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] [-f config_file] [-g login_grace_time] 9 [-h host_key_file] [-k key_gen_time] [-o option] [-p port] [-u len] 10 11DESCRIPTION 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'', ``laddr'', 44 ``lport'', and ``addr''. All are required and may be supplied in 45 any order, either with multiple -C options or as a comma- 46 separated list. 47 48 -c host_certificate_file 49 Specifies a path to a certificate file to identify sshd during 50 key exchange. The certificate file must match a host key file 51 specified using the -h option or the HostKey configuration 52 directive. 53 54 -D When this option is specified, sshd will not detach and does not 55 become a daemon. This allows easy monitoring of sshd. 56 57 -d Debug mode. The server sends verbose debug output to standard 58 error, and does not put itself in the background. The server 59 also will not fork and will only process one connection. This 60 option is only intended for debugging for the server. Multiple 61 -d options increase the debugging level. Maximum is 3. 62 63 -e When this option is specified, sshd will send the output to the 64 standard error instead of the system log. 65 66 -f config_file 67 Specifies the name of the configuration file. The default is 68 /etc/ssh/sshd_config. sshd refuses to start if there is no 69 configuration file. 70 71 -g login_grace_time 72 Gives the grace time for clients to authenticate themselves 73 (default 120 seconds). If the client fails to authenticate the 74 user within this many seconds, the server disconnects and exits. 75 A value of zero indicates no limit. 76 77 -h host_key_file 78 Specifies a file from which a host key is read. This option must 79 be given if sshd is not run as root (as the normal host key files 80 are normally not readable by anyone but root). The default is 81 /etc/ssh/ssh_host_key for protocol version 1, and 82 /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_ecdsa_key and 83 /etc/ssh/ssh_host_rsa_key for protocol version 2. It is possible 84 to have multiple host key files for the different protocol 85 versions and host key algorithms. 86 87 -i Specifies that sshd is being run from inetd(8). sshd is normally 88 not run from inetd because it needs to generate the server key 89 before it can respond to the client, and this may take tens of 90 seconds. Clients would have to wait too long if the key was 91 regenerated every time. However, with small key sizes (e.g. 512) 92 using sshd from inetd may be feasible. 93 94 -k key_gen_time 95 Specifies how often the ephemeral protocol version 1 server key 96 is regenerated (default 3600 seconds, or one hour). The 97 motivation for regenerating the key fairly often is that the key 98 is not stored anywhere, and after about an hour it becomes 99 impossible to recover the key for decrypting intercepted 100 communications even if the machine is cracked into or physically 101 seized. A value of zero indicates that the key will never be 102 regenerated. 103 104 -o option 105 Can be used to give options in the format used in the 106 configuration file. This is useful for specifying options for 107 which there is no separate command-line flag. For full details 108 of the options, and their values, see sshd_config(5). 109 110 -p port 111 Specifies the port on which the server listens for connections 112 (default 22). Multiple port options are permitted. Ports 113 specified in the configuration file with the Port option are 114 ignored when a command-line port is specified. Ports specified 115 using the ListenAddress option override command-line ports. 116 117 -q Quiet mode. Nothing is sent to the system log. Normally the 118 beginning, authentication, and termination of each connection is 119 logged. 120 121 -T Extended test mode. Check the validity of the configuration 122 file, output the effective configuration to stdout and then exit. 123 Optionally, Match rules may be applied by specifying the 124 connection parameters using one or more -C options. 125 126 -t Test mode. Only check the validity of the configuration file and 127 sanity of the keys. This is useful for updating sshd reliably as 128 configuration options may change. 129 130 -u len This option is used to specify the size of the field in the utmp 131 structure that holds the remote host name. If the resolved host 132 name is longer than len, the dotted decimal value will be used 133 instead. This allows hosts with very long host names that 134 overflow this field to still be uniquely identified. Specifying 135 -u0 indicates that only dotted decimal addresses should be put 136 into the utmp file. -u0 may also be used to prevent sshd from 137 making DNS requests unless the authentication mechanism or 138 configuration requires it. Authentication mechanisms that may 139 require DNS include RhostsRSAAuthentication, 140 HostbasedAuthentication, and using a from="pattern-list" option 141 in a key file. Configuration options that require DNS include 142 using a USER@HOST pattern in AllowUsers or DenyUsers. 