sshd.0 revision 218767
150477SpeterSSHD(8) OpenBSD System Manager's Manual SSHD(8) 222379Spst 322401SphkNAME 422379Spst sshd - OpenSSH SSH daemon 522379Spst 622379SpstSYNOPSIS 788857Sache sshd [-46DdeiqTt] [-b bits] [-C connection_spec] 888857Sache [-c host_certificate_file] [-f config_file] [-g login_grace_time] 979467Smarkm [-h host_key_file] [-k key_gen_time] [-o option] [-p port] [-u len] 1079467Smarkm 1122379SpstDESCRIPTION 1222379Spst sshd (OpenSSH Daemon) is the daemon program for ssh(1). Together these 1322379Spst programs replace rlogin(1) and rsh(1), and provide secure encrypted 1460566Sobrien communications between two untrusted hosts over an insecure network. 1560566Sobrien 1679712Smarkm sshd listens for connections from clients. It is normally started at 1760566Sobrien boot from /etc/rc. It forks a new daemon for each incoming connection. 1879712Smarkm The forked daemons handle key exchange, encryption, authentication, 1960566Sobrien command execution, and data exchange. 2022379Spst 2122379Spst sshd can be configured using command-line options or a configuration file 2222379Spst (by default sshd_config(5)); command-line options override values 23 specified in the configuration file. sshd rereads its configuration file 24 when it receives a hangup signal, SIGHUP, by executing itself with the 25 name and options it was started with, e.g. /usr/sbin/sshd. 26 27 The options are as follows: 28 29 -4 Forces sshd to use IPv4 addresses only. 30 31 -6 Forces sshd to use IPv6 addresses only. 32 33 -b bits 34 Specifies the number of bits in the ephemeral protocol version 1 35 server key (default 1024). 36 37 -C connection_spec 38 Specify the connection parameters to use for the -T extended test 39 mode. If provided, any Match directives in the configuration 40 file that would apply to the specified user, host, and address 41 will be set before the configuration is written to standard 42 output. The connection parameters are supplied as keyword=value 43 pairs. The keywords are ``user'', ``host'', and ``addr''. All 44 are required and may be supplied in any order, either with 45 multiple -C options or as a comma-separated list. 46 47 -c host_certificate_file 48 Specifies a path to a certificate file to identify sshd during 49 key exchange. The certificate file must match a host key file 50 specified using the -h option or the HostKey configuration 51 directive. 52 53 -D When this option is specified, sshd will not detach and does not 54 become a daemon. This allows easy monitoring of sshd. 55 56 -d Debug mode. The server sends verbose debug output to standard 57 error, and does not put itself in the background. The server 58 also will not fork and will only process one connection. This 59 option is only intended for debugging for the server. Multiple 60 -d options increase the debugging level. Maximum is 3. 61 62 -e When this option is specified, sshd will send the output to the 63 standard error instead of the system log. 64 65 -f config_file 66 Specifies the name of the configuration file. The default is 67 /etc/ssh/sshd_config. sshd refuses to start if there is no 68 configuration file. 69 70 -g login_grace_time 71 Gives the grace time for clients to authenticate themselves 72 (default 120 seconds). If the client fails to authenticate the 73 user within this many seconds, the server disconnects and exits. 74 A value of zero indicates no limit. 75 76 -h host_key_file 77 Specifies a file from which a host key is read. This option must 78 be given if sshd is not run as root (as the normal host key files 79 are normally not readable by anyone but root). The default is 80 /etc/ssh/ssh_host_key for protocol version 1, and 81 /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_ecdsa_key and 82 /etc/ssh/ssh_host_rsa_key for protocol version 2. It is possible 83 to have multiple host key files for the different protocol 84 versions and host key algorithms. 85 86 -i Specifies that sshd is being run from inetd(8). sshd is normally 87 not run from inetd because it needs to generate the server key 88 before it can respond to the client, and this may take tens of 89 seconds. Clients would have to wait too long if the key was 90 regenerated every time. However, with small key sizes (e.g. 512) 91 using sshd from inetd may be feasible. 92 93 -k key_gen_time 94 Specifies how often the ephemeral protocol version 1 server key 95 is regenerated (default 3600 seconds, or one hour). The 96 motivation for regenerating the key fairly often is that the key 97 is not stored anywhere, and after about an hour it becomes 98 impossible to recover the key for decrypting intercepted 99 communications even if the machine is cracked into or physically 100 seized. A value of zero indicates that the key will never be 101 regenerated. 102 103 -o option 104 Can be used to give options in the format used in the 105 configuration file. This is useful for specifying options for 106 which there is no separate command-line flag. For full details 107 of the options, and their values, see sshd_config(5). 