1SSHD(8) System Manager's Manual SSHD(8) 2 3NAME 4 sshd M-bM-^@M-^S 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 and rsh, 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 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 45 M-bM-^@M-^\addrM-bM-^@M-^]. All are required and may be supplied in any order, 46 either with multiple -C options or as a comma-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 log_file 64 Append debug logs to log_file instead of the system log. 65 66 -e Write debug logs to standard error instead of the system log. 67 68 -f config_file 69 Specifies the name of the configuration file. The default is 70 /etc/ssh/sshd_config. sshd refuses to start if there is no 71 configuration file. 72 73 -g login_grace_time 74 Gives the grace time for clients to authenticate themselves 75 (default 120 seconds). If the client fails to authenticate the 76 user within this many seconds, the server disconnects and exits. 77 A value of zero indicates no limit. 78 79 -h host_key_file 80 Specifies a file from which a host key is read. This option must 81 be given if sshd is not run as root (as the normal host key files 82 are normally not readable by anyone but root). The default is 83 /etc/ssh/ssh_host_key for protocol version 1, and 84 /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_ecdsa_key. 85 /etc/ssh/ssh_host_ed25519_key and /etc/ssh/ssh_host_rsa_key for 86 protocol version 2. It is possible to have multiple host key 87 files for the different protocol versions and host key 88 algorithms. 89 90 -i Specifies that sshd is being run from inetd(8). If SSH protocol 91 1 is enabled, sshd should not normally be run from inetd because 92 it needs to generate the server key before it can respond to the 93 client, and this may take some time. Clients may have to wait 94 too long if the key was regenerated every time. 95 96 -k key_gen_time 97 Specifies how often the ephemeral protocol version 1 server key 98 is regenerated (default 3600 seconds, or one hour). The 99 motivation for regenerating the key fairly often is that the key 100 is not stored anywhere, and after about an hour it becomes 101 impossible to recover the key for decrypting intercepted 102 communications even if the machine is cracked into or physically 103 seized. A value of zero indicates that the key will never be 104 regenerated. 105 106 -o option 107 Can be used to give options in the format used in the 108 configuration file. This is useful for specifying options for 109 which there is no separate command-line flag. For full details 110 of the options, and their values, see sshd_config(5). 111 112 -p port 113 Specifies the port on which the server listens for connections 114 (default 22). Multiple port options are permitted. Ports 115 specified in the configuration file with the Port option are 116 ignored when a command-line port is specified. Ports specified 117 using the ListenAddress option override command-line ports. 118 119 -q Quiet mode. Nothing is sent to the system log. Normally the 120 beginning, authentication, and termination of each connection is 121 logged. 122 123 -T Extended test mode. Check the validity of the configuration 124 file, output the effective configuration to stdout and then exit. 125 Optionally, Match rules may be applied by specifying the 126 connection parameters using one or more -C options. 127 128 -t Test mode. Only check the validity of the configuration file and 129 sanity of the keys. This is useful for updating sshd reliably as 130 configuration options may change. 131 132 -u len This option is used to specify the size of the field in the utmp 133 structure that holds the remote host name. If the resolved host 134 name is longer than len, the dotted decimal value will be used 135 instead. This allows hosts with very long host names that 136 overflow this field to still be uniquely identified. Specifying 137 -u0 indicates that only dotted decimal addresses should be put 138 into the utmp file. -u0 may also be used to prevent sshd from 139 making DNS requests unless the authentication mechanism or 140 configuration requires it. Authentication mechanisms that may 141 require DNS include RhostsRSAAuthentication, 142 HostbasedAuthentication, and using a from="pattern-list" option 143 in a key file. Configuration options that require DNS include 144 using a USER@HOST pattern in AllowUsers or DenyUsers. 