1.\" 2.\" Author: Tatu Ylonen <ylo@cs.hut.fi> 3.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland 4.\" All rights reserved 5.\" 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". 11.\" 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. 15.\" 16.\" Redistribution and use in source and binary forms, with or without 17.\" modification, are permitted provided that the following conditions 18.\" are met: 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. 24.\" 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. 35.\" 36.\" $OpenBSD: ssh_config.5,v 1.413 2025/03/03 06:53:09 dtucker Exp $ 37.Dd $Mdocdate: March 3 2025 $ 38.Dt SSH_CONFIG 5 39.Os 40.Sh NAME 41.Nm ssh_config 42.Nd OpenSSH client configuration file 43.Sh DESCRIPTION 44.Xr ssh 1 45obtains configuration data from the following sources in 46the following order: 47.Pp 48.Bl -enum -offset indent -compact 49.It 50command-line options 51.It 52user's configuration file 53.Pq Pa ~/.ssh/config 54.It 55system-wide configuration file 56.Pq Pa /etc/ssh/ssh_config 57.El 58.Pp 59Unless noted otherwise, for each parameter, the first obtained value 60will be used. 61The configuration files contain sections separated by 62.Cm Host 63specifications, and that section is only applied for hosts that 64match one of the patterns given in the specification. 65The matched host name is usually the one given on the command line 66(see the 67.Cm CanonicalizeHostname 68option for exceptions). 69.Pp 70Since the first obtained value for each parameter is used, more 71host-specific declarations should be given near the beginning of the 72file, and general defaults at the end. 73.Pp 74The file contains keyword-argument pairs, one per line. 75Lines starting with 76.Ql # 77and empty lines are interpreted as comments. 78Arguments may optionally be enclosed in double quotes 79.Pq \&" 80in order to represent arguments containing spaces. 81Configuration options may be separated by whitespace or 82optional whitespace and exactly one 83.Ql = ; 84the latter format is useful to avoid the need to quote whitespace 85when specifying configuration options using the 86.Nm ssh , 87.Nm scp , 88and 89.Nm sftp 90.Fl o 91option. 92.Pp 93The possible 94keywords and their meanings are as follows (note that 95keywords are case-insensitive and arguments are case-sensitive): 96.Bl -tag -width Ds 97.It Cm Host 98Restricts the following declarations (up to the next 99.Cm Host 100or 101.Cm Match 102keyword) to be only for those hosts that match one of the patterns 103given after the keyword. 104If more than one pattern is provided, they should be separated by whitespace. 105A single 106.Ql * 107as a pattern can be used to provide global 108defaults for all hosts. 109The host is usually the 110.Ar hostname 111argument given on the command line 112(see the 113.Cm CanonicalizeHostname 114keyword for exceptions). 115.Pp 116A pattern entry may be negated by prefixing it with an exclamation mark 117.Pq Sq !\& . 118If a negated entry is matched, then the 119.Cm Host 120entry is ignored, regardless of whether any other patterns on the line 121match. 122Negated matches are therefore useful to provide exceptions for wildcard 123matches. 124.Pp 125See 126.Sx PATTERNS 127for more information on patterns. 128.It Cm Match 129Restricts the following declarations (up to the next 130.Cm Host 131or 132.Cm Match 133keyword) to be used only when the conditions following the 134.Cm Match 135keyword are satisfied. 136Match conditions are specified using one or more criteria 137or the single token 138.Cm all 139which always matches. 140The available criteria keywords are: 141.Cm canonical , 142.Cm final , 143.Cm exec , 144.Cm localnetwork , 145.Cm host , 146.Cm originalhost , 147.Cm tagged , 148.Cm command , 149.Cm user , 150.Cm localuser , 151and 152.Cm version . 153The 154.Cm all 155criteria must appear alone or immediately after 156.Cm canonical 157or 158.Cm final . 159Other criteria may be combined arbitrarily. 160All criteria but 161.Cm all , 162.Cm canonical , 163and 164.Cm final 165require an argument. 166Criteria may be negated by prepending an exclamation mark 167.Pq Sq !\& . 168.Pp 169The 170.Cm canonical 171keyword matches only when the configuration file is being re-parsed 172after hostname canonicalization (see the 173.Cm CanonicalizeHostname 174option). 175This may be useful to specify conditions that work with canonical host 176names only. 177.Pp 178The 179.Cm final 180keyword requests that the configuration be re-parsed (regardless of whether 181.Cm CanonicalizeHostname 182is enabled), and matches only during this final pass. 183If 184.Cm CanonicalizeHostname 185is enabled, then 186.Cm canonical 187and 188.Cm final 189match during the same pass. 190.Pp 191The 192.Cm exec 193keyword executes the specified command under the user's shell. 194If the command returns a zero exit status then the condition is considered true. 195Commands containing whitespace characters must be quoted. 196Arguments to 197.Cm exec 198accept the tokens described in the 199.Sx TOKENS 200section. 201.Pp 202The 203.Cm localnetwork 204keyword matches the addresses of active local network interfaces against the 205supplied list of networks in CIDR format. 206This may be convenient for varying the effective configuration on devices that 207roam between networks. 208Note that network address is not a trustworthy criteria in many 209situations (e.g. when the network is automatically configured using DHCP) 210and so caution should be applied if using it to control security-sensitive 211configuration. 212.Pp 213The other keywords' criteria must be single entries or comma-separated 214lists and may use the wildcard and negation operators described in the 215.Sx PATTERNS 216section. 217.Pp 218The criteria for the 219.Cm host 220keyword are matched against the target hostname, after any substitution 221by the 222.Cm Hostname 223or 224.Cm CanonicalizeHostname 225options. 226The 227.Cm originalhost 228keyword matches against the hostname as it was specified on the command-line. 229.Pp 230The 231.Cm tagged 232keyword matches a tag name specified by a prior 233.Cm Tag 234directive or on the 235.Xr ssh 1 236command-line using the 237.Fl P 238flag. 239The 240.Cm command 241keyword matches the remote command that has been requested, or the subsystem 242name that is being invoked (e.g.\& 243.Qq sftp 244for an SFTP session). 