108 109 -p port 110 Specifies the port on which the server listens for connections 111 (default 22). Multiple port options are permitted. Ports 112 specified in the configuration file with the Port option are 113 ignored when a command-line port is specified. Ports specified 114 using the ListenAddress option override command-line ports. 115 116 -q Quiet mode. Nothing is sent to the system log. Normally the 117 beginning, authentication, and termination of each connection is 118 logged. 119 120 -T Extended test mode. Check the validity of the configuration 121 file, output the effective configuration to stdout and then exit. 122 Optionally, Match rules may be applied by specifying the 123 connection parameters using one or more -C options. 124 125 -t Test mode. Only check the validity of the configuration file and 126 sanity of the keys. This is useful for updating sshd reliably as 127 configuration options may change. 128 129 -u len This option is used to specify the size of the field in the utmp 130 structure that holds the remote host name. If the resolved host 131 name is longer than len, the dotted decimal value will be used 132 instead. This allows hosts with very long host names that 133 overflow this field to still be uniquely identified. Specifying 134 -u0 indicates that only dotted decimal addresses should be put 135 into the utmp file. -u0 may also be used to prevent sshd from 136 making DNS requests unless the authentication mechanism or 137 configuration requires it. Authentication mechanisms that may 138 require DNS include RhostsRSAAuthentication, 139 HostbasedAuthentication, and using a from="pattern-list" option 140 in a key file. Configuration options that require DNS include 141 using a USER@HOST pattern in AllowUsers or DenyUsers. 142 143AUTHENTICATION 144 The OpenSSH SSH daemon supports SSH protocols 1 and 2. The default is to 145 use protocol 2 only, though this can be changed via the Protocol option 146 in sshd_config(5). Protocol 2 supports DSA, ECDSA and RSA keys; protocol 147 1 only supports RSA keys. For both protocols, each host has a host- 148 specific key, normally 2048 bits, used to identify the host. 149 150 Forward security for protocol 1 is provided through an additional server 151 key, normally 768 bits, generated when the server starts. This key is 152 normally regenerated every hour if it has been used, and is never stored 153 on disk. Whenever a client connects, the daemon responds with its public 154 host and server keys. The client compares the RSA host key against its 155 own database to verify that it has not changed. The client then 156 generates a 256-bit random number. It encrypts this random number using 157 both the host key and the server key, and sends the encrypted number to 158 the server. Both sides then use this random number as a session key 159 which is used to encrypt all further communications in the session. The 160 rest of the session is encrypted using a conventional cipher, currently 161 Blowfish or 3DES, with 3DES being used by default. The client selects 162 the encryption algorithm to use from those offered by the server. 163 164 For protocol 2, forward security is provided through a Diffie-Hellman key 165 agreement. This key agreement results in a shared session key. The rest 166 of the session is encrypted using a symmetric cipher, currently 128-bit 167 AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES. The 168 client selects the encryption algorithm to use from those offered by the 169 server. Additionally, session integrity is provided through a 170 cryptographic message authentication code (hmac-md5, hmac-sha1, umac-64 171 or hmac-ripemd160). 172 173 Finally, the server and the client enter an authentication dialog. The 174 client tries to authenticate itself using host-based authentication, 175 public key authentication, challenge-response authentication, or password 176 authentication. 177 178 Regardless of the authentication type, the account is checked to ensure 179 that it is accessible. An account is not accessible if it is locked, 180 listed in DenyUsers or its group is listed in DenyGroups . The 181 definition of a locked account is system dependant. Some platforms have 182 their own account database (eg AIX) and some modify the passwd field ( 183 `*LK*' on Solaris and UnixWare, `*' on HP-UX, containing `Nologin' on 184 Tru64, a leading `*LOCKED*' on FreeBSD and a leading `!' on most 185 Linuxes). If there is a requirement to disable password authentication 186 for the account while allowing still public-key, then the passwd field 187 should be set to something other than these values (eg `NP' or `*NP*' ). 188 189 If the client successfully authenticates itself, a dialog for preparing 190 the session is entered. At this time the client may request things like 191 allocating a pseudo-tty, forwarding X11 connections, forwarding TCP 192 connections, or forwarding the authentication agent connection over the 193 secure channel. 194 195 After this, the client either requests a shell or execution of a command. 