sshd_config.0 revision 214979
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- 12 argument pairs, one per line. Lines starting with `#' and empty lines 13 are interpreted as comments. Arguments may optionally be enclosed in 14 double quotes (") in order to represent arguments containing spaces. 15 16 The possible keywords and their meanings are as follows (note that 17 keywords 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 23 environment passing is only supported for protocol 2. Variables 24 are 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 39 default is ``yes''. Note that disabling agent forwarding does 40 not improve security unless users are also denied shell access, 41 as 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 58 security unless users are also denied shell access, as they can 59 always 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 64 user 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 67 USER@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. The format is described in the 77 AUTHORIZED_KEYS FILE FORMAT section of sshd(8). 78 AuthorizedKeysFile may contain tokens of the form %T which are 79 substituted during connection setup. The following tokens are 80 defined: %% is replaced by a literal '%', %h is replaced by the 81 home directory of the user being authenticated, and %u is 82 replaced by the username of that user. After expansion, 83 AuthorizedKeysFile is taken to be an absolute path or one 84 relative to the user's home directory. The default is 85 ``.ssh/authorized_keys''. 86 87 AuthorizedPrincipalsFile 88 Specifies a file that lists principal names that are accepted for 89 certificate authentication. When using certificates signed by a 90 key listed in TrustedUserCAKeys, this file lists names, one of 91 which must appear in the certificate for it to be accepted for 92 authentication. Names are listed one per line preceded by key 93 options (as described in AUTHORIZED_KEYS FILE FORMAT in sshd(8)). 94 Empty lines and comments starting with `#' are ignored. 95 96 AuthorizedPrincipalsFile may contain tokens of the form %T which 97 are substituted during connection setup. The following tokens 98 are defined: %% is replaced by a literal '%', %h is replaced by 99 the home directory of the user being authenticated, and %u is 100 replaced by the username of that user. After expansion, 101 AuthorizedPrincipalsFile is taken to be an absolute path or one 102 relative to the user's home directory. 103 104 The default is not to use a principals file - in this case, the 105 username of the user must appear in a certificate's principals 106 list for it to be accepted. Note that AuthorizedPrincipalsFile 107 is only used when authentication proceeds using a CA listed in 108 TrustedUserCAKeys and is not consulted for certification 109 authorities trusted via ~/.ssh/authorized_keys, though the 110 principals= key option offers a similar facility (see sshd(8) for 111 details). 112 113 Banner The contents of the specified file are sent to the remote user 114 before authentication is allowed. If the argument is ``none'' 115 then no banner is displayed. This option is only available for 116 protocol version 2. By default, no banner is displayed. 117 118 ChallengeResponseAuthentication 119 Specifies whether challenge-response authentication is allowed 120 (e.g. via PAM or though authentication styles supported in 121 login.conf(5)) The default is ``yes''. 122 123 ChrootDirectory 124 Specifies the pathname of a directory to chroot(2) to after 125 authentication. All components of the pathname must be root- 126 owned directories that are not writable by any other user or 127 group. After the chroot, sshd(8) changes the working directory 128 to the user's home directory. 129 130 The pathname may contain the following tokens that are expanded 131 at runtime once the connecting user has been authenticated: %% is 132 replaced by a literal '%', %h is replaced by the home directory 133 of the user being authenticated, and %u is replaced by the 134 username of that user. 135 136 The ChrootDirectory must contain the necessary files and 137 directories to support the user's session. For an interactive 138 session this requires at least a shell, typically sh(1), and 139 basic /dev nodes such as null(4), zero(4), stdin(4), stdout(4), 140 stderr(4), arandom(4) and tty(4) devices. For file transfer 141 sessions using ``sftp'', no additional configuration of the 142 environment is necessary if the in-process sftp server is used, 143 though sessions which use logging do require /dev/log inside the 144 chroot directory (see sftp-server(8) for details). 145 146 The default is not to chroot(2). 