ssh_config.0 revision 264377
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 or 42 Match 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 Match Restricts the following declarations (up to the next Host or 59 Match keyword) to be used only when the conditions following the 60 Match keyword are satisfied. Match conditions are specified 61 using one or more keyword/criteria pairs or the single token all 62 which matches all criteria. The available keywords are: exec, 63 host, originalhost, user, and localuser. 64 65 The exec keyword executes the specified command under the user's 66 shell. If the command returns a zero exit status then the 67 condition is considered true. Commands containing whitespace 68 characters must be quoted. The following character sequences in 69 the command will be expanded prior to execution: `%L' will be 70 substituted by the first component of the local host name, `%l' 71 will be substituted by the local host name (including any domain 72 name), `%h' will be substituted by the target host name, `%n' 73 will be substituted by the original target host name specified on 74 the command-line, `%p' the destination port, `%r' by the remote 75 login username, and `%u' by the username of the user running 76 ssh(1). 77 78 The other keywords' criteria must be single entries or comma- 79 separated lists and may use the wildcard and negation operators 80 described in the PATTERNS section. The criteria for the host 81 keyword are matched against the target hostname, after any 82 substitution by the Hostname option. The originalhost keyword 83 matches against the hostname as it was specified on the command- 84 line. The user keyword matches against the target username on 85 the remote host. The localuser keyword matches against the name 86 of the local user running ssh(1) (this keyword may be useful in 87 system-wide ssh_config files). 88 89 AddressFamily 90 Specifies which address family to use when connecting. Valid 91 arguments are ``any'', ``inet'' (use IPv4 only), or ``inet6'' 92 (use IPv6 only). 93 94 BatchMode 95 If set to ``yes'', passphrase/password querying will be disabled. 96 This option is useful in scripts and other batch jobs where no 97 user is present to supply the password. The argument must be 98 ``yes'' or ``no''. The default is ``no''. 99 100 BindAddress 101 Use the specified address on the local machine as the source 102 address of the connection. Only useful on systems with more than 103 one address. Note that this option does not work if 104 UsePrivilegedPort is set to ``yes''. 105 106 CanonicalDomains 107 When CanonicalizeHostname is enabled, this option specifies the 108 list of domain suffixes in which to search for the specified 109 destination host. 110 111 CanonicalizeFallbackLocal 112 Specifies whether to fail with an error when hostname 113 canonicalization fails. The default, ``yes'', will attempt to 114 look up the unqualified hostname using the system resolver's 115 search rules. A value of ``no'' will cause ssh(1) to fail 116 instantly if CanonicalizeHostname is enabled and the target 117 hostname cannot be found in any of the domains specified by 118 CanonicalDomains. 119 120 CanonicalizeHostname 121 Controls whether explicit hostname canonicalization is performed. 122 The default, ``no'', is not to perform any name rewriting and let 123 the system resolver handle all hostname lookups. If set to 124 ``yes'' then, for connections that do not use a ProxyCommand, 125 ssh(1) will attempt to canonicalize the hostname specified on the 126 command line using the CanonicalDomains suffixes and 127 CanonicalizePermittedCNAMEs rules. If CanonicalizeHostname is 128 set to ``always'', then canonicalization is applied to proxied 129 connections too. 130 131 If this option is enabled and canonicalisation results in the 132 target hostname changing, then the configuration files are 133 processed again using the new target name to pick up any new 134 configuration in matching Host stanzas. 135 136 CanonicalizeMaxDots 137 Specifies the maximum number of dot characters in a hostname 138 before canonicalization is disabled. The default, ``1'', allows 139 a single dot (i.e. hostname.subdomain). 140 141 CanonicalizePermittedCNAMEs 142 Specifies rules to determine whether CNAMEs should be followed 143 when canonicalizing hostnames. The rules consist of one or more 144 arguments of source_domain_list:target_domain_list, where 145 source_domain_list is a pattern-list of domains that may follow 146 CNAMEs in canonicalization, and target_domain_list is a pattern- 147 list of domains that they may resolve to. 148 149 For example, ``*.a.example.com:*.b.example.com,*.c.example.com'' 150 will allow hostnames matching ``*.a.example.com'' to be 151 canonicalized to names in the ``*.b.example.com'' or 152 ``*.c.example.com'' domains. 153 154 ChallengeResponseAuthentication 155 Specifies whether to use challenge-response authentication. The 156 argument to this keyword must be ``yes'' or ``no''. The default 157 is ``yes''. 