1 SSH_CONFIG(5) OpenBSD Programmer's Manual SSH_CONFIG(5) 2 3 NAME 4 ssh_config - OpenSSH SSH client configuration files 5 6 SYNOPSIS 7 ~/.ssh/config 8 /etc/ssh/ssh_config 9 10 DESCRIPTION 11 ssh(1) obtains configuration data from the following sources in the 12 following order: 13 14 1. command-line options 15 2. user's configuration file (~/.ssh/config) 16 3. system-wide configuration file (/etc/ssh/ssh_config) 17 18 For each parameter, the first obtained value will be used. The 19 configuration files contain sections separated by ``Host'' 20 specifications, and that section is only applied for hosts that match one 21 of the patterns given in the specification. The matched host name is the 22 one given on the command line. 23 24 Since the first obtained value for each parameter is used, more host- 25 specific declarations should be given near the beginning of the file, and 26 general defaults at the end. 27 28 The configuration file has the following format: 29 30 Empty lines and lines starting with `#' are comments. Otherwise a line 31 is of the format ``keyword arguments''. Configuration options may be 32 separated by whitespace or optional whitespace and exactly one `='; the 33 latter format is useful to avoid the need to quote whitespace when 34 specifying configuration options using the ssh, scp, and sftp -o option. 35 Arguments may optionally be enclosed in double quotes (") in order to 36 represent arguments containing spaces. 37 38 The possible keywords and their meanings are as follows (note that 39 keywords are case-insensitive and arguments are case-sensitive): 40 41 Host Restricts the following declarations (up to the next Host 42 keyword) to be only for those hosts that match one of the 43 patterns given after the keyword. If more than one pattern is 44 provided, they should be separated by whitespace. A single `*' 45 as a pattern can be used to provide global defaults for all 46 hosts. The host is the hostname argument given on the command 47 line (i.e. the name is not converted to a canonicalized host name 48 before matching). 49 50 A pattern entry may be negated by prefixing it with an 51 exclamation mark (`!'). If a negated entry is matched, then the 52 Host entry is ignored, regardless of whether any other patterns 53 on the line match. Negated matches are therefore useful to 54 provide exceptions for wildcard matches. 55 56 See PATTERNS for more information on patterns. 57 58 AddressFamily 59 Specifies which address family to use when connecting. Valid 60 arguments are ``any'', ``inet'' (use IPv4 only), or ``inet6'' 61 (use IPv6 only). 62 63 BatchMode 64 If set to ``yes'', passphrase/password querying will be disabled. 65 This option is useful in scripts and other batch jobs where no 66 user is present to supply the password. The argument must be 67 ``yes'' or ``no''. The default is ``no''. 68 69 BindAddress 70 Use the specified address on the local machine as the source 71 address of the connection. Only useful on systems with more than 72 one address. Note that this option does not work if 73 UsePrivilegedPort is set to ``yes''. 74 75 ChallengeResponseAuthentication 76 Specifies whether to use challenge-response authentication. The 77 argument to this keyword must be ``yes'' or ``no''. The default 78 is ``yes''. 79 80 CheckHostIP 81 If this flag is set to ``yes'', ssh(1) will additionally check 82 the host IP address in the known_hosts file. This allows ssh to 83 detect if a host key changed due to DNS spoofing. If the option 84 is set to ``no'', the check will not be executed. The default is 85 ``yes''. 86 87 Cipher Specifies the cipher to use for encrypting the session in 88 protocol version 1. Currently, ``blowfish'', ``3des'', and 89 ``des'' are supported. des is only supported in the ssh(1) 90 client for interoperability with legacy protocol 1 91 implementations that do not support the 3des cipher. Its use is 92 strongly discouraged due to cryptographic weaknesses. The 93 default is ``3des''. 94 95 Ciphers 96 Specifies the ciphers allowed for protocol version 2 in order of 97 preference. Multiple ciphers must be comma-separated. The 98 supported ciphers are ``3des-cbc'', ``aes128-cbc'', 99 ``aes192-cbc'', ``aes256-cbc'', ``aes128-ctr'', ``aes192-ctr'', 100 ``aes256-ctr'', ``arcfour128'', ``arcfour256'', ``arcfour'', 101 ``blowfish-cbc'', and ``cast128-cbc''. The default is: 102 103 aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128, 104 aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc, 105 aes256-cbc,arcfour 106 107 ClearAllForwardings 108 Specifies that all local, remote, and dynamic port forwardings 109 specified in the configuration files or on the command line be 110 cleared. This option is primarily useful when used from the 111 ssh(1) command line to clear port forwardings set in 112 configuration files, and is automatically set by scp(1) and 113 sftp(1). The argument must be ``yes'' or ``no''. The default is 114 ``no''. 