147 148 Ciphers 149 Specifies the ciphers allowed for protocol version 2. Multiple 150 ciphers must be comma-separated. The supported ciphers are 151 ``3des-cbc'', ``aes128-cbc'', ``aes192-cbc'', ``aes256-cbc'', 152 ``aes128-ctr'', ``aes192-ctr'', ``aes256-ctr'', ``arcfour128'', 153 ``arcfour256'', ``arcfour'', ``blowfish-cbc'', and 154 ``cast128-cbc''. The default is: 155 156 aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128, 157 aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc, 158 aes256-cbc,arcfour 159 160 ClientAliveCountMax 161 Sets the number of client alive messages (see below) which may be 162 sent without sshd(8) receiving any messages back from the client. 163 If this threshold is reached while client alive messages are 164 being sent, sshd will disconnect the client, terminating the 165 session. It is important to note that the use of client alive 166 messages is very different from TCPKeepAlive (below). The client 167 alive messages are sent through the encrypted channel and 168 therefore will not be spoofable. The TCP keepalive option 169 enabled by TCPKeepAlive is spoofable. The client alive mechanism 170 is valuable when the client or server depend on knowing when a 171 connection has become inactive. 172 173 The default value is 3. If ClientAliveInterval (see below) is 174 set to 15, and ClientAliveCountMax is left at the default, 175 unresponsive SSH clients will be disconnected after approximately 176 45 seconds. This option applies to protocol version 2 only. 177 178 ClientAliveInterval 179 Sets a timeout interval in seconds after which if no data has 180 been received from the client, sshd(8) will send a message 181 through the encrypted channel to request a response from the 182 client. The default is 0, indicating that these messages will 183 not be sent to the client. This option applies to protocol 184 version 2 only. 185 186 Compression 187 Specifies whether compression is allowed, or delayed until the 188 user has authenticated successfully. The argument must be 189 ``yes'', ``delayed'', or ``no''. The default is ``delayed''. 190 191 DenyGroups 192 This keyword can be followed by a list of group name patterns, 193 separated by spaces. Login is disallowed for users whose primary 194 group or supplementary group list matches one of the patterns. 195 Only group names are valid; a numerical group ID is not 196 recognized. By default, login is allowed for all groups. The 197 allow/deny directives are processed in the following order: 198 DenyUsers, AllowUsers, DenyGroups, and finally AllowGroups. 199 200 See PATTERNS in ssh_config(5) for more information on patterns. 201 202 DenyUsers 203 This keyword can be followed by a list of user name patterns, 204 separated by spaces. Login is disallowed for user names that 205 match one of the patterns. Only user names are valid; a 206 numerical user ID is not recognized. By default, login is 207 allowed for all users. If the pattern takes the form USER@HOST 208 then USER and HOST are separately checked, restricting logins to 209 particular users from particular hosts. The allow/deny 210 directives are processed in the following order: DenyUsers, 211 AllowUsers, DenyGroups, and finally AllowGroups. 212 213 See PATTERNS in ssh_config(5) for more information on patterns. 214 215 ForceCommand 216 Forces the execution of the command specified by ForceCommand, 217 ignoring any command supplied by the client and ~/.ssh/rc if 218 present. The command is invoked by using the user's login shell 219 with the -c option. This applies to shell, command, or subsystem 220 execution. It is most useful inside a Match block. The command 221 originally supplied by the client is available in the 222 SSH_ORIGINAL_COMMAND environment variable. Specifying a command 223 of ``internal-sftp'' will force the use of an in-process sftp 224 server that requires no support files when used with 225 ChrootDirectory. 226 227 GatewayPorts 228 Specifies whether remote hosts are allowed to connect to ports 229 forwarded for the client. By default, sshd(8) binds remote port 230 forwardings to the loopback address. This prevents other remote 231 hosts from connecting to forwarded ports. GatewayPorts can be 232 used to specify that sshd should allow remote port forwardings to 233 bind to non-loopback addresses, thus allowing other hosts to 234 connect. The argument may be ``no'' to force remote port 235 forwardings to be available to the local host only, ``yes'' to 236 force remote port forwardings to bind to the wildcard address, or 237 ``clientspecified'' to allow the client to select the address to 238 which the forwarding is bound. The default is ``no''. 239 240 GSSAPIAuthentication 241 Specifies whether user authentication based on GSSAPI is allowed. 