1 SSH_CONFIG(5) File Formats Manual SSH_CONFIG(5)
4 ssh_config M-bM-^@M-^S OpenSSH SSH client configuration files
11 ssh(1) obtains configuration data from the following sources in the
14 1. command-line options
15 2. user's configuration file (~/.ssh/config)
16 3. system-wide configuration file (/etc/ssh/ssh_config)
18 For each parameter, the first obtained value will be used. The
19 configuration files contain sections separated by Host specifications,
20 and that section is only applied for hosts that match one of the patterns
21 given in the specification. The matched host name is usually the one
22 given on the command line (see the CanonicalizeHostname option for
25 Since the first obtained value for each parameter is used, more host-
26 specific declarations should be given near the beginning of the file, and
27 general defaults at the end.
29 The file contains keyword-argument pairs, one per line. Lines starting
30 with M-bM-^@M-^X#M-bM-^@M-^Y and empty lines are interpreted as comments. Arguments may
31 optionally be enclosed in double quotes (") in order to represent
32 arguments containing spaces. Configuration options may be separated by
33 whitespace or optional whitespace and exactly one M-bM-^@M-^X=M-bM-^@M-^Y; the latter format
34 is useful to avoid the need to quote whitespace when specifying
35 configuration options using the ssh, scp, and sftp -o option.
37 The possible keywords and their meanings are as follows (note that
38 keywords are case-insensitive and arguments are case-sensitive):
40 Host Restricts the following declarations (up to the next Host or
41 Match keyword) to be only for those hosts that match one of the
42 patterns given after the keyword. If more than one pattern is
43 provided, they should be separated by whitespace. A single M-bM-^@M-^X*M-bM-^@M-^Y
44 as a pattern can be used to provide global defaults for all
45 hosts. The host is usually the hostname argument given on the
46 command line (see the CanonicalizeHostname keyword for
49 A pattern entry may be negated by prefixing it with an
50 exclamation mark (M-bM-^@M-^X!M-bM-^@M-^Y). If a negated entry is matched, then the
51 Host entry is ignored, regardless of whether any other patterns
52 on the line match. Negated matches are therefore useful to
53 provide exceptions for wildcard matches.
55 See PATTERNS for more information on patterns.
57 Match Restricts the following declarations (up to the next Host or
58 Match keyword) to be used only when the conditions following the
59 Match keyword are satisfied. Match conditions are specified
60 using one or more criteria or the single token all which always
61 matches. The available criteria keywords are: canonical, exec,
62 host, originalhost, user, and localuser. The all criteria must
63 appear alone or immediately after canonical. Other criteria may
64 be combined arbitrarily. All criteria but all and canonical
65 require an argument. Criteria may be negated by prepending an
66 exclamation mark (M-bM-^@M-^X!M-bM-^@M-^Y).
68 The canonical keyword matches only when the configuration file is
69 being re-parsed after hostname canonicalization (see the
70 CanonicalizeHostname option.) This may be useful to specify
71 conditions that work with canonical host names only. The exec
72 keyword executes the specified command under the user's shell.
73 If the command returns a zero exit status then the condition is
74 considered true. Commands containing whitespace characters must
75 be quoted. Arguments to exec accept the tokens described in the
78 The other keywords' criteria must be single entries or comma-
79 separated lists and may use the wildcard and negation operators
80 described in the PATTERNS section. The criteria for the host
81 keyword are matched against the target hostname, after any
82 substitution by the Hostname or CanonicalizeHostname options.
83 The originalhost keyword matches against the hostname as it was
84 specified on the command-line. The user keyword matches against
85 the target username on the remote host. The localuser keyword
86 matches against the name of the local user running ssh(1) (this
87 keyword may be useful in system-wide ssh_config files).
90 Specifies whether keys should be automatically added to a running
91 ssh-agent(1). If this option is set to yes and a key is loaded
92 from a file, the key and its passphrase are added to the agent
93 with the default lifetime, as if by ssh-add(1). If this option
94 is set to ask, ssh(1) will require confirmation using the
95 SSH_ASKPASS program before adding a key (see ssh-add(1) for
96 details). If this option is set to confirm, each use of the key
97 must be confirmed, as if the -c option was specified to
98 ssh-add(1). If this option is set to no, no keys are added to
99 the agent. The argument must be yes, confirm, ask, or no (the
103 Specifies which address family to use when connecting. Valid
104 arguments are any (the default), inet (use IPv4 only), or inet6
108 If set to yes, passphrase/password querying will be disabled.
109 This option is useful in scripts and other batch jobs where no
110 user is present to supply the password. The argument must be yes
114 Use the specified address on the local machine as the source
115 address of the connection. Only useful on systems with more than
116 one address. Note that this option does not work if
117 UsePrivilegedPort is set to yes.
120 When CanonicalizeHostname is enabled, this option specifies the
121 list of domain suffixes in which to search for the specified
124 CanonicalizeFallbackLocal
125 Specifies whether to fail with an error when hostname
126 canonicalization fails. The default, yes, will attempt to look
127 up the unqualified hostname using the system resolver's search
128 rules. A value of no will cause ssh(1) to fail instantly if
129 CanonicalizeHostname is enabled and the target hostname cannot be
130 found in any of the domains specified by CanonicalDomains.
