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1 | SSH(1) General Commands Manual SSH(1) | ||
2 | |||
3 | NAME | ||
4 | ssh M-bM-^@M-^S OpenSSH SSH client (remote login program) | ||
5 | |||
6 | SYNOPSIS | ||
7 | ssh [-46AaCfGgKkMNnqsTtVvXxYy] [-b bind_address] [-c cipher_spec] | ||
8 | [-D [bind_address:]port] [-E log_file] [-e escape_char] | ||
9 | [-F configfile] [-I pkcs11] [-i identity_file] | ||
10 | [-J [user@]host[:port]] [-L address] [-l login_name] [-m mac_spec] | ||
11 | [-O ctl_cmd] [-o option] [-p port] [-Q query_option] [-R address] | ||
12 | [-S ctl_path] [-W host:port] [-w local_tun[:remote_tun]] | ||
13 | [user@]hostname [command] | ||
14 | |||
15 | DESCRIPTION | ||
16 | ssh (SSH client) is a program for logging into a remote machine and for | ||
17 | executing commands on a remote machine. It is intended to provide secure | ||
18 | encrypted communications between two untrusted hosts over an insecure | ||
19 | network. X11 connections, arbitrary TCP ports and UNIX-domain sockets | ||
20 | can also be forwarded over the secure channel. | ||
21 | |||
22 | ssh connects and logs into the specified hostname (with optional user | ||
23 | name). The user must prove his/her identity to the remote machine using | ||
24 | one of several methods (see below). | ||
25 | |||
26 | If command is specified, it is executed on the remote host instead of a | ||
27 | login shell. | ||
28 | |||
29 | The options are as follows: | ||
30 | |||
31 | -4 Forces ssh to use IPv4 addresses only. | ||
32 | |||
33 | -6 Forces ssh to use IPv6 addresses only. | ||
34 | |||
35 | -A Enables forwarding of the authentication agent connection. This | ||
36 | can also be specified on a per-host basis in a configuration | ||
37 | file. | ||
38 | |||
39 | Agent forwarding should be enabled with caution. Users with the | ||
40 | ability to bypass file permissions on the remote host (for the | ||
41 | agent's UNIX-domain socket) can access the local agent through | ||
42 | the forwarded connection. An attacker cannot obtain key material | ||
43 | from the agent, however they can perform operations on the keys | ||
44 | that enable them to authenticate using the identities loaded into | ||
45 | the agent. | ||
46 | |||
47 | -a Disables forwarding of the authentication agent connection. | ||
48 | |||
49 | -b bind_address | ||
50 | Use bind_address on the local machine as the source address of | ||
51 | the connection. Only useful on systems with more than one | ||
52 | address. | ||
53 | |||
54 | -C Requests compression of all data (including stdin, stdout, | ||
55 | stderr, and data for forwarded X11, TCP and UNIX-domain | ||
56 | connections). The compression algorithm is the same used by | ||
57 | gzip(1). Compression is desirable on modem lines and other slow | ||
58 | connections, but will only slow down things on fast networks. | ||
59 | The default value can be set on a host-by-host basis in the | ||
60 | configuration files; see the Compression option. | ||
61 | |||
62 | -c cipher_spec | ||
63 | Selects the cipher specification for encrypting the session. | ||
64 | cipher_spec is a comma-separated list of ciphers listed in order | ||
65 | of preference. See the Ciphers keyword in ssh_config(5) for more | ||
66 | information. | ||
67 | |||
68 | -D [bind_address:]port | ||
69 | Specifies a local M-bM-^@M-^\dynamicM-bM-^@M-^] application-level port forwarding. | ||
70 | This works by allocating a socket to listen to port on the local | ||
71 | side, optionally bound to the specified bind_address. Whenever a | ||
72 | connection is made to this port, the connection is forwarded over | ||
73 | the secure channel, and the application protocol is then used to | ||
74 | determine where to connect to from the remote machine. Currently | ||
75 | the SOCKS4 and SOCKS5 protocols are supported, and ssh will act | ||
76 | as a SOCKS server. Only root can forward privileged ports. | ||
77 | Dynamic port forwardings can also be specified in the | ||
78 | configuration file. | ||
79 | |||
80 | IPv6 addresses can be specified by enclosing the address in | ||
81 | square brackets. Only the superuser can forward privileged | ||
82 | ports. By default, the local port is bound in accordance with | ||
83 | the GatewayPorts setting. However, an explicit bind_address may | ||
84 | be used to bind the connection to a specific address. The | ||
85 | bind_address of M-bM-^@M-^\localhostM-bM-^@M-^] indicates that the listening port be | ||
86 | bound for local use only, while an empty address or M-bM-^@M-^X*M-bM-^@M-^Y indicates | ||
87 | that the port should be available from all interfaces. | ||
88 | |||
89 | -E log_file | ||
90 | Append debug logs to log_file instead of standard error. | ||
91 | |||
92 | -e escape_char | ||
93 | Sets the escape character for sessions with a pty (default: M-bM-^@M-^X~M-bM-^@M-^Y). | ||
94 | The escape character is only recognized at the beginning of a | ||
95 | line. The escape character followed by a dot (M-bM-^@M-^X.M-bM-^@M-^Y) closes the | ||
96 | connection; followed by control-Z suspends the connection; and | ||
97 | followed by itself sends the escape character once. Setting the | ||
98 | character to M-bM-^@M-^\noneM-bM-^@M-^] disables any escapes and makes the session | ||
99 | fully transparent. | ||
100 | |||
101 | -F configfile | ||
102 | Specifies an alternative per-user configuration file. If a | ||
103 | configuration file is given on the command line, the system-wide | ||
104 | configuration file (/etc/ssh/ssh_config) will be ignored. The | ||
105 | default for the per-user configuration file is ~/.ssh/config. | ||
106 | |||
107 | -f Requests ssh to go to background just before command execution. | ||
108 | This is useful if ssh is going to ask for passwords or | ||
109 | passphrases, but the user wants it in the background. This | ||
110 | implies -n. The recommended way to start X11 programs at a | ||
111 | remote site is with something like ssh -f host xterm. | ||
112 | |||
113 | If the ExitOnForwardFailure configuration option is set to M-bM-^@M-^\yesM-bM-^@M-^], | ||
114 | then a client started with -f will wait for all remote port | ||
115 | forwards to be successfully established before placing itself in | ||
