sshd_config.0 revision 189006
1SSHD_CONFIG(5) OpenBSD Programmer's Manual SSHD_CONFIG(5) 2 3NAME 4 sshd_config - OpenSSH SSH daemon configuration file 5 6SYNOPSIS 7 /etc/ssh/sshd_config 8 9DESCRIPTION 10 sshd(8) reads configuration data from /etc/ssh/sshd_config (or the file 11 specified with -f on the command line). The file contains keyword-argu- 12 ment pairs, one per line. Lines starting with `#' and empty lines are 13 interpreted as comments. Arguments may optionally be enclosed in double 14 quotes (") in order to represent arguments containing spaces. 15 16 The possible keywords and their meanings are as follows (note that key- 17 words are case-insensitive and arguments are case-sensitive): 18 19 AcceptEnv 20 Specifies what environment variables sent by the client will be 21 copied into the session's environ(7). See SendEnv in 22 ssh_config(5) for how to configure the client. Note that envi- 23 ronment passing is only supported for protocol 2. Variables are 24 specified by name, which may contain the wildcard characters `*' 25 and `?'. Multiple environment variables may be separated by 26 whitespace or spread across multiple AcceptEnv directives. Be 27 warned that some environment variables could be used to bypass 28 restricted user environments. For this reason, care should be 29 taken in the use of this directive. The default is not to accept 30 any environment variables. 31 32 AddressFamily 33 Specifies which address family should be used by sshd(8). Valid 34 arguments are ``any'', ``inet'' (use IPv4 only), or ``inet6'' 35 (use IPv6 only). The default is ``any''. 36 37 AllowAgentForwarding 38 Specifies whether ssh-agent(1) forwarding is permitted. The de- 39 fault is ``yes''. Note that disabling agent forwarding does not 40 improve security unless users are also denied shell access, as 41 they can always install their own forwarders. 42 43 AllowGroups 44 This keyword can be followed by a list of group name patterns, 45 separated by spaces. If specified, login is allowed only for 46 users whose primary group or supplementary group list matches one 47 of the patterns. Only group names are valid; a numerical group 48 ID is not recognized. By default, login is allowed for all 49 groups. The allow/deny directives are processed in the following 50 order: DenyUsers, AllowUsers, DenyGroups, and finally 51 AllowGroups. 52 53 See PATTERNS in ssh_config(5) for more information on patterns. 54 55 AllowTcpForwarding 56 Specifies whether TCP forwarding is permitted. The default is 57 ``yes''. Note that disabling TCP forwarding does not improve se- 58 curity unless users are also denied shell access, as they can al- 59 ways install their own forwarders. 60 61 AllowUsers 62 This keyword can be followed by a list of user name patterns, 63 separated by spaces. If specified, login is allowed only for us- 64 er names that match one of the patterns. Only user names are 65 valid; a numerical user ID is not recognized. By default, login 66 is allowed for all users. If the pattern takes the form US- 67 ER@HOST then USER and HOST are separately checked, restricting 68 logins to particular users from particular hosts. The allow/deny 69 directives are processed in the following order: DenyUsers, 70 AllowUsers, DenyGroups, and finally AllowGroups. 71 72 See PATTERNS in ssh_config(5) for more information on patterns. 73 74 AuthorizedKeysFile 75 Specifies the file that contains the public keys that can be used 76 for user authentication. AuthorizedKeysFile may contain tokens 77 of the form %T which are substituted during connection setup. 78 The following tokens are defined: %% is replaced by a literal 79 '%', %h is replaced by the home directory of the user being au- 80 thenticated, and %u is replaced by the username of that user. 81 After expansion, AuthorizedKeysFile is taken to be an absolute 82 path or one relative to the user's home directory. The default 83 is ``.ssh/authorized_keys''. 84 85 Banner The contents of the specified file are sent to the remote user 86 before authentication is allowed. If the argument is ``none'' 87 then no banner is displayed. This option is only available for 88 protocol version 2. By default, no banner is displayed. 