133 Controls whether explicit hostname canonicalization is performed.
134 The default, no, is not to perform any name rewriting and let the
135 system resolver handle all hostname lookups. If set to yes then,
136 for connections that do not use a ProxyCommand, ssh(1) will
137 attempt to canonicalize the hostname specified on the command
138 line using the CanonicalDomains suffixes and
139 CanonicalizePermittedCNAMEs rules. If CanonicalizeHostname is
140 set to always, then canonicalization is applied to proxied
143 If this option is enabled, then the configuration files are
144 processed again using the new target name to pick up any new
145 configuration in matching Host and Match stanzas.
148 Specifies the maximum number of dot characters in a hostname
149 before canonicalization is disabled. The default, 1, allows a
150 single dot (i.e. hostname.subdomain).
152 CanonicalizePermittedCNAMEs
153 Specifies rules to determine whether CNAMEs should be followed
154 when canonicalizing hostnames. The rules consist of one or more
155 arguments of source_domain_list:target_domain_list, where
156 source_domain_list is a pattern-list of domains that may follow
157 CNAMEs in canonicalization, and target_domain_list is a pattern-
158 list of domains that they may resolve to.
160 For example, "*.a.example.com:*.b.example.com,*.c.example.com"
161 will allow hostnames matching "*.a.example.com" to be
162 canonicalized to names in the "*.b.example.com" or
163 "*.c.example.com" domains.
166 Specifies a file from which the user's certificate is read. A
167 corresponding private key must be provided separately in order to
168 use this certificate either from an IdentityFile directive or -i
169 flag to ssh(1), via ssh-agent(1), or via a PKCS11Provider.
171 Arguments to CertificateFile may use the tilde syntax to refer to
172 a user's home directory or the tokens described in the TOKENS
175 It is possible to have multiple certificate files specified in
176 configuration files; these certificates will be tried in
177 sequence. Multiple CertificateFile directives will add to the
178 list of certificates used for authentication.
180 ChallengeResponseAuthentication
181 Specifies whether to use challenge-response authentication. The
182 argument to this keyword must be yes (the default) or no.
185 If set to yes (the default), ssh(1) will additionally check the
186 host IP address in the known_hosts file. This allows it to
187 detect if a host key changed due to DNS spoofing and will add
188 addresses of destination hosts to ~/.ssh/known_hosts in the
189 process, regardless of the setting of StrictHostKeyChecking. If
190 the option is set to no, the check will not be executed.
192 Cipher Specifies the cipher to use for encrypting the session in
193 protocol version 1. Currently, blowfish, 3des (the default), and
194 des are supported, though des is only supported in the ssh(1)
195 client for interoperability with legacy protocol 1
196 implementations; its use is strongly discouraged due to
197 cryptographic weaknesses.
200 Specifies the ciphers allowed for protocol version 2 in order of
201 preference. Multiple ciphers must be comma-separated. If the
202 specified value begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the specified
203 ciphers will be appended to the default set instead of replacing
204 them. If the specified value begins with a M-bM-^@M-^X-M-bM-^@M-^Y character, then
205 the specified ciphers (including wildcards) will be removed from
206 the default set instead of replacing them.
208 The supported ciphers are:
217 aes128-gcm@openssh.com
218 aes256-gcm@openssh.com
224 chacha20-poly1305@openssh.com
228 chacha20-poly1305@openssh.com,
229 aes128-ctr,aes192-ctr,aes256-ctr,
230 aes128-gcm@openssh.com,aes256-gcm@openssh.com,
231 aes128-cbc,aes192-cbc,aes256-cbc
233 The list of available ciphers may also be obtained using "ssh -Q
237 Specifies that all local, remote, and dynamic port forwardings
238 specified in the configuration files or on the command line be
239 cleared. This option is primarily useful when used from the
240 ssh(1) command line to clear port forwardings set in
241 configuration files, and is automatically set by scp(1) and
242 sftp(1). The argument must be yes or no (the default).
245 Specifies whether to use compression. The argument must be yes
249 Specifies the compression level to use if compression is enabled.
250 The argument must be an integer from 1 (fast) to 9 (slow, best).
251 The default level is 6, which is good for most applications. The
252 meaning of the values is the same as in gzip(1). Note that this
253 option applies to protocol version 1 only.
256 Specifies the number of tries (one per second) to make before
257 exiting. The argument must be an integer. This may be useful in
258 scripts if the connection sometimes fails. The default is 1.
261 Specifies the timeout (in seconds) used when connecting to the
262 SSH server, instead of using the default system TCP timeout.
263 This value is used only when the target is down or really
264 unreachable, not when it refuses the connection.
267 Enables the sharing of multiple sessions over a single network
268 connection. When set to yes, ssh(1) will listen for connections
269 on a control socket specified using the ControlPath argument.
270 Additional sessions can connect to this socket using the same
271 ControlPath with ControlMaster set to no (the default). These
272 sessions will try to reuse the master instance's network
273 connection rather than initiating new ones, but will fall back to
274 connecting normally if the control socket does not exist, or is
277 Setting this to ask will cause ssh(1) to listen for control
278 connections, but require confirmation using ssh-askpass(1). If
279 the ControlPath cannot be opened, ssh(1) will continue without
280 connecting to a master instance.