116 | the background. | ||
117 | |||
118 | -G Causes ssh to print its configuration after evaluating Host and | ||
119 | Match blocks and exit. | ||
120 | |||
121 | -g Allows remote hosts to connect to local forwarded ports. If used | ||
122 | on a multiplexed connection, then this option must be specified | ||
123 | on the master process. | ||
124 | |||
125 | -I pkcs11 | ||
126 | Specify the PKCS#11 shared library ssh should use to communicate | ||
127 | with a PKCS#11 token providing the user's private RSA key. | ||
128 | |||
129 | -i identity_file | ||
130 | Selects a file from which the identity (private key) for public | ||
131 | key authentication is read. The default is ~/.ssh/id_dsa, | ||
132 | ~/.ssh/id_ecdsa, ~/.ssh/id_ed25519 and ~/.ssh/id_rsa. Identity | ||
133 | files may also be specified on a per-host basis in the | ||
134 | configuration file. It is possible to have multiple -i options | ||
135 | (and multiple identities specified in configuration files). If | ||
136 | no certificates have been explicitly specified by the | ||
137 | CertificateFile directive, ssh will also try to load certificate | ||
138 | information from the filename obtained by appending -cert.pub to | ||
139 | identity filenames. | ||
140 | |||
141 | -J [user@]host[:port] | ||
142 | Connect to the target host by first making a ssh connection to | ||
143 | the jump host and then establishing a TCP forwarding to the | ||
144 | ultimate destination from there. Multiple jump hops may be | ||
145 | specified separated by comma characters. This is a shortcut to | ||
146 | specify a ProxyJump configuration directive. | ||
147 | |||
148 | -K Enables GSSAPI-based authentication and forwarding (delegation) | ||
149 | of GSSAPI credentials to the server. | ||
150 | |||
151 | -k Disables forwarding (delegation) of GSSAPI credentials to the | ||
152 | server. | ||
153 | |||
154 | -L [bind_address:]port:host:hostport | ||
155 | -L [bind_address:]port:remote_socket | ||
156 | -L local_socket:host:hostport | ||
157 | -L local_socket:remote_socket | ||
158 | Specifies that connections to the given TCP port or Unix socket | ||
159 | on the local (client) host are to be forwarded to the given host | ||
160 | and port, or Unix socket, on the remote side. This works by | ||
161 | allocating a socket to listen to either a TCP port on the local | ||
162 | side, optionally bound to the specified bind_address, or to a | ||
163 | Unix socket. Whenever a connection is made to the local port or | ||
164 | socket, the connection is forwarded over the secure channel, and | ||
165 | a connection is made to either host port hostport, or the Unix | ||
166 | socket remote_socket, from the remote machine. | ||
167 | |||
168 | Port forwardings can also be specified in the configuration file. | ||
169 | Only the superuser can forward privileged ports. IPv6 addresses | ||
170 | can be specified by enclosing the address in square brackets. | ||
171 | |||
172 | By default, the local port is bound in accordance with the | ||
173 | GatewayPorts setting. However, an explicit bind_address may be | ||
174 | used to bind the connection to a specific address. The | ||
175 | bind_address of M-bM-^@M-^\localhostM-bM-^@M-^] indicates that the listening port be | ||
176 | bound for local use only, while an empty address or M-bM-^@M-^X*M-bM-^@M-^Y indicates | ||
177 | that the port should be available from all interfaces. | ||
178 | |||
179 | -l login_name | ||
180 | Specifies the user to log in as on the remote machine. This also | ||
181 | may be specified on a per-host basis in the configuration file. | ||
182 | |||
183 | -M Places the ssh client into M-bM-^@M-^\masterM-bM-^@M-^] mode for connection sharing. | ||
184 | Multiple -M options places ssh into M-bM-^@M-^\masterM-bM-^@M-^] mode with | ||
185 | confirmation required before slave connections are accepted. | ||
186 | Refer to the description of ControlMaster in ssh_config(5) for | ||
187 | details. | ||
188 | |||
189 | -m mac_spec | ||
190 | A comma-separated list of MAC (message authentication code) | ||
191 | algorithms, specified in order of preference. See the MACs | ||
192 | keyword for more information. | ||
193 | |||
194 | -N Do not execute a remote command. This is useful for just | ||
195 | forwarding ports. | ||
196 | |||
197 | -n Redirects stdin from /dev/null (actually, prevents reading from | ||
198 | stdin). This must be used when ssh is run in the background. A | ||
199 | common trick is to use this to run X11 programs on a remote | ||
200 | machine. For example, ssh -n shadows.cs.hut.fi emacs & will | ||
201 | start an emacs on shadows.cs.hut.fi, and the X11 connection will | ||
202 | be automatically forwarded over an encrypted channel. The ssh | ||
203 | program will be put in the background. (This does not work if | ||
204 | ssh needs to ask for a password or passphrase; see also the -f | ||
205 | option.) | ||
206 | |||
207 | -O ctl_cmd | ||
208 | Control an active connection multiplexing master process. When | ||
209 | the -O option is specified, the ctl_cmd argument is interpreted | ||
210 | and passed to the master process. Valid commands are: M-bM-^@M-^\checkM-bM-^@M-^] | ||
211 | (check that the master process is running), M-bM-^@M-^\forwardM-bM-^@M-^] (request | ||
212 | forwardings without command execution), M-bM-^@M-^\cancelM-bM-^@M-^] (cancel | ||
213 | forwardings), M-bM-^@M-^\exitM-bM-^@M-^] (request the master to exit), and M-bM-^@M-^\stopM-bM-^@M-^] | ||
214 | (request the master to stop accepting further multiplexing | ||
215 | requests). | ||
216 | |||
217 | -o option | ||
218 | Can be used to give options in the format used in the | ||
219 | configuration file. This is useful for specifying options for | ||
220 | which there is no separate command-line flag. For full details | ||
221 | of the options listed below, and their possible values, see | ||
222 | ssh_config(5). | ||
223 | |||
224 | AddKeysToAgent | ||
225 | AddressFamily | ||
226 | BatchMode | ||
227 | BindAddress | ||
228 | CanonicalDomains | ||
229 | CanonicalizeFallbackLocal | ||
230 | CanonicalizeHostname | ||
231 | CanonicalizeMaxDots | ||
