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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 are applied before the configuration is
37 written to standard output. The connection parameters are
38 supplied as keyword=value pairs and may be supplied in any order,
39 either with multiple -C options or as a comma-separated list.
40 The keywords are M-bM-^@M-^\addr,M-bM-^@M-^] 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
41 M-bM-^@M-^\rdomainM-bM-^@M-^] and correspond to source address, user, resolved source
42 host name, local address, local port number and routing domain
43 respectively.
44
45 -c host_certificate_file
46 Specifies a path to a certificate file to identify sshd during
47 key exchange. The certificate file must match a host key file
48 specified using the -h option or the HostKey configuration
49 directive.
50
51 -D When this option is specified, sshd will not detach and does not
52 become a daemon. This allows easy monitoring of sshd.
53
54 -d Debug mode. The server sends verbose debug output to standard
55 error, and does not put itself in the background. The server
56 also will not fork and will only process one connection. This
57 option is only intended for debugging for the server. Multiple
58 -d options increase the debugging level. Maximum is 3.
59
60 -E log_file
61 Append debug logs to log_file instead of the system log.
62
63 -e Write debug logs to standard error instead of the system log.
64
65 -f config_file
66 Specifies the name of the configuration file. The default is
67 /etc/ssh/sshd_config. sshd refuses to start if there is no
68 configuration file.
69
70 -g login_grace_time
71 Gives the grace time for clients to authenticate themselves
72 (default 120 seconds). If the client fails to authenticate the
73 user within this many seconds, the server disconnects and exits.
74 A value of zero indicates no limit.
75
76 -h host_key_file
77 Specifies a file from which a host key is read. This option must
78 be given if sshd is not run as root (as the normal host key files
79 are normally not readable by anyone but root). The default is
80 /etc/ssh/ssh_host_ecdsa_key, /etc/ssh/ssh_host_ed25519_key and
81 /etc/ssh/ssh_host_rsa_key. It is possible to have multiple host
82 key files for the different host key algorithms.
83
84 -i Specifies that sshd is being run from inetd(8).
85
86 -o option
87 Can be used to give options in the format used in the
88 configuration file. This is useful for specifying options for
89 which there is no separate command-line flag. For full details
90 of the options, and their values, see sshd_config(5).
91
92 -p port
93 Specifies the port on which the server listens for connections
94 (default 22). Multiple port options are permitted. Ports
95 specified in the configuration file with the Port option are
96 ignored when a command-line port is specified. Ports specified
97 using the ListenAddress option override command-line ports.
98
99 -q Quiet mode. Nothing is sent to the system log. Normally the
100 beginning, authentication, and termination of each connection is
101 logged.
102
103 -T Extended test mode. Check the validity of the configuration
104 file, output the effective configuration to stdout and then exit.
105 Optionally, Match rules may be applied by specifying the
106 connection parameters using one or more -C options.
107
108 -t Test mode. Only check the validity of the configuration file and
109 sanity of the keys. This is useful for updating sshd reliably as
110 configuration options may change.
111
112 -u len This option is used to specify the size of the field in the utmp
113 structure that holds the remote host name. If the resolved host
114 name is longer than len, the dotted decimal value will be used
115 instead. This allows hosts with very long host names that
116 overflow this field to still be uniquely identified. Specifying
117 -u0 indicates that only dotted decimal addresses should be put
118 into the utmp file. -u0 may also be used to prevent sshd from
119 making DNS requests unless the authentication mechanism or
120 configuration requires it. Authentication mechanisms that may
121 require DNS include HostbasedAuthentication and using a
122 from="pattern-list" option in a key file. Configuration options
123 that require DNS include using a USER@HOST pattern in AllowUsers
124 or DenyUsers.
125
126AUTHENTICATION
127 The OpenSSH SSH daemon supports SSH protocol 2 only. Each host has a
128 host-specific key, used to identify the host. Whenever a client
129 connects, the daemon responds with its public host key. The client
130 compares the host key against its own database to verify that it has not
131 changed. Forward security is provided through a Diffie-Hellman key
132 agreement. This key agreement results in a shared session key. The rest
133 of the session is encrypted using a symmetric cipher, currently 128-bit
134 AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES. The
135 client selects the encryption algorithm to use from those offered by the
136 server. Additionally, session integrity is provided through a
137 cryptographic message authentication code (hmac-md5, hmac-sha1, umac-64,
138 umac-128, hmac-sha2-256 or hmac-sha2-512).
