1SSHD(8) OpenBSD System Manager's Manual SSHD(8) 2 3NAME 4 sshd - OpenSSH SSH daemon 5 6SYNOPSIS 7 sshd [-46DdeiqTt] [-b bits] [-C connection_spec] 8 [-c host_certificate_file] [-E log_file] [-f config_file] 9 [-g login_grace_time] [-h host_key_file] [-k key_gen_time] 10 [-o option] [-p port] [-u len] 11 12DESCRIPTION 13 sshd (OpenSSH Daemon) is the daemon program for ssh(1). Together these 14 programs replace rlogin(1) and rsh(1), and provide secure encrypted 15 communications between two untrusted hosts over an insecure network. 16 17 sshd listens for connections from clients. It is normally started at 18 boot from /etc/rc. It forks a new daemon for each incoming connection. 19 The forked daemons handle key exchange, encryption, authentication, 20 command execution, and data exchange. 21 22 sshd can be configured using command-line options or a configuration file 23 (by default sshd_config(5)); command-line options override values 24 specified in the configuration file. sshd rereads its configuration file 25 when it receives a hangup signal, SIGHUP, by executing itself with the 26 name and options it was started with, e.g. /usr/sbin/sshd. 27 28 The options are as follows: 29 30 -4 Forces sshd to use IPv4 addresses only. 31 32 -6 Forces sshd to use IPv6 addresses only. 33 34 -b bits 35 Specifies the number of bits in the ephemeral protocol version 1 36 server key (default 1024). 37 38 -C connection_spec 39 Specify the connection parameters to use for the -T extended test 40 mode. If provided, any Match directives in the configuration 41 file that would apply to the specified user, host, and address 42 will be set before the configuration is written to standard 43 output. The connection parameters are supplied as keyword=value 44 pairs. The keywords are ``user'', ``host'', ``laddr'', 45 ``lport'', and ``addr''. All are required and may be supplied in 46 any order, either with multiple -C options or as a comma- 47 separated list. 48 49 -c host_certificate_file 50 Specifies a path to a certificate file to identify sshd during 51 key exchange. The certificate file must match a host key file 52 specified using the -h option or the HostKey configuration 53 directive. 54 55 -D When this option is specified, sshd will not detach and does not 56 become a daemon. This allows easy monitoring of sshd. 57 58 -d Debug mode. The server sends verbose debug output to standard 59 error, and does not put itself in the background. The server 60 also will not fork and will only process one connection. This 61 option is only intended for debugging for the server. Multiple 62 -d options increase the debugging level. Maximum is 3. 63 64 -E log_file 65 Append debug logs to log_file instead of the system log. 66 67 -e Write debug logs to standard error instead of the system log. 68 69 -f config_file 70 Specifies the name of the configuration file. The default is 71 /etc/ssh/sshd_config. sshd refuses to start if there is no 72 configuration file. 73 74 -g login_grace_time 75 Gives the grace time for clients to authenticate themselves 76 (default 120 seconds). If the client fails to authenticate the 77 user within this many seconds, the server disconnects and exits. 78 A value of zero indicates no limit. 79 80 -h host_key_file 81 Specifies a file from which a host key is read. This option must 82 be given if sshd is not run as root (as the normal host key files 83 are normally not readable by anyone but root). The default is 84 /etc/ssh/ssh_host_key for protocol version 1, and 85 /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_ecdsa_key and 86 /etc/ssh/ssh_host_rsa_key for protocol version 2. It is possible 87 to have multiple host key files for the different protocol 88 versions and host key algorithms. 89 90 -i Specifies that sshd is being run from inetd(8). sshd is normally 91 not run from inetd because it needs to generate the server key 92 before it can respond to the client, and this may take tens of 93 seconds. Clients would have to wait too long if the key was 94 regenerated every time. However, with small key sizes (e.g. 512) 95 using sshd from inetd may be feasible. 96 97 -k key_gen_time 98 Specifies how often the ephemeral protocol version 1 server key 99 is regenerated (default 3600 seconds, or one hour). The 100 motivation for regenerating the key fairly often is that the key 101 is not stored anywhere, and after about an hour it becomes 102 impossible to recover the key for decrypting intercepted 103 communications even if the machine is cracked into or physically 104 seized. A value of zero indicates that the key will never be 105 regenerated. 106 107 -o option 108 Can be used to give options in the format used in the 109 configuration file. This is useful for specifying options for 110 which there is no separate command-line flag. For full details 111 of the options, and their values, see sshd_config(5). 