245The empty string will match the case where a command or tag has not been 246specified, i.e.\& 247.Sq Match tag \&"\&" . 248The 249.Cm version 250keyword matches against the version string of 251.Xr ssh 1 , 252for example 253.Dq OpenSSH_10.0 . 254.Pp 255The 256.Cm user 257keyword matches against the target username on the remote host. 258The 259.Cm localuser 260keyword matches against the name of the local user running 261.Xr ssh 1 262(this keyword may be useful in system-wide 263.Nm 264files). 265.Pp 266Finally, the 267.Cm sessiontype 268keyword matches the requested session type, which may be one of 269.Cm shell 270for interactive sessions, 271.Cm exec 272for command execution sessions, 273.Cm subsystem 274for subsystem invocations such as 275.Xr sftp 1 , 276or 277.Cm none 278for transport-only sessions, such as when 279.Xr ssh 1 280is started with the 281.Fl N 282flag. 283.It Cm AddKeysToAgent 284Specifies whether keys should be automatically added to a running 285.Xr ssh-agent 1 . 286If this option is set to 287.Cm yes 288and a key is loaded from a file, the key and its passphrase are added to 289the agent with the default lifetime, as if by 290.Xr ssh-add 1 . 291If this option is set to 292.Cm ask , 293.Xr ssh 1 294will require confirmation using the 295.Ev SSH_ASKPASS 296program before adding a key (see 297.Xr ssh-add 1 298for details). 299If this option is set to 300.Cm confirm , 301each use of the key must be confirmed, as if the 302.Fl c 303option was specified to 304.Xr ssh-add 1 . 305If this option is set to 306.Cm no , 307no keys are added to the agent. 308Alternately, this option may be specified as a time interval 309using the format described in the 310.Sx TIME FORMATS 311section of 312.Xr sshd_config 5 313to specify the key's lifetime in 314.Xr ssh-agent 1 , 315after which it will automatically be removed. 316The argument must be 317.Cm no 318(the default), 319.Cm yes , 320.Cm confirm 321(optionally followed by a time interval), 322.Cm ask 323or a time interval. 324.It Cm AddressFamily 325Specifies which address family to use when connecting. 326Valid arguments are 327.Cm any 328(the default), 329.Cm inet 330(use IPv4 only), or 331.Cm inet6 332(use IPv6 only). 333.It Cm BatchMode 334If set to 335.Cm yes , 336user interaction such as password prompts and host key confirmation requests 337will be disabled. 338This option is useful in scripts and other batch jobs where no user 339is present to interact with 340.Xr ssh 1 . 341The argument must be 342.Cm yes 343or 344.Cm no 345(the default). 346.It Cm BindAddress 347Use the specified address on the local machine as the source address of 348the connection. 349Only useful on systems with more than one address. 350.It Cm BindInterface 351Use the address of the specified interface on the local machine as the 352source address of the connection. 353.It Cm CanonicalDomains 354When 355.Cm CanonicalizeHostname 356is enabled, this option specifies the list of domain suffixes in which to 357search for the specified destination host. 358.It Cm CanonicalizeFallbackLocal 359Specifies whether to fail with an error when hostname canonicalization fails. 360The default, 361.Cm yes , 362will attempt to look up the unqualified hostname using the system resolver's 363search rules. 364A value of 365.Cm no 366will cause 367.Xr ssh 1 368to fail instantly if 369.Cm CanonicalizeHostname 370is enabled and the target hostname cannot be found in any of the domains 371specified by 372.Cm CanonicalDomains . 373.It Cm CanonicalizeHostname 374Controls whether explicit hostname canonicalization is performed. 375The default, 376.Cm no , 377is not to perform any name rewriting and let the system resolver handle all 378hostname lookups. 379If set to 380.Cm yes 381then, for connections that do not use a 382.Cm ProxyCommand 383or 384.Cm ProxyJump , 385.Xr ssh 1 386will attempt to canonicalize the hostname specified on the command line 387using the 388.Cm CanonicalDomains 389suffixes and 390.Cm CanonicalizePermittedCNAMEs 391rules. 392If 393.Cm CanonicalizeHostname 394is set to 395.Cm always , 396then canonicalization is applied to proxied connections too. 397.Pp 398If this option is enabled, then the configuration files are processed 399again using the new target name to pick up any new configuration in matching 400.Cm Host 401and 402.Cm Match 403stanzas. 404A value of 405.Cm none 406disables the use of a 407.Cm ProxyJump 408host. 409.It Cm CanonicalizeMaxDots 410Specifies the maximum number of dot characters in a hostname before 411canonicalization is disabled. 412The default, 1, 413allows a single dot (i.e. hostname.subdomain). 414.It Cm CanonicalizePermittedCNAMEs 415Specifies rules to determine whether CNAMEs should be followed when 416canonicalizing hostnames. 417The rules consist of one or more arguments of 418.Ar source_domain_list : Ns Ar target_domain_list , 419where 420.Ar source_domain_list 421is a pattern-list of domains that may follow CNAMEs in canonicalization, 422and 423.Ar target_domain_list 424is a pattern-list of domains that they may resolve to. 425.Pp 426For example, 427.Qq *.a.example.com:*.b.example.com,*.c.example.com 428will allow hostnames matching 429.Qq *.a.example.com 430to be canonicalized to names in the 431.Qq *.b.example.com 432or 433.Qq *.c.example.com 434domains. 435.Pp 436A single argument of 437.Qq none 438causes no CNAMEs to be considered for canonicalization. 439This is the default behaviour. 440.It Cm CASignatureAlgorithms 441Specifies which algorithms are allowed for signing of certificates 442by certificate authorities (CAs). 443The default is: 444.Bd -literal -offset indent 445ssh-ed25519,ecdsa-sha2-nistp256, 446ecdsa-sha2-nistp384,ecdsa-sha2-nistp521, 447sk-ssh-ed25519@openssh.com, 448sk-ecdsa-sha2-nistp256@openssh.com, 449rsa-sha2-512,rsa-sha2-256 450.Ed 451.Pp 452If the specified list begins with a 453.Sq + 454character, then the specified algorithms will be appended to the default set 455instead of replacing them. 456If the specified list begins with a 457.Sq - 458character, then the specified algorithms (including wildcards) will be removed 459from the default set instead of replacing them. 460.Pp 461.Xr ssh 1 462will not accept host certificates signed using algorithms other than those 463specified. 