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 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'', ``aes128-gcm@openssh.com'', 101 ``aes256-gcm@openssh.com'', ``arcfour128'', ``arcfour256'', 102 ``arcfour'', ``blowfish-cbc'', and ``cast128-cbc''. The default 103 is: 104 105 aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128, 106 aes128-gcm@openssh.com,aes256-gcm@openssh.com, 107 aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc, 108 aes256-cbc,arcfour 109 110 ClearAllForwardings 111 Specifies that all local, remote, and dynamic port forwardings 112 specified in the configuration files or on the command line be 113 cleared. This option is primarily useful when used from the 114 ssh(1) command line to clear port forwardings set in 115 configuration files, and is automatically set by scp(1) and 116 sftp(1). The argument must be ``yes'' or ``no''. The default is 117 ``no''. 118 119 Compression 120 Specifies whether to use compression. The argument must be 121 ``yes'' or ``no''. The default is ``no''. 122 123 CompressionLevel 124 Specifies the compression level to use if compression is enabled. 125 The argument must be an integer from 1 (fast) to 9 (slow, best). 126 The default level is 6, which is good for most applications. The 127 meaning of the values is the same as in gzip(1). Note that this 128 option applies to protocol version 1 only. 129 130 ConnectionAttempts 131 Specifies the number of tries (one per second) to make before 132 exiting. The argument must be an integer. This may be useful in 133 scripts if the connection sometimes fails. The default is 1. 134 135 ConnectTimeout 136 Specifies the timeout (in seconds) used when connecting to the 137 SSH server, instead of using the default system TCP timeout. 138 This value is used only when the target is down or really 139 unreachable, not when it refuses the connection. 140 141 ControlMaster 142 Enables the sharing of multiple sessions over a single network 143 connection. When set to ``yes'', ssh(1) will listen for 144 connections on a control socket specified using the ControlPath 145 argument. Additional sessions can connect to this socket using 146 the same ControlPath with ControlMaster set to ``no'' (the 147 default). These sessions will try to reuse the master instance's 148 network connection rather than initiating new ones, but will fall 149 back to connecting normally if the control socket does not exist, 150 or is not listening. 151 152 Setting this to ``ask'' will cause ssh to listen for control 153 connections, but require confirmation using the SSH_ASKPASS 154 program before they are accepted (see ssh-add(1) for details). 155 If the ControlPath cannot be opened, ssh will continue without 156 connecting to a master instance. 157 158 X11 and ssh-agent(1) forwarding is supported over these 159 multiplexed connections, however the display and agent forwarded 160 will be the one belonging to the master connection i.e. it is not 161 possible to forward multiple displays or agents. 162 163 Two additional options allow for opportunistic multiplexing: try 164 to use a master connection but fall back to creating a new one if 165 one does not already exist. These options are: ``auto'' and 166 ``autoask''. The latter requires confirmation like the ``ask'' 167 option. 168 169 ControlPath 170 Specify the path to the control socket used for connection 171 sharing as described in the ControlMaster section above or the 172 string ``none'' to disable connection sharing. In the path, `%L' 173 will be substituted by the first component of the local host 174 name, `%l' will be substituted by the local host name (including 175 any domain name), `%h' will be substituted by the target host 176 name, `%n' will be substituted by the original target host name 177 specified on the command line, `%p' the port, `%r' by the remote 178 login username, and `%u' by the username of the user running 179 ssh(1). It is recommended that any ControlPath used for 180 opportunistic connection sharing include at least %h, %p, and %r. 181 This ensures that shared connections are uniquely identified. 