1SSHD(8) System Manager's Manual SSHD(8) 2 3NAME 4 sshd M-bM-^@M-^S OpenSSH SSH daemon 5 6SYNOPSIS 7 sshd [-46DdeiqTt] [-C connection_spec] [-c host_certificate_file] 8 [-E log_file] [-f config_file] [-g login_grace_time] 9 [-h host_key_file] [-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 and rsh, 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 -C connection_spec 34 Specify the connection parameters to use for the -T extended test 35 mode. If provided, any Match directives in the configuration 36 file that would apply to the specified user, host, and address 37 will be set before the configuration is written to standard 38 output. The connection parameters are supplied as keyword=value 39 pairs. The keywords are M-bM-^@M-^\userM-bM-^@M-^], M-bM-^@M-^\hostM-bM-^@M-^], M-bM-^@M-^\laddrM-bM-^@M-^], M-bM-^@M-^\lportM-bM-^@M-^], and 40 M-bM-^@M-^\addrM-bM-^@M-^]. All are required and may be supplied in any order, 41 either with multiple -C options or as a comma-separated list. 42 43 -c host_certificate_file 44 Specifies a path to a certificate file to identify sshd during 45 key exchange. The certificate file must match a host key file 46 specified using the -h option or the HostKey configuration 47 directive. 48 49 -D When this option is specified, sshd will not detach and does not 50 become a daemon. This allows easy monitoring of sshd. 51 52 -d Debug mode. The server sends verbose debug output to standard 53 error, and does not put itself in the background. The server 54 also will not fork and will only process one connection. This 55 option is only intended for debugging for the server. Multiple 56 -d options increase the debugging level. Maximum is 3. 57 58 -E log_file 59 Append debug logs to log_file instead of the system log. 60 61 -e Write debug logs to standard error instead of the system log. 62 63 -f config_file 64 Specifies the name of the configuration file. The default is 65 /etc/ssh/sshd_config. sshd refuses to start if there is no 66 configuration file. 67 68 -g login_grace_time 69 Gives the grace time for clients to authenticate themselves 70 (default 120 seconds). If the client fails to authenticate the 71 user within this many seconds, the server disconnects and exits. 72 A value of zero indicates no limit. 73 74 -h host_key_file 75 Specifies a file from which a host key is read. This option must 76 be given if sshd is not run as root (as the normal host key files 77 are normally not readable by anyone but root). The default is 78 /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_ecdsa_key, 79 /etc/ssh/ssh_host_ed25519_key and /etc/ssh/ssh_host_rsa_key. It 80 is possible to have multiple host key files for the different 81 host key algorithms. 82 83 -i Specifies that sshd is being run from inetd(8). 84 85 -o option 86 Can be used to give options in the format used in the 87 configuration file. This is useful for specifying options for 88 which there is no separate command-line flag. For full details 89 of the options, and their values, see sshd_config(5). 90 91 -p port 92 Specifies the port on which the server listens for connections 93 (default 22). Multiple port options are permitted. Ports 94 specified in the configuration file with the Port option are 95 ignored when a command-line port is specified. Ports specified 96 using the ListenAddress option override command-line ports. 97 98 -q Quiet mode. Nothing is sent to the system log. Normally the 99 beginning, authentication, and termination of each connection is 100 logged. 101 102 -T Extended test mode. Check the validity of the configuration 103 file, output the effective configuration to stdout and then exit. 104 Optionally, Match rules may be applied by specifying the 105 connection parameters using one or more -C options. 106 107 -t Test mode. Only check the validity of the configuration file and 108 sanity of the keys. This is useful for updating sshd reliably as 109 configuration options may change. 110 111 -u len This option is used to specify the size of the field in the utmp 112 structure that holds the remote host name. If the resolved host 113 name is longer than len, the dotted decimal value will be used 114 instead. This allows hosts with very long host names that 115 overflow this field to still be uniquely identified. Specifying 116 -u0 indicates that only dotted decimal addresses should be put 117 into the utmp file. -u0 may also be used to prevent sshd from 118 making DNS requests unless the authentication mechanism or 119 configuration requires it. Authentication mechanisms that may 120 require DNS include HostbasedAuthentication and using a 121 from="pattern-list" option in a key file. Configuration options 122 that require DNS include using a USER@HOST pattern in AllowUsers 123 or DenyUsers. 