464.It Cm CertificateFile 465Specifies a file from which the user's certificate is read. 466A corresponding private key must be provided separately in order 467to use this certificate either 468from an 469.Cm IdentityFile 470directive or 471.Fl i 472flag to 473.Xr ssh 1 , 474via 475.Xr ssh-agent 1 , 476or via a 477.Cm PKCS11Provider 478or 479.Cm SecurityKeyProvider . 480.Pp 481Arguments to 482.Cm CertificateFile 483may use the tilde syntax to refer to a user's home directory, 484the tokens described in the 485.Sx TOKENS 486section and environment variables as described in the 487.Sx ENVIRONMENT VARIABLES 488section. 489.Pp 490It is possible to have multiple certificate files specified in 491configuration files; these certificates will be tried in sequence. 492Multiple 493.Cm CertificateFile 494directives will add to the list of certificates used for 495authentication. 496.It Cm ChannelTimeout 497Specifies whether and how quickly 498.Xr ssh 1 499should close inactive channels. 500Timeouts are specified as one or more 501.Dq type=interval 502pairs separated by whitespace, where the 503.Dq type 504must be the special keyword 505.Dq global 506or a channel type name from the list below, optionally containing 507wildcard characters. 508.Pp 509The timeout value 510.Dq interval 511is specified in seconds or may use any of the units documented in the 512.Sx TIME FORMATS 513section. 514For example, 515.Dq session=5m 516would cause interactive sessions to terminate after five minutes of 517inactivity. 518Specifying a zero value disables the inactivity timeout. 519.Pp 520The special timeout 521.Dq global 522applies to all active channels, taken together. 523Traffic on any active channel will reset the timeout, but when the timeout 524expires then all open channels will be closed. 525Note that this global timeout is not matched by wildcards and must be 526specified explicitly. 527.Pp 528The available channel type names include: 529.Bl -tag -width Ds 530.It Cm agent-connection 531Open connections to 532.Xr ssh-agent 1 . 533.It Cm direct-tcpip , Cm direct-streamlocal@openssh.com 534Open TCP or Unix socket (respectively) connections that have 535been established from a 536.Xr ssh 1 537local forwarding, i.e.\& 538.Cm LocalForward 539or 540.Cm DynamicForward . 541.It Cm forwarded-tcpip , Cm forwarded-streamlocal@openssh.com 542Open TCP or Unix socket (respectively) connections that have been 543established to a 544.Xr sshd 8 545listening on behalf of a 546.Xr ssh 1 547remote forwarding, i.e.\& 548.Cm RemoteForward . 549.It Cm session 550The interactive main session, including shell session, command execution, 551.Xr scp 1 , 552.Xr sftp 1 , 553etc. 554.It Cm tun-connection 555Open 556.Cm TunnelForward 557connections. 558.It Cm x11-connection 559Open X11 forwarding sessions. 560.El 561.Pp 562Note that in all the above cases, terminating an inactive session does not 563guarantee to remove all resources associated with the session, e.g. shell 564processes or X11 clients relating to the session may continue to execute. 565.Pp 566Moreover, terminating an inactive channel or session does not necessarily 567close the SSH connection, nor does it prevent a client from 568requesting another channel of the same type. 569In particular, expiring an inactive forwarding session does not prevent 570another identical forwarding from being subsequently created. 571.Pp 572The default is not to expire channels of any type for inactivity. 573.It Cm CheckHostIP 574If set to 575.Cm yes , 576.Xr ssh 1 577will additionally check the host IP address in the 578.Pa known_hosts 579file. 580This allows it to detect if a host key changed due to DNS spoofing 581and will add addresses of destination hosts to 582.Pa ~/.ssh/known_hosts 583in the process, regardless of the setting of 584.Cm StrictHostKeyChecking . 585If the option is set to 586.Cm no 587(the default), 588the check will not be executed. 589.It Cm Ciphers 590Specifies the ciphers allowed and their order of preference. 591Multiple ciphers must be comma-separated. 592If the specified list begins with a 593.Sq + 594character, then the specified ciphers will be appended to the default set 595instead of replacing them. 596If the specified list begins with a 597.Sq - 598character, then the specified ciphers (including wildcards) will be removed 599from the default set instead of replacing them. 600If the specified list begins with a 601.Sq ^ 602character, then the specified ciphers will be placed at the head of the 603default set. 604.Pp 605The supported ciphers are: 606.Bd -literal -offset indent 6073des-cbc 608aes128-cbc 609aes192-cbc 610aes256-cbc 611aes128-ctr 612aes192-ctr 613aes256-ctr 614aes128-gcm@openssh.com 615aes256-gcm@openssh.com 616chacha20-poly1305@openssh.com 617.Ed 618.Pp 619The default is: 620.Bd -literal -offset indent 621chacha20-poly1305@openssh.com, 622aes128-gcm@openssh.com,aes256-gcm@openssh.com, 623aes128-ctr,aes192-ctr,aes256-ctr 624.Ed 625.Pp 626The list of available ciphers may also be obtained using 627.Qq ssh -Q cipher . 628.It Cm ClearAllForwardings 629Specifies that all local, remote, and dynamic port forwardings 630specified in the configuration files or on the command line be 631cleared. 632This option is primarily useful when used from the 633.Xr ssh 1 634command line to clear port forwardings set in 635configuration files, and is automatically set by 636.Xr scp 1 637and 638.Xr sftp 1 . 639The argument must be 640.Cm yes 641or 642.Cm no 643(the default). 644.It Cm Compression 645Specifies whether to use compression. 646The argument must be 647.Cm yes 648or 649.Cm no 650(the default). 651.It Cm ConnectionAttempts 652Specifies the number of tries (one per second) to make before exiting. 653The argument must be an integer. 654This may be useful in scripts if the connection sometimes fails. 655The default is 1. 656.It Cm ConnectTimeout 657Specifies the timeout (in seconds) used when connecting to the 658SSH server, instead of using the default system TCP timeout. 659This timeout is applied both to establishing the connection and to performing 660the initial SSH protocol handshake and key exchange. 661.It Cm ControlMaster 662Enables the sharing of multiple sessions over a single network connection. 663When set to 664.Cm yes , 665.Xr ssh 1 666will listen for connections on a control socket specified using the 667.Cm ControlPath 668argument. 669Additional sessions can connect to this socket using the same 670.Cm ControlPath 671with 672.Cm ControlMaster 673set to 674.Cm no 675(the default). 