1SSHD(8) BSD System Manager's Manual SSHD(8)
2
4 sshd — OpenSSH daemon
5
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
12 sshd (OpenSSH Daemon) is the daemon program for ssh(1). It provides se‐
13 cure encrypted communications between two untrusted hosts over an inse‐
14 cure network.
15 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, com‐
19 mand execution, and data exchange.
20 sshd can be configured using command-line options or a configuration file
22 (by default sshd_config(5)); command-line options override values speci‐
23 fied in the configuration file. sshd rereads its configuration file when
24 it receives a hangup signal, SIGHUP, by executing itself with the name
25 and options it was started with, e.g. /usr/sbin/sshd.
26 The options are as follows:
28 -4 Forces sshd to use IPv4 addresses only.
30 -6 Forces sshd to use IPv6 addresses only.
32 -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 sup‐
38 plied 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 “addr”, “user”, “host”, “laddr”, “lport”, and
41 “rdomain” and correspond to source address, user, resolved source
42 host name, local address, local port number and routing domain
43 respectively.
44 -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 direc‐
49 tive.
50 -D When this option is specified, sshd will not detach and does not
52 become a daemon. This allows easy monitoring of sshd.
53 -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(2) 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 -E log_file
61 Append debug logs to log_file instead of the system log.
62 -e Write debug logs to standard error instead of the system log.
64 -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 con‐
68 figuration file.
69 -g login_grace_time
71 Gives the grace time for clients to authenticate themselves (de‐
72 fault 120 seconds). If the client fails to authenticate the user
73 within this many seconds, the server disconnects and exits. A
74 value of zero indicates no limit.
75 -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 -i Specifies that sshd is being run from inetd(8).
85 -o option
87 Can be used to give options in the format used in the configura‐
88 tion file. This is useful for specifying options for which there
89 is no separate command-line flag. For full details of the op‐
90 tions, and their values, see sshd_config(5).
91 -p port
93 Specifies the port on which the server listens for connections
94 (default 22). Multiple port options are permitted. Ports speci‐
95 fied in the configuration file with the Port option are ignored
96 when a command-line port is specified. Ports specified using the
97 ListenAddress option override command-line ports.
98 -q Quiet mode. Nothing is sent to the system log. Normally the be‐
100 ginning, authentication, and termination of each connection is
101 logged.
102 -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 connec‐
106 tion parameters using one or more -C options.
107 -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 -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 over‐
116 flow this field to still be uniquely identified. Specifying -u0
117 indicates that only dotted decimal addresses should be put into
118 the utmp file. -u0 may also be used to prevent sshd from making
119 DNS requests unless the authentication mechanism or configuration
120 requires it. Authentication mechanisms that may require DNS in‐
121 clude HostbasedAuthentication and using a from="pattern-list" op‐
122 tion in a key file. Configuration options that require DNS in‐
123 clude using a USER@HOST pattern in AllowUsers or DenyUsers.
124
126 The OpenSSH SSH daemon supports SSH protocol 2 only. Each host has a
127 host-specific key, used to identify the host. Whenever a client con‐
128 nects, the daemon responds with its public host key. The client compares
129 the host key against its own database to verify that it has not changed.
130 Forward secrecy is provided through a Diffie-Hellman key agreement. This
131 key agreement results in a shared session key. The rest of the session
132 is encrypted using a symmetric cipher. The client selects the encryption
133 algorithm to use from those offered by the server. Additionally, session
134 integrity is provided through a cryptographic message authentication code
135 (MAC).
136 Finally, the server and the client enter an authentication dialog. The
138 client tries to authenticate itself using host-based authentication, pub‐
139 lic key authentication, GSSAPI authentication, challenge-response authen‐
140 tication, or password authentication.
141 Regardless of the authentication type, the account is checked to ensure
143 that it is accessible. An account is not accessible if it is locked,
144 listed in DenyUsers or its group is listed in DenyGroups . The defini‐
145 tion of a locked account is system dependent. Some platforms have their
146 own account database (eg AIX) and some modify the passwd field ( ‘*LK*’
147 on Solaris and UnixWare, ‘*’ on HP-UX, containing ‘Nologin’ on Tru64, a
148 leading ‘*LOCKED*’ on FreeBSD and a leading ‘!’ on most Linuxes). If
149 there is a requirement to disable password authentication for the account
150 while allowing still public-key, then the passwd field should be set to
151 something other than these values (eg ‘NP’ or ‘*NP*’ ).