282 X11 and ssh-agent(1) forwarding is supported over these
283 multiplexed connections, however the display and agent forwarded
284 will be the one belonging to the master connection i.e. it is not
285 possible to forward multiple displays or agents.
287 Two additional options allow for opportunistic multiplexing: try
288 to use a master connection but fall back to creating a new one if
289 one does not already exist. These options are: auto and autoask.
290 The latter requires confirmation like the ask option.
293 Specify the path to the control socket used for connection
294 sharing as described in the ControlMaster section above or the
295 string none to disable connection sharing. Arguments to
296 ControlPath may use the tilde syntax to refer to a user's home
297 directory or the tokens described in the TOKENS section. It is
298 recommended that any ControlPath used for opportunistic
299 connection sharing include at least %h, %p, and %r (or
300 alternatively %C) and be placed in a directory that is not
301 writable by other users. This ensures that shared connections
302 are uniquely identified.
305 When used in conjunction with ControlMaster, specifies that the
306 master connection should remain open in the background (waiting
307 for future client connections) after the initial client
308 connection has been closed. If set to no, then the master
309 connection will not be placed into the background, and will close
310 as soon as the initial client connection is closed. If set to
311 yes or 0, then the master connection will remain in the
312 background indefinitely (until killed or closed via a mechanism
313 such as the "ssh -O exit"). If set to a time in seconds, or a
314 time in any of the formats documented in sshd_config(5), then the
315 backgrounded master connection will automatically terminate after
316 it has remained idle (with no client connections) for the
320 Specifies that a TCP port on the local machine be forwarded over
321 the secure channel, and the application protocol is then used to
322 determine where to connect to from the remote machine.
324 The argument must be [bind_address:]port. IPv6 addresses can be
325 specified by enclosing addresses in square brackets. By default,
326 the local port is bound in accordance with the GatewayPorts
327 setting. However, an explicit bind_address may be used to bind
328 the connection to a specific address. The bind_address of
329 localhost indicates that the listening port be bound for local
330 use only, while an empty address or M-bM-^@M-^X*M-bM-^@M-^Y indicates that the port
331 should be available from all interfaces.
333 Currently the SOCKS4 and SOCKS5 protocols are supported, and
334 ssh(1) will act as a SOCKS server. Multiple forwardings may be
335 specified, and additional forwardings can be given on the command
336 line. Only the superuser can forward privileged ports.
339 Setting this option to yes in the global client configuration
340 file /etc/ssh/ssh_config enables the use of the helper program
341 ssh-keysign(8) during HostbasedAuthentication. The argument must
342 be yes or no (the default). This option should be placed in the
343 non-hostspecific section. See ssh-keysign(8) for more
347 Sets the escape character (default: M-bM-^@M-^X~M-bM-^@M-^Y). The escape character
348 can also be set on the command line. The argument should be a
349 single character, M-bM-^@M-^X^M-bM-^@M-^Y followed by a letter, or none to disable
350 the escape character entirely (making the connection transparent
354 Specifies whether ssh(1) should terminate the connection if it
355 cannot set up all requested dynamic, tunnel, local, and remote
356 port forwardings, (e.g. if either end is unable to bind and
357 listen on a specified port). Note that ExitOnForwardFailure does
358 not apply to connections made over port forwardings and will not,
359 for example, cause ssh(1) to exit if TCP connections to the
360 ultimate forwarding destination fail. The argument must be yes
364 Specifies the hash algorithm used when displaying key
365 fingerprints. Valid options are: md5 and sha256 (the default).
368 Specifies whether the connection to the authentication agent (if
369 any) will be forwarded to the remote machine. The argument must
370 be yes or no (the default).
372 Agent forwarding should be enabled with caution. Users with the
373 ability to bypass file permissions on the remote host (for the
374 agent's Unix-domain socket) can access the local agent through
375 the forwarded connection. An attacker cannot obtain key material
376 from the agent, however they can perform operations on the keys
377 that enable them to authenticate using the identities loaded into
381 Specifies whether X11 connections will be automatically
382 redirected over the secure channel and DISPLAY set. The argument
383 must be yes or no (the default).
385 X11 forwarding should be enabled with caution. Users with the
386 ability to bypass file permissions on the remote host (for the
387 user's X11 authorization database) can access the local X11
388 display through the forwarded connection. An attacker may then
389 be able to perform activities such as keystroke monitoring if the
390 ForwardX11Trusted option is also enabled.
393 Specify a timeout for untrusted X11 forwarding using the format
394 described in the TIME FORMATS section of sshd_config(5). X11
395 connections received by ssh(1) after this time will be refused.
396 The default is to disable untrusted X11 forwarding after twenty
400 If this option is set to yes, remote X11 clients will have full
401 access to the original X11 display.
403 If this option is set to no (the default), remote X11 clients
404 will be considered untrusted and prevented from stealing or
405 tampering with data belonging to trusted X11 clients.
406 Furthermore, the xauth(1) token used for the session will be set
407 to expire after 20 minutes. Remote clients will be refused
408 access after this time.
410 See the X11 SECURITY extension specification for full details on
411 the restrictions imposed on untrusted clients.
