2 .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
3 .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4 .\" All rights reserved
6 .\" As far as I am concerned, the code I have written for this software
7 .\" can be used freely for any purpose. Any derived versions of this
8 .\" software must be clearly marked as such, and if the derived work is
9 .\" incompatible with the protocol description in the RFC file, it must be
10 .\" called by a name other than "ssh" or "Secure Shell".
12 .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
13 .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
14 .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
16 .\" Redistribution and use in source and binary forms, with or without
17 .\" modification, are permitted provided that the following conditions
19 .\" 1. Redistributions of source code must retain the above copyright
20 .\" notice, this list of conditions and the following disclaimer.
21 .\" 2. Redistributions in binary form must reproduce the above copyright
22 .\" notice, this list of conditions and the following disclaimer in the
23 .\" documentation and/or other materials provided with the distribution.
25 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
26 .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
27 .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
28 .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
29 .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
30 .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
31 .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
32 .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
33 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
34 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
36 .\" $OpenBSD: ssh_config.5,v 1.242 2017/02/27 14:30:33 jmc Exp $
37 .Dd $Mdocdate: February 27 2017 $
42 .Nd OpenSSH SSH client configuration files
45 .Nm /etc/ssh/ssh_config
48 obtains configuration data from the following sources in
51 .Bl -enum -offset indent -compact
55 user's configuration file
58 system-wide configuration file
59 .Pq Pa /etc/ssh/ssh_config
62 For each parameter, the first obtained value
64 The configuration files contain sections separated by
66 specifications, and that section is only applied for hosts that
67 match one of the patterns given in the specification.
68 The matched host name is usually the one given on the command line
70 .Cm CanonicalizeHostname
71 option for exceptions).
73 Since the first obtained value for each parameter is used, more
74 host-specific declarations should be given near the beginning of the
75 file, and general defaults at the end.
77 The file contains keyword-argument pairs, one per line.
80 and empty lines are interpreted as comments.
81 Arguments may optionally be enclosed in double quotes
83 in order to represent arguments containing spaces.
84 Configuration options may be separated by whitespace or
85 optional whitespace and exactly one
87 the latter format is useful to avoid the need to quote whitespace
88 when specifying configuration options using the
97 keywords and their meanings are as follows (note that
98 keywords are case-insensitive and arguments are case-sensitive):
101 Restricts the following declarations (up to the next
105 keyword) to be only for those hosts that match one of the patterns
106 given after the keyword.
107 If more than one pattern is provided, they should be separated by whitespace.
110 as a pattern can be used to provide global
111 defaults for all hosts.
112 The host is usually the
114 argument given on the command line
116 .Cm CanonicalizeHostname
117 keyword for exceptions).
119 A pattern entry may be negated by prefixing it with an exclamation mark
121 If a negated entry is matched, then the
123 entry is ignored, regardless of whether any other patterns on the line
125 Negated matches are therefore useful to provide exceptions for wildcard
130 for more information on patterns.
132 Restricts the following declarations (up to the next
136 keyword) to be used only when the conditions following the
138 keyword are satisfied.
139 Match conditions are specified using one or more criteria
142 which always matches.
143 The available criteria keywords are:
153 criteria must appear alone or immediately after
155 Other criteria may be combined arbitrarily.
161 Criteria may be negated by prepending an exclamation mark
166 keyword matches only when the configuration file is being re-parsed
167 after hostname canonicalization (see the
168 .Cm CanonicalizeHostname
170 This may be useful to specify conditions that work with canonical host
174 keyword executes the specified command under the user's shell.
175 If the command returns a zero exit status then the condition is considered true.
176 Commands containing whitespace characters must be quoted.
179 accept the tokens described in the
183 The other keywords' criteria must be single entries or comma-separated
184 lists and may use the wildcard and negation operators described in the
189 keyword are matched against the target hostname, after any substitution
193 .Cm CanonicalizeHostname
197 keyword matches against the hostname as it was specified on the command-line.
200 keyword matches against the target username on the remote host.
203 keyword matches against the name of the local user running
205 (this keyword may be useful in system-wide
208 .It Cm AddKeysToAgent
209 Specifies whether keys should be automatically added to a running
211 If this option is set to
213 and a key is loaded from a file, the key and its passphrase are added to
214 the agent with the default lifetime, as if by
216 If this option is set to
219 will require confirmation using the
221 program before adding a key (see
224 If this option is set to
226 each use of the key must be confirmed, as if the
228 option was specified to
230 If this option is set to
232 no keys are added to the agent.
241 Specifies which address family to use when connecting.
252 passphrase/password querying will be disabled.
253 This option is useful in scripts and other batch jobs where no user
254 is present to supply the password.
261 Use the specified address on the local machine as the source address of
263 Only useful on systems with more than one address.
264 Note that this option does not work if
265 .Cm UsePrivilegedPort
268 .It Cm CanonicalDomains
270 .Cm CanonicalizeHostname
271 is enabled, this option specifies the list of domain suffixes in which to
272 search for the specified destination host.
