1SSHD(8) BSD System Manager's Manual SSHD(8)
2
4 sshd — OpenSSH SSH daemon
5
7 sshd [-46DdeiqTt] [-b bits] [-C connection_spec]
8 [-c host_certificate_file] [-f config_file] [-g login_grace_time]
9 [-h host_key_file] [-k key_gen_time] [-o option] [-p port] [-u len]
10
12 sshd (OpenSSH Daemon) is the daemon program for ssh(1). Together these
13 programs replace rlogin(1) and rsh(1), and provide secure encrypted com‐
14 munications between two untrusted hosts over an insecure 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 -b bits
34 Specifies the number of bits in the ephemeral protocol version 1
35 server key (default 1024).
36 -C connection_spec
38 Specify the connection parameters to use for the -T extended test
39 mode. If provided, any Match directives in the configuration
40 file that would apply to the specified user, host, and address
41 will be set before the configuration is written to standard out‐
42 put. The connection parameters are supplied as keyword=value
43 pairs. The keywords are “user”, “host”, and “addr”. All are
44 required and may be supplied in any order, either with multiple
45 -C options or as a comma-separated list.
46 -c host_certificate_file
48 Specifies a path to a certificate file to identify sshd during
49 key exchange. The certificate file must match a host key file
50 specified using the -h option or the HostKey configuration direc‐
51 tive.
52 -D When this option is specified, sshd will not detach and does not
54 become a daemon. This allows easy monitoring of sshd.
55 -d Debug mode. The server sends verbose debug output to standard
57 error, and does not put itself in the background. The server
58 also will not fork and will only process one connection. This
59 option is only intended for debugging for the server. Multiple
60 -d options increase the debugging level. Maximum is 3.
61 -e When this option is specified, sshd will send the output to the
63 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
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 -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_key for protocol version 1, and
81 /etc/ssh/ssh_host_rsa_key and /etc/ssh/ssh_host_dsa_key for pro‐
82 tocol version 2. It is possible to have multiple host key files
83 for the different protocol versions and host key algorithms.
84 -i Specifies that sshd is being run from inetd(8). sshd is normally
86 not run from inetd because it needs to generate the server key
87 before it can respond to the client, and this may take tens of
88 seconds. Clients would have to wait too long if the key was
89 regenerated every time. However, with small key sizes (e.g. 512)
90 using sshd from inetd may be feasible.
91 -k key_gen_time
93 Specifies how often the ephemeral protocol version 1 server key
94 is regenerated (default 3600 seconds, or one hour). The motiva‐
95 tion for regenerating the key fairly often is that the key is not
96 stored anywhere, and after about an hour it becomes impossible to
97 recover the key for decrypting intercepted communications even if
98 the machine is cracked into or physically seized. A value of
99 zero indicates that the key will never be regenerated.
100 -o option
102 Can be used to give options in the format used in the configura‐
103 tion file. This is useful for specifying options for which there
104 is no separate command-line flag. For full details of the
105 options, and their values, see sshd_config(5).
106 -p port
108 Specifies the port on which the server listens for connections
109 (default 22). Multiple port options are permitted. Ports speci‐
110 fied in the configuration file with the Port option are ignored
111 when a command-line port is specified. Ports specified using the
112 ListenAddress option override command-line ports.
113 -q Quiet mode. Nothing is sent to the system log. Normally the
115 beginning, authentication, and termination of each connection is
116 logged.
117 -T Extended test mode. Check the validity of the configuration
119 file, output the effective configuration to stdout and then exit.
120 Optionally, Match rules may be applied by specifying the connec‐
121 tion parameters using one or more -C options.
122 -t Test mode. Only check the validity of the configuration file and
124 sanity of the keys. This is useful for updating sshd reliably as
125 configuration options may change.