414 Specifies whether remote hosts are allowed to connect to local
415 forwarded ports. By default, ssh(1) binds local port forwardings
416 to the loopback address. This prevents other remote hosts from
417 connecting to forwarded ports. GatewayPorts can be used to
418 specify that ssh should bind local port forwardings to the
419 wildcard address, thus allowing remote hosts to connect to
420 forwarded ports. The argument must be yes or no (the default).
423 Specifies one or more files to use for the global host key
424 database, separated by whitespace. The default is
425 /etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2.
428 Specifies whether user authentication based on GSSAPI is allowed.
431 GSSAPIDelegateCredentials
432 Forward (delegate) credentials to the server. The default is no.
435 Indicates that ssh(1) should hash host names and addresses when
436 they are added to ~/.ssh/known_hosts. These hashed names may be
437 used normally by ssh(1) and sshd(8), but they do not reveal
438 identifying information should the file's contents be disclosed.
439 The default is no. Note that existing names and addresses in
440 known hosts files will not be converted automatically, but may be
441 manually hashed using ssh-keygen(1).
443 HostbasedAuthentication
444 Specifies whether to try rhosts based authentication with public
445 key authentication. The argument must be yes or no (the
449 Specifies the key types that will be used for hostbased
450 authentication as a comma-separated pattern list. Alternately if
451 the specified value begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the
452 specified key types will be appended to the default set instead
453 of replacing them. If the specified value begins with a M-bM-^@M-^X-M-bM-^@M-^Y
454 character, then the specified key types (including wildcards)
455 will be removed from the default set instead of replacing them.
456 The default for this option is:
458 ecdsa-sha2-nistp256-cert-v01@openssh.com,
459 ecdsa-sha2-nistp384-cert-v01@openssh.com,
460 ecdsa-sha2-nistp521-cert-v01@openssh.com,
461 ssh-ed25519-cert-v01@openssh.com,
462 ssh-rsa-cert-v01@openssh.com,
463 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
466 The -Q option of ssh(1) may be used to list supported key types.
469 Specifies the host key algorithms that the client wants to use in
470 order of preference. Alternately if the specified value begins
471 with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the specified key types will be
472 appended to the default set instead of replacing them. If the
473 specified value begins with a M-bM-^@M-^X-M-bM-^@M-^Y character, then the specified
474 key types (including wildcards) will be removed from the default
475 set instead of replacing them. The default for this option is:
477 ecdsa-sha2-nistp256-cert-v01@openssh.com,
478 ecdsa-sha2-nistp384-cert-v01@openssh.com,
479 ecdsa-sha2-nistp521-cert-v01@openssh.com,
480 ssh-ed25519-cert-v01@openssh.com,
481 ssh-rsa-cert-v01@openssh.com,
482 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
485 If hostkeys are known for the destination host then this default
486 is modified to prefer their algorithms.
488 The list of available key types may also be obtained using "ssh
492 Specifies an alias that should be used instead of the real host
493 name when looking up or saving the host key in the host key
494 database files. This option is useful for tunneling SSH
495 connections or for multiple servers running on a single host.
498 Specifies the real host name to log into. This can be used to
499 specify nicknames or abbreviations for hosts. Arguments to
500 HostName accept the tokens described in the TOKENS section.
501 Numeric IP addresses are also permitted (both on the command line
502 and in HostName specifications). The default is the name given
506 Specifies that ssh(1) should only use the authentication identity
507 and certificate files explicitly configured in the ssh_config
508 files or passed on the ssh(1) command-line, even if ssh-agent(1)
509 or a PKCS11Provider offers more identities. The argument to this
510 keyword must be yes or no (the default). This option is intended
511 for situations where ssh-agent offers many different identities.
514 Specifies the UNIX-domain socket used to communicate with the
515 authentication agent.
517 This option overrides the SSH_AUTH_SOCK environment variable and
518 can be used to select a specific agent. Setting the socket name
519 to none disables the use of an authentication agent. If the
520 string "SSH_AUTH_SOCK" is specified, the location of the socket
521 will be read from the SSH_AUTH_SOCK environment variable.
523 Arguments to IdentityAgent may use the tilde syntax to refer to a
524 user's home directory or the tokens described in the TOKENS
528 Specifies a file from which the user's DSA, ECDSA, Ed25519 or RSA
529 authentication identity is read. The default is ~/.ssh/identity
530 for protocol version 1, and ~/.ssh/id_dsa, ~/.ssh/id_ecdsa,
531 ~/.ssh/id_ed25519 and ~/.ssh/id_rsa for protocol version 2.
532 Additionally, any identities represented by the authentication
533 agent will be used for authentication unless IdentitiesOnly is
534 set. If no certificates have been explicitly specified by
535 CertificateFile, ssh(1) will try to load certificate information
536 from the filename obtained by appending -cert.pub to the path of
537 a specified IdentityFile.
539 Arguments to IdentityFile may use the tilde syntax to refer to a
540 user's home directory or the tokens described in the TOKENS
543 It is possible to have multiple identity files specified in
544 configuration files; all these identities will be tried in
545 sequence. Multiple IdentityFile directives will add to the list
546 of identities tried (this behaviour differs from that of other
547 configuration directives).
549 IdentityFile may be used in conjunction with IdentitiesOnly to
550 select which identities in an agent are offered during
551 authentication. IdentityFile may also be used in conjunction
552 with CertificateFile in order to provide any certificate also
553 needed for authentication with the identity.