143 144AUTHENTICATION 145 The OpenSSH SSH daemon supports SSH protocols 1 and 2. The default is to 146 use protocol 2 only, though this can be changed via the Protocol option 147 in sshd_config(5). Protocol 2 supports DSA, ECDSA and RSA keys; protocol 148 1 only supports RSA keys. For both protocols, each host has a host- 149 specific key, normally 2048 bits, used to identify the host. 150 151 Forward security for protocol 1 is provided through an additional server 152 key, normally 768 bits, generated when the server starts. This key is 153 normally regenerated every hour if it has been used, and is never stored 154 on disk. Whenever a client connects, the daemon responds with its public 155 host and server keys. The client compares the RSA host key against its 156 own database to verify that it has not changed. The client then 157 generates a 256-bit random number. It encrypts this random number using 158 both the host key and the server key, and sends the encrypted number to 159 the server. Both sides then use this random number as a session key 160 which is used to encrypt all further communications in the session. The 161 rest of the session is encrypted using a conventional cipher, currently 162 Blowfish or 3DES, with 3DES being used by default. The client selects 163 the encryption algorithm to use from those offered by the server. 164 165 For protocol 2, forward security is provided through a Diffie-Hellman key 166 agreement. This key agreement results in a shared session key. The rest 167 of the session is encrypted using a symmetric cipher, currently 128-bit 168 AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES. The 169 client selects the encryption algorithm to use from those offered by the 170 server. Additionally, session integrity is provided through a 171 cryptographic message authentication code (hmac-md5, hmac-sha1, umac-64, 172 umac-128, hmac-ripemd160, hmac-sha2-256 or hmac-sha2-512). 173 174 Finally, the server and the client enter an authentication dialog. The 175 client tries to authenticate itself using host-based authentication, 176 public key authentication, challenge-response authentication, or password 177 authentication. 178 179 Regardless of the authentication type, the account is checked to ensure 180 that it is accessible. An account is not accessible if it is locked, 181 listed in DenyUsers or its group is listed in DenyGroups . The 182 definition of a locked account is system dependant. Some platforms have 183 their own account database (eg AIX) and some modify the passwd field ( 184 `*LK*' on Solaris and UnixWare, `*' on HP-UX, containing `Nologin' on 185 Tru64, a leading `*LOCKED*' on FreeBSD and a leading `!' on most 186 Linuxes). If there is a requirement to disable password authentication 187 for the account while allowing still public-key, then the passwd field 188 should be set to something other than these values (eg `NP' or `*NP*' ). 189 190 If the client successfully authenticates itself, a dialog for preparing 191 the session is entered. At this time the client may request things like 192 allocating a pseudo-tty, forwarding X11 connections, forwarding TCP 193 connections, or forwarding the authentication agent connection over the 194 secure channel. 195 196 After this, the client either requests a shell or execution of a command. 197 The sides then enter session mode. In this mode, either side may send 198 data at any time, and such data is forwarded to/from the shell or command 199 on the server side, and the user terminal in the client side. 200 201 When the user program terminates and all forwarded X11 and other 202 connections have been closed, the server sends command exit status to the 203 client, and both sides exit. 204 205LOGIN PROCESS 206 When a user successfully logs in, sshd does the following: 207 208 1. If the login is on a tty, and no command has been specified, 209 prints last login time and /etc/motd (unless prevented in the 210 configuration file or by ~/.hushlogin; see the FILES section). 211 212 2. If the login is on a tty, records login time. 213 214 3. Checks /etc/nologin; if it exists, prints contents and quits 215 (unless root). 216 217 4. Changes to run with normal user privileges. 218 219 5. Sets up basic environment. 220 221 6. Reads the file ~/.ssh/environment, if it exists, and users are 222 allowed to change their environment. See the 223 PermitUserEnvironment option in sshd_config(5). 224 225 7. Changes to user's home directory. 