2-nistp384' |
933 'ecdh-sha2-nistp521'
934 pubkey_alg() =
936 'ecdsa-sha2-nistp256' | 'ecdsa-sha2-nistp384' |
937 'ecdsa-sha2-nistp521' | 'ssh-ed25519' | 'ssh-ed448' |
938 'rsa-sha2-256' | 'rsa-sha2-512' | 'ssh-dss' | 'ssh-rsa'
939 cipher_alg() =
941 '3des-cbc' | 'AEAD_AES_128_GCM' | 'AEAD_AES_256_GCM' |
942 'aes128-cbc' | 'aes128-ctr' | 'aes128-gcm@openssh.com' |
943 'aes192-ctr' | 'aes192-cbc' | 'aes256-cbc' | 'aes256-ctr' |
944 'aes256-gcm@openssh.com' | 'chacha20-poly1305@openssh.com'
945 mac_alg() =
947 'AEAD_AES_128_GCM' | 'AEAD_AES_256_GCM' | 'hmac-sha1' |
948 'hmac-sha1-etm@openssh.com' | 'hmac-sha1-96' |
949 'hmac-sha2-256' | 'hmac-sha2-512' |
950 'hmac-sha2-256-etm@openssh.com' |
951 'hmac-sha2-512-etm@openssh.com'
952 compression_alg() = none | zlib | 'zlib@openssh.com'
954 double_algs(AlgType) =
956 [{client2server, [AlgType]} | {server2client, [AlgType]}] |
957 [AlgType]
958 List of algorithms to use in the algorithm negotiation. The de‐
960 fault algs_list() can be obtained from default_algorithms/0.
961 If an alg_entry() is missing in the algs_list(), the default
963 value is used for that entry.
964 Here is an example of this option:
966 {preferred_algorithms,
968 [{public_key,['ssh-rsa','ssh-dss']},
969 {cipher,[{client2server,['aes128-ctr']},
970 {server2client,['aes128-cbc','3des-cbc']}]},
971 {mac,['hmac-sha2-256','hmac-sha1']},
972 {compression,[none,zlib]}
973 ]
974 }
975 The example specifies different algorithms in the two directions
978 (client2server and server2client), for cipher but specifies the
979 same algorithms for mac and compression in both directions. The
980 kex (key exchange) is implicit but public_key is set explicitly.
981 For background and more examples see the User's Guide.
983 If an algorithm name occurs more than once in a list, the behav‐
985 iour is undefined. The tags in the property lists are also as‐
986 sumed to occur at most one time.
987 Warning:
989 Changing the values can make a connection less secure. Do not
990 change unless you know exactly what you are doing. If you do not
991 understand the values then you are not supposed to change them.
992 modify_algorithms_common_option() =
995 {modify_algorithms, modify_algs_list()}
996 modify_algs_list() =
998 [{append, algs_list()} |
999 {prepend, algs_list()} |
1000 {rm, algs_list()}]
1001 Modifies the list of algorithms to use in the algorithm negotia‐
1003 tion. The modifications are applied after the option pre‐
1004 ferred_algorithms (if existing) is applied.
1005 The algoritm for modifications works like this:
1007 * Input is the modify_algs_list() and a set of algorithms A
1009 obtained from the preferred_algorithms option if existing,
1010 or else from the ssh:default_algorithms/0.
1011 * The head of the modify_algs_list() modifies A giving the re‐
1013 sult A'.
1014 The possible modifications are:
1016 * Append or prepend supported but not enabled algorithm(s)
1018 to the list of algorithms. If the wanted algorithms al‐
1019 ready are in A they will first be removed and then ap‐
1020 pended or prepended,
1021 * Remove (rm) one or more algorithms from A.
1023 * Repeat the modification step with the tail of mod‐
1025 ify_algs_list() and the resulting A'.
1026 If an unsupported algorithm is in the modify_algs_list(), it
1028 will be silently ignored
1029 If there are more than one modify_algorithms options, the result
1031 is undefined.
1032 Here is an example of this option:
1034 {modify_algorithms,
1036 [{prepend, [{kex, ['diffie-hellman-group1-sha1']}],
1037 {rm, [{compression, [none]}]}
1038 ]
1039 }
1040 The example specifies that:
1043 * the old key exchange algorithm 'diffie-hellman-group1-sha1'
1045 should be the main alternative. It will be the main alterna‐
1046 tive since it is prepened to the list
1047 * The compression algorithm none (= no compression) is removed
1049 so compression is enforced
1050 For background and more examples see the User's Guide.
1052 inet_common_option() = {inet, inet | inet6}
1054 IP version to use when the host address is specified as any.
1056 auth_methods_common_option() = {auth_methods, string()}
1058 Comma-separated string that determines which authentication
1060 methods that the client shall support and in which order they
1061 are tried. Defaults to "publickey,keyboard-interactive,password"
1062 Note that the client is free to use any order and to exclude
1064 methods.
