1 SSHD(8) System Manager's Manual SSHD(8) 2 3 NAME 4 sshd M-bM-^@M-^S OpenSSH SSH daemon 5 6 SYNOPSIS 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 12 DESCRIPTION 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). sshd is normally 91 not run from inetd because it needs to generate the server key 92 before it can respond to the client, and this may take tens of 93 seconds. Clients would have to wait too long if the key was 94 regenerated every time. However, with small key sizes (e.g. 512) 95 using sshd from inetd may be feasible. 96 97 -k key_gen_time 98 Specifies how often the ephemeral protocol version 1 server key 99 is regenerated (default 3600 seconds, or one hour). The 100 motivation for regenerating the key fairly often is that the key 101 is not stored anywhere, and after about an hour it becomes 102 impossible to recover the key for decrypting intercepted 103 communications even if the machine is cracked into or physically 104 seized. A value of zero indicates that the key will never be 105 regenerated. 106 107 -o option 108 Can be used to give options in the format used in the 109 configuration file. This is useful for specifying options for 110 which there is no separate command-line flag. For full details 111 of the options, and their values, see sshd_config(5). 112 113 -p port 114 Specifies the port on which the server listens for connections 115 (default 22). Multiple port options are permitted. Ports 116 specified in the configuration file with the Port option are 117 ignored when a command-line port is specified. Ports specified 118 using the ListenAddress option override command-line ports. 119 120 -q Quiet mode. Nothing is sent to the system log. Normally the 121 beginning, authentication, and termination of each connection is 122 logged. 123 124 -T Extended test mode. Check the validity of the configuration 125 file, output the effective configuration to stdout and then exit. 126 Optionally, Match rules may be applied by specifying the 127 connection parameters using one or more -C options. 128 129 -t Test mode. Only check the validity of the configuration file and 130 sanity of the keys. This is useful for updating sshd reliably as 131 configuration options may change. 132 133 -u len This option is used to specify the size of the field in the utmp 134 structure that holds the remote host name. If the resolved host 135 name is longer than len, the dotted decimal value will be used 136 instead. This allows hosts with very long host names that 137 overflow this field to still be uniquely identified. Specifying 138 -u0 indicates that only dotted decimal addresses should be put 139 into the utmp file. -u0 may also be used to prevent sshd from 140 making DNS requests unless the authentication mechanism or 141 configuration requires it. Authentication mechanisms that may 142 require DNS include RhostsRSAAuthentication, 143 HostbasedAuthentication, and using a from="pattern-list" option 144 in a key file. Configuration options that require DNS include 145 using a USER@HOST pattern in AllowUsers or DenyUsers. 146 147 AUTHENTICATION 148 The OpenSSH SSH daemon supports SSH protocols 1 and 2. The default is to 149 use protocol 2 only, though this can be changed via the Protocol option 150 in sshd_config(5). Protocol 2 supports DSA, ECDSA, Ed25519 and RSA keys; 151 protocol 1 only supports RSA keys. For both protocols, each host has a 152 host-specific key, normally 2048 bits, used to identify the host. 153 154 Forward security for protocol 1 is provided through an additional server 155 key, normally 768 bits, generated when the server starts. This key is 156 normally regenerated every hour if it has been used, and is never stored 157 on disk. Whenever a client connects, the daemon responds with its public 158 host and server keys. The client compares the RSA host key against its 159 own database to verify that it has not changed. The client then 160 generates a 256-bit random number. It encrypts this random number using 161 both the host key and the server key, and sends the encrypted number to 162 the server. Both sides then use this random number as a session key 163 which is used to encrypt all further communications in the session. The 164 rest of the session is encrypted using a conventional cipher, currently 165 Blowfish or 3DES, with 3DES being used by default. The client selects 166 the encryption algorithm to use from those offered by the server. 