676These sessions will try to reuse the master instance's network connection 677rather than initiating new ones, but will fall back to connecting normally 678if the control socket does not exist, or is not listening. 679.Pp 680Setting this to 681.Cm ask 682will cause 683.Xr ssh 1 684to listen for control connections, but require confirmation using 685.Xr ssh-askpass 1 . 686If the 687.Cm ControlPath 688cannot be opened, 689.Xr ssh 1 690will continue without connecting to a master instance. 691.Pp 692X11 and 693.Xr ssh-agent 1 694forwarding is supported over these multiplexed connections, however the 695display and agent forwarded will be the one belonging to the master 696connection i.e. it is not possible to forward multiple displays or agents. 697.Pp 698Two additional options allow for opportunistic multiplexing: try to use a 699master connection but fall back to creating a new one if one does not already 700exist. 701These options are: 702.Cm auto 703and 704.Cm autoask . 705The latter requires confirmation like the 706.Cm ask 707option. 708.It Cm ControlPath 709Specify the path to the control socket used for connection sharing as described 710in the 711.Cm ControlMaster 712section above or the string 713.Cm none 714to disable connection sharing. 715Arguments to 716.Cm ControlPath 717may use the tilde syntax to refer to a user's home directory, 718the tokens described in the 719.Sx TOKENS 720section and environment variables as described in the 721.Sx ENVIRONMENT VARIABLES 722section. 723It is recommended that any 724.Cm ControlPath 725used for opportunistic connection sharing include 726at least %h, %p, and %r (or alternatively %C) and be placed in a directory 727that is not writable by other users. 728This ensures that shared connections are uniquely identified. 729.It Cm ControlPersist 730When used in conjunction with 731.Cm ControlMaster , 732specifies that the master connection should remain open 733in the background (waiting for future client connections) 734after the initial client connection has been closed. 735If set to 736.Cm no 737(the default), 738then the master connection will not be placed into the background, 739and will close as soon as the initial client connection is closed. 740If set to 741.Cm yes 742or 0, 743then the master connection will remain in the background indefinitely 744(until killed or closed via a mechanism such as the 745.Qq ssh -O exit ) . 746If set to a time in seconds, or a time in any of the formats documented in 747.Xr sshd_config 5 , 748then the backgrounded master connection will automatically terminate 749after it has remained idle (with no client connections) for the 750specified time. 751.It Cm DynamicForward 752Specifies that a TCP port on the local machine be forwarded 753over the secure channel, and the application 754protocol is then used to determine where to connect to from the 755remote machine. 756.Pp 757The argument must be 758.Sm off 759.Oo Ar bind_address : Oc Ar port . 760.Sm on 761IPv6 addresses can be specified by enclosing addresses in square brackets. 762By default, the local port is bound in accordance with the 763.Cm GatewayPorts 764setting. 765However, an explicit 766.Ar bind_address 767may be used to bind the connection to a specific address. 768The 769.Ar bind_address 770of 771.Cm localhost 772indicates that the listening port be bound for local use only, while an 773empty address or 774.Sq * 775indicates that the port should be available from all interfaces. 776.Pp 777Currently the SOCKS4 and SOCKS5 protocols are supported, and 778.Xr ssh 1 779will act as a SOCKS server. 780Multiple forwardings may be specified, and 781additional forwardings can be given on the command line. 782Only the superuser can forward privileged ports. 783.It Cm EnableEscapeCommandline 784Enables the command line option in the 785.Cm EscapeChar 786menu for interactive sessions (default 787.Ql ~C ) . 788By default, the command line is disabled. 789.It Cm EnableSSHKeysign 790Setting this option to 791.Cm yes 792in the global client configuration file 793.Pa /etc/ssh/ssh_config 794enables the use of the helper program 795.Xr ssh-keysign 8 796during 797.Cm HostbasedAuthentication . 798The argument must be 799.Cm yes 800or 801.Cm no 802(the default). 803This option should be placed in the non-hostspecific section. 804See 805.Xr ssh-keysign 8 806for more information. 807.It Cm EscapeChar 808Sets the escape character (default: 809.Ql ~ ) . 810The escape character can also 811be set on the command line. 812The argument should be a single character, 813.Ql ^ 814followed by a letter, or 815.Cm none 816to disable the escape 817character entirely (making the connection transparent for binary 818data). 819.It Cm ExitOnForwardFailure 820Specifies whether 821.Xr ssh 1 822should terminate the connection if it cannot set up all requested 823dynamic, tunnel, local, and remote port forwardings, (e.g.\& 824if either end is unable to bind and listen on a specified port). 825Note that 826.Cm ExitOnForwardFailure 827does not apply to connections made over port forwardings and will not, 828for example, cause 829.Xr ssh 1 830to exit if TCP connections to the ultimate forwarding destination fail. 831The argument must be 832.Cm yes 833or 834.Cm no 835(the default). 836.It Cm FingerprintHash 837Specifies the hash algorithm used when displaying key fingerprints. 838Valid options are: 839.Cm md5 840and 841.Cm sha256 842(the default). 843.It Cm ForkAfterAuthentication 844Requests 845.Nm ssh 846to go to background just before command execution. 847This is useful if 848.Nm ssh 849is going to ask for passwords or passphrases, but the user 850wants it in the background. 851This implies the 852.Cm StdinNull 853configuration option being set to 854.Dq yes . 855The recommended way to start X11 programs at a remote site is with 856something like 857.Ic ssh -f host xterm , 858which is the same as 859.Ic ssh host xterm 860if the 861.Cm ForkAfterAuthentication 862configuration option is set to 863.Dq yes . 864.Pp 865If the 866.Cm ExitOnForwardFailure 867configuration option is set to 868.Dq yes , 869then a client started with the 870.Cm ForkAfterAuthentication 871configuration option being set to 872.Dq yes 873will wait for all remote port forwards to be successfully established 874before placing itself in the background. 875The argument to this keyword must be 876.Cm yes 877(same as the 878.Fl f 879option) or 880.Cm no 881(the default). 