1SSH_CONFIG(5) File Formats Manual SSH_CONFIG(5) 2 3NAME 4 ssh_config M-bM-^@M-^S 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 M-bM-^@M-^\HostM-bM-^@M-^] specifications, 20 and that section is only applied for hosts that match one of the patterns 21 given in the specification. The matched host name is usually the one 22 given on the command line (see the CanonicalizeHostname option for 23 exceptions.) 24 25 Since the first obtained value for each parameter is used, more host- 26 specific declarations should be given near the beginning of the file, and 27 general defaults at the end. 28 29 The configuration file has the following format: 30 31 Empty lines and lines starting with M-bM-^@M-^X#M-bM-^@M-^Y are comments. Otherwise a line 32 is of the format M-bM-^@M-^\keyword argumentsM-bM-^@M-^]. Configuration options may be 33 separated by whitespace or optional whitespace and exactly one M-bM-^@M-^X=M-bM-^@M-^Y; the 34 latter format is useful to avoid the need to quote whitespace when 35 specifying configuration options using the ssh, scp, and sftp -o option. 36 Arguments may optionally be enclosed in double quotes (") in order to 37 represent arguments containing spaces. 38 39 The possible keywords and their meanings are as follows (note that 40 keywords are case-insensitive and arguments are case-sensitive): 41 42 Host Restricts the following declarations (up to the next Host or 43 Match keyword) to be only for those hosts that match one of the 44 patterns given after the keyword. If more than one pattern is 45 provided, they should be separated by whitespace. A single M-bM-^@M-^X*M-bM-^@M-^Y 46 as a pattern can be used to provide global defaults for all 47 hosts. The host is usually the hostname argument given on the 48 command line (see the CanonicalizeHostname option for 49 exceptions.) 50 51 A pattern entry may be negated by prefixing it with an 52 exclamation mark (M-bM-^@M-^X!M-bM-^@M-^Y). If a negated entry is matched, then the 53 Host entry is ignored, regardless of whether any other patterns 54 on the line match. Negated matches are therefore useful to 55 provide exceptions for wildcard matches. 56 57 See PATTERNS for more information on patterns. 58 59 Match Restricts the following declarations (up to the next Host or 60 Match keyword) to be used only when the conditions following the 61 Match keyword are satisfied. Match conditions are specified 62 using one or more critera or the single token all which always 63 matches. The available criteria keywords are: canonical, exec, 64 host, originalhost, user, and localuser. The all criteria must 65 appear alone or immediately after canonical. Other criteria may 66 be combined arbitrarily. All criteria but all and canonical 67 require an argument. Criteria may be negated by prepending an 68 exclamation mark (M-bM-^@M-^X!M-bM-^@M-^Y). 69 70 The canonical keyword matches only when the configuration file is 71 being re-parsed after hostname canonicalization (see the 72 CanonicalizeHostname option.) This may be useful to specify 73 conditions that work with canonical host names only. The exec 74 keyword executes the specified command under the user's shell. 75 If the command returns a zero exit status then the condition is 76 considered true. Commands containing whitespace characters must 77 be quoted. The following character sequences in the command will 78 be expanded prior to execution: M-bM-^@M-^X%LM-bM-^@M-^Y will be substituted by the 79 first component of the local host name, M-bM-^@M-^X%lM-bM-^@M-^Y will be substituted 80 by the local host name (including any domain name), M-bM-^@M-^X%hM-bM-^@M-^Y will be 81 substituted by the target host name, M-bM-^@M-^X%nM-bM-^@M-^Y will be substituted by 82 the original target host name specified on the command-line, M-bM-^@M-^X%pM-bM-^@M-^Y 83 the destination port, M-bM-^@M-^X%rM-bM-^@M-^Y by the remote login username, and M-bM-^@M-^X%uM-bM-^@M-^Y 84 by the username of the user running ssh(1). 85 86 The other keywords' criteria must be single entries or comma- 87 separated lists and may use the wildcard and negation operators 88 described in the PATTERNS section. The criteria for the host 89 keyword are matched against the target hostname, after any 90 substitution by the Hostname or CanonicalizeHostname options. 91 The originalhost keyword matches against the hostname as it was 92 specified on the command-line. The user keyword matches against 93 the target username on the remote host. The localuser keyword 94 matches against the name of the local user running ssh(1) (this 95 keyword may be useful in system-wide ssh_config files). 96 97 AddressFamily 98 Specifies which address family to use when connecting. Valid 99 arguments are M-bM-^@M-^\anyM-bM-^@M-^], M-bM-^@M-^\inetM-bM-^@M-^] (use IPv4 only), or M-bM-^@M-^\inet6M-bM-^@M-^] (use IPv6 100 only). 101 102 BatchMode 103 If set to M-bM-^@M-^\yesM-bM-^@M-^], passphrase/password querying will be disabled. 104 This option is useful in scripts and other batch jobs where no 105 user is present to supply the password. The argument must be 106 M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^]. 107 108 BindAddress 109 Use the specified address on the local machine as the source 110 address of the connection. Only useful on systems with more than 111 one address. Note that this option does not work if 112 UsePrivilegedPort is set to M-bM-^@M-^\yesM-bM-^@M-^]. 113 114 CanonicalDomains 115 When CanonicalizeHostname is enabled, this option specifies the 116 list of domain suffixes in which to search for the specified 117 destination host. 118 119 CanonicalizeFallbackLocal 120 Specifies whether to fail with an error when hostname 121 canonicalization fails. The default, M-bM-^@M-^\yesM-bM-^@M-^], will attempt to look 122 up the unqualified hostname using the system resolver's search 123 rules. A value of M-bM-^@M-^\noM-bM-^@M-^] will cause ssh(1) to fail instantly if 124 CanonicalizeHostname is enabled and the target hostname cannot be 125 found in any of the domains specified by CanonicalDomains. 126 127 CanonicalizeHostname 128 Controls whether explicit hostname canonicalization is performed. 