232 | CanonicalizePermittedCNAMEs | ||
233 | CertificateFile | ||
234 | ChallengeResponseAuthentication | ||
235 | CheckHostIP | ||
236 | Ciphers | ||
237 | ClearAllForwardings | ||
238 | Compression | ||
239 | ConnectionAttempts | ||
240 | ConnectTimeout | ||
241 | ControlMaster | ||
242 | ControlPath | ||
243 | ControlPersist | ||
244 | DynamicForward | ||
245 | EscapeChar | ||
246 | ExitOnForwardFailure | ||
247 | FingerprintHash | ||
248 | ForwardAgent | ||
249 | ForwardX11 | ||
250 | ForwardX11Timeout | ||
251 | ForwardX11Trusted | ||
252 | GatewayPorts | ||
253 | GlobalKnownHostsFile | ||
254 | GSSAPIAuthentication | ||
255 | GSSAPIDelegateCredentials | ||
256 | HashKnownHosts | ||
257 | Host | ||
258 | HostbasedAuthentication | ||
259 | HostbasedKeyTypes | ||
260 | HostKeyAlgorithms | ||
261 | HostKeyAlias | ||
262 | HostName | ||
263 | IdentitiesOnly | ||
264 | IdentityAgent | ||
265 | IdentityFile | ||
266 | Include | ||
267 | IPQoS | ||
268 | KbdInteractiveAuthentication | ||
269 | KbdInteractiveDevices | ||
270 | KexAlgorithms | ||
271 | LocalCommand | ||
272 | LocalForward | ||
273 | LogLevel | ||
274 | MACs | ||
275 | Match | ||
276 | NoHostAuthenticationForLocalhost | ||
277 | NumberOfPasswordPrompts | ||
278 | PasswordAuthentication | ||
279 | PermitLocalCommand | ||
280 | PKCS11Provider | ||
281 | Port | ||
282 | PreferredAuthentications | ||
283 | ProxyCommand | ||
284 | ProxyJump | ||
285 | ProxyUseFdpass | ||
286 | PubkeyAcceptedKeyTypes | ||
287 | PubkeyAuthentication | ||
288 | RekeyLimit | ||
289 | RemoteCommand | ||
290 | RemoteForward | ||
291 | RequestTTY | ||
292 | SendEnv | ||
293 | ServerAliveInterval | ||
294 | ServerAliveCountMax | ||
295 | StreamLocalBindMask | ||
296 | StreamLocalBindUnlink | ||
297 | StrictHostKeyChecking | ||
298 | TCPKeepAlive | ||
299 | Tunnel | ||
300 | TunnelDevice | ||
301 | UpdateHostKeys | ||
302 | UsePrivilegedPort | ||
303 | User | ||
304 | UserKnownHostsFile | ||
305 | VerifyHostKeyDNS | ||
306 | VisualHostKey | ||
307 | XAuthLocation | ||
308 | |||
309 | -p port | ||
310 | Port to connect to on the remote host. This can be specified on | ||
311 | a per-host basis in the configuration file. | ||
312 | |||
313 | -Q query_option | ||
314 | Queries ssh for the algorithms supported for the specified | ||
315 | version 2. The available features are: cipher (supported | ||
316 | symmetric ciphers), cipher-auth (supported symmetric ciphers that | ||
317 | support authenticated encryption), mac (supported message | ||
318 | integrity codes), kex (key exchange algorithms), key (key types), | ||
319 | key-cert (certificate key types), key-plain (non-certificate key | ||
320 | types), and protocol-version (supported SSH protocol versions). | ||
321 | |||
322 | -q Quiet mode. Causes most warning and diagnostic messages to be | ||
323 | suppressed. | ||
324 | |||
325 | -R [bind_address:]port:host:hostport | ||
326 | -R [bind_address:]port:local_socket | ||
327 | -R remote_socket:host:hostport | ||
328 | -R remote_socket:local_socket | ||
329 | -R [bind_address:]port | ||
330 | Specifies that connections to the given TCP port or Unix socket | ||
331 | on the remote (server) host are to be forwarded to the local | ||
332 | side. | ||
333 | |||
334 | This works by allocating a socket to listen to either a TCP port | ||
335 | or to a Unix socket on the remote side. Whenever a connection is | ||
336 | made to this port or Unix socket, the connection is forwarded | ||
337 | over the secure channel, and a connection is made from the local | ||
338 | machine to either an explicit destination specified by host port | ||
339 | hostport, or local_socket, or, if no explicit destination was | ||
340 | specified, ssh will act as a SOCKS 4/5 proxy and forward | ||
341 | connections to the destinations requested by the remote SOCKS | ||
342 | client. | ||
343 | |||
344 | Port forwardings can also be specified in the configuration file. | ||
345 | Privileged ports can be forwarded only when logging in as root on | ||
346 | the remote machine. IPv6 addresses can be specified by enclosing | ||
347 | the address in square brackets. | ||
348 | |||
349 | By default, TCP listening sockets on the server will be bound to | ||
350 | the loopback interface only. This may be overridden by | ||
351 | specifying a bind_address. An empty bind_address, or the address | ||
352 | M-bM-^@M-^X*M-bM-^@M-^Y, indicates that the remote socket should listen on all | ||
353 | interfaces. Specifying a remote bind_address will only succeed | ||
354 | if the server's GatewayPorts option is enabled (see | ||
355 | sshd_config(5)). | ||
356 | |||
357 | If the port argument is M-bM-^@M-^X0M-bM-^@M-^Y, the listen port will be dynamically | ||
358 | allocated on the server and reported to the client at run time. | ||
359 | When used together with -O forward the allocated port will be | ||
360 | printed to the standard output. | ||
361 | |||
362 | -S ctl_path | ||
363 | Specifies the location of a control socket for connection | ||
364 | sharing, or the string M-bM-^@M-^\noneM-bM-^@M-^] to disable connection sharing. | ||
365 | Refer to the description of ControlPath and ControlMaster in | ||
366 | ssh_config(5) for details. | ||
367 | |||
368 | -s May be used to request invocation of a subsystem on the remote | ||
369 | system. Subsystems facilitate the use of SSH as a secure | ||
370 | transport for other applications (e.g. sftp(1)). The subsystem | ||
371 | is specified as the remote command. | ||
372 | |||
373 | -T Disable pseudo-terminal allocation. | ||
374 | |||
375 | -t Force pseudo-terminal allocation. This can be used to execute | ||
376 | arbitrary screen-based programs on a remote machine, which can be | ||
377 | very useful, e.g. when implementing menu services. Multiple -t | ||
378 | options force tty allocation, even if ssh has no local tty. | ||
379 | |||
380 | -V Display the version number and exit. | ||
381 | |||
382 | -v Verbose mode. Causes ssh to print debugging messages about its | ||
383 | progress. This is helpful in debugging connection, | ||
384 | authentication, and configuration problems. Multiple -v options | ||
385 | increase the verbosity. The maximum is 3. | ||
386 | |||
