ssh_config.0 revision 218767
1SSH_CONFIG(5) OpenBSD Programmer's Manual SSH_CONFIG(5) 2 3NAME 4 ssh_config - OpenSSH SSH client configuration files 5 6SYNOPSIS 7 ~/.ssh/config 8 /etc/ssh/ssh_config 9 10DESCRIPTION 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 See PATTERNS for more information on patterns. 51 52 AddressFamily 53 Specifies which address family to use when connecting. Valid 54 arguments are ``any'', ``inet'' (use IPv4 only), or ``inet6'' 55 (use IPv6 only). 56 57 BatchMode 58 If set to ``yes'', passphrase/password querying will be disabled. 59 This option is useful in scripts and other batch jobs where no 60 user is present to supply the password. The argument must be 61 ``yes'' or ``no''. The default is ``no''. 62 63 BindAddress 64 Use the specified address on the local machine as the source 65 address of the connection. Only useful on systems with more than 66 one address. Note that this option does not work if 67 UsePrivilegedPort is set to ``yes''. 68 69 ChallengeResponseAuthentication 70 Specifies whether to use challenge-response authentication. The 71 argument to this keyword must be ``yes'' or ``no''. The default 72 is ``yes''. 73 74 CheckHostIP 75 If this flag is set to ``yes'', ssh(1) will additionally check 76 the host IP address in the known_hosts file. This allows ssh to 77 detect if a host key changed due to DNS spoofing. If the option 78 is set to ``no'', the check will not be executed. The default is 79 ``yes''. 80 81 Cipher Specifies the cipher to use for encrypting the session in 82 protocol version 1. Currently, ``blowfish'', ``3des'', and 83 ``des'' are supported. des is only supported in the ssh(1) 84 client for interoperability with legacy protocol 1 85 implementations that do not support the 3des cipher. Its use is 86 strongly discouraged due to cryptographic weaknesses. The 87 default is ``3des''. 88 89 Ciphers 90 Specifies the ciphers allowed for protocol version 2 in order of 91 preference. Multiple ciphers must be comma-separated. The 92 supported ciphers are ``3des-cbc'', ``aes128-cbc'', 93 ``aes192-cbc'', ``aes256-cbc'', ``aes128-ctr'', ``aes192-ctr'', 94 ``aes256-ctr'', ``arcfour128'', ``arcfour256'', ``arcfour'', 95 ``blowfish-cbc'', and ``cast128-cbc''. The default is: 96 97 aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128, 98 aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc, 99 aes256-cbc,arcfour 100 101 ClearAllForwardings 102 Specifies that all local, remote, and dynamic port forwardings 103 specified in the configuration files or on the command line be 104 cleared. This option is primarily useful when used from the 105 ssh(1) command line to clear port forwardings set in 106 configuration files, and is automatically set by scp(1) and 107 sftp(1). The argument must be ``yes'' or ``no''. The default is 108 ``no''. 109 110 Compression 111 Specifies whether to use compression. The argument must be 112 ``yes'' or ``no''. The default is ``no''. 113 114 CompressionLevel 115 Specifies the compression level to use if compression is enabled. 116 The argument must be an integer from 1 (fast) to 9 (slow, best). 117 The default level is 6, which is good for most applications. The 118 meaning of the values is the same as in gzip(1). Note that this 119 option applies to protocol version 1 only. 120 121 ConnectionAttempts 122 Specifies the number of tries (one per second) to make before 123 exiting. The argument must be an integer. This may be useful in 124 scripts if the connection sometimes fails. The default is 1. 125 126 ConnectTimeout 127 Specifies the timeout (in seconds) used when connecting to the 128 SSH server, instead of using the default system TCP timeout. 129 This value is used only when the target is down or really 130 unreachable, not when it refuses the connection. 131 132 ControlMaster 133 Enables the sharing of multiple sessions over a single network 134 connection. When set to ``yes'', ssh(1) will listen for 135 connections on a control socket specified using the ControlPath 136 argument. Additional sessions can connect to this socket using 137 the same ControlPath with ControlMaster set to ``no'' (the 138 default). These sessions will try to reuse the master instance's 139 network connection rather than initiating new ones, but will fall 140 back to connecting normally if the control socket does not exist, 141 or is not listening. 142 143 Setting this to ``ask'' will cause ssh to listen for control 144 connections, but require confirmation using the SSH_ASKPASS 145 program before they are accepted (see ssh-add(1) for details). 146 If the ControlPath cannot be opened, ssh will continue without 147 connecting to a master instance. 