139
140 Finally, the server and the client enter an authentication dialog. The
141 client tries to authenticate itself using host-based authentication,
142 public key authentication, challenge-response authentication, or password
143 authentication.
144
145 Regardless of the authentication type, the account is checked to ensure
146 that it is accessible. An account is not accessible if it is locked,
147 listed in DenyUsers or its group is listed in DenyGroups . The
148 definition of a locked account is system dependant. Some platforms have
149 their own account database (eg AIX) and some modify the passwd field (
150 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
151 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
152 Linuxes). If there is a requirement to disable password authentication
153 for the account while allowing still public-key, then the passwd field
154 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 ).
155
156 If the client successfully authenticates itself, a dialog for preparing
157 the session is entered. At this time the client may request things like
158 allocating a pseudo-tty, forwarding X11 connections, forwarding TCP
159 connections, or forwarding the authentication agent connection over the
160 secure channel.
161
162 After this, the client either requests a shell or execution of a command.
163 The sides then enter session mode. In this mode, either side may send
164 data at any time, and such data is forwarded to/from the shell or command
165 on the server side, and the user terminal in the client side.
166
167 When the user program terminates and all forwarded X11 and other
168 connections have been closed, the server sends command exit status to the
169 client, and both sides exit.
170
171LOGIN PROCESS
172 When a user successfully logs in, sshd does the following:
173
174 1. If the login is on a tty, and no command has been specified,
175 prints last login time and /etc/motd (unless prevented in the
176 configuration file or by ~/.hushlogin; see the FILES section).
177
178 2. If the login is on a tty, records login time.
179
180 3. Checks /etc/nologin; if it exists, prints contents and quits
181 (unless root).
182
183 4. Changes to run with normal user privileges.
184
185 5. Sets up basic environment.
186
187 6. Reads the file ~/.ssh/environment, if it exists, and users are
188 allowed to change their environment. See the
189 PermitUserEnvironment option in sshd_config(5).
190
191 7. Changes to user's home directory.
192
193 8. If ~/.ssh/rc exists and the sshd_config(5) PermitUserRC option
194 is set, runs it; else if /etc/ssh/sshrc exists, runs it;
195 otherwise runs xauth. The M-bM-^@M-^\rcM-bM-^@M-^] files are given the X11
196 authentication protocol and cookie in standard input. See
197 SSHRC, below.
198
199 9. Runs user's shell or command. All commands are run under the
200 user's login shell as specified in the system password
201 database.
202
203SSHRC
204 If the file ~/.ssh/rc exists, sh(1) runs it after reading the environment
205 files but before starting the user's shell or command. It must not
206 produce any output on stdout; stderr must be used instead. If X11
207 forwarding is in use, it will receive the "proto cookie" pair in its
208 standard input (and DISPLAY in its environment). The script must call
209 xauth(1) because sshd will not run xauth automatically to add X11
210 cookies.
211
212 The primary purpose of this file is to run any initialization routines
213 which may be needed before the user's home directory becomes accessible;
214 AFS is a particular example of such an environment.
215
216 This file will probably contain some initialization code followed by
217 something similar to:
218
219 if read proto cookie && [ -n "$DISPLAY" ]; then
220 if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then
221 # X11UseLocalhost=yes
222 echo add unix:`echo $DISPLAY |
223 cut -c11-` $proto $cookie
224 else
225 # X11UseLocalhost=no
226 echo add $DISPLAY $proto $cookie
227 fi | xauth -q -
228 fi
229
230 If this file does not exist, /etc/ssh/sshrc is run, and if that does not
231 exist either, xauth is used to add the cookie.