158 159 CheckHostIP 160 If this flag is set to ``yes'', ssh(1) will additionally check 161 the host IP address in the known_hosts file. This allows ssh to 162 detect if a host key changed due to DNS spoofing. If the option 163 is set to ``no'', the check will not be executed. The default is 164 ``yes''. 165 166 Cipher Specifies the cipher to use for encrypting the session in 167 protocol version 1. Currently, ``blowfish'', ``3des'', and 168 ``des'' are supported. des is only supported in the ssh(1) 169 client for interoperability with legacy protocol 1 170 implementations that do not support the 3des cipher. Its use is 171 strongly discouraged due to cryptographic weaknesses. The 172 default is ``3des''. 173 174 Ciphers 175 Specifies the ciphers allowed for protocol version 2 in order of 176 preference. Multiple ciphers must be comma-separated. The 177 supported ciphers are: 178 179 ``3des-cbc'', ``aes128-cbc'', ``aes192-cbc'', ``aes256-cbc'', 180 ``aes128-ctr'', ``aes192-ctr'', ``aes256-ctr'', 181 ``aes128-gcm@openssh.com'', ``aes256-gcm@openssh.com'', 182 ``arcfour128'', ``arcfour256'', ``arcfour'', ``blowfish-cbc'', 183 ``cast128-cbc'', and ``chacha20-poly1305@openssh.com''. 184 185 The default is: 186 187 aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128, 188 aes128-gcm@openssh.com,aes256-gcm@openssh.com, 189 chacha20-poly1305@openssh.com, 190 aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc, 191 aes256-cbc,arcfour 192 193 The list of available ciphers may also be obtained using the -Q 194 option of ssh(1). 195 196 ClearAllForwardings 197 Specifies that all local, remote, and dynamic port forwardings 198 specified in the configuration files or on the command line be 199 cleared. This option is primarily useful when used from the 200 ssh(1) command line to clear port forwardings set in 201 configuration files, and is automatically set by scp(1) and 202 sftp(1). The argument must be ``yes'' or ``no''. The default is 203 ``no''. 204 205 Compression 206 Specifies whether to use compression. The argument must be 207 ``yes'' or ``no''. The default is ``no''. 208 209 CompressionLevel 210 Specifies the compression level to use if compression is enabled. 211 The argument must be an integer from 1 (fast) to 9 (slow, best). 212 The default level is 6, which is good for most applications. The 213 meaning of the values is the same as in gzip(1). Note that this 214 option applies to protocol version 1 only. 215 216 ConnectionAttempts 217 Specifies the number of tries (one per second) to make before 218 exiting. The argument must be an integer. This may be useful in 219 scripts if the connection sometimes fails. The default is 1. 220 221 ConnectTimeout 222 Specifies the timeout (in seconds) used when connecting to the 223 SSH server, instead of using the default system TCP timeout. 224 This value is used only when the target is down or really 225 unreachable, not when it refuses the connection. 226 227 ControlMaster 228 Enables the sharing of multiple sessions over a single network 229 connection. When set to ``yes'', ssh(1) will listen for 230 connections on a control socket specified using the ControlPath 231 argument. Additional sessions can connect to this socket using 232 the same ControlPath with ControlMaster set to ``no'' (the 233 default). These sessions will try to reuse the master instance's 234 network connection rather than initiating new ones, but will fall 235 back to connecting normally if the control socket does not exist, 236 or is not listening. 237 238 Setting this to ``ask'' will cause ssh to listen for control 239 connections, but require confirmation using the SSH_ASKPASS 240 program before they are accepted (see ssh-add(1) for details). 241 If the ControlPath cannot be opened, ssh will continue without 242 connecting to a master instance. 243 244 X11 and ssh-agent(1) forwarding is supported over these 245 multiplexed connections, however the display and agent forwarded 246 will be the one belonging to the master connection i.e. it is not 247 possible to forward multiple displays or agents. 248 249 Two additional options allow for opportunistic multiplexing: try 250 to use a master connection but fall back to creating a new one if 251 one does not already exist. These options are: ``auto'' and 252 ``autoask''. The latter requires confirmation like the ``ask'' 253 option. 254 255 ControlPath 256 Specify the path to the control socket used for connection 257 sharing as described in the ControlMaster section above or the 258 string ``none'' to disable connection sharing. In the path, `%L' 259 will be substituted by the first component of the local host 260 name, `%l' will be substituted by the local host name (including 261 any domain name), `%h' will be substituted by the target host 262 name, `%n' will be substituted by the original target host name 263 specified on the command line, `%p' the destination port, `%r' by 264 the remote login username, and `%u' by the username of the user 265 running ssh(1). It is recommended that any ControlPath used for 266 opportunistic connection sharing include at least %h, %p, and %r. 267 This ensures that shared connections are uniquely identified. 