148 149 X11 and ssh-agent(1) forwarding is supported over these 150 multiplexed connections, however the display and agent forwarded 151 will be the one belonging to the master connection i.e. it is not 152 possible to forward multiple displays or agents. 153 154 Two additional options allow for opportunistic multiplexing: try 155 to use a master connection but fall back to creating a new one if 156 one does not already exist. These options are: ``auto'' and 157 ``autoask''. The latter requires confirmation like the ``ask'' 158 option. 159 160 ControlPath 161 Specify the path to the control socket used for connection 162 sharing as described in the ControlMaster section above or the 163 string ``none'' to disable connection sharing. In the path, `%l' 164 will be substituted by the local host name, `%h' will be 165 substituted by the target host name, `%p' the port, and `%r' by 166 the remote login username. It is recommended that any 167 ControlPath used for opportunistic connection sharing include at 168 least %h, %p, and %r. This ensures that shared connections are 169 uniquely identified. 170 171 ControlPersist 172 When used in conjunction with ControlMaster, specifies that the 173 master connection should remain open in the background (waiting 174 for future client connections) after the initial client 175 connection has been closed. If set to ``no'', then the master 176 connection will not be placed into the background, and will close 177 as soon as the initial client connection is closed. If set to 178 ``yes'', then the master connection will remain in the background 179 indefinitely (until killed or closed via a mechanism such as the 180 ssh(1) ``-O exit'' option). If set to a time in seconds, or a 181 time in any of the formats documented in sshd_config(5), then the 182 backgrounded master connection will automatically terminate after 183 it has remained idle (with no client connections) for the 184 specified time. 185 186 DynamicForward 187 Specifies that a TCP port on the local machine be forwarded over 188 the secure channel, and the application protocol is then used to 189 determine where to connect to from the remote machine. 190 191 The argument must be [bind_address:]port. IPv6 addresses can be 192 specified by enclosing addresses in square brackets. By default, 193 the local port is bound in accordance with the GatewayPorts 194 setting. However, an explicit bind_address may be used to bind 195 the connection to a specific address. The bind_address of 196 ``localhost'' indicates that the listening port be bound for 197 local use only, while an empty address or `*' indicates that the 198 port should be available from all interfaces. 199 200 Currently the SOCKS4 and SOCKS5 protocols are supported, and 201 ssh(1) will act as a SOCKS server. Multiple forwardings may be 202 specified, and additional forwardings can be given on the command 203 line. Only the superuser can forward privileged ports. 204 205 EnableSSHKeysign 206 Setting this option to ``yes'' in the global client configuration 207 file /etc/ssh/ssh_config enables the use of the helper program 208 ssh-keysign(8) during HostbasedAuthentication. The argument must 209 be ``yes'' or ``no''. The default is ``no''. This option should 210 be placed in the non-hostspecific section. See ssh-keysign(8) 211 for more information. 212 213 EscapeChar 214 Sets the escape character (default: `~'). The escape character 215 can also be set on the command line. The argument should be a 216 single character, `^' followed by a letter, or ``none'' to 217 disable the escape character entirely (making the connection 218 transparent for binary data). 219 220 ExitOnForwardFailure 221 Specifies whether ssh(1) should terminate the connection if it 222 cannot set up all requested dynamic, tunnel, local, and remote 223 port forwardings. The argument must be ``yes'' or ``no''. The 224 default is ``no''. 225 226 ForwardAgent 227 Specifies whether the connection to the authentication agent (if 228 any) will be forwarded to the remote machine. The argument must 229 be ``yes'' or ``no''. The default is ``no''. 230 231 Agent forwarding should be enabled with caution. Users with the 232 ability to bypass file permissions on the remote host (for the 233 agent's Unix-domain socket) can access the local agent through 234 the forwarded connection. An attacker cannot obtain key material 235 from the agent, however they can perform operations on the keys 236 that enable them to authenticate using the identities loaded into 237 the agent. 238 239 ForwardX11 240 Specifies whether X11 connections will be automatically 241 redirected over the secure channel and DISPLAY set. The argument 242 must be ``yes'' or ``no''. The default is ``no''. 