273 .It Cm CanonicalizeFallbackLocal
274 Specifies whether to fail with an error when hostname canonicalization fails.
277 will attempt to look up the unqualified hostname using the system resolver's
284 .Cm CanonicalizeHostname
285 is enabled and the target hostname cannot be found in any of the domains
287 .Cm CanonicalDomains .
288 .It Cm CanonicalizeHostname
289 Controls whether explicit hostname canonicalization is performed.
292 is not to perform any name rewriting and let the system resolver handle all
296 then, for connections that do not use a
299 will attempt to canonicalize the hostname specified on the command line
303 .Cm CanonicalizePermittedCNAMEs
306 .Cm CanonicalizeHostname
309 then canonicalization is applied to proxied connections too.
311 If this option is enabled, then the configuration files are processed
312 again using the new target name to pick up any new configuration in matching
317 .It Cm CanonicalizeMaxDots
318 Specifies the maximum number of dot characters in a hostname before
319 canonicalization is disabled.
321 allows a single dot (i.e. hostname.subdomain).
322 .It Cm CanonicalizePermittedCNAMEs
323 Specifies rules to determine whether CNAMEs should be followed when
324 canonicalizing hostnames.
325 The rules consist of one or more arguments of
326 .Ar source_domain_list : Ns Ar target_domain_list ,
328 .Ar source_domain_list
329 is a pattern-list of domains that may follow CNAMEs in canonicalization,
331 .Ar target_domain_list
332 is a pattern-list of domains that they may resolve to.
335 .Qq *.a.example.com:*.b.example.com,*.c.example.com
336 will allow hostnames matching
338 to be canonicalized to names in the
343 .It Cm CertificateFile
344 Specifies a file from which the user's certificate is read.
345 A corresponding private key must be provided separately in order
346 to use this certificate either
360 may use the tilde syntax to refer to a user's home directory
361 or the tokens described in the
365 It is possible to have multiple certificate files specified in
366 configuration files; these certificates will be tried in sequence.
369 directives will add to the list of certificates used for
371 .It Cm ChallengeResponseAuthentication
372 Specifies whether to use challenge-response authentication.
373 The argument to this keyword must be
383 will additionally check the host IP address in the
386 This allows it to detect if a host key changed due to DNS spoofing
387 and will add addresses of destination hosts to
388 .Pa ~/.ssh/known_hosts
389 in the process, regardless of the setting of
390 .Cm StrictHostKeyChecking .
391 If the option is set to
393 the check will not be executed.
395 Specifies the cipher to use for encrypting the session
396 in protocol version 1.
406 is only supported in the
408 client for interoperability with legacy protocol 1 implementations;
409 its use is strongly discouraged due to cryptographic weaknesses.
411 Specifies the ciphers allowed for protocol version 2
412 in order of preference.
413 Multiple ciphers must be comma-separated.
414 If the specified value begins with a
416 character, then the specified ciphers will be appended to the default set
417 instead of replacing them.
418 If the specified value begins with a
420 character, then the specified ciphers (including wildcards) will be removed
421 from the default set instead of replacing them.
423 The supported ciphers are:
424 .Bd -literal -offset indent
432 aes128-gcm@openssh.com
433 aes256-gcm@openssh.com
439 chacha20-poly1305@openssh.com
443 .Bd -literal -offset indent
444 chacha20-poly1305@openssh.com,
445 aes128-ctr,aes192-ctr,aes256-ctr,
446 aes128-gcm@openssh.com,aes256-gcm@openssh.com,
447 aes128-cbc,aes192-cbc,aes256-cbc
450 The list of available ciphers may also be obtained using
452 .It Cm ClearAllForwardings
453 Specifies that all local, remote, and dynamic port forwardings
454 specified in the configuration files or on the command line be
456 This option is primarily useful when used from the
458 command line to clear port forwardings set in
459 configuration files, and is automatically set by
469 Specifies whether to use compression.
475 .It Cm CompressionLevel
476 Specifies the compression level to use if compression is enabled.
477 The argument must be an integer from 1 (fast) to 9 (slow, best).
478 The default level is 6, which is good for most applications.
479 The meaning of the values is the same as in
481 Note that this option applies to protocol version 1 only.
482 .It Cm ConnectionAttempts
483 Specifies the number of tries (one per second) to make before exiting.
484 The argument must be an integer.
485 This may be useful in scripts if the connection sometimes fails.
487 .It Cm ConnectTimeout
488 Specifies the timeout (in seconds) used when connecting to the
489 SSH server, instead of using the default system TCP timeout.
490 This value is used only when the target is down or really unreachable,
491 not when it refuses the connection.
493 Enables the sharing of multiple sessions over a single network connection.
497 will listen for connections on a control socket specified using the
500 Additional sessions can connect to this socket using the same
507 These sessions will try to reuse the master instance's network connection
508 rather than initiating new ones, but will fall back to connecting normally
509 if the control socket does not exist, or is not listening.