167 168 For protocol 2, forward security is provided through a Diffie-Hellman key 169 agreement. This key agreement results in a shared session key. The rest 170 of the session is encrypted using a symmetric cipher, currently 128-bit 171 AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES. The 172 client selects the encryption algorithm to use from those offered by the 173 server. Additionally, session integrity is provided through a 174 cryptographic message authentication code (hmac-md5, hmac-sha1, umac-64, 175 umac-128, hmac-ripemd160, hmac-sha2-256 or hmac-sha2-512). 176 177 Finally, the server and the client enter an authentication dialog. The 178 client tries to authenticate itself using host-based authentication, 179 public key authentication, challenge-response authentication, or password 180 authentication. 181 182 Regardless of the authentication type, the account is checked to ensure 183 that it is accessible. An account is not accessible if it is locked, 184 listed in DenyUsers or its group is listed in DenyGroups . The 185 definition of a locked account is system dependant. Some platforms have 186 their own account database (eg AIX) and some modify the passwd field ( 187 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 188 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 189 Linuxes). If there is a requirement to disable password authentication 190 for the account while allowing still public-key, then the passwd field 191 should be set to something other than these values (eg M-bM-^@M-^XNPM-bM-^@M-^Y or M-bM-^@M-^X*NP*M-bM-^@M-^Y ). 192 193 If the client successfully authenticates itself, a dialog for preparing 194 the session is entered. At this time the client may request things like 195 allocating a pseudo-tty, forwarding X11 connections, forwarding TCP 196 connections, or forwarding the authentication agent connection over the 197 secure channel. 198 199 After this, the client either requests a shell or execution of a command. 200 The sides then enter session mode. In this mode, either side may send 201 data at any time, and such data is forwarded to/from the shell or command 202 on the server side, and the user terminal in the client side. 203 204 When the user program terminates and all forwarded X11 and other 205 connections have been closed, the server sends command exit status to the 206 client, and both sides exit. 207 208 LOGIN PROCESS 209 When a user successfully logs in, sshd does the following: 210 211 1. If the login is on a tty, and no command has been specified, 212 prints last login time and /etc/motd (unless prevented in the 213 configuration file or by ~/.hushlogin; see the FILES section). 214 215 2. If the login is on a tty, records login time. 216 217 3. Checks /etc/nologin; if it exists, prints contents and quits 218 (unless root). 219 220 4. Changes to run with normal user privileges. 221 222 5. Sets up basic environment. 223 224 6. Reads the file ~/.ssh/environment, if it exists, and users are 225 allowed to change their environment. See the 226 PermitUserEnvironment option in sshd_config(5). 227 228 7. Changes to user's home directory. 229 230 8. If ~/.ssh/rc exists and the sshd_config(5) PermitUserRC option 231 is set, runs it; else if /etc/ssh/sshrc exists, runs it; 232 otherwise runs xauth. The M-bM-^@M-^\rcM-bM-^@M-^] files are given the X11 233 authentication protocol and cookie in standard input. See 234 SSHRC, below. 235 236 9. Runs user's shell or command. 237 238 SSHRC 239 If the file ~/.ssh/rc exists, sh(1) runs it after reading the environment 240 files but before starting the user's shell or command. It must not 241 produce any output on stdout; stderr must be used instead. If X11 242 forwarding is in use, it will receive the "proto cookie" pair in its 243 standard input (and DISPLAY in its environment). The script must call 244 xauth(1) because sshd will not run xauth automatically to add X11 245 cookies. 246 247 The primary purpose of this file is to run any initialization routines 248 which may be needed before the user's home directory becomes accessible; 249 AFS is a particular example of such an environment. 