268 269 ControlPersist 270 When used in conjunction with ControlMaster, specifies that the 271 master connection should remain open in the background (waiting 272 for future client connections) after the initial client 273 connection has been closed. If set to ``no'', then the master 274 connection will not be placed into the background, and will close 275 as soon as the initial client connection is closed. If set to 276 ``yes'', then the master connection will remain in the background 277 indefinitely (until killed or closed via a mechanism such as the 278 ssh(1) ``-O exit'' option). If set to a time in seconds, or a 279 time in any of the formats documented in sshd_config(5), then the 280 backgrounded master connection will automatically terminate after 281 it has remained idle (with no client connections) for the 282 specified time. 283 284 DynamicForward 285 Specifies that a TCP port on the local machine be forwarded over 286 the secure channel, and the application protocol is then used to 287 determine where to connect to from the remote machine. 288 289 The argument must be [bind_address:]port. IPv6 addresses can be 290 specified by enclosing addresses in square brackets. By default, 291 the local port is bound in accordance with the GatewayPorts 292 setting. However, an explicit bind_address may be used to bind 293 the connection to a specific address. The bind_address of 294 ``localhost'' indicates that the listening port be bound for 295 local use only, while an empty address or `*' indicates that the 296 port should be available from all interfaces. 297 298 Currently the SOCKS4 and SOCKS5 protocols are supported, and 299 ssh(1) will act as a SOCKS server. Multiple forwardings may be 300 specified, and additional forwardings can be given on the command 301 line. Only the superuser can forward privileged ports. 302 303 EnableSSHKeysign 304 Setting this option to ``yes'' in the global client configuration 305 file /etc/ssh/ssh_config enables the use of the helper program 306 ssh-keysign(8) during HostbasedAuthentication. The argument must 307 be ``yes'' or ``no''. The default is ``no''. This option should 308 be placed in the non-hostspecific section. See ssh-keysign(8) 309 for more information. 310 311 EscapeChar 312 Sets the escape character (default: `~'). The escape character 313 can also be set on the command line. The argument should be a 314 single character, `^' followed by a letter, or ``none'' to 315 disable the escape character entirely (making the connection 316 transparent for binary data). 317 318 ExitOnForwardFailure 319 Specifies whether ssh(1) should terminate the connection if it 320 cannot set up all requested dynamic, tunnel, local, and remote 321 port forwardings. The argument must be ``yes'' or ``no''. The 322 default is ``no''. 323 324 ForwardAgent 325 Specifies whether the connection to the authentication agent (if 326 any) will be forwarded to the remote machine. The argument must 327 be ``yes'' or ``no''. The default is ``no''. 328 329 Agent forwarding should be enabled with caution. Users with the 330 ability to bypass file permissions on the remote host (for the 331 agent's Unix-domain socket) can access the local agent through 332 the forwarded connection. An attacker cannot obtain key material 333 from the agent, however they can perform operations on the keys 334 that enable them to authenticate using the identities loaded into 335 the agent. 336 337 ForwardX11 338 Specifies whether X11 connections will be automatically 339 redirected over the secure channel and DISPLAY set. The argument 340 must be ``yes'' or ``no''. The default is ``no''. 341 342 X11 forwarding should be enabled with caution. Users with the 343 ability to bypass file permissions on the remote host (for the 344 user's X11 authorization database) can access the local X11 345 display through the forwarded connection. An attacker may then 346 be able to perform activities such as keystroke monitoring if the 347 ForwardX11Trusted option is also enabled. 348 349 ForwardX11Timeout 350 Specify a timeout for untrusted X11 forwarding using the format 351 described in the TIME FORMATS section of sshd_config(5). X11 352 connections received by ssh(1) after this time will be refused. 353 The default is to disable untrusted X11 forwarding after twenty 354 minutes has elapsed. 355 356 ForwardX11Trusted 357 If this option is set to ``yes'', remote X11 clients will have 358 full access to the original X11 display. 