556 Specifies a pattern-list of unknown options to be ignored if they
557 are encountered in configuration parsing. This may be used to
558 suppress errors if ssh_config contains options that are
559 unrecognised by ssh(1). It is recommended that IgnoreUnknown be
560 listed early in the configuration file as it will not be applied
561 to unknown options that appear before it.
564 Include the specified configuration file(s). Multiple pathnames
565 may be specified and each pathname may contain glob(3) wildcards
566 and, for user configurations, shell-like M-bM-^@M-^X~M-bM-^@M-^Y references to user
567 home directories. Files without absolute paths are assumed to be
568 in ~/.ssh if included in a user configuration file or /etc/ssh if
569 included from the system configuration file. Include directive
570 may appear inside a Match or Host block to perform conditional
573 IPQoS Specifies the IPv4 type-of-service or DSCP class for connections.
574 Accepted values are af11, af12, af13, af21, af22, af23, af31,
575 af32, af33, af41, af42, af43, cs0, cs1, cs2, cs3, cs4, cs5, cs6,
576 cs7, ef, lowdelay, throughput, reliability, or a numeric value.
577 This option may take one or two arguments, separated by
578 whitespace. If one argument is specified, it is used as the
579 packet class unconditionally. If two values are specified, the
580 first is automatically selected for interactive sessions and the
581 second for non-interactive sessions. The default is lowdelay for
582 interactive sessions and throughput for non-interactive sessions.
584 KbdInteractiveAuthentication
585 Specifies whether to use keyboard-interactive authentication.
586 The argument to this keyword must be yes (the default) or no.
588 KbdInteractiveDevices
589 Specifies the list of methods to use in keyboard-interactive
590 authentication. Multiple method names must be comma-separated.
591 The default is to use the server specified list. The methods
592 available vary depending on what the server supports. For an
593 OpenSSH server, it may be zero or more of: bsdauth, pam, and
597 Specifies the available KEX (Key Exchange) algorithms. Multiple
598 algorithms must be comma-separated. Alternately if the specified
599 value begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the specified methods
600 will be appended to the default set instead of replacing them.
601 If the specified value begins with a M-bM-^@M-^X-M-bM-^@M-^Y character, then the
602 specified methods (including wildcards) will be removed from the
603 default set instead of replacing them. The default is:
605 curve25519-sha256,curve25519-sha256@libssh.org,
606 ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
607 diffie-hellman-group-exchange-sha256,
608 diffie-hellman-group-exchange-sha1,
609 diffie-hellman-group14-sha1
611 The list of available key exchange algorithms may also be
612 obtained using "ssh -Q kex".
615 Specifies a command to execute on the local machine after
616 successfully connecting to the server. The command string
617 extends to the end of the line, and is executed with the user's
618 shell. Arguments to LocalCommand accept the tokens described in
621 The command is run synchronously and does not have access to the
622 session of the ssh(1) that spawned it. It should not be used for
623 interactive commands.
625 This directive is ignored unless PermitLocalCommand has been
629 Specifies that a TCP port on the local machine be forwarded over
630 the secure channel to the specified host and port from the remote
631 machine. The first argument must be [bind_address:]port and the
632 second argument must be host:hostport. IPv6 addresses can be
633 specified by enclosing addresses in square brackets. Multiple
634 forwardings may be specified, and additional forwardings can be
635 given on the command line. Only the superuser can forward
636 privileged ports. By default, the local port is bound in
637 accordance with the GatewayPorts setting. However, an explicit
638 bind_address may be used to bind the connection to a specific
639 address. The bind_address of localhost indicates that the
640 listening port be bound for local use only, while an empty
641 address or M-bM-^@M-^X*M-bM-^@M-^Y indicates that the port should be available from
645 Gives the verbosity level that is used when logging messages from
646 ssh(1). The possible values are: QUIET, FATAL, ERROR, INFO,
647 VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO.
648 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify
649 higher levels of verbose output.
651 MACs Specifies the MAC (message authentication code) algorithms in
652 order of preference. The MAC algorithm is used for data
653 integrity protection. Multiple algorithms must be comma-
654 separated. If the specified value begins with a M-bM-^@M-^X+M-bM-^@M-^Y character,
655 then the specified algorithms will be appended to the default set
656 instead of replacing them. If the specified value begins with a
657 M-bM-^@M-^X-M-bM-^@M-^Y character, then the specified algorithms (including
658 wildcards) will be removed from the default set instead of
661 The algorithms that contain "-etm" calculate the MAC after
662 encryption (encrypt-then-mac). These are considered safer and
663 their use recommended.
667 umac-64-etm@openssh.com,umac-128-etm@openssh.com,
668 hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
669 hmac-sha1-etm@openssh.com,
670 umac-64@openssh.com,umac-128@openssh.com,
671 hmac-sha2-256,hmac-sha2-512,hmac-sha1
673 The list of available MAC algorithms may also be obtained using
676 NoHostAuthenticationForLocalhost
677 This option can be used if the home directory is shared across
678 machines. In this case localhost will refer to a different
679 machine on each of the machines and the user will get many
680 warnings about changed host keys. However, this option disables
681 host authentication for localhost. The argument to this keyword
682 must be yes or no (the default).