250 251 This file will probably contain some initialization code followed by 252 something similar to: 253 254 if read proto cookie && [ -n "$DISPLAY" ]; then 255 if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then 256 # X11UseLocalhost=yes 257 echo add unix:`echo $DISPLAY | 258 cut -c11-` $proto $cookie 259 else 260 # X11UseLocalhost=no 261 echo add $DISPLAY $proto $cookie 262 fi | xauth -q - 263 fi 264 265 If this file does not exist, /etc/ssh/sshrc is run, and if that does not 266 exist either, xauth is used to add the cookie. 267 268 AUTHORIZED_KEYS FILE FORMAT 269 AuthorizedKeysFile specifies the files containing public keys for public 270 key authentication; if none is specified, the default is 271 ~/.ssh/authorized_keys and ~/.ssh/authorized_keys2. Each line of the 272 file contains one key (empty lines and lines starting with a M-bM-^@M-^X#M-bM-^@M-^Y are 273 ignored as comments). Protocol 1 public keys consist of the following 274 space-separated fields: options, bits, exponent, modulus, comment. 275 Protocol 2 public key consist of: options, keytype, base64-encoded key, 276 comment. The options field is optional; its presence is determined by 277 whether the line starts with a number or not (the options field never 278 starts with a number). The bits, exponent, modulus, and comment fields 279 give the RSA key for protocol version 1; the comment field is not used 280 for anything (but may be convenient for the user to identify the key). 281 For protocol version 2 the keytype is M-bM-^@M-^\ecdsa-sha2-nistp256M-bM-^@M-^], 282 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 283 M-bM-^@M-^\ssh-rsaM-bM-^@M-^]. 284 285 Note that lines in this file are usually several hundred bytes long 286 (because of the size of the public key encoding) up to a limit of 8 287 kilobytes, which permits DSA keys up to 8 kilobits and RSA keys up to 16 288 kilobits. You don't want to type them in; instead, copy the 289 identity.pub, id_dsa.pub, id_ecdsa.pub, id_ed25519.pub, or the id_rsa.pub 290 file and edit it. 291 292 sshd enforces a minimum RSA key modulus size for protocol 1 and protocol 293 2 keys of 768 bits. 294 295 The options (if present) consist of comma-separated option 296 specifications. No spaces are permitted, except within double quotes. 297 The following option specifications are supported (note that option 298 keywords are case-insensitive): 299 300 cert-authority 301 Specifies that the listed key is a certification authority (CA) 302 that is trusted to validate signed certificates for user 303 authentication. 304 305 Certificates may encode access restrictions similar to these key 306 options. If both certificate restrictions and key options are 307 present, the most restrictive union of the two is applied. 308 309 command="command" 310 Specifies that the command is executed whenever this key is used 311 for authentication. The command supplied by the user (if any) is 312 ignored. The command is run on a pty if the client requests a 313 pty; otherwise it is run without a tty. If an 8-bit clean 314 channel is required, one must not request a pty or should specify 315 no-pty. A quote may be included in the command by quoting it 316 with a backslash. This option might be useful to restrict 317 certain public keys to perform just a specific operation. An 318 example might be a key that permits remote backups but nothing 319 else. Note that the client may specify TCP and/or X11 forwarding 320 unless they are explicitly prohibited. The command originally 321 supplied by the client is available in the SSH_ORIGINAL_COMMAND 322 environment variable. Note that this option applies to shell, 323 command or subsystem execution. Also note that this command may 324 be superseded by either a sshd_config(5) ForceCommand directive 325 or a command embedded in a certificate. 326 327 environment="NAME=value" 328 Specifies that the string is to be added to the environment when 329 logging in using this key. Environment variables set this way 330 override other default environment values. Multiple options of 331 this type are permitted. Environment processing is disabled by 332 default and is controlled via the PermitUserEnvironment option. 333 This option is automatically disabled if UseLogin is enabled. 334 335 from="pattern-list" 336 Specifies that in addition to public key authentication, either 337 the canonical name of the remote host or its IP address must be 338 present in the comma-separated list of patterns. See PATTERNS in 339 ssh_config(5) for more information on patterns. 