89 90 ChallengeResponseAuthentication 91 Specifies whether challenge-response authentication is allowed. 92 All authentication styles from login.conf(5) are supported. The 93 default is ``yes''. 94 95 ChrootDirectory 96 Specifies a path to chroot(2) to after authentication. This 97 path, and all its components, must be root-owned directories that 98 are not writable by any other user or group. 99 100 The path may contain the following tokens that are expanded at 101 runtime once the connecting user has been authenticated: %% is 102 replaced by a literal '%', %h is replaced by the home directory 103 of the user being authenticated, and %u is replaced by the user- 104 name of that user. 105 106 The ChrootDirectory must contain the necessary files and directo- 107 ries to support the users' session. For an interactive session 108 this requires at least a shell, typically sh(1), and basic /dev 109 nodes such as null(4), zero(4), stdin(4), stdout(4), stderr(4), 110 arandom(4) and tty(4) devices. For file transfer sessions using 111 ``sftp'', no additional configuration of the environment is nec- 112 essary if the in-process sftp server is used (see Subsystem for 113 details). 114 115 The default is not to chroot(2). 116 117 Ciphers 118 Specifies the ciphers allowed for protocol version 2. Multiple 119 ciphers must be comma-separated. The supported ciphers are 120 ``3des-cbc'', ``aes128-cbc'', ``aes192-cbc'', ``aes256-cbc'', 121 ``aes128-ctr'', ``aes192-ctr'', ``aes256-ctr'', ``arcfour128'', 122 ``arcfour256'', ``arcfour'', ``blowfish-cbc'', and 123 ``cast128-cbc''. The default is: 124 125 aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128, 126 aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc, 127 aes256-cbc,arcfour 128 129 ClientAliveCountMax 130 Sets the number of client alive messages (see below) which may be 131 sent without sshd(8) receiving any messages back from the client. 132 If this threshold is reached while client alive messages are be- 133 ing sent, sshd will disconnect the client, terminating the ses- 134 sion. It is important to note that the use of client alive mes- 135 sages is very different from TCPKeepAlive (below). The client 136 alive messages are sent through the encrypted channel and there- 137 fore will not be spoofable. The TCP keepalive option enabled by 138 TCPKeepAlive is spoofable. The client alive mechanism is valu- 139 able when the client or server depend on knowing when a connec- 140 tion has become inactive. 141 142 The default value is 3. If ClientAliveInterval (see below) is 143 set to 15, and ClientAliveCountMax is left at the default, unre- 144 sponsive SSH clients will be disconnected after approximately 45 145 seconds. This option applies to protocol version 2 only. 146 147 ClientAliveInterval 148 Sets a timeout interval in seconds after which if no data has 149 been received from the client, sshd(8) will send a message 150 through the encrypted channel to request a response from the 151 client. The default is 0, indicating that these messages will 152 not be sent to the client. This option applies to protocol ver- 153 sion 2 only. 154 155 Compression 156 Specifies whether compression is allowed, or delayed until the 157 user has authenticated successfully. The argument must be 158 ``yes'', ``delayed'', or ``no''. The default is ``delayed''. 159 160 DenyGroups 161 This keyword can be followed by a list of group name patterns, 162 separated by spaces. Login is disallowed for users whose primary 163 group or supplementary group list matches one of the patterns. 164 Only group names are valid; a numerical group ID is not recog- 165 nized. By default, login is allowed for all groups. The al- 166 low/deny directives are processed in the following order: 167 DenyUsers, AllowUsers, DenyGroups, and finally AllowGroups. 168 169 See PATTERNS in ssh_config(5) for more information on patterns. 