243 244 X11 forwarding should be enabled with caution. Users with the 245 ability to bypass file permissions on the remote host (for the 246 user's X11 authorization database) can access the local X11 247 display through the forwarded connection. An attacker may then 248 be able to perform activities such as keystroke monitoring if the 249 ForwardX11Trusted option is also enabled. 250 251 ForwardX11Timeout 252 Specify a timeout for untrusted X11 forwarding using the format 253 described in the TIME FORMATS section of sshd_config(5). X11 254 connections received by ssh(1) after this time will be refused. 255 The default is to disable untrusted X11 forwarding after twenty 256 minutes has elapsed. 257 258 ForwardX11Trusted 259 If this option is set to ``yes'', remote X11 clients will have 260 full access to the original X11 display. 261 262 If this option is set to ``no'', remote X11 clients will be 263 considered untrusted and prevented from stealing or tampering 264 with data belonging to trusted X11 clients. Furthermore, the 265 xauth(1) token used for the session will be set to expire after 266 20 minutes. Remote clients will be refused access after this 267 time. 268 269 The default is ``no''. 270 271 See the X11 SECURITY extension specification for full details on 272 the restrictions imposed on untrusted clients. 273 274 GatewayPorts 275 Specifies whether remote hosts are allowed to connect to local 276 forwarded ports. By default, ssh(1) binds local port forwardings 277 to the loopback address. This prevents other remote hosts from 278 connecting to forwarded ports. GatewayPorts can be used to 279 specify that ssh should bind local port forwardings to the 280 wildcard address, thus allowing remote hosts to connect to 281 forwarded ports. The argument must be ``yes'' or ``no''. The 282 default is ``no''. 283 284 GlobalKnownHostsFile 285 Specifies a file to use for the global host key database instead 286 of /etc/ssh/ssh_known_hosts. 287 288 GSSAPIAuthentication 289 Specifies whether user authentication based on GSSAPI is allowed. 290 The default is ``no''. Note that this option applies to protocol 291 version 2 only. 292 293 GSSAPIDelegateCredentials 294 Forward (delegate) credentials to the server. The default is 295 ``no''. Note that this option applies to protocol version 2 296 only. 297 298 HashKnownHosts 299 Indicates that ssh(1) should hash host names and addresses when 300 they are added to ~/.ssh/known_hosts. These hashed names may be 301 used normally by ssh(1) and sshd(8), but they do not reveal 302 identifying information should the file's contents be disclosed. 303 The default is ``no''. Note that existing names and addresses in 304 known hosts files will not be converted automatically, but may be 305 manually hashed using ssh-keygen(1). 306 307 HostbasedAuthentication 308 Specifies whether to try rhosts based authentication with public 309 key authentication. The argument must be ``yes'' or ``no''. The 310 default is ``no''. This option applies to protocol version 2 311 only and is similar to RhostsRSAAuthentication. 312 313 HostKeyAlgorithms 314 Specifies the protocol version 2 host key algorithms that the 315 client wants to use in order of preference. The default for this 316 option is: 317 318 ecdsa-sha2-nistp256-cert-v01@openssh.com, 319 ecdsa-sha2-nistp384-cert-v01@openssh.com, 320 ecdsa-sha2-nistp521-cert-v01@openssh.com, 321 ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com, 322 ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com, 323 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521, 324 ssh-rsa,ssh-dss 325 326 If hostkeys are known for the destination host then this default 327 is modified to prefer their algorithms. 328 329 HostKeyAlias 330 Specifies an alias that should be used instead of the real host 331 name when looking up or saving the host key in the host key 332 database files. This option is useful for tunneling SSH 333 connections or for multiple servers running on a single host. 334 335 HostName 336 Specifies the real host name to log into. This can be used to 337 specify nicknames or abbreviations for hosts. If the hostname 338 contains the character sequence `%h', then this will be replaced 339 with the host name specified on the commandline (this is useful 340 for manipulating unqualified names). The default is the name 341 given on the command line. Numeric IP addresses are also 342 permitted (both on the command line and in HostName 343 specifications). 