340 341 In addition to the wildcard matching that may be applied to 342 hostnames or addresses, a from stanza may match IP addresses 343 using CIDR address/masklen notation. 344 345 The purpose of this option is to optionally increase security: 346 public key authentication by itself does not trust the network or 347 name servers or anything (but the key); however, if somebody 348 somehow steals the key, the key permits an intruder to log in 349 from anywhere in the world. This additional option makes using a 350 stolen key more difficult (name servers and/or routers would have 351 to be compromised in addition to just the key). 352 353 no-agent-forwarding 354 Forbids authentication agent forwarding when this key is used for 355 authentication. 356 357 no-port-forwarding 358 Forbids TCP forwarding when this key is used for authentication. 359 Any port forward requests by the client will return an error. 360 This might be used, e.g. in connection with the command option. 361 362 no-pty Prevents tty allocation (a request to allocate a pty will fail). 363 364 no-user-rc 365 Disables execution of ~/.ssh/rc. 366 367 no-X11-forwarding 368 Forbids X11 forwarding when this key is used for authentication. 369 Any X11 forward requests by the client will return an error. 370 371 permitopen="host:port" 372 Limit local port forwarding with ssh(1) -L such that it may only 373 connect to the specified host and port. IPv6 addresses can be 374 specified by enclosing the address in square brackets. Multiple 375 permitopen options may be applied separated by commas. No 376 pattern matching is performed on the specified hostnames, they 377 must be literal domains or addresses. A port specification of * 378 matches any port. 379 380 principals="principals" 381 On a cert-authority line, specifies allowed principals for 382 certificate authentication as a comma-separated list. At least 383 one name from the list must appear in the certificate's list of 384 principals for the certificate to be accepted. This option is 385 ignored for keys that are not marked as trusted certificate 386 signers using the cert-authority option. 387 388 tunnel="n" 389 Force a tun(4) device on the server. Without this option, the 390 next available device will be used if the client requests a 391 tunnel. 392 393 An example authorized_keys file: 394 395 # Comments allowed at start of line 396 ssh-rsa AAAAB3Nza...LiPk== user (a] example.net 397 from="*.sales.example.net,!pc.sales.example.net" ssh-rsa 398 AAAAB2...19Q== john (a] example.net 399 command="dump /home",no-pty,no-port-forwarding ssh-dss 400 AAAAC3...51R== example.net 401 permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-dss 402 AAAAB5...21S== 403 tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...== 404 jane (a] example.net 405 406 SSH_KNOWN_HOSTS FILE FORMAT 407 The /etc/ssh/ssh_known_hosts and ~/.ssh/known_hosts files contain host 408 public keys for all known hosts. The global file should be prepared by 409 the administrator (optional), and the per-user file is maintained 410 automatically: whenever the user connects from an unknown host, its key 411 is added to the per-user file. 412 413 Each line in these files contains the following fields: markers 414 (optional), hostnames, bits, exponent, modulus, comment. The fields are 415 separated by spaces. 416 417 The marker is optional, but if it is present then it must be one of 418 M-bM-^@M-^\@cert-authorityM-bM-^@M-^], to indicate that the line contains a certification 419 authority (CA) key, or M-bM-^@M-^\@revokedM-bM-^@M-^], to indicate that the key contained on 420 the line is revoked and must not ever be accepted. Only one marker 421 should be used on a key line. 422 423 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 424 wildcards); each pattern in turn is matched against the canonical host 425 name (when authenticating a client) or against the user-supplied name 426 (when authenticating a server). A pattern may also be preceded by M-bM-^@M-^X!M-bM-^@M-^Y to 427 indicate negation: if the host name matches a negated pattern, it is not 428 accepted (by that line) even if it matched another pattern on the line. 429 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 430 brackets then followed by M-bM-^@M-^X:M-bM-^@M-^Y and a non-standard port number. 