115 116 Compression 117 Specifies whether to use compression. The argument must be 118 ``yes'' or ``no''. The default is ``no''. 119 120 CompressionLevel 121 Specifies the compression level to use if compression is enabled. 122 The argument must be an integer from 1 (fast) to 9 (slow, best). 123 The default level is 6, which is good for most applications. The 124 meaning of the values is the same as in gzip(1). Note that this 125 option applies to protocol version 1 only. 126 127 ConnectionAttempts 128 Specifies the number of tries (one per second) to make before 129 exiting. The argument must be an integer. This may be useful in 130 scripts if the connection sometimes fails. The default is 1. 131 132 ConnectTimeout 133 Specifies the timeout (in seconds) used when connecting to the 134 SSH server, instead of using the default system TCP timeout. 135 This value is used only when the target is down or really 136 unreachable, not when it refuses the connection. 137 138 ControlMaster 139 Enables the sharing of multiple sessions over a single network 140 connection. When set to ``yes'', ssh(1) will listen for 141 connections on a control socket specified using the ControlPath 142 argument. Additional sessions can connect to this socket using 143 the same ControlPath with ControlMaster set to ``no'' (the 144 default). These sessions will try to reuse the master instance's 145 network connection rather than initiating new ones, but will fall 146 back to connecting normally if the control socket does not exist, 147 or is not listening. 148 149 Setting this to ``ask'' will cause ssh to listen for control 150 connections, but require confirmation using the SSH_ASKPASS 151 program before they are accepted (see ssh-add(1) for details). 152 If the ControlPath cannot be opened, ssh will continue without 153 connecting to a master instance. 154 155 X11 and ssh-agent(1) forwarding is supported over these 156 multiplexed connections, however the display and agent forwarded 157 will be the one belonging to the master connection i.e. it is not 158 possible to forward multiple displays or agents. 159 160 Two additional options allow for opportunistic multiplexing: try 161 to use a master connection but fall back to creating a new one if 162 one does not already exist. These options are: ``auto'' and 163 ``autoask''. The latter requires confirmation like the ``ask'' 164 option. 165 166 ControlPath 167 Specify the path to the control socket used for connection 168 sharing as described in the ControlMaster section above or the 169 string ``none'' to disable connection sharing. In the path, `%L' 170 will be substituted by the first component of the local host 171 name, `%l' will be substituted by the local host name (including 172 any domain name), `%h' will be substituted by the target host 173 name, `%n' will be substituted by the original target host name 174 specified on the command line, `%p' the port, `%r' by the remote 175 login username, and `%u' by the username of the user running 176 ssh(1). It is recommended that any ControlPath used for 177 opportunistic connection sharing include at least %h, %p, and %r. 178 This ensures that shared connections are uniquely identified. 179 180 ControlPersist 181 When used in conjunction with ControlMaster, specifies that the 182 master connection should remain open in the background (waiting 183 for future client connections) after the initial client 184 connection has been closed. If set to ``no'', then the master 185 connection will not be placed into the background, and will close 186 as soon as the initial client connection is closed. If set to 187 ``yes'', then the master connection will remain in the background 188 indefinitely (until killed or closed via a mechanism such as the 189 ssh(1) ``-O exit'' option). If set to a time in seconds, or a 190 time in any of the formats documented in sshd_config(5), then the 191 backgrounded master connection will automatically terminate after 192 it has remained idle (with no client connections) for the 193 specified time. 194 195 DynamicForward 196 Specifies that a TCP port on the local machine be forwarded over 197 the secure channel, and the application protocol is then used to 198 determine where to connect to from the remote machine. 