126 -u len This option is used to specify the size of the field in the utmp
128 structure that holds the remote host name. If the resolved host
129 name is longer than len, the dotted decimal value will be used
130 instead. This allows hosts with very long host names that over‐
131 flow this field to still be uniquely identified. Specifying -u0
132 indicates that only dotted decimal addresses should be put into
133 the utmp file. -u0 may also be used to prevent sshd from making
134 DNS requests unless the authentication mechanism or configuration
135 requires it. Authentication mechanisms that may require DNS
136 include RhostsRSAAuthentication, HostbasedAuthentication, and
137 using a from="pattern-list" option in a key file. Configuration
138 options that require DNS include using a USER@HOST pattern in
139 AllowUsers or DenyUsers.
140
142 The OpenSSH SSH daemon supports SSH protocols 1 and 2. The default is to
143 use protocol 2 only, though this can be changed via the Protocol option
144 in sshd_config(5). Protocol 2 supports both RSA and DSA keys; protocol 1
145 only supports RSA keys. For both protocols, each host has a host-spe‐
146 cific key, normally 2048 bits, used to identify the host.
147 Forward security for protocol 1 is provided through an additional server
149 key, normally 768 bits, generated when the server starts. This key is
150 normally regenerated every hour if it has been used, and is never stored
151 on disk. Whenever a client connects, the daemon responds with its public
152 host and server keys. The client compares the RSA host key against its
153 own database to verify that it has not changed. The client then gener‐
154 ates a 256-bit random number. It encrypts this random number using both
155 the host key and the server key, and sends the encrypted number to the
156 server. Both sides then use this random number as a session key which is
157 used to encrypt all further communications in the session. The rest of
158 the session is encrypted using a conventional cipher, currently Blowfish
159 or 3DES, with 3DES being used by default. The client selects the encryp‐
160 tion algorithm to use from those offered by the server.
161 For protocol 2, forward security is provided through a Diffie-Hellman key
163 agreement. This key agreement results in a shared session key. The rest
164 of the session is encrypted using a symmetric cipher, currently 128-bit
165 AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES. The
166 client selects the encryption algorithm to use from those offered by the
167 server. Additionally, session integrity is provided through a crypto‐
168 graphic message authentication code (hmac-md5, hmac-sha1, umac-64 or
169 hmac-ripemd160).
170 Finally, the server and the client enter an authentication dialog. The
172 client tries to authenticate itself using host-based authentication, pub‐
173 lic key authentication, challenge-response authentication, or password
174 authentication.
175 Regardless of the authentication type, the account is checked to ensure
177 that it is accessible. An account is not accessible if it is locked,
178 listed in DenyUsers or its group is listed in DenyGroups . The defini‐
179 tion of a locked account is system dependant. Some platforms have their
180 own account database (eg AIX) and some modify the passwd field ( ‘*LK*’
181 on Solaris and UnixWare, ‘*’ on HP-UX, containing ‘Nologin’ on Tru64, a
182 leading ‘*LOCKED*’ on FreeBSD and a leading ‘!’ on most Linuxes). If
183 there is a requirement to disable password authentication for the account
184 while allowing still public-key, then the passwd field should be set to
185 something other than these values (eg ‘NP’ or ‘*NP*’ ).
186 If the client successfully authenticates itself, a dialog for preparing
188 the session is entered. At this time the client may request things like
189 allocating a pseudo-tty, forwarding X11 connections, forwarding TCP con‐
190 nections, or forwarding the authentication agent connection over the
191 secure channel.
192 After this, the client either requests a shell or execution of a command.
194 The sides then enter session mode. In this mode, either side may send
195 data at any time, and such data is forwarded to/from the shell or command
196 on the server side, and the user terminal in the client side.
197 When the user program terminates and all forwarded X11 and other connec‐
199 tions have been closed, the server sends command exit status to the
200 client, and both sides exit.
201
203 When a user successfully logs in, sshd does the following:
204 1. If the login is on a tty, and no command has been specified,
206 prints last login time and /etc/motd (unless prevented in the
207 configuration file or by ~/.hushlogin; see the FILES section).
208 2. If the login is on a tty, records login time.
210 3. Checks /etc/nologin; if it exists, prints contents and quits
212 (unless root).
213 4. Changes to run with normal user privileges.
215 5. Sets up basic environment.