129 The default, M-bM-^@M-^\noM-bM-^@M-^], is not to perform any name rewriting and let 130 the system resolver handle all hostname lookups. If set to M-bM-^@M-^\yesM-bM-^@M-^] 131 then, for connections that do not use a ProxyCommand, ssh(1) will 132 attempt to canonicalize the hostname specified on the command 133 line using the CanonicalDomains suffixes and 134 CanonicalizePermittedCNAMEs rules. If CanonicalizeHostname is 135 set to M-bM-^@M-^\alwaysM-bM-^@M-^], then canonicalization is applied to proxied 136 connections too. 137 138 If this option is enabled, then the configuration files are 139 processed again using the new target name to pick up any new 140 configuration in matching Host and Match stanzas. 141 142 CanonicalizeMaxDots 143 Specifies the maximum number of dot characters in a hostname 144 before canonicalization is disabled. The default, M-bM-^@M-^\1M-bM-^@M-^], allows a 145 single dot (i.e. hostname.subdomain). 146 147 CanonicalizePermittedCNAMEs 148 Specifies rules to determine whether CNAMEs should be followed 149 when canonicalizing hostnames. The rules consist of one or more 150 arguments of source_domain_list:target_domain_list, where 151 source_domain_list is a pattern-list of domains that may follow 152 CNAMEs in canonicalization, and target_domain_list is a pattern- 153 list of domains that they may resolve to. 154 155 For example, M-bM-^@M-^\*.a.example.com:*.b.example.com,*.c.example.comM-bM-^@M-^] 156 will allow hostnames matching M-bM-^@M-^\*.a.example.comM-bM-^@M-^] to be 157 canonicalized to names in the M-bM-^@M-^\*.b.example.comM-bM-^@M-^] or 158 M-bM-^@M-^\*.c.example.comM-bM-^@M-^] domains. 159 160 ChallengeResponseAuthentication 161 Specifies whether to use challenge-response authentication. The 162 argument to this keyword must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is 163 M-bM-^@M-^\yesM-bM-^@M-^]. 164 165 CheckHostIP 166 If this flag is set to M-bM-^@M-^\yesM-bM-^@M-^], ssh(1) will additionally check the 167 host IP address in the known_hosts file. This allows ssh to 168 detect if a host key changed due to DNS spoofing and will add 169 addresses of destination hosts to ~/.ssh/known_hosts in the 170 process, regardless of the setting of StrictHostKeyChecking. If 171 the option is set to M-bM-^@M-^\noM-bM-^@M-^], the check will not be executed. The 172 default is M-bM-^@M-^\yesM-bM-^@M-^]. 173 174 Cipher Specifies the cipher to use for encrypting the session in 175 protocol version 1. Currently, M-bM-^@M-^\blowfishM-bM-^@M-^], M-bM-^@M-^\3desM-bM-^@M-^], and M-bM-^@M-^\desM-bM-^@M-^] are 176 supported. des is only supported in the ssh(1) client for 177 interoperability with legacy protocol 1 implementations that do 178 not support the 3des cipher. Its use is strongly discouraged due 179 to cryptographic weaknesses. The default is M-bM-^@M-^\3desM-bM-^@M-^]. 180 181 Ciphers 182 Specifies the ciphers allowed for protocol version 2 in order of 183 preference. Multiple ciphers must be comma-separated. If the 184 specified value begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the specified 185 ciphers will be appended to the default set instead of replacing 186 them. 187 188 The supported ciphers are: 189 190 3des-cbc 191 aes128-cbc 192 aes192-cbc 193 aes256-cbc 194 aes128-ctr 195 aes192-ctr 196 aes256-ctr 197 aes128-gcm@openssh.com 198 aes256-gcm@openssh.com 199 arcfour 200 arcfour128 201 arcfour256 202 blowfish-cbc 203 cast128-cbc 204 chacha20-poly1305@openssh.com 205 206 The default is: 207 208 chacha20-poly1305@openssh.com, 209 aes128-ctr,aes192-ctr,aes256-ctr, 210 aes128-gcm@openssh.com,aes256-gcm@openssh.com, 211 arcfour256,arcfour128, 212 aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc, 213 aes192-cbc,aes256-cbc,arcfour 214 215 The list of available ciphers may also be obtained using the -Q 216 option of ssh(1) with an argument of M-bM-^@M-^\cipherM-bM-^@M-^]. 217 218 ClearAllForwardings 219 Specifies that all local, remote, and dynamic port forwardings 220 specified in the configuration files or on the command line be 221 cleared. This option is primarily useful when used from the 222 ssh(1) command line to clear port forwardings set in 223 configuration files, and is automatically set by scp(1) and 224 sftp(1). The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is 225 M-bM-^@M-^\noM-bM-^@M-^]. 226 227 Compression 228 Specifies whether to use compression. The argument must be M-bM-^@M-^\yesM-bM-^@M-^] 229 or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^]. 230 231 CompressionLevel 232 Specifies the compression level to use if compression is enabled. 233 The argument must be an integer from 1 (fast) to 9 (slow, best). 234 The default level is 6, which is good for most applications. The 235 meaning of the values is the same as in gzip(1). Note that this 236 option applies to protocol version 1 only. 237 238 ConnectionAttempts 239 Specifies the number of tries (one per second) to make before 240 exiting. The argument must be an integer. This may be useful in 241 scripts if the connection sometimes fails. The default is 1. 242 243 ConnectTimeout 244 Specifies the timeout (in seconds) used when connecting to the 245 SSH server, instead of using the default system TCP timeout. 246 This value is used only when the target is down or really 247 unreachable, not when it refuses the connection. 248 249 ControlMaster 250 Enables the sharing of multiple sessions over a single network 251 connection. When set to M-bM-^@M-^\yesM-bM-^@M-^], ssh(1) will listen for 252 connections on a control socket specified using the ControlPath 253 argument. Additional sessions can connect to this socket using 254 the same ControlPath with ControlMaster set to M-bM-^@M-^\noM-bM-^@M-^] (the 255 default). These sessions will try to reuse the master instance's 256 network connection rather than initiating new ones, but will fall 257 back to connecting normally if the control socket does not exist, 258 or is not listening. 259 260 Setting this to M-bM-^@M-^\askM-bM-^@M-^] will cause ssh to listen for control 261 connections, but require confirmation using ssh-askpass(1). If 262 the ControlPath cannot be opened, ssh will continue without 263 connecting to a master instance. 264 265 X11 and ssh-agent(1) forwarding is supported over these 266 multiplexed connections, however the display and agent forwarded 267 will be the one belonging to the master connection i.e. it is not 268 possible to forward multiple displays or agents. 269 270 Two additional options allow for opportunistic multiplexing: try 271 to use a master connection but fall back to creating a new one if 272 one does not already exist. These options are: M-bM-^@M-^\autoM-bM-^@M-^] and 273 M-bM-^@M-^\autoaskM-bM-^@M-^]. The latter requires confirmation like the M-bM-^@M-^\askM-bM-^@M-^] 274 option. 