112 113 -p port 114 Specifies the port on which the server listens for connections 115 (default 22). Multiple port options are permitted. Ports 116 specified in the configuration file with the Port option are 117 ignored when a command-line port is specified. Ports specified 118 using the ListenAddress option override command-line ports. 119 120 -q Quiet mode. Nothing is sent to the system log. Normally the 121 beginning, authentication, and termination of each connection is 122 logged. 123 124 -T Extended test mode. Check the validity of the configuration 125 file, output the effective configuration to stdout and then exit. 126 Optionally, Match rules may be applied by specifying the 127 connection parameters using one or more -C options. 128 129 -t Test mode. Only check the validity of the configuration file and 130 sanity of the keys. This is useful for updating sshd reliably as 131 configuration options may change. 132 133 -u len This option is used to specify the size of the field in the utmp 134 structure that holds the remote host name. If the resolved host 135 name is longer than len, the dotted decimal value will be used 136 instead. This allows hosts with very long host names that 137 overflow this field to still be uniquely identified. Specifying 138 -u0 indicates that only dotted decimal addresses should be put 139 into the utmp file. -u0 may also be used to prevent sshd from 140 making DNS requests unless the authentication mechanism or 141 configuration requires it. Authentication mechanisms that may 142 require DNS include RhostsRSAAuthentication, 143 HostbasedAuthentication, and using a from="pattern-list" option 144 in a key file. Configuration options that require DNS include 145 using a USER@HOST pattern in AllowUsers or DenyUsers. 146 147AUTHENTICATION 148 The OpenSSH SSH daemon supports SSH protocols 1 and 2. The default is to 149 use protocol 2 only, though this can be changed via the Protocol option 150 in sshd_config(5). Protocol 2 supports DSA, ECDSA and RSA keys; protocol 151 1 only supports RSA keys. For both protocols, each host has a host- 152 specific key, normally 2048 bits, used to identify the host. 153 154 Forward security for protocol 1 is provided through an additional server 155 key, normally 768 bits, generated when the server starts. This key is 156 normally regenerated every hour if it has been used, and is never stored 157 on disk. Whenever a client connects, the daemon responds with its public 158 host and server keys. The client compares the RSA host key against its 159 own database to verify that it has not changed. The client then 160 generates a 256-bit random number. It encrypts this random number using 161 both the host key and the server key, and sends the encrypted number to 162 the server. Both sides then use this random number as a session key 163 which is used to encrypt all further communications in the session. The 164 rest of the session is encrypted using a conventional cipher, currently 165 Blowfish or 3DES, with 3DES being used by default. The client selects 166 the encryption algorithm to use from those offered by the server. 167 168 For protocol 2, forward security is provided through a Diffie-Hellman key 169 agreement. This key agreement results in a shared session key. The rest 170 of the session is encrypted using a symmetric cipher, currently 128-bit 171 AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES. The 172 client selects the encryption algorithm to use from those offered by the 173 server. Additionally, session integrity is provided through a 174 cryptographic message authentication code (hmac-md5, hmac-sha1, umac-64, 175 umac-128, hmac-ripemd160, hmac-sha2-256 or hmac-sha2-512). 176 177 Finally, the server and the client enter an authentication dialog. The 178 client tries to authenticate itself using host-based authentication, 179 public key authentication, challenge-response authentication, or password 180 authentication. 181 182 Regardless of the authentication type, the account is checked to ensure 183 that it is accessible. An account is not accessible if it is locked, 184 listed in DenyUsers or its group is listed in DenyGroups . The 185 definition of a locked account is system dependant. Some platforms have 186 their own account database (eg AIX) and some modify the passwd field ( 187 `*LK*' on Solaris and UnixWare, `*' on HP-UX, containing `Nologin' on 188 Tru64, a leading `*LOCKED*' on FreeBSD and a leading `!' on most 189 Linuxes). If there is a requirement to disable password authentication 190 for the account while allowing still public-key, then the passwd field 191 should be set to something other than these values (eg `NP' or `*NP*' ). 192 193 If the client successfully authenticates itself, a dialog for preparing 194 the session is entered. At this time the client may request things like 195 allocating a pseudo-tty, forwarding X11 connections, forwarding TCP 196 connections, or forwarding the authentication agent connection over the 197 secure channel. 198 199 After this, the client either requests a shell or execution of a command. 