515 to listen for control connections, but require confirmation using
521 will continue without connecting to a master instance.
525 forwarding is supported over these multiplexed connections, however the
526 display and agent forwarded will be the one belonging to the master
527 connection i.e. it is not possible to forward multiple displays or agents.
529 Two additional options allow for opportunistic multiplexing: try to use a
530 master connection but fall back to creating a new one if one does not already
536 The latter requires confirmation like the
540 Specify the path to the control socket used for connection sharing as described
543 section above or the string
545 to disable connection sharing.
548 may use the tilde syntax to refer to a user's home directory
549 or the tokens described in the
552 It is recommended that any
554 used for opportunistic connection sharing include
555 at least %h, %p, and %r (or alternatively %C) and be placed in a directory
556 that is not writable by other users.
557 This ensures that shared connections are uniquely identified.
558 .It Cm ControlPersist
559 When used in conjunction with
561 specifies that the master connection should remain open
562 in the background (waiting for future client connections)
563 after the initial client connection has been closed.
566 then the master connection will not be placed into the background,
567 and will close as soon as the initial client connection is closed.
571 then the master connection will remain in the background indefinitely
572 (until killed or closed via a mechanism such as the
574 If set to a time in seconds, or a time in any of the formats documented in
576 then the backgrounded master connection will automatically terminate
577 after it has remained idle (with no client connections) for the
579 .It Cm DynamicForward
580 Specifies that a TCP port on the local machine be forwarded
581 over the secure channel, and the application
582 protocol is then used to determine where to connect to from the
587 .Oo Ar bind_address : Oc Ar port .
589 IPv6 addresses can be specified by enclosing addresses in square brackets.
590 By default, the local port is bound in accordance with the
595 may be used to bind the connection to a specific address.
600 indicates that the listening port be bound for local use only, while an
603 indicates that the port should be available from all interfaces.
605 Currently the SOCKS4 and SOCKS5 protocols are supported, and
607 will act as a SOCKS server.
608 Multiple forwardings may be specified, and
609 additional forwardings can be given on the command line.
610 Only the superuser can forward privileged ports.
611 .It Cm EnableSSHKeysign
612 Setting this option to
614 in the global client configuration file
615 .Pa /etc/ssh/ssh_config
616 enables the use of the helper program
619 .Cm HostbasedAuthentication .
625 This option should be placed in the non-hostspecific section.
628 for more information.
630 Sets the escape character (default:
632 The escape character can also
633 be set on the command line.
634 The argument should be a single character,
636 followed by a letter, or
638 to disable the escape
639 character entirely (making the connection transparent for binary
641 .It Cm ExitOnForwardFailure
644 should terminate the connection if it cannot set up all requested
645 dynamic, tunnel, local, and remote port forwardings, (e.g.\&
646 if either end is unable to bind and listen on a specified port).
648 .Cm ExitOnForwardFailure
649 does not apply to connections made over port forwardings and will not,
652 to exit if TCP connections to the ultimate forwarding destination fail.
658 .It Cm FingerprintHash
659 Specifies the hash algorithm used when displaying key fingerprints.
666 Specifies whether the connection to the authentication agent (if any)
667 will be forwarded to the remote machine.
674 Agent forwarding should be enabled with caution.
675 Users with the ability to bypass file permissions on the remote host
676 (for the agent's Unix-domain socket)
677 can access the local agent through the forwarded connection.
678 An attacker cannot obtain key material from the agent,
679 however they can perform operations on the keys that enable them to
680 authenticate using the identities loaded into the agent.
682 Specifies whether X11 connections will be automatically redirected
683 over the secure channel and
692 X11 forwarding should be enabled with caution.
693 Users with the ability to bypass file permissions on the remote host
694 (for the user's X11 authorization database)
695 can access the local X11 display through the forwarded connection.
696 An attacker may then be able to perform activities such as keystroke monitoring
698 .Cm ForwardX11Trusted
699 option is also enabled.
700 .It Cm ForwardX11Timeout
701 Specify a timeout for untrusted X11 forwarding
702 using the format described in the
706 X11 connections received by
708 after this time will be refused.
709 The default is to disable untrusted X11 forwarding after twenty minutes has
711 .It Cm ForwardX11Trusted
712 If this option is set to
714 remote X11 clients will have full access to the original X11 display.
716 If this option is set to
719 remote X11 clients will be considered untrusted and prevented
720 from stealing or tampering with data belonging to trusted X11
724 token used for the session will be set to expire after 20 minutes.
725 Remote clients will be refused access after this time.
727 See the X11 SECURITY extension specification for full details on
728 the restrictions imposed on untrusted clients.
730 Specifies whether remote hosts are allowed to connect to local
734 binds local port forwardings to the loopback address.