226 227 8. If ~/.ssh/rc exists, runs it; else if /etc/ssh/sshrc exists, 228 runs it; otherwise runs xauth. The ``rc'' files are given the 229 X11 authentication protocol and cookie in standard input. See 230 SSHRC, below. 231 232 9. Runs user's shell or command. 233 234SSHRC 235 If the file ~/.ssh/rc exists, sh(1) runs it after reading the environment 236 files but before starting the user's shell or command. It must not 237 produce any output on stdout; stderr must be used instead. If X11 238 forwarding is in use, it will receive the "proto cookie" pair in its 239 standard input (and DISPLAY in its environment). The script must call 240 xauth(1) because sshd will not run xauth automatically to add X11 241 cookies. 242 243 The primary purpose of this file is to run any initialization routines 244 which may be needed before the user's home directory becomes accessible; 245 AFS is a particular example of such an environment. 246 247 This file will probably contain some initialization code followed by 248 something similar to: 249 250 if read proto cookie && [ -n "$DISPLAY" ]; then 251 if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then 252 # X11UseLocalhost=yes 253 echo add unix:`echo $DISPLAY | 254 cut -c11-` $proto $cookie 255 else 256 # X11UseLocalhost=no 257 echo add $DISPLAY $proto $cookie 258 fi | xauth -q - 259 fi 260 261 If this file does not exist, /etc/ssh/sshrc is run, and if that does not 262 exist either, xauth is used to add the cookie. 263 264AUTHORIZED_KEYS FILE FORMAT 265 AuthorizedKeysFile specifies the files containing public keys for public 266 key authentication; if none is specified, the default is 267 ~/.ssh/authorized_keys and ~/.ssh/authorized_keys2. Each line of the 268 file contains one key (empty lines and lines starting with a `#' are 269 ignored as comments). Protocol 1 public keys consist of the following 270 space-separated fields: options, bits, exponent, modulus, comment. 271 Protocol 2 public key consist of: options, keytype, base64-encoded key, 272 comment. The options field is optional; its presence is determined by 273 whether the line starts with a number or not (the options field never 274 starts with a number). The bits, exponent, modulus, and comment fields 275 give the RSA key for protocol version 1; the comment field is not used 276 for anything (but may be convenient for the user to identify the key). 277 For protocol version 2 the keytype is ``ecdsa-sha2-nistp256'', 278 ``ecdsa-sha2-nistp384'', ``ecdsa-sha2-nistp521'', ``ssh-dss'' or 279 ``ssh-rsa''. 280 281 Note that lines in this file are usually several hundred bytes long 282 (because of the size of the public key encoding) up to a limit of 8 283 kilobytes, which permits DSA keys up to 8 kilobits and RSA keys up to 16 284 kilobits. You don't want to type them in; instead, copy the 285 identity.pub, id_dsa.pub, id_ecdsa.pub, or the id_rsa.pub file and edit 286 it. 287 288 sshd enforces a minimum RSA key modulus size for protocol 1 and protocol 289 2 keys of 768 bits. 290 291 The options (if present) consist of comma-separated option 292 specifications. No spaces are permitted, except within double quotes. 293 The following option specifications are supported (note that option 294 keywords are case-insensitive): 295 296 cert-authority 297 Specifies that the listed key is a certification authority (CA) 298 that is trusted to validate signed certificates for user 299 authentication. 300 301 Certificates may encode access restrictions similar to these key 302 options. If both certificate restrictions and key options are 303 present, the most restrictive union of the two is applied. 304 305 command="command" 306 Specifies that the command is executed whenever this key is used 307 for authentication. The command supplied by the user (if any) is 308 ignored. The command is run on a pty if the client requests a 309 pty; otherwise it is run without a tty. If an 8-bit clean 310 channel is required, one must not request a pty or should specify 311 no-pty. A quote may be included in the command by quoting it 312 with a backslash. This option might be useful to restrict 313 certain public keys to perform just a specific operation. An 314 example might be a key that permits remote backups but nothing 315 else. Note that the client may specify TCP and/or X11 forwarding 316 unless they are explicitly prohibited. The command originally 317 supplied by the client is available in the SSH_ORIGINAL_COMMAND 318 environment variable. Note that this option applies to shell, 319 command or subsystem execution. Also note that this command may 320 be superseded by either a sshd_config(5) ForceCommand directive 321 or a command embedded in a certificate. 