275 276 ControlPath 277 Specify the path to the control socket used for connection 278 sharing as described in the ControlMaster section above or the 279 string M-bM-^@M-^\noneM-bM-^@M-^] to disable connection sharing. In the path, M-bM-^@M-^X%LM-bM-^@M-^Y 280 will be substituted by the first component of the local host 281 name, M-bM-^@M-^X%lM-bM-^@M-^Y will be substituted by the local host name (including 282 any domain name), M-bM-^@M-^X%hM-bM-^@M-^Y will be substituted by the target host 283 name, M-bM-^@M-^X%nM-bM-^@M-^Y will be substituted by the original target host name 284 specified on the command line, M-bM-^@M-^X%pM-bM-^@M-^Y the destination port, M-bM-^@M-^X%rM-bM-^@M-^Y by 285 the remote login username, M-bM-^@M-^X%uM-bM-^@M-^Y by the username of the user 286 running ssh(1), and M-bM-^@M-^X%CM-bM-^@M-^Y by a hash of the concatenation: 287 %l%h%p%r. It is recommended that any ControlPath used for 288 opportunistic connection sharing include at least %h, %p, and %r 289 (or alternatively %C) and be placed in a directory that is not 290 writable by other users. This ensures that shared connections 291 are uniquely identified. 292 293 ControlPersist 294 When used in conjunction with ControlMaster, specifies that the 295 master connection should remain open in the background (waiting 296 for future client connections) after the initial client 297 connection has been closed. If set to M-bM-^@M-^\noM-bM-^@M-^], then the master 298 connection will not be placed into the background, and will close 299 as soon as the initial client connection is closed. If set to 300 M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\0M-bM-^@M-^], then the master connection will remain in the 301 background indefinitely (until killed or closed via a mechanism 302 such as the ssh(1) M-bM-^@M-^\-O exitM-bM-^@M-^] option). If set to a time in 303 seconds, or a time in any of the formats documented in 304 sshd_config(5), then the backgrounded master connection will 305 automatically terminate after it has remained idle (with no 306 client connections) for the specified time. 307 308 DynamicForward 309 Specifies that a TCP port on the local machine be forwarded over 310 the secure channel, and the application protocol is then used to 311 determine where to connect to from the remote machine. 312 313 The argument must be [bind_address:]port. IPv6 addresses can be 314 specified by enclosing addresses in square brackets. By default, 315 the local port is bound in accordance with the GatewayPorts 316 setting. However, an explicit bind_address may be used to bind 317 the connection to a specific address. The bind_address of 318 M-bM-^@M-^\localhostM-bM-^@M-^] indicates that the listening port be bound for local 319 use only, while an empty address or M-bM-^@M-^X*M-bM-^@M-^Y indicates that the port 320 should be available from all interfaces. 321 322 Currently the SOCKS4 and SOCKS5 protocols are supported, and 323 ssh(1) will act as a SOCKS server. Multiple forwardings may be 324 specified, and additional forwardings can be given on the command 325 line. Only the superuser can forward privileged ports. 326 327 EnableSSHKeysign 328 Setting this option to M-bM-^@M-^\yesM-bM-^@M-^] in the global client configuration 329 file /etc/ssh/ssh_config enables the use of the helper program 330 ssh-keysign(8) during HostbasedAuthentication. The argument must 331 be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^]. This option should be 332 placed in the non-hostspecific section. See ssh-keysign(8) for 333 more information. 334 335 EscapeChar 336 Sets the escape character (default: M-bM-^@M-^X~M-bM-^@M-^Y). The escape character 337 can also be set on the command line. The argument should be a 338 single character, M-bM-^@M-^X^M-bM-^@M-^Y followed by a letter, or M-bM-^@M-^\noneM-bM-^@M-^] to disable 339 the escape character entirely (making the connection transparent 340 for binary data). 341 342 ExitOnForwardFailure 343 Specifies whether ssh(1) should terminate the connection if it 344 cannot set up all requested dynamic, tunnel, local, and remote 345 port forwardings. The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The 346 default is M-bM-^@M-^\noM-bM-^@M-^]. 347 348 FingerprintHash 349 Specifies the hash algorithm used when displaying key 350 fingerprints. Valid options are: M-bM-^@M-^\md5M-bM-^@M-^] and M-bM-^@M-^\sha256M-bM-^@M-^]. The 351 default is M-bM-^@M-^\sha256M-bM-^@M-^]. 352 353 ForwardAgent 354 Specifies whether the connection to the authentication agent (if 355 any) will be forwarded to the remote machine. The argument must 356 be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^]. 357 358 Agent forwarding should be enabled with caution. Users with the 359 ability to bypass file permissions on the remote host (for the 360 agent's Unix-domain socket) can access the local agent through 361 the forwarded connection. An attacker cannot obtain key material 362 from the agent, however they can perform operations on the keys 363 that enable them to authenticate using the identities loaded into 364 the agent. 365 366 ForwardX11 367 Specifies whether X11 connections will be automatically 368 redirected over the secure channel and DISPLAY set. The argument 369 must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^]. 370 371 X11 forwarding should be enabled with caution. Users with the 372 ability to bypass file permissions on the remote host (for the 373 user's X11 authorization database) can access the local X11 374 display through the forwarded connection. An attacker may then 375 be able to perform activities such as keystroke monitoring if the 376 ForwardX11Trusted option is also enabled. 377 378 ForwardX11Timeout 379 Specify a timeout for untrusted X11 forwarding using the format 380 described in the TIME FORMATS section of sshd_config(5). X11 381 connections received by ssh(1) after this time will be refused. 382 The default is to disable untrusted X11 forwarding after twenty 383 minutes has elapsed. 384 385 ForwardX11Trusted 386 If this option is set to M-bM-^@M-^\yesM-bM-^@M-^], remote X11 clients will have full 387 access to the original X11 display. 388 389 If this option is set to M-bM-^@M-^\noM-bM-^@M-^], remote X11 clients will be 390 considered untrusted and prevented from stealing or tampering 391 with data belonging to trusted X11 clients. Furthermore, the 392 xauth(1) token used for the session will be set to expire after 393 20 minutes. Remote clients will be refused access after this 394 time. 395 396 The default is M-bM-^@M-^\noM-bM-^@M-^]. 