735 This prevents other remote hosts from connecting to forwarded ports.
737 can be used to specify that ssh
738 should bind local port forwardings to the wildcard address,
739 thus allowing remote hosts to connect to forwarded ports.
745 .It Cm GlobalKnownHostsFile
746 Specifies one or more files to use for the global
747 host key database, separated by whitespace.
749 .Pa /etc/ssh/ssh_known_hosts ,
750 .Pa /etc/ssh/ssh_known_hosts2 .
751 .It Cm GSSAPIAuthentication
752 Specifies whether user authentication based on GSSAPI is allowed.
755 .It Cm GSSAPIDelegateCredentials
756 Forward (delegate) credentials to the server.
759 .It Cm HashKnownHosts
762 should hash host names and addresses when they are added to
763 .Pa ~/.ssh/known_hosts .
764 These hashed names may be used normally by
768 but they do not reveal identifying information should the file's contents
772 Note that existing names and addresses in known hosts files
773 will not be converted automatically,
774 but may be manually hashed using
776 .It Cm HostbasedAuthentication
777 Specifies whether to try rhosts based authentication with public key
784 .It Cm HostbasedKeyTypes
785 Specifies the key types that will be used for hostbased authentication
786 as a comma-separated pattern list.
787 Alternately if the specified value begins with a
789 character, then the specified key types will be appended to the default set
790 instead of replacing them.
791 If the specified value begins with a
793 character, then the specified key types (including wildcards) will be removed
794 from the default set instead of replacing them.
795 The default for this option is:
796 .Bd -literal -offset 3n
797 ecdsa-sha2-nistp256-cert-v01@openssh.com,
798 ecdsa-sha2-nistp384-cert-v01@openssh.com,
799 ecdsa-sha2-nistp521-cert-v01@openssh.com,
800 ssh-ed25519-cert-v01@openssh.com,
801 ssh-rsa-cert-v01@openssh.com,
802 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
810 may be used to list supported key types.
811 .It Cm HostKeyAlgorithms
812 Specifies the host key algorithms
813 that the client wants to use in order of preference.
814 Alternately if the specified value begins with a
816 character, then the specified key types will be appended to the default set
817 instead of replacing them.
818 If the specified value begins with a
820 character, then the specified key types (including wildcards) will be removed
821 from the default set instead of replacing them.
822 The default for this option is:
823 .Bd -literal -offset 3n
824 ecdsa-sha2-nistp256-cert-v01@openssh.com,
825 ecdsa-sha2-nistp384-cert-v01@openssh.com,
826 ecdsa-sha2-nistp521-cert-v01@openssh.com,
827 ssh-ed25519-cert-v01@openssh.com,
828 ssh-rsa-cert-v01@openssh.com,
829 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
833 If hostkeys are known for the destination host then this default is modified
834 to prefer their algorithms.
836 The list of available key types may also be obtained using
839 Specifies an alias that should be used instead of the
840 real host name when looking up or saving the host key
841 in the host key database files.
842 This option is useful for tunneling SSH connections
843 or for multiple servers running on a single host.
845 Specifies the real host name to log into.
846 This can be used to specify nicknames or abbreviations for hosts.
849 accept the tokens described in the
852 Numeric IP addresses are also permitted (both on the command line and in
855 The default is the name given on the command line.
856 .It Cm IdentitiesOnly
859 should only use the authentication identity and certificate files explicitly
870 offers more identities.
871 The argument to this keyword must be
876 This option is intended for situations where ssh-agent
877 offers many different identities.
881 socket used to communicate with the authentication agent.
883 This option overrides the
885 environment variable and can be used to select a specific agent.
886 Setting the socket name to
888 disables the use of an authentication agent.
891 is specified, the location of the socket will be read from the
893 environment variable.
897 may use the tilde syntax to refer to a user's home directory
898 or the tokens described in the
902 Specifies a file from which the user's DSA, ECDSA, Ed25519 or RSA authentication
906 for protocol version 1, and
908 .Pa ~/.ssh/id_ecdsa ,
909 .Pa ~/.ssh/id_ed25519
912 for protocol version 2.
913 Additionally, any identities represented by the authentication agent
914 will be used for authentication unless
917 If no certificates have been explicitly specified by
918 .Cm CertificateFile ,
920 will try to load certificate information from the filename obtained by
923 to the path of a specified
928 may use the tilde syntax to refer to a user's home directory
929 or the tokens described in the
933 It is possible to have
934 multiple identity files specified in configuration files; all these
935 identities will be tried in sequence.
938 directives will add to the list of identities tried (this behaviour
939 differs from that of other configuration directives).
942 may be used in conjunction with
944 to select which identities in an agent are offered during authentication.
946 may also be used in conjunction with
948 in order to provide any certificate also needed for authentication with
951 Specifies a pattern-list of unknown options to be ignored if they are
952 encountered in configuration parsing.