431 432 Alternately, hostnames may be stored in a hashed form which hides host 433 names and addresses should the file's contents be disclosed. Hashed 434 hostnames start with a M-bM-^@M-^X|M-bM-^@M-^Y character. Only one hashed hostname may 435 appear on a single line and none of the above negation or wildcard 436 operators may be applied. 437 438 Bits, exponent, and modulus are taken directly from the RSA host key; 439 they can be obtained, for example, from /etc/ssh/ssh_host_key.pub. The 440 optional comment field continues to the end of the line, and is not used. 441 442 Lines starting with M-bM-^@M-^X#M-bM-^@M-^Y and empty lines are ignored as comments. 443 444 When performing host authentication, authentication is accepted if any 445 matching line has the proper key; either one that matches exactly or, if 446 the server has presented a certificate for authentication, the key of the 447 certification authority that signed the certificate. For a key to be 448 trusted as a certification authority, it must use the M-bM-^@M-^\@cert-authorityM-bM-^@M-^] 449 marker described above. 450 451 The known hosts file also provides a facility to mark keys as revoked, 452 for example when it is known that the associated private key has been 453 stolen. Revoked keys are specified by including the M-bM-^@M-^\@revokedM-bM-^@M-^] marker at 454 the beginning of the key line, and are never accepted for authentication 455 or as certification authorities, but instead will produce a warning from 456 ssh(1) when they are encountered. 457 458 It is permissible (but not recommended) to have several lines or 459 different host keys for the same names. This will inevitably happen when 460 short forms of host names from different domains are put in the file. It 461 is possible that the files contain conflicting information; 462 authentication is accepted if valid information can be found from either 463 file. 464 465 Note that the lines in these files are typically hundreds of characters 466 long, and you definitely don't want to type in the host keys by hand. 467 Rather, generate them by a script, ssh-keyscan(1) or by taking 468 /etc/ssh/ssh_host_key.pub and adding the host names at the front. 469 ssh-keygen(1) also offers some basic automated editing for 470 ~/.ssh/known_hosts including removing hosts matching a host name and 471 converting all host names to their hashed representations. 472 473 An example ssh_known_hosts file: 474 475 # Comments allowed at start of line 476 closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net 477 cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....= 478 # A hashed hostname 479 |1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa 480 AAAA1234.....= 481 # A revoked key 482 @revoked * ssh-rsa AAAAB5W... 483 # A CA key, accepted for any host in *.mydomain.com or *.mydomain.org 484 @cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W... 485 486 FILES 487 ~/.hushlogin 488 This file is used to suppress printing the last login time and 489 /etc/motd, if PrintLastLog and PrintMotd, respectively, are 490 enabled. It does not suppress printing of the banner specified 491 by Banner. 492 493 ~/.rhosts 494 This file is used for host-based authentication (see ssh(1) for 495 more information). On some machines this file may need to be 496 world-readable if the user's home directory is on an NFS 497 partition, because sshd reads it as root. Additionally, this 498 file must be owned by the user, and must not have write 499 permissions for anyone else. The recommended permission for most 500 machines is read/write for the user, and not accessible by 501 others. 502 503 ~/.shosts 504 This file is used in exactly the same way as .rhosts, but allows 505 host-based authentication without permitting login with 506 rlogin/rsh. 507 508 ~/.ssh/ 509 This directory is the default location for all user-specific 510 configuration and authentication information. There is no 511 general requirement to keep the entire contents of this directory 512 secret, but the recommended permissions are read/write/execute 513 for the user, and not accessible by others. 514 515 ~/.ssh/authorized_keys 516 Lists the public keys (DSA, ECDSA, Ed25519, RSA) that can be used 517 for logging in as this user. The format of this file is 518 described above. The content of the file is not highly 519 sensitive, but the recommended permissions are read/write for the 520 user, and not accessible by others. 