397 398 See the X11 SECURITY extension specification for full details on 399 the restrictions imposed on untrusted clients. 400 401 GatewayPorts 402 Specifies whether remote hosts are allowed to connect to local 403 forwarded ports. By default, ssh(1) binds local port forwardings 404 to the loopback address. This prevents other remote hosts from 405 connecting to forwarded ports. GatewayPorts can be used to 406 specify that ssh should bind local port forwardings to the 407 wildcard address, thus allowing remote hosts to connect to 408 forwarded ports. The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The 409 default is M-bM-^@M-^\noM-bM-^@M-^]. 410 411 GlobalKnownHostsFile 412 Specifies one or more files to use for the global host key 413 database, separated by whitespace. The default is 414 /etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2. 415 416 GSSAPIAuthentication 417 Specifies whether user authentication based on GSSAPI is allowed. 418 The default is M-bM-^@M-^\noM-bM-^@M-^]. Note that this option applies to protocol 419 version 2 only. 420 421 GSSAPIDelegateCredentials 422 Forward (delegate) credentials to the server. The default is 423 M-bM-^@M-^\noM-bM-^@M-^]. Note that this option applies to protocol version 2 only. 424 425 HashKnownHosts 426 Indicates that ssh(1) should hash host names and addresses when 427 they are added to ~/.ssh/known_hosts. These hashed names may be 428 used normally by ssh(1) and sshd(8), but they do not reveal 429 identifying information should the file's contents be disclosed. 430 The default is M-bM-^@M-^\noM-bM-^@M-^]. Note that existing names and addresses in 431 known hosts files will not be converted automatically, but may be 432 manually hashed using ssh-keygen(1). 433 434 HostbasedAuthentication 435 Specifies whether to try rhosts based authentication with public 436 key authentication. The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The 437 default is M-bM-^@M-^\noM-bM-^@M-^]. This option applies to protocol version 2 only 438 and is similar to RhostsRSAAuthentication. 439 440 HostbasedKeyTypes 441 Specifies the key types that will be used for hostbased 442 authentication as a comma-separated pattern list. Alternately if 443 the specified value begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the 444 specified key types will be appended to the default set instead 445 of replacing them. The default for this option is: 446 447 ecdsa-sha2-nistp256-cert-v01@openssh.com, 448 ecdsa-sha2-nistp384-cert-v01@openssh.com, 449 ecdsa-sha2-nistp521-cert-v01@openssh.com, 450 ssh-ed25519-cert-v01@openssh.com, 451 ssh-rsa-cert-v01@openssh.com, 452 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521, 453 ssh-ed25519,ssh-rsa 454 455 The -Q option of ssh(1) may be used to list supported key types. 456 457 HostKeyAlgorithms 458 Specifies the protocol version 2 host key algorithms that the 459 client wants to use in order of preference. Alternately if the 460 specified value begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the specified 461 key types will be appended to the default set instead of 462 replacing them. The default for this option is: 463 464 ecdsa-sha2-nistp256-cert-v01@openssh.com, 465 ecdsa-sha2-nistp384-cert-v01@openssh.com, 466 ecdsa-sha2-nistp521-cert-v01@openssh.com, 467 ssh-ed25519-cert-v01@openssh.com, 468 ssh-rsa-cert-v01@openssh.com, 469 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521, 470 ssh-ed25519,ssh-rsa 471 472 If hostkeys are known for the destination host then this default 473 is modified to prefer their algorithms. 474 475 The list of available key types may also be obtained using the -Q 476 option of ssh(1) with an argument of M-bM-^@M-^\keyM-bM-^@M-^]. 477 478 HostKeyAlias 479 Specifies an alias that should be used instead of the real host 480 name when looking up or saving the host key in the host key 481 database files. This option is useful for tunneling SSH 482 connections or for multiple servers running on a single host. 483 484 HostName 485 Specifies the real host name to log into. This can be used to 486 specify nicknames or abbreviations for hosts. If the hostname 487 contains the character sequence M-bM-^@M-^X%hM-bM-^@M-^Y, then this will be replaced 488 with the host name specified on the command line (this is useful 489 for manipulating unqualified names). The character sequence M-bM-^@M-^X%%M-bM-^@M-^Y 490 will be replaced by a single M-bM-^@M-^X%M-bM-^@M-^Y character, which may be used 491 when specifying IPv6 link-local addresses. 492 493 The default is the name given on the command line. Numeric IP 494 addresses are also permitted (both on the command line and in 495 HostName specifications). 496 497 IdentitiesOnly 498 Specifies that ssh(1) should only use the authentication identity 499 files configured in the ssh_config files, even if ssh-agent(1) or 500 a PKCS11Provider offers more identities. The argument to this 501 keyword must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. This option is intended for 502 situations where ssh-agent offers many different identities. The 503 default is M-bM-^@M-^\noM-bM-^@M-^]. 504 505 IdentityFile 506 Specifies a file from which the user's DSA, ECDSA, Ed25519 or RSA 507 authentication identity is read. The default is ~/.ssh/identity 508 for protocol version 1, and ~/.ssh/id_dsa, ~/.ssh/id_ecdsa, 509 ~/.ssh/id_ed25519 and ~/.ssh/id_rsa for protocol version 2. 510 Additionally, any identities represented by the authentication 511 agent will be used for authentication unless IdentitiesOnly is 512 set. ssh(1) will try to load certificate information from the 513 filename obtained by appending -cert.pub to the path of a 514 specified IdentityFile. 515 516 The file name may use the tilde syntax to refer to a user's home 517 directory or one of the following escape characters: M-bM-^@M-^X%dM-bM-^@M-^Y (local 518 user's home directory), M-bM-^@M-^X%uM-bM-^@M-^Y (local user name), M-bM-^@M-^X%lM-bM-^@M-^Y (local host 519 name), M-bM-^@M-^X%hM-bM-^@M-^Y (remote host name) or M-bM-^@M-^X%rM-bM-^@M-^Y (remote user name). 520 521 It is possible to have multiple identity files specified in 522 configuration files; all these identities will be tried in 523 sequence. Multiple IdentityFile directives will add to the list 524 of identities tried (this behaviour differs from that of other 525 configuration directives). 