170 171 DenyUsers 172 This keyword can be followed by a list of user name patterns, 173 separated by spaces. Login is disallowed for user names that 174 match one of the patterns. Only user names are valid; a numeri- 175 cal user ID is not recognized. By default, login is allowed for 176 all users. If the pattern takes the form USER@HOST then USER and 177 HOST are separately checked, restricting logins to particular 178 users from particular hosts. The allow/deny directives are pro- 179 cessed in the following order: DenyUsers, AllowUsers, DenyGroups, 180 and finally AllowGroups. 181 182 See PATTERNS in ssh_config(5) for more information on patterns. 183 184 ForceCommand 185 Forces the execution of the command specified by ForceCommand, 186 ignoring any command supplied by the client and ~/.ssh/rc if pre- 187 sent. The command is invoked by using the user's login shell 188 with the -c option. This applies to shell, command, or subsystem 189 execution. It is most useful inside a Match block. The command 190 originally supplied by the client is available in the 191 SSH_ORIGINAL_COMMAND environment variable. Specifying a command 192 of ``internal-sftp'' will force the use of an in-process sftp 193 server that requires no support files when used with 194 ChrootDirectory. 195 196 GatewayPorts 197 Specifies whether remote hosts are allowed to connect to ports 198 forwarded for the client. By default, sshd(8) binds remote port 199 forwardings to the loopback address. This prevents other remote 200 hosts from connecting to forwarded ports. GatewayPorts can be 201 used to specify that sshd should allow remote port forwardings to 202 bind to non-loopback addresses, thus allowing other hosts to con- 203 nect. The argument may be ``no'' to force remote port forward- 204 ings to be available to the local host only, ``yes'' to force re- 205 mote port forwardings to bind to the wildcard address, or 206 ``clientspecified'' to allow the client to select the address to 207 which the forwarding is bound. The default is ``no''. 208 209 GSSAPIAuthentication 210 Specifies whether user authentication based on GSSAPI is allowed. 211 The default is ``no''. Note that this option applies to protocol 212 version 2 only. 213 214 GSSAPICleanupCredentials 215 Specifies whether to automatically destroy the user's credentials 216 cache on logout. The default is ``yes''. Note that this option 217 applies to protocol version 2 only. 218 219 HostbasedAuthentication 220 Specifies whether rhosts or /etc/hosts.equiv authentication to- 221 gether with successful public key client host authentication is 222 allowed (host-based authentication). This option is similar to 223 RhostsRSAAuthentication and applies to protocol version 2 only. 224 The default is ``no''. 225 226 HostbasedUsesNameFromPacketOnly 227 Specifies whether or not the server will attempt to perform a re- 228 verse name lookup when matching the name in the ~/.shosts, 229 ~/.rhosts, and /etc/hosts.equiv files during 230 HostbasedAuthentication. A setting of ``yes'' means that sshd(8) 231 uses the name supplied by the client rather than attempting to 232 resolve the name from the TCP connection itself. The default is 233 ``no''. 234 235 HostKey 236 Specifies a file containing a private host key used by SSH. The 237 default is /etc/ssh/ssh_host_key for protocol version 1, and 238 /etc/ssh/ssh_host_rsa_key and /etc/ssh/ssh_host_dsa_key for pro- 239 tocol version 2. Note that sshd(8) will refuse to use a file if 240 it is group/world-accessible. It is possible to have multiple 241 host key files. ``rsa1'' keys are used for version 1 and ``dsa'' 242 or ``rsa'' are used for version 2 of the SSH protocol. 243 244 IgnoreRhosts 245 Specifies that .rhosts and .shosts files will not be used in 246 RhostsRSAAuthentication or HostbasedAuthentication. 247 248 /etc/hosts.equiv and /etc/shosts.equiv are still used. The de- 249 fault is ``yes''. 250 251 IgnoreUserKnownHosts 252 Specifies whether sshd(8) should ignore the user's 253 ~/.ssh/known_hosts during RhostsRSAAuthentication or 254 HostbasedAuthentication. The default is ``no''. 