145 146AUTHENTICATION 147 The OpenSSH SSH daemon supports SSH protocols 1 and 2. The default is to 148 use protocol 2 only, though this can be changed via the Protocol option 149 in sshd_config(5). Protocol 2 supports DSA, ECDSA, Ed25519 and RSA keys; 150 protocol 1 only supports RSA keys. For both protocols, each host has a 151 host-specific key, normally 2048 bits, used to identify the host. 152 153 Forward security for protocol 1 is provided through an additional server 154 key, normally 1024 bits, generated when the server starts. This key is 155 normally regenerated every hour if it has been used, and is never stored 156 on disk. Whenever a client connects, the daemon responds with its public 157 host and server keys. The client compares the RSA host key against its 158 own database to verify that it has not changed. The client then 159 generates a 256-bit random number. It encrypts this random number using 160 both the host key and the server key, and sends the encrypted number to 161 the server. Both sides then use this random number as a session key 162 which is used to encrypt all further communications in the session. The 163 rest of the session is encrypted using a conventional cipher, currently 164 Blowfish or 3DES, with 3DES being used by default. The client selects 165 the encryption algorithm to use from those offered by the server. 166 167 For protocol 2, forward security is provided through a Diffie-Hellman key 168 agreement. This key agreement results in a shared session key. The rest 169 of the session is encrypted using a symmetric cipher, currently 128-bit 170 AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES. The 171 client selects the encryption algorithm to use from those offered by the 172 server. Additionally, session integrity is provided through a 173 cryptographic message authentication code (hmac-md5, hmac-sha1, umac-64, 174 umac-128, hmac-ripemd160, hmac-sha2-256 or hmac-sha2-512). 175 176 Finally, the server and the client enter an authentication dialog. The 177 client tries to authenticate itself using host-based authentication, 178 public key authentication, challenge-response authentication, or password 179 authentication. 180 181 Regardless of the authentication type, the account is checked to ensure 182 that it is accessible. An account is not accessible if it is locked, 183 listed in DenyUsers or its group is listed in DenyGroups . The 184 definition of a locked account is system dependant. Some platforms have 185 their own account database (eg AIX) and some modify the passwd field ( 186 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 187 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 188 Linuxes). If there is a requirement to disable password authentication 189 for the account while allowing still public-key, then the passwd field 190 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 ). 191 192 If the client successfully authenticates itself, a dialog for preparing 193 the session is entered. At this time the client may request things like 194 allocating a pseudo-tty, forwarding X11 connections, forwarding TCP 195 connections, or forwarding the authentication agent connection over the 196 secure channel. 197 198 After this, the client either requests a shell or execution of a command. 199 The sides then enter session mode. In this mode, either side may send 200 data at any time, and such data is forwarded to/from the shell or command 201 on the server side, and the user terminal in the client side. 202 203 When the user program terminates and all forwarded X11 and other 204 connections have been closed, the server sends command exit status to the 205 client, and both sides exit. 206 207LOGIN PROCESS 208 When a user successfully logs in, sshd does the following: 209 210 1. If the login is on a tty, and no command has been specified, 211 prints last login time and /etc/motd (unless prevented in the 212 configuration file or by ~/.hushlogin; see the FILES section). 213 214 2. If the login is on a tty, records login time. 215 216 3. Checks /etc/nologin; if it exists, prints contents and quits 217 (unless root). 218 219 4. Changes to run with normal user privileges. 220 221 5. Sets up basic environment. 222 223 6. Reads the file ~/.ssh/environment, if it exists, and users are 224 allowed to change their environment. See the 225 PermitUserEnvironment option in sshd_config(5). 226 227 7. Changes to user's home directory. 228 229 8. If ~/.ssh/rc exists and the sshd_config(5) PermitUserRC option 230 is set, runs it; else if /etc/ssh/sshrc exists, runs it; 231 otherwise runs xauth. The M-bM-^@M-^\rcM-bM-^@M-^] files are given the X11 232 authentication protocol and cookie in standard input. See 233 SSHRC, below. 