200 The sides then enter session mode. In this mode, either side may send 201 data at any time, and such data is forwarded to/from the shell or command 202 on the server side, and the user terminal in the client side. 203 204 When the user program terminates and all forwarded X11 and other 205 connections have been closed, the server sends command exit status to the 206 client, and both sides exit. 207 208LOGIN PROCESS 209 When a user successfully logs in, sshd does the following: 210 211 1. If the login is on a tty, and no command has been specified, 212 prints last login time and /etc/motd (unless prevented in the 213 configuration file or by ~/.hushlogin; see the FILES section). 214 215 2. If the login is on a tty, records login time. 216 217 3. Checks /etc/nologin; if it exists, prints contents and quits 218 (unless root). 219 220 4. Changes to run with normal user privileges. 221 222 5. Sets up basic environment. 223 224 6. Reads the file ~/.ssh/environment, if it exists, and users are 225 allowed to change their environment. See the 226 PermitUserEnvironment option in sshd_config(5). 227 228 7. Changes to user's home directory. 229 230 8. If ~/.ssh/rc exists, runs it; else if /etc/ssh/sshrc exists, 231 runs it; otherwise runs xauth. The ``rc'' files are given the 232 X11 authentication protocol and cookie in standard input. See 233 SSHRC, below. 234 235 9. Runs user's shell or command. 236 237SSHRC 238 If the file ~/.ssh/rc exists, sh(1) runs it after reading the environment 239 files but before starting the user's shell or command. It must not 240 produce any output on stdout; stderr must be used instead. If X11 241 forwarding is in use, it will receive the "proto cookie" pair in its 242 standard input (and DISPLAY in its environment). The script must call 243 xauth(1) because sshd will not run xauth automatically to add X11 244 cookies. 245 246 The primary purpose of this file is to run any initialization routines 247 which may be needed before the user's home directory becomes accessible; 248 AFS is a particular example of such an environment. 249 250 This file will probably contain some initialization code followed by 251 something similar to: 252 253 if read proto cookie && [ -n "$DISPLAY" ]; then 254 if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then 255 # X11UseLocalhost=yes 256 echo add unix:`echo $DISPLAY | 257 cut -c11-` $proto $cookie 258 else 259 # X11UseLocalhost=no 260 echo add $DISPLAY $proto $cookie 261 fi | xauth -q - 262 fi 263 264 If this file does not exist, /etc/ssh/sshrc is run, and if that does not 265 exist either, xauth is used to add the cookie. 266 267AUTHORIZED_KEYS FILE FORMAT 268 AuthorizedKeysFile specifies the files containing public keys for public 269 key authentication; if none is specified, the default is 270 ~/.ssh/authorized_keys and ~/.ssh/authorized_keys2. Each line of the 271 file contains one key (empty lines and lines starting with a `#' are 272 ignored as comments). Protocol 1 public keys consist of the following 273 space-separated fields: options, bits, exponent, modulus, comment. 274 Protocol 2 public key consist of: options, keytype, base64-encoded key, 275 comment. The options field is optional; its presence is determined by 276 whether the line starts with a number or not (the options field never 277 starts with a number). The bits, exponent, modulus, and comment fields 278 give the RSA key for protocol version 1; the comment field is not used 279 for anything (but may be convenient for the user to identify the key). 280 For protocol version 2 the keytype is ``ecdsa-sha2-nistp256'', 281 ``ecdsa-sha2-nistp384'', ``ecdsa-sha2-nistp521'', ``ssh-dss'' or 282 ``ssh-rsa''. 283 284 Note that lines in this file are usually several hundred bytes long 285 (because of the size of the public key encoding) up to a limit of 8 286 kilobytes, which permits DSA keys up to 8 kilobits and RSA keys up to 16 287 kilobits. You don't want to type them in; instead, copy the 288 identity.pub, id_dsa.pub, id_ecdsa.pub, or the id_rsa.pub file and edit 289 it. 290 291 sshd enforces a minimum RSA key modulus size for protocol 1 and protocol 292 2 keys of 768 bits. 293 294 The options (if present) consist of comma-separated option 295 specifications. No spaces are permitted, except within double quotes. 296 The following option specifications are supported (note that option 297 keywords are case-insensitive): 298 299 cert-authority 300 Specifies that the listed key is a certification authority (CA) 301 that is trusted to validate signed certificates for user 302 authentication. 303 304 Certificates may encode access restrictions similar to these key 305 options. If both certificate restrictions and key options are 306 present, the most restrictive union of the two is applied. 