255 256 KerberosAuthentication 257 Specifies whether the password provided by the user for 258 PasswordAuthentication will be validated through the Kerberos 259 KDC. To use this option, the server needs a Kerberos servtab 260 which allows the verification of the KDC's identity. The default 261 is ``no''. 262 263 KerberosGetAFSToken 264 If AFS is active and the user has a Kerberos 5 TGT, attempt to 265 acquire an AFS token before accessing the user's home directory. 266 The default is ``no''. 267 268 KerberosOrLocalPasswd 269 If password authentication through Kerberos fails then the pass- 270 word will be validated via any additional local mechanism such as 271 /etc/passwd. The default is ``yes''. 272 273 KerberosTicketCleanup 274 Specifies whether to automatically destroy the user's ticket 275 cache file on logout. The default is ``yes''. 276 277 KeyRegenerationInterval 278 In protocol version 1, the ephemeral server key is automatically 279 regenerated after this many seconds (if it has been used). The 280 purpose of regeneration is to prevent decrypting captured ses- 281 sions by later breaking into the machine and stealing the keys. 282 The key is never stored anywhere. If the value is 0, the key is 283 never regenerated. The default is 3600 (seconds). 284 285 ListenAddress 286 Specifies the local addresses sshd(8) should listen on. The fol- 287 lowing forms may be used: 288 289 ListenAddress host|IPv4_addr|IPv6_addr 290 ListenAddress host|IPv4_addr:port 291 ListenAddress [host|IPv6_addr]:port 292 293 If port is not specified, sshd will listen on the address and all 294 prior Port options specified. The default is to listen on all 295 local addresses. Multiple ListenAddress options are permitted. 296 Additionally, any Port options must precede this option for non- 297 port qualified addresses. 298 299 LoginGraceTime 300 The server disconnects after this time if the user has not suc- 301 cessfully logged in. If the value is 0, there is no time limit. 302 The default is 120 seconds. 303 304 LogLevel 305 Gives the verbosity level that is used when logging messages from 306 sshd(8). The possible values are: QUIET, FATAL, ERROR, INFO, 307 VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO. 308 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify 309 higher levels of debugging output. Logging with a DEBUG level 310 violates the privacy of users and is not recommended. 311 312 MACs Specifies the available MAC (message authentication code) algo- 313 rithms. The MAC algorithm is used in protocol version 2 for data 314 integrity protection. Multiple algorithms must be comma-separat- 315 ed. The default is: 316 317 hmac-md5,hmac-sha1,umac-64@openssh.com, 318 hmac-ripemd160,hmac-sha1-96,hmac-md5-96 319 320 Match Introduces a conditional block. If all of the criteria on the 321 Match line are satisfied, the keywords on the following lines 322 override those set in the global section of the config file, un- 323 til either another Match line or the end of the file. 324 325 The arguments to Match are one or more criteria-pattern pairs. 326 The available criteria are User, Group, Host, and Address. The 327 match patterns may consist of single entries or comma-separated 328 lists and may use the wildcard and negation operators described 329 in the PATTERNS section of ssh_config(5). 330 331 The patterns in an Address criteria may additionally contain ad- 332 dresses to match in CIDR address/masklen format, e.g. 333 ``192.0.2.0/24'' or ``3ffe:ffff::/32''. Note that the mask 334 length provided must be consistent with the address - it is an 335 error to specify a mask length that is too long for the address 336 or one with bits set in this host portion of the address. For 337 example, ``192.0.2.0/33'' and ``192.0.2.0/8'' respectively. 338 339 Only a subset of keywords may be used on the lines following a 340 Match keyword. Available keywords are AllowAgentForwarding, 341 AllowTcpForwarding, Banner, ChrootDirectory, ForceCommand, 342 GatewayPorts, GSSAPIAuthentication, HostbasedAuthentication, 343 KbdInteractiveAuthentication, KerberosAuthentication, 344 MaxAuthTries, MaxSessions, PasswordAuthentication, 345 PermitEmptyPasswords, PermitOpen, PermitRootLogin, 346 RhostsRSAAuthentication, RSAAuthentication, X11DisplayOffset, 347 X11Forwarding and X11UseLocalHost. 