387 | -W host:port | ||
388 | Requests that standard input and output on the client be | ||
389 | forwarded to host on port over the secure channel. Implies -N, | ||
390 | -T, ExitOnForwardFailure and ClearAllForwardings, though these | ||
391 | can be overridden in the configuration file or using -o command | ||
392 | line options. | ||
393 | |||
394 | -w local_tun[:remote_tun] | ||
395 | Requests tunnel device forwarding with the specified tun(4) | ||
396 | devices between the client (local_tun) and the server | ||
397 | (remote_tun). | ||
398 | |||
399 | The devices may be specified by numerical ID or the keyword | ||
400 | M-bM-^@M-^\anyM-bM-^@M-^], which uses the next available tunnel device. If | ||
401 | remote_tun is not specified, it defaults to M-bM-^@M-^\anyM-bM-^@M-^]. See also the | ||
402 | Tunnel and TunnelDevice directives in ssh_config(5). If the | ||
403 | Tunnel directive is unset, it is set to the default tunnel mode, | ||
404 | which is M-bM-^@M-^\point-to-pointM-bM-^@M-^]. | ||
405 | |||
406 | -X Enables X11 forwarding. This can also be specified on a per-host | ||
407 | basis in a configuration file. | ||
408 | |||
409 | X11 forwarding should be enabled with caution. Users with the | ||
410 | ability to bypass file permissions on the remote host (for the | ||
411 | user's X authorization database) can access the local X11 display | ||
412 | through the forwarded connection. An attacker may then be able | ||
413 | to perform activities such as keystroke monitoring. | ||
414 | |||
415 | For this reason, X11 forwarding is subjected to X11 SECURITY | ||
416 | extension restrictions by default. Please refer to the ssh -Y | ||
417 | option and the ForwardX11Trusted directive in ssh_config(5) for | ||
418 | more information. | ||
419 | |||
420 | -x Disables X11 forwarding. | ||
421 | |||
422 | -Y Enables trusted X11 forwarding. Trusted X11 forwardings are not | ||
423 | subjected to the X11 SECURITY extension controls. | ||
424 | |||
425 | -y Send log information using the syslog(3) system module. By | ||
426 | default this information is sent to stderr. | ||
427 | |||
428 | ssh may additionally obtain configuration data from a per-user | ||
429 | configuration file and a system-wide configuration file. The file format | ||
430 | and configuration options are described in ssh_config(5). | ||
431 | |||
432 | AUTHENTICATION | ||
433 | The OpenSSH SSH client supports SSH protocol 2. | ||
434 | |||
435 | The methods available for authentication are: GSSAPI-based | ||
436 | authentication, host-based authentication, public key authentication, | ||
437 | challenge-response authentication, and password authentication. | ||
438 | Authentication methods are tried in the order specified above, though | ||
439 | PreferredAuthentications can be used to change the default order. | ||
440 | |||
441 | Host-based authentication works as follows: If the machine the user logs | ||
442 | in from is listed in /etc/hosts.equiv or /etc/shosts.equiv on the remote | ||
443 | machine, and the user names are the same on both sides, or if the files | ||
444 | ~/.rhosts or ~/.shosts exist in the user's home directory on the remote | ||
445 | machine and contain a line containing the name of the client machine and | ||
446 | the name of the user on that machine, the user is considered for login. | ||
447 | Additionally, the server must be able to verify the client's host key | ||
448 | (see the description of /etc/ssh/ssh_known_hosts and ~/.ssh/known_hosts, | ||
449 | below) for login to be permitted. This authentication method closes | ||
450 | security holes due to IP spoofing, DNS spoofing, and routing spoofing. | ||
451 | [Note to the administrator: /etc/hosts.equiv, ~/.rhosts, and the | ||
452 | rlogin/rsh protocol in general, are inherently insecure and should be | ||
453 | disabled if security is desired.] | ||
454 | |||
455 | Public key authentication works as follows: The scheme is based on | ||
456 | public-key cryptography, using cryptosystems where encryption and | ||
457 | decryption are done using separate keys, and it is unfeasible to derive | ||
458 | the decryption key from the encryption key. The idea is that each user | ||
459 | creates a public/private key pair for authentication purposes. The | ||
460 | server knows the public key, and only the user knows the private key. | ||
461 | ssh implements public key authentication protocol automatically, using | ||
462 | one of the DSA, ECDSA, Ed25519 or RSA algorithms. The HISTORY section of | ||
463 | ssl(8) contains a brief discussion of the DSA and RSA algorithms. | ||
464 | |||
465 | The file ~/.ssh/authorized_keys lists the public keys that are permitted | ||
466 | for logging in. When the user logs in, the ssh program tells the server | ||
467 | which key pair it would like to use for authentication. The client | ||
468 | proves that it has access to the private key and the server checks that | ||
469 | the corresponding public key is authorized to accept the account. | ||
470 | |||
471 | The server may inform the client of errors that prevented public key | ||
472 | authentication from succeeding after authentication completes using a | ||
473 | different method. These may be viewed by increasing the LogLevel to | ||
474 | DEBUG or higher (e.g. by using the -v flag). | ||
475 | |||
476 | The user creates his/her key pair by running ssh-keygen(1). This stores | ||
477 | the private key in ~/.ssh/id_dsa (DSA), ~/.ssh/id_ecdsa (ECDSA), | ||
478 | ~/.ssh/id_ed25519 (Ed25519), or ~/.ssh/id_rsa (RSA) and stores the public | ||
479 | key in ~/.ssh/id_dsa.pub (DSA), ~/.ssh/id_ecdsa.pub (ECDSA), | ||
480 | ~/.ssh/id_ed25519.pub (Ed25519), or ~/.ssh/id_rsa.pub (RSA) in the user's | ||
481 | home directory. The user should then copy the public key to | ||
482 | ~/.ssh/authorized_keys in his/her home directory on the remote machine. | ||
483 | The authorized_keys file corresponds to the conventional ~/.rhosts file, | ||
484 | and has one key per line, though the lines can be very long. After this, | ||
485 | the user can log in without giving the password. | ||
486 | |||
487 | A variation on public key authentication is available in the form of | ||