217 6. Reads the file ~/.ssh/environment, if it exists, and users are
219 allowed to change their environment. See the
220 PermitUserEnvironment option in sshd_config(5).
221 7. Changes to user's home directory.
223 8. If ~/.ssh/rc exists, runs it; else if /etc/ssh/sshrc exists,
225 runs it; otherwise runs xauth. The “rc” files are given the
226 X11 authentication protocol and cookie in standard input. See
227 SSHRC, below.
228 9. Runs user's shell or command.
230
232 If the file ~/.ssh/rc exists, sh(1) runs it after reading the environment
233 files but before starting the user's shell or command. It must not pro‐
234 duce any output on stdout; stderr must be used instead. If X11 forward‐
235 ing is in use, it will receive the "proto cookie" pair in its standard
236 input (and DISPLAY in its environment). The script must call xauth(1)
237 because sshd will not run xauth automatically to add X11 cookies.
238 The primary purpose of this file is to run any initialization routines
240 which may be needed before the user's home directory becomes accessible;
241 AFS is a particular example of such an environment.
242 This file will probably contain some initialization code followed by
244 something similar to:
245 if read proto cookie && [ -n "$DISPLAY" ]; then
247 if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then
248 # X11UseLocalhost=yes
249 echo add unix:`echo $DISPLAY |
250 cut -c11-` $proto $cookie
251 else
252 # X11UseLocalhost=no
253 echo add $DISPLAY $proto $cookie
254 fi | xauth -q -
255 fi
256 If this file does not exist, /etc/ssh/sshrc is run, and if that does not
258 exist either, xauth is used to add the cookie.
259
261 AuthorizedKeysFile specifies the file containing public keys for public
262 key authentication; if none is specified, the default is
263 ~/.ssh/authorized_keys. Each line of the file contains one key (empty
264 lines and lines starting with a ‘#’ are ignored as comments). Protocol 1
265 public keys consist of the following space-separated fields: options,
266 bits, exponent, modulus, comment. Protocol 2 public key consist of:
267 options, keytype, base64-encoded key, comment. The options field is
268 optional; its presence is determined by whether the line starts with a
269 number or not (the options field never starts with a number). The bits,
270 exponent, modulus, and comment fields give the RSA key for protocol ver‐
271 sion 1; the comment field is not used for anything (but may be convenient
272 for the user to identify the key). For protocol version 2 the keytype is
273 “ssh-dss” or “ssh-rsa”.
274 Note that lines in this file are usually several hundred bytes long
276 (because of the size of the public key encoding) up to a limit of 8 kilo‐
277 bytes, which permits DSA keys up to 8 kilobits and RSA keys up to 16
278 kilobits. You don't want to type them in; instead, copy the
279 identity.pub, id_dsa.pub, or the id_rsa.pub file and edit it.
280 sshd enforces a minimum RSA key modulus size for protocol 1 and protocol
282 2 keys of 768 bits.
283 The options (if present) consist of comma-separated option specifica‐
285 tions. No spaces are permitted, except within double quotes. The fol‐
286 lowing option specifications are supported (note that option keywords are
287 case-insensitive):
288 cert-authority
290 Specifies that the listed key is a certification authority (CA)
291 that is trusted to validate signed certificates for user authen‐
292 tication.
293 Certificates may encode access restrictions similar to these key
295 options. If both certificate restrictions and key options are
296 present, the most restrictive union of the two is applied.
297 command="command"
299 Specifies that the command is executed whenever this key is used
300 for authentication. The command supplied by the user (if any) is
301 ignored. The command is run on a pty if the client requests a
302 pty; otherwise it is run without a tty. If an 8-bit clean chan‐
303 nel is required, one must not request a pty or should specify
304 no-pty. A quote may be included in the command by quoting it
305 with a backslash. This option might be useful to restrict cer‐
306 tain public keys to perform just a specific operation. An exam‐
307 ple might be a key that permits remote backups but nothing else.