232
233AUTHORIZED_KEYS FILE FORMAT
234 AuthorizedKeysFile specifies the files containing public keys for public
235 key authentication; if this option is not specified, the default is
236 ~/.ssh/authorized_keys and ~/.ssh/authorized_keys2. Each line of the
237 file contains one key (empty lines and lines starting with a M-bM-^@M-^X#M-bM-^@M-^Y are
238 ignored as comments). Public keys consist of the following space-
239 separated fields: options, keytype, base64-encoded key, comment. The
240 options field is optional. The keytype is M-bM-^@M-^\ecdsa-sha2-nistp256M-bM-^@M-^],
241 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
242 M-bM-^@M-^\ssh-rsaM-bM-^@M-^]; the comment field is not used for anything (but may be
243 convenient for the user to identify the key).
244
245 Note that lines in this file can be several hundred bytes long (because
246 of the size of the public key encoding) up to a limit of 8 kilobytes,
247 which permits DSA keys up to 8 kilobits and RSA keys up to 16 kilobits.
248 You don't want to type them in; instead, copy the id_dsa.pub,
249 id_ecdsa.pub, id_ed25519.pub, or the id_rsa.pub file and edit it.
250
251 sshd enforces a minimum RSA key modulus size of 1024 bits.
252
253 The options (if present) consist of comma-separated option
254 specifications. No spaces are permitted, except within double quotes.
255 The following option specifications are supported (note that option
256 keywords are case-insensitive):
257
258 agent-forwarding
259 Enable authentication agent forwarding previously disabled by the
260 restrict option.
261
262 cert-authority
263 Specifies that the listed key is a certification authority (CA)
264 that is trusted to validate signed certificates for user
265 authentication.
266
267 Certificates may encode access restrictions similar to these key
268 options. If both certificate restrictions and key options are
269 present, the most restrictive union of the two is applied.
270
271 command="command"
272 Specifies that the command is executed whenever this key is used
273 for authentication. The command supplied by the user (if any) is
274 ignored. The command is run on a pty if the client requests a
275 pty; otherwise it is run without a tty. If an 8-bit clean
276 channel is required, one must not request a pty or should specify
277 no-pty. A quote may be included in the command by quoting it
278 with a backslash.
279
280 This option might be useful to restrict certain public keys to
281 perform just a specific operation. An example might be a key
282 that permits remote backups but nothing else. Note that the
283 client may specify TCP and/or X11 forwarding unless they are
284 explicitly prohibited, e.g. using the restrict key option.
285
286 The command originally supplied by the client is available in the
287 SSH_ORIGINAL_COMMAND environment variable. Note that this option
288 applies to shell, command or subsystem execution. Also note that
289 this command may be superseded by a sshd_config(5) ForceCommand
290 directive.
291
292 If a command is specified and a forced-command is embedded in a
293 certificate used for authentication, then the certificate will be
294 accepted only if the two commands are identical.
295
296 environment="NAME=value"
297 Specifies that the string is to be added to the environment when
298 logging in using this key. Environment variables set this way
299 override other default environment values. Multiple options of
300 this type are permitted. Environment processing is disabled by
301 default and is controlled via the PermitUserEnvironment option.
302
303 expiry-time="timespec"
304 Specifies a time after which the key will not be accepted. The
305 time may be specified as a YYYYMMDD date or a YYYYMMDDHHMM[SS]
306 time in the system time-zone.
307
308 from="pattern-list"
309 Specifies that in addition to public key authentication, either
310 the canonical name of the remote host or its IP address must be
311 present in the comma-separated list of patterns. See PATTERNS in
312 ssh_config(5) for more information on patterns.
313
314 In addition to the wildcard matching that may be applied to
315 hostnames or addresses, a from stanza may match IP addresses
316 using CIDR address/masklen notation.
317
318 The purpose of this option is to optionally increase security:
319 public key authentication by itself does not trust the network or
320 name servers or anything (but the key); however, if somebody
321 somehow steals the key, the key permits an intruder to log in
322 from anywhere in the world. This additional option makes using a
323 stolen key more difficult (name servers and/or routers would have
324 to be compromised in addition to just the key).
325
326 no-agent-forwarding
327 Forbids authentication agent forwarding when this key is used for
328 authentication.
329
330 no-port-forwarding
331 Forbids TCP forwarding when this key is used for authentication.
332 Any port forward requests by the client will return an error.
333 This might be used, e.g. in connection with the command option.
334
335 no-pty Prevents tty allocation (a request to allocate a pty will fail).