242 The default is ``no''. Note that this option applies to protocol 243 version 2 only. 244 245 GSSAPICleanupCredentials 246 Specifies whether to automatically destroy the user's credentials 247 cache on logout. The default is ``yes''. Note that this option 248 applies to protocol version 2 only. 249 250 HostbasedAuthentication 251 Specifies whether rhosts or /etc/hosts.equiv authentication 252 together with successful public key client host authentication is 253 allowed (host-based authentication). This option is similar to 254 RhostsRSAAuthentication and applies to protocol version 2 only. 255 The default is ``no''. 256 257 HostbasedUsesNameFromPacketOnly 258 Specifies whether or not the server will attempt to perform a 259 reverse name lookup when matching the name in the ~/.shosts, 260 ~/.rhosts, and /etc/hosts.equiv files during 261 HostbasedAuthentication. A setting of ``yes'' means that sshd(8) 262 uses the name supplied by the client rather than attempting to 263 resolve the name from the TCP connection itself. The default is 264 ``no''. 265 266 HostCertificate 267 Specifies a file containing a public host certificate. The 268 certificate's public key must match a private host key already 269 specified by HostKey. The default behaviour of sshd(8) is not to 270 load any certificates. 271 272 HostKey 273 Specifies a file containing a private host key used by SSH. The 274 default is /etc/ssh/ssh_host_key for protocol version 1, and 275 /etc/ssh/ssh_host_rsa_key and /etc/ssh/ssh_host_dsa_key for 276 protocol version 2. Note that sshd(8) will refuse to use a file 277 if it is group/world-accessible. It is possible to have multiple 278 host key files. ``rsa1'' keys are used for version 1 and ``dsa'' 279 or ``rsa'' are used for version 2 of the SSH protocol. 280 281 IgnoreRhosts 282 Specifies that .rhosts and .shosts files will not be used in 283 RhostsRSAAuthentication or HostbasedAuthentication. 284 285 /etc/hosts.equiv and /etc/shosts.equiv are still used. The 286 default is ``yes''. 287 288 IgnoreUserKnownHosts 289 Specifies whether sshd(8) should ignore the user's 290 ~/.ssh/known_hosts during RhostsRSAAuthentication or 291 HostbasedAuthentication. The default is ``no''. 292 293 KerberosAuthentication 294 Specifies whether the password provided by the user for 295 PasswordAuthentication will be validated through the Kerberos 296 KDC. To use this option, the server needs a Kerberos servtab 297 which allows the verification of the KDC's identity. The default 298 is ``no''. 299 300 KerberosGetAFSToken 301 If AFS is active and the user has a Kerberos 5 TGT, attempt to 302 acquire an AFS token before accessing the user's home directory. 303 The default is ``no''. 304 305 KerberosOrLocalPasswd 306 If password authentication through Kerberos fails then the 307 password will be validated via any additional local mechanism 308 such as /etc/passwd. The default is ``yes''. 309 310 KerberosTicketCleanup 311 Specifies whether to automatically destroy the user's ticket 312 cache file on logout. The default is ``yes''. 313 314 KeyRegenerationInterval 315 In protocol version 1, the ephemeral server key is automatically 316 regenerated after this many seconds (if it has been used). The 317 purpose of regeneration is to prevent decrypting captured 318 sessions by later breaking into the machine and stealing the 319 keys. The key is never stored anywhere. If the value is 0, the 320 key is never regenerated. The default is 3600 (seconds). 321 322 ListenAddress 323 Specifies the local addresses sshd(8) should listen on. The 324 following forms may be used: 325 326 ListenAddress host | IPv4_addr | IPv6_addr 327 ListenAddress host | IPv4_addr:port 328 ListenAddress [host|IPv6_addr]:port 329 330 If port is not specified, sshd will listen on the address and all 331 prior Port options specified. The default is to listen on all 332 local addresses. Multiple ListenAddress options are permitted. 333 Additionally, any Port options must precede this option for non- 334 port qualified addresses. 335 336 LoginGraceTime 337 The server disconnects after this time if the user has not 338 successfully logged in. If the value is 0, there is no time 339 limit. The default is 120 seconds. 340 341 LogLevel 342 Gives the verbosity level that is used when logging messages from 343 sshd(8). The possible values are: QUIET, FATAL, ERROR, INFO, 344 VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO. 345 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify 346 higher levels of debugging output. Logging with a DEBUG level 347 violates the privacy of users and is not recommended. 348 349 MACs Specifies the available MAC (message authentication code) 350 algorithms. The MAC algorithm is used in protocol version 2 for 351 data integrity protection. Multiple algorithms must be comma- 352 separated. The default is: 353 354 hmac-md5,hmac-sha1,umac-64@openssh.com, 355 hmac-ripemd160,hmac-sha1-96,hmac-md5-96 356 357 Match Introduces a conditional block. If all of the criteria on the 358 Match line are satisfied, the keywords on the following lines 359 override those set in the global section of the config file, 360 until either another Match line or the end of the file. 361 362 The arguments to Match are one or more criteria-pattern pairs. 