234 235 9. Runs user's shell or command. All commands are run under the 236 user's login shell as specified in the system password 237 database. 238 239SSHRC 240 If the file ~/.ssh/rc exists, sh(1) runs it after reading the environment 241 files but before starting the user's shell or command. It must not 242 produce any output on stdout; stderr must be used instead. If X11 243 forwarding is in use, it will receive the "proto cookie" pair in its 244 standard input (and DISPLAY in its environment). The script must call 245 xauth(1) because sshd will not run xauth automatically to add X11 246 cookies. 247 248 The primary purpose of this file is to run any initialization routines 249 which may be needed before the user's home directory becomes accessible; 250 AFS is a particular example of such an environment. 251 252 This file will probably contain some initialization code followed by 253 something similar to: 254 255 if read proto cookie && [ -n "$DISPLAY" ]; then 256 if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then 257 # X11UseLocalhost=yes 258 echo add unix:`echo $DISPLAY | 259 cut -c11-` $proto $cookie 260 else 261 # X11UseLocalhost=no 262 echo add $DISPLAY $proto $cookie 263 fi | xauth -q - 264 fi 265 266 If this file does not exist, /etc/ssh/sshrc is run, and if that does not 267 exist either, xauth is used to add the cookie. 268 269AUTHORIZED_KEYS FILE FORMAT 270 AuthorizedKeysFile specifies the files containing public keys for public 271 key authentication; if none is specified, the default is 272 ~/.ssh/authorized_keys and ~/.ssh/authorized_keys2. Each line of the 273 file contains one key (empty lines and lines starting with a M-bM-^@M-^X#M-bM-^@M-^Y are 274 ignored as comments). Protocol 1 public keys consist of the following 275 space-separated fields: options, bits, exponent, modulus, comment. 276 Protocol 2 public key consist of: options, keytype, base64-encoded key, 277 comment. The options field is optional; its presence is determined by 278 whether the line starts with a number or not (the options field never 279 starts with a number). The bits, exponent, modulus, and comment fields 280 give the RSA key for protocol version 1; the comment field is not used 281 for anything (but may be convenient for the user to identify the key). 282 For protocol version 2 the keytype is M-bM-^@M-^\ecdsa-sha2-nistp256M-bM-^@M-^], 283 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 284 M-bM-^@M-^\ssh-rsaM-bM-^@M-^]. 285 286 Note that lines in this file are usually several hundred bytes long 287 (because of the size of the public key encoding) up to a limit of 8 288 kilobytes, which permits DSA keys up to 8 kilobits and RSA keys up to 16 289 kilobits. You don't want to type them in; instead, copy the 290 identity.pub, id_dsa.pub, id_ecdsa.pub, id_ed25519.pub, or the id_rsa.pub 291 file and edit it. 292 293 sshd enforces a minimum RSA key modulus size for protocol 1 and protocol 294 2 keys of 768 bits. 295 296 The options (if present) consist of comma-separated option 297 specifications. No spaces are permitted, except within double quotes. 298 The following option specifications are supported (note that option 299 keywords are case-insensitive): 300 301 cert-authority 302 Specifies that the listed key is a certification authority (CA) 303 that is trusted to validate signed certificates for user 304 authentication. 305 306 Certificates may encode access restrictions similar to these key 307 options. If both certificate restrictions and key options are 308 present, the most restrictive union of the two is applied. 309 310 command="command" 311 Specifies that the command is executed whenever this key is used 312 for authentication. The command supplied by the user (if any) is 313 ignored. The command is run on a pty if the client requests a 314 pty; otherwise it is run without a tty. If an 8-bit clean 315 channel is required, one must not request a pty or should specify 316 no-pty. A quote may be included in the command by quoting it 317 with a backslash. This option might be useful to restrict 318 certain public keys to perform just a specific operation. An 319 example might be a key that permits remote backups but nothing 320 else. Note that the client may specify TCP and/or X11 forwarding 321 unless they are explicitly prohibited. The command originally 322 supplied by the client is available in the SSH_ORIGINAL_COMMAND 323 environment variable. Note that this option applies to shell, 324 command or subsystem execution. Also note that this command may 325 be superseded by either a sshd_config(5) ForceCommand directive 326 or a command embedded in a certificate. 