199 200 The argument must be [bind_address:]port. IPv6 addresses can be 201 specified by enclosing addresses in square brackets. By default, 202 the local port is bound in accordance with the GatewayPorts 203 setting. However, an explicit bind_address may be used to bind 204 the connection to a specific address. The bind_address of 205 ``localhost'' indicates that the listening port be bound for 206 local use only, while an empty address or `*' indicates that the 207 port should be available from all interfaces. 208 209 Currently the SOCKS4 and SOCKS5 protocols are supported, and 210 ssh(1) will act as a SOCKS server. Multiple forwardings may be 211 specified, and additional forwardings can be given on the command 212 line. Only the superuser can forward privileged ports. 213 214 EnableSSHKeysign 215 Setting this option to ``yes'' in the global client configuration 216 file /etc/ssh/ssh_config enables the use of the helper program 217 ssh-keysign(8) during HostbasedAuthentication. The argument must 218 be ``yes'' or ``no''. The default is ``no''. This option should 219 be placed in the non-hostspecific section. See ssh-keysign(8) 220 for more information. 221 222 EscapeChar 223 Sets the escape character (default: `~'). The escape character 224 can also be set on the command line. The argument should be a 225 single character, `^' followed by a letter, or ``none'' to 226 disable the escape character entirely (making the connection 227 transparent for binary data). 228 229 ExitOnForwardFailure 230 Specifies whether ssh(1) should terminate the connection if it 231 cannot set up all requested dynamic, tunnel, local, and remote 232 port forwardings. The argument must be ``yes'' or ``no''. The 233 default is ``no''. 234 235 ForwardAgent 236 Specifies whether the connection to the authentication agent (if 237 any) will be forwarded to the remote machine. The argument must 238 be ``yes'' or ``no''. The default is ``no''. 239 240 Agent forwarding should be enabled with caution. Users with the 241 ability to bypass file permissions on the remote host (for the 242 agent's Unix-domain socket) can access the local agent through 243 the forwarded connection. An attacker cannot obtain key material 244 from the agent, however they can perform operations on the keys 245 that enable them to authenticate using the identities loaded into 246 the agent. 247 248 ForwardX11 249 Specifies whether X11 connections will be automatically 250 redirected over the secure channel and DISPLAY set. The argument 251 must be ``yes'' or ``no''. The default is ``no''. 252 253 X11 forwarding should be enabled with caution. Users with the 254 ability to bypass file permissions on the remote host (for the 255 user's X11 authorization database) can access the local X11 256 display through the forwarded connection. An attacker may then 257 be able to perform activities such as keystroke monitoring if the 258 ForwardX11Trusted option is also enabled. 259 260 ForwardX11Timeout 261 Specify a timeout for untrusted X11 forwarding using the format 262 described in the TIME FORMATS section of sshd_config(5). X11 263 connections received by ssh(1) after this time will be refused. 264 The default is to disable untrusted X11 forwarding after twenty 265 minutes has elapsed. 266 267 ForwardX11Trusted 268 If this option is set to ``yes'', remote X11 clients will have 269 full access to the original X11 display. 270 271 If this option is set to ``no'', remote X11 clients will be 272 considered untrusted and prevented from stealing or tampering 273 with data belonging to trusted X11 clients. Furthermore, the 274 xauth(1) token used for the session will be set to expire after 275 20 minutes. Remote clients will be refused access after this 276 time. 277 278 The default is ``no''. 279 280 See the X11 SECURITY extension specification for full details on 281 the restrictions imposed on untrusted clients. 282 283 GatewayPorts 284 Specifies whether remote hosts are allowed to connect to local 285 forwarded ports. By default, ssh(1) binds local port forwardings 286 to the loopback address. This prevents other remote hosts from 287 connecting to forwarded ports. GatewayPorts can be used to 288 specify that ssh should bind local port forwardings to the 289 wildcard address, thus allowing remote hosts to connect to 290 forwarded ports. The argument must be ``yes'' or ``no''. The 291 default is ``no''. 