882.It Cm ForwardAgent 883Specifies whether the connection to the authentication agent (if any) 884will be forwarded to the remote machine. 885The argument may be 886.Cm yes , 887.Cm no 888(the default), 889an explicit path to an agent socket or the name of an environment variable 890(beginning with 891.Sq $ ) 892in which to find the path. 893.Pp 894Agent forwarding should be enabled with caution. 895Users with the ability to bypass file permissions on the remote host 896(for the agent's Unix-domain socket) 897can access the local agent through the forwarded connection. 898An attacker cannot obtain key material from the agent, 899however they can perform operations on the keys that enable them to 900authenticate using the identities loaded into the agent. 901.It Cm ForwardX11 902Specifies whether X11 connections will be automatically redirected 903over the secure channel and 904.Ev DISPLAY 905set. 906The argument must be 907.Cm yes 908or 909.Cm no 910(the default). 911.Pp 912X11 forwarding should be enabled with caution. 913Users with the ability to bypass file permissions on the remote host 914(for the user's X11 authorization database) 915can access the local X11 display through the forwarded connection. 916An attacker may then be able to perform activities such as keystroke monitoring 917if the 918.Cm ForwardX11Trusted 919option is also enabled. 920.It Cm ForwardX11Timeout 921Specify a timeout for untrusted X11 forwarding 922using the format described in the 923.Sx TIME FORMATS 924section of 925.Xr sshd_config 5 . 926X11 connections received by 927.Xr ssh 1 928after this time will be refused. 929Setting 930.Cm ForwardX11Timeout 931to zero will disable the timeout and permit X11 forwarding for the life 932of the connection. 933The default is to disable untrusted X11 forwarding after twenty minutes has 934elapsed. 935.It Cm ForwardX11Trusted 936If this option is set to 937.Cm yes , 938remote X11 clients will have full access to the original X11 display. 939.Pp 940If this option is set to 941.Cm no 942(the default), 943remote X11 clients will be considered untrusted and prevented 944from stealing or tampering with data belonging to trusted X11 945clients. 946Furthermore, the 947.Xr xauth 1 948token used for the session will be set to expire after 20 minutes. 949Remote clients will be refused access after this time. 950.Pp 951See the X11 SECURITY extension specification for full details on 952the restrictions imposed on untrusted clients. 953.It Cm GatewayPorts 954Specifies whether remote hosts are allowed to connect to local 955forwarded ports. 956By default, 957.Xr ssh 1 958binds local port forwardings to the loopback address. 959This prevents other remote hosts from connecting to forwarded ports. 960.Cm GatewayPorts 961can be used to specify that ssh 962should bind local port forwardings to the wildcard address, 963thus allowing remote hosts to connect to forwarded ports. 964The argument must be 965.Cm yes 966or 967.Cm no 968(the default). 969.It Cm GlobalKnownHostsFile 970Specifies one or more files to use for the global 971host key database, separated by whitespace. 972The default is 973.Pa /etc/ssh/ssh_known_hosts , 974.Pa /etc/ssh/ssh_known_hosts2 . 975.It Cm GSSAPIAuthentication 976Specifies whether user authentication based on GSSAPI is allowed. 977The default is 978.Cm no . 979.It Cm GSSAPIDelegateCredentials 980Forward (delegate) credentials to the server. 981The default is 982.Cm no . 983.It Cm HashKnownHosts 984Indicates that 985.Xr ssh 1 986should hash host names and addresses when they are added to 987.Pa ~/.ssh/known_hosts . 988These hashed names may be used normally by 989.Xr ssh 1 990and 991.Xr sshd 8 , 992but they do not visually reveal identifying information if the 993file's contents are disclosed. 994The default is 995.Cm no . 996Note that existing names and addresses in known hosts files 997will not be converted automatically, 998but may be manually hashed using 999.Xr ssh-keygen 1 . 1000.It Cm HostbasedAcceptedAlgorithms 1001Specifies the signature algorithms that will be used for hostbased 1002authentication as a comma-separated list of patterns. 1003Alternately if the specified list begins with a 1004.Sq + 1005character, then the specified signature algorithms will be appended 1006to the default set instead of replacing them. 1007If the specified list begins with a 1008.Sq - 1009character, then the specified signature algorithms (including wildcards) 1010will be removed from the default set instead of replacing them. 1011If the specified list begins with a 1012.Sq ^ 1013character, then the specified signature algorithms will be placed 1014at the head of the default set. 1015The default for this option is: 1016.Bd -literal -offset 3n 1017ssh-ed25519-cert-v01@openssh.com, 1018ecdsa-sha2-nistp256-cert-v01@openssh.com, 1019ecdsa-sha2-nistp384-cert-v01@openssh.com, 1020ecdsa-sha2-nistp521-cert-v01@openssh.com, 1021sk-ssh-ed25519-cert-v01@openssh.com, 1022sk-ecdsa-sha2-nistp256-cert-v01@openssh.com, 1023rsa-sha2-512-cert-v01@openssh.com, 1024rsa-sha2-256-cert-v01@openssh.com, 1025ssh-ed25519, 1026ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521, 1027sk-ssh-ed25519@openssh.com, 1028sk-ecdsa-sha2-nistp256@openssh.com, 1029rsa-sha2-512,rsa-sha2-256 1030.Ed 1031.Pp 1032The 1033.Fl Q 1034option of 1035.Xr ssh 1 1036may be used to list supported signature algorithms. 1037This was formerly named HostbasedKeyTypes. 1038.It Cm HostbasedAuthentication 1039Specifies whether to try rhosts based authentication with public key 1040authentication. 1041The argument must be 1042.Cm yes 1043or 1044.Cm no 1045(the default). 1046.It Cm HostKeyAlgorithms 1047Specifies the host key signature algorithms 1048that the client wants to use in order of preference. 1049Alternately if the specified list begins with a 1050.Sq + 1051character, then the specified signature algorithms will be appended to 1052the default set instead of replacing them. 1053If the specified list begins with a 1054.Sq - 1055character, then the specified signature algorithms (including wildcards) 1056will be removed from the default set instead of replacing them. 1057If the specified list begins with a 1058.Sq ^ 1059character, then the specified signature algorithms will be placed 1060at the head of the default set. 1061The default for this option is: 1062.Bd -literal -offset 3n 1063ssh-ed25519-cert-v01@openssh.com, 1064ecdsa-sha2-nistp256-cert-v01@openssh.com, 1065ecdsa-sha2-nistp384-cert-v01@openssh.com, 1066ecdsa-sha2-nistp521-cert-v01@openssh.com, 1067sk-ssh-ed25519-cert-v01@openssh.com, 1068sk-ecdsa-sha2-nistp256-cert-v01@openssh.com, 1069rsa-sha2-512-cert-v01@openssh.com, 1070rsa-sha2-256-cert-v01@openssh.com, 1071ssh-ed25519, 1072ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521, 1073sk-ecdsa-sha2-nistp256@openssh.com, 1074sk-ssh-ed25519@openssh.com, 1075rsa-sha2-512,rsa-sha2-256 1076.Ed 1077.Pp 1078If hostkeys are known for the destination host then this default is modified 1079to prefer their algorithms. 