327 328 environment="NAME=value" 329 Specifies that the string is to be added to the environment when 330 logging in using this key. Environment variables set this way 331 override other default environment values. Multiple options of 332 this type are permitted. Environment processing is disabled by 333 default and is controlled via the PermitUserEnvironment option. 334 This option is automatically disabled if UseLogin is enabled. 335 336 from="pattern-list" 337 Specifies that in addition to public key authentication, either 338 the canonical name of the remote host or its IP address must be 339 present in the comma-separated list of patterns. See PATTERNS in 340 ssh_config(5) for more information on patterns. 341 342 In addition to the wildcard matching that may be applied to 343 hostnames or addresses, a from stanza may match IP addresses 344 using CIDR address/masklen notation. 345 346 The purpose of this option is to optionally increase security: 347 public key authentication by itself does not trust the network or 348 name servers or anything (but the key); however, if somebody 349 somehow steals the key, the key permits an intruder to log in 350 from anywhere in the world. This additional option makes using a 351 stolen key more difficult (name servers and/or routers would have 352 to be compromised in addition to just the key). 353 354 no-agent-forwarding 355 Forbids authentication agent forwarding when this key is used for 356 authentication. 357 358 no-port-forwarding 359 Forbids TCP forwarding when this key is used for authentication. 360 Any port forward requests by the client will return an error. 361 This might be used, e.g. in connection with the command option. 362 363 no-pty Prevents tty allocation (a request to allocate a pty will fail). 364 365 no-user-rc 366 Disables execution of ~/.ssh/rc. 367 368 no-X11-forwarding 369 Forbids X11 forwarding when this key is used for authentication. 370 Any X11 forward requests by the client will return an error. 371 372 permitopen="host:port" 373 Limit local port forwarding with ssh(1) -L such that it may only 374 connect to the specified host and port. IPv6 addresses can be 375 specified by enclosing the address in square brackets. Multiple 376 permitopen options may be applied separated by commas. No 377 pattern matching is performed on the specified hostnames, they 378 must be literal domains or addresses. A port specification of * 379 matches any port. 380 381 principals="principals" 382 On a cert-authority line, specifies allowed principals for 383 certificate authentication as a comma-separated list. At least 384 one name from the list must appear in the certificate's list of 385 principals for the certificate to be accepted. This option is 386 ignored for keys that are not marked as trusted certificate 387 signers using the cert-authority option. 388 389 tunnel="n" 390 Force a tun(4) device on the server. Without this option, the 391 next available device will be used if the client requests a 392 tunnel. 393 394 An example authorized_keys file: 395 396 # Comments allowed at start of line 397 ssh-rsa AAAAB3Nza...LiPk== user@example.net 398 from="*.sales.example.net,!pc.sales.example.net" ssh-rsa 399 AAAAB2...19Q== john@example.net 400 command="dump /home",no-pty,no-port-forwarding ssh-dss 401 AAAAC3...51R== example.net 402 permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-dss 403 AAAAB5...21S== 404 tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...== 405 jane@example.net 406 407SSH_KNOWN_HOSTS FILE FORMAT 408 The /etc/ssh/ssh_known_hosts and ~/.ssh/known_hosts files contain host 409 public keys for all known hosts. The global file should be prepared by 410 the administrator (optional), and the per-user file is maintained 411 automatically: whenever the user connects from an unknown host, its key 412 is added to the per-user file. 413 414 Each line in these files contains the following fields: markers 415 (optional), hostnames, bits, exponent, modulus, comment. The fields are 416 separated by spaces. 