1065 fd_common_option() = {fd, gen_tcp:socket()}
1067 Allows an existing file-descriptor to be used (passed on to the
1069 transport protocol).
1070 Other data types
1072 host() = string() | inet:ip_address() | loopback
1073 ip_port() = {inet:ip_address(), inet:port_number()}
1075 mod_args() = {Module :: atom(), Args :: list()}
1077 mod_fun_args() =
1079 {Module :: atom(), Function :: atom(), Args :: list()}
1080 open_socket() = gen_tcp:socket()
1082 The socket is supposed to be result of a gen_tcp:connect or a
1084 gen_tcp:accept. The socket must be in passive mode (that is,
1085 opened with the option {active,false}).
1086 daemon_ref()
1088 Opaque data type representing a daemon.
1090 Returned by the functions daemon/1,2,3.
1092 connection_ref()
1094 Opaque data type representing a connection between a client and
1096 a server (daemon).
1097 Returned by the functions connect/2,3,4 and ssh_sftp:start_chan‐
1099 nel/2,3.
1100 channel_id()
1102 Opaque data type representing a channel inside a connection.
1104 Returned by the functions ssh_connection:session_channel/2,4.
1106 connection_info_tuple() =
1108 {client_version, version()} |
1109 {server_version, version()} |
1110 {user, string()} |
1111 {peer, {inet:hostname(), ip_port()}} |
1112 {sockname, ip_port()} |
1113 {options, client_options()} |
1114 {algorithms, conn_info_algs()} |
1115 {channels, conn_info_channels()}
1116 version() = {protocol_version(), software_version()}
1118 protocol_version() =
1120 {Major :: integer() >= 1, Minor :: integer() >= 0}
1121 software_version() = string()
1123 conn_info_algs() =
1125 [{kex, kex_alg()} |
1126 {hkey, pubkey_alg()} |
1127 {encrypt, cipher_alg()} |
1128 {decrypt, cipher_alg()} |
1129 {send_mac, mac_alg()} |
1130 {recv_mac, mac_alg()} |
1131 {compress, compression_alg()} |
1132 {decompress, compression_alg()} |
1133 {send_ext_info, boolean()} |
1134 {recv_ext_info, boolean()}]
1135 conn_info_channels() = [proplists:proplist()]
1137 Return values from the connection_info/1 and connection_info/2
1139 functions.
1140 In the option info tuple are only the options included that dif‐
1142 fers from the default values.
1143 daemon_info_tuple() =
1145 {port, inet:port_number()} |
1146 {ip, inet:ip_address()} |
1147 {profile, atom()} |
1148 {options, daemon_options()}
1149 Return values from the daemon_info/1 and daemon_info/2 func‐
1151 tions.
1152 In the option info tuple are only the options included that dif‐
1154 fers from the default values.
1155 opaque_client_options()
1157 opaque_daemon_options()
1159 opaque_common_options()
1161 Opaque types that define experimental options that are not to be
1163 used in products.
1164
1166 close(ConnectionRef) -> ok | {error, term()}
1167 Types:
1169 ConnectionRef = connection_ref()
1171 Closes an SSH connection.
1173 connect(Host, Port, Options) -> Result
1175 connect(Host, Port, Options, NegotiationTimeout) -> Result
1176 connect(TcpSocket, Options) -> Result
1177 connect(TcpSocket, Options, NegotiationTimeout) -> Result
1178 Types:
1180 Host = host()
1182 Port = inet:port_number()
1183 Options = client_options()
1184 TcpSocket = open_socket()
1185 NegotiationTimeout = timeout()
1186 Result = {ok, connection_ref()} | {error, term()}
1187 Connects to an SSH server at the Host on Port.
1189 As an alternative, an already open TCP socket could be passed to
1191 the function in TcpSocket. The SSH initiation and negotiation
1192 will be initiated on that one with the SSH that should be at the
1193 other end.
1194 No channel is started. This is done by calling ssh_connec‐
1196 tion:session_channel/[2, 4].
1197 The NegotiationTimeout is in milli-seconds. The default value is
1199 infinity. For connection timeout, use the option connect_time‐
1200 out.