322 323 environment="NAME=value" 324 Specifies that the string is to be added to the environment when 325 logging in using this key. Environment variables set this way 326 override other default environment values. Multiple options of 327 this type are permitted. Environment processing is disabled by 328 default and is controlled via the PermitUserEnvironment option. 329 This option is automatically disabled if UseLogin is enabled. 330 331 from="pattern-list" 332 Specifies that in addition to public key authentication, either 333 the canonical name of the remote host or its IP address must be 334 present in the comma-separated list of patterns. See PATTERNS in 335 ssh_config(5) for more information on patterns. 336 337 In addition to the wildcard matching that may be applied to 338 hostnames or addresses, a from stanza may match IP addresses 339 using CIDR address/masklen notation. 340 341 The purpose of this option is to optionally increase security: 342 public key authentication by itself does not trust the network or 343 name servers or anything (but the key); however, if somebody 344 somehow steals the key, the key permits an intruder to log in 345 from anywhere in the world. This additional option makes using a 346 stolen key more difficult (name servers and/or routers would have 347 to be compromised in addition to just the key). 348 349 no-agent-forwarding 350 Forbids authentication agent forwarding when this key is used for 351 authentication. 352 353 no-port-forwarding 354 Forbids TCP forwarding when this key is used for authentication. 355 Any port forward requests by the client will return an error. 356 This might be used, e.g. in connection with the command option. 357 358 no-pty Prevents tty allocation (a request to allocate a pty will fail). 359 360 no-user-rc 361 Disables execution of ~/.ssh/rc. 362 363 no-X11-forwarding 364 Forbids X11 forwarding when this key is used for authentication. 365 Any X11 forward requests by the client will return an error. 366 367 permitopen="host:port" 368 Limit local ``ssh -L'' port forwarding such that it may only 369 connect to the specified host and port. IPv6 addresses can be 370 specified by enclosing the address in square brackets. Multiple 371 permitopen options may be applied separated by commas. No 372 pattern matching is performed on the specified hostnames, they 373 must be literal domains or addresses. A port specification of * 374 matches any port. 375 376 principals="principals" 377 On a cert-authority line, specifies allowed principals for 378 certificate authentication as a comma-separated list. At least 379 one name from the list must appear in the certificate's list of 380 principals for the certificate to be accepted. This option is 381 ignored for keys that are not marked as trusted certificate 382 signers using the cert-authority option. 383 384 tunnel="n" 385 Force a tun(4) device on the server. Without this option, the 386 next available device will be used if the client requests a 387 tunnel. 388 389 An example authorized_keys file: 390 391 # Comments allowed at start of line 392 ssh-rsa AAAAB3Nza...LiPk== user@example.net 393 from="*.sales.example.net,!pc.sales.example.net" ssh-rsa 394 AAAAB2...19Q== john@example.net 395 command="dump /home",no-pty,no-port-forwarding ssh-dss 396 AAAAC3...51R== example.net 397 permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-dss 398 AAAAB5...21S== 399 tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...== 400 jane@example.net 401 402SSH_KNOWN_HOSTS FILE FORMAT 403 The /etc/ssh/ssh_known_hosts and ~/.ssh/known_hosts files contain host 404 public keys for all known hosts. The global file should be prepared by 405 the administrator (optional), and the per-user file is maintained 406 automatically: whenever the user connects from an unknown host, its key 407 is added to the per-user file. 408 409 Each line in these files contains the following fields: markers 410 (optional), hostnames, bits, exponent, modulus, comment. The fields are 411 separated by spaces. 412 413 The marker is optional, but if it is present then it must be one of 414 ``@cert-authority'', to indicate that the line contains a certification 415 authority (CA) key, or ``@revoked'', to indicate that the key contained 416 on the line is revoked and must not ever be accepted. Only one marker 417 should be used on a key line. 418 419 Hostnames is a comma-separated list of patterns (`*' and `?' act as 420 wildcards); each pattern in turn is matched against the canonical host 421 name (when authenticating a client) or against the user-supplied name 422 (when authenticating a server). A pattern may also be preceded by `!' to 423 indicate negation: if the host name matches a negated pattern, it is not 424 accepted (by that line) even if it matched another pattern on the line. 425 A hostname or address may optionally be enclosed within `[' and `]' 426 brackets then followed by `:' and a non-standard port number. 