182 183 ControlPersist 184 When used in conjunction with ControlMaster, specifies that the 185 master connection should remain open in the background (waiting 186 for future client connections) after the initial client 187 connection has been closed. If set to ``no'', then the master 188 connection will not be placed into the background, and will close 189 as soon as the initial client connection is closed. If set to 190 ``yes'', then the master connection will remain in the background 191 indefinitely (until killed or closed via a mechanism such as the 192 ssh(1) ``-O exit'' option). If set to a time in seconds, or a 193 time in any of the formats documented in sshd_config(5), then the 194 backgrounded master connection will automatically terminate after 195 it has remained idle (with no client connections) for the 196 specified time. 197 198 DynamicForward 199 Specifies that a TCP port on the local machine be forwarded over 200 the secure channel, and the application protocol is then used to 201 determine where to connect to from the remote machine. 202 203 The argument must be [bind_address:]port. IPv6 addresses can be 204 specified by enclosing addresses in square brackets. By default, 205 the local port is bound in accordance with the GatewayPorts 206 setting. However, an explicit bind_address may be used to bind 207 the connection to a specific address. The bind_address of 208 ``localhost'' indicates that the listening port be bound for 209 local use only, while an empty address or `*' indicates that the 210 port should be available from all interfaces. 211 212 Currently the SOCKS4 and SOCKS5 protocols are supported, and 213 ssh(1) will act as a SOCKS server. Multiple forwardings may be 214 specified, and additional forwardings can be given on the command 215 line. Only the superuser can forward privileged ports. 216 217 EnableSSHKeysign 218 Setting this option to ``yes'' in the global client configuration 219 file /etc/ssh/ssh_config enables the use of the helper program 220 ssh-keysign(8) during HostbasedAuthentication. The argument must 221 be ``yes'' or ``no''. The default is ``no''. This option should 222 be placed in the non-hostspecific section. See ssh-keysign(8) 223 for more information. 224 225 EscapeChar 226 Sets the escape character (default: `~'). The escape character 227 can also be set on the command line. The argument should be a 228 single character, `^' followed by a letter, or ``none'' to 229 disable the escape character entirely (making the connection 230 transparent for binary data). 231 232 ExitOnForwardFailure 233 Specifies whether ssh(1) should terminate the connection if it 234 cannot set up all requested dynamic, tunnel, local, and remote 235 port forwardings. The argument must be ``yes'' or ``no''. The 236 default is ``no''. 237 238 ForwardAgent 239 Specifies whether the connection to the authentication agent (if 240 any) will be forwarded to the remote machine. The argument must 241 be ``yes'' or ``no''. The default is ``no''. 242 243 Agent forwarding should be enabled with caution. Users with the 244 ability to bypass file permissions on the remote host (for the 245 agent's Unix-domain socket) can access the local agent through 246 the forwarded connection. An attacker cannot obtain key material 247 from the agent, however they can perform operations on the keys 248 that enable them to authenticate using the identities loaded into 249 the agent. 250 251 ForwardX11 252 Specifies whether X11 connections will be automatically 253 redirected over the secure channel and DISPLAY set. The argument 254 must be ``yes'' or ``no''. The default is ``no''. 255 256 X11 forwarding should be enabled with caution. Users with the 257 ability to bypass file permissions on the remote host (for the 258 user's X11 authorization database) can access the local X11 259 display through the forwarded connection. An attacker may then 260 be able to perform activities such as keystroke monitoring if the 261 ForwardX11Trusted option is also enabled. 262 263 ForwardX11Timeout 264 Specify a timeout for untrusted X11 forwarding using the format 265 described in the TIME FORMATS section of sshd_config(5). X11 266 connections received by ssh(1) after this time will be refused. 267 The default is to disable untrusted X11 forwarding after twenty 268 minutes has elapsed. 269 270 ForwardX11Trusted 271 If this option is set to ``yes'', remote X11 clients will have 272 full access to the original X11 display. 273 274 If this option is set to ``no'', remote X11 clients will be 275 considered untrusted and prevented from stealing or tampering 276 with data belonging to trusted X11 clients. Furthermore, the 277 xauth(1) token used for the session will be set to expire after 278 20 minutes. Remote clients will be refused access after this 279 time. 280 281 The default is ``no''. 282 283 See the X11 SECURITY extension specification for full details on 284 the restrictions imposed on untrusted clients. 