488 | certificate authentication: instead of a set of public/private keys, | ||
489 | signed certificates are used. This has the advantage that a single | ||
490 | trusted certification authority can be used in place of many | ||
491 | public/private keys. See the CERTIFICATES section of ssh-keygen(1) for | ||
492 | more information. | ||
493 | |||
494 | The most convenient way to use public key or certificate authentication | ||
495 | may be with an authentication agent. See ssh-agent(1) and (optionally) | ||
496 | the AddKeysToAgent directive in ssh_config(5) for more information. | ||
497 | |||
498 | Challenge-response authentication works as follows: The server sends an | ||
499 | arbitrary "challenge" text, and prompts for a response. Examples of | ||
500 | challenge-response authentication include BSD Authentication (see | ||
501 | login.conf(5)) and PAM (some non-OpenBSD systems). | ||
502 | |||
503 | Finally, if other authentication methods fail, ssh prompts the user for a | ||
504 | password. The password is sent to the remote host for checking; however, | ||
505 | since all communications are encrypted, the password cannot be seen by | ||
506 | someone listening on the network. | ||
507 | |||
508 | ssh automatically maintains and checks a database containing | ||
509 | identification for all hosts it has ever been used with. Host keys are | ||
510 | stored in ~/.ssh/known_hosts in the user's home directory. Additionally, | ||
511 | the file /etc/ssh/ssh_known_hosts is automatically checked for known | ||
512 | hosts. Any new hosts are automatically added to the user's file. If a | ||
513 | host's identification ever changes, ssh warns about this and disables | ||
514 | password authentication to prevent server spoofing or man-in-the-middle | ||
515 | attacks, which could otherwise be used to circumvent the encryption. The | ||
516 | StrictHostKeyChecking option can be used to control logins to machines | ||
517 | whose host key is not known or has changed. | ||
518 | |||
519 | When the user's identity has been accepted by the server, the server | ||
520 | either executes the given command in a non-interactive session or, if no | ||
521 | command has been specified, logs into the machine and gives the user a | ||
522 | normal shell as an interactive session. All communication with the | ||
523 | remote command or shell will be automatically encrypted. | ||
524 | |||
525 | If an interactive session is requested ssh by default will only request a | ||
526 | pseudo-terminal (pty) for interactive sessions when the client has one. | ||
527 | The flags -T and -t can be used to override this behaviour. | ||
528 | |||
529 | If a pseudo-terminal has been allocated the user may use the escape | ||
530 | characters noted below. | ||
531 | |||
532 | If no pseudo-terminal has been allocated, the session is transparent and | ||
533 | can be used to reliably transfer binary data. On most systems, setting | ||
534 | the escape character to M-bM-^@M-^\noneM-bM-^@M-^] will also make the session transparent | ||
535 | even if a tty is used. | ||
536 | |||
537 | The session terminates when the command or shell on the remote machine | ||
538 | exits and all X11 and TCP connections have been closed. | ||
539 | |||
540 | ESCAPE CHARACTERS | ||
541 | When a pseudo-terminal has been requested, ssh supports a number of | ||
542 | functions through the use of an escape character. | ||
543 | |||
544 | A single tilde character can be sent as ~~ or by following the tilde by a | ||
545 | character other than those described below. The escape character must | ||
546 | always follow a newline to be interpreted as special. The escape | ||
547 | character can be changed in configuration files using the EscapeChar | ||
548 | configuration directive or on the command line by the -e option. | ||
549 | |||
550 | The supported escapes (assuming the default M-bM-^@M-^X~M-bM-^@M-^Y) are: | ||
551 | |||
552 | ~. Disconnect. | ||
553 | |||
554 | ~^Z Background ssh. | ||
555 | |||
556 | ~# List forwarded connections. | ||
557 | |||
558 | ~& Background ssh at logout when waiting for forwarded connection / | ||
559 | X11 sessions to terminate. | ||
560 | |||
561 | ~? Display a list of escape characters. | ||
562 | |||
563 | ~B Send a BREAK to the remote system (only useful if the peer | ||
564 | supports it). | ||
565 | |||
566 | ~C Open command line. Currently this allows the addition of port | ||
567 | forwardings using the -L, -R and -D options (see above). It also | ||
568 | allows the cancellation of existing port-forwardings with | ||
569 | -KL[bind_address:]port for local, -KR[bind_address:]port for | ||
570 | remote and -KD[bind_address:]port for dynamic port-forwardings. | ||
571 | !command allows the user to execute a local command if the | ||
572 | PermitLocalCommand option is enabled in ssh_config(5). Basic | ||
573 | help is available, using the -h option. | ||
574 | |||
575 | ~R Request rekeying of the connection (only useful if the peer | ||
576 | supports it). | ||
577 | |||
578 | ~V Decrease the verbosity (LogLevel) when errors are being written | ||
579 | to stderr. | ||
580 | |||
581 | ~v Increase the verbosity (LogLevel) when errors are being written | ||
582 | to stderr. | ||
583 | |||
584 | TCP FORWARDING | ||
585 | Forwarding of arbitrary TCP connections over the secure channel can be | ||
586 | specified either on the command line or in a configuration file. One | ||
587 | possible application of TCP forwarding is a secure connection to a mail | ||
588 | server; another is going through firewalls. | ||
589 | |||
590 | In the example below, we look at encrypting communication between an IRC | ||
591 | client and server, even though the IRC server does not directly support | ||
592 | encrypted communications. This works as follows: the user connects to | ||
593 | the remote host using ssh, specifying a port to be used to forward | ||
594 | connections to the remote server. After that it is possible to start the | ||
595 | service which is to be encrypted on the client machine, connecting to the | ||
596 | same local port, and ssh will encrypt and forward the connection. | ||
597 | |||