427 428 Alternately, hostnames may be stored in a hashed form which hides host 429 names and addresses should the file's contents be disclosed. Hashed 430 hostnames start with a `|' character. Only one hashed hostname may 431 appear on a single line and none of the above negation or wildcard 432 operators may be applied. 433 434 Bits, exponent, and modulus are taken directly from the RSA host key; 435 they can be obtained, for example, from /etc/ssh/ssh_host_key.pub. The 436 optional comment field continues to the end of the line, and is not used. 437 438 Lines starting with `#' and empty lines are ignored as comments. 439 440 When performing host authentication, authentication is accepted if any 441 matching line has the proper key; either one that matches exactly or, if 442 the server has presented a certificate for authentication, the key of the 443 certification authority that signed the certificate. For a key to be 444 trusted as a certification authority, it must use the ``@cert-authority'' 445 marker described above. 446 447 The known hosts file also provides a facility to mark keys as revoked, 448 for example when it is known that the associated private key has been 449 stolen. Revoked keys are specified by including the ``@revoked'' marker 450 at the beginning of the key line, and are never accepted for 451 authentication or as certification authorities, but instead will produce 452 a warning from ssh(1) when they are encountered. 453 454 It is permissible (but not recommended) to have several lines or 455 different host keys for the same names. This will inevitably happen when 456 short forms of host names from different domains are put in the file. It 457 is possible that the files contain conflicting information; 458 authentication is accepted if valid information can be found from either 459 file. 460 461 Note that the lines in these files are typically hundreds of characters 462 long, and you definitely don't want to type in the host keys by hand. 463 Rather, generate them by a script, ssh-keyscan(1) or by taking 464 /etc/ssh/ssh_host_key.pub and adding the host names at the front. 465 ssh-keygen(1) also offers some basic automated editing for 466 ~/.ssh/known_hosts including removing hosts matching a host name and 467 converting all host names to their hashed representations. 468 469 An example ssh_known_hosts file: 470 471 # Comments allowed at start of line 472 closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net 473 cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....= 474 # A hashed hostname 475 |1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa 476 AAAA1234.....= 477 # A revoked key 478 @revoked * ssh-rsa AAAAB5W... 479 # A CA key, accepted for any host in *.mydomain.com or *.mydomain.org 480 @cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W... 481 482FILES 483 ~/.hushlogin 484 This file is used to suppress printing the last login time and 485 /etc/motd, if PrintLastLog and PrintMotd, respectively, are 486 enabled. It does not suppress printing of the banner specified 487 by Banner. 488 489 ~/.rhosts 490 This file is used for host-based authentication (see ssh(1) for 491 more information). On some machines this file may need to be 492 world-readable if the user's home directory is on an NFS 493 partition, because sshd reads it as root. Additionally, this 494 file must be owned by the user, and must not have write 495 permissions for anyone else. The recommended permission for most 496 machines is read/write for the user, and not accessible by 497 others. 498 499 ~/.shosts 500 This file is used in exactly the same way as .rhosts, but allows 501 host-based authentication without permitting login with 502 rlogin/rsh. 503 504 ~/.ssh/ 505 This directory is the default location for all user-specific 506 configuration and authentication information. There is no 507 general requirement to keep the entire contents of this directory 508 secret, but the recommended permissions are read/write/execute 509 for the user, and not accessible by others. 510 511 ~/.ssh/authorized_keys 512 Lists the public keys (DSA/ECDSA/RSA) that can be used for 513 logging in as this user. The format of this file is described 514 above. The content of the file is not highly sensitive, but the 515 recommended permissions are read/write for the user, and not 516 accessible by others. 517 518 If this file, the ~/.ssh directory, or the user's home directory 519 are writable by other users, then the file could be modified or 520 replaced by unauthorized users. In this case, sshd will not 521 allow it to be used unless the StrictModes option has been set to 522 ``no''. 