359 360 If this option is set to ``no'', remote X11 clients will be 361 considered untrusted and prevented from stealing or tampering 362 with data belonging to trusted X11 clients. Furthermore, the 363 xauth(1) token used for the session will be set to expire after 364 20 minutes. Remote clients will be refused access after this 365 time. 366 367 The default is ``no''. 368 369 See the X11 SECURITY extension specification for full details on 370 the restrictions imposed on untrusted clients. 371 372 GatewayPorts 373 Specifies whether remote hosts are allowed to connect to local 374 forwarded ports. By default, ssh(1) binds local port forwardings 375 to the loopback address. This prevents other remote hosts from 376 connecting to forwarded ports. GatewayPorts can be used to 377 specify that ssh should bind local port forwardings to the 378 wildcard address, thus allowing remote hosts to connect to 379 forwarded ports. The argument must be ``yes'' or ``no''. The 380 default is ``no''. 381 382 GlobalKnownHostsFile 383 Specifies one or more files to use for the global host key 384 database, separated by whitespace. The default is 385 /etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2. 386 387 GSSAPIAuthentication 388 Specifies whether user authentication based on GSSAPI is allowed. 389 The default is ``no''. Note that this option applies to protocol 390 version 2 only. 391 392 GSSAPIDelegateCredentials 393 Forward (delegate) credentials to the server. The default is 394 ``no''. Note that this option applies to protocol version 2 395 only. 396 397 HashKnownHosts 398 Indicates that ssh(1) should hash host names and addresses when 399 they are added to ~/.ssh/known_hosts. These hashed names may be 400 used normally by ssh(1) and sshd(8), but they do not reveal 401 identifying information should the file's contents be disclosed. 402 The default is ``no''. Note that existing names and addresses in 403 known hosts files will not be converted automatically, but may be 404 manually hashed using ssh-keygen(1). 405 406 HostbasedAuthentication 407 Specifies whether to try rhosts based authentication with public 408 key authentication. The argument must be ``yes'' or ``no''. The 409 default is ``no''. This option applies to protocol version 2 410 only and is similar to RhostsRSAAuthentication. 411 412 HostKeyAlgorithms 413 Specifies the protocol version 2 host key algorithms that the 414 client wants to use in order of preference. The default for this 415 option is: 416 417 ecdsa-sha2-nistp256-cert-v01@openssh.com, 418 ecdsa-sha2-nistp384-cert-v01@openssh.com, 419 ecdsa-sha2-nistp521-cert-v01@openssh.com, 420 ssh-ed25519-cert-v01@openssh.com, 421 ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com, 422 ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com, 423 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521, 424 ssh-ed25519,ssh-rsa,ssh-dss 425 426 If hostkeys are known for the destination host then this default 427 is modified to prefer their algorithms. 428 429 HostKeyAlias 430 Specifies an alias that should be used instead of the real host 431 name when looking up or saving the host key in the host key 432 database files. This option is useful for tunneling SSH 433 connections or for multiple servers running on a single host. 434 435 HostName 436 Specifies the real host name to log into. This can be used to 437 specify nicknames or abbreviations for hosts. If the hostname 438 contains the character sequence `%h', then this will be replaced 439 with the host name specified on the command line (this is useful 440 for manipulating unqualified names). The default is the name 441 given on the command line. Numeric IP addresses are also 442 permitted (both on the command line and in HostName 443 specifications). 444 445 IdentitiesOnly 446 Specifies that ssh(1) should only use the authentication identity 447 files configured in the ssh_config files, even if ssh-agent(1) or 448 a PKCS11Provider offers more identities. The argument to this 449 keyword must be ``yes'' or ``no''. This option is intended for 450 situations where ssh-agent offers many different identities. The 451 default is ``no''. 452 453 IdentityFile 454 Specifies a file from which the user's DSA, ECDSA, ED25519 or RSA 455 authentication identity is read. The default is ~/.ssh/identity 456 for protocol version 1, and ~/.ssh/id_dsa, ~/.ssh/id_ecdsa, 457 ~/.ssh/id_ed25519 and ~/.ssh/id_rsa for protocol version 2. 458 Additionally, any identities represented by the authentication 459 agent will be used for authentication unless IdentitiesOnly is 460 set. ssh(1) will try to load certificate information from the 461 filename obtained by appending -cert.pub to the path of a 462 specified IdentityFile. 463 464 The file name may use the tilde syntax to refer to a user's home 465 directory or one of the following escape characters: `%d' (local 466 user's home directory), `%u' (local user name), `%l' (local host 467 name), `%h' (remote host name) or `%r' (remote user name). 