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authorColin Watson <cjwatson@debian.org>2003-09-17 00:32:19 +0000
committerColin Watson <cjwatson@debian.org>2003-09-17 00:32:19 +0000
commit22f9b945efa61bba12a4778b889df07cf851838a (patch)
tree77a3f749ea589c590db930cff12d804a4d7893b5 /ssh.0
parent9d1471514608023cda6456f5a2e875cc5e4b9e77 (diff)
parent854156dd39acbde9b4a47ec0fc54a042ea7358e0 (diff)
Import OpenSSH 3.7p1.
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1SSH(1) BSD General Commands Manual SSH(1)
2
3NAME
4 ssh - OpenSSH SSH client (remote login program)
5
6SYNOPSIS
7 ssh [-l login_name] hostname | user@hostname [command]
8
9 ssh [-afgknqstvxACNTVX1246] [-b bind_address] [-c cipher_spec]
10 [-e escape_char] [-i identity_file] [-l login_name] [-m mac_spec]
11 [-o option] [-p port] [-F configfile] [-L port:host:hostport]
12 [-R port:host:hostport] [-D port] hostname | user@hostname [command]
13
14DESCRIPTION
15 ssh (SSH client) is a program for logging into a remote machine and for
16 executing commands on a remote machine. It is intended to replace rlogin
17 and rsh, and provide secure encrypted communications between two
18 untrusted hosts over an insecure network. X11 connections and arbitrary
19 TCP/IP ports can also be forwarded over the secure channel.
20
21 ssh connects and logs into the specified hostname. The user must prove
22 his/her identity to the remote machine using one of several methods
23 depending on the protocol version used:
24
25 SSH protocol version 1
26 First, if the machine the user logs in from is listed in /etc/hosts.equiv
27 or /etc/shosts.equiv on the remote machine, and the user names are the
28 same on both sides, the user is immediately permitted to log in. Second,
29 if .rhosts or .shosts exists in the userM-bM-^@M-^Ys home directory on the remote
30 machine and contains a line containing the name of the client machine and
31 the name of the user on that machine, the user is permitted to log in.
32 This form of authentication alone is normally not allowed by the server
33 because it is not secure.
34
35 The second authentication method is the rhosts or hosts.equiv method com-
36 bined with RSA-based host authentication. It means that if the login
37 would be permitted by $HOME/.rhosts, $HOME/.shosts, /etc/hosts.equiv, or
38 /etc/shosts.equiv, and if additionally the server can verify the clientM-bM-^@M-^Ys
39 host key (see /etc/ssh/ssh_known_hosts and $HOME/.ssh/known_hosts in the
40 FILES section), only then login is permitted. This authentication method
41 closes security holes due to IP spoofing, DNS spoofing and routing spoof-
42 ing. [Note to the administrator: /etc/hosts.equiv, $HOME/.rhosts, and
43 the rlogin/rsh protocol in general, are inherently insecure and should be
44 disabled if security is desired.]
45
46 As a third authentication method, ssh supports RSA based authentication.
47 The scheme is based on public-key cryptography: there are cryptosystems
48 where encryption and decryption are done using separate keys, and it is
49 not possible to derive the decryption key from the encryption key. RSA
50 is one such system. The idea is that each user creates a public/private
51 key pair for authentication purposes. The server knows the public key,
52 and only the user knows the private key. The file
53 $HOME/.ssh/authorized_keys lists the public keys that are permitted for
54 logging in. When the user logs in, the ssh program tells the server
55 which key pair it would like to use for authentication. The server
56 checks if this key is permitted, and if so, sends the user (actually the
57 ssh program running on behalf of the user) a challenge, a random number,
58 encrypted by the userM-bM-^@M-^Ys public key. The challenge can only be decrypted
59 using the proper private key. The userM-bM-^@M-^Ys client then decrypts the chal-
60 lenge using the private key, proving that he/she knows the private key
61 but without disclosing it to the server.