285 286 GatewayPorts 287 Specifies whether remote hosts are allowed to connect to local 288 forwarded ports. By default, ssh(1) binds local port forwardings 289 to the loopback address. This prevents other remote hosts from 290 connecting to forwarded ports. GatewayPorts can be used to 291 specify that ssh should bind local port forwardings to the 292 wildcard address, thus allowing remote hosts to connect to 293 forwarded ports. The argument must be ``yes'' or ``no''. The 294 default is ``no''. 295 296 GlobalKnownHostsFile 297 Specifies one or more files to use for the global host key 298 database, separated by whitespace. The default is 299 /etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2. 300 301 GSSAPIAuthentication 302 Specifies whether user authentication based on GSSAPI is allowed. 303 The default is ``no''. Note that this option applies to protocol 304 version 2 only. 305 306 GSSAPIDelegateCredentials 307 Forward (delegate) credentials to the server. The default is 308 ``no''. Note that this option applies to protocol version 2 309 only. 310 311 HashKnownHosts 312 Indicates that ssh(1) should hash host names and addresses when 313 they are added to ~/.ssh/known_hosts. These hashed names may be 314 used normally by ssh(1) and sshd(8), but they do not reveal 315 identifying information should the file's contents be disclosed. 316 The default is ``no''. Note that existing names and addresses in 317 known hosts files will not be converted automatically, but may be 318 manually hashed using ssh-keygen(1). 319 320 HostbasedAuthentication 321 Specifies whether to try rhosts based authentication with public 322 key authentication. The argument must be ``yes'' or ``no''. The 323 default is ``no''. This option applies to protocol version 2 324 only and is similar to RhostsRSAAuthentication. 325 326 HostKeyAlgorithms 327 Specifies the protocol version 2 host key algorithms that the 328 client wants to use in order of preference. The default for this 329 option is: 330 331 ecdsa-sha2-nistp256-cert-v01@openssh.com, 332 ecdsa-sha2-nistp384-cert-v01@openssh.com, 333 ecdsa-sha2-nistp521-cert-v01@openssh.com, 334 ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com, 335 ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com, 336 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521, 337 ssh-rsa,ssh-dss 338 339 If hostkeys are known for the destination host then this default 340 is modified to prefer their algorithms. 341 342 HostKeyAlias 343 Specifies an alias that should be used instead of the real host 344 name when looking up or saving the host key in the host key 345 database files. This option is useful for tunneling SSH 346 connections or for multiple servers running on a single host. 347 348 HostName 349 Specifies the real host name to log into. This can be used to 350 specify nicknames or abbreviations for hosts. If the hostname 351 contains the character sequence `%h', then this will be replaced 352 with the host name specified on the command line (this is useful 353 for manipulating unqualified names). The default is the name 354 given on the command line. Numeric IP addresses are also 355 permitted (both on the command line and in HostName 356 specifications). 357 358 IdentitiesOnly 359 Specifies that ssh(1) should only use the authentication identity 360 files configured in the ssh_config files, even if ssh-agent(1) or 361 a PKCS11Provider offers more identities. The argument to this 362 keyword must be ``yes'' or ``no''. This option is intended for 363 situations where ssh-agent offers many different identities. The 364 default is ``no''. 365 366 IdentityFile 367 Specifies a file from which the user's DSA, ECDSA or RSA 368 authentication identity is read. The default is ~/.ssh/identity 369 for protocol version 1, and ~/.ssh/id_dsa, ~/.ssh/id_ecdsa and 370 ~/.ssh/id_rsa for protocol version 2. Additionally, any 371 identities represented by the authentication agent will be used 372 for authentication. ssh(1) will try to load certificate 373 information from the filename obtained by appending -cert.pub to 374 the path of a specified IdentityFile. 375 376 The file name may use the tilde syntax to refer to a user's home 377 directory or one of the following escape characters: `%d' (local 378 user's home directory), `%u' (local user name), `%l' (local host 379 name), `%h' (remote host name) or `%r' (remote user name). 380 381 It is possible to have multiple identity files specified in 382 configuration files; all these identities will be tried in 383 sequence. Multiple IdentityFile directives will add to the list 384 of identities tried (this behaviour differs from that of other 385 configuration directives). 