292 293 GlobalKnownHostsFile 294 Specifies one or more files to use for the global host key 295 database, separated by whitespace. The default is 296 /etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2. 297 298 GSSAPIAuthentication 299 Specifies whether user authentication based on GSSAPI is allowed. 300 The default is ``no''. Note that this option applies to protocol 301 version 2 only. 302 303 GSSAPIDelegateCredentials 304 Forward (delegate) credentials to the server. The default is 305 ``no''. Note that this option applies to protocol version 2 306 only. 307 308 HashKnownHosts 309 Indicates that ssh(1) should hash host names and addresses when 310 they are added to ~/.ssh/known_hosts. These hashed names may be 311 used normally by ssh(1) and sshd(8), but they do not reveal 312 identifying information should the file's contents be disclosed. 313 The default is ``no''. Note that existing names and addresses in 314 known hosts files will not be converted automatically, but may be 315 manually hashed using ssh-keygen(1). 316 317 HostbasedAuthentication 318 Specifies whether to try rhosts based authentication with public 319 key authentication. The argument must be ``yes'' or ``no''. The 320 default is ``no''. This option applies to protocol version 2 321 only and is similar to RhostsRSAAuthentication. 322 323 HostKeyAlgorithms 324 Specifies the protocol version 2 host key algorithms that the 325 client wants to use in order of preference. The default for this 326 option is: 327 328 ecdsa-sha2-nistp256-cert-v01 (a] openssh.com, 329 ecdsa-sha2-nistp384-cert-v01 (a] openssh.com, 330 ecdsa-sha2-nistp521-cert-v01 (a] openssh.com, 331 ssh-rsa-cert-v01 (a] openssh.com,ssh-dss-cert-v01 (a] openssh.com, 332 ssh-rsa-cert-v00 (a] openssh.com,ssh-dss-cert-v00 (a] openssh.com, 333 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521, 334 ssh-rsa,ssh-dss 335 336 If hostkeys are known for the destination host then this default 337 is modified to prefer their algorithms. 338 339 HostKeyAlias 340 Specifies an alias that should be used instead of the real host 341 name when looking up or saving the host key in the host key 342 database files. This option is useful for tunneling SSH 343 connections or for multiple servers running on a single host. 344 345 HostName 346 Specifies the real host name to log into. This can be used to 347 specify nicknames or abbreviations for hosts. If the hostname 348 contains the character sequence `%h', then this will be replaced 349 with the host name specified on the command line (this is useful 350 for manipulating unqualified names). The default is the name 351 given on the command line. Numeric IP addresses are also 352 permitted (both on the command line and in HostName 353 specifications). 354 355 IdentitiesOnly 356 Specifies that ssh(1) should only use the authentication identity 357 files configured in the ssh_config files, even if ssh-agent(1) 358 offers more identities. The argument to this keyword must be 359 ``yes'' or ``no''. This option is intended for situations where 360 ssh-agent offers many different identities. The default is 361 ``no''. 362 363 IdentityFile 364 Specifies a file from which the user's DSA, ECDSA or DSA 365 authentication identity is read. The default is ~/.ssh/identity 366 for protocol version 1, and ~/.ssh/id_dsa, ~/.ssh/id_ecdsa and 367 ~/.ssh/id_rsa for protocol version 2. Additionally, any 368 identities represented by the authentication agent will be used 369 for authentication. ssh(1) will try to load certificate 370 information from the filename obtained by appending -cert.pub to 371 the path of a specified IdentityFile. 372 373 The file name may use the tilde syntax to refer to a user's home 374 directory or one of the following escape characters: `%d' (local 375 user's home directory), `%u' (local user name), `%l' (local host 376 name), `%h' (remote host name) or `%r' (remote user name). 377 378 It is possible to have multiple identity files specified in 379 configuration files; all these identities will be tried in 380 sequence. Multiple IdentityFile directives will add to the list 381 of identities tried (this behaviour differs from that of other 382 configuration directives). 383 384 IPQoS Specifies the IPv4 type-of-service or DSCP class for connections. 