152 If the client successfully authenticates itself, a dialog for preparing
154 the session is entered. At this time the client may request things like
155 allocating a pseudo-tty, forwarding X11 connections, forwarding TCP con‐
156 nections, or forwarding the authentication agent connection over the se‐
157 cure channel.
158 After this, the client either requests an interactive shell or execution
160 or a non-interactive command, which sshd will execute via the user's
161 shell using its -c option. The sides then enter session mode. In this
162 mode, either side may send data at any time, and such data is forwarded
163 to/from the shell or command on the server side, and the user terminal in
164 the client side.
165 When the user program terminates and all forwarded X11 and other connec‐
167 tions have been closed, the server sends command exit status to the
168 client, and both sides exit.
169
171 When a user successfully logs in, sshd does the following:
172 1. If the login is on a tty, and no command has been specified,
174 prints last login time and /etc/motd (unless prevented in the
175 configuration file or by ~/.hushlogin; see the FILES section).
176 2. If the login is on a tty, records login time.
178 3. Checks /etc/nologin; if it exists, prints contents and quits
180 (unless root).
181 4. Changes to run with normal user privileges.
183 5. Sets up basic environment.
185 6. Reads the file ~/.ssh/environment, if it exists, and users are
187 allowed to change their environment. See the
188 PermitUserEnvironment option in sshd_config(5).
189 7. Changes to user's home directory.
191 8. If ~/.ssh/rc exists and the sshd_config(5) PermitUserRC option
193 is set, runs it; else if /etc/ssh/sshrc exists, runs it; oth‐
194 erwise runs xauth(1). The “rc” files are given the X11 au‐
195 thentication protocol and cookie in standard input. See
196 SSHRC, below.
197 9. Runs user's shell or command. All commands are run under the
199 user's login shell as specified in the system password data‐
200 base.
201
203 If the file ~/.ssh/rc exists, sh(1) runs it after reading the environment
204 files but before starting the user's shell or command. It must not pro‐
205 duce any output on stdout; stderr must be used instead. If X11 forward‐
206 ing is in use, it will receive the "proto cookie" pair in its standard
207 input (and DISPLAY in its environment). The script must call xauth(1)
208 because sshd will not run xauth automatically to add X11 cookies.
209 The primary purpose of this file is to run any initialization routines
211 which may be needed before the user's home directory becomes accessible;
212 AFS is a particular example of such an environment.
213 This file will probably contain some initialization code followed by
215 something similar to:
216 if read proto cookie && [ -n "$DISPLAY" ]; then
218 if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then
219 # X11UseLocalhost=yes
220 echo add unix:`echo $DISPLAY |
221 cut -c11-` $proto $cookie
222 else
223 # X11UseLocalhost=no
224 echo add $DISPLAY $proto $cookie
225 fi | xauth -q -
226 fi
227 If this file does not exist, /etc/ssh/sshrc is run, and if that does not
229 exist either, xauth is used to add the cookie.
230
232 AuthorizedKeysFile specifies the files containing public keys for public
233 key authentication; if this option is not specified, the default is
234 ~/.ssh/authorized_keys and ~/.ssh/authorized_keys2. Each line of the
235 file contains one key (empty lines and lines starting with a ‘#’ are ig‐
236 nored as comments). Public keys consist of the following space-separated
237 fields: options, keytype, base64-encoded key, comment. The options field
238 is optional. The supported key types are:
239 sk-ecdsa-sha2-nistp256@openssh.com
241 ecdsa-sha2-nistp256
242 ecdsa-sha2-nistp384
243 ecdsa-sha2-nistp521
244 sk-ssh-ed25519@openssh.com
245 ssh-ed25519
246 ssh-dss
247 ssh-rsa
248 The comment field is not used for anything (but may be convenient for the
250 user to identify the key).
251 Note that lines in this file can be several hundred bytes long (because
253 of the size of the public key encoding) up to a limit of 8 kilobytes,
254 which permits RSA keys up to 16 kilobits. You don't want to type them
255 in; instead, copy the id_dsa.pub, id_ecdsa.pub, id_ecdsa_sk.pub,
256 id_ed25519.pub, id_ed25519_sk.pub, or the id_rsa.pub file and edit it.