307 308 command="command" 309 Specifies that the command is executed whenever this key is used 310 for authentication. The command supplied by the user (if any) is 311 ignored. The command is run on a pty if the client requests a 312 pty; otherwise it is run without a tty. If an 8-bit clean 313 channel is required, one must not request a pty or should specify 314 no-pty. A quote may be included in the command by quoting it 315 with a backslash. This option might be useful to restrict 316 certain public keys to perform just a specific operation. An 317 example might be a key that permits remote backups but nothing 318 else. Note that the client may specify TCP and/or X11 forwarding 319 unless they are explicitly prohibited. The command originally 320 supplied by the client is available in the SSH_ORIGINAL_COMMAND 321 environment variable. Note that this option applies to shell, 322 command or subsystem execution. Also note that this command may 323 be superseded by either a sshd_config(5) ForceCommand directive 324 or a command embedded in a certificate. 325 326 environment="NAME=value" 327 Specifies that the string is to be added to the environment when 328 logging in using this key. Environment variables set this way 329 override other default environment values. Multiple options of 330 this type are permitted. Environment processing is disabled by 331 default and is controlled via the PermitUserEnvironment option. 332 This option is automatically disabled if UseLogin is enabled. 333 334 from="pattern-list" 335 Specifies that in addition to public key authentication, either 336 the canonical name of the remote host or its IP address must be 337 present in the comma-separated list of patterns. See PATTERNS in 338 ssh_config(5) for more information on patterns. 339 340 In addition to the wildcard matching that may be applied to 341 hostnames or addresses, a from stanza may match IP addresses 342 using CIDR address/masklen notation. 343 344 The purpose of this option is to optionally increase security: 345 public key authentication by itself does not trust the network or 346 name servers or anything (but the key); however, if somebody 347 somehow steals the key, the key permits an intruder to log in 348 from anywhere in the world. This additional option makes using a 349 stolen key more difficult (name servers and/or routers would have 350 to be compromised in addition to just the key). 351 352 no-agent-forwarding 353 Forbids authentication agent forwarding when this key is used for 354 authentication. 355 356 no-port-forwarding 357 Forbids TCP forwarding when this key is used for authentication. 358 Any port forward requests by the client will return an error. 359 This might be used, e.g. in connection with the command option. 360 361 no-pty Prevents tty allocation (a request to allocate a pty will fail). 362 363 no-user-rc 364 Disables execution of ~/.ssh/rc. 365 366 no-X11-forwarding 367 Forbids X11 forwarding when this key is used for authentication. 368 Any X11 forward requests by the client will return an error. 369 370 permitopen="host:port" 371 Limit local ``ssh -L'' port forwarding such that it may only 372 connect to the specified host and port. IPv6 addresses can be 373 specified by enclosing the address in square brackets. Multiple 374 permitopen options may be applied separated by commas. No 375 pattern matching is performed on the specified hostnames, they 376 must be literal domains or addresses. A port specification of * 377 matches any port. 378 379 principals="principals" 380 On a cert-authority line, specifies allowed principals for 381 certificate authentication as a comma-separated list. At least 382 one name from the list must appear in the certificate's list of 383 principals for the certificate to be accepted. This option is 384 ignored for keys that are not marked as trusted certificate 385 signers using the cert-authority option. 386 387 tunnel="n" 388 Force a tun(4) device on the server. Without this option, the 389 next available device will be used if the client requests a 390 tunnel. 391 392 An example authorized_keys file: 393 394 # Comments allowed at start of line 395 ssh-rsa AAAAB3Nza...LiPk== user@example.net 396 from="*.sales.example.net,!pc.sales.example.net" ssh-rsa 397 AAAAB2...19Q== john@example.net 398 command="dump /home",no-pty,no-port-forwarding ssh-dss 399 AAAAC3...51R== example.net 400 permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-dss 401 AAAAB5...21S== 402 tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...== 403 jane@example.net 404 405SSH_KNOWN_HOSTS FILE FORMAT 406 The /etc/ssh/ssh_known_hosts and ~/.ssh/known_hosts files contain host 407 public keys for all known hosts. The global file should be prepared by 408 the administrator (optional), and the per-user file is maintained 409 automatically: whenever the user connects from an unknown host, its key 410 is added to the per-user file. 411 412 Each line in these files contains the following fields: markers 413 (optional), hostnames, bits, exponent, modulus, comment. The fields are 414 separated by spaces. 