684 NumberOfPasswordPrompts
685 Specifies the number of password prompts before giving up. The
686 argument to this keyword must be an integer. The default is 3.
688 PasswordAuthentication
689 Specifies whether to use password authentication. The argument
690 to this keyword must be yes (the default) or no.
693 Allow local command execution via the LocalCommand option or
694 using the !command escape sequence in ssh(1). The argument must
695 be yes or no (the default).
698 Specifies which PKCS#11 provider to use. The argument to this
699 keyword is the PKCS#11 shared library ssh(1) should use to
700 communicate with a PKCS#11 token providing the user's private RSA
703 Port Specifies the port number to connect on the remote host. The
706 PreferredAuthentications
707 Specifies the order in which the client should try authentication
708 methods. This allows a client to prefer one method (e.g.
709 keyboard-interactive) over another method (e.g. password). The
712 gssapi-with-mic,hostbased,publickey,
713 keyboard-interactive,password
716 Specifies the protocol versions ssh(1) should support in order of
717 preference. The possible values are 1 and 2. Multiple versions
718 must be comma-separated. When this option is set to 2,1 ssh will
719 try version 2 and fall back to version 1 if version 2 is not
720 available. The default is version 2. Protocol 1 suffers from a
721 number of cryptographic weaknesses and should not be used. It is
722 only offered to support legacy devices.
725 Specifies the command to use to connect to the server. The
726 command string extends to the end of the line, and is executed
727 using the user's shell M-bM-^@M-^XexecM-bM-^@M-^Y directive to avoid a lingering
730 Arguments to ProxyCommand accept the tokens described in the
731 TOKENS section. The command can be basically anything, and
732 should read from its standard input and write to its standard
733 output. It should eventually connect an sshd(8) server running
734 on some machine, or execute sshd -i somewhere. Host key
735 management will be done using the HostName of the host being
736 connected (defaulting to the name typed by the user). Setting
737 the command to none disables this option entirely. Note that
738 CheckHostIP is not available for connects with a proxy command.
740 This directive is useful in conjunction with nc(1) and its proxy
741 support. For example, the following directive would connect via
742 an HTTP proxy at 192.0.2.0:
744 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
747 Specifies one or more jump proxies as [user@]host[:port].
748 Multiple proxies may be separated by comma characters and will be
749 visited sequentially. Setting this option will cause ssh(1) to
750 connect to the target host by first making a ssh(1) connection to
751 the specified ProxyJump host and then establishing a TCP
752 forwarding to the ultimate target from there.
754 Note that this option will compete with the ProxyCommand option -
755 whichever is specified first will prevent later instances of the
756 other from taking effect.
759 Specifies that ProxyCommand will pass a connected file descriptor
760 back to ssh(1) instead of continuing to execute and pass data.
763 PubkeyAcceptedKeyTypes
764 Specifies the key types that will be used for public key
765 authentication as a comma-separated pattern list. Alternately if
766 the specified value begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the key
767 types after it will be appended to the default instead of
768 replacing it. If the specified value begins with a M-bM-^@M-^X-M-bM-^@M-^Y
769 character, then the specified key types (including wildcards)
770 will be removed from the default set instead of replacing them.
771 The default for this option is:
773 ecdsa-sha2-nistp256-cert-v01@openssh.com,
774 ecdsa-sha2-nistp384-cert-v01@openssh.com,
775 ecdsa-sha2-nistp521-cert-v01@openssh.com,
776 ssh-ed25519-cert-v01@openssh.com,
777 ssh-rsa-cert-v01@openssh.com,
778 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
781 The list of available key types may also be obtained using "ssh
785 Specifies whether to try public key authentication. The argument
786 to this keyword must be yes (the default) or no.
789 Specifies the maximum amount of data that may be transmitted
790 before the session key is renegotiated, optionally followed a
791 maximum amount of time that may pass before the session key is
792 renegotiated. The first argument is specified in bytes and may
793 have a suffix of M-bM-^@M-^XKM-bM-^@M-^Y, M-bM-^@M-^XMM-bM-^@M-^Y, or M-bM-^@M-^XGM-bM-^@M-^Y to indicate Kilobytes,
794 Megabytes, or Gigabytes, respectively. The default is between
795 M-bM-^@M-^X1GM-bM-^@M-^Y and M-bM-^@M-^X4GM-bM-^@M-^Y, depending on the cipher. The optional second
796 value is specified in seconds and may use any of the units
797 documented in the TIME FORMATS section of sshd_config(5). The
798 default value for RekeyLimit is default none, which means that
799 rekeying is performed after the cipher's default amount of data
800 has been sent or received and no time based rekeying is done.
803 Specifies that a TCP port on the remote machine be forwarded over
804 the secure channel to the specified host and port from the local
805 machine. The first argument must be [bind_address:]port and the
806 second argument must be host:hostport. IPv6 addresses can be
807 specified by enclosing addresses in square brackets. Multiple
808 forwardings may be specified, and additional forwardings can be
809 given on the command line. Privileged ports can be forwarded
810 only when logging in as root on the remote machine.
812 If the port argument is 0, the listen port will be dynamically
813 allocated on the server and reported to the client at run time.
