1 SSHD(8) OpenBSD System Manager's Manual SSHD(8) 2 3 NAME 4 sshd - OpenSSH SSH daemon 5 6 SYNOPSIS 7 sshd [-46DdeiqTt] [-b bits] [-C connection_spec] 8 [-c host_certificate_file] [-f config_file] [-g login_grace_time] 9 [-h host_key_file] [-k key_gen_time] [-o option] [-p port] [-u len] 10 11 DESCRIPTION 12 sshd (OpenSSH Daemon) is the daemon program for ssh(1). Together these 13 programs replace rlogin(1) and rsh(1), and provide secure encrypted 14 communications between two untrusted hosts over an insecure network. 15 16 sshd listens for connections from clients. It is normally started at 17 boot from /etc/rc. It forks a new daemon for each incoming connection. 18 The forked daemons handle key exchange, encryption, authentication, 19 command execution, and data exchange. 20 21 sshd can be configured using command-line options or a configuration file 22 (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. 142 143 AUTHENTICATION 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 hmac-ripemd160, hmac-sha2-256 or hmac-sha2-512). 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. 203 204 LOGIN 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. 232 233 SSHRC 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. 262 263 AUTHORIZED_KEYS FILE FORMAT 264 AuthorizedKeysFile specifies the files containing public keys for public 265 key authentication; if none is specified, the default is 266 ~/.ssh/authorized_keys and ~/.ssh/authorized_keys2. Each line of the 267 file contains one key (empty lines and lines starting with a `#' are 268 ignored as comments). Protocol 1 public keys consist of the following 269 space-separated fields: options, bits, exponent, modulus, comment. 270 Protocol 2 public key consist of: options, keytype, base64-encoded key, 271 comment. The options field is optional; its presence is determined by 272 whether the line starts with a number or not (the options field never 273 starts with a number). The bits, exponent, modulus, and comment fields 274 give the RSA key for protocol version 1; the comment field is not used 275 for anything (but may be convenient for the user to identify the key). 276 For protocol version 2 the keytype is ``ecdsa-sha2-nistp256'', 277 ``ecdsa-sha2-nistp384'', ``ecdsa-sha2-nistp521'', ``ssh-dss'' or 278 ``ssh-rsa''. 279 280 Note that lines in this file are usually several hundred bytes long 281 (because of the size of the public key encoding) up to a limit of 8 282 kilobytes, which permits DSA keys up to 8 kilobits and RSA keys up to 16 283 kilobits. You don't want to type them in; instead, copy the 284 identity.pub, id_dsa.pub, id_ecdsa.pub, or the id_rsa.pub file and edit 285 it. 286 287 sshd enforces a minimum RSA key modulus size for protocol 1 and protocol 288 2 keys of 768 bits. 289 290 The options (if present) consist of comma-separated option 291 specifications. No spaces are permitted, except within double quotes. 292 The following option specifications are supported (note that option 293 keywords are case-insensitive): 294 295 cert-authority 296 Specifies that the listed key is a certification authority (CA) 297 that is trusted to validate signed certificates for user 298 authentication. 299 300 Certificates may encode access restrictions similar to these key 301 options. If both certificate restrictions and key options are 302 present, the most restrictive union of the two is applied. 303 304 command="command" 305 Specifies that the command is executed whenever this key is used 306 for authentication. The command supplied by the user (if any) is 307 ignored. The command is run on a pty if the client requests a 308 pty; otherwise it is run without a tty. If an 8-bit clean 309 channel is required, one must not request a pty or should specify 310 no-pty. A quote may be included in the command by quoting it 311 with a backslash. This option might be useful to restrict 312 certain public keys to perform just a specific operation. An 313 example might be a key that permits remote backups but nothing 314 else. Note that the client may specify TCP and/or X11 forwarding 315 unless they are explicitly prohibited. The command originally 316 supplied by the client is available in the SSH_ORIGINAL_COMMAND 317 environment variable. Note that this option applies to shell, 318 command or subsystem execution. Also note that this command may 319 be superseded by either a sshd_config(5) ForceCommand directive 320 or a command embedded in a certificate. 321 322 environment="NAME=value" 323 Specifies that the string is to be added to the environment when 324 logging in using this key. Environment variables set this way 325 override other default environment values. Multiple options of 326 this type are permitted. Environment processing is disabled by 327 default and is controlled via the PermitUserEnvironment option. 