308 Note that the client may specify TCP and/or X11 forwarding unless
309 they are explicitly prohibited. The command originally supplied
310 by the client is available in the SSH_ORIGINAL_COMMAND environ‐
311 ment variable. Note that this option applies to shell, command
312 or subsystem execution. Also note that this command may be
313 superseded by either a sshd_config(5) ForceCommand directive or a
314 command embedded in a certificate.
315 environment="NAME=value"
317 Specifies that the string is to be added to the environment when
318 logging in using this key. Environment variables set this way
319 override other default environment values. Multiple options of
320 this type are permitted. Environment processing is disabled by
321 default and is controlled via the PermitUserEnvironment option.
322 This option is automatically disabled if UseLogin is enabled.
323 from="pattern-list"
325 Specifies that in addition to public key authentication, either
326 the canonical name of the remote host or its IP address must be
327 present in the comma-separated list of patterns. See PATTERNS in
328 ssh_config(5) for more information on patterns.
329 In addition to the wildcard matching that may be applied to host‐
331 names or addresses, a from stanza may match IP addresses using
332 CIDR address/masklen notation.
333 The purpose of this option is to optionally increase security:
335 public key authentication by itself does not trust the network or
336 name servers or anything (but the key); however, if somebody
337 somehow steals the key, the key permits an intruder to log in
338 from anywhere in the world. This additional option makes using a
339 stolen key more difficult (name servers and/or routers would have
340 to be compromised in addition to just the key).
341 no-agent-forwarding
343 Forbids authentication agent forwarding when this key is used for
344 authentication.
345 no-port-forwarding
347 Forbids TCP forwarding when this key is used for authentication.
348 Any port forward requests by the client will return an error.
349 This might be used, e.g. in connection with the command option.
350 no-pty Prevents tty allocation (a request to allocate a pty will fail).
352 no-user-rc
354 Disables execution of ~/.ssh/rc.
355 no-X11-forwarding
357 Forbids X11 forwarding when this key is used for authentication.
358 Any X11 forward requests by the client will return an error.
359 permitopen="host:port"
361 Limit local ``ssh -L'' port forwarding such that it may only con‐
362 nect to the specified host and port. IPv6 addresses can be spec‐
363 ified with an alternative syntax: host/port. Multiple permitopen
364 options may be applied separated by commas. No pattern matching
365 is performed on the specified hostnames, they must be literal
366 domains or addresses.
367 tunnel="n"
369 Force a tun(4) device on the server. Without this option, the
370 next available device will be used if the client requests a tun‐
371 nel.
372 An example authorized_keys file:
374 # Comments allowed at start of line
376 ssh-rsa AAAAB3Nza...LiPk== user@example.net
377 from="*.sales.example.net,!pc.sales.example.net" ssh-rsa
378 AAAAB2...19Q== john@example.net
379 command="dump /home",no-pty,no-port-forwarding ssh-dss
380 AAAAC3...51R== example.net
381 permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-dss
382 AAAAB5...21S==
383 tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...==
384 jane@example.net
385
387 The /etc/ssh/ssh_known_hosts and ~/.ssh/known_hosts files contain host
388 public keys for all known hosts. The global file should be prepared by
389 the administrator (optional), and the per-user file is maintained auto‐
390 matically: whenever the user connects from an unknown host, its key is
391 added to the per-user file.
392 Each line in these files contains the following fields: markers
394 (optional), hostnames, bits, exponent, modulus, comment. The fields are
395 separated by spaces.
396 The marker is optional, but if it is present then it must be one of
398 “@cert-authority”, to indicate that the line contains a certification
399 authority (CA) key, or “@revoked”, to indicate that the key contained on
400 the line is revoked and must not ever be accepted. Only one marker
401 should be used on a key line.
402 Hostnames is a comma-separated list of patterns (‘*’ and ‘?’ act as wild‐
404 cards); each pattern in turn is matched against the canonical host name
405 (when authenticating a client) or against the user-supplied name (when
406 authenticating a server). A pattern may also be preceded by ‘!’ to indi‐
407 cate negation: if the host name matches a negated pattern, it is not
408 accepted (by that line) even if it matched another pattern on the line.