953 This may be used to suppress errors if
955 contains options that are unrecognised by
957 It is recommended that
959 be listed early in the configuration file as it will not be applied
960 to unknown options that appear before it.
962 Include the specified configuration file(s).
963 Multiple pathnames may be specified and each pathname may contain
965 wildcards and, for user configurations, shell-like
967 references to user home directories.
968 Files without absolute paths are assumed to be in
970 if included in a user configuration file or
972 if included from the system configuration file.
974 directive may appear inside a
979 to perform conditional inclusion.
981 Specifies the IPv4 type-of-service or DSCP class for connections.
1008 This option may take one or two arguments, separated by whitespace.
1009 If one argument is specified, it is used as the packet class unconditionally.
1010 If two values are specified, the first is automatically selected for
1011 interactive sessions and the second for non-interactive sessions.
1014 for interactive sessions and
1016 for non-interactive sessions.
1017 .It Cm KbdInteractiveAuthentication
1018 Specifies whether to use keyboard-interactive authentication.
1019 The argument to this keyword must be
1024 .It Cm KbdInteractiveDevices
1025 Specifies the list of methods to use in keyboard-interactive authentication.
1026 Multiple method names must be comma-separated.
1027 The default is to use the server specified list.
1028 The methods available vary depending on what the server supports.
1029 For an OpenSSH server,
1030 it may be zero or more of:
1035 .It Cm KexAlgorithms
1036 Specifies the available KEX (Key Exchange) algorithms.
1037 Multiple algorithms must be comma-separated.
1038 Alternately if the specified value begins with a
1040 character, then the specified methods will be appended to the default set
1041 instead of replacing them.
1042 If the specified value begins with a
1044 character, then the specified methods (including wildcards) will be removed
1045 from the default set instead of replacing them.
1047 .Bd -literal -offset indent
1048 curve25519-sha256,curve25519-sha256@libssh.org,
1049 ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
1050 diffie-hellman-group-exchange-sha256,
1051 diffie-hellman-group-exchange-sha1,
1052 diffie-hellman-group14-sha1
1055 The list of available key exchange algorithms may also be obtained using
1058 Specifies a command to execute on the local machine after successfully
1059 connecting to the server.
1060 The command string extends to the end of the line, and is executed with
1064 accept the tokens described in the
1068 The command is run synchronously and does not have access to the
1072 It should not be used for interactive commands.
1074 This directive is ignored unless
1075 .Cm PermitLocalCommand
1078 Specifies that a TCP port on the local machine be forwarded over
1079 the secure channel to the specified host and port from the remote machine.
1080 The first argument must be
1082 .Oo Ar bind_address : Oc Ar port
1084 and the second argument must be
1085 .Ar host : Ns Ar hostport .
1086 IPv6 addresses can be specified by enclosing addresses in square brackets.
1087 Multiple forwardings may be specified, and additional forwardings can be
1088 given on the command line.
1089 Only the superuser can forward privileged ports.
1090 By default, the local port is bound in accordance with the
1093 However, an explicit
1095 may be used to bind the connection to a specific address.
1100 indicates that the listening port be bound for local use only, while an
1103 indicates that the port should be available from all interfaces.
1105 Gives the verbosity level that is used when logging messages from
1107 The possible values are:
1108 QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1109 The default is INFO.
1110 DEBUG and DEBUG1 are equivalent.
1111 DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1113 Specifies the MAC (message authentication code) algorithms
1114 in order of preference.
1115 The MAC algorithm is used for data integrity protection.
1116 Multiple algorithms must be comma-separated.
1117 If the specified value begins with a
1119 character, then the specified algorithms will be appended to the default set
1120 instead of replacing them.
1121 If the specified value begins with a
1123 character, then the specified algorithms (including wildcards) will be removed
1124 from the default set instead of replacing them.
1126 The algorithms that contain
1128 calculate the MAC after encryption (encrypt-then-mac).
1129 These are considered safer and their use recommended.
1132 .Bd -literal -offset indent
1133 umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1134 hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1135 hmac-sha1-etm@openssh.com,
1136 umac-64@openssh.com,umac-128@openssh.com,
1137 hmac-sha2-256,hmac-sha2-512,hmac-sha1
1140 The list of available MAC algorithms may also be obtained using
1142 .It Cm NoHostAuthenticationForLocalhost
1143 This option can be used if the home directory is shared across machines.
1144 In this case localhost will refer to a different machine on each of
1145 the machines and the user will get many warnings about changed host keys.