62
63 ssh implements the RSA authentication protocol automatically. The user
64 creates his/her RSA key pair by running ssh-keygen(1). This stores the
65 private key in $HOME/.ssh/identity and the public key in
66 $HOME/.ssh/identity.pub in the userM-bM-^@M-^Ys home directory. The user should
67 then copy the identity.pub to $HOME/.ssh/authorized_keys in his/her home
68 directory on the remote machine (the authorized_keys file corresponds to
69 the conventional $HOME/.rhosts file, and has one key per line, though the
70 lines can be very long). After this, the user can log in without giving
71 the password. RSA authentication is much more secure than rhosts authen-
72 tication.
73
74 The most convenient way to use RSA authentication may be with an authen-
75 tication agent. See ssh-agent(1) for more information.
76
77 If other authentication methods fail, ssh prompts the user for a pass-
78 word. The password is sent to the remote host for checking; however,
79 since all communications are encrypted, the password cannot be seen by
80 someone listening on the network.
81
82 SSH protocol version 2
83 When a user connects using protocol version 2 similar authentication
84 methods are available. Using the default values for
85 PreferredAuthentications, the client will try to authenticate first using
86 the hostbased method; if this method fails public key authentication is
87 attempted, and finally if this method fails keyboard-interactive and
88 password authentication are tried.
89
90 The public key method is similar to RSA authentication described in the
91 previous section and allows the RSA or DSA algorithm to be used: The
92 client uses his private key, $HOME/.ssh/id_dsa or $HOME/.ssh/id_rsa, to
93 sign the session identifier and sends the result to the server. The
94 server checks whether the matching public key is listed in
95 $HOME/.ssh/authorized_keys and grants access if both the key is found and
96 the signature is correct. The session identifier is derived from a
97 shared Diffie-Hellman value and is only known to the client and the
98 server.
99
100 If public key authentication fails or is not available a password can be
101 sent encrypted to the remote host for proving the userM-bM-^@M-^Ys identity.
102
103 Additionally, ssh supports hostbased or challenge response authentica-
104 tion.
105
106 Protocol 2 provides additional mechanisms for confidentiality (the traf-
107 fic is encrypted using 3DES, Blowfish, CAST128 or Arcfour) and integrity
108 (hmac-md5, hmac-sha1). Note that protocol 1 lacks a strong mechanism for
109 ensuring the integrity of the connection.
110
111 Login session and remote execution
112 When the userM-bM-^@M-^Ys identity has been accepted by the server, the server
113 either executes the given command, or logs into the machine and gives the
114 user a normal shell on the remote machine. All communication with the
115 remote command or shell will be automatically encrypted.
116
117 If a pseudo-terminal has been allocated (normal login session), the user
118 may use the escape characters noted below.
119
120 If no pseudo tty has been allocated, the session is transparent and can
121 be used to reliably transfer binary data. On most systems, setting the
122 escape character to M-bM-^@M-^\noneM-bM-^@M-^] will also make the session transparent even if
123 a tty is used.
124
125 The session terminates when the command or shell on the remote machine
126 exits and all X11 and TCP/IP connections have been closed. The exit sta-
127 tus of the remote program is returned as the exit status of ssh.
128
129 Escape Characters
130 When a pseudo terminal has been requested, ssh supports a number of func-
131 tions through the use of an escape character.
132
133 A single tilde character can be sent as ~~ or by following the tilde by a
134 character other than those described below. The escape character must
135 always follow a newline to be interpreted as special. The escape charac-
136 ter can be changed in configuration files using the EscapeChar configura-
137 tion directive or on the command line by the -e option.