521 522 If this file, the ~/.ssh directory, or the user's home directory 523 are writable by other users, then the file could be modified or 524 replaced by unauthorized users. In this case, sshd will not 525 allow it to be used unless the StrictModes option has been set to 526 M-bM-^@M-^\noM-bM-^@M-^]. 527 528 ~/.ssh/environment 529 This file is read into the environment at login (if it exists). 530 It can only contain empty lines, comment lines (that start with 531 M-bM-^@M-^X#M-bM-^@M-^Y), and assignment lines of the form name=value. The file 532 should be writable only by the user; it need not be readable by 533 anyone else. Environment processing is disabled by default and 534 is controlled via the PermitUserEnvironment option. 535 536 ~/.ssh/known_hosts 537 Contains a list of host keys for all hosts the user has logged 538 into that are not already in the systemwide list of known host 539 keys. The format of this file is described above. This file 540 should be writable only by root/the owner and can, but need not 541 be, world-readable. 542 543 ~/.ssh/rc 544 Contains initialization routines to be run before the user's home 545 directory becomes accessible. This file should be writable only 546 by the user, and need not be readable by anyone else. 547 548 /etc/hosts.equiv 549 This file is for host-based authentication (see ssh(1)). It 550 should only be writable by root. 551 552 /etc/moduli 553 Contains Diffie-Hellman groups used for the "Diffie-Hellman Group 554 Exchange". The file format is described in moduli(5). 555 556 /etc/motd 557 See motd(5). 558 559 /etc/nologin 560 If this file exists, sshd refuses to let anyone except root log 561 in. The contents of the file are displayed to anyone trying to 562 log in, and non-root connections are refused. The file should be 563 world-readable. 564 565 /etc/shosts.equiv 566 This file is used in exactly the same way as hosts.equiv, but 567 allows host-based authentication without permitting login with 568 rlogin/rsh. 569 570 /etc/ssh/ssh_host_key 571 /etc/ssh/ssh_host_dsa_key 572 /etc/ssh/ssh_host_ecdsa_key 573 /etc/ssh/ssh_host_ed25519_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_ed25519_key.pub 584 /etc/ssh/ssh_host_rsa_key.pub 585 These files contain the public parts of the host keys. These 586 files should be world-readable but writable only by root. Their 587 contents should match the respective private parts. These files 588 are not really used for anything; they are provided for the 589 convenience of the user so their contents can be copied to known 590 hosts files. These files are created using ssh-keygen(1). 591 592 /etc/ssh/ssh_known_hosts 593 Systemwide list of known host keys. This file should be prepared 594 by the system administrator to contain the public host keys of 595 all machines in the organization. The format of this file is 596 described above. This file should be writable only by root/the 597 owner and should be world-readable. 598 599 /etc/ssh/sshd_config 600 Contains configuration data for sshd. The file format and 601 configuration options are described in sshd_config(5). 602 603 /etc/ssh/sshrc 604 Similar to ~/.ssh/rc, it can be used to specify machine-specific 605 login-time initializations globally. This file should be 606 writable only by root, and should be world-readable. 607 608 /var/empty 609 chroot(2) directory used by sshd during privilege separation in 610 the pre-authentication phase. The directory should not contain 611 any files and must be owned by root and not group or world- 612 writable. 613 614 /var/run/sshd.pid 615 Contains the process ID of the sshd listening for connections (if 616 there are several daemons running concurrently for different 617 ports, this contains the process ID of the one started last). 618 The content of this file is not sensitive; it can be world- 619 readable. 620 621 SEE ALSO 622 scp(1), sftp(1), ssh(1), ssh-add(1), ssh-agent(1), ssh-keygen(1), 623 ssh-keyscan(1), chroot(2), login.conf(5), moduli(5), sshd_config(5), 624 inetd(8), sftp-server(8) 625 626 AUTHORS 627 OpenSSH is a derivative of the original and free ssh 1.2.12 release by 628 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo 629 de Raadt and Dug Song removed many bugs, re-added newer features and 630 created OpenSSH. Markus Friedl contributed the support for SSH protocol 631 versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support 632 for privilege separation. 633 634 OpenBSD 5.7 November 15, 2014 OpenBSD 5.7 635