1146 However, this option disables host authentication for localhost.
1147 The argument to this keyword must be
1152 .It Cm NumberOfPasswordPrompts
1153 Specifies the number of password prompts before giving up.
1154 The argument to this keyword must be an integer.
1156 .It Cm PasswordAuthentication
1157 Specifies whether to use password authentication.
1158 The argument to this keyword must be
1163 .It Cm PermitLocalCommand
1164 Allow local command execution via the
1167 .Ic !\& Ns Ar command
1170 The argument must be
1175 .It Cm PKCS11Provider
1176 Specifies which PKCS#11 provider to use.
1177 The argument to this keyword is the PKCS#11 shared library
1179 should use to communicate with a PKCS#11 token providing the user's
1182 Specifies the port number to connect on the remote host.
1184 .It Cm PreferredAuthentications
1185 Specifies the order in which the client should try authentication methods.
1186 This allows a client to prefer one method (e.g.\&
1187 .Cm keyboard-interactive )
1188 over another method (e.g.\&
1191 .Bd -literal -offset indent
1192 gssapi-with-mic,hostbased,publickey,
1193 keyboard-interactive,password
1196 Specifies the protocol versions
1198 should support in order of preference.
1199 The possible values are 1 and 2.
1200 Multiple versions must be comma-separated.
1201 When this option is set to
1204 will try version 2 and fall back to version 1
1205 if version 2 is not available.
1206 The default is version 2.
1207 Protocol 1 suffers from a number of cryptographic weaknesses and should
1209 It is only offered to support legacy devices.
1211 Specifies the command to use to connect to the server.
1213 string extends to the end of the line, and is executed
1214 using the user's shell
1216 directive to avoid a lingering shell process.
1220 accept the tokens described in the
1223 The command can be basically anything,
1224 and should read from its standard input and write to its standard output.
1225 It should eventually connect an
1227 server running on some machine, or execute
1230 Host key management will be done using the
1231 HostName of the host being connected (defaulting to the name typed by
1233 Setting the command to
1235 disables this option entirely.
1238 is not available for connects with a proxy command.
1240 This directive is useful in conjunction with
1242 and its proxy support.
1243 For example, the following directive would connect via an HTTP proxy at
1245 .Bd -literal -offset 3n
1246 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1249 Specifies one or more jump proxies as
1257 Multiple proxies may be separated by comma characters and will be visited
1259 Setting this option will cause
1261 to connect to the target host by first making a
1263 connection to the specified
1265 host and then establishing a
1266 TCP forwarding to the ultimate target from there.
1268 Note that this option will compete with the
1270 option - whichever is specified first will prevent later instances of the
1271 other from taking effect.
1272 .It Cm ProxyUseFdpass
1275 will pass a connected file descriptor back to
1277 instead of continuing to execute and pass data.
1280 .It Cm PubkeyAcceptedKeyTypes
1281 Specifies the key types that will be used for public key authentication
1282 as a comma-separated pattern list.
1283 Alternately if the specified value begins with a
1285 character, then the key types after it will be appended to the default
1286 instead of replacing it.
1287 If the specified value begins with a
1289 character, then the specified key types (including wildcards) will be removed
1290 from the default set instead of replacing them.
1291 The default for this option is:
1292 .Bd -literal -offset 3n
1293 ecdsa-sha2-nistp256-cert-v01@openssh.com,
1294 ecdsa-sha2-nistp384-cert-v01@openssh.com,
1295 ecdsa-sha2-nistp521-cert-v01@openssh.com,
1296 ssh-ed25519-cert-v01@openssh.com,
1297 ssh-rsa-cert-v01@openssh.com,
1298 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1302 The list of available key types may also be obtained using
1304 .It Cm PubkeyAuthentication
1305 Specifies whether to try public key authentication.
1306 The argument to this keyword must be
1312 Specifies the maximum amount of data that may be transmitted before the
1313 session key is renegotiated, optionally followed a maximum amount of
1314 time that may pass before the session key is renegotiated.
1315 The first argument is specified in bytes and may have a suffix of
1320 to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1321 The default is between
1325 depending on the cipher.
1326 The optional second value is specified in seconds and may use any of the
1327 units documented in the
1331 The default value for
1335 which means that rekeying is performed after the cipher's default amount
1336 of data has been sent or received and no time based rekeying is done.
1337 .It Cm RemoteForward
1338 Specifies that a TCP port on the remote machine be forwarded over
1339 the secure channel to the specified host and port from the local machine.
1340 The first argument must be
1342 .Oo Ar bind_address : Oc Ar port
1344 and the second argument must be
1345 .Ar host : Ns Ar hostport .
1346 IPv6 addresses can be specified by enclosing addresses in square brackets.
1347 Multiple forwardings may be specified, and additional
1348 forwardings can be given on the command line.
1349 Privileged ports can be forwarded only when
1350 logging in as root on the remote machine.
1355 the listen port will be dynamically allocated on the server and reported
1356 to the client at run time.
1360 is not specified, the default is to only bind to loopback addresses.
1365 or an empty string, then the forwarding is requested to listen on all
1369 will only succeed if the server's
1371 option is enabled (see
1372 .Xr sshd_config 5 ) .
1374 Specifies whether to request a pseudo-tty for the session.
1375 The argument may be one of:
1377 (never request a TTY),
1379 (always request a TTY when standard input is a TTY),
1381 (always request a TTY) or
1383 (request a TTY when opening a login session).