1080.Pp 1081The list of available signature algorithms may also be obtained using 1082.Qq ssh -Q HostKeyAlgorithms . 1083.It Cm HostKeyAlias 1084Specifies an alias that should be used instead of the 1085real host name when looking up or saving the host key 1086in the host key database files and when validating host certificates. 1087This option is useful for tunneling SSH connections 1088or for multiple servers running on a single host. 1089.It Cm Hostname 1090Specifies the real host name to log into. 1091This can be used to specify nicknames or abbreviations for hosts. 1092Arguments to 1093.Cm Hostname 1094accept the tokens described in the 1095.Sx TOKENS 1096section. 1097Numeric IP addresses are also permitted (both on the command line and in 1098.Cm Hostname 1099specifications). 1100The default is the name given on the command line. 1101.It Cm IdentitiesOnly 1102Specifies that 1103.Xr ssh 1 1104should only use the configured authentication identity and certificate files 1105(either the default files, or those explicitly configured in the 1106.Nm 1107files 1108or passed on the 1109.Xr ssh 1 1110command-line), 1111even if 1112.Xr ssh-agent 1 1113or a 1114.Cm PKCS11Provider 1115or 1116.Cm SecurityKeyProvider 1117offers more identities. 1118The argument to this keyword must be 1119.Cm yes 1120or 1121.Cm no 1122(the default). 1123This option is intended for situations where ssh-agent 1124offers many different identities. 1125.It Cm IdentityAgent 1126Specifies the 1127.Ux Ns -domain 1128socket used to communicate with the authentication agent. 1129.Pp 1130This option overrides the 1131.Ev SSH_AUTH_SOCK 1132environment variable and can be used to select a specific agent. 1133Setting the socket name to 1134.Cm none 1135disables the use of an authentication agent. 1136If the string 1137.Qq SSH_AUTH_SOCK 1138is specified, the location of the socket will be read from the 1139.Ev SSH_AUTH_SOCK 1140environment variable. 1141Otherwise if the specified value begins with a 1142.Sq $ 1143character, then it will be treated as an environment variable containing 1144the location of the socket. 1145.Pp 1146Arguments to 1147.Cm IdentityAgent 1148may use the tilde syntax to refer to a user's home directory, 1149the tokens described in the 1150.Sx TOKENS 1151section and environment variables as described in the 1152.Sx ENVIRONMENT VARIABLES 1153section. 1154.It Cm IdentityFile 1155Specifies a file from which the user's ECDSA, authenticator-hosted ECDSA, 1156Ed25519, authenticator-hosted Ed25519 or RSA authentication identity is read. 1157You can also specify a public key file to use the corresponding 1158private key that is loaded in 1159.Xr ssh-agent 1 1160when the private key file is not present locally. 1161The default is 1162.Pa ~/.ssh/id_rsa , 1163.Pa ~/.ssh/id_ecdsa , 1164.Pa ~/.ssh/id_ecdsa_sk , 1165.Pa ~/.ssh/id_ed25519 1166and 1167.Pa ~/.ssh/id_ed25519_sk . 1168Additionally, any identities represented by the authentication agent 1169will be used for authentication unless 1170.Cm IdentitiesOnly 1171is set. 1172If no certificates have been explicitly specified by 1173.Cm CertificateFile , 1174.Xr ssh 1 1175will try to load certificate information from the filename obtained by 1176appending 1177.Pa -cert.pub 1178to the path of a specified 1179.Cm IdentityFile . 1180.Pp 1181Arguments to 1182.Cm IdentityFile 1183may use the tilde syntax to refer to a user's home directory 1184or the tokens described in the 1185.Sx TOKENS 1186section. 1187Alternately an argument of 1188.Cm none 1189may be used to indicate no identity files should be loaded. 1190.Pp 1191It is possible to have 1192multiple identity files specified in configuration files; all these 1193identities will be tried in sequence. 1194Multiple 1195.Cm IdentityFile 1196directives will add to the list of identities tried (this behaviour 1197differs from that of other configuration directives). 1198.Pp 1199.Cm IdentityFile 1200may be used in conjunction with 1201.Cm IdentitiesOnly 1202to select which identities in an agent are offered during authentication. 1203.Cm IdentityFile 1204may also be used in conjunction with 1205.Cm CertificateFile 1206in order to provide any certificate also needed for authentication with 1207the identity. 1208.It Cm IgnoreUnknown 1209Specifies a pattern-list of unknown options to be ignored if they are 1210encountered in configuration parsing. 1211This may be used to suppress errors if 1212.Nm 1213contains options that are unrecognised by 1214.Xr ssh 1 . 1215It is recommended that 1216.Cm IgnoreUnknown 1217be listed early in the configuration file as it will not be applied 1218to unknown options that appear before it. 1219.It Cm Include 1220Include the specified configuration file(s). 1221Multiple pathnames may be specified and each pathname may contain 1222.Xr glob 7 1223wildcards, 1224tokens as described in the 1225.Sx TOKENS 1226section, environment variables as described in the 1227.Sx ENVIRONMENT VARIABLES 1228section and, for user configurations, shell-like 1229.Sq ~ 1230references to user home directories. 1231Wildcards will be expanded and processed in lexical order. 1232Files without absolute paths are assumed to be in 1233.Pa ~/.ssh 1234if included in a user configuration file or 1235.Pa /etc/ssh 1236if included from the system configuration file. 1237.Cm Include 1238directive may appear inside a 1239.Cm Match 1240or 1241.Cm Host 1242block 1243to perform conditional inclusion. 1244.It Cm IPQoS 1245Specifies the IPv4 type-of-service or DSCP class for connections. 1246Accepted values are 1247.Cm af11 , 1248.Cm af12 , 1249.Cm af13 , 1250.Cm af21 , 1251.Cm af22 , 1252.Cm af23 , 1253.Cm af31 , 1254.Cm af32 , 1255.Cm af33 , 1256.Cm af41 , 1257.Cm af42 , 1258.Cm af43 , 1259.Cm cs0 , 1260.Cm cs1 , 1261.Cm cs2 , 1262.Cm cs3 , 1263.Cm cs4 , 1264.Cm cs5 , 1265.Cm cs6 , 1266.Cm cs7 , 1267.Cm ef , 1268.Cm le , 1269.Cm lowdelay , 1270.Cm throughput , 1271.Cm reliability , 1272a numeric value, or 1273.Cm none 1274to use the operating system default. 