328 This option is automatically disabled if UseLogin is enabled. 329 330 from="pattern-list" 331 Specifies that in addition to public key authentication, either 332 the canonical name of the remote host or its IP address must be 333 present in the comma-separated list of patterns. See PATTERNS in 334 ssh_config(5) for more information on patterns. 335 336 In addition to the wildcard matching that may be applied to 337 hostnames or addresses, a from stanza may match IP addresses 338 using CIDR address/masklen notation. 339 340 The purpose of this option is to optionally increase security: 341 public key authentication by itself does not trust the network or 342 name servers or anything (but the key); however, if somebody 343 somehow steals the key, the key permits an intruder to log in 344 from anywhere in the world. This additional option makes using a 345 stolen key more difficult (name servers and/or routers would have 346 to be compromised in addition to just the key). 347 348 no-agent-forwarding 349 Forbids authentication agent forwarding when this key is used for 350 authentication. 351 352 no-port-forwarding 353 Forbids TCP forwarding when this key is used for authentication. 354 Any port forward requests by the client will return an error. 355 This might be used, e.g. in connection with the command option. 356 357 no-pty Prevents tty allocation (a request to allocate a pty will fail). 358 359 no-user-rc 360 Disables execution of ~/.ssh/rc. 361 362 no-X11-forwarding 363 Forbids X11 forwarding when this key is used for authentication. 364 Any X11 forward requests by the client will return an error. 365 366 permitopen="host:port" 367 Limit local ``ssh -L'' port forwarding such that it may only 368 connect to the specified host and port. IPv6 addresses can be 369 specified by enclosing the address in square brackets. Multiple 370 permitopen options may be applied separated by commas. No 371 pattern matching is performed on the specified hostnames, they 372 must be literal domains or addresses. 373 374 principals="principals" 375 On a cert-authority line, specifies allowed principals for 376 certificate authentication as a comma-separated list. At least 377 one name from the list must appear in the certificate's list of 378 principals for the certificate to be accepted. This option is 379 ignored for keys that are not marked as trusted certificate 380 signers using the cert-authority option. 381 382 tunnel="n" 383 Force a tun(4) device on the server. Without this option, the 384 next available device will be used if the client requests a 385 tunnel. 386 387 An example authorized_keys file: 388 389 # Comments allowed at start of line 390 ssh-rsa AAAAB3Nza...LiPk== user (a] example.net 391 from="*.sales.example.net,!pc.sales.example.net" ssh-rsa 392 AAAAB2...19Q== john (a] example.net 393 command="dump /home",no-pty,no-port-forwarding ssh-dss 394 AAAAC3...51R== example.net 395 permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-dss 396 AAAAB5...21S== 397 tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...== 398 jane (a] example.net 399 400 SSH_KNOWN_HOSTS FILE FORMAT 401 The /etc/ssh/ssh_known_hosts and ~/.ssh/known_hosts files contain host 402 public keys for all known hosts. The global file should be prepared by 403 the administrator (optional), and the per-user file is maintained 404 automatically: whenever the user connects from an unknown host, its key 405 is added to the per-user file. 406 407 Each line in these files contains the following fields: markers 408 (optional), hostnames, bits, exponent, modulus, comment. The fields are 409 separated by spaces. 410 411 The marker is optional, but if it is present then it must be one of 412 ``@cert-authority'', to indicate that the line contains a certification 413 authority (CA) key, or ``@revoked'', to indicate that the key contained 414 on the line is revoked and must not ever be accepted. Only one marker 415 should be used on a key line. 416 417 Hostnames is a comma-separated list of patterns (`*' and `?' act as 418 wildcards); each pattern in turn is matched against the canonical host 419 name (when authenticating a client) or against the user-supplied name 420 (when authenticating a server). A pattern may also be preceded by `!' to 421 indicate negation: if the host name matches a negated pattern, it is not 422 accepted (by that line) even if it matched another pattern on the line. 423 A hostname or address may optionally be enclosed within `[' and `]' 424 brackets then followed by `:' and a non-standard port number. 