386 387 IPQoS Specifies the IPv4 type-of-service or DSCP class for connections. 388 Accepted values are ``af11'', ``af12'', ``af13'', ``af21'', 389 ``af22'', ``af23'', ``af31'', ``af32'', ``af33'', ``af41'', 390 ``af42'', ``af43'', ``cs0'', ``cs1'', ``cs2'', ``cs3'', ``cs4'', 391 ``cs5'', ``cs6'', ``cs7'', ``ef'', ``lowdelay'', ``throughput'', 392 ``reliability'', or a numeric value. This option may take one or 393 two arguments, separated by whitespace. If one argument is 394 specified, it is used as the packet class unconditionally. If 395 two values are specified, the first is automatically selected for 396 interactive sessions and the second for non-interactive sessions. 397 The default is ``lowdelay'' for interactive sessions and 398 ``throughput'' for non-interactive sessions. 399 400 KbdInteractiveAuthentication 401 Specifies whether to use keyboard-interactive authentication. 402 The argument to this keyword must be ``yes'' or ``no''. The 403 default is ``yes''. 404 405 KbdInteractiveDevices 406 Specifies the list of methods to use in keyboard-interactive 407 authentication. Multiple method names must be comma-separated. 408 The default is to use the server specified list. The methods 409 available vary depending on what the server supports. For an 410 OpenSSH server, it may be zero or more of: ``bsdauth'', ``pam'', 411 and ``skey''. 412 413 KexAlgorithms 414 Specifies the available KEX (Key Exchange) algorithms. Multiple 415 algorithms must be comma-separated. The default is: 416 417 ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521, 418 diffie-hellman-group-exchange-sha256, 419 diffie-hellman-group-exchange-sha1, 420 diffie-hellman-group14-sha1, 421 diffie-hellman-group1-sha1 422 423 LocalCommand 424 Specifies a command to execute on the local machine after 425 successfully connecting to the server. The command string 426 extends to the end of the line, and is executed with the user's 427 shell. The following escape character substitutions will be 428 performed: `%d' (local user's home directory), `%h' (remote host 429 name), `%l' (local host name), `%n' (host name as provided on the 430 command line), `%p' (remote port), `%r' (remote user name) or 431 `%u' (local user name). 432 433 The command is run synchronously and does not have access to the 434 session of the ssh(1) that spawned it. It should not be used for 435 interactive commands. 436 437 This directive is ignored unless PermitLocalCommand has been 438 enabled. 439 440 LocalForward 441 Specifies that a TCP port on the local machine be forwarded over 442 the secure channel to the specified host and port from the remote 443 machine. The first argument must be [bind_address:]port and the 444 second argument must be host:hostport. IPv6 addresses can be 445 specified by enclosing addresses in square brackets. Multiple 446 forwardings may be specified, and additional forwardings can be 447 given on the command line. Only the superuser can forward 448 privileged ports. By default, the local port is bound in 449 accordance with the GatewayPorts setting. However, an explicit 450 bind_address may be used to bind the connection to a specific 451 address. The bind_address of ``localhost'' indicates that the 452 listening port be bound for local use only, while an empty 453 address or `*' indicates that the port should be available from 454 all interfaces. 455 456 LogLevel 457 Gives the verbosity level that is used when logging messages from 458 ssh(1). The possible values are: QUIET, FATAL, ERROR, INFO, 459 VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO. 460 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify 461 higher levels of verbose output. 462 463 MACs Specifies the MAC (message authentication code) algorithms in 464 order of preference. The MAC algorithm is used in protocol 465 version 2 for data integrity protection. Multiple algorithms 466 must be comma-separated. The algorithms that contain ``-etm'' 467 calculate the MAC after encryption (encrypt-then-mac). These are 468 considered safer and their use recommended. The default is: 469 470 hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com, 471 umac-64-etm@openssh.com,umac-128-etm@openssh.com, 472 hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com, 473 hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com, 474 hmac-md5-96-etm@openssh.com, 475 hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com, 476 hmac-sha2-256,hmac-sha2-512,hmac-ripemd160, 477 hmac-sha1-96,hmac-md5-96 478 479 NoHostAuthenticationForLocalhost 480 This option can be used if the home directory is shared across 481 machines. In this case localhost will refer to a different 482 machine on each of the machines and the user will get many 483 warnings about changed host keys. However, this option disables 484 host authentication for localhost. The argument to this keyword 485 must be ``yes'' or ``no''. The default is to check the host key 486 for localhost. 