344 345 IdentitiesOnly 346 Specifies that ssh(1) should only use the authentication identity 347 files configured in the ssh_config files, even if ssh-agent(1) 348 offers more identities. The argument to this keyword must be 349 ``yes'' or ``no''. This option is intended for situations where 350 ssh-agent offers many different identities. The default is 351 ``no''. 352 353 IdentityFile 354 Specifies a file from which the user's DSA, ECDSA or DSA 355 authentication identity is read. The default is ~/.ssh/identity 356 for protocol version 1, and ~/.ssh/id_dsa, ~/.ssh/id_ecdsa and 357 ~/.ssh/id_rsa for protocol version 2. Additionally, any 358 identities represented by the authentication agent will be used 359 for authentication. ssh(1) will try to load certificate 360 information from the filename obtained by appending -cert.pub to 361 the path of a specified IdentityFile. 362 363 The file name may use the tilde syntax to refer to a user's home 364 directory or one of the following escape characters: `%d' (local 365 user's home directory), `%u' (local user name), `%l' (local host 366 name), `%h' (remote host name) or `%r' (remote user name). 367 368 It is possible to have multiple identity files specified in 369 configuration files; all these identities will be tried in 370 sequence. 371 372 IPQoS Specifies the IPv4 type-of-service or DSCP class for connections. 373 Accepted values are ``af11'', ``af12'', ``af13'', ``af14'', 374 ``af22'', ``af23'', ``af31'', ``af32'', ``af33'', ``af41'', 375 ``af42'', ``af43'', ``cs0'', ``cs1'', ``cs2'', ``cs3'', ``cs4'', 376 ``cs5'', ``cs6'', ``cs7'', ``ef'', ``lowdelay'', ``throughput'', 377 ``reliability'', or a numeric value. This option may take one or 378 two arguments, separated by whitespace. If one argument is 379 specified, it is used as the packet class unconditionally. If 380 two values are specified, the first is automatically selected for 381 interactive sessions and the second for non-interactive sessions. 382 The default is ``lowdelay'' for interactive sessions and 383 ``throughput'' for non-interactive sessions. 384 385 KbdInteractiveAuthentication 386 Specifies whether to use keyboard-interactive authentication. 387 The argument to this keyword must be ``yes'' or ``no''. The 388 default is ``yes''. 389 390 KbdInteractiveDevices 391 Specifies the list of methods to use in keyboard-interactive 392 authentication. Multiple method names must be comma-separated. 393 The default is to use the server specified list. The methods 394 available vary depending on what the server supports. For an 395 OpenSSH server, it may be zero or more of: ``bsdauth'', ``pam'', 396 and ``skey''. 397 398 KexAlgorithms 399 Specifies the available KEX (Key Exchange) algorithms. Multiple 400 algorithms must be comma-separated. The default is: 401 402 ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521, 403 diffie-hellman-group-exchange-sha256, 404 diffie-hellman-group-exchange-sha1, 405 diffie-hellman-group14-sha1, 406 diffie-hellman-group1-sha1 407 408 LocalCommand 409 Specifies a command to execute on the local machine after 410 successfully connecting to the server. The command string 411 extends to the end of the line, and is executed with the user's 412 shell. The following escape character substitutions will be 413 performed: `%d' (local user's home directory), `%h' (remote host 414 name), `%l' (local host name), `%n' (host name as provided on the 415 command line), `%p' (remote port), `%r' (remote user name) or 416 `%u' (local user name). 417 418 The command is run synchronously and does not have access to the 419 session of the ssh(1) that spawned it. It should not be used for 420 interactive commands. 421 422 This directive is ignored unless PermitLocalCommand has been 423 enabled. 424 425 LocalForward 426 Specifies that a TCP port on the local machine be forwarded over 427 the secure channel to the specified host and port from the remote 428 machine. The first argument must be [bind_address:]port and the 429 second argument must be host:hostport. IPv6 addresses can be 430 specified by enclosing addresses in square brackets. Multiple 431 forwardings may be specified, and additional forwardings can be 432 given on the command line. Only the superuser can forward 433 privileged ports. By default, the local port is bound in 434 accordance with the GatewayPorts setting. However, an explicit 435 bind_address may be used to bind the connection to a specific 436 address. The bind_address of ``localhost'' indicates that the 437 listening port be bound for local use only, while an empty 438 address or `*' indicates that the port should be available from 439 all interfaces. 