523 524 ~/.ssh/environment 525 This file is read into the environment at login (if it exists). 526 It can only contain empty lines, comment lines (that start with 527 `#'), and assignment lines of the form name=value. The file 528 should be writable only by the user; it need not be readable by 529 anyone else. Environment processing is disabled by default and 530 is controlled via the PermitUserEnvironment option. 531 532 ~/.ssh/known_hosts 533 Contains a list of host keys for all hosts the user has logged 534 into that are not already in the systemwide list of known host 535 keys. The format of this file is described above. This file 536 should be writable only by root/the owner and can, but need not 537 be, world-readable. 538 539 ~/.ssh/rc 540 Contains initialization routines to be run before the user's home 541 directory becomes accessible. This file should be writable only 542 by the user, and need not be readable by anyone else. 543 544 /etc/hosts.allow 545 /etc/hosts.deny 546 Access controls that should be enforced by tcp-wrappers are 547 defined here. Further details are described in hosts_access(5). 548 549 /etc/hosts.equiv 550 This file is for host-based authentication (see ssh(1)). It 551 should only be writable by root. 552 553 /etc/moduli 554 Contains Diffie-Hellman groups used for the "Diffie-Hellman Group 555 Exchange". The file format is described in moduli(5). 556 557 /etc/motd 558 See motd(5). 559 560 /etc/nologin 561 If this file exists, sshd refuses to let anyone except root log 562 in. The contents of the file are displayed to anyone trying to 563 log in, and non-root connections are refused. The file should be 564 world-readable. 565 566 /etc/shosts.equiv 567 This file is used in exactly the same way as hosts.equiv, but 568 allows host-based authentication without permitting login with 569 rlogin/rsh. 570 571 /etc/ssh/ssh_host_key 572 /etc/ssh/ssh_host_dsa_key 573 /etc/ssh/ssh_host_ecdsa_key 574 /etc/ssh/ssh_host_rsa_key 575 These files contain the private parts of the host keys. These 576 files should only be owned by root, readable only by root, and 577 not accessible to others. Note that sshd does not start if these 578 files are group/world-accessible. 579 580 /etc/ssh/ssh_host_key.pub 581 /etc/ssh/ssh_host_dsa_key.pub 582 /etc/ssh/ssh_host_ecdsa_key.pub 583 /etc/ssh/ssh_host_rsa_key.pub 584 These files contain the public parts of the host keys. These 585 files should be world-readable but writable only by root. Their 586 contents should match the respective private parts. These files 587 are not really used for anything; they are provided for the 588 convenience of the user so their contents can be copied to known 589 hosts files. These files are created using ssh-keygen(1). 590 591 /etc/ssh/ssh_known_hosts 592 Systemwide list of known host keys. This file should be prepared 593 by the system administrator to contain the public host keys of 594 all machines in the organization. The format of this file is 595 described above. This file should be writable only by root/the 596 owner and should be world-readable. 597 598 /etc/ssh/sshd_config 599 Contains configuration data for sshd. The file format and 600 configuration options are described in sshd_config(5). 601 602 /etc/ssh/sshrc 603 Similar to ~/.ssh/rc, it can be used to specify machine-specific 604 login-time initializations globally. This file should be 605 writable only by root, and should be world-readable. 606 607 /var/empty 608 chroot(2) directory used by sshd during privilege separation in 609 the pre-authentication phase. The directory should not contain 610 any files and must be owned by root and not group or world- 611 writable. 612 613 /var/run/sshd.pid 614 Contains the process ID of the sshd listening for connections (if 615 there are several daemons running concurrently for different 616 ports, this contains the process ID of the one started last). 617 The content of this file is not sensitive; it can be world- 618 readable. 619 620SEE ALSO 621 scp(1), sftp(1), ssh(1), ssh-add(1), ssh-agent(1), ssh-keygen(1), 622 ssh-keyscan(1), chroot(2), hosts_access(5), sshd_config(5) 623 sftp-server(8) 624 625AUTHORS 626 OpenSSH is a derivative of the original and free ssh 1.2.12 release by 627 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo 628 de Raadt and Dug Song removed many bugs, re-added newer features and 629 created OpenSSH. Markus Friedl contributed the support for SSH protocol 630 versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support 631 for privilege separation. 632 633CAVEATS 634 System security is not improved unless rshd, rlogind, and rexecd are 635 disabled (thus completely disabling rlogin and rsh into the machine). 636 637OpenBSD 5.3 October 4, 2012 OpenBSD 5.3 638