487 488 NumberOfPasswordPrompts 489 Specifies the number of password prompts before giving up. The 490 argument to this keyword must be an integer. The default is 3. 491 492 PasswordAuthentication 493 Specifies whether to use password authentication. The argument 494 to this keyword must be ``yes'' or ``no''. The default is 495 ``yes''. 496 497 PermitLocalCommand 498 Allow local command execution via the LocalCommand option or 499 using the !command escape sequence in ssh(1). The argument must 500 be ``yes'' or ``no''. The default is ``no''. 501 502 PKCS11Provider 503 Specifies which PKCS#11 provider to use. The argument to this 504 keyword is the PKCS#11 shared library ssh(1) should use to 505 communicate with a PKCS#11 token providing the user's private RSA 506 key. 507 508 Port Specifies the port number to connect on the remote host. The 509 default is 22. 510 511 PreferredAuthentications 512 Specifies the order in which the client should try protocol 2 513 authentication methods. This allows a client to prefer one 514 method (e.g. keyboard-interactive) over another method (e.g. 515 password). The default is: 516 517 gssapi-with-mic,hostbased,publickey, 518 keyboard-interactive,password 519 520 Protocol 521 Specifies the protocol versions ssh(1) should support in order of 522 preference. The possible values are `1' and `2'. Multiple 523 versions must be comma-separated. When this option is set to 524 ``2,1'' ssh will try version 2 and fall back to version 1 if 525 version 2 is not available. The default is `2'. 526 527 ProxyCommand 528 Specifies the command to use to connect to the server. The 529 command string extends to the end of the line, and is executed 530 with the user's shell. In the command string, any occurrence of 531 `%h' will be substituted by the host name to connect, `%p' by the 532 port, and `%r' by the remote user name. The command can be 533 basically anything, and should read from its standard input and 534 write to its standard output. It should eventually connect an 535 sshd(8) server running on some machine, or execute sshd -i 536 somewhere. Host key management will be done using the HostName 537 of the host being connected (defaulting to the name typed by the 538 user). Setting the command to ``none'' disables this option 539 entirely. Note that CheckHostIP is not available for connects 540 with a proxy command. 541 542 This directive is useful in conjunction with nc(1) and its proxy 543 support. For example, the following directive would connect via 544 an HTTP proxy at 192.0.2.0: 545 546 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p 547 548 PubkeyAuthentication 549 Specifies whether to try public key authentication. The argument 550 to this keyword must be ``yes'' or ``no''. The default is 551 ``yes''. This option applies to protocol version 2 only. 552 553 RekeyLimit 554 Specifies the maximum amount of data that may be transmitted 555 before the session key is renegotiated. The argument is the 556 number of bytes, with an optional suffix of `K', `M', or `G' to 557 indicate Kilobytes, Megabytes, or Gigabytes, respectively. The 558 default is between `1G' and `4G', depending on the cipher. This 559 option applies to protocol version 2 only. 560 561 RemoteForward 562 Specifies that a TCP port on the remote machine be forwarded over 563 the secure channel to the specified host and port from the local 564 machine. The first argument must be [bind_address:]port and the 565 second argument must be host:hostport. IPv6 addresses can be 566 specified by enclosing addresses in square brackets. Multiple 567 forwardings may be specified, and additional forwardings can be 568 given on the command line. Privileged ports can be forwarded 569 only when logging in as root on the remote machine. 570 571 If the port argument is `0', the listen port will be dynamically 572 allocated on the server and reported to the client at run time. 573 574 If the bind_address is not specified, the default is to only bind 575 to loopback addresses. If the bind_address is `*' or an empty 576 string, then the forwarding is requested to listen on all 577 interfaces. Specifying a remote bind_address will only succeed 578 if the server's GatewayPorts option is enabled (see 579 sshd_config(5)). 