124 125AUTHENTICATION 126 The OpenSSH SSH daemon supports SSH protocol 2 only. Each host has a 127 host-specific key, used to identify the host. Whenever a client 128 connects, the daemon responds with its public host key. The client 129 compares the host key against its own database to verify that it has not 130 changed. Forward security is provided through a Diffie-Hellman key 131 agreement. This key agreement results in a shared session key. The rest 132 of the session is encrypted using a symmetric cipher, currently 128-bit 133 AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES. The 134 client selects the encryption algorithm to use from those offered by the 135 server. Additionally, session integrity is provided through a 136 cryptographic message authentication code (hmac-md5, hmac-sha1, umac-64, 137 umac-128, hmac-ripemd160, hmac-sha2-256 or hmac-sha2-512). 138 139 Finally, the server and the client enter an authentication dialog. The 140 client tries to authenticate itself using host-based authentication, 141 public key authentication, challenge-response authentication, or password 142 authentication. 143 144 Regardless of the authentication type, the account is checked to ensure 145 that it is accessible. An account is not accessible if it is locked, 146 listed in DenyUsers or its group is listed in DenyGroups . The 147 definition of a locked account is system dependant. Some platforms have 148 their own account database (eg AIX) and some modify the passwd field ( 149 M-bM-^@M-^X*LK*M-bM-^@M-^Y on Solaris and UnixWare, M-bM-^@M-^X*M-bM-^@M-^Y on HP-UX, containing M-bM-^@M-^XNologinM-bM-^@M-^Y on 150 Tru64, a leading M-bM-^@M-^X*LOCKED*M-bM-^@M-^Y on FreeBSD and a leading M-bM-^@M-^X!M-bM-^@M-^Y on most 151 Linuxes). If there is a requirement to disable password authentication 152 for the account while allowing still public-key, then the passwd field 153 should be set to something other than these values (eg M-bM-^@M-^XNPM-bM-^@M-^Y or M-bM-^@M-^X*NP*M-bM-^@M-^Y ). 154 155 If the client successfully authenticates itself, a dialog for preparing 156 the session is entered. At this time the client may request things like 157 allocating a pseudo-tty, forwarding X11 connections, forwarding TCP 158 connections, or forwarding the authentication agent connection over the 159 secure channel. 160 161 After this, the client either requests a shell or execution of a command. 162 The sides then enter session mode. In this mode, either side may send 163 data at any time, and such data is forwarded to/from the shell or command 164 on the server side, and the user terminal in the client side. 165 166 When the user program terminates and all forwarded X11 and other 167 connections have been closed, the server sends command exit status to the 168 client, and both sides exit. 169 170LOGIN PROCESS 171 When a user successfully logs in, sshd does the following: 172 173 1. If the login is on a tty, and no command has been specified, 174 prints last login time and /etc/motd (unless prevented in the 175 configuration file or by ~/.hushlogin; see the FILES section). 176 177 2. If the login is on a tty, records login time. 178 179 3. Checks /etc/nologin; if it exists, prints contents and quits 180 (unless root). 181 182 4. Changes to run with normal user privileges. 183 184 5. Sets up basic environment. 185 186 6. Reads the file ~/.ssh/environment, if it exists, and users are 187 allowed to change their environment. See the 188 PermitUserEnvironment option in sshd_config(5). 189 190 7. Changes to user's home directory. 191 192 8. If ~/.ssh/rc exists and the sshd_config(5) PermitUserRC option 193 is set, runs it; else if /etc/ssh/sshrc exists, runs it; 194 otherwise runs xauth. The M-bM-^@M-^\rcM-bM-^@M-^] files are given the X11 195 authentication protocol and cookie in standard input. See 196 SSHRC, below. 197 198 9. Runs user's shell or command. All commands are run under the 199 user's login shell as specified in the system password 200 database. 201 202SSHRC 203 If the file ~/.ssh/rc exists, sh(1) runs it after reading the environment 204 files but before starting the user's shell or command. It must not 205 produce any output on stdout; stderr must be used instead. If X11 206 forwarding is in use, it will receive the "proto cookie" pair in its 207 standard input (and DISPLAY in its environment). The script must call 208 xauth(1) because sshd will not run xauth automatically to add X11 209 cookies. 210 211 The primary purpose of this file is to run any initialization routines 212 which may be needed before the user's home directory becomes accessible; 213 AFS is a particular example of such an environment. 