385 Accepted values are ``af11'', ``af12'', ``af13'', ``af14'', 386 ``af22'', ``af23'', ``af31'', ``af32'', ``af33'', ``af41'', 387 ``af42'', ``af43'', ``cs0'', ``cs1'', ``cs2'', ``cs3'', ``cs4'', 388 ``cs5'', ``cs6'', ``cs7'', ``ef'', ``lowdelay'', ``throughput'', 389 ``reliability'', or a numeric value. This option may take one or 390 two arguments, separated by whitespace. If one argument is 391 specified, it is used as the packet class unconditionally. If 392 two values are specified, the first is automatically selected for 393 interactive sessions and the second for non-interactive sessions. 394 The default is ``lowdelay'' for interactive sessions and 395 ``throughput'' for non-interactive sessions. 396 397 KbdInteractiveAuthentication 398 Specifies whether to use keyboard-interactive authentication. 399 The argument to this keyword must be ``yes'' or ``no''. The 400 default is ``yes''. 401 402 KbdInteractiveDevices 403 Specifies the list of methods to use in keyboard-interactive 404 authentication. Multiple method names must be comma-separated. 405 The default is to use the server specified list. The methods 406 available vary depending on what the server supports. For an 407 OpenSSH server, it may be zero or more of: ``bsdauth'', ``pam'', 408 and ``skey''. 409 410 KexAlgorithms 411 Specifies the available KEX (Key Exchange) algorithms. Multiple 412 algorithms must be comma-separated. The default is: 413 414 ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521, 415 diffie-hellman-group-exchange-sha256, 416 diffie-hellman-group-exchange-sha1, 417 diffie-hellman-group14-sha1, 418 diffie-hellman-group1-sha1 419 420 LocalCommand 421 Specifies a command to execute on the local machine after 422 successfully connecting to the server. The command string 423 extends to the end of the line, and is executed with the user's 424 shell. The following escape character substitutions will be 425 performed: `%d' (local user's home directory), `%h' (remote host 426 name), `%l' (local host name), `%n' (host name as provided on the 427 command line), `%p' (remote port), `%r' (remote user name) or 428 `%u' (local user name). 429 430 The command is run synchronously and does not have access to the 431 session of the ssh(1) that spawned it. It should not be used for 432 interactive commands. 433 434 This directive is ignored unless PermitLocalCommand has been 435 enabled. 436 437 LocalForward 438 Specifies that a TCP port on the local machine be forwarded over 439 the secure channel to the specified host and port from the remote 440 machine. The first argument must be [bind_address:]port and the 441 second argument must be host:hostport. IPv6 addresses can be 442 specified by enclosing addresses in square brackets. Multiple 443 forwardings may be specified, and additional forwardings can be 444 given on the command line. Only the superuser can forward 445 privileged ports. By default, the local port is bound in 446 accordance with the GatewayPorts setting. However, an explicit 447 bind_address may be used to bind the connection to a specific 448 address. The bind_address of ``localhost'' indicates that the 449 listening port be bound for local use only, while an empty 450 address or `*' indicates that the port should be available from 451 all interfaces. 452 453 LogLevel 454 Gives the verbosity level that is used when logging messages from 455 ssh(1). The possible values are: QUIET, FATAL, ERROR, INFO, 456 VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO. 457 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify 458 higher levels of verbose output. 459 460 MACs Specifies the MAC (message authentication code) algorithms in 461 order of preference. The MAC algorithm is used in protocol 462 version 2 for data integrity protection. Multiple algorithms 463 must be comma-separated. The default is: 464 465 hmac-md5,hmac-sha1,umac-64 (a] openssh.com, 466 hmac-ripemd160,hmac-sha1-96,hmac-md5-96, 467 hmac-sha2-256,hmac-sha2-256-96,hmac-sha2-512, 468 hmac-sha2-512-96 469 470 NoHostAuthenticationForLocalhost 471 This option can be used if the home directory is shared across 472 machines. In this case localhost will refer to a different 473 machine on each of the machines and the user will get many 474 warnings about changed host keys. However, this option disables 475 host authentication for localhost. The argument to this keyword 476 must be ``yes'' or ``no''. The default is to check the host key 477 for localhost. 