580 581 RequestTTY 582 Specifies whether to request a pseudo-tty for the session. The 583 argument may be one of: ``no'' (never request a TTY), ``yes'' 584 (always request a TTY when standard input is a TTY), ``force'' 585 (always request a TTY) or ``auto'' (request a TTY when opening a 586 login session). This option mirrors the -t and -T flags for 587 ssh(1). 588 589 RhostsRSAAuthentication 590 Specifies whether to try rhosts based authentication with RSA 591 host authentication. The argument must be ``yes'' or ``no''. 592 The default is ``no''. This option applies to protocol version 1 593 only and requires ssh(1) to be setuid root. 594 595 RSAAuthentication 596 Specifies whether to try RSA authentication. The argument to 597 this keyword must be ``yes'' or ``no''. RSA authentication will 598 only be attempted if the identity file exists, or an 599 authentication agent is running. The default is ``yes''. Note 600 that this option applies to protocol version 1 only. 601 602 SendEnv 603 Specifies what variables from the local environ(7) should be sent 604 to the server. Note that environment passing is only supported 605 for protocol 2. The server must also support it, and the server 606 must be configured to accept these environment variables. Refer 607 to AcceptEnv in sshd_config(5) for how to configure the server. 608 Variables are specified by name, which may contain wildcard 609 characters. Multiple environment variables may be separated by 610 whitespace or spread across multiple SendEnv directives. The 611 default is not to send any environment variables. 612 613 See PATTERNS for more information on patterns. 614 615 ServerAliveCountMax 616 Sets the number of server alive messages (see below) which may be 617 sent without ssh(1) receiving any messages back from the server. 618 If this threshold is reached while server alive messages are 619 being sent, ssh will disconnect from the server, terminating the 620 session. It is important to note that the use of server alive 621 messages is very different from TCPKeepAlive (below). The server 622 alive messages are sent through the encrypted channel and 623 therefore will not be spoofable. The TCP keepalive option 624 enabled by TCPKeepAlive is spoofable. The server alive mechanism 625 is valuable when the client or server depend on knowing when a 626 connection has become inactive. 627 628 The default value is 3. If, for example, ServerAliveInterval 629 (see below) is set to 15 and ServerAliveCountMax is left at the 630 default, if the server becomes unresponsive, ssh will disconnect 631 after approximately 45 seconds. This option applies to protocol 632 version 2 only. 633 634 ServerAliveInterval 635 Sets a timeout interval in seconds after which if no data has 636 been received from the server, ssh(1) will send a message through 637 the encrypted channel to request a response from the server. The 638 default is 0, indicating that these messages will not be sent to 639 the server. This option applies to protocol version 2 only. 640 641 StrictHostKeyChecking 642 If this flag is set to ``yes'', ssh(1) will never automatically 643 add host keys to the ~/.ssh/known_hosts file, and refuses to 644 connect to hosts whose host key has changed. This provides 645 maximum protection against trojan horse attacks, though it can be 646 annoying when the /etc/ssh/ssh_known_hosts file is poorly 647 maintained or when connections to new hosts are frequently made. 648 This option forces the user to manually add all new hosts. If 649 this flag is set to ``no'', ssh will automatically add new host 650 keys to the user known hosts files. If this flag is set to 651 ``ask'', new host keys will be added to the user known host files 652 only after the user has confirmed that is what they really want 653 to do, and ssh will refuse to connect to hosts whose host key has 654 changed. The host keys of known hosts will be verified 655 automatically in all cases. The argument must be ``yes'', 656 ``no'', or ``ask''. The default is ``ask''. 657 658 TCPKeepAlive 659 Specifies whether the system should send TCP keepalive messages 660 to the other side. If they are sent, death of the connection or 661 crash of one of the machines will be properly noticed. However, 662 this means that connections will die if the route is down 663 temporarily, and some people find it annoying. 664 665 The default is ``yes'' (to send TCP keepalive messages), and the 666 client will notice if the network goes down or the remote host 667 dies. This is important in scripts, and many users want it too. 668 669 To disable TCP keepalive messages, the value should be set to 670 ``no''. 