526 527 IdentityFile may be used in conjunction with IdentitiesOnly to 528 select which identities in an agent are offered during 529 authentication. 530 531 IgnoreUnknown 532 Specifies a pattern-list of unknown options to be ignored if they 533 are encountered in configuration parsing. This may be used to 534 suppress errors if ssh_config contains options that are 535 unrecognised by ssh(1). It is recommended that IgnoreUnknown be 536 listed early in the configuration file as it will not be applied 537 to unknown options that appear before it. 538 539 IPQoS Specifies the IPv4 type-of-service or DSCP class for connections. 540 Accepted values are M-bM-^@M-^\af11M-bM-^@M-^], M-bM-^@M-^\af12M-bM-^@M-^], M-bM-^@M-^\af13M-bM-^@M-^], M-bM-^@M-^\af21M-bM-^@M-^], M-bM-^@M-^\af22M-bM-^@M-^], 541 M-bM-^@M-^\af23M-bM-^@M-^], M-bM-^@M-^\af31M-bM-^@M-^], M-bM-^@M-^\af32M-bM-^@M-^], M-bM-^@M-^\af33M-bM-^@M-^], M-bM-^@M-^\af41M-bM-^@M-^], M-bM-^@M-^\af42M-bM-^@M-^], M-bM-^@M-^\af43M-bM-^@M-^], M-bM-^@M-^\cs0M-bM-^@M-^], 542 M-bM-^@M-^\cs1M-bM-^@M-^], M-bM-^@M-^\cs2M-bM-^@M-^], M-bM-^@M-^\cs3M-bM-^@M-^], M-bM-^@M-^\cs4M-bM-^@M-^], M-bM-^@M-^\cs5M-bM-^@M-^], M-bM-^@M-^\cs6M-bM-^@M-^], M-bM-^@M-^\cs7M-bM-^@M-^], M-bM-^@M-^\efM-bM-^@M-^], 543 M-bM-^@M-^\lowdelayM-bM-^@M-^], M-bM-^@M-^\throughputM-bM-^@M-^], M-bM-^@M-^\reliabilityM-bM-^@M-^], or a numeric value. 544 This option may take one or two arguments, separated by 545 whitespace. If one argument is specified, it is used as the 546 packet class unconditionally. If two values are specified, the 547 first is automatically selected for interactive sessions and the 548 second for non-interactive sessions. The default is M-bM-^@M-^\lowdelayM-bM-^@M-^] 549 for interactive sessions and M-bM-^@M-^\throughputM-bM-^@M-^] for non-interactive 550 sessions. 551 552 KbdInteractiveAuthentication 553 Specifies whether to use keyboard-interactive authentication. 554 The argument to this keyword must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default 555 is M-bM-^@M-^\yesM-bM-^@M-^]. 556 557 KbdInteractiveDevices 558 Specifies the list of methods to use in keyboard-interactive 559 authentication. Multiple method names must be comma-separated. 560 The default is to use the server specified list. The methods 561 available vary depending on what the server supports. For an 562 OpenSSH server, it may be zero or more of: M-bM-^@M-^\bsdauthM-bM-^@M-^], M-bM-^@M-^\pamM-bM-^@M-^], and 563 M-bM-^@M-^\skeyM-bM-^@M-^]. 564 565 KexAlgorithms 566 Specifies the available KEX (Key Exchange) algorithms. Multiple 567 algorithms must be comma-separated. Alternately if the specified 568 value begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the specified methods 569 will be appended to the default set instead of replacing them. 570 The default is: 571 572 curve25519-sha256@libssh.org, 573 ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521, 574 diffie-hellman-group-exchange-sha256, 575 diffie-hellman-group-exchange-sha1, 576 diffie-hellman-group14-sha1 577 578 The list of available key exchange algorithms may also be 579 obtained using the -Q option of ssh(1) with an argument of M-bM-^@M-^\kexM-bM-^@M-^]. 580 581 LocalCommand 582 Specifies a command to execute on the local machine after 583 successfully connecting to the server. The command string 584 extends to the end of the line, and is executed with the user's 585 shell. The following escape character substitutions will be 586 performed: M-bM-^@M-^X%dM-bM-^@M-^Y (local user's home directory), M-bM-^@M-^X%hM-bM-^@M-^Y (remote host 587 name), M-bM-^@M-^X%lM-bM-^@M-^Y (local host name), M-bM-^@M-^X%nM-bM-^@M-^Y (host name as provided on the 588 command line), M-bM-^@M-^X%pM-bM-^@M-^Y (remote port), M-bM-^@M-^X%rM-bM-^@M-^Y (remote user name) or 589 M-bM-^@M-^X%uM-bM-^@M-^Y (local user name) or M-bM-^@M-^X%CM-bM-^@M-^Y by a hash of the concatenation: 590 %l%h%p%r. 591 592 The command is run synchronously and does not have access to the 593 session of the ssh(1) that spawned it. It should not be used for 594 interactive commands. 595 596 This directive is ignored unless PermitLocalCommand has been 597 enabled. 598 599 LocalForward 600 Specifies that a TCP port on the local machine be forwarded over 601 the secure channel to the specified host and port from the remote 602 machine. The first argument must be [bind_address:]port and the 603 second argument must be host:hostport. IPv6 addresses can be 604 specified by enclosing addresses in square brackets. Multiple 605 forwardings may be specified, and additional forwardings can be 606 given on the command line. Only the superuser can forward 607 privileged ports. By default, the local port is bound in 608 accordance with the GatewayPorts setting. However, an explicit 609 bind_address may be used to bind the connection to a specific 610 address. The bind_address of M-bM-^@M-^\localhostM-bM-^@M-^] indicates that the 611 listening port be bound for local use only, while an empty 612 address or M-bM-^@M-^X*M-bM-^@M-^Y indicates that the port should be available from 613 all interfaces. 614 615 LogLevel 616 Gives the verbosity level that is used when logging messages from 617 ssh(1). The possible values are: QUIET, FATAL, ERROR, INFO, 618 VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO. 619 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify 620 higher levels of verbose output. 621 622 MACs Specifies the MAC (message authentication code) algorithms in 623 order of preference. The MAC algorithm is used in protocol 624 version 2 for data integrity protection. Multiple algorithms 625 must be comma-separated. If the specified value begins with a 626 M-bM-^@M-^X+M-bM-^@M-^Y character, then the specified algorithms will be appended to 627 the default set instead of replacing them. 628 629 The algorithms that contain M-bM-^@M-^\-etmM-bM-^@M-^] calculate the MAC after 630 encryption (encrypt-then-mac). These are considered safer and 631 their use recommended. 632 633 The default is: 634 635 umac-64-etm@openssh.com,umac-128-etm@openssh.com, 636 hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com, 637 umac-64@openssh.com,umac-128@openssh.com, 638 hmac-sha2-256,hmac-sha2-512, 639 hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com, 640 hmac-ripemd160-etm@openssh.com, 641 hmac-sha1-96-etm@openssh.com,hmac-md5-96-etm@openssh.com, 642 hmac-md5,hmac-sha1,hmac-ripemd160, 643 hmac-sha1-96,hmac-md5-96 644 645 The list of available MAC algorithms may also be obtained using 646 the -Q option of ssh(1) with an argument of M-bM-^@M-^\macM-bM-^@M-^]. 