214 215 This file will probably contain some initialization code followed by 216 something similar to: 217 218 if read proto cookie && [ -n "$DISPLAY" ]; then 219 if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then 220 # X11UseLocalhost=yes 221 echo add unix:`echo $DISPLAY | 222 cut -c11-` $proto $cookie 223 else 224 # X11UseLocalhost=no 225 echo add $DISPLAY $proto $cookie 226 fi | xauth -q - 227 fi 228 229 If this file does not exist, /etc/ssh/sshrc is run, and if that does not 230 exist either, xauth is used to add the cookie. 231 232AUTHORIZED_KEYS FILE FORMAT 233 AuthorizedKeysFile specifies the files containing public keys for public 234 key authentication; if this option is not specified, the default is 235 ~/.ssh/authorized_keys and ~/.ssh/authorized_keys2. Each line of the 236 file contains one key (empty lines and lines starting with a M-bM-^@M-^X#M-bM-^@M-^Y are 237 ignored as comments). Public keys consist of the following space- 238 separated fields: options, keytype, base64-encoded key, comment. The 239 options field is optional. The keytype is M-bM-^@M-^\ecdsa-sha2-nistp256M-bM-^@M-^], 240 M-bM-^@M-^\ecdsa-sha2-nistp384M-bM-^@M-^], M-bM-^@M-^\ecdsa-sha2-nistp521M-bM-^@M-^], M-bM-^@M-^\ssh-ed25519M-bM-^@M-^], M-bM-^@M-^\ssh-dssM-bM-^@M-^] or 241 M-bM-^@M-^\ssh-rsaM-bM-^@M-^]; the comment field is not used for anything (but may be 242 convenient for the user to identify the key). 243 244 Note that lines in this file can be several hundred bytes long (because 245 of the size of the public key encoding) up to a limit of 8 kilobytes, 246 which permits DSA keys up to 8 kilobits and RSA keys up to 16 kilobits. 247 You don't want to type them in; instead, copy the id_dsa.pub, 248 id_ecdsa.pub, id_ed25519.pub, or the id_rsa.pub file and edit it. 249 250 sshd enforces a minimum RSA key modulus size of 768 bits. 251 252 The options (if present) consist of comma-separated option 253 specifications. No spaces are permitted, except within double quotes. 254 The following option specifications are supported (note that option 255 keywords are case-insensitive): 256 257 agent-forwarding 258 Enable authentication agent forwarding previously disabled by the 259 restrict option. 260 261 cert-authority 262 Specifies that the listed key is a certification authority (CA) 263 that is trusted to validate signed certificates for user 264 authentication. 265 266 Certificates may encode access restrictions similar to these key 267 options. If both certificate restrictions and key options are 268 present, the most restrictive union of the two is applied. 269 270 command="command" 271 Specifies that the command is executed whenever this key is used 272 for authentication. The command supplied by the user (if any) is 273 ignored. The command is run on a pty if the client requests a 274 pty; otherwise it is run without a tty. If an 8-bit clean 275 channel is required, one must not request a pty or should specify 276 no-pty. A quote may be included in the command by quoting it 277 with a backslash. 278 279 This option might be useful to restrict certain public keys to 280 perform just a specific operation. An example might be a key 281 that permits remote backups but nothing else. Note that the 282 client may specify TCP and/or X11 forwarding unless they are 283 explicitly prohibited, e.g. using the restrict key option. 284 285 The command originally supplied by the client is available in the 286 SSH_ORIGINAL_COMMAND environment variable. Note that this option 287 applies to shell, command or subsystem execution. Also note that 288 this command may be superseded by a sshd_config(5) ForceCommand 289 directive. 290 291 If a command is specified and a forced-command is embedded in a 292 certificate used for authentication, then the certificate will be 293 accepted only if the two commands are identical. 294 295 environment="NAME=value" 296 Specifies that the string is to be added to the environment when 297 logging in using this key. Environment variables set this way 298 override other default environment values. Multiple options of 299 this type are permitted. Environment processing is disabled by 300 default and is controlled via the PermitUserEnvironment option. 301 302 from="pattern-list" 303 Specifies that in addition to public key authentication, either 304 the canonical name of the remote host or its IP address must be 305 present in the comma-separated list of patterns. See PATTERNS in 306 ssh_config(5) for more information on patterns. 307 308 In addition to the wildcard matching that may be applied to 309 hostnames or addresses, a from stanza may match IP addresses 310 using CIDR address/masklen notation. 