336
337 no-user-rc
338 Disables execution of ~/.ssh/rc.
339
340 no-X11-forwarding
341 Forbids X11 forwarding when this key is used for authentication.
342 Any X11 forward requests by the client will return an error.
343
344 permitopen="host:port"
345 Limit local port forwarding with ssh(1) -L such that it may only
346 connect to the specified host and port. IPv6 addresses can be
347 specified by enclosing the address in square brackets. Multiple
348 permitopen options may be applied separated by commas. No
349 pattern matching is performed on the specified hostnames, they
350 must be literal domains or addresses. A port specification of *
351 matches any port.
352
353 port-forwarding
354 Enable port forwarding previously disabled by the restrict
355 option.
356
357 principals="principals"
358 On a cert-authority line, specifies allowed principals for
359 certificate authentication as a comma-separated list. At least
360 one name from the list must appear in the certificate's list of
361 principals for the certificate to be accepted. This option is
362 ignored for keys that are not marked as trusted certificate
363 signers using the cert-authority option.
364
365 pty Permits tty allocation previously disabled by the restrict
366 option.
367
368 restrict
369 Enable all restrictions, i.e. disable port, agent and X11
370 forwarding, as well as disabling PTY allocation and execution of
371 ~/.ssh/rc. If any future restriction capabilities are added to
372 authorized_keys files they will be included in this set.
373
374 tunnel="n"
375 Force a tun(4) device on the server. Without this option, the
376 next available device will be used if the client requests a
377 tunnel.
378
379 user-rc
380 Enables execution of ~/.ssh/rc previously disabled by the
381 restrict option.
382
383 X11-forwarding
384 Permits X11 forwarding previously disabled by the restrict
385 option.
386
387 An example authorized_keys file:
388
389 # Comments allowed at start of line
390 ssh-rsa AAAAB3Nza...LiPk== user@example.net
391 from="*.sales.example.net,!pc.sales.example.net" ssh-rsa
392 AAAAB2...19Q== john@example.net
393 command="dump /home",no-pty,no-port-forwarding ssh-dss
394 AAAAC3...51R== example.net
395 permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-dss
396 AAAAB5...21S==
397 tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...==
398 jane@example.net
399 restrict,command="uptime" ssh-rsa AAAA1C8...32Tv==
400 user@example.net
401 restrict,pty,command="nethack" ssh-rsa AAAA1f8...IrrC5==
402 user@example.net
403
404SSH_KNOWN_HOSTS FILE FORMAT
405 The /etc/ssh/ssh_known_hosts and ~/.ssh/known_hosts files contain host
406 public keys for all known hosts. The global file should be prepared by
407 the administrator (optional), and the per-user file is maintained
408 automatically: whenever the user connects to an unknown host, its key is
409 added to the per-user file.
410
411 Each line in these files contains the following fields: markers
412 (optional), hostnames, keytype, base64-encoded key, comment. The fields
413 are separated by spaces.
414
415 The marker is optional, but if it is present then it must be one of
416 M-bM-^@M-^\@cert-authorityM-bM-^@M-^], to indicate that the line contains a certification
417 authority (CA) key, or M-bM-^@M-^\@revokedM-bM-^@M-^], to indicate that the key contained on
418 the line is revoked and must not ever be accepted. Only one marker
419 should be used on a key line.
420
421 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
422 wildcards); each pattern in turn is matched against the host name. When
423 sshd is authenticating a client, such as when using
424 HostbasedAuthentication, this will be the canonical client host name.
425 When ssh(1) is authenticating a server, this will be the host name given
426 by the user, the value of the ssh(1) HostkeyAlias if it was specified, or
427 the canonical server hostname if the ssh(1) CanonicalizeHostname option
428 was used.
429
430 A pattern may also be preceded by M-bM-^@M-^X!M-bM-^@M-^Y to indicate negation: if the host
431 name matches a negated pattern, it is not accepted (by that line) even if
432 it matched another pattern on the line. A hostname or address may
433 optionally be enclosed within M-bM-^@M-^X[M-bM-^@M-^Y and M-bM-^@M-^X]M-bM-^@M-^Y brackets then followed by M-bM-^@M-^X:M-bM-^@M-^Y
434 and a non-standard port number.