417 418 The marker is optional, but if it is present then it must be one of 419 M-bM-^@M-^\@cert-authorityM-bM-^@M-^], to indicate that the line contains a certification 420 authority (CA) key, or M-bM-^@M-^\@revokedM-bM-^@M-^], to indicate that the key contained on 421 the line is revoked and must not ever be accepted. Only one marker 422 should be used on a key line. 423 424 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 425 wildcards); each pattern in turn is matched against the canonical host 426 name (when authenticating a client) or against the user-supplied name 427 (when authenticating a server). A pattern may also be preceded by M-bM-^@M-^X!M-bM-^@M-^Y to 428 indicate negation: if the host name matches a negated pattern, it is not 429 accepted (by that line) even if it matched another pattern on the line. 430 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 431 brackets then followed by M-bM-^@M-^X:M-bM-^@M-^Y and a non-standard port number. 432 433 Alternately, hostnames may be stored in a hashed form which hides host 434 names and addresses should the file's contents be disclosed. Hashed 435 hostnames start with a M-bM-^@M-^X|M-bM-^@M-^Y character. Only one hashed hostname may 436 appear on a single line and none of the above negation or wildcard 437 operators may be applied. 438 439 Bits, exponent, and modulus are taken directly from the RSA host key; 440 they can be obtained, for example, from /etc/ssh/ssh_host_key.pub. The 441 optional comment field continues to the end of the line, and is not used. 442 443 Lines starting with M-bM-^@M-^X#M-bM-^@M-^Y and empty lines are ignored as comments. 444 445 When performing host authentication, authentication is accepted if any 446 matching line has the proper key; either one that matches exactly or, if 447 the server has presented a certificate for authentication, the key of the 448 certification authority that signed the certificate. For a key to be 449 trusted as a certification authority, it must use the M-bM-^@M-^\@cert-authorityM-bM-^@M-^] 450 marker described above. 451 452 The known hosts file also provides a facility to mark keys as revoked, 453 for example when it is known that the associated private key has been 454 stolen. Revoked keys are specified by including the M-bM-^@M-^\@revokedM-bM-^@M-^] marker at 455 the beginning of the key line, and are never accepted for authentication 456 or as certification authorities, but instead will produce a warning from 457 ssh(1) when they are encountered. 458 459 It is permissible (but not recommended) to have several lines or 460 different host keys for the same names. This will inevitably happen when 461 short forms of host names from different domains are put in the file. It 462 is possible that the files contain conflicting information; 463 authentication is accepted if valid information can be found from either 464 file. 465 466 Note that the lines in these files are typically hundreds of characters 467 long, and you definitely don't want to type in the host keys by hand. 468 Rather, generate them by a script, ssh-keyscan(1) or by taking 469 /etc/ssh/ssh_host_key.pub and adding the host names at the front. 470 ssh-keygen(1) also offers some basic automated editing for 471 ~/.ssh/known_hosts including removing hosts matching a host name and 472 converting all host names to their hashed representations. 473 474 An example ssh_known_hosts file: 475 476 # Comments allowed at start of line 477 closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net 478 cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....= 479 # A hashed hostname 480 |1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa 481 AAAA1234.....= 482 # A revoked key 483 @revoked * ssh-rsa AAAAB5W... 484 # A CA key, accepted for any host in *.mydomain.com or *.mydomain.org 485 @cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W... 486 487FILES 488 ~/.hushlogin 489 This file is used to suppress printing the last login time and 490 /etc/motd, if PrintLastLog and PrintMotd, respectively, are 491 enabled. It does not suppress printing of the banner specified 492 by Banner. 493 494 ~/.rhosts 495 This file is used for host-based authentication (see ssh(1) for 496 more information). On some machines this file may need to be 497 world-readable if the user's home directory is on an NFS 498 partition, because sshd reads it as root. Additionally, this 499 file must be owned by the user, and must not have write 500 permissions for anyone else. The recommended permission for most 501 machines is read/write for the user, and not accessible by 502 others. 503 504 ~/.shosts 505 This file is used in exactly the same way as .rhosts, but allows 506 host-based authentication without permitting login with 507 rlogin/rsh. 508 509 ~/.ssh/ 510 This directory is the default location for all user-specific 511 configuration and authentication information. There is no 512 general requirement to keep the entire contents of this directory 513 secret, but the recommended permissions are read/write/execute 514 for the user, and not accessible by others. 