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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] [-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). 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
147AUTHENTICATION
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
208LOGIN 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. All commands are run under the
237 user's login shell as specified in the system password
238 database.
239
240SSHRC
241 If the file ~/.ssh/rc exists, sh(1) runs it after reading the environment
242 files but before starting the user's shell or command. It must not
243 produce any output on stdout; stderr must be used instead. If X11
244 forwarding is in use, it will receive the "proto cookie" pair in its
245 standard input (and DISPLAY in its environment). The script must call
246 xauth(1) because sshd will not run xauth automatically to add X11
247 cookies.
248
249 The primary purpose of this file is to run any initialization routines
250 which may be needed before the user's home directory becomes accessible;
251 AFS is a particular example of such an environment.
252
253 This file will probably contain some initialization code followed by
254 something similar to:
255
256 if read proto cookie && [ -n "$DISPLAY" ]; then
257 if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then
258 # X11UseLocalhost=yes
259 echo add unix:`echo $DISPLAY |
260 cut -c11-` $proto $cookie
261 else
262 # X11UseLocalhost=no
263 echo add $DISPLAY $proto $cookie
264 fi | xauth -q -
265 fi
266
267 If this file does not exist, /etc/ssh/sshrc is run, and if that does not
268 exist either, xauth is used to add the cookie.
269
270AUTHORIZED_KEYS FILE FORMAT
271 AuthorizedKeysFile specifies the files containing public keys for public
272 key authentication; if none is specified, the default is
273 ~/.ssh/authorized_keys and ~/.ssh/authorized_keys2. Each line of the
274 file contains one key (empty lines and lines starting with a M-bM-^@M-^X#M-bM-^@M-^Y are
275 ignored as comments). Protocol 1 public keys consist of the following
276 space-separated fields: options, bits, exponent, modulus, comment.
277 Protocol 2 public key consist of: options, keytype, base64-encoded key,
278 comment. The options field is optional; its presence is determined by
279 whether the line starts with a number or not (the options field never
280 starts with a number). The bits, exponent, modulus, and comment fields
281 give the RSA key for protocol version 1; the comment field is not used
282 for anything (but may be convenient for the user to identify the key).
283 For protocol version 2 the keytype is M-bM-^@M-^\ecdsa-sha2-nistp256M-bM-^@M-^],
284 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
285 M-bM-^@M-^\ssh-rsaM-bM-^@M-^].
286
287 Note that lines in this file are usually several hundred bytes long
288 (because of the size of the public key encoding) up to a limit of 8
289 kilobytes, which permits DSA keys up to 8 kilobits and RSA keys up to 16
290 kilobits. You don't want to type them in; instead, copy the
291 identity.pub, id_dsa.pub, id_ecdsa.pub, id_ed25519.pub, or the id_rsa.pub
292 file and edit it.
293
294 sshd enforces a minimum RSA key modulus size for protocol 1 and protocol
295 2 keys of 768 bits.
296
297 The options (if present) consist of comma-separated option
298 specifications. No spaces are permitted, except within double quotes.
299 The following option specifications are supported (note that option
300 keywords are case-insensitive):
301
302 cert-authority
303 Specifies that the listed key is a certification authority (CA)
304 that is trusted to validate signed certificates for user
305 authentication.
306
307 Certificates may encode access restrictions similar to these key
308 options. If both certificate restrictions and key options are
309 present, the most restrictive union of the two is applied.
310
311 command="command"
312 Specifies that the command is executed whenever this key is used
313 for authentication. The command supplied by the user (if any) is
314 ignored. The command is run on a pty if the client requests a
315 pty; otherwise it is run without a tty. If an 8-bit clean
316 channel is required, one must not request a pty or should specify
317 no-pty. A quote may be included in the command by quoting it
318 with a backslash. This option might be useful to restrict
319 certain public keys to perform just a specific operation. An
320 example might be a key that permits remote backups but nothing
321 else. Note that the client may specify TCP and/or X11 forwarding
322 unless they are explicitly prohibited. The command originally
323 supplied by the client is available in the SSH_ORIGINAL_COMMAND
324 environment variable. Note that this option applies to shell,
325 command or subsystem execution. Also note that this command may
326 be superseded by either a sshd_config(5) ForceCommand directive
327 or a command embedded in a certificate.