598 | The following example tunnels an IRC session from client machine | ||
599 | M-bM-^@M-^\127.0.0.1M-bM-^@M-^] (localhost) to remote server M-bM-^@M-^\server.example.comM-bM-^@M-^]: | ||
600 | |||
601 | $ ssh -f -L 1234:localhost:6667 server.example.com sleep 10 | ||
602 | $ irc -c '#users' -p 1234 pinky 127.0.0.1 | ||
603 | |||
604 | This tunnels a connection to IRC server M-bM-^@M-^\server.example.comM-bM-^@M-^], joining | ||
605 | channel M-bM-^@M-^\#usersM-bM-^@M-^], nickname M-bM-^@M-^\pinkyM-bM-^@M-^], using port 1234. It doesn't matter | ||
606 | which port is used, as long as it's greater than 1023 (remember, only | ||
607 | root can open sockets on privileged ports) and doesn't conflict with any | ||
608 | ports already in use. The connection is forwarded to port 6667 on the | ||
609 | remote server, since that's the standard port for IRC services. | ||
610 | |||
611 | The -f option backgrounds ssh and the remote command M-bM-^@M-^\sleep 10M-bM-^@M-^] is | ||
612 | specified to allow an amount of time (10 seconds, in the example) to | ||
613 | start the service which is to be tunnelled. If no connections are made | ||
614 | within the time specified, ssh will exit. | ||
615 | |||
616 | X11 FORWARDING | ||
617 | If the ForwardX11 variable is set to M-bM-^@M-^\yesM-bM-^@M-^] (or see the description of the | ||
618 | -X, -x, and -Y options above) and the user is using X11 (the DISPLAY | ||
619 | environment variable is set), the connection to the X11 display is | ||
620 | automatically forwarded to the remote side in such a way that any X11 | ||
621 | programs started from the shell (or command) will go through the | ||
622 | encrypted channel, and the connection to the real X server will be made | ||
623 | from the local machine. The user should not manually set DISPLAY. | ||
624 | Forwarding of X11 connections can be configured on the command line or in | ||
625 | configuration files. | ||
626 | |||
627 | The DISPLAY value set by ssh will point to the server machine, but with a | ||
628 | display number greater than zero. This is normal, and happens because | ||
629 | ssh creates a M-bM-^@M-^\proxyM-bM-^@M-^] X server on the server machine for forwarding the | ||
630 | connections over the encrypted channel. | ||
631 | |||
632 | ssh will also automatically set up Xauthority data on the server machine. | ||
633 | For this purpose, it will generate a random authorization cookie, store | ||
634 | it in Xauthority on the server, and verify that any forwarded connections | ||
635 | carry this cookie and replace it by the real cookie when the connection | ||
636 | is opened. The real authentication cookie is never sent to the server | ||
637 | machine (and no cookies are sent in the plain). | ||
638 | |||
639 | If the ForwardAgent variable is set to M-bM-^@M-^\yesM-bM-^@M-^] (or see the description of | ||
640 | the -A and -a options above) and the user is using an authentication | ||
641 | agent, the connection to the agent is automatically forwarded to the | ||
642 | remote side. | ||
643 | |||
644 | VERIFYING HOST KEYS | ||
645 | When connecting to a server for the first time, a fingerprint of the | ||
646 | server's public key is presented to the user (unless the option | ||
647 | StrictHostKeyChecking has been disabled). Fingerprints can be determined | ||
648 | using ssh-keygen(1): | ||
649 | |||
650 | $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key | ||
651 | |||
652 | If the fingerprint is already known, it can be matched and the key can be | ||
653 | accepted or rejected. If only legacy (MD5) fingerprints for the server | ||
654 | are available, the ssh-keygen(1) -E option may be used to downgrade the | ||
655 | fingerprint algorithm to match. | ||
656 | |||
657 | Because of the difficulty of comparing host keys just by looking at | ||
658 | fingerprint strings, there is also support to compare host keys visually, | ||
659 | using random art. By setting the VisualHostKey option to M-bM-^@M-^\yesM-bM-^@M-^], a small | ||
660 | ASCII graphic gets displayed on every login to a server, no matter if the | ||
661 | session itself is interactive or not. By learning the pattern a known | ||
662 | server produces, a user can easily find out that the host key has changed | ||
663 | when a completely different pattern is displayed. Because these patterns | ||
664 | are not unambiguous however, a pattern that looks similar to the pattern | ||
665 | remembered only gives a good probability that the host key is the same, | ||
666 | not guaranteed proof. | ||
667 | |||
668 | To get a listing of the fingerprints along with their random art for all | ||
669 | known hosts, the following command line can be used: | ||
670 | |||
671 | $ ssh-keygen -lv -f ~/.ssh/known_hosts | ||
672 | |||
673 | If the fingerprint is unknown, an alternative method of verification is | ||
674 | available: SSH fingerprints verified by DNS. An additional resource | ||
675 | record (RR), SSHFP, is added to a zonefile and the connecting client is | ||
676 | able to match the fingerprint with that of the key presented. | ||
677 | |||
678 | In this example, we are connecting a client to a server, | ||
679 | M-bM-^@M-^\host.example.comM-bM-^@M-^]. The SSHFP resource records should first be added to | ||
680 | the zonefile for host.example.com: | ||
681 | |||
682 | $ ssh-keygen -r host.example.com. | ||
683 | |||
684 | The output lines will have to be added to the zonefile. To check that | ||
685 | the zone is answering fingerprint queries: | ||
686 | |||
687 | $ dig -t SSHFP host.example.com | ||
688 | |||
689 | Finally the client connects: | ||
690 | |||
691 | $ ssh -o "VerifyHostKeyDNS ask" host.example.com | ||
692 | [...] | ||
693 | Matching host key fingerprint found in DNS. | ||
694 | Are you sure you want to continue connecting (yes/no)? | ||
695 | |||
696 | See the VerifyHostKeyDNS option in ssh_config(5) for more information. | ||
697 | |||
698 | SSH-BASED VIRTUAL PRIVATE NETWORKS | ||
699 | ssh contains support for Virtual Private Network (VPN) tunnelling using | ||
700 | the tun(4) network pseudo-device, allowing two networks to be joined | ||
701 | securely. The sshd_config(5) configuration option PermitTunnel controls | ||