440 441 LogLevel 442 Gives the verbosity level that is used when logging messages from 443 ssh(1). The possible values are: QUIET, FATAL, ERROR, INFO, 444 VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO. 445 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify 446 higher levels of verbose output. 447 448 MACs Specifies the MAC (message authentication code) algorithms in 449 order of preference. The MAC algorithm is used in protocol 450 version 2 for data integrity protection. Multiple algorithms 451 must be comma-separated. The default is: 452 453 hmac-md5,hmac-sha1,umac-64@openssh.com, 454 hmac-ripemd160,hmac-sha1-96,hmac-md5-96 455 456 NoHostAuthenticationForLocalhost 457 This option can be used if the home directory is shared across 458 machines. In this case localhost will refer to a different 459 machine on each of the machines and the user will get many 460 warnings about changed host keys. However, this option disables 461 host authentication for localhost. The argument to this keyword 462 must be ``yes'' or ``no''. The default is to check the host key 463 for localhost. 464 465 NumberOfPasswordPrompts 466 Specifies the number of password prompts before giving up. The 467 argument to this keyword must be an integer. The default is 3. 468 469 PasswordAuthentication 470 Specifies whether to use password authentication. The argument 471 to this keyword must be ``yes'' or ``no''. The default is 472 ``yes''. 473 474 PermitLocalCommand 475 Allow local command execution via the LocalCommand option or 476 using the !command escape sequence in ssh(1). The argument must 477 be ``yes'' or ``no''. The default is ``no''. 478 479 PKCS11Provider 480 Specifies which PKCS#11 provider to use. The argument to this 481 keyword is the PKCS#11 shared library ssh(1) should use to 482 communicate with a PKCS#11 token providing the user's private RSA 483 key. 484 485 Port Specifies the port number to connect on the remote host. The 486 default is 22. 487 488 PreferredAuthentications 489 Specifies the order in which the client should try protocol 2 490 authentication methods. This allows a client to prefer one 491 method (e.g. keyboard-interactive) over another method (e.g. 492 password). The default is: 493 494 gssapi-with-mic,hostbased,publickey, 495 keyboard-interactive,password 496 497 Protocol 498 Specifies the protocol versions ssh(1) should support in order of 499 preference. The possible values are `1' and `2'. Multiple 500 versions must be comma-separated. When this option is set to 501 ``2,1'' ssh will try version 2 and fall back to version 1 if 502 version 2 is not available. The default is `2'. 503 504 ProxyCommand 505 Specifies the command to use to connect to the server. The 506 command string extends to the end of the line, and is executed 507 with the user's shell. In the command string, any occurrence of 508 `%h' will be substituted by the host name to connect, `%p' by the 509 port, and `%r' by the remote user name. The command can be 510 basically anything, and should read from its standard input and 511 write to its standard output. It should eventually connect an 512 sshd(8) server running on some machine, or execute sshd -i 513 somewhere. Host key management will be done using the HostName 514 of the host being connected (defaulting to the name typed by the 515 user). Setting the command to ``none'' disables this option 516 entirely. Note that CheckHostIP is not available for connects 517 with a proxy command. 518 519 This directive is useful in conjunction with nc(1) and its proxy 520 support. For example, the following directive would connect via 521 an HTTP proxy at 192.0.2.0: 522 523 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p 524 525 PubkeyAuthentication 526 Specifies whether to try public key authentication. The argument 527 to this keyword must be ``yes'' or ``no''. The default is 528 ``yes''. This option applies to protocol version 2 only. 529 530 RekeyLimit 531 Specifies the maximum amount of data that may be transmitted 532 before the session key is renegotiated. The argument is the 533 number of bytes, with an optional suffix of `K', `M', or `G' to 534 indicate Kilobytes, Megabytes, or Gigabytes, respectively. The 535 default is between `1G' and `4G', depending on the cipher. This 536 option applies to protocol version 2 only. 537 538 RemoteForward 539 Specifies that a TCP port on the remote machine be forwarded over 540 the secure channel to the specified host and port from the local 541 machine. The first argument must be [bind_address:]port and the 542 second argument must be host:hostport. IPv6 addresses can be 543 specified by enclosing addresses in square brackets. Multiple 544 forwardings may be specified, and additional forwardings can be 545 given on the command line. Privileged ports can be forwarded 546 only when logging in as root on the remote machine. 