328
329 environment="NAME=value"
330 Specifies that the string is to be added to the environment when
331 logging in using this key. Environment variables set this way
332 override other default environment values. Multiple options of
333 this type are permitted. Environment processing is disabled by
334 default and is controlled via the PermitUserEnvironment option.
335 This option is automatically disabled if UseLogin is enabled.
336
337 from="pattern-list"
338 Specifies that in addition to public key authentication, either
339 the canonical name of the remote host or its IP address must be
340 present in the comma-separated list of patterns. See PATTERNS in
341 ssh_config(5) for more information on patterns.
342
343 In addition to the wildcard matching that may be applied to
344 hostnames or addresses, a from stanza may match IP addresses
345 using CIDR address/masklen notation.
346
347 The purpose of this option is to optionally increase security:
348 public key authentication by itself does not trust the network or
349 name servers or anything (but the key); however, if somebody
350 somehow steals the key, the key permits an intruder to log in
351 from anywhere in the world. This additional option makes using a
352 stolen key more difficult (name servers and/or routers would have
353 to be compromised in addition to just the key).
354
355 no-agent-forwarding
356 Forbids authentication agent forwarding when this key is used for
357 authentication.
358
359 no-port-forwarding
360 Forbids TCP forwarding when this key is used for authentication.
361 Any port forward requests by the client will return an error.
362 This might be used, e.g. in connection with the command option.
363
364 no-pty Prevents tty allocation (a request to allocate a pty will fail).
365
366 no-user-rc
367 Disables execution of ~/.ssh/rc.
368
369 no-X11-forwarding
370 Forbids X11 forwarding when this key is used for authentication.
371 Any X11 forward requests by the client will return an error.
372
373 permitopen="host:port"
374 Limit local port forwarding with ssh(1) -L such that it may only
375 connect to the specified host and port. IPv6 addresses can be
376 specified by enclosing the address in square brackets. Multiple
377 permitopen options may be applied separated by commas. No
378 pattern matching is performed on the specified hostnames, they
379 must be literal domains or addresses. A port specification of *
380 matches any port.
381
382 principals="principals"
383 On a cert-authority line, specifies allowed principals for
384 certificate authentication as a comma-separated list. At least
385 one name from the list must appear in the certificate's list of
386 principals for the certificate to be accepted. This option is
387 ignored for keys that are not marked as trusted certificate
388 signers using the cert-authority option.
389
390 tunnel="n"
391 Force a tun(4) device on the server. Without this option, the
392 next available device will be used if the client requests a
393 tunnel.
394
395 An example authorized_keys file:
396
397 # Comments allowed at start of line
398 ssh-rsa AAAAB3Nza...LiPk== user@example.net
399 from="*.sales.example.net,!pc.sales.example.net" ssh-rsa
400 AAAAB2...19Q== john@example.net
401 command="dump /home",no-pty,no-port-forwarding ssh-dss
402 AAAAC3...51R== example.net
403 permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-dss
404 AAAAB5...21S==
405 tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...==
406 jane@example.net
407
408SSH_KNOWN_HOSTS FILE FORMAT
409 The /etc/ssh/ssh_known_hosts and ~/.ssh/known_hosts files contain host
410 public keys for all known hosts. The global file should be prepared by
411 the administrator (optional), and the per-user file is maintained
412 automatically: whenever the user connects from an unknown host, its key
413 is added to the per-user file.
414
415 Each line in these files contains the following fields: markers
416 (optional), hostnames, bits, exponent, modulus, comment. The fields are
417 separated by spaces.
418
419 The marker is optional, but if it is present then it must be one of
420 M-bM-^@M-^\@cert-authorityM-bM-^@M-^], to indicate that the line contains a certification
421 authority (CA) key, or M-bM-^@M-^\@revokedM-bM-^@M-^], to indicate that the key contained on
422 the line is revoked and must not ever be accepted. Only one marker
423 should be used on a key line.
424
425 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
426 wildcards); each pattern in turn is matched against the canonical host
427 name (when authenticating a client) or against the user-supplied name
428 (when authenticating a server). A pattern may also be preceded by M-bM-^@M-^X!M-bM-^@M-^Y to
429 indicate negation: if the host name matches a negated pattern, it is not
430 accepted (by that line) even if it matched another pattern on the line.