348 349 MaxAuthTries 350 Specifies the maximum number of authentication attempts permitted 351 per connection. Once the number of failures reaches half this 352 value, additional failures are logged. The default is 6. 353 354 MaxSessions 355 Specifies the maximum number of open sessions permitted per net- 356 work connection. The default is 10. 357 358 MaxStartups 359 Specifies the maximum number of concurrent unauthenticated con- 360 nections to the SSH daemon. Additional connections will be 361 dropped until authentication succeeds or the LoginGraceTime ex- 362 pires for a connection. The default is 10. 363 364 Alternatively, random early drop can be enabled by specifying the 365 three colon separated values ``start:rate:full'' (e.g. 366 "10:30:60"). sshd(8) will refuse connection attempts with a 367 probability of ``rate/100'' (30%) if there are currently 368 ``start'' (10) unauthenticated connections. The probability in- 369 creases linearly and all connection attempts are refused if the 370 number of unauthenticated connections reaches ``full'' (60). 371 372 PasswordAuthentication 373 Specifies whether password authentication is allowed. The de- 374 fault is ``yes''. 375 376 PermitEmptyPasswords 377 When password authentication is allowed, it specifies whether the 378 server allows login to accounts with empty password strings. The 379 default is ``no''. 380 381 PermitOpen 382 Specifies the destinations to which TCP port forwarding is per- 383 mitted. The forwarding specification must be one of the follow- 384 ing forms: 385 386 PermitOpen host:port 387 PermitOpen IPv4_addr:port 388 PermitOpen [IPv6_addr]:port 389 390 Multiple forwards may be specified by separating them with 391 whitespace. An argument of ``any'' can be used to remove all re- 392 strictions and permit any forwarding requests. By default all 393 port forwarding requests are permitted. 394 395 PermitRootLogin 396 Specifies whether root can log in using ssh(1). The argument 397 must be ``yes'', ``without-password'', ``forced-commands-only'', 398 or ``no''. The default is ``yes''. 399 400 If this option is set to ``without-password'', password authenti- 401 cation is disabled for root. 402 403 If this option is set to ``forced-commands-only'', root login 404 with public key authentication will be allowed, but only if the 405 command option has been specified (which may be useful for taking 406 remote backups even if root login is normally not allowed). All 407 other authentication methods are disabled for root. 408 409 If this option is set to ``no'', root is not allowed to log in. 410 411 PermitTunnel 412 Specifies whether tun(4) device forwarding is allowed. The argu- 413 ment must be ``yes'', ``point-to-point'' (layer 3), ``ethernet'' 414 (layer 2), or ``no''. Specifying ``yes'' permits both ``point- 415 to-point'' and ``ethernet''. The default is ``no''. 416 417 PermitUserEnvironment 418 Specifies whether ~/.ssh/environment and environment= options in 419 ~/.ssh/authorized_keys are processed by sshd(8). The default is 420 ``no''. Enabling environment processing may enable users to by- 421 pass access restrictions in some configurations using mechanisms 422 such as LD_PRELOAD. 423 424 PidFile 425 Specifies the file that contains the process ID of the SSH dae- 426 mon. The default is /var/run/sshd.pid. 427 428 Port Specifies the port number that sshd(8) listens on. The default 429 is 22. Multiple options of this type are permitted. See also 430 ListenAddress. 431 432 PrintLastLog 433 Specifies whether sshd(8) should print the date and time of the 434 last user login when a user logs in interactively. The default 435 is ``yes''. 436 437 PrintMotd 438 Specifies whether sshd(8) should print /etc/motd when a user logs 439 in interactively. (On some systems it is also printed by the 440 shell, /etc/profile, or equivalent.) The default is ``yes''. 