815 If the bind_address is not specified, the default is to only bind
816 to loopback addresses. If the bind_address is M-bM-^@M-^X*M-bM-^@M-^Y or an empty
817 string, then the forwarding is requested to listen on all
818 interfaces. Specifying a remote bind_address will only succeed
819 if the server's GatewayPorts option is enabled (see
823 Specifies whether to request a pseudo-tty for the session. The
824 argument may be one of: no (never request a TTY), yes (always
825 request a TTY when standard input is a TTY), force (always
826 request a TTY) or auto (request a TTY when opening a login
827 session). This option mirrors the -t and -T flags for ssh(1).
830 Specifies revoked host public keys. Keys listed in this file
831 will be refused for host authentication. Note that if this file
832 does not exist or is not readable, then host authentication will
833 be refused for all hosts. Keys may be specified as a text file,
834 listing one public key per line, or as an OpenSSH Key Revocation
835 List (KRL) as generated by ssh-keygen(1). For more information
836 on KRLs, see the KEY REVOCATION LISTS section in ssh-keygen(1).
838 RhostsRSAAuthentication
839 Specifies whether to try rhosts based authentication with RSA
840 host authentication. The argument must be yes or no (the
841 default). This option applies to protocol version 1 only and
842 requires ssh(1) to be setuid root.
845 Specifies whether to try RSA authentication. The argument to
846 this keyword must be yes (the default) or no. RSA authentication
847 will only be attempted if the identity file exists, or an
848 authentication agent is running. Note that this option applies
849 to protocol version 1 only.
852 Specifies what variables from the local environ(7) should be sent
853 to the server. The server must also support it, and the server
854 must be configured to accept these environment variables. Note
855 that the TERM environment variable is always sent whenever a
856 pseudo-terminal is requested as it is required by the protocol.
857 Refer to AcceptEnv in sshd_config(5) for how to configure the
858 server. Variables are specified by name, which may contain
859 wildcard characters. Multiple environment variables may be
860 separated by whitespace or spread across multiple SendEnv
861 directives. The default is not to send any environment
864 See PATTERNS for more information on patterns.
867 Sets the number of server alive messages (see below) which may be
868 sent without ssh(1) receiving any messages back from the server.
869 If this threshold is reached while server alive messages are
870 being sent, ssh will disconnect from the server, terminating the
871 session. It is important to note that the use of server alive
872 messages is very different from TCPKeepAlive (below). The server
873 alive messages are sent through the encrypted channel and
874 therefore will not be spoofable. The TCP keepalive option
875 enabled by TCPKeepAlive is spoofable. The server alive mechanism
876 is valuable when the client or server depend on knowing when a
877 connection has become inactive.
879 The default value is 3. If, for example, ServerAliveInterval
880 (see below) is set to 15 and ServerAliveCountMax is left at the
881 default, if the server becomes unresponsive, ssh will disconnect
882 after approximately 45 seconds.
885 Sets a timeout interval in seconds after which if no data has
886 been received from the server, ssh(1) will send a message through
887 the encrypted channel to request a response from the server. The
888 default is 0, indicating that these messages will not be sent to
892 Sets the octal file creation mode mask (umask) used when creating
893 a Unix-domain socket file for local or remote port forwarding.
894 This option is only used for port forwarding to a Unix-domain
897 The default value is 0177, which creates a Unix-domain socket
898 file that is readable and writable only by the owner. Note that
899 not all operating systems honor the file mode on Unix-domain
902 StreamLocalBindUnlink
903 Specifies whether to remove an existing Unix-domain socket file
904 for local or remote port forwarding before creating a new one.
905 If the socket file already exists and StreamLocalBindUnlink is
906 not enabled, ssh will be unable to forward the port to the Unix-
907 domain socket file. This option is only used for port forwarding
908 to a Unix-domain socket file.
910 The argument must be yes or no (the default).
912 StrictHostKeyChecking
913 If this flag is set to yes, ssh(1) will never automatically add
914 host keys to the ~/.ssh/known_hosts file, and refuses to connect
915 to hosts whose host key has changed. This provides maximum
916 protection against trojan horse attacks, though it can be
917 annoying when the /etc/ssh/ssh_known_hosts file is poorly
918 maintained or when connections to new hosts are frequently made.
919 This option forces the user to manually add all new hosts. If
920 this flag is set to no, ssh will automatically add new host keys
921 to the user known hosts files. If this flag is set to ask (the
922 default), new host keys will be added to the user known host
923 files only after the user has confirmed that is what they really
924 want to do, and ssh will refuse to connect to hosts whose host
925 key has changed. The host keys of known hosts will be verified
926 automatically in all cases.
929 Specifies whether the system should send TCP keepalive messages
930 to the other side. If they are sent, death of the connection or
931 crash of one of the machines will be properly noticed. However,
932 this means that connections will die if the route is down
933 temporarily, and some people find it annoying.
935 The default is yes (to send TCP keepalive messages), and the
936 client will notice if the network goes down or the remote host
937 dies. This is important in scripts, and many users want it too.
939 To disable TCP keepalive messages, the value should be set to no.
941 Tunnel Request tun(4) device forwarding between the client and the
942 server. The argument must be yes, point-to-point (layer 3),
943 ethernet (layer 2), or no (the default). Specifying yes requests
944 the default tunnel mode, which is point-to-point.