425 426 Alternately, hostnames may be stored in a hashed form which hides host 427 names and addresses should the file's contents be disclosed. Hashed 428 hostnames start with a `|' character. Only one hashed hostname may 429 appear on a single line and none of the above negation or wildcard 430 operators may be applied. 431 432 Bits, exponent, and modulus are taken directly from the RSA host key; 433 they can be obtained, for example, from /etc/ssh/ssh_host_key.pub. The 434 optional comment field continues to the end of the line, and is not used. 435 436 Lines starting with `#' and empty lines are ignored as comments. 437 438 When performing host authentication, authentication is accepted if any 439 matching line has the proper key; either one that matches exactly or, if 440 the server has presented a certificate for authentication, the key of the 441 certification authority that signed the certificate. For a key to be 442 trusted as a certification authority, it must use the ``@cert-authority'' 443 marker described above. 444 445 The known hosts file also provides a facility to mark keys as revoked, 446 for example when it is known that the associated private key has been 447 stolen. Revoked keys are specified by including the ``@revoked'' marker 448 at the beginning of the key line, and are never accepted for 449 authentication or as certification authorities, but instead will produce 450 a warning from ssh(1) when they are encountered. 451 452 It is permissible (but not recommended) to have several lines or 453 different host keys for the same names. This will inevitably happen when 454 short forms of host names from different domains are put in the file. It 455 is possible that the files contain conflicting information; 456 authentication is accepted if valid information can be found from either 457 file. 458 459 Note that the lines in these files are typically hundreds of characters 460 long, and you definitely don't want to type in the host keys by hand. 461 Rather, generate them by a script, ssh-keyscan(1) or by taking 462 /etc/ssh/ssh_host_key.pub and adding the host names at the front. 463 ssh-keygen(1) also offers some basic automated editing for 464 ~/.ssh/known_hosts including removing hosts matching a host name and 465 converting all host names to their hashed representations. 466 467 An example ssh_known_hosts file: 468 469 # Comments allowed at start of line 470 closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net 471 cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....= 472 # A hashed hostname 473 |1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa 474 AAAA1234.....= 475 # A revoked key 476 @revoked * ssh-rsa AAAAB5W... 477 # A CA key, accepted for any host in *.mydomain.com or *.mydomain.org 478 @cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W... 479 480 FILES 481 ~/.hushlogin 482 This file is used to suppress printing the last login time and 483 /etc/motd, if PrintLastLog and PrintMotd, respectively, are 484 enabled. It does not suppress printing of the banner specified 485 by Banner. 486 487 ~/.rhosts 488 This file is used for host-based authentication (see ssh(1) for 489 more information). On some machines this file may need to be 490 world-readable if the user's home directory is on an NFS 491 partition, because sshd reads it as root. Additionally, this 492 file must be owned by the user, and must not have write 493 permissions for anyone else. The recommended permission for most 494 machines is read/write for the user, and not accessible by 495 others. 496 497 ~/.shosts 498 This file is used in exactly the same way as .rhosts, but allows 499 host-based authentication without permitting login with 500 rlogin/rsh. 501 502 ~/.ssh/ 503 This directory is the default location for all user-specific 504 configuration and authentication information. There is no 505 general requirement to keep the entire contents of this directory 506 secret, but the recommended permissions are read/write/execute 507 for the user, and not accessible by others. 508 509 ~/.ssh/authorized_keys 510 Lists the public keys (DSA/ECDSA/RSA) that can be used for 511 logging in as this user. The format of this file is described 512 above. The content of the file is not highly sensitive, but the 513 recommended permissions are read/write for the user, and not 514 accessible by others. 515 516 If this file, the ~/.ssh directory, or the user's home directory 517 are writable by other users, then the file could be modified or 518 replaced by unauthorized users. In this case, sshd will not 519 allow it to be used unless the StrictModes option has been set to 520 ``no''. 521 522 ~/.ssh/environment 523 This file is read into the environment at login (if it exists). 