415 416 The marker is optional, but if it is present then it must be one of 417 ``@cert-authority'', to indicate that the line contains a certification 418 authority (CA) key, or ``@revoked'', to indicate that the key contained 419 on the line is revoked and must not ever be accepted. Only one marker 420 should be used on a key line. 421 422 Hostnames is a comma-separated list of patterns (`*' and `?' act as 423 wildcards); each pattern in turn is matched against the canonical host 424 name (when authenticating a client) or against the user-supplied name 425 (when authenticating a server). A pattern may also be preceded by `!' to 426 indicate negation: if the host name matches a negated pattern, it is not 427 accepted (by that line) even if it matched another pattern on the line. 428 A hostname or address may optionally be enclosed within `[' and `]' 429 brackets then followed by `:' and a non-standard port number. 430 431 Alternately, hostnames may be stored in a hashed form which hides host 432 names and addresses should the file's contents be disclosed. Hashed 433 hostnames start with a `|' character. Only one hashed hostname may 434 appear on a single line and none of the above negation or wildcard 435 operators may be applied. 436 437 Bits, exponent, and modulus are taken directly from the RSA host key; 438 they can be obtained, for example, from /etc/ssh/ssh_host_key.pub. The 439 optional comment field continues to the end of the line, and is not used. 440 441 Lines starting with `#' and empty lines are ignored as comments. 442 443 When performing host authentication, authentication is accepted if any 444 matching line has the proper key; either one that matches exactly or, if 445 the server has presented a certificate for authentication, the key of the 446 certification authority that signed the certificate. For a key to be 447 trusted as a certification authority, it must use the ``@cert-authority'' 448 marker described above. 449 450 The known hosts file also provides a facility to mark keys as revoked, 451 for example when it is known that the associated private key has been 452 stolen. Revoked keys are specified by including the ``@revoked'' marker 453 at the beginning of the key line, and are never accepted for 454 authentication or as certification authorities, but instead will produce 455 a warning from ssh(1) when they are encountered. 456 457 It is permissible (but not recommended) to have several lines or 458 different host keys for the same names. This will inevitably happen when 459 short forms of host names from different domains are put in the file. It 460 is possible that the files contain conflicting information; 461 authentication is accepted if valid information can be found from either 462 file. 463 464 Note that the lines in these files are typically hundreds of characters 465 long, and you definitely don't want to type in the host keys by hand. 466 Rather, generate them by a script, ssh-keyscan(1) or by taking 467 /etc/ssh/ssh_host_key.pub and adding the host names at the front. 468 ssh-keygen(1) also offers some basic automated editing for 469 ~/.ssh/known_hosts including removing hosts matching a host name and 470 converting all host names to their hashed representations. 471 472 An example ssh_known_hosts file: 473 474 # Comments allowed at start of line 475 closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net 476 cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....= 477 # A hashed hostname 478 |1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa 479 AAAA1234.....= 480 # A revoked key 481 @revoked * ssh-rsa AAAAB5W... 482 # A CA key, accepted for any host in *.mydomain.com or *.mydomain.org 483 @cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W... 484 485FILES 486 ~/.hushlogin 487 This file is used to suppress printing the last login time and 488 /etc/motd, if PrintLastLog and PrintMotd, respectively, are 489 enabled. It does not suppress printing of the banner specified 490 by Banner. 491 492 ~/.rhosts 493 This file is used for host-based authentication (see ssh(1) for 494 more information). On some machines this file may need to be 495 world-readable if the user's home directory is on an NFS 496 partition, because sshd reads it as root. Additionally, this 497 file must be owned by the user, and must not have write 498 permissions for anyone else. The recommended permission for most 499 machines is read/write for the user, and not accessible by 500 others. 501 502 ~/.shosts 503 This file is used in exactly the same way as .rhosts, but allows 504 host-based authentication without permitting login with 505 rlogin/rsh. 506 507 ~/.ssh/ 508 This directory is the default location for all user-specific 509 configuration and authentication information. There is no 510 general requirement to keep the entire contents of this directory 511 secret, but the recommended permissions are read/write/execute 512 for the user, and not accessible by others. 513 514 ~/.ssh/authorized_keys 515 Lists the public keys (DSA/ECDSA/RSA) that can be used for 516 logging in as this user. The format of this file is described 517 above. The content of the file is not highly sensitive, but the 518 recommended permissions are read/write for the user, and not 519 accessible by others. 