311 312 The purpose of this option is to optionally increase security: 313 public key authentication by itself does not trust the network or 314 name servers or anything (but the key); however, if somebody 315 somehow steals the key, the key permits an intruder to log in 316 from anywhere in the world. This additional option makes using a 317 stolen key more difficult (name servers and/or routers would have 318 to be compromised in addition to just the key). 319 320 no-agent-forwarding 321 Forbids authentication agent forwarding when this key is used for 322 authentication. 323 324 no-port-forwarding 325 Forbids TCP forwarding when this key is used for authentication. 326 Any port forward requests by the client will return an error. 327 This might be used, e.g. in connection with the command option. 328 329 no-pty Prevents tty allocation (a request to allocate a pty will fail). 330 331 no-user-rc 332 Disables execution of ~/.ssh/rc. 333 334 no-X11-forwarding 335 Forbids X11 forwarding when this key is used for authentication. 336 Any X11 forward requests by the client will return an error. 337 338 permitopen="host:port" 339 Limit local port forwarding with ssh(1) -L such that it may only 340 connect to the specified host and port. IPv6 addresses can be 341 specified by enclosing the address in square brackets. Multiple 342 permitopen options may be applied separated by commas. No 343 pattern matching is performed on the specified hostnames, they 344 must be literal domains or addresses. A port specification of * 345 matches any port. 346 347 port-forwarding 348 Enable port forwarding previously disabled by the restrict 349 350 principals="principals" 351 On a cert-authority line, specifies allowed principals for 352 certificate authentication as a comma-separated list. At least 353 one name from the list must appear in the certificate's list of 354 principals for the certificate to be accepted. This option is 355 ignored for keys that are not marked as trusted certificate 356 signers using the cert-authority option. 357 358 pty Permits tty allocation previously disabled by the restrict 359 option. 360 361 restrict 362 Enable all restrictions, i.e. disable port, agent and X11 363 forwarding, as well as disabling PTY allocation and execution of 364 ~/.ssh/rc. If any future restriction capabilities are added to 365 authorized_keys files they will be included in this set. 366 367 tunnel="n" 368 Force a tun(4) device on the server. Without this option, the 369 next available device will be used if the client requests a 370 tunnel. 371 372 user-rc 373 Enables execution of ~/.ssh/rc previously disabled by the 374 restrict option. 375 376 X11-forwarding 377 Permits X11 forwarding previously disabled by the restrict 378 option. 379 380 An example authorized_keys file: 381 382 # Comments allowed at start of line 383 ssh-rsa AAAAB3Nza...LiPk== user@example.net 384 from="*.sales.example.net,!pc.sales.example.net" ssh-rsa 385 AAAAB2...19Q== john@example.net 386 command="dump /home",no-pty,no-port-forwarding ssh-dss 387 AAAAC3...51R== example.net 388 permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-dss 389 AAAAB5...21S== 390 tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...== 391 jane@example.net 392 restrict,command="uptime" ssh-rsa AAAA1C8...32Tv== 393 user@example.net 394 restrict,pty,command="nethack" ssh-rsa AAAA1f8...IrrC5== 395 user@example.net 396 397SSH_KNOWN_HOSTS FILE FORMAT 398 The /etc/ssh/ssh_known_hosts and ~/.ssh/known_hosts files contain host 399 public keys for all known hosts. The global file should be prepared by 400 the administrator (optional), and the per-user file is maintained 401 automatically: whenever the user connects to an unknown host, its key is 402 added to the per-user file. 403 404 Each line in these files contains the following fields: markers 405 (optional), hostnames, keytype, base64-encoded key, comment. The fields 406 are separated by spaces. 407 408 The marker is optional, but if it is present then it must be one of 409 M-bM-^@M-^\@cert-authorityM-bM-^@M-^], to indicate that the line contains a certification 410 authority (CA) key, or M-bM-^@M-^\@revokedM-bM-^@M-^], to indicate that the key contained on 411 the line is revoked and must not ever be accepted. Only one marker 412 should be used on a key line. 413 414 Hostnames is a comma-separated list of patterns (M-bM-^@M-^X*M-bM-^@M-^Y and M-bM-^@M-^X?M-bM-^@M-^Y act as 415 wildcards); each pattern in turn is matched against the canonical host 416 name (when authenticating a client) or against the user-supplied name 417 (when authenticating a server). A pattern may also be preceded by M-bM-^@M-^X!M-bM-^@M-^Y to 418 indicate negation: if the host name matches a negated pattern, it is not 419 accepted (by that line) even if it matched another pattern on the line. 420 A hostname or address may optionally be enclosed within M-bM-^@M-^X[M-bM-^@M-^Y and M-bM-^@M-^X]M-bM-^@M-^Y 421 brackets then followed by M-bM-^@M-^X:M-bM-^@M-^Y and a non-standard port number. 