478 479 NumberOfPasswordPrompts 480 Specifies the number of password prompts before giving up. The 481 argument to this keyword must be an integer. The default is 3. 482 483 PasswordAuthentication 484 Specifies whether to use password authentication. The argument 485 to this keyword must be ``yes'' or ``no''. The default is 486 ``yes''. 487 488 PermitLocalCommand 489 Allow local command execution via the LocalCommand option or 490 using the !command escape sequence in ssh(1). The argument must 491 be ``yes'' or ``no''. The default is ``no''. 492 493 PKCS11Provider 494 Specifies which PKCS#11 provider to use. The argument to this 495 keyword is the PKCS#11 shared library ssh(1) should use to 496 communicate with a PKCS#11 token providing the user's private RSA 497 key. 498 499 Port Specifies the port number to connect on the remote host. The 500 default is 22. 501 502 PreferredAuthentications 503 Specifies the order in which the client should try protocol 2 504 authentication methods. This allows a client to prefer one 505 method (e.g. keyboard-interactive) over another method (e.g. 506 password). The default is: 507 508 gssapi-with-mic,hostbased,publickey, 509 keyboard-interactive,password 510 511 Protocol 512 Specifies the protocol versions ssh(1) should support in order of 513 preference. The possible values are `1' and `2'. Multiple 514 versions must be comma-separated. When this option is set to 515 ``2,1'' ssh will try version 2 and fall back to version 1 if 516 version 2 is not available. The default is `2'. 517 518 ProxyCommand 519 Specifies the command to use to connect to the server. The 520 command string extends to the end of the line, and is executed 521 with the user's shell. In the command string, any occurrence of 522 `%h' will be substituted by the host name to connect, `%p' by the 523 port, and `%r' by the remote user name. The command can be 524 basically anything, and should read from its standard input and 525 write to its standard output. It should eventually connect an 526 sshd(8) server running on some machine, or execute sshd -i 527 somewhere. Host key management will be done using the HostName 528 of the host being connected (defaulting to the name typed by the 529 user). Setting the command to ``none'' disables this option 530 entirely. Note that CheckHostIP is not available for connects 531 with a proxy command. 532 533 This directive is useful in conjunction with nc(1) and its proxy 534 support. For example, the following directive would connect via 535 an HTTP proxy at 192.0.2.0: 536 537 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p 538 539 PubkeyAuthentication 540 Specifies whether to try public key authentication. The argument 541 to this keyword must be ``yes'' or ``no''. The default is 542 ``yes''. This option applies to protocol version 2 only. 543 544 RekeyLimit 545 Specifies the maximum amount of data that may be transmitted 546 before the session key is renegotiated. The argument is the 547 number of bytes, with an optional suffix of `K', `M', or `G' to 548 indicate Kilobytes, Megabytes, or Gigabytes, respectively. The 549 default is between `1G' and `4G', depending on the cipher. This 550 option applies to protocol version 2 only. 551 552 RemoteForward 553 Specifies that a TCP port on the remote machine be forwarded over 554 the secure channel to the specified host and port from the local 555 machine. The first argument must be [bind_address:]port and the 556 second argument must be host:hostport. IPv6 addresses can be 557 specified by enclosing addresses in square brackets. Multiple 558 forwardings may be specified, and additional forwardings can be 559 given on the command line. Privileged ports can be forwarded 560 only when logging in as root on the remote machine. 561 562 If the port argument is `0', the listen port will be dynamically 563 allocated on the server and reported to the client at run time. 564 565 If the bind_address is not specified, the default is to only bind 566 to loopback addresses. If the bind_address is `*' or an empty 567 string, then the forwarding is requested to listen on all 568 interfaces. Specifying a remote bind_address will only succeed 569 if the server's GatewayPorts option is enabled (see 570 sshd_config(5)). 