431 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
432 brackets then followed by M-bM-^@M-^X:M-bM-^@M-^Y and a non-standard port number.
433
434 Alternately, hostnames may be stored in a hashed form which hides host
435 names and addresses should the file's contents be disclosed. Hashed
436 hostnames start with a M-bM-^@M-^X|M-bM-^@M-^Y character. Only one hashed hostname may
437 appear on a single line and none of the above negation or wildcard
438 operators may be applied.
439
440 Bits, exponent, and modulus are taken directly from the RSA host key;
441 they can be obtained, for example, from /etc/ssh/ssh_host_key.pub. The
442 optional comment field continues to the end of the line, and is not used.
443
444 Lines starting with M-bM-^@M-^X#M-bM-^@M-^Y and empty lines are ignored as comments.
445
446 When performing host authentication, authentication is accepted if any
447 matching line has the proper key; either one that matches exactly or, if
448 the server has presented a certificate for authentication, the key of the
449 certification authority that signed the certificate. For a key to be
450 trusted as a certification authority, it must use the M-bM-^@M-^\@cert-authorityM-bM-^@M-^]
451 marker described above.
452
453 The known hosts file also provides a facility to mark keys as revoked,
454 for example when it is known that the associated private key has been
455 stolen. Revoked keys are specified by including the M-bM-^@M-^\@revokedM-bM-^@M-^] marker at
456 the beginning of the key line, and are never accepted for authentication
457 or as certification authorities, but instead will produce a warning from
458 ssh(1) when they are encountered.
459
460 It is permissible (but not recommended) to have several lines or
461 different host keys for the same names. This will inevitably happen when
462 short forms of host names from different domains are put in the file. It
463 is possible that the files contain conflicting information;
464 authentication is accepted if valid information can be found from either
465 file.
466
467 Note that the lines in these files are typically hundreds of characters
468 long, and you definitely don't want to type in the host keys by hand.
469 Rather, generate them by a script, ssh-keyscan(1) or by taking
470 /etc/ssh/ssh_host_key.pub and adding the host names at the front.
471 ssh-keygen(1) also offers some basic automated editing for
472 ~/.ssh/known_hosts including removing hosts matching a host name and
473 converting all host names to their hashed representations.
474
475 An example ssh_known_hosts file:
476
477 # Comments allowed at start of line
478 closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net
479 cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....=
480 # A hashed hostname
481 |1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa
482 AAAA1234.....=
483 # A revoked key
484 @revoked * ssh-rsa AAAAB5W...
485 # A CA key, accepted for any host in *.mydomain.com or *.mydomain.org
486 @cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W...
487
488FILES
489 ~/.hushlogin
490 This file is used to suppress printing the last login time and
491 /etc/motd, if PrintLastLog and PrintMotd, respectively, are
492 enabled. It does not suppress printing of the banner specified
493 by Banner.
494
495 ~/.rhosts
496 This file is used for host-based authentication (see ssh(1) for
497 more information). On some machines this file may need to be
498 world-readable if the user's home directory is on an NFS
499 partition, because sshd reads it as root. Additionally, this
500 file must be owned by the user, and must not have write
501 permissions for anyone else. The recommended permission for most
502 machines is read/write for the user, and not accessible by
503 others.
504
505 ~/.shosts
506 This file is used in exactly the same way as .rhosts, but allows
507 host-based authentication without permitting login with
508 rlogin/rsh.
509
510 ~/.ssh/
511 This directory is the default location for all user-specific
512 configuration and authentication information. There is no
513 general requirement to keep the entire contents of this directory
514 secret, but the recommended permissions are read/write/execute
515 for the user, and not accessible by others.
516
517 ~/.ssh/authorized_keys
518 Lists the public keys (DSA, ECDSA, Ed25519, RSA) that can be used
519 for logging in as this user. The format of this file is
520 described above. The content of the file is not highly
521 sensitive, but the recommended permissions are read/write for the
522 user, and not accessible by others.
523
524 If this file, the ~/.ssh directory, or the user's home directory
525 are writable by other users, then the file could be modified or
526 replaced by unauthorized users. In this case, sshd will not
527 allow it to be used unless the StrictModes option has been set to
528 M-bM-^@M-^\noM-bM-^@M-^].
529
530 ~/.ssh/environment
531 This file is read into the environment at login (if it exists).
532 It can only contain empty lines, comment lines (that start with
533 M-bM-^@M-^X#M-bM-^@M-^Y), and assignment lines of the form name=value. The file
534 should be writable only by the user; it need not be readable by
535 anyone else. Environment processing is disabled by default and
536 is controlled via the PermitUserEnvironment option.