257 sshd enforces a minimum RSA key modulus size of 1024 bits.
259 The options (if present) consist of comma-separated option specifica‐
261 tions. No spaces are permitted, except within double quotes. The fol‐
262 lowing option specifications are supported (note that option keywords are
263 case-insensitive):
264 agent-forwarding
266 Enable authentication agent forwarding previously disabled by the
267 restrict option.
268 cert-authority
270 Specifies that the listed key is a certification authority (CA)
271 that is trusted to validate signed certificates for user authen‐
272 tication.
273 Certificates may encode access restrictions similar to these key
275 options. If both certificate restrictions and key options are
276 present, the most restrictive union of the two is applied.
277 command="command"
279 Specifies that the command is executed whenever this key is used
280 for authentication. The command supplied by the user (if any) is
281 ignored. The command is run on a pty if the client requests a
282 pty; otherwise it is run without a tty. If an 8-bit clean chan‐
283 nel is required, one must not request a pty or should specify
284 no-pty. A quote may be included in the command by quoting it
285 with a backslash.
286 This option might be useful to restrict certain public keys to
288 perform just a specific operation. An example might be a key
289 that permits remote backups but nothing else. Note that the
290 client may specify TCP and/or X11 forwarding unless they are ex‐
291 plicitly prohibited, e.g. using the restrict key option.
292 The command originally supplied by the client is available in the
294 SSH_ORIGINAL_COMMAND environment variable. Note that this option
295 applies to shell, command or subsystem execution. Also note that
296 this command may be superseded by a sshd_config(5) ForceCommand
297 directive.
298 If a command is specified and a forced-command is embedded in a
300 certificate used for authentication, then the certificate will be
301 accepted only if the two commands are identical.
302 environment="NAME=value"
304 Specifies that the string is to be added to the environment when
305 logging in using this key. Environment variables set this way
306 override other default environment values. Multiple options of
307 this type are permitted. Environment processing is disabled by
308 default and is controlled via the PermitUserEnvironment option.
309 expiry-time="timespec"
311 Specifies a time after which the key will not be accepted. The
312 time may be specified as a YYYYMMDD date or a YYYYMMDDHHMM[SS]
313 time in the system time-zone.
314 from="pattern-list"
316 Specifies that in addition to public key authentication, either
317 the canonical name of the remote host or its IP address must be
318 present in the comma-separated list of patterns. See PATTERNS in
319 ssh_config(5) for more information on patterns.
320 In addition to the wildcard matching that may be applied to host‐
322 names or addresses, a from stanza may match IP addresses using
323 CIDR address/masklen notation.
324 The purpose of this option is to optionally increase security:
326 public key authentication by itself does not trust the network or
327 name servers or anything (but the key); however, if somebody
328 somehow steals the key, the key permits an intruder to log in
329 from anywhere in the world. This additional option makes using a
330 stolen key more difficult (name servers and/or routers would have
331 to be compromised in addition to just the key).
332 no-agent-forwarding
334 Forbids authentication agent forwarding when this key is used for
335 authentication.
336 no-port-forwarding
338 Forbids TCP forwarding when this key is used for authentication.
339 Any port forward requests by the client will return an error.
340 This might be used, e.g. in connection with the command option.
341 no-pty Prevents tty allocation (a request to allocate a pty will fail).
343 no-user-rc
345 Disables execution of ~/.ssh/rc.
346 no-X11-forwarding
348 Forbids X11 forwarding when this key is used for authentication.
349 Any X11 forward requests by the client will return an error.
350 permitlisten="[host:]port"
352 Limit remote port forwarding with the ssh(1) -R option such that
353 it may only listen on the specified host (optional) and port.
354 IPv6 addresses can be specified by enclosing the address in
355 square brackets. Multiple permitlisten options may be applied
356 separated by commas. Hostnames may include wildcards as de‐
357 scribed in the PATTERNS section in ssh_config(5). A port speci‐
358 fication of * matches any port. Note that the setting of
359 GatewayPorts may further restrict listen addresses. Note that
360 ssh(1) will send a hostname of “localhost” if a listen host was
361 not specified when the forwarding was requested, and that this
362 name is treated differently to the explicit localhost addresses
363 “127.0.0.1” and “::1”.