571 572 RequestTTY 573 Specifies whether to request a pseudo-tty for the session. The 574 argument may be one of: ``no'' (never request a TTY), ``yes'' 575 (always request a TTY when standard input is a TTY), ``force'' 576 (always request a TTY) or ``auto'' (request a TTY when opening a 577 login session). This option mirrors the -t and -T flags for 578 ssh(1). 579 580 RhostsRSAAuthentication 581 Specifies whether to try rhosts based authentication with RSA 582 host authentication. The argument must be ``yes'' or ``no''. 583 The default is ``no''. This option applies to protocol version 1 584 only and requires ssh(1) to be setuid root. 585 586 RSAAuthentication 587 Specifies whether to try RSA authentication. The argument to 588 this keyword must be ``yes'' or ``no''. RSA authentication will 589 only be attempted if the identity file exists, or an 590 authentication agent is running. The default is ``yes''. Note 591 that this option applies to protocol version 1 only. 592 593 SendEnv 594 Specifies what variables from the local environ(7) should be sent 595 to the server. Note that environment passing is only supported 596 for protocol 2. The server must also support it, and the server 597 must be configured to accept these environment variables. Refer 598 to AcceptEnv in sshd_config(5) for how to configure the server. 599 Variables are specified by name, which may contain wildcard 600 characters. Multiple environment variables may be separated by 601 whitespace or spread across multiple SendEnv directives. The 602 default is not to send any environment variables. 603 604 See PATTERNS for more information on patterns. 605 606 ServerAliveCountMax 607 Sets the number of server alive messages (see below) which may be 608 sent without ssh(1) receiving any messages back from the server. 609 If this threshold is reached while server alive messages are 610 being sent, ssh will disconnect from the server, terminating the 611 session. It is important to note that the use of server alive 612 messages is very different from TCPKeepAlive (below). The server 613 alive messages are sent through the encrypted channel and 614 therefore will not be spoofable. The TCP keepalive option 615 enabled by TCPKeepAlive is spoofable. The server alive mechanism 616 is valuable when the client or server depend on knowing when a 617 connection has become inactive. 618 619 The default value is 3. If, for example, ServerAliveInterval 620 (see below) is set to 15 and ServerAliveCountMax is left at the 621 default, if the server becomes unresponsive, ssh will disconnect 622 after approximately 45 seconds. This option applies to protocol 623 version 2 only. 624 625 ServerAliveInterval 626 Sets a timeout interval in seconds after which if no data has 627 been received from the server, ssh(1) will send a message through 628 the encrypted channel to request a response from the server. The 629 default is 0, indicating that these messages will not be sent to 630 the server. This option applies to protocol version 2 only. 631 632 StrictHostKeyChecking 633 If this flag is set to ``yes'', ssh(1) will never automatically 634 add host keys to the ~/.ssh/known_hosts file, and refuses to 635 connect to hosts whose host key has changed. This provides 636 maximum protection against trojan horse attacks, though it can be 637 annoying when the /etc/ssh/ssh_known_hosts file is poorly 638 maintained or when connections to new hosts are frequently made. 639 This option forces the user to manually add all new hosts. If 640 this flag is set to ``no'', ssh will automatically add new host 641 keys to the user known hosts files. If this flag is set to 642 ``ask'', new host keys will be added to the user known host files 643 only after the user has confirmed that is what they really want 644 to do, and ssh will refuse to connect to hosts whose host key has 645 changed. The host keys of known hosts will be verified 646 automatically in all cases. The argument must be ``yes'', 647 ``no'', or ``ask''. The default is ``ask''. 648 649 TCPKeepAlive 650 Specifies whether the system should send TCP keepalive messages 651 to the other side. If they are sent, death of the connection or 652 crash of one of the machines will be properly noticed. However, 653 this means that connections will die if the route is down 654 temporarily, and some people find it annoying. 655 656 The default is ``yes'' (to send TCP keepalive messages), and the 657 client will notice if the network goes down or the remote host 658 dies. This is important in scripts, and many users want it too. 659 660 To disable TCP keepalive messages, the value should be set to 661 ``no''. 