1201 connection_info(ConnectionRef) -> InfoTupleList
1203 connection_info(ConnectionRef, Key :: ItemList | Item) ->
1205 InfoTupleList | InfoTuple
1206 Types:
1208 ConnectionRef = connection_ref()
1210 ItemList = [Item]
1211 Item =
1212 client_version | server_version | user | peer | sockname
1213 |
1214 options | algorithms | sockname
1215 InfoTupleList = [InfoTuple]
1216 InfoTuple = connection_info_tuple()
1217 Returns information about a connection intended for e.g debug‐
1219 ging or logging.
1220 When the Key is a single Item, the result is a single InfoTuple
1222 set_sock_opts(ConnectionRef, SocketOptions) ->
1224 ok | {error, inet:posix()}
1225 Types:
1227 ConnectionRef = connection_ref()
1229 SocketOptions = [gen_tcp:option()]
1230 Sets tcp socket options on the tcp-socket below an ssh connec‐
1232 tion.
1233 This function calls the inet:setopts/2, read that documentation
1235 and for gen_tcp:option().
1236 All gen_tcp socket options except
1238 * active
1240 * deliver
1242 * mode and
1244 * packet
1246 are allowed. The excluded options are reserved by the SSH appli‐
1248 cation.
1249 Warning:
1251 This is an extremly dangerous function. You use it on your own
1252 risk.
1253 Some options are OS and OS version dependent. Do not use it un‐
1255 less you know what effect your option values will have on an TCP
1256 stream.
1257 Some values may destroy the functionality of the SSH protocol.
1259 get_sock_opts(ConnectionRef, SocketGetOptions) ->
1262 ok | {error, inet:posix()}
1263 Types:
1265 ConnectionRef = connection_ref()
1267 SocketGetOptions = [gen_tcp:option_name()]
1268 Get tcp socket option values of the tcp-socket below an ssh con‐
1270 nection.
1271 This function calls the inet:getopts/2, read that documentation.
1273 daemon(Port | TcpSocket) -> Result
1275 daemon(Port | TcpSocket, Options) -> Result
1276 daemon(HostAddress, Port, Options) -> Result
1277 Types:
1279 Port = integer()
1281 TcpSocket = open_socket()
1282 Options = daemon_options()
1283 HostAddress = host() | any
1284 Result = {ok, daemon_ref()} | {error, atom()}
1285 Starts a server listening for SSH connections on the given port.
1287 If the Port is 0, a random free port is selected. See dae‐
1288 mon_info/1 about how to find the selected port number.
1289 As an alternative, an already open TCP socket could be passed to
1291 the function in TcpSocket. The SSH initiation and negotiation
1292 will be initiated on that one when an SSH starts at the other
1293 end of the TCP socket.
1294 For a description of the options, see Daemon Options.
1296 Please note that by historical reasons both the HostAddress ar‐
1298 gument and the gen_tcp connect_option() {ip,Address} set the
1299 listening address. This is a source of possible inconsistent
1300 settings.
1301 The rules for handling the two address passing options are:
1303 * if HostAddress is an IP-address, that IP-address is the lis‐
1305 tening address. An 'ip'-option will be discarded if present.
1306 * if HostAddress is the atom loopback, the listening address
1308 is loopback and an loopback address will be choosen by the
1309 underlying layers. An 'ip'-option will be discarded if
1310 present.
1311 * if HostAddress is the atom any and no 'ip'-option is
1313 present, the listening address is any and the socket will
1314 listen to all addresses
1315 * if HostAddress is any and an 'ip'-option is present, the
1317 listening address is set to the value of the 'ip'-option
1318 daemon_info(DaemonRef) ->
1320 {ok, InfoTupleList} | {error, bad_daemon_ref}
1321 daemon_info(DaemonRef, Key :: ItemList | Item) ->
1323 InfoTupleList | InfoTuple | {error, bad_daemon_ref}
1324 Types:
1326 DaemonRef = daemon_ref()
1328 ItemList = [Item]
1329 Item = ip | port | profile | options
1330 InfoTupleList = [InfoTuple]
1331 InfoTuple = daemon_info_tuple()
1332 Returns information about a daemon intended for e.g debugging or
1334 logging.
1335 When the Key is a single Item, the result is a single InfoTuple
1337 Note that daemon_info/1 and daemon_info/2 returns different
1339 types due to compatibility reasons.
1340 default_algorithms() -> algs_list()
1342 Returns a key-value list, where the keys are the different types
1344 of algorithms and the values are the algorithms themselves.
1345 See the User's Guide for an example.
1347 shell(Host | TcpSocket) -> Result
1349 shell(Host | TcpSocket, Options) -> Result
1350 shell(Host, Port, Options) -> Result
1351 Types:
1353 Host = host()
1355 TcpSocket = open_socket()
1356 Port = inet:port_number()
1357 Options = client_options()
1358 Result = ok | {error, Reason::term()}
1359 Connects to an SSH server at Host and Port (defaults to 22) and
1361 starts an interactive shell on that remote host.