1384 This option mirrors the
1390 .It Cm RevokedHostKeys
1391 Specifies revoked host public keys.
1392 Keys listed in this file will be refused for host authentication.
1393 Note that if this file does not exist or is not readable,
1394 then host authentication will be refused for all hosts.
1395 Keys may be specified as a text file, listing one public key per line, or as
1396 an OpenSSH Key Revocation List (KRL) as generated by
1398 For more information on KRLs, see the KEY REVOCATION LISTS section in
1400 .It Cm RhostsRSAAuthentication
1401 Specifies whether to try rhosts based authentication with RSA host
1403 The argument must be
1408 This option applies to protocol version 1 only and requires
1411 .It Cm RSAAuthentication
1412 Specifies whether to try RSA authentication.
1413 The argument to this keyword must be
1418 RSA authentication will only be
1419 attempted if the identity file exists, or an authentication agent is
1421 Note that this option applies to protocol version 1 only.
1423 Specifies what variables from the local
1425 should be sent to the server.
1426 The server must also support it, and the server must be configured to
1427 accept these environment variables.
1430 environment variable is always sent whenever a
1431 pseudo-terminal is requested as it is required by the protocol.
1436 for how to configure the server.
1437 Variables are specified by name, which may contain wildcard characters.
1438 Multiple environment variables may be separated by whitespace or spread
1442 The default is not to send any environment variables.
1446 for more information on patterns.
1447 .It Cm ServerAliveCountMax
1448 Sets the number of server alive messages (see below) which may be
1451 receiving any messages back from the server.
1452 If this threshold is reached while server alive messages are being sent,
1453 ssh will disconnect from the server, terminating the session.
1454 It is important to note that the use of server alive messages is very
1458 The server alive messages are sent through the encrypted channel
1459 and therefore will not be spoofable.
1460 The TCP keepalive option enabled by
1463 The server alive mechanism is valuable when the client or
1464 server depend on knowing when a connection has become inactive.
1466 The default value is 3.
1468 .Cm ServerAliveInterval
1469 (see below) is set to 15 and
1470 .Cm ServerAliveCountMax
1471 is left at the default, if the server becomes unresponsive,
1472 ssh will disconnect after approximately 45 seconds.
1473 .It Cm ServerAliveInterval
1474 Sets a timeout interval in seconds after which if no data has been received
1477 will send a message through the encrypted
1478 channel to request a response from the server.
1480 is 0, indicating that these messages will not be sent to the server.
1481 .It Cm StreamLocalBindMask
1482 Sets the octal file creation mode mask
1484 used when creating a Unix-domain socket file for local or remote
1486 This option is only used for port forwarding to a Unix-domain socket file.
1488 The default value is 0177, which creates a Unix-domain socket file that is
1489 readable and writable only by the owner.
1490 Note that not all operating systems honor the file mode on Unix-domain
1492 .It Cm StreamLocalBindUnlink
1493 Specifies whether to remove an existing Unix-domain socket file for local
1494 or remote port forwarding before creating a new one.
1495 If the socket file already exists and
1496 .Cm StreamLocalBindUnlink
1499 will be unable to forward the port to the Unix-domain socket file.
1500 This option is only used for port forwarding to a Unix-domain socket file.
1502 The argument must be
1507 .It Cm StrictHostKeyChecking
1508 If this flag is set to
1511 will never automatically add host keys to the
1512 .Pa ~/.ssh/known_hosts
1513 file, and refuses to connect to hosts whose host key has changed.
1514 This provides maximum protection against trojan horse attacks,
1515 though it can be annoying when the
1516 .Pa /etc/ssh/ssh_known_hosts
1517 file is poorly maintained or when connections to new hosts are
1519 This option forces the user to manually
1521 If this flag is set to
1523 ssh will automatically add new host keys to the
1524 user known hosts files.
1525 If this flag is set to
1529 will be added to the user known host files only after the user
1530 has confirmed that is what they really want to do, and
1531 ssh will refuse to connect to hosts whose host key has changed.
1533 known hosts will be verified automatically in all cases.
1535 Specifies whether the system should send TCP keepalive messages to the
1537 If they are sent, death of the connection or crash of one
1538 of the machines will be properly noticed.
1539 However, this means that
1540 connections will die if the route is down temporarily, and some people
1545 (to send TCP keepalive messages), and the client will notice
1546 if the network goes down or the remote host dies.
1547 This is important in scripts, and many users want it too.
1549 To disable TCP keepalive messages, the value should be set to
1554 device forwarding between the client and the server.
1555 The argument must be
1566 requests the default tunnel mode, which is
1567 .Cm point-to-point .
1571 devices to open on the client
1576 The argument must be
1578 .Ar local_tun Op : Ar remote_tun .
1580 The devices may be specified by numerical ID or the keyword
1582 which uses the next available tunnel device.
