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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 dependent. 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 permitlisten="[host:]port"
345 Limit remote port forwarding with the ssh(1) -R option such that
346 it may only listen on the specified host (optional) and port.
347 IPv6 addresses can be specified by enclosing the address in
348 square brackets. Multiple permitlisten options may be applied
349 separated by commas. Hostnames may include wildcards as
350 described in the PATTERNS section in ssh_config(5). A port
351 specification of * matches any port. Note that the setting of
352 GatewayPorts may further restrict listen addresses. Note that
353 ssh(1) will send a hostname of M-bM-^@M-^\localhostM-bM-^@M-^] if a listen host was
354 not specified when the forwarding was requested, and that this
355 name is treated differently to the explicit localhost addresses
356 M-bM-^@M-^\127.0.0.1M-bM-^@M-^] and M-bM-^@M-^\::1M-bM-^@M-^].
357
358 permitopen="host:port"
359 Limit local port forwarding with the ssh(1) -L option such that
360 it may only connect to the specified host and port. IPv6
361 addresses can be specified by enclosing the address in square
362 brackets. Multiple permitopen options may be applied separated
363 by commas. No pattern matching is performed on the specified
364 hostnames, they must be literal domains or addresses. A port
365 specification of * matches any port.
366
367 port-forwarding
368 Enable port forwarding previously disabled by the restrict
369 option.
370
371 principals="principals"
372 On a cert-authority line, specifies allowed principals for
373 certificate authentication as a comma-separated list. At least
374 one name from the list must appear in the certificate's list of
375 principals for the certificate to be accepted. This option is
376 ignored for keys that are not marked as trusted certificate
377 signers using the cert-authority option.
378
379 pty Permits tty allocation previously disabled by the restrict
380 option.
381
382 restrict
383 Enable all restrictions, i.e. disable port, agent and X11
384 forwarding, as well as disabling PTY allocation and execution of
385 ~/.ssh/rc. If any future restriction capabilities are added to
386 authorized_keys files they will be included in this set.
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 user-rc
394 Enables execution of ~/.ssh/rc previously disabled by the
395 restrict option.
396
397 X11-forwarding
398 Permits X11 forwarding previously disabled by the restrict
399 option.
400
401 An example authorized_keys file:
402
403 # Comments allowed at start of line
404 ssh-rsa AAAAB3Nza...LiPk== user@example.net
405 from="*.sales.example.net,!pc.sales.example.net" ssh-rsa
406 AAAAB2...19Q== john@example.net
407 command="dump /home",no-pty,no-port-forwarding ssh-rsa
408 AAAAC3...51R== example.net
409 permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-rsa
410 AAAAB5...21S==
411 permitlisten="localhost:8080",permitopen="localhost:22000" ssh-rsa
412 AAAAB5...21S==
413 tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...==
414 jane@example.net
415 restrict,command="uptime" ssh-rsa AAAA1C8...32Tv==
416 user@example.net
417 restrict,pty,command="nethack" ssh-rsa AAAA1f8...IrrC5==
418 user@example.net
419
420SSH_KNOWN_HOSTS FILE FORMAT
421 The /etc/ssh/ssh_known_hosts and ~/.ssh/known_hosts files contain host
422 public keys for all known hosts. The global file should be prepared by
423 the administrator (optional), and the per-user file is maintained
424 automatically: whenever the user connects to an unknown host, its key is
425 added to the per-user file.
426
427 Each line in these files contains the following fields: markers
428 (optional), hostnames, keytype, base64-encoded key, comment. The fields
429 are separated by spaces.
430
431 The marker is optional, but if it is present then it must be one of
432 M-bM-^@M-^\@cert-authorityM-bM-^@M-^], to indicate that the line contains a certification
433 authority (CA) key, or M-bM-^@M-^\@revokedM-bM-^@M-^], to indicate that the key contained on
434 the line is revoked and must not ever be accepted. Only one marker
435 should be used on a key line.
436
437 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
438 wildcards); each pattern in turn is matched against the host name. When
439 sshd is authenticating a client, such as when using
440 HostbasedAuthentication, this will be the canonical client host name.
441 When ssh(1) is authenticating a server, this will be the host name given
442 by the user, the value of the ssh(1) HostkeyAlias if it was specified, or
443 the canonical server hostname if the ssh(1) CanonicalizeHostname option
444 was used.