702 | whether the server supports this, and at what level (layer 2 or 3 | ||
703 | traffic). | ||
704 | |||
705 | The following example would connect client network 10.0.50.0/24 with | ||
706 | remote network 10.0.99.0/24 using a point-to-point connection from | ||
707 | 10.1.1.1 to 10.1.1.2, provided that the SSH server running on the gateway | ||
708 | to the remote network, at 192.168.1.15, allows it. | ||
709 | |||
710 | On the client: | ||
711 | |||
712 | # ssh -f -w 0:1 192.168.1.15 true | ||
713 | # ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252 | ||
714 | # route add 10.0.99.0/24 10.1.1.2 | ||
715 | |||
716 | On the server: | ||
717 | |||
718 | # ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252 | ||
719 | # route add 10.0.50.0/24 10.1.1.1 | ||
720 | |||
721 | Client access may be more finely tuned via the /root/.ssh/authorized_keys | ||
722 | file (see below) and the PermitRootLogin server option. The following | ||
723 | entry would permit connections on tun(4) device 1 from user M-bM-^@M-^\janeM-bM-^@M-^] and on | ||
724 | tun device 2 from user M-bM-^@M-^\johnM-bM-^@M-^], if PermitRootLogin is set to | ||
725 | M-bM-^@M-^\forced-commands-onlyM-bM-^@M-^]: | ||
726 | |||
727 | tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane | ||
728 | tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john | ||
729 | |||
730 | Since an SSH-based setup entails a fair amount of overhead, it may be | ||
731 | more suited to temporary setups, such as for wireless VPNs. More | ||
732 | permanent VPNs are better provided by tools such as ipsecctl(8) and | ||
733 | isakmpd(8). | ||
734 | |||
735 | ENVIRONMENT | ||
736 | ssh will normally set the following environment variables: | ||
737 | |||
738 | DISPLAY The DISPLAY variable indicates the location of the | ||
739 | X11 server. It is automatically set by ssh to | ||
740 | point to a value of the form M-bM-^@M-^\hostname:nM-bM-^@M-^], where | ||
741 | M-bM-^@M-^\hostnameM-bM-^@M-^] indicates the host where the shell runs, | ||
742 | and M-bM-^@M-^XnM-bM-^@M-^Y is an integer M-bM-^IM-% 1. ssh uses this special | ||
743 | value to forward X11 connections over the secure | ||
744 | channel. The user should normally not set DISPLAY | ||
745 | explicitly, as that will render the X11 connection | ||
746 | insecure (and will require the user to manually | ||
747 | copy any required authorization cookies). | ||
748 | |||
749 | HOME Set to the path of the user's home directory. | ||
750 | |||
751 | LOGNAME Synonym for USER; set for compatibility with | ||
752 | systems that use this variable. | ||
753 | |||
754 | MAIL Set to the path of the user's mailbox. | ||
755 | |||
756 | PATH Set to the default PATH, as specified when | ||
757 | compiling ssh. | ||
758 | |||
759 | SSH_ASKPASS If ssh needs a passphrase, it will read the | ||
760 | passphrase from the current terminal if it was run | ||
761 | from a terminal. If ssh does not have a terminal | ||
762 | associated with it but DISPLAY and SSH_ASKPASS are | ||
763 | set, it will execute the program specified by | ||
764 | SSH_ASKPASS and open an X11 window to read the | ||
765 | passphrase. This is particularly useful when | ||
766 | calling ssh from a .xsession or related script. | ||
767 | (Note that on some machines it may be necessary to | ||
768 | redirect the input from /dev/null to make this | ||
769 | work.) | ||
770 | |||
771 | SSH_AUTH_SOCK Identifies the path of a UNIX-domain socket used to | ||
772 | communicate with the agent. | ||
773 | |||
774 | SSH_CONNECTION Identifies the client and server ends of the | ||
775 | connection. The variable contains four space- | ||
776 | separated values: client IP address, client port | ||
777 | number, server IP address, and server port number. | ||
778 | |||
779 | SSH_ORIGINAL_COMMAND This variable contains the original command line if | ||
780 | a forced command is executed. It can be used to | ||
781 | extract the original arguments. | ||
782 | |||
783 | SSH_TTY This is set to the name of the tty (path to the | ||
784 | device) associated with the current shell or | ||
785 | command. If the current session has no tty, this | ||
786 | variable is not set. | ||
787 | |||
788 | TZ This variable is set to indicate the present time | ||
789 | zone if it was set when the daemon was started | ||
790 | (i.e. the daemon passes the value on to new | ||
791 | connections). | ||
792 | |||
793 | USER Set to the name of the user logging in. | ||
794 | |||
795 | Additionally, ssh reads ~/.ssh/environment, and adds lines of the format | ||
796 | M-bM-^@M-^\VARNAME=valueM-bM-^@M-^] to the environment if the file exists and users are | ||
797 | allowed to change their environment. For more information, see the | ||
798 | PermitUserEnvironment option in sshd_config(5). | ||
799 | |||
800 | FILES | ||
801 | ~/.rhosts | ||
802 | This file is used for host-based authentication (see above). On | ||
803 | some machines this file may need to be world-readable if the | ||
804 | user's home directory is on an NFS partition, because sshd(8) | ||
805 | reads it as root. Additionally, this file must be owned by the | ||
806 | user, and must not have write permissions for anyone else. The | ||
807 | recommended permission for most machines is read/write for the | ||
808 | user, and not accessible by others. | ||
809 | |||
810 | ~/.shosts | ||
811 | This file is used in exactly the same way as .rhosts, but allows | ||
812 | host-based authentication without permitting login with | ||
813 | rlogin/rsh. | ||
814 | |||
815 | ~/.ssh/ | ||
816 | This directory is the default location for all user-specific | ||
817 | configuration and authentication information. There is no | ||
818 | general requirement to keep the entire contents of this directory | ||
819 | secret, but the recommended permissions are read/write/execute | ||
820 | for the user, and not accessible by others. | ||
821 | |||
822 | ~/.ssh/authorized_keys | ||
823 | Lists the public keys (DSA, ECDSA, Ed25519, RSA) that can be used | ||
824 | for logging in as this user. The format of this file is | ||
825 | described in the sshd(8) manual page. This file is not highly | ||