422 423 Alternately, hostnames may be stored in a hashed form which hides host 424 names and addresses should the file's contents be disclosed. Hashed 425 hostnames start with a M-bM-^@M-^X|M-bM-^@M-^Y character. Only one hashed hostname may 426 appear on a single line and none of the above negation or wildcard 427 operators may be applied. 428 429 The keytype and base64-encoded key are taken directly from the host key; 430 they can be obtained, for example, from /etc/ssh/ssh_host_rsa_key.pub. 431 The optional comment field continues to the end of the line, and is not 432 used. 433 434 Lines starting with M-bM-^@M-^X#M-bM-^@M-^Y and empty lines are ignored as comments. 435 436 When performing host authentication, authentication is accepted if any 437 matching line has the proper key; either one that matches exactly or, if 438 the server has presented a certificate for authentication, the key of the 439 certification authority that signed the certificate. For a key to be 440 trusted as a certification authority, it must use the M-bM-^@M-^\@cert-authorityM-bM-^@M-^] 441 marker described above. 442 443 The known hosts file also provides a facility to mark keys as revoked, 444 for example when it is known that the associated private key has been 445 stolen. Revoked keys are specified by including the M-bM-^@M-^\@revokedM-bM-^@M-^] marker at 446 the beginning of the key line, and are never accepted for authentication 447 or as certification authorities, but instead will produce a warning from 448 ssh(1) when they are encountered. 449 450 It is permissible (but not recommended) to have several lines or 451 different host keys for the same names. This will inevitably happen when 452 short forms of host names from different domains are put in the file. It 453 is possible that the files contain conflicting information; 454 authentication is accepted if valid information can be found from either 455 file. 456 457 Note that the lines in these files are typically hundreds of characters 458 long, and you definitely don't want to type in the host keys by hand. 459 Rather, generate them by a script, ssh-keyscan(1) or by taking, for 460 example, /etc/ssh/ssh_host_rsa_key.pub and adding the host names at the 461 front. ssh-keygen(1) also offers some basic automated editing for 462 ~/.ssh/known_hosts including removing hosts matching a host name and 463 converting all host names to their hashed representations. 464 465 An example ssh_known_hosts file: 466 467 # Comments allowed at start of line 468 closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net 469 cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....= 470 # A hashed hostname 471 |1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa 472 AAAA1234.....= 473 # A revoked key 474 @revoked * ssh-rsa AAAAB5W... 475 # A CA key, accepted for any host in *.mydomain.com or *.mydomain.org 476 @cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W... 477 478FILES 479 ~/.hushlogin 480 This file is used to suppress printing the last login time and 481 /etc/motd, if PrintLastLog and PrintMotd, respectively, are 482 enabled. It does not suppress printing of the banner specified 483 by Banner. 484 485 ~/.rhosts 486 This file is used for host-based authentication (see ssh(1) for 487 more information). On some machines this file may need to be 488 world-readable if the user's home directory is on an NFS 489 partition, because sshd reads it as root. Additionally, this 490 file must be owned by the user, and must not have write 491 permissions for anyone else. The recommended permission for most 492 machines is read/write for the user, and not accessible by 493 others. 494 495 ~/.shosts 496 This file is used in exactly the same way as .rhosts, but allows 497 host-based authentication without permitting login with 498 rlogin/rsh. 499 500 ~/.ssh/ 501 This directory is the default location for all user-specific 502 configuration and authentication information. There is no 503 general requirement to keep the entire contents of this directory 504 secret, but the recommended permissions are read/write/execute 505 for the user, and not accessible by others. 506 507 ~/.ssh/authorized_keys 508 Lists the public keys (DSA, ECDSA, Ed25519, RSA) that can be used 509 for logging in as this user. The format of this file is 510 described above. The content of the file is not highly 511 sensitive, but the recommended permissions are read/write for the 512 user, and not accessible by others. 