524 It can only contain empty lines, comment lines (that start with 525 `#'), and assignment lines of the form name=value. The file 526 should be writable only by the user; it need not be readable by 527 anyone else. Environment processing is disabled by default and 528 is controlled via the PermitUserEnvironment option. 529 530 ~/.ssh/known_hosts 531 Contains a list of host keys for all hosts the user has logged 532 into that are not already in the systemwide list of known host 533 keys. The format of this file is described above. This file 534 should be writable only by root/the owner and can, but need not 535 be, world-readable. 536 537 ~/.ssh/rc 538 Contains initialization routines to be run before the user's home 539 directory becomes accessible. This file should be writable only 540 by the user, and need not be readable by anyone else. 541 542 /etc/hosts.allow 543 /etc/hosts.deny 544 Access controls that should be enforced by tcp-wrappers are 545 defined here. Further details are described in hosts_access(5). 546 547 /etc/hosts.equiv 548 This file is for host-based authentication (see ssh(1)). It 549 should only be writable by root. 550 551 /etc/moduli 552 Contains Diffie-Hellman groups used for the "Diffie-Hellman Group 553 Exchange". The file format is described in moduli(5). 554 555 /etc/motd 556 See motd(5). 557 558 /etc/nologin 559 If this file exists, sshd refuses to let anyone except root log 560 in. The contents of the file are displayed to anyone trying to 561 log in, and non-root connections are refused. The file should be 562 world-readable. 563 564 /etc/shosts.equiv 565 This file is used in exactly the same way as hosts.equiv, but 566 allows host-based authentication without permitting login with 567 rlogin/rsh. 568 569 /etc/ssh/ssh_host_key 570 /etc/ssh/ssh_host_dsa_key 571 /etc/ssh/ssh_host_ecdsa_key 572 /etc/ssh/ssh_host_rsa_key 573 These three files contain the private parts of the host keys. 574 These files should only be owned by root, readable only by root, 575 and not accessible to others. Note that sshd does not start if 576 these files are group/world-accessible. 577 578 /etc/ssh/ssh_host_key.pub 579 /etc/ssh/ssh_host_dsa_key.pub 580 /etc/ssh/ssh_host_ecdsa_key.pub 581 /etc/ssh/ssh_host_rsa_key.pub 582 These three files contain the public parts of the host keys. 583 These files should be world-readable but writable only by root. 584 Their contents should match the respective private parts. These 585 files are not really used for anything; they are provided for the 586 convenience of the user so their contents can be copied to known 587 hosts files. These files are created using ssh-keygen(1). 588 589 /etc/ssh/ssh_known_hosts 590 Systemwide list of known host keys. This file should be prepared 591 by the system administrator to contain the public host keys of 592 all machines in the organization. The format of this file is 593 described above. This file should be writable only by root/the 594 owner and should be world-readable. 595 596 /etc/ssh/sshd_config 597 Contains configuration data for sshd. The file format and 598 configuration options are described in sshd_config(5). 599 600 /etc/ssh/sshrc 601 Similar to ~/.ssh/rc, it can be used to specify machine-specific 602 login-time initializations globally. This file should be 603 writable only by root, and should be world-readable. 604 605 /var/empty 606 chroot(2) directory used by sshd during privilege separation in 607 the pre-authentication phase. The directory should not contain 608 any files and must be owned by root and not group or world- 609 writable. 610 611 /var/run/sshd.pid 612 Contains the process ID of the sshd listening for connections (if 613 there are several daemons running concurrently for different 614 ports, this contains the process ID of the one started last). 615 The content of this file is not sensitive; it can be world- 616 readable. 617 618 SEE ALSO 619 scp(1), sftp(1), ssh(1), ssh-add(1), ssh-agent(1), ssh-keygen(1), 620 ssh-keyscan(1), chroot(2), hosts_access(5), login.conf(5), moduli(5), 621 sshd_config(5), inetd(8), sftp-server(8) 622 623 AUTHORS 624 OpenSSH is a derivative of the original and free ssh 1.2.12 release by 625 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo 626 de Raadt and Dug Song removed many bugs, re-added newer features and 627 created OpenSSH. Markus Friedl contributed the support for SSH protocol 628 versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support 629 for privilege separation. 630 631 CAVEATS 632 System security is not improved unless rshd, rlogind, and rexecd are 633 disabled (thus completely disabling rlogin and rsh into the machine). 634 635 OpenBSD 5.0 August 2, 2011 OpenBSD 5.0 636