826 | sensitive, but the recommended permissions are read/write for the | ||
827 | user, and not accessible by others. | ||
828 | |||
829 | ~/.ssh/config | ||
830 | This is the per-user configuration file. The file format and | ||
831 | configuration options are described in ssh_config(5). Because of | ||
832 | the potential for abuse, this file must have strict permissions: | ||
833 | read/write for the user, and not writable by others. | ||
834 | |||
835 | ~/.ssh/environment | ||
836 | Contains additional definitions for environment variables; see | ||
837 | ENVIRONMENT, above. | ||
838 | |||
839 | ~/.ssh/id_dsa | ||
840 | ~/.ssh/id_ecdsa | ||
841 | ~/.ssh/id_ed25519 | ||
842 | ~/.ssh/id_rsa | ||
843 | Contains the private key for authentication. These files contain | ||
844 | sensitive data and should be readable by the user but not | ||
845 | accessible by others (read/write/execute). ssh will simply | ||
846 | ignore a private key file if it is accessible by others. It is | ||
847 | possible to specify a passphrase when generating the key which | ||
848 | will be used to encrypt the sensitive part of this file using | ||
849 | 3DES. | ||
850 | |||
851 | ~/.ssh/id_dsa.pub | ||
852 | ~/.ssh/id_ecdsa.pub | ||
853 | ~/.ssh/id_ed25519.pub | ||
854 | ~/.ssh/id_rsa.pub | ||
855 | Contains the public key for authentication. These files are not | ||
856 | sensitive and can (but need not) be readable by anyone. | ||
857 | |||
858 | ~/.ssh/known_hosts | ||
859 | Contains a list of host keys for all hosts the user has logged | ||
860 | into that are not already in the systemwide list of known host | ||
861 | keys. See sshd(8) for further details of the format of this | ||
862 | file. | ||
863 | |||
864 | ~/.ssh/rc | ||
865 | Commands in this file are executed by ssh when the user logs in, | ||
866 | just before the user's shell (or command) is started. See the | ||
867 | sshd(8) manual page for more information. | ||
868 | |||
869 | /etc/hosts.equiv | ||
870 | This file is for host-based authentication (see above). It | ||
871 | should only be writable by root. | ||
872 | |||
873 | /etc/shosts.equiv | ||
874 | This file is used in exactly the same way as hosts.equiv, but | ||
875 | allows host-based authentication without permitting login with | ||
876 | rlogin/rsh. | ||
877 | |||
878 | /etc/ssh/ssh_config | ||
879 | Systemwide configuration file. The file format and configuration | ||
880 | options are described in ssh_config(5). | ||
881 | |||
882 | /etc/ssh/ssh_host_key | ||
883 | /etc/ssh/ssh_host_dsa_key | ||
884 | /etc/ssh/ssh_host_ecdsa_key | ||
885 | /etc/ssh/ssh_host_ed25519_key | ||
886 | /etc/ssh/ssh_host_rsa_key | ||
887 | These files contain the private parts of the host keys and are | ||
888 | used for host-based authentication. | ||
889 | |||
890 | /etc/ssh/ssh_known_hosts | ||
891 | Systemwide list of known host keys. This file should be prepared | ||
892 | by the system administrator to contain the public host keys of | ||
893 | all machines in the organization. It should be world-readable. | ||
894 | See sshd(8) for further details of the format of this file. | ||
895 | |||
896 | /etc/ssh/sshrc | ||
897 | Commands in this file are executed by ssh when the user logs in, | ||
898 | just before the user's shell (or command) is started. See the | ||
899 | sshd(8) manual page for more information. | ||
900 | |||
901 | EXIT STATUS | ||
902 | ssh exits with the exit status of the remote command or with 255 if an | ||
903 | error occurred. | ||
904 | |||
905 | SEE ALSO | ||
906 | scp(1), sftp(1), ssh-add(1), ssh-agent(1), ssh-keygen(1), ssh-keyscan(1), | ||
907 | tun(4), ssh_config(5), ssh-keysign(8), sshd(8) | ||
908 | |||
909 | STANDARDS | ||
910 | S. Lehtinen and C. Lonvick, The Secure Shell (SSH) Protocol Assigned | ||
911 | Numbers, RFC 4250, January 2006. | ||
912 | |||
913 | T. Ylonen and C. Lonvick, The Secure Shell (SSH) Protocol Architecture, | ||
914 | RFC 4251, January 2006. | ||
915 | |||
916 | T. Ylonen and C. Lonvick, The Secure Shell (SSH) Authentication Protocol, | ||
917 | RFC 4252, January 2006. | ||
918 | |||
919 | T. Ylonen and C. Lonvick, The Secure Shell (SSH) Transport Layer | ||
920 | Protocol, RFC 4253, January 2006. | ||
921 | |||
922 | T. Ylonen and C. Lonvick, The Secure Shell (SSH) Connection Protocol, RFC | ||
923 | 4254, January 2006. | ||
924 | |||
925 | J. Schlyter and W. Griffin, Using DNS to Securely Publish Secure Shell | ||
926 | (SSH) Key Fingerprints, RFC 4255, January 2006. | ||
927 | |||
928 | F. Cusack and M. Forssen, Generic Message Exchange Authentication for the | ||
929 | Secure Shell Protocol (SSH), RFC 4256, January 2006. | ||
930 | |||
931 | J. Galbraith and P. Remaker, The Secure Shell (SSH) Session Channel Break | ||
932 | Extension, RFC 4335, January 2006. | ||
933 | |||
934 | M. Bellare, T. Kohno, and C. Namprempre, The Secure Shell (SSH) Transport | ||
935 | Layer Encryption Modes, RFC 4344, January 2006. | ||
936 | |||
937 | B. Harris, Improved Arcfour Modes for the Secure Shell (SSH) Transport | ||
938 | Layer Protocol, RFC 4345, January 2006. | ||
939 | |||
940 | M. Friedl, N. Provos, and W. Simpson, Diffie-Hellman Group Exchange for | ||
941 | the Secure Shell (SSH) Transport Layer Protocol, RFC 4419, March 2006. | ||
942 | |||
943 | J. Galbraith and R. Thayer, The Secure Shell (SSH) Public Key File | ||
944 | Format, RFC 4716, November 2006. | ||
945 | |||
946 | D. Stebila and J. Green, Elliptic Curve Algorithm Integration in the | ||
947 | Secure Shell Transport Layer, RFC 5656, December 2009. | ||
948 | |||
949 | A. Perrig and D. Song, Hash Visualization: a New Technique to improve | ||
950 | Real-World Security, 1999, International Workshop on Cryptographic | ||
951 | Techniques and E-Commerce (CrypTEC '99). | ||
952 | |||
953 | AUTHORS | ||
954 | OpenSSH is a derivative of the original and free ssh 1.2.12 release by | ||
955 | Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo | ||
956 | de Raadt and Dug Song removed many bugs, re-added newer features and | ||
957 | created OpenSSH. Markus Friedl contributed the support for SSH protocol | ||
958 | versions 1.5 and 2.0. | ||
959 | |||
960 | OpenBSD 6.2 September 21, 2017 OpenBSD 6.2 | ||