196 The sides then enter session mode. In this mode, either side may send 197 data at any time, and such data is forwarded to/from the shell or command 198 on the server side, and the user terminal in the client side. 199 200 When the user program terminates and all forwarded X11 and other 201 connections have been closed, the server sends command exit status to the 202 client, and both sides exit. 203 204LOGIN PROCESS 205 When a user successfully logs in, sshd does the following: 206 207 1. If the login is on a tty, and no command has been specified, 208 prints last login time and /etc/motd (unless prevented in the 209 configuration file or by ~/.hushlogin; see the FILES section). 210 211 2. If the login is on a tty, records login time. 212 213 3. Checks /etc/nologin; if it exists, prints contents and quits 214 (unless root). 215 216 4. Changes to run with normal user privileges. 217 218 5. Sets up basic environment. 219 220 6. Reads the file ~/.ssh/environment, if it exists, and users are 221 allowed to change their environment. See the 222 PermitUserEnvironment option in sshd_config(5). 223 224 7. Changes to user's home directory. 225 226 8. If ~/.ssh/rc exists, runs it; else if /etc/ssh/sshrc exists, 227 runs it; otherwise runs xauth. The ``rc'' files are given the 228 X11 authentication protocol and cookie in standard input. See 229 SSHRC, below. 230 231 9. Runs user's shell or command. 232 233SSHRC 234 If the file ~/.ssh/rc exists, sh(1) runs it after reading the environment 235 files but before starting the user's shell or command. It must not 236 produce any output on stdout; stderr must be used instead. If X11 237 forwarding is in use, it will receive the "proto cookie" pair in its 238 standard input (and DISPLAY in its environment). The script must call 239 xauth(1) because sshd will not run xauth automatically to add X11 240 cookies. 241 242 The primary purpose of this file is to run any initialization routines 243 which may be needed before the user's home directory becomes accessible; 244 AFS is a particular example of such an environment. 245 246 This file will probably contain some initialization code followed by 247 something similar to: 248 249 if read proto cookie && [ -n "$DISPLAY" ]; then 250 if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then 251 # X11UseLocalhost=yes 252 echo add unix:`echo $DISPLAY | 253 cut -c11-` $proto $cookie 254 else 255 # X11UseLocalhost=no 256 echo add $DISPLAY $proto $cookie 257 fi | xauth -q - 258 fi 259 260 If this file does not exist, /etc/ssh/sshrc is run, and if that does not 261 exist either, xauth is used to add the cookie. 262 263AUTHORIZED_KEYS FILE FORMAT 264 AuthorizedKeysFile specifies the file containing public keys for public 265 key authentication; if none is specified, the default is 266 ~/.ssh/authorized_keys. Each line of the file contains one key (empty 267 lines and lines starting with a `#' are ignored as comments). Protocol 1 268 public keys consist of the following space-separated fields: options, 269 bits, exponent, modulus, comment. Protocol 2 public key consist of: 270 options, keytype, base64-encoded key, comment. The options field is 271 optional; its presence is determined by whether the line starts with a 272 number or not (the options field never starts with a number). The bits, 273 exponent, modulus, and comment fields give the RSA key for protocol 274 version 1; the comment field is not used for anything (but may be 275 convenient for the user to identify the key). For protocol version 2 the 276 keytype is ``ecdsa-sha2-nistp256'', ``ecdsa-sha2-nistp384'', 277 ``ecdsa-sha2-nistp521'', ``ssh-dss'' or ``ssh-rsa''. 278 279 Note that lines in this file are usually several hundred bytes long 280 (because of the size of the public key encoding) up to a limit of 8 281 kilobytes, which permits DSA keys up to 8 kilobits and RSA keys up to 16 282 kilobits. You don't want to type them in; instead, copy the 283 identity.pub, id_dsa.pub, id_ecdsa.pub, or the id_rsa.pub file and edit 284 it. 285 286 sshd enforces a minimum RSA key modulus size for protocol 1 and protocol 287 2 keys of 768 bits. 288 289 The options (if present) consist of comma-separated option 290 specifications. No spaces are permitted, except within double quotes. 291 The following option specifications are supported (note that option 292 keywords are case-insensitive): 293 294 cert-authority 295 Specifies that the listed key is a certification authority (CA) 296 that is trusted to validate signed certificates for user 297 authentication. 298 299 Certificates may encode access restrictions similar to these key 300 options. If both certificate restrictions and key options are 301 present, the most restrictive union of the two is applied. 