1275This option may take one or two arguments, separated by whitespace. 1276If one argument is specified, it is used as the packet class unconditionally. 1277If two values are specified, the first is automatically selected for 1278interactive sessions and the second for non-interactive sessions. 1279The default is 1280.Cm af21 1281(Low-Latency Data) 1282for interactive sessions and 1283.Cm cs1 1284(Lower Effort) 1285for non-interactive sessions. 1286.It Cm KbdInteractiveAuthentication 1287Specifies whether to use keyboard-interactive authentication. 1288The argument to this keyword must be 1289.Cm yes 1290(the default) 1291or 1292.Cm no . 1293.Cm ChallengeResponseAuthentication 1294is a deprecated alias for this. 1295.It Cm KbdInteractiveDevices 1296Specifies the list of methods to use in keyboard-interactive authentication. 1297Multiple method names must be comma-separated. 1298The default is to use the server specified list. 1299The methods available vary depending on what the server supports. 1300For an OpenSSH server, 1301it may be zero or more of: 1302.Cm bsdauth 1303and 1304.Cm pam . 1305.It Cm KexAlgorithms 1306Specifies the permitted KEX (Key Exchange) algorithms that will be used and 1307their preference order. 1308The selected algorithm will be the first algorithm in this list that 1309the server also supports. 1310Multiple algorithms must be comma-separated. 1311.Pp 1312If the specified list begins with a 1313.Sq + 1314character, then the specified algorithms will be appended to the default set 1315instead of replacing them. 1316If the specified list begins with a 1317.Sq - 1318character, then the specified algorithms (including wildcards) will be removed 1319from the default set instead of replacing them. 1320If the specified list begins with a 1321.Sq ^ 1322character, then the specified algorithms will be placed at the head of the 1323default set. 1324.Pp 1325The default is: 1326.Bd -literal -offset indent 1327mlkem768x25519-sha256, 1328sntrup761x25519-sha512,sntrup761x25519-sha512@openssh.com, 1329curve25519-sha256,curve25519-sha256@libssh.org, 1330ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521, 1331diffie-hellman-group-exchange-sha256, 1332diffie-hellman-group16-sha512, 1333diffie-hellman-group18-sha512, 1334diffie-hellman-group14-sha256 1335.Ed 1336.Pp 1337The list of supported key exchange algorithms may also be obtained using 1338.Qq ssh -Q kex . 1339.It Cm KnownHostsCommand 1340Specifies a command to use to obtain a list of host keys, in addition to 1341those listed in 1342.Cm UserKnownHostsFile 1343and 1344.Cm GlobalKnownHostsFile . 1345This command is executed after the files have been read. 1346It may write host key lines to standard output in identical format to the 1347usual files (described in the 1348.Sx VERIFYING HOST KEYS 1349section in 1350.Xr ssh 1 ) . 1351Arguments to 1352.Cm KnownHostsCommand 1353accept the tokens described in the 1354.Sx TOKENS 1355section. 1356The command may be invoked multiple times per connection: once when preparing 1357the preference list of host key algorithms to use, again to obtain the 1358host key for the requested host name and, if 1359.Cm CheckHostIP 1360is enabled, one more time to obtain the host key matching the server's 1361address. 1362If the command exits abnormally or returns a non-zero exit status then the 1363connection is terminated. 1364.It Cm LocalCommand 1365Specifies a command to execute on the local machine after successfully 1366connecting to the server. 1367The command string extends to the end of the line, and is executed with 1368the user's shell. 1369Arguments to 1370.Cm LocalCommand 1371accept the tokens described in the 1372.Sx TOKENS 1373section. 1374.Pp 1375The command is run synchronously and does not have access to the 1376session of the 1377.Xr ssh 1 1378that spawned it. 1379It should not be used for interactive commands. 1380.Pp 1381This directive is ignored unless 1382.Cm PermitLocalCommand 1383has been enabled. 1384.It Cm LocalForward 1385Specifies that a TCP port or Unix-domain socket on the local machine 1386be forwarded over 1387the secure channel to the specified host and port (or Unix-domain socket) 1388from the remote machine. 1389For a TCP port, the first argument must be 1390.Sm off 1391.Oo Ar bind_address : Oc Ar port 1392.Sm on 1393or a Unix domain socket path. 1394The second argument is the destination and may be 1395.Ar host : Ns Ar hostport 1396or a Unix domain socket path if the remote host supports it. 1397.Pp 1398IPv6 addresses can be specified by enclosing addresses in square brackets. 1399.Pp 1400If either argument contains a '/' in it, that argument will be 1401interpreted as a Unix-domain socket (on the corresponding host) rather 1402than a TCP port. 1403.Pp 1404Multiple forwardings may be specified, and additional forwardings can be 1405given on the command line. 1406Only the superuser can forward privileged ports. 1407By default, the local port is bound in accordance with the 1408.Cm GatewayPorts 1409setting. 1410However, an explicit 1411.Ar bind_address 1412may be used to bind the connection to a specific address. 1413The 1414.Ar bind_address 1415of 1416.Cm localhost 1417indicates that the listening port be bound for local use only, while an 1418empty address or 1419.Sq * 1420indicates that the port should be available from all interfaces. 1421Unix domain socket paths may use the tokens described in the 1422.Sx TOKENS 1423section and environment variables as described in the 1424.Sx ENVIRONMENT VARIABLES 1425section. 1426.It Cm LogLevel 1427Gives the verbosity level that is used when logging messages from 1428.Xr ssh 1 . 1429The possible values are: 1430QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. 1431The default is INFO. 1432DEBUG and DEBUG1 are equivalent. 1433DEBUG2 and DEBUG3 each specify higher levels of verbose output. 1434.It Cm LogVerbose 1435Specify one or more overrides to LogLevel. 1436An override consists of one or more pattern lists that matches the 1437source file, function and line number to force detailed logging for. 1438For example, an override pattern of: 1439.Bd -literal -offset indent 1440kex.c:*:1000,*:kex_exchange_identification():*,packet.c:* 1441.Ed 1442.Pp 1443would enable detailed logging for line 1000 of 1444.Pa kex.c , 1445everything in the 1446.Fn kex_exchange_identification 1447function, and all code in the 1448.Pa packet.c 1449file. 1450This option is intended for debugging and no overrides are enabled by default. 