647 648 NoHostAuthenticationForLocalhost 649 This option can be used if the home directory is shared across 650 machines. In this case localhost will refer to a different 651 machine on each of the machines and the user will get many 652 warnings about changed host keys. However, this option disables 653 host authentication for localhost. The argument to this keyword 654 must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is to check the host key for 655 localhost. 656 657 NumberOfPasswordPrompts 658 Specifies the number of password prompts before giving up. The 659 argument to this keyword must be an integer. The default is 3. 660 661 PasswordAuthentication 662 Specifies whether to use password authentication. The argument 663 to this keyword must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\yesM-bM-^@M-^]. 664 665 PermitLocalCommand 666 Allow local command execution via the LocalCommand option or 667 using the !command escape sequence in ssh(1). The argument must 668 be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^]. 669 670 PKCS11Provider 671 Specifies which PKCS#11 provider to use. The argument to this 672 keyword is the PKCS#11 shared library ssh(1) should use to 673 communicate with a PKCS#11 token providing the user's private RSA 674 key. 675 676 Port Specifies the port number to connect on the remote host. The 677 default is 22. 678 679 PreferredAuthentications 680 Specifies the order in which the client should try protocol 2 681 authentication methods. This allows a client to prefer one 682 method (e.g. keyboard-interactive) over another method (e.g. 683 password). The default is: 684 685 gssapi-with-mic,hostbased,publickey, 686 keyboard-interactive,password 687 688 Protocol 689 Specifies the protocol versions ssh(1) should support in order of 690 preference. The possible values are M-bM-^@M-^X1M-bM-^@M-^Y and M-bM-^@M-^X2M-bM-^@M-^Y. Multiple 691 versions must be comma-separated. When this option is set to 692 M-bM-^@M-^\2,1M-bM-^@M-^] ssh will try version 2 and fall back to version 1 if 693 version 2 is not available. The default is M-bM-^@M-^X2M-bM-^@M-^Y. 694 695 ProxyCommand 696 Specifies the command to use to connect to the server. The 697 command string extends to the end of the line, and is executed 698 using the user's shell M-bM-^@M-^XexecM-bM-^@M-^Y directive to avoid a lingering 699 shell process. 700 701 In the command string, any occurrence of M-bM-^@M-^X%hM-bM-^@M-^Y will be substituted 702 by the host name to connect, M-bM-^@M-^X%pM-bM-^@M-^Y by the port, and M-bM-^@M-^X%rM-bM-^@M-^Y by the 703 remote user name. The command can be basically anything, and 704 should read from its standard input and write to its standard 705 output. It should eventually connect an sshd(8) server running 706 on some machine, or execute sshd -i somewhere. Host key 707 management will be done using the HostName of the host being 708 connected (defaulting to the name typed by the user). Setting 709 the command to M-bM-^@M-^\noneM-bM-^@M-^] disables this option entirely. Note that 710 CheckHostIP is not available for connects with a proxy command. 711 712 This directive is useful in conjunction with nc(1) and its proxy 713 support. For example, the following directive would connect via 714 an HTTP proxy at 192.0.2.0: 715 716 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p 717 718 ProxyUseFdpass 719 Specifies that ProxyCommand will pass a connected file descriptor 720 back to ssh(1) instead of continuing to execute and pass data. 721 The default is M-bM-^@M-^\noM-bM-^@M-^]. 722 723 PubkeyAcceptedKeyTypes 724 Specifies the key types that will be used for public key 725 authentication as a comma-separated pattern list. Alternately if 726 the specified value begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the key 727 types after it will be appended to the default instead of 728 replacing it. The default for this option is: 729 730 ecdsa-sha2-nistp256-cert-v01@openssh.com, 731 ecdsa-sha2-nistp384-cert-v01@openssh.com, 732 ecdsa-sha2-nistp521-cert-v01@openssh.com, 733 ssh-ed25519-cert-v01@openssh.com, 734 ssh-rsa-cert-v01@openssh.com, 735 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521, 736 ssh-ed25519,ssh-rsa 737 738 The -Q option of ssh(1) may be used to list supported key types. 739 740 PubkeyAuthentication 741 Specifies whether to try public key authentication. The argument 742 to this keyword must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\yesM-bM-^@M-^]. 743 This option applies to protocol version 2 only. 744 745 RekeyLimit 746 Specifies the maximum amount of data that may be transmitted 747 before the session key is renegotiated, optionally followed a 748 maximum amount of time that may pass before the session key is 749 renegotiated. The first argument is specified in bytes and may 750 have a suffix of M-bM-^@M-^XKM-bM-^@M-^Y, M-bM-^@M-^XMM-bM-^@M-^Y, or M-bM-^@M-^XGM-bM-^@M-^Y to indicate Kilobytes, 751 Megabytes, or Gigabytes, respectively. The default is between 752 M-bM-^@M-^X1GM-bM-^@M-^Y and M-bM-^@M-^X4GM-bM-^@M-^Y, depending on the cipher. The optional second 753 value is specified in seconds and may use any of the units 754 documented in the TIME FORMATS section of sshd_config(5). The 755 default value for RekeyLimit is M-bM-^@M-^\default noneM-bM-^@M-^], which means that 756 rekeying is performed after the cipher's default amount of data 757 has been sent or received and no time based rekeying is done. 758 This option applies to protocol version 2 only. 759 760 RemoteForward 761 Specifies that a TCP port on the remote machine be forwarded over 762 the secure channel to the specified host and port from the local 763 machine. The first argument must be [bind_address:]port and the 764 second argument must be host:hostport. IPv6 addresses can be 765 specified by enclosing addresses in square brackets. Multiple 766 forwardings may be specified, and additional forwardings can be 767 given on the command line. Privileged ports can be forwarded 768 only when logging in as root on the remote machine. 