138
139 The supported escapes (assuming the default M-bM-^@M-^X~M-bM-^@M-^Y) are:
140
141 ~. Disconnect
142
143 ~^Z Background ssh
144
145 ~# List forwarded connections
146
147 ~& Background ssh at logout when waiting for forwarded connection /
148 X11 sessions to terminate
149
150 ~? Display a list of escape characters
151
152 ~B Send a BREAK to the remote system (only useful for SSH protocol
153 version 2 and if the peer supports it)
154
155 ~C Open command line (only useful for adding port forwardings using
156 the -L and -R options)
157
158 ~R Request rekeying of the connection (only useful for SSH protocol
159 version 2 and if the peer supports it)
160
161 X11 and TCP forwarding
162 If the ForwardX11 variable is set to M-bM-^@M-^\yesM-bM-^@M-^] (or, see the description of
163 the -X and -x options described later) and the user is using X11 (the
164 DISPLAY environment variable is set), the connection to the X11 display
165 is automatically forwarded to the remote side in such a way that any X11
166 programs started from the shell (or command) will go through the
167 encrypted channel, and the connection to the real X server will be made
168 from the local machine. The user should not manually set DISPLAY. For-
169 warding of X11 connections can be configured on the command line or in
170 configuration files.
171
172 The DISPLAY value set by ssh will point to the server machine, but with a
173 display number greater than zero. This is normal, and happens because
174 ssh creates a M-bM-^@M-^\proxyM-bM-^@M-^] X server on the server machine for forwarding the
175 connections over the encrypted channel.
176
177 ssh will also automatically set up Xauthority data on the server machine.
178 For this purpose, it will generate a random authorization cookie, store
179 it in Xauthority on the server, and verify that any forwarded connections
180 carry this cookie and replace it by the real cookie when the connection
181 is opened. The real authentication cookie is never sent to the server
182 machine (and no cookies are sent in the plain).
183
184 If the ForwardAgent variable is set to M-bM-^@M-^\yesM-bM-^@M-^] (or, see the description of
185 the -A and -a options described later) and the user is using an authenti-
186 cation agent, the connection to the agent is automatically forwarded to
187 the remote side.
188
189 Forwarding of arbitrary TCP/IP connections over the secure channel can be
190 specified either on the command line or in a configuration file. One
191 possible application of TCP/IP forwarding is a secure connection to an
192 electronic purse; another is going through firewalls.
193
194 Server authentication
195 ssh automatically maintains and checks a database containing identifica-
196 tions for all hosts it has ever been used with. Host keys are stored in
197 $HOME/.ssh/known_hosts in the userM-bM-^@M-^Ys home directory. Additionally, the
198 file /etc/ssh/ssh_known_hosts is automatically checked for known hosts.
199 Any new hosts are automatically added to the userM-bM-^@M-^Ys file. If a hostM-bM-^@M-^Ys
200 identification ever changes, ssh warns about this and disables password
201 authentication to prevent a trojan horse from getting the userM-bM-^@M-^Ys pass-
202 word. Another purpose of this mechanism is to prevent man-in-the-middle
203 attacks which could otherwise be used to circumvent the encryption. The
204 StrictHostKeyChecking option can be used to prevent logins to machines
205 whose host key is not known or has changed.
206
207 The options are as follows:
208
209 -a Disables forwarding of the authentication agent connection.
210
211 -A Enables forwarding of the authentication agent connection. This
212 can also be specified on a per-host basis in a configuration
213 file.
214
215 Agent forwarding should be enabled with caution. Users with the
216 ability to bypass file permissions on the remote host (for the
217 agentM-bM-^@M-^Ys Unix-domain socket) can access the local agent through
218 the forwarded connection. An attacker cannot obtain key material
219 from the agent, however they can perform operations on the keys
220 that enable them to authenticate using the identities loaded into
221 the agent.
222
223 -b bind_address
224 Specify the interface to transmit from on machines with multiple
225 interfaces or aliased addresses.
226
227 -c blowfish|3des|des
228 Selects the cipher to use for encrypting the session. 3des is
229 used by default. It is believed to be secure. 3des (triple-des)
230 is an encrypt-decrypt-encrypt triple with three different keys.
231 blowfish is a fast block cipher, it appears very secure and is
232 much faster than 3des. des is only supported in the ssh client
233 for interoperability with legacy protocol 1 implementations that
234 do not support the 3des cipher. Its use is strongly discouraged
235 due to cryptographic weaknesses.
236
237 -c cipher_spec
238 Additionally, for protocol version 2 a comma-separated list of
239 ciphers can be specified in order of preference. See Ciphers for
240 more information.