468 469 It is possible to have multiple identity files specified in 470 configuration files; all these identities will be tried in 471 sequence. Multiple IdentityFile directives will add to the list 472 of identities tried (this behaviour differs from that of other 473 configuration directives). 474 475 IdentityFile may be used in conjunction with IdentitiesOnly to 476 select which identities in an agent are offered during 477 authentication. 478 479 IgnoreUnknown 480 Specifies a pattern-list of unknown options to be ignored if they 481 are encountered in configuration parsing. This may be used to 482 suppress errors if ssh_config contains options that are 483 unrecognised by ssh(1). It is recommended that IgnoreUnknown be 484 listed early in the configuration file as it will not be applied 485 to unknown options that appear before it. 486 487 IPQoS Specifies the IPv4 type-of-service or DSCP class for connections. 488 Accepted values are ``af11'', ``af12'', ``af13'', ``af21'', 489 ``af22'', ``af23'', ``af31'', ``af32'', ``af33'', ``af41'', 490 ``af42'', ``af43'', ``cs0'', ``cs1'', ``cs2'', ``cs3'', ``cs4'', 491 ``cs5'', ``cs6'', ``cs7'', ``ef'', ``lowdelay'', ``throughput'', 492 ``reliability'', or a numeric value. This option may take one or 493 two arguments, separated by whitespace. If one argument is 494 specified, it is used as the packet class unconditionally. If 495 two values are specified, the first is automatically selected for 496 interactive sessions and the second for non-interactive sessions. 497 The default is ``lowdelay'' for interactive sessions and 498 ``throughput'' for non-interactive sessions. 499 500 KbdInteractiveAuthentication 501 Specifies whether to use keyboard-interactive authentication. 502 The argument to this keyword must be ``yes'' or ``no''. The 503 default is ``yes''. 504 505 KbdInteractiveDevices 506 Specifies the list of methods to use in keyboard-interactive 507 authentication. Multiple method names must be comma-separated. 508 The default is to use the server specified list. The methods 509 available vary depending on what the server supports. For an 510 OpenSSH server, it may be zero or more of: ``bsdauth'', ``pam'', 511 and ``skey''. 512 513 KexAlgorithms 514 Specifies the available KEX (Key Exchange) algorithms. Multiple 515 algorithms must be comma-separated. The default is: 516 517 curve25519-sha256@libssh.org, 518 ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521, 519 diffie-hellman-group-exchange-sha256, 520 diffie-hellman-group-exchange-sha1, 521 diffie-hellman-group14-sha1, 522 diffie-hellman-group1-sha1 523 524 LocalCommand 525 Specifies a command to execute on the local machine after 526 successfully connecting to the server. The command string 527 extends to the end of the line, and is executed with the user's 528 shell. The following escape character substitutions will be 529 performed: `%d' (local user's home directory), `%h' (remote host 530 name), `%l' (local host name), `%n' (host name as provided on the 531 command line), `%p' (remote port), `%r' (remote user name) or 532 `%u' (local user name). 533 534 The command is run synchronously and does not have access to the 535 session of the ssh(1) that spawned it. It should not be used for 536 interactive commands. 537 538 This directive is ignored unless PermitLocalCommand has been 539 enabled. 540 541 LocalForward 542 Specifies that a TCP port on the local machine be forwarded over 543 the secure channel to the specified host and port from the remote 544 machine. The first argument must be [bind_address:]port and the 545 second argument must be host:hostport. IPv6 addresses can be 546 specified by enclosing addresses in square brackets. Multiple 547 forwardings may be specified, and additional forwardings can be 548 given on the command line. Only the superuser can forward 549 privileged ports. By default, the local port is bound in 550 accordance with the GatewayPorts setting. However, an explicit 551 bind_address may be used to bind the connection to a specific 552 address. The bind_address of ``localhost'' indicates that the 553 listening port be bound for local use only, while an empty 554 address or `*' indicates that the port should be available from 555 all interfaces. 556 557 LogLevel 558 Gives the verbosity level that is used when logging messages from 559 ssh(1). The possible values are: QUIET, FATAL, ERROR, INFO, 560 VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO. 561 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify 562 higher levels of verbose output. 