520 521 If this file, the ~/.ssh directory, or the user's home directory 522 are writable by other users, then the file could be modified or 523 replaced by unauthorized users. In this case, sshd will not 524 allow it to be used unless the StrictModes option has been set to 525 ``no''. 526 527 ~/.ssh/environment 528 This file is read into the environment at login (if it exists). 529 It can only contain empty lines, comment lines (that start with 530 `#'), and assignment lines of the form name=value. The file 531 should be writable only by the user; it need not be readable by 532 anyone else. Environment processing is disabled by default and 533 is controlled via the PermitUserEnvironment option. 534 535 ~/.ssh/known_hosts 536 Contains a list of host keys for all hosts the user has logged 537 into that are not already in the systemwide list of known host 538 keys. The format of this file is described above. This file 539 should be writable only by root/the owner and can, but need not 540 be, world-readable. 541 542 ~/.ssh/rc 543 Contains initialization routines to be run before the user's home 544 directory becomes accessible. This file should be writable only 545 by the user, and need not be readable by anyone else. 546 547 /etc/hosts.allow 548 /etc/hosts.deny 549 Access controls that should be enforced by tcp-wrappers are 550 defined here. Further details are described in hosts_access(5). 551 552 /etc/hosts.equiv 553 This file is for host-based authentication (see ssh(1)). It 554 should only be writable by root. 555 556 /etc/moduli 557 Contains Diffie-Hellman groups used for the "Diffie-Hellman Group 558 Exchange". The file format is described in moduli(5). 559 560 /etc/motd 561 See motd(5). 562 563 /etc/nologin 564 If this file exists, sshd refuses to let anyone except root log 565 in. The contents of the file are displayed to anyone trying to 566 log in, and non-root connections are refused. The file should be 567 world-readable. 568 569 /etc/shosts.equiv 570 This file is used in exactly the same way as hosts.equiv, but 571 allows host-based authentication without permitting login with 572 rlogin/rsh. 573 574 /etc/ssh/ssh_host_key 575 /etc/ssh/ssh_host_dsa_key 576 /etc/ssh/ssh_host_ecdsa_key 577 /etc/ssh/ssh_host_rsa_key 578 These files contain the private parts of the host keys. These 579 files should only be owned by root, readable only by root, and 580 not accessible to others. Note that sshd does not start if these 581 files are group/world-accessible. 582 583 /etc/ssh/ssh_host_key.pub 584 /etc/ssh/ssh_host_dsa_key.pub 585 /etc/ssh/ssh_host_ecdsa_key.pub 586 /etc/ssh/ssh_host_rsa_key.pub 587 These files contain the public parts of the host keys. These 588 files should be world-readable but writable only by root. Their 589 contents should match the respective private parts. These files 590 are not really used for anything; they are provided for the 591 convenience of the user so their contents can be copied to known 592 hosts files. These files are created using ssh-keygen(1). 593 594 /etc/ssh/ssh_known_hosts 595 Systemwide list of known host keys. This file should be prepared 596 by the system administrator to contain the public host keys of 597 all machines in the organization. The format of this file is 598 described above. This file should be writable only by root/the 599 owner and should be world-readable. 600 601 /etc/ssh/sshd_config 602 Contains configuration data for sshd. The file format and 603 configuration options are described in sshd_config(5). 604 605 /etc/ssh/sshrc 606 Similar to ~/.ssh/rc, it can be used to specify machine-specific 607 login-time initializations globally. This file should be 608 writable only by root, and should be world-readable. 609 610 /var/empty 611 chroot(2) directory used by sshd during privilege separation in 612 the pre-authentication phase. The directory should not contain 613 any files and must be owned by root and not group or world- 614 writable. 615 616 /var/run/sshd.pid 617 Contains the process ID of the sshd listening for connections (if 618 there are several daemons running concurrently for different 619 ports, this contains the process ID of the one started last). 620 The content of this file is not sensitive; it can be world- 621 readable. 622 623SEE ALSO 624 scp(1), sftp(1), ssh(1), ssh-add(1), ssh-agent(1), ssh-keygen(1), 625 ssh-keyscan(1), chroot(2), hosts_access(5), login.conf(5), moduli(5), 626 sshd_config(5), inetd(8), sftp-server(8) 627 628AUTHORS 629 OpenSSH is a derivative of the original and free ssh 1.2.12 release by 630 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo 631 de Raadt and Dug Song removed many bugs, re-added newer features and 632 created OpenSSH. Markus Friedl contributed the support for SSH protocol 633 versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support 634 for privilege separation. 635 636CAVEATS 637 System security is not improved unless rshd, rlogind, and rexecd are 638 disabled (thus completely disabling rlogin and rsh into the machine). 639 640OpenBSD 5.4 June 27, 2013 OpenBSD 5.4 641