364 permitopen="host:port"
366 Limit local port forwarding with the ssh(1) -L option such that
367 it may only connect to the specified host and port. IPv6 ad‐
368 dresses can be specified by enclosing the address in square
369 brackets. Multiple permitopen options may be applied separated
370 by commas. No pattern matching or name lookup is performed on
371 the specified hostnames, they must be literal host names and/or
372 addresses. A port specification of * matches any port.
373 port-forwarding
375 Enable port forwarding previously disabled by the restrict op‐
376 tion.
377 principals="principals"
379 On a cert-authority line, specifies allowed principals for cer‐
380 tificate authentication as a comma-separated list. At least one
381 name from the list must appear in the certificate's list of prin‐
382 cipals for the certificate to be accepted. This option is ig‐
383 nored for keys that are not marked as trusted certificate signers
384 using the cert-authority option.
385 pty Permits tty allocation previously disabled by the restrict op‐
387 tion.
388 no-touch-required
390 Do not require demonstration of user presence for signatures made
391 using this key. This option only makes sense for the FIDO au‐
392 thenticator algorithms ecdsa-sk and ed25519-sk.
393 verify-required
395 Require that signatures made using this key attest that they ver‐
396 ified the user, e.g. via a PIN. This option only makes sense for
397 the FIDO authenticator algorithms ecdsa-sk and ed25519-sk.
398 restrict
400 Enable all restrictions, i.e. disable port, agent and X11 for‐
401 warding, as well as disabling PTY allocation and execution of
402 ~/.ssh/rc. If any future restriction capabilities are added to
403 authorized_keys files, they will be included in this set.
404 tunnel="n"
406 Force a tun(4) device on the server. Without this option, the
407 next available device will be used if the client requests a tun‐
408 nel.
409 user-rc
411 Enables execution of ~/.ssh/rc previously disabled by the
412 restrict option.
413 X11-forwarding
415 Permits X11 forwarding previously disabled by the restrict op‐
416 tion.
417 An example authorized_keys file:
419 # Comments are allowed at start of line. Blank lines are allowed.
421 # Plain key, no restrictions
422 ssh-rsa ...
423 # Forced command, disable PTY and all forwarding
424 restrict,command="dump /home" ssh-rsa ...
425 # Restriction of ssh -L forwarding destinations
426 permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-rsa ...
427 # Restriction of ssh -R forwarding listeners
428 permitlisten="localhost:8080",permitlisten="[::1]:22000" ssh-rsa ...
429 # Configuration for tunnel forwarding
430 tunnel="0",command="sh /etc/netstart tun0" ssh-rsa ...
431 # Override of restriction to allow PTY allocation
432 restrict,pty,command="nethack" ssh-rsa ...
433 # Allow FIDO key without requiring touch
434 no-touch-required sk-ecdsa-sha2-nistp256@openssh.com ...
435 # Require user-verification (e.g. PIN or biometric) for FIDO key
436 verify-required sk-ecdsa-sha2-nistp256@openssh.com ...
437 # Trust CA key, allow touch-less FIDO if requested in certificate
438 cert-authority,no-touch-required,principals="user_a" ssh-rsa ...
439
441 The /etc/ssh/ssh_known_hosts and ~/.ssh/known_hosts files contain host
442 public keys for all known hosts. The global file should be prepared by
443 the administrator (optional), and the per-user file is maintained auto‐
444 matically: whenever the user connects to an unknown host, its key is
445 added to the per-user file.
446 Each line in these files contains the following fields: marker (op‐
448 tional), hostnames, keytype, base64-encoded key, comment. The fields are
449 separated by spaces.
450 The marker is optional, but if it is present then it must be one of
452 “@cert-authority”, to indicate that the line contains a certification au‐
453 thority (CA) key, or “@revoked”, to indicate that the key contained on
454 the line is revoked and must not ever be accepted. Only one marker
455 should be used on a key line.
456 Hostnames is a comma-separated list of patterns (‘*’ and ‘?’ act as wild‐
458 cards); each pattern in turn is matched against the host name. When sshd
459 is authenticating a client, such as when using HostbasedAuthentication,
460 this will be the canonical client host name. When ssh(1) is authenticat‐
461 ing a server, this will be the host name given by the user, the value of
462 the ssh(1) HostkeyAlias if it was specified, or the canonical server
463 hostname if the ssh(1) CanonicalizeHostname option was used.