445
446 A pattern may also be preceded by M-bM-^@M-^X!M-bM-^@M-^Y to indicate negation: if the host
447 name matches a negated pattern, it is not accepted (by that line) even if
448 it matched another pattern on the line. A hostname or address may
449 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
450 and a non-standard port number.
451
452 Alternately, hostnames may be stored in a hashed form which hides host
453 names and addresses should the file's contents be disclosed. Hashed
454 hostnames start with a M-bM-^@M-^X|M-bM-^@M-^Y character. Only one hashed hostname may
455 appear on a single line and none of the above negation or wildcard
456 operators may be applied.
457
458 The keytype and base64-encoded key are taken directly from the host key;
459 they can be obtained, for example, from /etc/ssh/ssh_host_rsa_key.pub.
460 The optional comment field continues to the end of the line, and is not
461 used.
462
463 Lines starting with M-bM-^@M-^X#M-bM-^@M-^Y and empty lines are ignored as comments.
464
465 When performing host authentication, authentication is accepted if any
466 matching line has the proper key; either one that matches exactly or, if
467 the server has presented a certificate for authentication, the key of the
468 certification authority that signed the certificate. For a key to be
469 trusted as a certification authority, it must use the M-bM-^@M-^\@cert-authorityM-bM-^@M-^]
470 marker described above.
471
472 The known hosts file also provides a facility to mark keys as revoked,
473 for example when it is known that the associated private key has been
474 stolen. Revoked keys are specified by including the M-bM-^@M-^\@revokedM-bM-^@M-^] marker at
475 the beginning of the key line, and are never accepted for authentication
476 or as certification authorities, but instead will produce a warning from
477 ssh(1) when they are encountered.
478
479 It is permissible (but not recommended) to have several lines or
480 different host keys for the same names. This will inevitably happen when
481 short forms of host names from different domains are put in the file. It
482 is possible that the files contain conflicting information;
483 authentication is accepted if valid information can be found from either
484 file.
485
486 Note that the lines in these files are typically hundreds of characters
487 long, and you definitely don't want to type in the host keys by hand.
488 Rather, generate them by a script, ssh-keyscan(1) or by taking, for
489 example, /etc/ssh/ssh_host_rsa_key.pub and adding the host names at the
490 front. ssh-keygen(1) also offers some basic automated editing for
491 ~/.ssh/known_hosts including removing hosts matching a host name and
492 converting all host names to their hashed representations.
493
494 An example ssh_known_hosts file:
495
496 # Comments allowed at start of line
497 closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net
498 cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....=
499 # A hashed hostname
500 |1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa
501 AAAA1234.....=
502 # A revoked key
503 @revoked * ssh-rsa AAAAB5W...
504 # A CA key, accepted for any host in *.mydomain.com or *.mydomain.org
505 @cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W...
506
507FILES
508 ~/.hushlogin
509 This file is used to suppress printing the last login time and
510 /etc/motd, if PrintLastLog and PrintMotd, respectively, are
511 enabled. It does not suppress printing of the banner specified
512 by Banner.
513
514 ~/.rhosts
515 This file is used for host-based authentication (see ssh(1) for
516 more information). On some machines this file may need to be
517 world-readable if the user's home directory is on an NFS
518 partition, because sshd reads it as root. Additionally, this
519 file must be owned by the user, and must not have write
520 permissions for anyone else. The recommended permission for most
521 machines is read/write for the user, and not accessible by
522 others.
523
524 ~/.shosts
525 This file is used in exactly the same way as .rhosts, but allows
526 host-based authentication without permitting login with
527 rlogin/rsh.
528
529 ~/.ssh/
530 This directory is the default location for all user-specific
531 configuration and authentication information. There is no
532 general requirement to keep the entire contents of this directory
533 secret, but the recommended permissions are read/write/execute
534 for the user, and not accessible by others.
535
536 ~/.ssh/authorized_keys
537 Lists the public keys (DSA, ECDSA, Ed25519, RSA) that can be used
538 for logging in as this user. The format of this file is
539 described above. The content of the file is not highly
540 sensitive, but the recommended permissions are read/write for the
541 user, and not accessible by others.