409 A hostname or address may optionally be enclosed within ‘[’ and ‘]’
410 brackets then followed by ‘:’ and a non-standard port number.
411 Alternately, hostnames may be stored in a hashed form which hides host
413 names and addresses should the file's contents be disclosed. Hashed
414 hostnames start with a ‘|’ character. Only one hashed hostname may
415 appear on a single line and none of the above negation or wildcard opera‐
416 tors may be applied.
417 Bits, exponent, and modulus are taken directly from the RSA host key;
419 they can be obtained, for example, from /etc/ssh/ssh_host_key.pub. The
420 optional comment field continues to the end of the line, and is not used.
421 Lines starting with ‘#’ and empty lines are ignored as comments.
423 When performing host authentication, authentication is accepted if any
425 matching line has the proper key; either one that matches exactly or, if
426 the server has presented a certificate for authentication, the key of the
427 certification authority that signed the certificate. For a key to be
428 trusted as a certification authority, it must use the “@cert-authority”
429 marker described above.
430 The known hosts file also provides a facility to mark keys as revoked,
432 for example when it is known that the associated private key has been
433 stolen. Revoked keys are specified by including the “@revoked” marker at
434 the beginning of the key line, and are never accepted for authentication
435 or as certification authorities, but instead will produce a warning from
436 ssh(1) when they are encountered.
437 It is permissible (but not recommended) to have several lines or differ‐
439 ent host keys for the same names. This will inevitably happen when short
440 forms of host names from different domains are put in the file. It is
441 possible that the files contain conflicting information; authentication
442 is accepted if valid information can be found from either file.
443 Note that the lines in these files are typically hundreds of characters
445 long, and you definitely don't want to type in the host keys by hand.
446 Rather, generate them by a script, ssh-keyscan(1) or by taking
447 /etc/ssh/ssh_host_key.pub and adding the host names at the front.
448 ssh-keygen(1) also offers some basic automated editing for
449 ~/.ssh/known_hosts including removing hosts matching a host name and con‐
450 verting all host names to their hashed representations.
451 An example ssh_known_hosts file:
453 # Comments allowed at start of line
455 closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net
456 cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....=
457 # A hashed hostname
458 |1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa
459 AAAA1234.....=
460 # A revoked key
461 @revoked * ssh-rsa AAAAB5W...
462 # A CA key, accepted for any host in *.mydomain.com or *.mydomain.org
463 @cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W...
464
466 ~/.hushlogin
467 This file is used to suppress printing the last login time and
468 /etc/motd, if PrintLastLog and PrintMotd, respectively, are
469 enabled. It does not suppress printing of the banner specified
470 by Banner.
471 ~/.rhosts
473 This file is used for host-based authentication (see ssh(1) for
474 more information). On some machines this file may need to be
475 world-readable if the user's home directory is on an NFS parti‐
476 tion, because sshd reads it as root. Additionally, this file
477 must be owned by the user, and must not have write permissions
478 for anyone else. The recommended permission for most machines is
479 read/write for the user, and not accessible by others.
480 ~/.shosts
482 This file is used in exactly the same way as .rhosts, but allows
483 host-based authentication without permitting login with
484 rlogin/rsh.
485 ~/.ssh/
487 This directory is the default location for all user-specific con‐
488 figuration and authentication information. There is no general
489 requirement to keep the entire contents of this directory secret,
490 but the recommended permissions are read/write/execute for the
491 user, and not accessible by others.
492 ~/.ssh/authorized_keys
494 Lists the public keys (RSA/DSA) that can be used for logging in
495 as this user. The format of this file is described above. The
496 content of the file is not highly sensitive, but the recommended
497 permissions are read/write for the user, and not accessible by
498 others.
499 If this file, the ~/.ssh directory, or the user's home directory
501 are writable by other users, then the file could be modified or
502 replaced by unauthorized users. In this case, sshd will not
503 allow it to be used unless the StrictModes option has been set to
504 “no”.
505 ~/.ssh/environment
507 This file is read into the environment at login (if it exists).
508 It can only contain empty lines, comment lines (that start with
509 ‘#’), and assignment lines of the form name=value. The file
510 should be writable only by the user; it need not be readable by
511 anyone else. Environment processing is disabled by default and
512 is controlled via the PermitUserEnvironment option.