464 A pattern may also be preceded by ‘!’ to indicate negation: if the host
466 name matches a negated pattern, it is not accepted (by that line) even if
467 it matched another pattern on the line. A hostname or address may op‐
468 tionally be enclosed within ‘[’ and ‘]’ brackets then followed by ‘:’ and
469 a non-standard port number.
470 Alternately, hostnames may be stored in a hashed form which hides host
472 names and addresses should the file's contents be disclosed. Hashed
473 hostnames start with a ‘|’ character. Only one hashed hostname may ap‐
474 pear on a single line and none of the above negation or wildcard opera‐
475 tors may be applied.
476 The keytype and base64-encoded key are taken directly from the host key;
478 they can be obtained, for example, from /etc/ssh/ssh_host_rsa_key.pub.
479 The optional comment field continues to the end of the line, and is not
480 used.
481 Lines starting with ‘#’ and empty lines are ignored as comments.
483 When performing host authentication, authentication is accepted if any
485 matching line has the proper key; either one that matches exactly or, if
486 the server has presented a certificate for authentication, the key of the
487 certification authority that signed the certificate. For a key to be
488 trusted as a certification authority, it must use the “@cert-authority”
489 marker described above.
490 The known hosts file also provides a facility to mark keys as revoked,
492 for example when it is known that the associated private key has been
493 stolen. Revoked keys are specified by including the “@revoked” marker at
494 the beginning of the key line, and are never accepted for authentication
495 or as certification authorities, but instead will produce a warning from
496 ssh(1) when they are encountered.
497 It is permissible (but not recommended) to have several lines or differ‐
499 ent host keys for the same names. This will inevitably happen when short
500 forms of host names from different domains are put in the file. It is
501 possible that the files contain conflicting information; authentication
502 is accepted if valid information can be found from either file.
503 Note that the lines in these files are typically hundreds of characters
505 long, and you definitely don't want to type in the host keys by hand.
506 Rather, generate them by a script, ssh-keyscan(1) or by taking, for exam‐
507 ple, /etc/ssh/ssh_host_rsa_key.pub and adding the host names at the
508 front. ssh-keygen(1) also offers some basic automated editing for
509 ~/.ssh/known_hosts including removing hosts matching a host name and con‐
510 verting all host names to their hashed representations.
511 An example ssh_known_hosts file:
513 # Comments allowed at start of line
515 closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net
516 cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....=
517 # A hashed hostname
518 |1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa
519 AAAA1234.....=
520 # A revoked key
521 @revoked * ssh-rsa AAAAB5W...
522 # A CA key, accepted for any host in *.mydomain.com or *.mydomain.org
523 @cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W...
524
526 ~/.hushlogin
527 This file is used to suppress printing the last login time and
528 /etc/motd, if PrintLastLog and PrintMotd, respectively, are en‐
529 abled. It does not suppress printing of the banner specified by
530 Banner.
531 ~/.rhosts
533 This file is used for host-based authentication (see ssh(1) for
534 more information). On some machines this file may need to be
535 world-readable if the user's home directory is on an NFS parti‐
536 tion, because sshd reads it as root. Additionally, this file
537 must be owned by the user, and must not have write permissions
538 for anyone else. The recommended permission for most machines is
539 read/write for the user, and not accessible by others.
540 ~/.shosts
542 This file is used in exactly the same way as .rhosts, but allows
543 host-based authentication without permitting login with
544 rlogin/rsh.
545 ~/.k5login
547 ~/.k5users
548 These files enforce GSSAPI/Kerberos authentication access con‐
549 trol. Further details are described in ksu(1). The location of
550 the k5login file depends on the configuration option
551 k5login_directory in the krb5.conf(5).
552 ~/.ssh/
554 This directory is the default location for all user-specific con‐
555 figuration and authentication information. There is no general
556 requirement to keep the entire contents of this directory secret,
557 but the recommended permissions are read/write/execute for the
558 user, and not accessible by others.
559 ~/.ssh/authorized_keys
561 Lists the public keys (DSA, ECDSA, Ed25519, RSA) that can be used
562 for logging in as this user. The format of this file is de‐
563 scribed above. The content of the file is not highly sensitive,
564 but the recommended permissions are read/write for the user, and
565 not accessible by others.
566 If this file, the ~/.ssh directory, or the user's home directory
568 are writable by other users, then the file could be modified or
569 replaced by unauthorized users. In this case, sshd will not al‐
570 low it to be used unless the StrictModes option has been set to
571 “no”.