302 303 command="command" 304 Specifies that the command is executed whenever this key is used 305 for authentication. The command supplied by the user (if any) is 306 ignored. The command is run on a pty if the client requests a 307 pty; otherwise it is run without a tty. If an 8-bit clean 308 channel is required, one must not request a pty or should specify 309 no-pty. A quote may be included in the command by quoting it 310 with a backslash. This option might be useful to restrict 311 certain public keys to perform just a specific operation. An 312 example might be a key that permits remote backups but nothing 313 else. Note that the client may specify TCP and/or X11 forwarding 314 unless they are explicitly prohibited. The command originally 315 supplied by the client is available in the SSH_ORIGINAL_COMMAND 316 environment variable. Note that this option applies to shell, 317 command or subsystem execution. Also note that this command may 318 be superseded by either a sshd_config(5) ForceCommand directive 319 or a command embedded in a certificate. 320 321 environment="NAME=value" 322 Specifies that the string is to be added to the environment when 323 logging in using this key. Environment variables set this way 324 override other default environment values. Multiple options of 325 this type are permitted. Environment processing is disabled by 326 default and is controlled via the PermitUserEnvironment option. 327 This option is automatically disabled if UseLogin is enabled. 328 329 from="pattern-list" 330 Specifies that in addition to public key authentication, either 331 the canonical name of the remote host or its IP address must be 332 present in the comma-separated list of patterns. See PATTERNS in 333 ssh_config(5) for more information on patterns. 334 335 In addition to the wildcard matching that may be applied to 336 hostnames or addresses, a from stanza may match IP addresses 337 using CIDR address/masklen notation. 338 339 The purpose of this option is to optionally increase security: 340 public key authentication by itself does not trust the network or 341 name servers or anything (but the key); however, if somebody 342 somehow steals the key, the key permits an intruder to log in 343 from anywhere in the world. This additional option makes using a 344 stolen key more difficult (name servers and/or routers would have 345 to be compromised in addition to just the key). 346 347 no-agent-forwarding 348 Forbids authentication agent forwarding when this key is used for 349 authentication. 350 351 no-port-forwarding 352 Forbids TCP forwarding when this key is used for authentication. 353 Any port forward requests by the client will return an error. 354 This might be used, e.g. in connection with the command option. 355 356 no-pty Prevents tty allocation (a request to allocate a pty will fail). 357 358 no-user-rc 359 Disables execution of ~/.ssh/rc. 360 361 no-X11-forwarding 362 Forbids X11 forwarding when this key is used for authentication. 363 Any X11 forward requests by the client will return an error. 364 365 permitopen="host:port" 366 Limit local ``ssh -L'' port forwarding such that it may only 367 connect to the specified host and port. IPv6 addresses can be 368 specified by enclosing the address in square brackets. Multiple 369 permitopen options may be applied separated by commas. No 370 pattern matching is performed on the specified hostnames, they 371 must be literal domains or addresses. 372 373 principals="principals" 374 On a cert-authority line, specifies allowed principals for 375 certificate authentication as a comma-separated list. At least 376 one name from the list must appear in the certificate's list of 377 principals for the certificate to be accepted. This option is 378 ignored for keys that are not marked as trusted certificate 379 signers using the cert-authority option. 380 381 tunnel="n" 382 Force a tun(4) device on the server. Without this option, the 383 next available device will be used if the client requests a 384 tunnel. 385 386 An example authorized_keys file: 387 388 # Comments allowed at start of line 389 ssh-rsa AAAAB3Nza...LiPk== user@example.net 390 from="*.sales.example.net,!pc.sales.example.net" ssh-rsa 391 AAAAB2...19Q== john@example.net 392 command="dump /home",no-pty,no-port-forwarding ssh-dss 393 AAAAC3...51R== example.net 394 permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-dss 395 AAAAB5...21S== 396 tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...== 397 jane@example.net 398 399SSH_KNOWN_HOSTS FILE FORMAT 400 The /etc/ssh/ssh_known_hosts and ~/.ssh/known_hosts files contain host 401 public keys for all known hosts. The global file should be prepared by 402 the administrator (optional), and the per-user file is maintained 403 automatically: whenever the user connects from an unknown host, its key 404 is added to the per-user file. 405 406 Each line in these files contains the following fields: markers 407 (optional), hostnames, bits, exponent, modulus, comment. The fields are 408 separated by spaces. 