441 442 Protocol 443 Specifies the protocol versions sshd(8) supports. The possible 444 values are `1' and `2'. Multiple versions must be comma-separat- 445 ed. The default is ``2,1''. Note that the order of the protocol 446 list does not indicate preference, because the client selects 447 among multiple protocol versions offered by the server. Specify- 448 ing ``2,1'' is identical to ``1,2''. 449 450 PubkeyAuthentication 451 Specifies whether public key authentication is allowed. The de- 452 fault is ``yes''. Note that this option applies to protocol ver- 453 sion 2 only. 454 455 RhostsRSAAuthentication 456 Specifies whether rhosts or /etc/hosts.equiv authentication to- 457 gether with successful RSA host authentication is allowed. The 458 default is ``no''. This option applies to protocol version 1 on- 459 ly. 460 461 RSAAuthentication 462 Specifies whether pure RSA authentication is allowed. The de- 463 fault is ``yes''. This option applies to protocol version 1 on- 464 ly. 465 466 ServerKeyBits 467 Defines the number of bits in the ephemeral protocol version 1 468 server key. The minimum value is 512, and the default is 1024. 469 470 StrictModes 471 Specifies whether sshd(8) should check file modes and ownership 472 of the user's files and home directory before accepting login. 473 This is normally desirable because novices sometimes accidentally 474 leave their directory or files world-writable. The default is 475 ``yes''. 476 477 Subsystem 478 Configures an external subsystem (e.g. file transfer daemon). 479 Arguments should be a subsystem name and a command (with optional 480 arguments) to execute upon subsystem request. 481 482 The command sftp-server(8) implements the ``sftp'' file transfer 483 subsystem. 484 485 Alternately the name ``internal-sftp'' implements an in-process 486 ``sftp'' server. This may simplify configurations using 487 ChrootDirectory to force a different filesystem root on clients. 488 489 By default no subsystems are defined. Note that this option ap- 490 plies to protocol version 2 only. 491 492 SyslogFacility 493 Gives the facility code that is used when logging messages from 494 sshd(8). The possible values are: DAEMON, USER, AUTH, LOCAL0, 495 LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The de- 496 fault is AUTH. 497 498 TCPKeepAlive 499 Specifies whether the system should send TCP keepalive messages 500 to the other side. If they are sent, death of the connection or 501 crash of one of the machines will be properly noticed. However, 502 this means that connections will die if the route is down tem- 503 porarily, and some people find it annoying. On the other hand, 504 if TCP keepalives are not sent, sessions may hang indefinitely on 505 the server, leaving ``ghost'' users and consuming server re- 506 sources. 507 508 The default is ``yes'' (to send TCP keepalive messages), and the 509 server will notice if the network goes down or the client host 510 crashes. This avoids infinitely hanging sessions. 511 512 To disable TCP keepalive messages, the value should be set to 513 ``no''. 514 515 UseDNS Specifies whether sshd(8) should look up the remote host name and 516 check that the resolved host name for the remote IP address maps 517 back to the very same IP address. The default is ``yes''. 518 519 UseLogin 520 Specifies whether login(1) is used for interactive login ses- 521 sions. The default is ``no''. Note that login(1) is never used 522 for remote command execution. Note also, that if this is en- 523 abled, X11Forwarding will be disabled because login(1) does not 524 know how to handle xauth(1) cookies. If UsePrivilegeSeparation 525 is specified, it will be disabled after authentication. 526 527 UsePAM Enables the Pluggable Authentication Module interface. If set to 528 ``yes'' this will enable PAM authentication using 529 ChallengeResponseAuthentication and PasswordAuthentication in ad- 530 dition to PAM account and session module processing for all au- 531 thentication types. 