572 ~/.ssh/environment
574 This file is read into the environment at login (if it exists).
575 It can only contain empty lines, comment lines (that start with
576 ‘#’), and assignment lines of the form name=value. The file
577 should be writable only by the user; it need not be readable by
578 anyone else. Environment processing is disabled by default and
579 is controlled via the PermitUserEnvironment option.
580 ~/.ssh/known_hosts
582 Contains a list of host keys for all hosts the user has logged
583 into that are not already in the systemwide list of known host
584 keys. The format of this file is described above. This file
585 should be writable only by root/the owner and can, but need not
586 be, world-readable.
587 ~/.ssh/rc
589 Contains initialization routines to be run before the user's home
590 directory becomes accessible. This file should be writable only
591 by the user, and need not be readable by anyone else.
592 /etc/hosts.equiv
594 This file is for host-based authentication (see ssh(1)). It
595 should only be writable by root.
596 /etc/ssh/moduli
598 Contains Diffie-Hellman groups used for the "Diffie-Hellman Group
599 Exchange" key exchange method. The file format is described in
600 moduli(5). If no usable groups are found in this file then fixed
601 internal groups will be used.
602 /etc/motd
604 See motd(5).
605 /etc/nologin
607 If this file exists, sshd refuses to let anyone except root log
608 in. The contents of the file are displayed to anyone trying to
609 log in, and non-root connections are refused. The file should be
610 world-readable.
611 /etc/ssh/shosts.equiv
613 This file is used in exactly the same way as hosts.equiv, but al‐
614 lows host-based authentication without permitting login with
615 rlogin/rsh.
616 /etc/ssh/ssh_host_ecdsa_key
618 /etc/ssh/ssh_host_ed25519_key
619 /etc/ssh/ssh_host_rsa_key
620 These files contain the private parts of the host keys. These
621 files should only be owned by root, readable only by root, and
622 not accessible to others. Note that sshd does not start if these
623 files are group/world-accessible.
624 /etc/ssh/ssh_host_ecdsa_key.pub
626 /etc/ssh/ssh_host_ed25519_key.pub
627 /etc/ssh/ssh_host_rsa_key.pub
628 These files contain the public parts of the host keys. These
629 files should be world-readable but writable only by root. Their
630 contents should match the respective private parts. These files
631 are not really used for anything; they are provided for the con‐
632 venience of the user so their contents can be copied to known
633 hosts files. These files are created using ssh-keygen(1).
634 /etc/ssh/ssh_known_hosts
636 Systemwide list of known host keys. This file should be prepared
637 by the system administrator to contain the public host keys of
638 all machines in the organization. The format of this file is de‐
639 scribed above. This file should be writable only by root/the
640 owner and should be world-readable.
641 /etc/ssh/sshd_config
643 Contains configuration data for sshd. The file format and con‐
644 figuration options are described in sshd_config(5).
645 /etc/ssh/sshrc
647 Similar to ~/.ssh/rc, it can be used to specify machine-specific
648 login-time initializations globally. This file should be
649 writable only by root, and should be world-readable.
650 /usr/share/empty.sshd
652 chroot(2) directory used by sshd during privilege separation in
653 the pre-authentication phase. The directory should not contain
654 any files and must be owned by root and not group or world-
655 writable.
656 /var/run/sshd.pid
658 Contains the process ID of the sshd listening for connections (if
659 there are several daemons running concurrently for different
660 ports, this contains the process ID of the one started last).
661 The content of this file is not sensitive; it can be world-read‐
662 able.
663
665 IPv6 address can be used everywhere where IPv4 address. In all entries
666 must be the IPv6 address enclosed in square brackets. Note: The square
667 brackets are metacharacters for the shell and must be escaped in shell.
668
670 scp(1), sftp(1), ssh(1), ssh-add(1), ssh-agent(1), ssh-keygen(1),
671 ssh-keyscan(1), chroot(2), login.conf(5), moduli(5), sshd_config(5),
672 inetd(8), sftp-server(8)
673
675 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
676 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
677 de Raadt and Dug Song removed many bugs, re-added newer features and cre‐
678 ated OpenSSH. Markus Friedl contributed the support for SSH protocol
679 versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support
680 for privilege separation.
681BSD March 31, 2022 BSD