363 The available criteria are User, Group, Host, and Address. The 364 match patterns may consist of single entries or comma-separated 365 lists and may use the wildcard and negation operators described 366 in the PATTERNS section of ssh_config(5). 367 368 The patterns in an Address criteria may additionally contain 369 addresses to match in CIDR address/masklen format, e.g. 370 ``192.0.2.0/24'' or ``3ffe:ffff::/32''. Note that the mask 371 length provided must be consistent with the address - it is an 372 error to specify a mask length that is too long for the address 373 or one with bits set in this host portion of the address. For 374 example, ``192.0.2.0/33'' and ``192.0.2.0/8'' respectively. 375 376 Only a subset of keywords may be used on the lines following a 377 Match keyword. Available keywords are AllowAgentForwarding, 378 AllowTcpForwarding, AuthorizedKeysFile, AuthorizedPrincipalsFile, 379 Banner, ChrootDirectory, ForceCommand, GatewayPorts, 380 GSSAPIAuthentication, HostbasedAuthentication, 381 HostbasedUsesNameFromPacketOnly, KbdInteractiveAuthentication, 382 KerberosAuthentication, MaxAuthTries, MaxSessions, 383 PasswordAuthentication, PermitEmptyPasswords, PermitOpen, 384 PermitRootLogin, PermitTunnel, PubkeyAuthentication, 385 RhostsRSAAuthentication, RSAAuthentication, X11DisplayOffset, 386 X11Forwarding and X11UseLocalHost. 387 388 MaxAuthTries 389 Specifies the maximum number of authentication attempts permitted 390 per connection. Once the number of failures reaches half this 391 value, additional failures are logged. The default is 6. 392 393 MaxSessions 394 Specifies the maximum number of open sessions permitted per 395 network connection. The default is 10. 396 397 MaxStartups 398 Specifies the maximum number of concurrent unauthenticated 399 connections to the SSH daemon. Additional connections will be 400 dropped until authentication succeeds or the LoginGraceTime 401 expires for a connection. The default is 10. 402 403 Alternatively, random early drop can be enabled by specifying the 404 three colon separated values ``start:rate:full'' (e.g. 405 "10:30:60"). sshd(8) will refuse connection attempts with a 406 probability of ``rate/100'' (30%) if there are currently 407 ``start'' (10) unauthenticated connections. The probability 408 increases linearly and all connection attempts are refused if the 409 number of unauthenticated connections reaches ``full'' (60). 410 411 PasswordAuthentication 412 Specifies whether password authentication is allowed. The 413 default is ``yes''. 414 415 PermitEmptyPasswords 416 When password authentication is allowed, it specifies whether the 417 server allows login to accounts with empty password strings. The 418 default is ``no''. 419 420 PermitOpen 421 Specifies the destinations to which TCP port forwarding is 422 permitted. The forwarding specification must be one of the 423 following forms: 424 425 PermitOpen host:port 426 PermitOpen IPv4_addr:port 427 PermitOpen [ IPv6_addr ]:port 428 429 Multiple forwards may be specified by separating them with 430 whitespace. An argument of ``any'' can be used to remove all 431 restrictions and permit any forwarding requests. By default all 432 port forwarding requests are permitted. 433 434 PermitRootLogin 435 Specifies whether root can log in using ssh(1). The argument 436 must be ``yes'', ``without-password'', ``forced-commands-only'', 437 or ``no''. The default is ``yes''. 438 439 If this option is set to ``without-password'', password 440 authentication is disabled for root. 441 442 If this option is set to ``forced-commands-only'', root login 443 with public key authentication will be allowed, but only if the 444 command option has been specified (which may be useful for taking 445 remote backups even if root login is normally not allowed). All 446 other authentication methods are disabled for root. 447 448 If this option is set to ``no'', root is not allowed to log in. 449 450 PermitTunnel 451 Specifies whether tun(4) device forwarding is allowed. The 452 argument must be ``yes'', ``point-to-point'' (layer 3), 453 ``ethernet'' (layer 2), or ``no''. Specifying ``yes'' permits 454 both ``point-to-point'' and ``ethernet''. The default is ``no''. 455 456 PermitUserEnvironment 457 Specifies whether ~/.ssh/environment and environment= options in 458 ~/.ssh/authorized_keys are processed by sshd(8). The default is 459 ``no''. Enabling environment processing may enable users to 460 bypass access restrictions in some configurations using 461 mechanisms such as LD_PRELOAD. 