435
436 Alternately, hostnames may be stored in a hashed form which hides host
437 names and addresses should the file's contents be disclosed. Hashed
438 hostnames start with a M-bM-^@M-^X|M-bM-^@M-^Y character. Only one hashed hostname may
439 appear on a single line and none of the above negation or wildcard
440 operators may be applied.
441
442 The keytype and base64-encoded key are taken directly from the host key;
443 they can be obtained, for example, from /etc/ssh/ssh_host_rsa_key.pub.
444 The optional comment field continues to the end of the line, and is not
445 used.
446
447 Lines starting with M-bM-^@M-^X#M-bM-^@M-^Y and empty lines are ignored as comments.
448
449 When performing host authentication, authentication is accepted if any
450 matching line has the proper key; either one that matches exactly or, if
451 the server has presented a certificate for authentication, the key of the
452 certification authority that signed the certificate. For a key to be
453 trusted as a certification authority, it must use the M-bM-^@M-^\@cert-authorityM-bM-^@M-^]
454 marker described above.
455
456 The known hosts file also provides a facility to mark keys as revoked,
457 for example when it is known that the associated private key has been
458 stolen. Revoked keys are specified by including the M-bM-^@M-^\@revokedM-bM-^@M-^] marker at
459 the beginning of the key line, and are never accepted for authentication
460 or as certification authorities, but instead will produce a warning from
461 ssh(1) when they are encountered.
462
463 It is permissible (but not recommended) to have several lines or
464 different host keys for the same names. This will inevitably happen when
465 short forms of host names from different domains are put in the file. It
466 is possible that the files contain conflicting information;
467 authentication is accepted if valid information can be found from either
468 file.
469
470 Note that the lines in these files are typically hundreds of characters
471 long, and you definitely don't want to type in the host keys by hand.
472 Rather, generate them by a script, ssh-keyscan(1) or by taking, for
473 example, /etc/ssh/ssh_host_rsa_key.pub and adding the host names at the
474 front. ssh-keygen(1) also offers some basic automated editing for
475 ~/.ssh/known_hosts including removing hosts matching a host name and
476 converting all host names to their hashed representations.
477
478 An example ssh_known_hosts file:
479
480 # Comments allowed at start of line
481 closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net
482 cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....=
483 # A hashed hostname
484 |1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa
485 AAAA1234.....=
486 # A revoked key
487 @revoked * ssh-rsa AAAAB5W...
488 # A CA key, accepted for any host in *.mydomain.com or *.mydomain.org
489 @cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W...
490
491FILES
492 ~/.hushlogin
493 This file is used to suppress printing the last login time and
494 /etc/motd, if PrintLastLog and PrintMotd, respectively, are
495 enabled. It does not suppress printing of the banner specified
496 by Banner.
497
498 ~/.rhosts
499 This file is used for host-based authentication (see ssh(1) for
500 more information). On some machines this file may need to be
501 world-readable if the user's home directory is on an NFS
502 partition, because sshd reads it as root. Additionally, this
503 file must be owned by the user, and must not have write
504 permissions for anyone else. The recommended permission for most
505 machines is read/write for the user, and not accessible by
506 others.
507
508 ~/.shosts
509 This file is used in exactly the same way as .rhosts, but allows
510 host-based authentication without permitting login with
511 rlogin/rsh.
512
513 ~/.ssh/
514 This directory is the default location for all user-specific
515 configuration and authentication information. There is no
516 general requirement to keep the entire contents of this directory
517 secret, but the recommended permissions are read/write/execute
518 for the user, and not accessible by others.
519
520 ~/.ssh/authorized_keys
521 Lists the public keys (DSA, ECDSA, Ed25519, RSA) that can be used
522 for logging in as this user. The format of this file is
523 described above. The content of the file is not highly
524 sensitive, but the recommended permissions are read/write for the
525 user, and not accessible by others.
526
527 If this file, the ~/.ssh directory, or the user's home directory
528 are writable by other users, then the file could be modified or
529 replaced by unauthorized users. In this case, sshd will not
530 allow it to be used unless the StrictModes option has been set to
531 M-bM-^@M-^\noM-bM-^@M-^].
532
533 ~/.ssh/environment
534 This file is read into the environment at login (if it exists).
535 It can only contain empty lines, comment lines (that start with
536 M-bM-^@M-^X#M-bM-^@M-^Y), and assignment lines of the form name=value. The file
537 should be writable only by the user; it need not be readable by
538 anyone else. Environment processing is disabled by default and
539 is controlled via the PermitUserEnvironment option.