671 672 Tunnel Request tun(4) device forwarding between the client and the 673 server. The argument must be ``yes'', ``point-to-point'' (layer 674 3), ``ethernet'' (layer 2), or ``no''. Specifying ``yes'' 675 requests the default tunnel mode, which is ``point-to-point''. 676 The default is ``no''. 677 678 TunnelDevice 679 Specifies the tun(4) devices to open on the client (local_tun) 680 and the server (remote_tun). 681 682 The argument must be local_tun[:remote_tun]. The devices may be 683 specified by numerical ID or the keyword ``any'', which uses the 684 next available tunnel device. If remote_tun is not specified, it 685 defaults to ``any''. The default is ``any:any''. 686 687 UsePrivilegedPort 688 Specifies whether to use a privileged port for outgoing 689 connections. The argument must be ``yes'' or ``no''. The 690 default is ``no''. If set to ``yes'', ssh(1) must be setuid 691 root. Note that this option must be set to ``yes'' for 692 RhostsRSAAuthentication with older servers. 693 694 User Specifies the user to log in as. This can be useful when a 695 different user name is used on different machines. This saves 696 the trouble of having to remember to give the user name on the 697 command line. 698 699 UserKnownHostsFile 700 Specifies one or more files to use for the user host key 701 database, separated by whitespace. The default is 702 ~/.ssh/known_hosts, ~/.ssh/known_hosts2. 703 704 VerifyHostKeyDNS 705 Specifies whether to verify the remote key using DNS and SSHFP 706 resource records. If this option is set to ``yes'', the client 707 will implicitly trust keys that match a secure fingerprint from 708 DNS. Insecure fingerprints will be handled as if this option was 709 set to ``ask''. If this option is set to ``ask'', information on 710 fingerprint match will be displayed, but the user will still need 711 to confirm new host keys according to the StrictHostKeyChecking 712 option. The argument must be ``yes'', ``no'', or ``ask''. The 713 default is ``no''. Note that this option applies to protocol 714 version 2 only. 715 716 See also VERIFYING HOST KEYS in ssh(1). 717 718 VisualHostKey 719 If this flag is set to ``yes'', an ASCII art representation of 720 the remote host key fingerprint is printed in addition to the hex 721 fingerprint string at login and for unknown host keys. If this 722 flag is set to ``no'', no fingerprint strings are printed at 723 login and only the hex fingerprint string will be printed for 724 unknown host keys. The default is ``no''. 725 726 XAuthLocation 727 Specifies the full pathname of the xauth(1) program. The default 728 is /usr/X11R6/bin/xauth. 729 730PATTERNS 731 A pattern consists of zero or more non-whitespace characters, `*' (a 732 wildcard that matches zero or more characters), or `?' (a wildcard that 733 matches exactly one character). For example, to specify a set of 734 declarations for any host in the ``.co.uk'' set of domains, the following 735 pattern could be used: 736 737 Host *.co.uk 738 739 The following pattern would match any host in the 192.168.0.[0-9] network 740 range: 741 742 Host 192.168.0.? 743 744 A pattern-list is a comma-separated list of patterns. Patterns within 745 pattern-lists may be negated by preceding them with an exclamation mark 746 (`!'). For example, to allow a key to be used from anywhere within an 747 organisation except from the ``dialup'' pool, the following entry (in 748 authorized_keys) could be used: 749 750 from="!*.dialup.example.com,*.example.com" 751 752FILES 753 ~/.ssh/config 754 This is the per-user configuration file. The format of this file 755 is described above. This file is used by the SSH client. 756 Because of the potential for abuse, this file must have strict 757 permissions: read/write for the user, and not accessible by 758 others. 759 760 /etc/ssh/ssh_config 761 Systemwide configuration file. This file provides defaults for 762 those values that are not specified in the user's configuration 763 file, and for those users who do not have a configuration file. 764 This file must be world-readable. 765 766SEE ALSO 767 ssh(1) 768 769AUTHORS 770 OpenSSH is a derivative of the original and free ssh 1.2.12 release by 771 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo 772 de Raadt and Dug Song removed many bugs, re-added newer features and 773 created OpenSSH. Markus Friedl contributed the support for SSH protocol 774 versions 1.5 and 2.0. 775 776OpenBSD 5.3 January 8, 2013 OpenBSD 5.3 777