462 463 PidFile 464 Specifies the file that contains the process ID of the SSH 465 daemon. The default is /var/run/sshd.pid. 466 467 Port Specifies the port number that sshd(8) listens on. The default 468 is 22. Multiple options of this type are permitted. See also 469 ListenAddress. 470 471 PrintLastLog 472 Specifies whether sshd(8) should print the date and time of the 473 last user login when a user logs in interactively. The default 474 is ``yes''. 475 476 PrintMotd 477 Specifies whether sshd(8) should print /etc/motd when a user logs 478 in interactively. (On some systems it is also printed by the 479 shell, /etc/profile, or equivalent.) The default is ``yes''. 480 481 Protocol 482 Specifies the protocol versions sshd(8) supports. The possible 483 values are `1' and `2'. Multiple versions must be comma- 484 separated. The default is `2'. Note that the order of the 485 protocol list does not indicate preference, because the client 486 selects among multiple protocol versions offered by the server. 487 Specifying ``2,1'' is identical to ``1,2''. 488 489 PubkeyAuthentication 490 Specifies whether public key authentication is allowed. The 491 default is ``yes''. Note that this option applies to protocol 492 version 2 only. 493 494 RevokedKeys 495 Specifies a list of revoked public keys. Keys listed in this 496 file will be refused for public key authentication. Note that if 497 this file is not readable, then public key authentication will be 498 refused for all users. 499 500 RhostsRSAAuthentication 501 Specifies whether rhosts or /etc/hosts.equiv authentication 502 together with successful RSA host authentication is allowed. The 503 default is ``no''. This option applies to protocol version 1 504 only. 505 506 RSAAuthentication 507 Specifies whether pure RSA authentication is allowed. The 508 default is ``yes''. This option applies to protocol version 1 509 only. 510 511 ServerKeyBits 512 Defines the number of bits in the ephemeral protocol version 1 513 server key. The minimum value is 512, and the default is 1024. 514 515 StrictModes 516 Specifies whether sshd(8) should check file modes and ownership 517 of the user's files and home directory before accepting login. 518 This is normally desirable because novices sometimes accidentally 519 leave their directory or files world-writable. The default is 520 ``yes''. Note that this does not apply to ChrootDirectory, whose 521 permissions and ownership are checked unconditionally. 522 523 Subsystem 524 Configures an external subsystem (e.g. file transfer daemon). 525 Arguments should be a subsystem name and a command (with optional 526 arguments) to execute upon subsystem request. 527 528 The command sftp-server(8) implements the ``sftp'' file transfer 529 subsystem. 530 531 Alternately the name ``internal-sftp'' implements an in-process 532 ``sftp'' server. This may simplify configurations using 533 ChrootDirectory to force a different filesystem root on clients. 534 535 By default no subsystems are defined. Note that this option 536 applies to protocol version 2 only. 537 538 SyslogFacility 539 Gives the facility code that is used when logging messages from 540 sshd(8). The possible values are: DAEMON, USER, AUTH, LOCAL0, 541 LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The 542 default is AUTH. 543 544 TCPKeepAlive 545 Specifies whether the system should send TCP keepalive messages 546 to the other side. If they are sent, death of the connection or 547 crash of one of the machines will be properly noticed. However, 548 this means that connections will die if the route is down 549 temporarily, and some people find it annoying. On the other 550 hand, if TCP keepalives are not sent, sessions may hang 551 indefinitely on the server, leaving ``ghost'' users and consuming 552 server resources. 553 554 The default is ``yes'' (to send TCP keepalive messages), and the 555 server will notice if the network goes down or the client host 556 crashes. This avoids infinitely hanging sessions. 557 558 To disable TCP keepalive messages, the value should be set to 559 ``no''. 560 561 TrustedUserCAKeys 562 Specifies a file containing public keys of certificate 563 authorities that are trusted to sign user certificates for 564 authentication. Keys are listed one per line; empty lines and 565 comments starting with `#' are allowed. If a certificate is 566 presented for authentication and has its signing CA key listed in 567 this file, then it may be used for authentication for any user 568 listed in the certificate's principals list. Note that 569 certificates that lack a list of principals will not be permitted 570 for authentication using TrustedUserCAKeys. For more details on 571 certificates, see the CERTIFICATES section in ssh-keygen(1). 572 573 UseDNS Specifies whether sshd(8) should look up the remote host name and 574 check that the resolved host name for the remote IP address maps 575 back to the very same IP address. The default is ``yes''. 