409 410 The marker is optional, but if it is present then it must be one of 411 ``@cert-authority'', to indicate that the line contains a certification 412 authority (CA) key, or ``@revoked'', to indicate that the key contained 413 on the line is revoked and must not ever be accepted. Only one marker 414 should be used on a key line. 415 416 Hostnames is a comma-separated list of patterns (`*' and `?' act as 417 wildcards); each pattern in turn is matched against the canonical host 418 name (when authenticating a client) or against the user-supplied name 419 (when authenticating a server). A pattern may also be preceded by `!' to 420 indicate negation: if the host name matches a negated pattern, it is not 421 accepted (by that line) even if it matched another pattern on the line. 422 A hostname or address may optionally be enclosed within `[' and `]' 423 brackets then followed by `:' and a non-standard port number. 424 425 Alternately, hostnames may be stored in a hashed form which hides host 426 names and addresses should the file's contents be disclosed. Hashed 427 hostnames start with a `|' character. Only one hashed hostname may 428 appear on a single line and none of the above negation or wildcard 429 operators may be applied. 430 431 Bits, exponent, and modulus are taken directly from the RSA host key; 432 they can be obtained, for example, from /etc/ssh/ssh_host_key.pub. The 433 optional comment field continues to the end of the line, and is not used. 434 435 Lines starting with `#' and empty lines are ignored as comments. 436 437 When performing host authentication, authentication is accepted if any 438 matching line has the proper key; either one that matches exactly or, if 439 the server has presented a certificate for authentication, the key of the 440 certification authority that signed the certificate. For a key to be 441 trusted as a certification authority, it must use the ``@cert-authority'' 442 marker described above. 443 444 The known hosts file also provides a facility to mark keys as revoked, 445 for example when it is known that the associated private key has been 446 stolen. Revoked keys are specified by including the ``@revoked'' marker 447 at the beginning of the key line, and are never accepted for 448 authentication or as certification authorities, but instead will produce 449 a warning from ssh(1) when they are encountered. 450 451 It is permissible (but not recommended) to have several lines or 452 different host keys for the same names. This will inevitably happen when 453 short forms of host names from different domains are put in the file. It 454 is possible that the files contain conflicting information; 455 authentication is accepted if valid information can be found from either 456 file. 457 458 Note that the lines in these files are typically hundreds of characters 459 long, and you definitely don't want to type in the host keys by hand. 460 Rather, generate them by a script, ssh-keyscan(1) or by taking 461 /etc/ssh/ssh_host_key.pub and adding the host names at the front. 462 ssh-keygen(1) also offers some basic automated editing for 463 ~/.ssh/known_hosts including removing hosts matching a host name and 464 converting all host names to their hashed representations. 465 466 An example ssh_known_hosts file: 467 468 # Comments allowed at start of line 469 closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net 470 cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....= 471 # A hashed hostname 472 |1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa 473 AAAA1234.....= 474 # A revoked key 475 @revoked * ssh-rsa AAAAB5W... 476 # A CA key, accepted for any host in *.mydomain.com or *.mydomain.org 477 @cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W... 478 479FILES 480 ~/.hushlogin 481 This file is used to suppress printing the last login time and 482 /etc/motd, if PrintLastLog and PrintMotd, respectively, are 483 enabled. It does not suppress printing of the banner specified 484 by Banner. 485 486 ~/.rhosts 487 This file is used for host-based authentication (see ssh(1) for 488 more information). On some machines this file may need to be 489 world-readable if the user's home directory is on an NFS 490 partition, because sshd reads it as root. Additionally, this 491 file must be owned by the user, and must not have write 492 permissions for anyone else. The recommended permission for most 493 machines is read/write for the user, and not accessible by 494 others. 495 496 ~/.shosts 497 This file is used in exactly the same way as .rhosts, but allows 498 host-based authentication without permitting login with 499 rlogin/rsh. 500 501 ~/.ssh/ 502 This directory is the default location for all user-specific 503 configuration and authentication information. There is no 504 general requirement to keep the entire contents of this directory 505 secret, but the recommended permissions are read/write/execute 506 for the user, and not accessible by others. 507 508 ~/.ssh/authorized_keys 509 Lists the public keys (DSA/ECDSA/RSA) that can be used for 510 logging in as this user. The format of this file is described 511 above. The content of the file is not highly sensitive, but the 512 recommended permissions are read/write for the user, and not 513 accessible by others. 