537
538 ~/.ssh/known_hosts
539 Contains a list of host keys for all hosts the user has logged
540 into that are not already in the systemwide list of known host
541 keys. The format of this file is described above. This file
542 should be writable only by root/the owner and can, but need not
543 be, world-readable.
544
545 ~/.ssh/rc
546 Contains initialization routines to be run before the user's home
547 directory becomes accessible. This file should be writable only
548 by the user, and need not be readable by anyone else.
549
550 /etc/hosts.equiv
551 This file is for host-based authentication (see ssh(1)). It
552 should only be writable by root.
553
554 /etc/moduli
555 Contains Diffie-Hellman groups used for the "Diffie-Hellman Group
556 Exchange". The file format is described in moduli(5).
557
558 /etc/motd
559 See motd(5).
560
561 /etc/nologin
562 If this file exists, sshd refuses to let anyone except root log
563 in. The contents of the file are displayed to anyone trying to
564 log in, and non-root connections are refused. The file should be
565 world-readable.
566
567 /etc/shosts.equiv
568 This file is used in exactly the same way as hosts.equiv, but
569 allows host-based authentication without permitting login with
570 rlogin/rsh.
571
572 /etc/ssh/ssh_host_key
573 /etc/ssh/ssh_host_dsa_key
574 /etc/ssh/ssh_host_ecdsa_key
575 /etc/ssh/ssh_host_ed25519_key
576 /etc/ssh/ssh_host_rsa_key
577 These files contain the private parts of the host keys. These
578 files should only be owned by root, readable only by root, and
579 not accessible to others. Note that sshd does not start if these
580 files are group/world-accessible.
581
582 /etc/ssh/ssh_host_key.pub
583 /etc/ssh/ssh_host_dsa_key.pub
584 /etc/ssh/ssh_host_ecdsa_key.pub
585 /etc/ssh/ssh_host_ed25519_key.pub
586 /etc/ssh/ssh_host_rsa_key.pub
587 These files contain the public parts of the host keys. These
588 files should be world-readable but writable only by root. Their
589 contents should match the respective private parts. These files
590 are not really used for anything; they are provided for the
591 convenience of the user so their contents can be copied to known
592 hosts files. These files are created using ssh-keygen(1).
593
594 /etc/ssh/ssh_known_hosts
595 Systemwide list of known host keys. This file should be prepared
596 by the system administrator to contain the public host keys of
597 all machines in the organization. The format of this file is
598 described above. This file should be writable only by root/the
599 owner and should be world-readable.
600
601 /etc/ssh/sshd_config
602 Contains configuration data for sshd. The file format and
603 configuration options are described in sshd_config(5).
604
605 /etc/ssh/sshrc
606 Similar to ~/.ssh/rc, it can be used to specify machine-specific
607 login-time initializations globally. This file should be
608 writable only by root, and should be world-readable.
609
610 /var/empty
611 chroot(2) directory used by sshd during privilege separation in
612 the pre-authentication phase. The directory should not contain
613 any files and must be owned by root and not group or world-
614 writable.
615
616 /var/run/sshd.pid
617 Contains the process ID of the sshd listening for connections (if
618 there are several daemons running concurrently for different
619 ports, this contains the process ID of the one started last).
620 The content of this file is not sensitive; it can be world-
621 readable.
622
623SEE ALSO
624 scp(1), sftp(1), ssh(1), ssh-add(1), ssh-agent(1), ssh-keygen(1),
625 ssh-keyscan(1), chroot(2), login.conf(5), moduli(5), sshd_config(5),
626 inetd(8), sftp-server(8)
627
628AUTHORS
629 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
630 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
631 de Raadt and Dug Song removed many bugs, re-added newer features and
632 created OpenSSH. Markus Friedl contributed the support for SSH protocol
633 versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support
634 for privilege separation.
635
636OpenBSD 5.7 May 1, 2015 OpenBSD 5.7
generated by cgit v1.2.3 (git 2.39.1) at 2024-06-29 08:41:51 +0000