1585 is not specified, it defaults to
1589 .It Cm UpdateHostKeys
1592 should accept notifications of additional hostkeys from the server sent
1593 after authentication has completed and add them to
1594 .Cm UserKnownHostsFile .
1595 The argument must be
1600 Enabling this option allows learning alternate hostkeys for a server
1601 and supports graceful key rotation by allowing a server to send replacement
1602 public keys before old ones are removed.
1603 Additional hostkeys are only accepted if the key used to authenticate the
1604 host was already trusted or explicitly accepted by the user.
1609 then the user is asked to confirm the modifications to the known_hosts file.
1610 Confirmation is currently incompatible with
1611 .Cm ControlPersist ,
1612 and will be disabled if it is enabled.
1616 from OpenSSH 6.8 and greater support the
1617 .Qq hostkeys@openssh.com
1618 protocol extension used to inform the client of all the server's hostkeys.
1619 .It Cm UsePrivilegedPort
1620 Specifies whether to use a privileged port for outgoing connections.
1621 The argument must be
1629 must be setuid root.
1630 Note that this option must be set to
1633 .Cm RhostsRSAAuthentication
1636 Specifies the user to log in as.
1637 This can be useful when a different user name is used on different machines.
1638 This saves the trouble of
1639 having to remember to give the user name on the command line.
1640 .It Cm UserKnownHostsFile
1641 Specifies one or more files to use for the user
1642 host key database, separated by whitespace.
1644 .Pa ~/.ssh/known_hosts ,
1645 .Pa ~/.ssh/known_hosts2 .
1646 .It Cm VerifyHostKeyDNS
1647 Specifies whether to verify the remote key using DNS and SSHFP resource
1649 If this option is set to
1651 the client will implicitly trust keys that match a secure fingerprint
1653 Insecure fingerprints will be handled as if this option was set to
1655 If this option is set to
1657 information on fingerprint match will be displayed, but the user will still
1658 need to confirm new host keys according to the
1659 .Cm StrictHostKeyChecking
1665 .Sx VERIFYING HOST KEYS
1668 .It Cm VisualHostKey
1669 If this flag is set to
1671 an ASCII art representation of the remote host key fingerprint is
1672 printed in addition to the fingerprint string at login and
1673 for unknown host keys.
1674 If this flag is set to
1677 no fingerprint strings are printed at login and
1678 only the fingerprint string will be printed for unknown host keys.
1679 .It Cm XAuthLocation
1680 Specifies the full pathname of the
1684 .Pa /usr/X11R6/bin/xauth .
1689 consists of zero or more non-whitespace characters,
1691 (a wildcard that matches zero or more characters),
1694 (a wildcard that matches exactly one character).
1695 For example, to specify a set of declarations for any host in the
1698 the following pattern could be used:
1702 The following pattern
1703 would match any host in the 192.168.0.[0-9] network range:
1705 .Dl Host 192.168.0.?
1709 is a comma-separated list of patterns.
1710 Patterns within pattern-lists may be negated
1711 by preceding them with an exclamation mark
1714 to allow a key to be used from anywhere within an organization
1718 the following entry (in authorized_keys) could be used:
1720 .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1722 Arguments to some keywords can make use of tokens,
1723 which are expanded at runtime:
1725 .Bl -tag -width XXXX -offset indent -compact
1730 Shorthand for %l%h%p%r.
1732 Local user's home directory.
1734 The remote hostname.
1740 The local hostname, including the domain name.
1742 The original remote hostname, as given on the command line.
1746 The remote username.
1752 accepts the tokens %%, %h, %L, %l, %n, %p, %r, and %u.
1755 accepts the tokens %%, %d, %h, %l, %r, and %u.
1758 accepts the tokens %%, %C, %h, %i, %L, %l, %n, %p, %r, and %u.
1761 accepts the tokens %% and %h.
1766 accept the tokens %%, %d, %h, %l, %r, and %u.
1769 accepts the tokens %%, %C, %d, %h, %l, %n, %p, %r, and %u.
1772 accepts the tokens %%, %h, %p, and %r.
1775 .It Pa ~/.ssh/config
1776 This is the per-user configuration file.
1777 The format of this file is described above.
1778 This file is used by the SSH client.
1779 Because of the potential for abuse, this file must have strict permissions:
1780 read/write for the user, and not accessible by others.
1781 .It Pa /etc/ssh/ssh_config
1782 Systemwide configuration file.
1783 This file provides defaults for those
1784 values that are not specified in the user's configuration file, and
1785 for those users who do not have a configuration file.
1786 This file must be world-readable.
1792 OpenSSH is a derivative of the original and free
1793 ssh 1.2.12 release by
1795 .An Aaron Campbell , Bob Beck , Markus Friedl ,
1796 .An Niels Provos , Theo de Raadt
1799 removed many bugs, re-added newer features and
1802 contributed the support for SSH protocol versions 1.5 and 2.0.
OSDN Git Service