542
543 If this file, the ~/.ssh directory, or the user's home directory
544 are writable by other users, then the file could be modified or
545 replaced by unauthorized users. In this case, sshd will not
546 allow it to be used unless the StrictModes option has been set to
547 M-bM-^@M-^\noM-bM-^@M-^].
548
549 ~/.ssh/environment
550 This file is read into the environment at login (if it exists).
551 It can only contain empty lines, comment lines (that start with
552 M-bM-^@M-^X#M-bM-^@M-^Y), and assignment lines of the form name=value. The file
553 should be writable only by the user; it need not be readable by
554 anyone else. Environment processing is disabled by default and
555 is controlled via the PermitUserEnvironment option.
556
557 ~/.ssh/known_hosts
558 Contains a list of host keys for all hosts the user has logged
559 into that are not already in the systemwide list of known host
560 keys. The format of this file is described above. This file
561 should be writable only by root/the owner and can, but need not
562 be, world-readable.
563
564 ~/.ssh/rc
565 Contains initialization routines to be run before the user's home
566 directory becomes accessible. This file should be writable only
567 by the user, and need not be readable by anyone else.
568
569 /etc/hosts.equiv
570 This file is for host-based authentication (see ssh(1)). It
571 should only be writable by root.
572
573 /etc/moduli
574 Contains Diffie-Hellman groups used for the "Diffie-Hellman Group
575 Exchange" key exchange method. The file format is described in
576 moduli(5). If no usable groups are found in this file then fixed
577 internal groups will be used.
578
579 /etc/motd
580 See motd(5).
581
582 /etc/nologin
583 If this file exists, sshd refuses to let anyone except root log
584 in. The contents of the file are displayed to anyone trying to
585 log in, and non-root connections are refused. The file should be
586 world-readable.
587
588 /etc/shosts.equiv
589 This file is used in exactly the same way as hosts.equiv, but
590 allows host-based authentication without permitting login with
591 rlogin/rsh.
592
593 /etc/ssh/ssh_host_ecdsa_key
594 /etc/ssh/ssh_host_ed25519_key
595 /etc/ssh/ssh_host_rsa_key
596 These files contain the private parts of the host keys. These
597 files should only be owned by root, readable only by root, and
598 not accessible to others. Note that sshd does not start if these
599 files are group/world-accessible.
600
601 /etc/ssh/ssh_host_ecdsa_key.pub
602 /etc/ssh/ssh_host_ed25519_key.pub
603 /etc/ssh/ssh_host_rsa_key.pub
604 These files contain the public parts of the host keys. These
605 files should be world-readable but writable only by root. Their
606 contents should match the respective private parts. These files
607 are not really used for anything; they are provided for the
608 convenience of the user so their contents can be copied to known
609 hosts files. These files are created using ssh-keygen(1).
610
611 /etc/ssh/ssh_known_hosts
612 Systemwide list of known host keys. This file should be prepared
613 by the system administrator to contain the public host keys of
614 all machines in the organization. The format of this file is
615 described above. This file should be writable only by root/the
616 owner and should be world-readable.
617
618 /etc/ssh/sshd_config
619 Contains configuration data for sshd. The file format and
620 configuration options are described in sshd_config(5).
621
622 /etc/ssh/sshrc
623 Similar to ~/.ssh/rc, it can be used to specify machine-specific
624 login-time initializations globally. This file should be
625 writable only by root, and should be world-readable.
626
627 /var/empty
628 chroot(2) directory used by sshd during privilege separation in
629 the pre-authentication phase. The directory should not contain
630 any files and must be owned by root and not group or world-
631 writable.
632
633 /var/run/sshd.pid
634 Contains the process ID of the sshd listening for connections (if
635 there are several daemons running concurrently for different
636 ports, this contains the process ID of the one started last).
637 The content of this file is not sensitive; it can be world-
638 readable.
639
640SEE ALSO
641 scp(1), sftp(1), ssh(1), ssh-add(1), ssh-agent(1), ssh-keygen(1),
642 ssh-keyscan(1), chroot(2), login.conf(5), moduli(5), sshd_config(5),
643 inetd(8), sftp-server(8)
644
645AUTHORS
646 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
647 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
648 de Raadt and Dug Song removed many bugs, re-added newer features and
649 created OpenSSH. Markus Friedl contributed the support for SSH protocol
650 versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support
651 for privilege separation.
652
653OpenBSD 6.4 July 22, 2018 OpenBSD 6.4
generated by cgit v1.2.3 (git 2.39.1) at 2024-06-18 13:26:49 +0000