662 663 Tunnel Request tun(4) device forwarding between the client and the 664 server. The argument must be ``yes'', ``point-to-point'' (layer 665 3), ``ethernet'' (layer 2), or ``no''. Specifying ``yes'' 666 requests the default tunnel mode, which is ``point-to-point''. 667 The default is ``no''. 668 669 TunnelDevice 670 Specifies the tun(4) devices to open on the client (local_tun) 671 and the server (remote_tun). 672 673 The argument must be local_tun[:remote_tun]. The devices may be 674 specified by numerical ID or the keyword ``any'', which uses the 675 next available tunnel device. If remote_tun is not specified, it 676 defaults to ``any''. The default is ``any:any''. 677 678 UsePrivilegedPort 679 Specifies whether to use a privileged port for outgoing 680 connections. The argument must be ``yes'' or ``no''. The 681 default is ``no''. If set to ``yes'', ssh(1) must be setuid 682 root. Note that this option must be set to ``yes'' for 683 RhostsRSAAuthentication with older servers. 684 685 User Specifies the user to log in as. This can be useful when a 686 different user name is used on different machines. This saves 687 the trouble of having to remember to give the user name on the 688 command line. 689 690 UserKnownHostsFile 691 Specifies one or more files to use for the user host key 692 database, separated by whitespace. The default is 693 ~/.ssh/known_hosts, ~/.ssh/known_hosts2. 694 695 VerifyHostKeyDNS 696 Specifies whether to verify the remote key using DNS and SSHFP 697 resource records. If this option is set to ``yes'', the client 698 will implicitly trust keys that match a secure fingerprint from 699 DNS. Insecure fingerprints will be handled as if this option was 700 set to ``ask''. If this option is set to ``ask'', information on 701 fingerprint match will be displayed, but the user will still need 702 to confirm new host keys according to the StrictHostKeyChecking 703 option. The argument must be ``yes'', ``no'', or ``ask''. The 704 default is ``no''. Note that this option applies to protocol 705 version 2 only. 706 707 See also VERIFYING HOST KEYS in ssh(1). 708 709 VisualHostKey 710 If this flag is set to ``yes'', an ASCII art representation of 711 the remote host key fingerprint is printed in addition to the hex 712 fingerprint string at login and for unknown host keys. If this 713 flag is set to ``no'', no fingerprint strings are printed at 714 login and only the hex fingerprint string will be printed for 715 unknown host keys. The default is ``no''. 716 717 XAuthLocation 718 Specifies the full pathname of the xauth(1) program. The default 719 is /usr/X11R6/bin/xauth. 720 721 PATTERNS 722 A pattern consists of zero or more non-whitespace characters, `*' (a 723 wildcard that matches zero or more characters), or `?' (a wildcard that 724 matches exactly one character). For example, to specify a set of 725 declarations for any host in the ``.co.uk'' set of domains, the following 726 pattern could be used: 727 728 Host *.co.uk 729 730 The following pattern would match any host in the 192.168.0.[0-9] network 731 range: 732 733 Host 192.168.0.? 734 735 A pattern-list is a comma-separated list of patterns. Patterns within 736 pattern-lists may be negated by preceding them with an exclamation mark 737 (`!'). For example, to allow a key to be used from anywhere within an 738 organisation except from the ``dialup'' pool, the following entry (in 739 authorized_keys) could be used: 740 741 from="!*.dialup.example.com,*.example.com" 742 743 FILES 744 ~/.ssh/config 745 This is the per-user configuration file. The format of this file 746 is described above. This file is used by the SSH client. 747 Because of the potential for abuse, this file must have strict 748 permissions: read/write for the user, and not accessible by 749 others. 750 751 /etc/ssh/ssh_config 752 Systemwide configuration file. This file provides defaults for 753 those values that are not specified in the user's configuration 754 file, and for those users who do not have a configuration file. 755 This file must be world-readable. 756 757 SEE ALSO 758 ssh(1) 759 760 AUTHORS 761 OpenSSH is a derivative of the original and free ssh 1.2.12 release by 762 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo 763 de Raadt and Dug Song removed many bugs, re-added newer features and 764 created OpenSSH. Markus Friedl contributed the support for SSH protocol 765 versions 1.5 and 2.0. 766 767 OpenBSD 5.0 August 2, 2011 OpenBSD 5.0 768