1362 As an alternative, an already open TCP socket could be passed to
1364 the function in TcpSocket. The SSH initiation and negotiation
1365 will be initiated on that one and finaly a shell will be started
1366 on the host at the other end of the TCP socket.
1367 For a description of the options, see Client Options.
1369 The function waits for user input, and does not return until the
1371 remote shell is ended (that is, exit from the shell).
1372 start() -> ok | {error, term()}
1374 start(Type) -> ok | {error, term()}
1376 Types:
1378 Type = permanent | transient | temporary
1380 Utility function that starts the applications crypto, pub‐
1382 lic_key, and ssh. Default type is temporary. For more informa‐
1383 tion, see the application(3) manual page in Kernel.
1384 stop() -> ok | {error, term()}
1386 Stops the ssh application. For more information, see the appli‐
1388 cation(3) manual page in Kernel.
1389 stop_daemon(DaemonRef :: daemon_ref()) -> ok
1391 stop_daemon(Address :: inet:ip_address(),
1393 Port :: inet:port_number()) ->
1394 ok
1395 stop_daemon(Address :: any | inet:ip_address(),
1397 Port :: inet:port_number(),
1398 Profile :: atom()) ->
1399 ok
1400 Stops the listener and all connections started by the listener.
1402 stop_listener(SysSup :: daemon_ref()) -> ok
1404 stop_listener(Address :: inet:ip_address(),
1406 Port :: inet:port_number()) ->
1407 ok
1408 stop_listener(Address :: any | inet:ip_address(),
1410 Port :: inet:port_number(),
1411 Profile :: term()) ->
1412 ok
1413 Stops the listener, but leaves existing connections started by
1415 the listener operational.
1416 tcpip_tunnel_from_server(ConnectionRef, ListenHost, ListenPort,
1418 ConnectToHost, ConnectToPort) ->
1419 {ok, TrueListenPort} | {error, term()}
1420 tcpip_tunnel_from_server(ConnectionRef, ListenHost, ListenPort,
1422 ConnectToHost, ConnectToPort, Timeout) ->
1423 {ok, TrueListenPort} | {error, term()}
1424 Types:
1426 ConnectionRef = connection_ref()
1428 ListenHost = host()
1429 ListenPort = inet:port_number()
1430 ConnectToHost = host()
1431 ConnectToPort = inet:port_number()
1432 Timeout = timeout()
1433 TrueListenPort = inet:port_number()
1434 Asks the remote server of ConnectionRef to listen to Listen‐
1436 Host:ListenPort. When someone connects that address, the connec‐
1437 tion is forwarded in an encrypted channel from the server to the
1438 client. The client (that is, at the node that calls this func‐
1439 tion) then connects to ConnectToHost:ConnectToPort.
1440 The returned TrueListenPort is the port that is listened to. It
1442 is the same as ListenPort, except when ListenPort = 0. In that
1443 case a free port is selected by the underlying OS.
1444 Note that in case of an Erlang/OTP SSH server (daemon) as peer,
1446 that server must have been started with the option tcpip_tun‐
1447 nel_out to allow the connection.
1448 tcpip_tunnel_to_server(ConnectionRef, ListenHost, ListenPort,
1450 ConnectToHost, ConnectToPort) ->
1451 {ok, TrueListenPort} | {error, term()}
1452 tcpip_tunnel_to_server(ConnectionRef, ListenHost, ListenPort,
1454 ConnectToHost, ConnectToPort, Timeout) ->
1455 {ok, TrueListenPort} | {error, term()}
1456 Types:
1458 ConnectionRef = connection_ref()
1460 ListenHost = host()
1461 ListenPort = inet:port_number()
1462 ConnectToHost = host()
1463 ConnectToPort = inet:port_number()
1464 Timeout = timeout()
1465 TrueListenPort = inet:port_number()
1466 Tells the local client to listen to ListenHost:ListenPort. When
1468 someone connects to that address, the connection is forwarded in
1469 an encrypted channel to the peer server of ConnectionRef. That
1470 server then connects to ConnectToHost:ConnectToPort.
1471 The returned TrueListenPort is the port that is listened to. It
1473 is the same as ListenPort, except when ListenPort = 0. In that
1474 case a free port is selected by the underlying OS.
1475 Note that in case of an Erlang/OTP SSH server (daemon) as peer,
1477 that server must have been started with the option tcpip_tun‐
1478 nel_in to allow the connection.
1479Ericsson AB ssh 4.11.1.2 ssh(3)