769 770 If the port argument is M-bM-^@M-^X0M-bM-^@M-^Y, the listen port will be dynamically 771 allocated on the server and reported to the client at run time. 772 773 If the bind_address is not specified, the default is to only bind 774 to loopback addresses. If the bind_address is M-bM-^@M-^X*M-bM-^@M-^Y or an empty 775 string, then the forwarding is requested to listen on all 776 interfaces. Specifying a remote bind_address will only succeed 777 if the server's GatewayPorts option is enabled (see 778 sshd_config(5)). 779 780 RequestTTY 781 Specifies whether to request a pseudo-tty for the session. The 782 argument may be one of: M-bM-^@M-^\noM-bM-^@M-^] (never request a TTY), M-bM-^@M-^\yesM-bM-^@M-^] (always 783 request a TTY when standard input is a TTY), M-bM-^@M-^\forceM-bM-^@M-^] (always 784 request a TTY) or M-bM-^@M-^\autoM-bM-^@M-^] (request a TTY when opening a login 785 session). This option mirrors the -t and -T flags for ssh(1). 786 787 RevokedHostKeys 788 Specifies revoked host public keys. Keys listed in this file 789 will be refused for host authentication. Note that if this file 790 does not exist or is not readable, then host authentication will 791 be refused for all hosts. Keys may be specified as a text file, 792 listing one public key per line, or as an OpenSSH Key Revocation 793 List (KRL) as generated by ssh-keygen(1). For more information 794 on KRLs, see the KEY REVOCATION LISTS section in ssh-keygen(1). 795 796 RhostsRSAAuthentication 797 Specifies whether to try rhosts based authentication with RSA 798 host authentication. The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The 799 default is M-bM-^@M-^\noM-bM-^@M-^]. This option applies to protocol version 1 only 800 and requires ssh(1) to be setuid root. 801 802 RSAAuthentication 803 Specifies whether to try RSA authentication. The argument to 804 this keyword must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. RSA authentication will only 805 be attempted if the identity file exists, or an authentication 806 agent is running. The default is M-bM-^@M-^\yesM-bM-^@M-^]. Note that this option 807 applies to protocol version 1 only. 808 809 SendEnv 810 Specifies what variables from the local environ(7) should be sent 811 to the server. Note that environment passing is only supported 812 for protocol 2. The server must also support it, and the server 813 must be configured to accept these environment variables. Note 814 that the TERM environment variable is always sent whenever a 815 pseudo-terminal is requested as it is required by the protocol. 816 Refer to AcceptEnv in sshd_config(5) for how to configure the 817 server. Variables are specified by name, which may contain 818 wildcard characters. Multiple environment variables may be 819 separated by whitespace or spread across multiple SendEnv 820 directives. The default is not to send any environment 821 variables. 822 823 See PATTERNS for more information on patterns. 824 825 ServerAliveCountMax 826 Sets the number of server alive messages (see below) which may be 827 sent without ssh(1) receiving any messages back from the server. 828 If this threshold is reached while server alive messages are 829 being sent, ssh will disconnect from the server, terminating the 830 session. It is important to note that the use of server alive 831 messages is very different from TCPKeepAlive (below). The server 832 alive messages are sent through the encrypted channel and 833 therefore will not be spoofable. The TCP keepalive option 834 enabled by TCPKeepAlive is spoofable. The server alive mechanism 835 is valuable when the client or server depend on knowing when a 836 connection has become inactive. 837 838 The default value is 3. If, for example, ServerAliveInterval 839 (see below) is set to 15 and ServerAliveCountMax is left at the 840 default, if the server becomes unresponsive, ssh will disconnect 841 after approximately 45 seconds. This option applies to protocol 842 version 2 only. 843 844 ServerAliveInterval 845 Sets a timeout interval in seconds after which if no data has 846 been received from the server, ssh(1) will send a message through 847 the encrypted channel to request a response from the server. The 848 default is 0, indicating that these messages will not be sent to 849 the server. This option applies to protocol version 2 only. 850 851 StreamLocalBindMask 852 Sets the octal file creation mode mask (umask) used when creating 853 a Unix-domain socket file for local or remote port forwarding. 854 This option is only used for port forwarding to a Unix-domain 855 socket file. 856 857 The default value is 0177, which creates a Unix-domain socket 858 file that is readable and writable only by the owner. Note that 859 not all operating systems honor the file mode on Unix-domain 860 socket files. 861 862 StreamLocalBindUnlink 863 Specifies whether to remove an existing Unix-domain socket file 864 for local or remote port forwarding before creating a new one. 865 If the socket file already exists and StreamLocalBindUnlink is 866 not enabled, ssh will be unable to forward the port to the Unix- 867 domain socket file. This option is only used for port forwarding 868 to a Unix-domain socket file. 869 870 The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^]. 871 872 StrictHostKeyChecking 873 If this flag is set to M-bM-^@M-^\yesM-bM-^@M-^], ssh(1) will never automatically add 874 host keys to the ~/.ssh/known_hosts file, and refuses to connect 875 to hosts whose host key has changed. This provides maximum 876 protection against trojan horse attacks, though it can be 877 annoying when the /etc/ssh/ssh_known_hosts file is poorly 878 maintained or when connections to new hosts are frequently made. 879 This option forces the user to manually add all new hosts. If 880 this flag is set to M-bM-^@M-^\noM-bM-^@M-^], ssh will automatically add new host 881 keys to the user known hosts files. If this flag is set to 882 M-bM-^@M-^\askM-bM-^@M-^], new host keys will be added to the user known host files 883 only after the user has confirmed that is what they really want 884 to do, and ssh will refuse to connect to hosts whose host key has 885 changed. The host keys of known hosts will be verified 886 automatically in all cases. The argument must be M-bM-^@M-^\yesM-bM-^@M-^], M-bM-^@M-^\noM-bM-^@M-^], or 887 M-bM-^@M-^\askM-bM-^@M-^]. The default is M-bM-^@M-^\askM-bM-^@M-^]. 888 889 TCPKeepAlive 890 Specifies whether the system should send TCP keepalive messages 891 to the other side. If they are sent, death of the connection or 892 crash of one of the machines will be properly noticed. However, 893 this means that connections will die if the route is down 894 temporarily, and some people find it annoying. 