540
541 ~/.ssh/known_hosts
542 Contains a list of host keys for all hosts the user has logged
543 into that are not already in the systemwide list of known host
544 keys. The format of this file is described above. This file
545 should be writable only by root/the owner and can, but need not
546 be, world-readable.
547
548 ~/.ssh/rc
549 Contains initialization routines to be run before the user's home
550 directory becomes accessible. This file should be writable only
551 by the user, and need not be readable by anyone else.
552
553 /etc/hosts.equiv
554 This file is for host-based authentication (see ssh(1)). It
555 should only be writable by root.
556
557 /etc/moduli
558 Contains Diffie-Hellman groups used for the "Diffie-Hellman Group
559 Exchange" key exchange method. The file format is described in
560 moduli(5). If no usable groups are found in this file then fixed
561 internal groups will be used.
562
563 /etc/motd
564 See motd(5).
565
566 /etc/nologin
567 If this file exists, sshd refuses to let anyone except root log
568 in. The contents of the file are displayed to anyone trying to
569 log in, and non-root connections are refused. The file should be
570 world-readable.
571
572 /etc/shosts.equiv
573 This file is used in exactly the same way as hosts.equiv, but
574 allows host-based authentication without permitting login with
575 rlogin/rsh.
576
577 /etc/ssh/ssh_host_ecdsa_key
578 /etc/ssh/ssh_host_ed25519_key
579 /etc/ssh/ssh_host_rsa_key
580 These files contain the private parts of the host keys. These
581 files should only be owned by root, readable only by root, and
582 not accessible to others. Note that sshd does not start if these
583 files are group/world-accessible.
584
585 /etc/ssh/ssh_host_ecdsa_key.pub
586 /etc/ssh/ssh_host_ed25519_key.pub
587 /etc/ssh/ssh_host_rsa_key.pub
588 These files contain the public parts of the host keys. These
589 files should be world-readable but writable only by root. Their
590 contents should match the respective private parts. These files
591 are not really used for anything; they are provided for the
592 convenience of the user so their contents can be copied to known
593 hosts files. These files are created using ssh-keygen(1).
594
595 /etc/ssh/ssh_known_hosts
596 Systemwide list of known host keys. This file should be prepared
597 by the system administrator to contain the public host keys of
598 all machines in the organization. The format of this file is
599 described above. This file should be writable only by root/the
600 owner and should be world-readable.
601
602 /etc/ssh/sshd_config
603 Contains configuration data for sshd. The file format and
604 configuration options are described in sshd_config(5).
605
606 /etc/ssh/sshrc
607 Similar to ~/.ssh/rc, it can be used to specify machine-specific
608 login-time initializations globally. This file should be
609 writable only by root, and should be world-readable.
610
611 /var/empty
612 chroot(2) directory used by sshd during privilege separation in
613 the pre-authentication phase. The directory should not contain
614 any files and must be owned by root and not group or world-
615 writable.
616
617 /var/run/sshd.pid
618 Contains the process ID of the sshd listening for connections (if
619 there are several daemons running concurrently for different
620 ports, this contains the process ID of the one started last).
621 The content of this file is not sensitive; it can be world-
622 readable.
623
624SEE ALSO
625 scp(1), sftp(1), ssh(1), ssh-add(1), ssh-agent(1), ssh-keygen(1),
626 ssh-keyscan(1), chroot(2), login.conf(5), moduli(5), sshd_config(5),
627 inetd(8), sftp-server(8)
628
629AUTHORS
630 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
631 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
632 de Raadt and Dug Song removed many bugs, re-added newer features and
633 created OpenSSH. Markus Friedl contributed the support for SSH protocol
634 versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support
635 for privilege separation.
636
637OpenBSD 6.2 March 14, 2018 OpenBSD 6.2
generated by cgit v1.2.3 (git 2.39.1) at 2024-06-18 12:09:16 +0000