241
242 -e ch|^ch|none
243 Sets the escape character for sessions with a pty (default: M-bM-^@M-^X~M-bM-^@M-^Y).
244 The escape character is only recognized at the beginning of a
245 line. The escape character followed by a dot (M-bM-^@M-^X.M-bM-^@M-^Y) closes the
246 connection, followed by control-Z suspends the connection, and
247 followed by itself sends the escape character once. Setting the
248 character to M-bM-^@M-^\noneM-bM-^@M-^] disables any escapes and makes the session
249 fully transparent.
250
251 -f Requests ssh to go to background just before command execution.
252 This is useful if ssh is going to ask for passwords or
253 passphrases, but the user wants it in the background. This
254 implies -n. The recommended way to start X11 programs at a
255 remote site is with something like ssh -f host xterm.
256
257 -g Allows remote hosts to connect to local forwarded ports.
258
259 -i identity_file
260 Selects a file from which the identity (private key) for RSA or
261 DSA authentication is read. The default is $HOME/.ssh/identity
262 for protocol version 1, and $HOME/.ssh/id_rsa and
263 $HOME/.ssh/id_dsa for protocol version 2. Identity files may
264 also be specified on a per-host basis in the configuration file.
265 It is possible to have multiple -i options (and multiple identi-
266 ties specified in configuration files).
267
268 -I smartcard_device
269 Specifies which smartcard device to use. The argument is the
270 device ssh should use to communicate with a smartcard used for
271 storing the userM-bM-^@M-^Ys private RSA key.
272
273 -k Disables forwarding of Kerberos tickets. This may also be speci-
274 fied on a per-host basis in the configuration file.
275
276 -l login_name
277 Specifies the user to log in as on the remote machine. This also
278 may be specified on a per-host basis in the configuration file.
279
280 -m mac_spec
281 Additionally, for protocol version 2 a comma-separated list of
282 MAC (message authentication code) algorithms can be specified in
283 order of preference. See the MACs keyword for more information.
284
285 -n Redirects stdin from /dev/null (actually, prevents reading from
286 stdin). This must be used when ssh is run in the background. A
287 common trick is to use this to run X11 programs on a remote
288 machine. For example, ssh -n shadows.cs.hut.fi emacs & will
289 start an emacs on shadows.cs.hut.fi, and the X11 connection will
290 be automatically forwarded over an encrypted channel. The ssh
291 program will be put in the background. (This does not work if
292 ssh needs to ask for a password or passphrase; see also the -f
293 option.)
294
295 -N Do not execute a remote command. This is useful for just for-
296 warding ports (protocol version 2 only).
297
298 -o option
299 Can be used to give options in the format used in the configura-
300 tion file. This is useful for specifying options for which there
301 is no separate command-line flag.
302
303 -p port
304 Port to connect to on the remote host. This can be specified on
305 a per-host basis in the configuration file.
306
307 -q Quiet mode. Causes all warning and diagnostic messages to be
308 suppressed.
309
310 -s May be used to request invocation of a subsystem on the remote
311 system. Subsystems are a feature of the SSH2 protocol which
312 facilitate the use of SSH as a secure transport for other appli-
313 cations (eg. sftp). The subsystem is specified as the remote
314 command.
315
316 -t Force pseudo-tty allocation. This can be used to execute arbi-
317 trary screen-based programs on a remote machine, which can be
318 very useful, e.g., when implementing menu services. Multiple -t
319 options force tty allocation, even if ssh has no local tty.
320
321 -T Disable pseudo-tty allocation.
322
323 -v Verbose mode. Causes ssh to print debugging messages about its
324 progress. This is helpful in debugging connection, authentica-
325 tion, and configuration problems. Multiple -v options increase
326 the verbosity. The maximum is 3.
327
328 -V Display the version number and exit.
329
330 -x Disables X11 forwarding.
331
332 -X Enables X11 forwarding. This can also be specified on a per-host
333 basis in a configuration file.