547 548 If the port argument is `0', the listen port will be dynamically 549 allocated on the server and reported to the client at run time. 550 551 If the bind_address is not specified, the default is to only bind 552 to loopback addresses. If the bind_address is `*' or an empty 553 string, then the forwarding is requested to listen on all 554 interfaces. Specifying a remote bind_address will only succeed 555 if the server's GatewayPorts option is enabled (see 556 sshd_config(5)). 557 558 RhostsRSAAuthentication 559 Specifies whether to try rhosts based authentication with RSA 560 host authentication. The argument must be ``yes'' or ``no''. 561 The default is ``no''. This option applies to protocol version 1 562 only and requires ssh(1) to be setuid root. 563 564 RSAAuthentication 565 Specifies whether to try RSA authentication. The argument to 566 this keyword must be ``yes'' or ``no''. RSA authentication will 567 only be attempted if the identity file exists, or an 568 authentication agent is running. The default is ``yes''. Note 569 that this option applies to protocol version 1 only. 570 571 SendEnv 572 Specifies what variables from the local environ(7) should be sent 573 to the server. Note that environment passing is only supported 574 for protocol 2. The server must also support it, and the server 575 must be configured to accept these environment variables. Refer 576 to AcceptEnv in sshd_config(5) for how to configure the server. 577 Variables are specified by name, which may contain wildcard 578 characters. Multiple environment variables may be separated by 579 whitespace or spread across multiple SendEnv directives. The 580 default is not to send any environment variables. 581 582 See PATTERNS for more information on patterns. 583 584 ServerAliveCountMax 585 Sets the number of server alive messages (see below) which may be 586 sent without ssh(1) receiving any messages back from the server. 587 If this threshold is reached while server alive messages are 588 being sent, ssh will disconnect from the server, terminating the 589 session. It is important to note that the use of server alive 590 messages is very different from TCPKeepAlive (below). The server 591 alive messages are sent through the encrypted channel and 592 therefore will not be spoofable. The TCP keepalive option 593 enabled by TCPKeepAlive is spoofable. The server alive mechanism 594 is valuable when the client or server depend on knowing when a 595 connection has become inactive. 596 597 The default value is 3. If, for example, ServerAliveInterval 598 (see below) is set to 15 and ServerAliveCountMax is left at the 599 default, if the server becomes unresponsive, ssh will disconnect 600 after approximately 45 seconds. This option applies to protocol 601 version 2 only. 602 603 ServerAliveInterval 604 Sets a timeout interval in seconds after which if no data has 605 been received from the server, ssh(1) will send a message through 606 the encrypted channel to request a response from the server. The 607 default is 0, indicating that these messages will not be sent to 608 the server. This option applies to protocol version 2 only. 609 610 StrictHostKeyChecking 611 If this flag is set to ``yes'', ssh(1) will never automatically 612 add host keys to the ~/.ssh/known_hosts file, and refuses to 613 connect to hosts whose host key has changed. This provides 614 maximum protection against trojan horse attacks, though it can be 615 annoying when the /etc/ssh/ssh_known_hosts file is poorly 616 maintained or when connections to new hosts are frequently made. 617 This option forces the user to manually add all new hosts. If 618 this flag is set to ``no'', ssh will automatically add new host 619 keys to the user known hosts files. If this flag is set to 620 ``ask'', new host keys will be added to the user known host files 621 only after the user has confirmed that is what they really want 622 to do, and ssh will refuse to connect to hosts whose host key has 623 changed. The host keys of known hosts will be verified 624 automatically in all cases. The argument must be ``yes'', 625 ``no'', or ``ask''. The default is ``ask''. 626 627 TCPKeepAlive 628 Specifies whether the system should send TCP keepalive messages 629 to the other side. If they are sent, death of the connection or 630 crash of one of the machines will be properly noticed. However, 631 this means that connections will die if the route is down 632 temporarily, and some people find it annoying. 