563 564 MACs Specifies the MAC (message authentication code) algorithms in 565 order of preference. The MAC algorithm is used in protocol 566 version 2 for data integrity protection. Multiple algorithms 567 must be comma-separated. The algorithms that contain ``-etm'' 568 calculate the MAC after encryption (encrypt-then-mac). These are 569 considered safer and their use recommended. The default is: 570 571 hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com, 572 umac-64-etm@openssh.com,umac-128-etm@openssh.com, 573 hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com, 574 hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com, 575 hmac-md5-96-etm@openssh.com, 576 hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com, 577 hmac-sha2-256,hmac-sha2-512,hmac-ripemd160, 578 hmac-sha1-96,hmac-md5-96 579 580 NoHostAuthenticationForLocalhost 581 This option can be used if the home directory is shared across 582 machines. In this case localhost will refer to a different 583 machine on each of the machines and the user will get many 584 warnings about changed host keys. However, this option disables 585 host authentication for localhost. The argument to this keyword 586 must be ``yes'' or ``no''. The default is to check the host key 587 for localhost. 588 589 NumberOfPasswordPrompts 590 Specifies the number of password prompts before giving up. The 591 argument to this keyword must be an integer. The default is 3. 592 593 PasswordAuthentication 594 Specifies whether to use password authentication. The argument 595 to this keyword must be ``yes'' or ``no''. The default is 596 ``yes''. 597 598 PermitLocalCommand 599 Allow local command execution via the LocalCommand option or 600 using the !command escape sequence in ssh(1). The argument must 601 be ``yes'' or ``no''. The default is ``no''. 602 603 PKCS11Provider 604 Specifies which PKCS#11 provider to use. The argument to this 605 keyword is the PKCS#11 shared library ssh(1) should use to 606 communicate with a PKCS#11 token providing the user's private RSA 607 key. 608 609 Port Specifies the port number to connect on the remote host. The 610 default is 22. 611 612 PreferredAuthentications 613 Specifies the order in which the client should try protocol 2 614 authentication methods. This allows a client to prefer one 615 method (e.g. keyboard-interactive) over another method (e.g. 616 password). The default is: 617 618 gssapi-with-mic,hostbased,publickey, 619 keyboard-interactive,password 620 621 Protocol 622 Specifies the protocol versions ssh(1) should support in order of 623 preference. The possible values are `1' and `2'. Multiple 624 versions must be comma-separated. When this option is set to 625 ``2,1'' ssh will try version 2 and fall back to version 1 if 626 version 2 is not available. The default is `2'. 627 628 ProxyCommand 629 Specifies the command to use to connect to the server. The 630 command string extends to the end of the line, and is executed 631 with the user's shell. In the command string, any occurrence of 632 `%h' will be substituted by the host name to connect, `%p' by the 633 port, and `%r' by the remote user name. The command can be 634 basically anything, and should read from its standard input and 635 write to its standard output. It should eventually connect an 636 sshd(8) server running on some machine, or execute sshd -i 637 somewhere. Host key management will be done using the HostName 638 of the host being connected (defaulting to the name typed by the 639 user). Setting the command to ``none'' disables this option 640 entirely. Note that CheckHostIP is not available for connects 641 with a proxy command. 642 643 This directive is useful in conjunction with nc(1) and its proxy 644 support. For example, the following directive would connect via 645 an HTTP proxy at 192.0.2.0: 646 647 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p 648 649 ProxyUseFdpass 650 Specifies that ProxyCommand will pass a connected file descriptor 651 back to ssh(1) instead of continuing to execute and pass data. 652 The default is ``no''. 653 654 PubkeyAuthentication 655 Specifies whether to try public key authentication. The argument 656 to this keyword must be ``yes'' or ``no''. The default is 657 ``yes''. This option applies to protocol version 2 only. 658 659 RekeyLimit 660 Specifies the maximum amount of data that may be transmitted 661 before the session key is renegotiated, optionally followed a 662 maximum amount of time that may pass before the session key is 663 renegotiated. The first argument is specified in bytes and may 664 have a suffix of `K', `M', or `G' to indicate Kilobytes, 665 Megabytes, or Gigabytes, respectively. The default is between 666 `1G' and `4G', depending on the cipher. The optional second 667 value is specified in seconds and may use any of the units 668 documented in the TIME FORMATS section of sshd_config(5). The 669 default value for RekeyLimit is ``default none'', which means 670 that rekeying is performed after the cipher's default amount of 671 data has been sent or received and no time based rekeying is 672 done. This option applies to protocol version 2 only. 673 674 RemoteForward 675 Specifies that a TCP port on the remote machine be forwarded over 676 the secure channel to the specified host and port from the local 677 machine. The first argument must be [bind_address:]port and the 678 second argument must be host:hostport. IPv6 addresses can be 679 specified by enclosing addresses in square brackets. Multiple 680 forwardings may be specified, and additional forwardings can be 681 given on the command line. Privileged ports can be forwarded 682 only when logging in as root on the remote machine. 