513 514 If this file, the ~/.ssh directory, or the user's home directory 515 are writable by other users, then the file could be modified or 516 replaced by unauthorized users. In this case, sshd will not 517 allow it to be used unless the StrictModes option has been set to 518 M-bM-^@M-^\noM-bM-^@M-^]. 519 520 ~/.ssh/environment 521 This file is read into the environment at login (if it exists). 522 It can only contain empty lines, comment lines (that start with 523 M-bM-^@M-^X#M-bM-^@M-^Y), and assignment lines of the form name=value. The file 524 should be writable only by the user; it need not be readable by 525 anyone else. Environment processing is disabled by default and 526 is controlled via the PermitUserEnvironment option. 527 528 ~/.ssh/known_hosts 529 Contains a list of host keys for all hosts the user has logged 530 into that are not already in the systemwide list of known host 531 keys. The format of this file is described above. This file 532 should be writable only by root/the owner and can, but need not 533 be, world-readable. 534 535 ~/.ssh/rc 536 Contains initialization routines to be run before the user's home 537 directory becomes accessible. This file should be writable only 538 by the user, and need not be readable by anyone else. 539 540 /etc/hosts.equiv 541 This file is for host-based authentication (see ssh(1)). It 542 should only be writable by root. 543 544 /etc/moduli 545 Contains Diffie-Hellman groups used for the "Diffie-Hellman Group 546 Exchange" key exchange method. The file format is described in 547 moduli(5). If no usable groups are found in this file then fixed 548 internal groups will be used. 549 550 /etc/motd 551 See motd(5). 552 553 /etc/nologin 554 If this file exists, sshd refuses to let anyone except root log 555 in. The contents of the file are displayed to anyone trying to 556 log in, and non-root connections are refused. The file should be 557 world-readable. 558 559 /etc/shosts.equiv 560 This file is used in exactly the same way as hosts.equiv, but 561 allows host-based authentication without permitting login with 562 rlogin/rsh. 563 564 /etc/ssh/ssh_host_dsa_key 565 /etc/ssh/ssh_host_ecdsa_key 566 /etc/ssh/ssh_host_ed25519_key 567 /etc/ssh/ssh_host_rsa_key 568 These files contain the private parts of the host keys. These 569 files should only be owned by root, readable only by root, and 570 not accessible to others. Note that sshd does not start if these 571 files are group/world-accessible. 572 573 /etc/ssh/ssh_host_dsa_key.pub 574 /etc/ssh/ssh_host_ecdsa_key.pub 575 /etc/ssh/ssh_host_ed25519_key.pub 576 /etc/ssh/ssh_host_rsa_key.pub 577 These files contain the public parts of the host keys. These 578 files should be world-readable but writable only by root. Their 579 contents should match the respective private parts. These files 580 are not really used for anything; they are provided for the 581 convenience of the user so their contents can be copied to known 582 hosts files. These files are created using ssh-keygen(1). 583 584 /etc/ssh/ssh_known_hosts 585 Systemwide list of known host keys. This file should be prepared 586 by the system administrator to contain the public host keys of 587 all machines in the organization. The format of this file is 588 described above. This file should be writable only by root/the 589 owner and should be world-readable. 590 591 /etc/ssh/sshd_config 592 Contains configuration data for sshd. The file format and 593 configuration options are described in sshd_config(5). 594 595 /etc/ssh/sshrc 596 Similar to ~/.ssh/rc, it can be used to specify machine-specific 597 login-time initializations globally. This file should be 598 writable only by root, and should be world-readable. 599 600 /var/empty 601 chroot(2) directory used by sshd during privilege separation in 602 the pre-authentication phase. The directory should not contain 603 any files and must be owned by root and not group or world- 604 writable. 605 606 /var/run/sshd.pid 607 Contains the process ID of the sshd listening for connections (if 608 there are several daemons running concurrently for different 609 ports, this contains the process ID of the one started last). 610 The content of this file is not sensitive; it can be world- 611 readable. 612 613SEE ALSO 614 scp(1), sftp(1), ssh(1), ssh-add(1), ssh-agent(1), ssh-keygen(1), 615 ssh-keyscan(1), chroot(2), login.conf(5), moduli(5), sshd_config(5), 616 inetd(8), sftp-server(8) 617 618AUTHORS 619 OpenSSH is a derivative of the original and free ssh 1.2.12 release by 620 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo 621 de Raadt and Dug Song removed many bugs, re-added newer features and 622 created OpenSSH. Markus Friedl contributed the support for SSH protocol 623 versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support 624 for privilege separation. 625 626OpenBSD 6.0 January 30, 2017 OpenBSD 6.0 627