947 Specifies the tun(4) devices to open on the client (local_tun)
948 and the server (remote_tun).
950 The argument must be local_tun[:remote_tun]. The devices may be
951 specified by numerical ID or the keyword any, which uses the next
952 available tunnel device. If remote_tun is not specified, it
953 defaults to any. The default is any:any.
956 Specifies whether ssh(1) should accept notifications of
957 additional hostkeys from the server sent after authentication has
958 completed and add them to UserKnownHostsFile. The argument must
959 be yes, no (the default) or ask. Enabling this option allows
960 learning alternate hostkeys for a server and supports graceful
961 key rotation by allowing a server to send replacement public keys
962 before old ones are removed. Additional hostkeys are only
963 accepted if the key used to authenticate the host was already
964 trusted or explicitly accepted by the user. If UpdateHostKeys is
965 set to ask, then the user is asked to confirm the modifications
966 to the known_hosts file. Confirmation is currently incompatible
967 with ControlPersist, and will be disabled if it is enabled.
969 Presently, only sshd(8) from OpenSSH 6.8 and greater support the
970 "hostkeys@openssh.com" protocol extension used to inform the
971 client of all the server's hostkeys.
974 Specifies whether to use a privileged port for outgoing
975 connections. The argument must be yes or no (the default). If
976 set to yes, ssh(1) must be setuid root. Note that this option
977 must be set to yes for RhostsRSAAuthentication with older
980 User Specifies the user to log in as. This can be useful when a
981 different user name is used on different machines. This saves
982 the trouble of having to remember to give the user name on the
986 Specifies one or more files to use for the user host key
987 database, separated by whitespace. The default is
988 ~/.ssh/known_hosts, ~/.ssh/known_hosts2.
991 Specifies whether to verify the remote key using DNS and SSHFP
992 resource records. If this option is set to yes, the client will
993 implicitly trust keys that match a secure fingerprint from DNS.
994 Insecure fingerprints will be handled as if this option was set
995 to ask. If this option is set to ask, information on fingerprint
996 match will be displayed, but the user will still need to confirm
997 new host keys according to the StrictHostKeyChecking option. The
1000 See also VERIFYING HOST KEYS in ssh(1).
1003 If this flag is set to yes, an ASCII art representation of the
1004 remote host key fingerprint is printed in addition to the
1005 fingerprint string at login and for unknown host keys. If this
1006 flag is set to no (the default), no fingerprint strings are
1007 printed at login and only the fingerprint string will be printed
1008 for unknown host keys.
1011 Specifies the full pathname of the xauth(1) program. The default
1012 is /usr/X11R6/bin/xauth.
1015 A pattern consists of zero or more non-whitespace characters, M-bM-^@M-^X*M-bM-^@M-^Y (a
1016 wildcard that matches zero or more characters), or M-bM-^@M-^X?M-bM-^@M-^Y (a wildcard that
1017 matches exactly one character). For example, to specify a set of
1018 declarations for any host in the ".co.uk" set of domains, the following
1019 pattern could be used:
1023 The following pattern would match any host in the 192.168.0.[0-9] network
1028 A pattern-list is a comma-separated list of patterns. Patterns within
1029 pattern-lists may be negated by preceding them with an exclamation mark
1030 (M-bM-^@M-^X!M-bM-^@M-^Y). For example, to allow a key to be used from anywhere within an
1031 organization except from the "dialup" pool, the following entry (in
1032 authorized_keys) could be used:
1034 from="!*.dialup.example.com,*.example.com"
1037 Arguments to some keywords can make use of tokens, which are expanded at
1040 %% A literal M-bM-^@M-^X%M-bM-^@M-^Y.
1041 %C Shorthand for %l%h%p%r.
1042 %d Local user's home directory.
1043 %h The remote hostname.
1044 %i The local user ID.
1045 %L The local hostname.
1046 %l The local hostname, including the domain name.
1047 %n The original remote hostname, as given on the command line.
1049 %r The remote username.
1050 %u The local username.
1052 Match exec accepts the tokens %%, %h, %L, %l, %n, %p, %r, and %u.
1054 CertificateFile accepts the tokens %%, %d, %h, %l, %r, and %u.
1056 ControlPath accepts the tokens %%, %C, %h, %i, %L, %l, %n, %p, %r, and
1059 HostName accepts the tokens %% and %h.
1061 IdentityAgent and IdentityFile accept the tokens %%, %d, %h, %l, %r, and
1064 LocalCommand accepts the tokens %%, %C, %d, %h, %l, %n, %p, %r, and %u.
1066 ProxyCommand accepts the tokens %%, %h, %p, and %r.
1070 This is the per-user configuration file. The format of this file
1071 is described above. This file is used by the SSH client.
1072 Because of the potential for abuse, this file must have strict
1073 permissions: read/write for the user, and not accessible by
1077 Systemwide configuration file. This file provides defaults for
1078 those values that are not specified in the user's configuration
1079 file, and for those users who do not have a configuration file.
1080 This file must be world-readable.
1086 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
1087 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
1088 de Raadt and Dug Song removed many bugs, re-added newer features and
1089 created OpenSSH. Markus Friedl contributed the support for SSH protocol
1090 versions 1.5 and 2.0.
1092 OpenBSD 6.0 February 27, 2017 OpenBSD 6.0
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