683 684 If the port argument is `0', the listen port will be dynamically 685 allocated on the server and reported to the client at run time. 686 687 If the bind_address is not specified, the default is to only bind 688 to loopback addresses. If the bind_address is `*' or an empty 689 string, then the forwarding is requested to listen on all 690 interfaces. Specifying a remote bind_address will only succeed 691 if the server's GatewayPorts option is enabled (see 692 sshd_config(5)). 693 694 RequestTTY 695 Specifies whether to request a pseudo-tty for the session. The 696 argument may be one of: ``no'' (never request a TTY), ``yes'' 697 (always request a TTY when standard input is a TTY), ``force'' 698 (always request a TTY) or ``auto'' (request a TTY when opening a 699 login session). This option mirrors the -t and -T flags for 700 ssh(1). 701 702 RhostsRSAAuthentication 703 Specifies whether to try rhosts based authentication with RSA 704 host authentication. The argument must be ``yes'' or ``no''. 705 The default is ``no''. This option applies to protocol version 1 706 only and requires ssh(1) to be setuid root. 707 708 RSAAuthentication 709 Specifies whether to try RSA authentication. The argument to 710 this keyword must be ``yes'' or ``no''. RSA authentication will 711 only be attempted if the identity file exists, or an 712 authentication agent is running. The default is ``yes''. Note 713 that this option applies to protocol version 1 only. 714 715 SendEnv 716 Specifies what variables from the local environ(7) should be sent 717 to the server. Note that environment passing is only supported 718 for protocol 2. The server must also support it, and the server 719 must be configured to accept these environment variables. Refer 720 to AcceptEnv in sshd_config(5) for how to configure the server. 721 Variables are specified by name, which may contain wildcard 722 characters. Multiple environment variables may be separated by 723 whitespace or spread across multiple SendEnv directives. The 724 default is not to send any environment variables. 725 726 See PATTERNS for more information on patterns. 727 728 ServerAliveCountMax 729 Sets the number of server alive messages (see below) which may be 730 sent without ssh(1) receiving any messages back from the server. 731 If this threshold is reached while server alive messages are 732 being sent, ssh will disconnect from the server, terminating the 733 session. It is important to note that the use of server alive 734 messages is very different from TCPKeepAlive (below). The server 735 alive messages are sent through the encrypted channel and 736 therefore will not be spoofable. The TCP keepalive option 737 enabled by TCPKeepAlive is spoofable. The server alive mechanism 738 is valuable when the client or server depend on knowing when a 739 connection has become inactive. 740 741 The default value is 3. If, for example, ServerAliveInterval 742 (see below) is set to 15 and ServerAliveCountMax is left at the 743 default, if the server becomes unresponsive, ssh will disconnect 744 after approximately 45 seconds. This option applies to protocol 745 version 2 only. 746 747 ServerAliveInterval 748 Sets a timeout interval in seconds after which if no data has 749 been received from the server, ssh(1) will send a message through 750 the encrypted channel to request a response from the server. The 751 default is 0, indicating that these messages will not be sent to 752 the server. This option applies to protocol version 2 only. 753 754 StrictHostKeyChecking 755 If this flag is set to ``yes'', ssh(1) will never automatically 756 add host keys to the ~/.ssh/known_hosts file, and refuses to 757 connect to hosts whose host key has changed. This provides 758 maximum protection against trojan horse attacks, though it can be 759 annoying when the /etc/ssh/ssh_known_hosts file is poorly 760 maintained or when connections to new hosts are frequently made. 761 This option forces the user to manually add all new hosts. If 762 this flag is set to ``no'', ssh will automatically add new host 763 keys to the user known hosts files. If this flag is set to 764 ``ask'', new host keys will be added to the user known host files 765 only after the user has confirmed that is what they really want 766 to do, and ssh will refuse to connect to hosts whose host key has 767 changed. The host keys of known hosts will be verified 768 automatically in all cases. The argument must be ``yes'', 769 ``no'', or ``ask''. The default is ``ask''. 