514 515 If this file, the ~/.ssh directory, or the user's home directory 516 are writable by other users, then the file could be modified or 517 replaced by unauthorized users. In this case, sshd will not 518 allow it to be used unless the StrictModes option has been set to 519 ``no''. 520 521 ~/.ssh/environment 522 This file is read into the environment at login (if it exists). 523 It can only contain empty lines, comment lines (that start with 524 `#'), and assignment lines of the form name=value. The file 525 should be writable only by the user; it need not be readable by 526 anyone else. Environment processing is disabled by default and 527 is controlled via the PermitUserEnvironment option. 528 529 ~/.ssh/known_hosts 530 Contains a list of host keys for all hosts the user has logged 531 into that are not already in the systemwide list of known host 532 keys. The format of this file is described above. This file 533 should be writable only by root/the owner and can, but need not 534 be, world-readable. 535 536 ~/.ssh/rc 537 Contains initialization routines to be run before the user's home 538 directory becomes accessible. This file should be writable only 539 by the user, and need not be readable by anyone else. 540 541 /etc/hosts.allow 542 /etc/hosts.deny 543 Access controls that should be enforced by tcp-wrappers are 544 defined here. Further details are described in hosts_access(5). 545 546 /etc/hosts.equiv 547 This file is for host-based authentication (see ssh(1)). It 548 should only be writable by root. 549 550 /etc/moduli 551 Contains Diffie-Hellman groups used for the "Diffie-Hellman Group 552 Exchange". The file format is described in moduli(5). 553 554 /etc/motd 555 See motd(5). 556 557 /etc/nologin 558 If this file exists, sshd refuses to let anyone except root log 559 in. The contents of the file are displayed to anyone trying to 560 log in, and non-root connections are refused. The file should be 561 world-readable. 562 563 /etc/shosts.equiv 564 This file is used in exactly the same way as hosts.equiv, but 565 allows host-based authentication without permitting login with 566 rlogin/rsh. 567 568 /etc/ssh/ssh_host_key 569 /etc/ssh/ssh_host_dsa_key 570 /etc/ssh/ssh_host_ecdsa_key 571 /etc/ssh/ssh_host_rsa_key 572 These three files contain the private parts of the host keys. 573 These files should only be owned by root, readable only by root, 574 and not accessible to others. Note that sshd does not start if 575 these files are group/world-accessible. 576 577 /etc/ssh/ssh_host_key.pub 578 /etc/ssh/ssh_host_dsa_key.pub 579 /etc/ssh/ssh_host_ecdsa_key.pub 580 /etc/ssh/ssh_host_rsa_key.pub 581 These three files contain the public parts of the host keys. 582 These files should be world-readable but writable only by root. 583 Their contents should match the respective private parts. These 584 files are not really used for anything; they are provided for the 585 convenience of the user so their contents can be copied to known 586 hosts files. These files are created using ssh-keygen(1). 587 588 /etc/ssh/ssh_known_hosts 589 Systemwide list of known host keys. This file should be prepared 590 by the system administrator to contain the public host keys of 591 all machines in the organization. The format of this file is 592 described above. This file should be writable only by root/the 593 owner and should be world-readable. 594 595 /etc/ssh/sshd_config 596 Contains configuration data for sshd. The file format and 597 configuration options are described in sshd_config(5). 598 599 /etc/ssh/sshrc 600 Similar to ~/.ssh/rc, it can be used to specify machine-specific 601 login-time initializations globally. This file should be 602 writable only by root, and should be world-readable. 603 604 /var/empty 605 chroot(2) directory used by sshd during privilege separation in 606 the pre-authentication phase. The directory should not contain 607 any files and must be owned by root and not group or world- 608 writable. 609 610 /var/run/sshd.pid 611 Contains the process ID of the sshd listening for connections (if 612 there are several daemons running concurrently for different 613 ports, this contains the process ID of the one started last). 614 The content of this file is not sensitive; it can be world- 615 readable. 616 617SEE ALSO 618 scp(1), sftp(1), ssh(1), ssh-add(1), ssh-agent(1), ssh-keygen(1), 619 ssh-keyscan(1), chroot(2), hosts_access(5), login.conf(5), moduli(5), 620 sshd_config(5), inetd(8), sftp-server(8) 621 622AUTHORS 623 OpenSSH is a derivative of the original and free ssh 1.2.12 release by 624 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo 625 de Raadt and Dug Song removed many bugs, re-added newer features and 626 created OpenSSH. Markus Friedl contributed the support for SSH protocol 627 versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support 628 for privilege separation. 629 630CAVEATS 631 System security is not improved unless rshd, rlogind, and rexecd are 632 disabled (thus completely disabling rlogin and rsh into the machine). 633 634OpenBSD 4.8 October 28, 2010 OpenBSD 4.8 635