334
335 X11 forwarding should be enabled with caution. Users with the
336 ability to bypass file permissions on the remote host (for the
337 userM-bM-^@M-^Ys X authorization database) can access the local X11 display
338 through the forwarded connection. An attacker may then be able
339 to perform activities such as keystroke monitoring.
340
341 -C Requests compression of all data (including stdin, stdout,
342 stderr, and data for forwarded X11 and TCP/IP connections). The
343 compression algorithm is the same used by gzip(1), and the
344 M-bM-^@M-^\levelM-bM-^@M-^] can be controlled by the CompressionLevel option for pro-
345 tocol version 1. Compression is desirable on modem lines and
346 other slow connections, but will only slow down things on fast
347 networks. The default value can be set on a host-by-host basis
348 in the configuration files; see the Compression option.
349
350 -F configfile
351 Specifies an alternative per-user configuration file. If a con-
352 figuration file is given on the command line, the system-wide
353 configuration file (/etc/ssh/ssh_config) will be ignored. The
354 default for the per-user configuration file is $HOME/.ssh/config.
355
356 -L port:host:hostport
357 Specifies that the given port on the local (client) host is to be
358 forwarded to the given host and port on the remote side. This
359 works by allocating a socket to listen to port on the local side,
360 and whenever a connection is made to this port, the connection is
361 forwarded over the secure channel, and a connection is made to
362 host port hostport from the remote machine. Port forwardings can
363 also be specified in the configuration file. Only root can for-
364 ward privileged ports. IPv6 addresses can be specified with an
365 alternative syntax: port/host/hostport
366
367 -R port:host:hostport
368 Specifies that the given port on the remote (server) host is to
369 be forwarded to the given host and port on the local side. This
370 works by allocating a socket to listen to port on the remote
371 side, and whenever a connection is made to this port, the connec-
372 tion is forwarded over the secure channel, and a connection is
373 made to host port hostport from the local machine. Port forward-
374 ings can also be specified in the configuration file. Privileged
375 ports can be forwarded only when logging in as root on the remote
376 machine. IPv6 addresses can be specified with an alternative
377 syntax: port/host/hostport
378
379 -D port
380 Specifies a local M-bM-^@M-^\dynamicM-bM-^@M-^] application-level port forwarding.
381 This works by allocating a socket to listen to port on the local
382 side, and whenever a connection is made to this port, the connec-
383 tion is forwarded over the secure channel, and the application
384 protocol is then used to determine where to connect to from the
385 remote machine. Currently the SOCKS4 and SOCKS5 protocols are
386 supported, and ssh will act as a SOCKS server. Only root can
387 forward privileged ports. Dynamic port forwardings can also be
388 specified in the configuration file.
389
390 -1 Forces ssh to try protocol version 1 only.
391
392 -2 Forces ssh to try protocol version 2 only.
393
394 -4 Forces ssh to use IPv4 addresses only.
395
396 -6 Forces ssh to use IPv6 addresses only.
397
398CONFIGURATION FILES
399 ssh may additionally obtain configuration data from a per-user configura-
400 tion file and a system-wide configuration file. The file format and con-
401 figuration options are described in ssh_config(5).
402
403ENVIRONMENT
404 ssh will normally set the following environment variables:
405
406 DISPLAY
407 The DISPLAY variable indicates the location of the X11 server.
408 It is automatically set by ssh to point to a value of the form
409 M-bM-^@M-^\hostname:nM-bM-^@M-^] where hostname indicates the host where the shell
410 runs, and n is an integer >= 1. ssh uses this special value to
411 forward X11 connections over the secure channel. The user should
412 normally not set DISPLAY explicitly, as that will render the X11
413 connection insecure (and will require the user to manually copy
414 any required authorization cookies).
415
416 HOME Set to the path of the userM-bM-^@M-^Ys home directory.
417
418 LOGNAME
419 Synonym for USER; set for compatibility with systems that use
420 this variable.