633 634 The default is ``yes'' (to send TCP keepalive messages), and the 635 client will notice if the network goes down or the remote host 636 dies. This is important in scripts, and many users want it too. 637 638 To disable TCP keepalive messages, the value should be set to 639 ``no''. 640 641 Tunnel Request tun(4) device forwarding between the client and the 642 server. The argument must be ``yes'', ``point-to-point'' (layer 643 3), ``ethernet'' (layer 2), or ``no''. Specifying ``yes'' 644 requests the default tunnel mode, which is ``point-to-point''. 645 The default is ``no''. 646 647 TunnelDevice 648 Specifies the tun(4) devices to open on the client (local_tun) 649 and the server (remote_tun). 650 651 The argument must be local_tun[:remote_tun]. The devices may be 652 specified by numerical ID or the keyword ``any'', which uses the 653 next available tunnel device. If remote_tun is not specified, it 654 defaults to ``any''. The default is ``any:any''. 655 656 UsePrivilegedPort 657 Specifies whether to use a privileged port for outgoing 658 connections. The argument must be ``yes'' or ``no''. The 659 default is ``no''. If set to ``yes'', ssh(1) must be setuid 660 root. Note that this option must be set to ``yes'' for 661 RhostsRSAAuthentication with older servers. 662 663 User Specifies the user to log in as. This can be useful when a 664 different user name is used on different machines. This saves 665 the trouble of having to remember to give the user name on the 666 command line. 667 668 UserKnownHostsFile 669 Specifies a file to use for the user host key database instead of 670 ~/.ssh/known_hosts. 671 672 VerifyHostKeyDNS 673 Specifies whether to verify the remote key using DNS and SSHFP 674 resource records. If this option is set to ``yes'', the client 675 will implicitly trust keys that match a secure fingerprint from 676 DNS. Insecure fingerprints will be handled as if this option was 677 set to ``ask''. If this option is set to ``ask'', information on 678 fingerprint match will be displayed, but the user will still need 679 to confirm new host keys according to the StrictHostKeyChecking 680 option. The argument must be ``yes'', ``no'', or ``ask''. The 681 default is ``no''. Note that this option applies to protocol 682 version 2 only. 683 684 See also VERIFYING HOST KEYS in ssh(1). 685 686 VisualHostKey 687 If this flag is set to ``yes'', an ASCII art representation of 688 the remote host key fingerprint is printed in addition to the hex 689 fingerprint string at login and for unknown host keys. If this 690 flag is set to ``no'', no fingerprint strings are printed at 691 login and only the hex fingerprint string will be printed for 692 unknown host keys. The default is ``no''. 693 694 XAuthLocation 695 Specifies the full pathname of the xauth(1) program. The default 696 is /usr/X11R6/bin/xauth. 697 698PATTERNS 699 A pattern consists of zero or more non-whitespace characters, `*' (a 700 wildcard that matches zero or more characters), or `?' (a wildcard that 701 matches exactly one character). For example, to specify a set of 702 declarations for any host in the ``.co.uk'' set of domains, the following 703 pattern could be used: 704 705 Host *.co.uk 706 707 The following pattern would match any host in the 192.168.0.[0-9] network 708 range: 709 710 Host 192.168.0.? 711 712 A pattern-list is a comma-separated list of patterns. Patterns within 713 pattern-lists may be negated by preceding them with an exclamation mark 714 (`!'). For example, to allow a key to be used from anywhere within an 715 organisation except from the ``dialup'' pool, the following entry (in 716 authorized_keys) could be used: 717 718 from="!*.dialup.example.com,*.example.com" 719 720FILES 721 ~/.ssh/config 722 This is the per-user configuration file. The format of this file 723 is described above. This file is used by the SSH client. 724 Because of the potential for abuse, this file must have strict 725 permissions: read/write for the user, and not accessible by 726 others. 727 728 /etc/ssh/ssh_config 729 Systemwide configuration file. This file provides defaults for 730 those values that are not specified in the user's configuration 731 file, and for those users who do not have a configuration file. 732 This file must be world-readable. 733 734SEE ALSO 735 ssh(1) 736 737AUTHORS 738 OpenSSH is a derivative of the original and free ssh 1.2.12 release by 739 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo 740 de Raadt and Dug Song removed many bugs, re-added newer features and 741 created OpenSSH. Markus Friedl contributed the support for SSH protocol 742 versions 1.5 and 2.0. 743 744OpenBSD 4.8 December 8, 2010 OpenBSD 4.8 745