895 896 The default is M-bM-^@M-^\yesM-bM-^@M-^] (to send TCP keepalive messages), and the 897 client will notice if the network goes down or the remote host 898 dies. This is important in scripts, and many users want it too. 899 900 To disable TCP keepalive messages, the value should be set to 901 M-bM-^@M-^\noM-bM-^@M-^]. 902 903 Tunnel Request tun(4) device forwarding between the client and the 904 server. The argument must be M-bM-^@M-^\yesM-bM-^@M-^], M-bM-^@M-^\point-to-pointM-bM-^@M-^] (layer 3), 905 M-bM-^@M-^\ethernetM-bM-^@M-^] (layer 2), or M-bM-^@M-^\noM-bM-^@M-^]. Specifying M-bM-^@M-^\yesM-bM-^@M-^] requests the 906 default tunnel mode, which is M-bM-^@M-^\point-to-pointM-bM-^@M-^]. The default is 907 M-bM-^@M-^\noM-bM-^@M-^]. 908 909 TunnelDevice 910 Specifies the tun(4) devices to open on the client (local_tun) 911 and the server (remote_tun). 912 913 The argument must be local_tun[:remote_tun]. The devices may be 914 specified by numerical ID or the keyword M-bM-^@M-^\anyM-bM-^@M-^], which uses the 915 next available tunnel device. If remote_tun is not specified, it 916 defaults to M-bM-^@M-^\anyM-bM-^@M-^]. The default is M-bM-^@M-^\any:anyM-bM-^@M-^]. 917 918 UpdateHostKeys 919 Specifies whether ssh(1) should accept notifications of 920 additional hostkeys from the server sent after authentication has 921 completed and add them to UserKnownHostsFile. The argument must 922 be M-bM-^@M-^\yesM-bM-^@M-^], M-bM-^@M-^\noM-bM-^@M-^] (the default) or M-bM-^@M-^\askM-bM-^@M-^]. Enabling this option 923 allows learning alternate hostkeys for a server and supports 924 graceful key rotation by allowing a server to send replacement 925 public keys before old ones are removed. Additional hostkeys are 926 only accepted if the key used to authenticate the host was 927 already trusted or explicity accepted by the user. If 928 UpdateHostKeys is set to M-bM-^@M-^\askM-bM-^@M-^], then the user is asked to confirm 929 the modifications to the known_hosts file. Confirmation is 930 currently incompatible with ControlPersist, and will be disabled 931 if it is enabled. 932 933 Presently, only sshd(8) from OpenSSH 6.8 and greater support the 934 M-bM-^@M-^\hostkeys@openssh.comM-bM-^@M-^] protocol extension used to inform the 935 client of all the server's hostkeys. 936 937 UsePrivilegedPort 938 Specifies whether to use a privileged port for outgoing 939 connections. The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is 940 M-bM-^@M-^\noM-bM-^@M-^]. If set to M-bM-^@M-^\yesM-bM-^@M-^], ssh(1) must be setuid root. Note that 941 this option must be set to M-bM-^@M-^\yesM-bM-^@M-^] for RhostsRSAAuthentication with 942 older servers. 943 944 User Specifies the user to log in as. This can be useful when a 945 different user name is used on different machines. This saves 946 the trouble of having to remember to give the user name on the 947 command line. 948 949 UserKnownHostsFile 950 Specifies one or more files to use for the user host key 951 database, separated by whitespace. The default is 952 ~/.ssh/known_hosts, ~/.ssh/known_hosts2. 953 954 VerifyHostKeyDNS 955 Specifies whether to verify the remote key using DNS and SSHFP 956 resource records. If this option is set to M-bM-^@M-^\yesM-bM-^@M-^], the client 957 will implicitly trust keys that match a secure fingerprint from 958 DNS. Insecure fingerprints will be handled as if this option was 959 set to M-bM-^@M-^\askM-bM-^@M-^]. If this option is set to M-bM-^@M-^\askM-bM-^@M-^], information on 960 fingerprint match will be displayed, but the user will still need 961 to confirm new host keys according to the StrictHostKeyChecking 962 option. The argument must be M-bM-^@M-^\yesM-bM-^@M-^], M-bM-^@M-^\noM-bM-^@M-^], or M-bM-^@M-^\askM-bM-^@M-^]. The default 963 is M-bM-^@M-^\noM-bM-^@M-^]. Note that this option applies to protocol version 2 964 only. 965 966 See also VERIFYING HOST KEYS in ssh(1). 967 968 VisualHostKey 969 If this flag is set to M-bM-^@M-^\yesM-bM-^@M-^], an ASCII art representation of the 970 remote host key fingerprint is printed in addition to the 971 fingerprint string at login and for unknown host keys. If this 972 flag is set to M-bM-^@M-^\noM-bM-^@M-^], no fingerprint strings are printed at login 973 and only the fingerprint string will be printed for unknown host 974 keys. The default is M-bM-^@M-^\noM-bM-^@M-^]. 975 976 XAuthLocation 977 Specifies the full pathname of the xauth(1) program. The default 978 is /usr/X11R6/bin/xauth. 979 980PATTERNS 981 A pattern consists of zero or more non-whitespace characters, M-bM-^@M-^X*M-bM-^@M-^Y (a 982 wildcard that matches zero or more characters), or M-bM-^@M-^X?M-bM-^@M-^Y (a wildcard that 983 matches exactly one character). For example, to specify a set of 984 declarations for any host in the M-bM-^@M-^\.co.ukM-bM-^@M-^] set of domains, the following 985 pattern could be used: 986 987 Host *.co.uk 988 989 The following pattern would match any host in the 192.168.0.[0-9] network 990 range: 991 992 Host 192.168.0.? 993 994 A pattern-list is a comma-separated list of patterns. Patterns within 995 pattern-lists may be negated by preceding them with an exclamation mark 996 (M-bM-^@M-^X!M-bM-^@M-^Y). For example, to allow a key to be used from anywhere within an 997 organization except from the M-bM-^@M-^\dialupM-bM-^@M-^] pool, the following entry (in 998 authorized_keys) could be used: 999 1000 from="!*.dialup.example.com,*.example.com" 1001 1002FILES 1003 ~/.ssh/config 1004 This is the per-user configuration file. The format of this file 1005 is described above. This file is used by the SSH client. 1006 Because of the potential for abuse, this file must have strict 1007 permissions: read/write for the user, and not accessible by 1008 others. 1009 1010 /etc/ssh/ssh_config 1011 Systemwide configuration file. This file provides defaults for 1012 those values that are not specified in the user's configuration 1013 file, and for those users who do not have a configuration file. 1014 This file must be world-readable. 1015 1016SEE ALSO 1017 ssh(1) 1018 1019AUTHORS 1020 OpenSSH is a derivative of the original and free ssh 1.2.12 release by 1021 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo 1022 de Raadt and Dug Song removed many bugs, re-added newer features and 1023 created OpenSSH. Markus Friedl contributed the support for SSH protocol 1024 versions 1.5 and 2.0. 1025 1026OpenBSD 5.8 August 14, 2015 OpenBSD 5.8 1027