515 516 ~/.ssh/authorized_keys 517 Lists the public keys (DSA, ECDSA, Ed25519, RSA) that can be used 518 for logging in as this user. The format of this file is 519 described above. The content of the file is not highly 520 sensitive, but the recommended permissions are read/write for the 521 user, and not accessible by others. 522 523 If this file, the ~/.ssh directory, or the user's home directory 524 are writable by other users, then the file could be modified or 525 replaced by unauthorized users. In this case, sshd will not 526 allow it to be used unless the StrictModes option has been set to 527 M-bM-^@M-^\noM-bM-^@M-^]. 528 529 ~/.ssh/environment 530 This file is read into the environment at login (if it exists). 531 It can only contain empty lines, comment lines (that start with 532 M-bM-^@M-^X#M-bM-^@M-^Y), and assignment lines of the form name=value. The file 533 should be writable only by the user; it need not be readable by 534 anyone else. Environment processing is disabled by default and 535 is controlled via the PermitUserEnvironment option. 536 537 ~/.ssh/known_hosts 538 Contains a list of host keys for all hosts the user has logged 539 into that are not already in the systemwide list of known host 540 keys. The format of this file is described above. This file 541 should be writable only by root/the owner and can, but need not 542 be, world-readable. 543 544 ~/.ssh/rc 545 Contains initialization routines to be run before the user's home 546 directory becomes accessible. This file should be writable only 547 by the user, and need not be readable by anyone else. 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_ed25519_key 575 /etc/ssh/ssh_host_rsa_key 576 These files contain the private parts of the host keys. These 577 files should only be owned by root, readable only by root, and 578 not accessible to others. Note that sshd does not start if these 579 files are group/world-accessible. 580 581 /etc/ssh/ssh_host_key.pub 582 /etc/ssh/ssh_host_dsa_key.pub 583 /etc/ssh/ssh_host_ecdsa_key.pub 584 /etc/ssh/ssh_host_ed25519_key.pub 585 /etc/ssh/ssh_host_rsa_key.pub 586 These files contain the public parts of the host keys. These 587 files should be world-readable but writable only by root. Their 588 contents should match the respective private parts. These files 589 are not really used for anything; they are provided for the 590 convenience of the user so their contents can be copied to known 591 hosts files. These files are created using ssh-keygen(1). 592 593 /etc/ssh/ssh_known_hosts 594 Systemwide list of known host keys. This file should be prepared 595 by the system administrator to contain the public host keys of 596 all machines in the organization. The format of this file is 597 described above. This file should be writable only by root/the 598 owner and should be world-readable. 599 600 /etc/ssh/sshd_config 601 Contains configuration data for sshd. The file format and 602 configuration options are described in sshd_config(5). 603 604 /etc/ssh/sshrc 605 Similar to ~/.ssh/rc, it can be used to specify machine-specific 606 login-time initializations globally. This file should be 607 writable only by root, and should be world-readable. 608 609 /var/empty 610 chroot(2) directory used by sshd during privilege separation in 611 the pre-authentication phase. The directory should not contain 612 any files and must be owned by root and not group or world- 613 writable. 614 615 /var/run/sshd.pid 616 Contains the process ID of the sshd listening for connections (if 617 there are several daemons running concurrently for different 618 ports, this contains the process ID of the one started last). 619 The content of this file is not sensitive; it can be world- 620 readable. 621 622SEE ALSO 623 scp(1), sftp(1), ssh(1), ssh-add(1), ssh-agent(1), ssh-keygen(1), 624 ssh-keyscan(1), chroot(2), login.conf(5), moduli(5), sshd_config(5), 625 inetd(8), sftp-server(8) 626 627AUTHORS 628 OpenSSH is a derivative of the original and free ssh 1.2.12 release by 629 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo 630 de Raadt and Dug Song removed many bugs, re-added newer features and 631 created OpenSSH. Markus Friedl contributed the support for SSH protocol 632 versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support 633 for privilege separation. 634 635OpenBSD 5.8 July 3, 2015 OpenBSD 5.8 636