421
422 MAIL Set to the path of the userM-bM-^@M-^Ys mailbox.
423
424 PATH Set to the default PATH, as specified when compiling ssh.
425
426 SSH_ASKPASS
427 If ssh needs a passphrase, it will read the passphrase from the
428 current terminal if it was run from a terminal. If ssh does not
429 have a terminal associated with it but DISPLAY and SSH_ASKPASS
430 are set, it will execute the program specified by SSH_ASKPASS and
431 open an X11 window to read the passphrase. This is particularly
432 useful when calling ssh from a .Xsession or related script.
433 (Note that on some machines it may be necessary to redirect the
434 input from /dev/null to make this work.)
435
436 SSH_AUTH_SOCK
437 Identifies the path of a unix-domain socket used to communicate
438 with the agent.
439
440 SSH_CONNECTION
441 Identifies the client and server ends of the connection. The
442 variable contains four space-separated values: client ip-address,
443 client port number, server ip-address and server port number.
444
445 SSH_ORIGINAL_COMMAND
446 The variable contains the original command line if a forced com-
447 mand is executed. It can be used to extract the original argu-
448 ments.
449
450 SSH_TTY
451 This is set to the name of the tty (path to the device) associ-
452 ated with the current shell or command. If the current session
453 has no tty, this variable is not set.
454
455 TZ The timezone variable is set to indicate the present timezone if
456 it was set when the daemon was started (i.e., the daemon passes
457 the value on to new connections).
458
459 USER Set to the name of the user logging in.
460
461 Additionally, ssh reads $HOME/.ssh/environment, and adds lines of the
462 format M-bM-^@M-^\VARNAME=valueM-bM-^@M-^] to the environment if the file exists and if users
463 are allowed to change their environment. See the PermitUserEnvironment
464 option in sshd_config(5).
465
466FILES
467 $HOME/.ssh/known_hosts
468 Records host keys for all hosts the user has logged into that are
469 not in /etc/ssh/ssh_known_hosts. See sshd(8).
470
471 $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa
472 Contains the authentication identity of the user. They are for
473 protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
474 These files contain sensitive data and should be readable by the
475 user but not accessible by others (read/write/execute). Note
476 that ssh ignores a private key file if it is accessible by oth-
477 ers. It is possible to specify a passphrase when generating the
478 key; the passphrase will be used to encrypt the sensitive part of
479 this file using 3DES.
480
481 $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub, $HOME/.ssh/id_rsa.pub
482 Contains the public key for authentication (public part of the
483 identity file in human-readable form). The contents of the
484 $HOME/.ssh/identity.pub file should be added to
485 $HOME/.ssh/authorized_keys on all machines where the user wishes
486 to log in using protocol version 1 RSA authentication. The con-
487 tents of the $HOME/.ssh/id_dsa.pub and $HOME/.ssh/id_rsa.pub file
488 should be added to $HOME/.ssh/authorized_keys on all machines
489 where the user wishes to log in using protocol version 2 DSA/RSA
490 authentication. These files are not sensitive and can (but need
491 not) be readable by anyone. These files are never used automati-
492 cally and are not necessary; they are only provided for the con-
493 venience of the user.
494
495 $HOME/.ssh/config
496 This is the per-user configuration file. The file format and
497 configuration options are described in ssh_config(5).
498
499 $HOME/.ssh/authorized_keys
500 Lists the public keys (RSA/DSA) that can be used for logging in
501 as this user. The format of this file is described in the
502 sshd(8) manual page. In the simplest form the format is the same
503 as the .pub identity files. This file is not highly sensitive,
504 but the recommended permissions are read/write for the user, and
505 not accessible by others.
506
507 /etc/ssh/ssh_known_hosts
508 Systemwide list of known host keys. This file should be prepared
509 by the system administrator to contain the public host keys of
510 all machines in the organization. This file should be world-
511 readable. This file contains public keys, one per line, in the
512 following format (fields separated by spaces): system name, pub-
513 lic key and optional comment field. When different names are
514 used for the same machine, all such names should be listed, sepa-
515 rated by commas. The format is described on the sshd(8) manual
516 page.
517
518 The canonical system name (as returned by name servers) is used
519 by sshd(8) to verify the client host when logging in; other names
520 are needed because ssh does not convert the user-supplied name to
521 a canonical name before checking the key, because someone with
522 access to the name servers would then be able to fool host
523 authentication.