532 533 Because PAM challenge-response authentication usually serves an 534 equivalent role to password authentication, you should disable 535 either PasswordAuthentication or ChallengeResponseAuthentication. 536 537 If UsePAM is enabled, you will not be able to run sshd(8) as a 538 non-root user. The default is ``no''. 539 540 UsePrivilegeSeparation 541 Specifies whether sshd(8) separates privileges by creating an un- 542 privileged child process to deal with incoming network traffic. 543 After successful authentication, another process will be created 544 that has the privilege of the authenticated user. The goal of 545 privilege separation is to prevent privilege escalation by con- 546 taining any corruption within the unprivileged processes. The 547 default is ``yes''. 548 549 X11DisplayOffset 550 Specifies the first display number available for sshd(8)'s X11 551 forwarding. This prevents sshd from interfering with real X11 552 servers. The default is 10. 553 554 X11Forwarding 555 Specifies whether X11 forwarding is permitted. The argument must 556 be ``yes'' or ``no''. The default is ``no''. 557 558 When X11 forwarding is enabled, there may be additional exposure 559 to the server and to client displays if the sshd(8) proxy display 560 is configured to listen on the wildcard address (see 561 X11UseLocalhost below), though this is not the default. Addi- 562 tionally, the authentication spoofing and authentication data 563 verification and substitution occur on the client side. The se- 564 curity risk of using X11 forwarding is that the client's X11 dis- 565 play server may be exposed to attack when the SSH client requests 566 forwarding (see the warnings for ForwardX11 in ssh_config(5)). A 567 system administrator may have a stance in which they want to pro- 568 tect clients that may expose themselves to attack by unwittingly 569 requesting X11 forwarding, which can warrant a ``no'' setting. 570 571 Note that disabling X11 forwarding does not prevent users from 572 forwarding X11 traffic, as users can always install their own 573 forwarders. X11 forwarding is automatically disabled if UseLogin 574 is enabled. 575 576 X11UseLocalhost 577 Specifies whether sshd(8) should bind the X11 forwarding server 578 to the loopback address or to the wildcard address. By default, 579 sshd binds the forwarding server to the loopback address and sets 580 the hostname part of the DISPLAY environment variable to 581 ``localhost''. This prevents remote hosts from connecting to the 582 proxy display. However, some older X11 clients may not function 583 with this configuration. X11UseLocalhost may be set to ``no'' to 584 specify that the forwarding server should be bound to the wild- 585 card address. The argument must be ``yes'' or ``no''. The de- 586 fault is ``yes''. 587 588 XAuthLocation 589 Specifies the full pathname of the xauth(1) program. The default 590 is /usr/X11R6/bin/xauth. 591 592TIME FORMATS 593 sshd(8) command-line arguments and configuration file options that speci- 594 fy time may be expressed using a sequence of the form: time[qualifier], 595 where time is a positive integer value and qualifier is one of the fol- 596 lowing: 597 598 <none> seconds 599 s | S seconds 600 m | M minutes 601 h | H hours 602 d | D days 603 w | W weeks 604 605 Each member of the sequence is added together to calculate the total time 606 value. 607 608 Time format examples: 609 610 600 600 seconds (10 minutes) 611 10m 10 minutes 612 1h30m 1 hour 30 minutes (90 minutes) 613 614FILES 615 /etc/ssh/sshd_config 616 Contains configuration data for sshd(8). This file should be 617 writable by root only, but it is recommended (though not neces- 618 sary) that it be world-readable. 619 620SEE ALSO 621 sshd(8) 622 623AUTHORS 624 OpenSSH is a derivative of the original and free ssh 1.2.12 release by 625 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo 626 de Raadt and Dug Song removed many bugs, re-added newer features and cre- 627 ated OpenSSH. Markus Friedl contributed the support for SSH protocol 628 versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support 629 for privilege separation. 630 631OpenBSD 4.5 February 22, 2009 10 632