513 ~/.ssh/known_hosts
515 Contains a list of host keys for all hosts the user has logged
516 into that are not already in the systemwide list of known host
517 keys. The format of this file is described above. This file
518 should be writable only by root/the owner and can, but need not
519 be, world-readable.
520 ~/.ssh/rc
522 Contains initialization routines to be run before the user's home
523 directory becomes accessible. This file should be writable only
524 by the user, and need not be readable by anyone else.
525 /etc/hosts.allow
527 /etc/hosts.deny
528 Access controls that should be enforced by tcp-wrappers are
529 defined here. Further details are described in hosts_access(5).
530 /etc/hosts.equiv
532 This file is for host-based authentication (see ssh(1)). It
533 should only be writable by root.
534 /etc/ssh/moduli
536 Contains Diffie-Hellman groups used for the "Diffie-Hellman Group
537 Exchange". The file format is described in moduli(5).
538 /etc/motd
540 See motd(5).
541 /etc/nologin
543 If this file exists, sshd refuses to let anyone except root log
544 in. The contents of the file are displayed to anyone trying to
545 log in, and non-root connections are refused. The file should be
546 world-readable.
547 /etc/ssh/shosts.equiv
549 This file is used in exactly the same way as hosts.equiv, but
550 allows host-based authentication without permitting login with
551 rlogin/rsh.
552 /etc/ssh/ssh_host_key
554 /etc/ssh/ssh_host_dsa_key
555 /etc/ssh/ssh_host_rsa_key
556 These three files contain the private parts of the host keys.
557 These files should only be owned by root, readable only by root,
558 and not accessible to others. Note that sshd does not start if
559 these files are group/world-accessible.
560 /etc/ssh/ssh_host_key.pub
562 /etc/ssh/ssh_host_dsa_key.pub
563 /etc/ssh/ssh_host_rsa_key.pub
564 These three files contain the public parts of the host keys.
565 These files should be world-readable but writable only by root.
566 Their contents should match the respective private parts. These
567 files are not really used for anything; they are provided for the
568 convenience of the user so their contents can be copied to known
569 hosts files. These files are created using ssh-keygen(1).
570 /etc/ssh/ssh_known_hosts
572 Systemwide list of known host keys. This file should be prepared
573 by the system administrator to contain the public host keys of
574 all machines in the organization. The format of this file is
575 described above. This file should be writable only by root/the
576 owner and should be world-readable.
577 /etc/ssh/sshd_config
579 Contains configuration data for sshd. The file format and con‐
580 figuration options are described in sshd_config(5).
581 /etc/ssh/sshrc
583 Similar to ~/.ssh/rc, it can be used to specify machine-specific
584 login-time initializations globally. This file should be
585 writable only by root, and should be world-readable.
586 /var/empty/sshd
588 chroot(2) directory used by sshd during privilege separation in
589 the pre-authentication phase. The directory should not contain
590 any files and must be owned by root and not group or world-
591 writable.
592 /var/run/sshd.pid
594 Contains the process ID of the sshd listening for connections (if
595 there are several daemons running concurrently for different
596 ports, this contains the process ID of the one started last).
597 The content of this file is not sensitive; it can be world-read‐
598 able.
599
601 scp(1), sftp(1), ssh(1), ssh-add(1), ssh-agent(1), ssh-keygen(1),
602 ssh-keyscan(1), chroot(2), hosts_access(5), login.conf(5), moduli(5),
603 sshd_config(5), inetd(8), sftp-server(8)
604
606 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
607 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
608 de Raadt and Dug Song removed many bugs, re-added newer features and cre‐
609 ated OpenSSH. Markus Friedl contributed the support for SSH protocol
610 versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support
611 for privilege separation.
612
614 System security is not improved unless rshd, rlogind, and rexecd are dis‐
615 abled (thus completely disabling rlogin and rsh into the machine).
616BSD June 22, 2019 BSD