770 771 TCPKeepAlive 772 Specifies whether the system should send TCP keepalive messages 773 to the other side. If they are sent, death of the connection or 774 crash of one of the machines will be properly noticed. However, 775 this means that connections will die if the route is down 776 temporarily, and some people find it annoying. 777 778 The default is ``yes'' (to send TCP keepalive messages), and the 779 client will notice if the network goes down or the remote host 780 dies. This is important in scripts, and many users want it too. 781 782 To disable TCP keepalive messages, the value should be set to 783 ``no''. 784 785 Tunnel Request tun(4) device forwarding between the client and the 786 server. The argument must be ``yes'', ``point-to-point'' (layer 787 3), ``ethernet'' (layer 2), or ``no''. Specifying ``yes'' 788 requests the default tunnel mode, which is ``point-to-point''. 789 The default is ``no''. 790 791 TunnelDevice 792 Specifies the tun(4) devices to open on the client (local_tun) 793 and the server (remote_tun). 794 795 The argument must be local_tun[:remote_tun]. The devices may be 796 specified by numerical ID or the keyword ``any'', which uses the 797 next available tunnel device. If remote_tun is not specified, it 798 defaults to ``any''. The default is ``any:any''. 799 800 UsePrivilegedPort 801 Specifies whether to use a privileged port for outgoing 802 connections. The argument must be ``yes'' or ``no''. The 803 default is ``no''. If set to ``yes'', ssh(1) must be setuid 804 root. Note that this option must be set to ``yes'' for 805 RhostsRSAAuthentication with older servers. 806 807 User Specifies the user to log in as. This can be useful when a 808 different user name is used on different machines. This saves 809 the trouble of having to remember to give the user name on the 810 command line. 811 812 UserKnownHostsFile 813 Specifies one or more files to use for the user host key 814 database, separated by whitespace. The default is 815 ~/.ssh/known_hosts, ~/.ssh/known_hosts2. 816 817 VerifyHostKeyDNS 818 Specifies whether to verify the remote key using DNS and SSHFP 819 resource records. If this option is set to ``yes'', the client 820 will implicitly trust keys that match a secure fingerprint from 821 DNS. Insecure fingerprints will be handled as if this option was 822 set to ``ask''. If this option is set to ``ask'', information on 823 fingerprint match will be displayed, but the user will still need 824 to confirm new host keys according to the StrictHostKeyChecking 825 option. The argument must be ``yes'', ``no'', or ``ask''. The 826 default is ``no''. Note that this option applies to protocol 827 version 2 only. 828 829 See also VERIFYING HOST KEYS in ssh(1). 830 831 VisualHostKey 832 If this flag is set to ``yes'', an ASCII art representation of 833 the remote host key fingerprint is printed in addition to the hex 834 fingerprint string at login and for unknown host keys. If this 835 flag is set to ``no'', no fingerprint strings are printed at 836 login and only the hex fingerprint string will be printed for 837 unknown host keys. The default is ``no''. 838 839 XAuthLocation 840 Specifies the full pathname of the xauth(1) program. The default 841 is /usr/X11R6/bin/xauth. 842 843PATTERNS 844 A pattern consists of zero or more non-whitespace characters, `*' (a 845 wildcard that matches zero or more characters), or `?' (a wildcard that 846 matches exactly one character). For example, to specify a set of 847 declarations for any host in the ``.co.uk'' set of domains, the following 848 pattern could be used: 849 850 Host *.co.uk 851 852 The following pattern would match any host in the 192.168.0.[0-9] network 853 range: 854 855 Host 192.168.0.? 856 857 A pattern-list is a comma-separated list of patterns. Patterns within 858 pattern-lists may be negated by preceding them with an exclamation mark 859 (`!'). For example, to allow a key to be used from anywhere within an 860 organization except from the ``dialup'' pool, the following entry (in 861 authorized_keys) could be used: 862 863 from="!*.dialup.example.com,*.example.com" 864 865FILES 866 ~/.ssh/config 867 This is the per-user configuration file. The format of this file 868 is described above. This file is used by the SSH client. 869 Because of the potential for abuse, this file must have strict 870 permissions: read/write for the user, and not accessible by 871 others. 872 873 /etc/ssh/ssh_config 874 Systemwide configuration file. This file provides defaults for 875 those values that are not specified in the user's configuration 876 file, and for those users who do not have a configuration file. 877 This file must be world-readable. 878 879SEE ALSO 880 ssh(1) 881 882AUTHORS 883 OpenSSH is a derivative of the original and free ssh 1.2.12 release by 884 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo 885 de Raadt and Dug Song removed many bugs, re-added newer features and 886 created OpenSSH. Markus Friedl contributed the support for SSH protocol 887 versions 1.5 and 2.0. 888 889OpenBSD 5.5 February 23, 2014 OpenBSD 5.5 890