524
525 /etc/ssh/ssh_config
526 Systemwide configuration file. The file format and configuration
527 options are described in ssh_config(5).
528
529 /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key,
530 /etc/ssh/ssh_host_rsa_key
531 These three files contain the private parts of the host keys and
532 are used for RhostsRSAAuthentication and HostbasedAuthentication.
533 If the protocol version 1 RhostsRSAAuthentication method is used,
534 ssh must be setuid root, since the host key is readable only by
535 root. For protocol version 2, ssh uses ssh-keysign(8) to access
536 the host keys for HostbasedAuthentication. This eliminates the
537 requirement that ssh be setuid root when that authentication
538 method is used. By default ssh is not setuid root.
539
540 $HOME/.rhosts
541 This file is used in .rhosts authentication to list the host/user
542 pairs that are permitted to log in. (Note that this file is also
543 used by rlogin and rsh, which makes using this file insecure.)
544 Each line of the file contains a host name (in the canonical form
545 returned by name servers), and then a user name on that host,
546 separated by a space. On some machines this file may need to be
547 world-readable if the userM-bM-^@M-^Ys home directory is on a NFS parti-
548 tion, because sshd(8) reads it as root. Additionally, this file
549 must be owned by the user, and must not have write permissions
550 for anyone else. The recommended permission for most machines is
551 read/write for the user, and not accessible by others.
552
553 Note that by default sshd(8) will be installed so that it
554 requires successful RSA host authentication before permitting
555 .rhosts authentication. If the server machine does not have the
556 clientM-bM-^@M-^Ys host key in /etc/ssh/ssh_known_hosts, it can be stored
557 in $HOME/.ssh/known_hosts. The easiest way to do this is to con-
558 nect back to the client from the server machine using ssh; this
559 will automatically add the host key to $HOME/.ssh/known_hosts.
560
561 $HOME/.shosts
562 This file is used exactly the same way as .rhosts. The purpose
563 for having this file is to be able to use rhosts authentication
564 with ssh without permitting login with rlogin or rsh(1).
565
566 /etc/hosts.equiv
567 This file is used during .rhosts authentication. It contains
568 canonical hosts names, one per line (the full format is described
569 on the sshd(8) manual page). If the client host is found in this
570 file, login is automatically permitted provided client and server
571 user names are the same. Additionally, successful RSA host
572 authentication is normally required. This file should only be
573 writable by root.
574
575 /etc/shosts.equiv
576 This file is processed exactly as /etc/hosts.equiv. This file
577 may be useful to permit logins using ssh but not using
578 rsh/rlogin.
579
580 /etc/ssh/sshrc
581 Commands in this file are executed by ssh when the user logs in
582 just before the userM-bM-^@M-^Ys shell (or command) is started. See the
583 sshd(8) manual page for more information.
584
585 $HOME/.ssh/rc
586 Commands in this file are executed by ssh when the user logs in
587 just before the userM-bM-^@M-^Ys shell (or command) is started. See the
588 sshd(8) manual page for more information.
589
590 $HOME/.ssh/environment
591 Contains additional definitions for environment variables, see
592 section ENVIRONMENT above.
593
594DIAGNOSTICS
595 ssh exits with the exit status of the remote command or with 255 if an
596 error occurred.
597
598SEE ALSO
599 rsh(1), scp(1), sftp(1), ssh-add(1), ssh-agent(1), ssh-keygen(1),
600 telnet(1), ssh_config(5), ssh-keysign(8), sshd(8)
601
602 T. Ylonen, T. Kivinen, M. Saarinen, T. Rinne, and S. Lehtinen, SSH
603 Protocol Architecture, draft-ietf-secsh-architecture-12.txt, January
604 2002, work in progress material.
605
606AUTHORS
607 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
608 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
609 de Raadt and Dug Song removed many bugs, re-added newer features and cre-
610 ated OpenSSH. Markus Friedl contributed the support for SSH protocol
611 versions 1.5 and 2.0.
612
613BSD September 25, 1999 BSD