576 577 UseLogin 578 Specifies whether login(1) is used for interactive login 579 sessions. The default is ``no''. Note that login(1) is never 580 used for remote command execution. Note also, that if this is 581 enabled, X11Forwarding will be disabled because login(1) does not 582 know how to handle xauth(1) cookies. If UsePrivilegeSeparation 583 is specified, it will be disabled after authentication. 584 585 UsePAM Enables the Pluggable Authentication Module interface. If set to 586 ``yes'' this will enable PAM authentication using 587 ChallengeResponseAuthentication and PasswordAuthentication in 588 addition to PAM account and session module processing for all 589 authentication types. 590 591 Because PAM challenge-response authentication usually serves an 592 equivalent role to password authentication, you should disable 593 either PasswordAuthentication or ChallengeResponseAuthentication. 594 595 If UsePAM is enabled, you will not be able to run sshd(8) as a 596 non-root user. The default is ``no''. 597 598 UsePrivilegeSeparation 599 Specifies whether sshd(8) separates privileges by creating an 600 unprivileged child process to deal with incoming network traffic. 601 After successful authentication, another process will be created 602 that has the privilege of the authenticated user. The goal of 603 privilege separation is to prevent privilege escalation by 604 containing any corruption within the unprivileged processes. The 605 default is ``yes''. 606 607 X11DisplayOffset 608 Specifies the first display number available for sshd(8)'s X11 609 forwarding. This prevents sshd from interfering with real X11 610 servers. The default is 10. 611 612 X11Forwarding 613 Specifies whether X11 forwarding is permitted. The argument must 614 be ``yes'' or ``no''. The default is ``no''. 615 616 When X11 forwarding is enabled, there may be additional exposure 617 to the server and to client displays if the sshd(8) proxy display 618 is configured to listen on the wildcard address (see 619 X11UseLocalhost below), though this is not the default. 620 Additionally, the authentication spoofing and authentication data 621 verification and substitution occur on the client side. The 622 security risk of using X11 forwarding is that the client's X11 623 display server may be exposed to attack when the SSH client 624 requests forwarding (see the warnings for ForwardX11 in 625 ssh_config(5)). A system administrator may have a stance in 626 which they want to protect clients that may expose themselves to 627 attack by unwittingly requesting X11 forwarding, which can 628 warrant a ``no'' setting. 629 630 Note that disabling X11 forwarding does not prevent users from 631 forwarding X11 traffic, as users can always install their own 632 forwarders. X11 forwarding is automatically disabled if UseLogin 633 is enabled. 634 635 X11UseLocalhost 636 Specifies whether sshd(8) should bind the X11 forwarding server 637 to the loopback address or to the wildcard address. By default, 638 sshd binds the forwarding server to the loopback address and sets 639 the hostname part of the DISPLAY environment variable to 640 ``localhost''. This prevents remote hosts from connecting to the 641 proxy display. However, some older X11 clients may not function 642 with this configuration. X11UseLocalhost may be set to ``no'' to 643 specify that the forwarding server should be bound to the 644 wildcard address. The argument must be ``yes'' or ``no''. The 645 default is ``yes''. 646 647 XAuthLocation 648 Specifies the full pathname of the xauth(1) program. The default 649 is /usr/X11R6/bin/xauth. 650 651TIME FORMATS 652 sshd(8) command-line arguments and configuration file options that 653 specify time may be expressed using a sequence of the form: time 654 [qualifier], where time is a positive integer value and qualifier is one 655 of the following: 656 657 <none> seconds 658 s | S seconds 659 m | M minutes 660 h | H hours 661 d | D days 662 w | W weeks 663 664 Each member of the sequence is added together to calculate the total time 665 value. 666 667 Time format examples: 668 669 600 600 seconds (10 minutes) 670 10m 10 minutes 671 1h30m 1 hour 30 minutes (90 minutes) 672 673FILES 674 /etc/ssh/sshd_config 675 Contains configuration data for sshd(8). This file should be 676 writable by root only, but it is recommended (though not 677 necessary) that it be world-readable. 678 679SEE ALSO 680 sshd(8) 681 682AUTHORS 683 OpenSSH is a derivative of the original and free ssh 1.2.12 release by 684 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo 685 de Raadt and Dug Song removed many bugs, re-added newer features and 686 created OpenSSH. Markus Friedl contributed the support for SSH protocol 687 versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support 688 for privilege separation. 689 690OpenBSD 4.8 June 30, 2010 OpenBSD 4.8 691