1451.It Cm MACs 1452Specifies the MAC (message authentication code) algorithms 1453in order of preference. 1454The MAC algorithm is used for data integrity protection. 1455Multiple algorithms must be comma-separated. 1456If the specified list begins with a 1457.Sq + 1458character, then the specified algorithms will be appended to the default set 1459instead of replacing them. 1460If the specified list begins with a 1461.Sq - 1462character, then the specified algorithms (including wildcards) will be removed 1463from the default set instead of replacing them. 1464If the specified list begins with a 1465.Sq ^ 1466character, then the specified algorithms will be placed at the head of the 1467default set. 1468.Pp 1469The algorithms that contain 1470.Qq -etm 1471calculate the MAC after encryption (encrypt-then-mac). 1472These are considered safer and their use recommended. 1473.Pp 1474The default is: 1475.Bd -literal -offset indent 1476umac-64-etm@openssh.com,umac-128-etm@openssh.com, 1477hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com, 1478hmac-sha1-etm@openssh.com, 1479umac-64@openssh.com,umac-128@openssh.com, 1480hmac-sha2-256,hmac-sha2-512,hmac-sha1 1481.Ed 1482.Pp 1483The list of available MAC algorithms may also be obtained using 1484.Qq ssh -Q mac . 1485.It Cm NoHostAuthenticationForLocalhost 1486Disable host authentication for localhost (loopback addresses). 1487The argument to this keyword must be 1488.Cm yes 1489or 1490.Cm no 1491(the default). 1492.It Cm NumberOfPasswordPrompts 1493Specifies the number of password prompts before giving up. 1494The argument to this keyword must be an integer. 1495The default is 3. 1496.It Cm ObscureKeystrokeTiming 1497Specifies whether 1498.Xr ssh 1 1499should try to obscure inter-keystroke timings from passive observers of 1500network traffic. 1501If enabled, then for interactive sessions, 1502.Xr ssh 1 1503will send keystrokes at fixed intervals of a few tens of milliseconds 1504and will send fake keystroke packets for some time after typing ceases. 1505The argument to this keyword must be 1506.Cm yes , 1507.Cm no 1508or an interval specifier of the form 1509.Cm interval:milliseconds 1510(e.g.\& 1511.Cm interval:80 1512for 80 milliseconds). 1513The default is to obscure keystrokes using a 20ms packet interval. 1514Note that smaller intervals will result in higher fake keystroke packet rates. 1515.It Cm PasswordAuthentication 1516Specifies whether to use password authentication. 1517The argument to this keyword must be 1518.Cm yes 1519(the default) 1520or 1521.Cm no . 1522.It Cm PermitLocalCommand 1523Allow local command execution via the 1524.Ic LocalCommand 1525option or using the 1526.Ic !\& Ns Ar command 1527escape sequence in 1528.Xr ssh 1 . 1529The argument must be 1530.Cm yes 1531or 1532.Cm no 1533(the default). 1534.It Cm PermitRemoteOpen 1535Specifies the destinations to which remote TCP port forwarding is permitted when 1536.Cm RemoteForward 1537is used as a SOCKS proxy. 1538The forwarding specification must be one of the following forms: 1539.Pp 1540.Bl -item -offset indent -compact 1541.It 1542.Cm PermitRemoteOpen 1543.Sm off 1544.Ar host : port 1545.Sm on 1546.It 1547.Cm PermitRemoteOpen 1548.Sm off 1549.Ar IPv4_addr : port 1550.Sm on 1551.It 1552.Cm PermitRemoteOpen 1553.Sm off 1554.Ar \&[ IPv6_addr \&] : port 1555.Sm on 1556.El 1557.Pp 1558Multiple forwards may be specified by separating them with whitespace. 1559An argument of 1560.Cm any 1561can be used to remove all restrictions and permit any forwarding requests. 1562An argument of 1563.Cm none 1564can be used to prohibit all forwarding requests. 1565The wildcard 1566.Sq * 1567can be used for host or port to allow all hosts or ports respectively. 1568Otherwise, no pattern matching or address lookups are performed on supplied 1569names. 1570.It Cm PKCS11Provider 1571Specifies which PKCS#11 provider to use or 1572.Cm none 1573to indicate that no provider should be used (the default). 1574The argument to this keyword is a path to the PKCS#11 shared library 1575.Xr ssh 1 1576should use to communicate with a PKCS#11 token providing keys for user 1577authentication. 1578.It Cm Port 1579Specifies the port number to connect on the remote host. 1580The default is 22. 1581.It Cm PreferredAuthentications 1582Specifies the order in which the client should try authentication methods. 1583This allows a client to prefer one method (e.g.\& 1584.Cm keyboard-interactive ) 1585over another method (e.g.\& 1586.Cm password ) . 1587The default is: 1588.Bd -literal -offset indent 1589gssapi-with-mic,hostbased,publickey, 1590keyboard-interactive,password 1591.Ed 1592.It Cm ProxyCommand 1593Specifies the command to use to connect to the server. 1594The command 1595string extends to the end of the line, and is executed 1596using the user's shell 1597.Ql exec 1598directive to avoid a lingering shell process. 1599.Pp 1600Arguments to 1601.Cm ProxyCommand 1602accept the tokens described in the 1603.Sx TOKENS 1604section. 1605The command can be basically anything, 1606and should read from its standard input and write to its standard output. 1607It should eventually connect an 1608.Xr sshd 8 1609server running on some machine, or execute 1610.Ic sshd -i 1611somewhere. 1612Host key management will be done using the 1613.Cm Hostname 1614of the host being connected (defaulting to the name typed by the user). 1615Setting the command to 1616.Cm none 1617disables this option entirely. 1618Note that 1619.Cm CheckHostIP 1620is not available for connects with a proxy command. 1621.Pp 1622This directive is useful in conjunction with 1623.Xr nc 1 1624and its proxy support. 1625For example, the following directive would connect via an HTTP proxy at 1626192.0.2.0: 1627.Bd -literal -offset 3n 1628ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p 1629.Ed 1630.It Cm ProxyJump 1631Specifies one or more jump proxies as either 1632.Sm off 1633.Op Ar user No @ 1634.Ar host 1635.Op : Ns Ar port 1636.Sm on 1637or an ssh URI. 1638Multiple proxies may be separated by comma characters and will be visited 1639sequentially. 1640Setting this option will cause 1641.Xr ssh 1 1642to connect to the target host by first making a 1643.Xr ssh 1 1644connection to the specified 1645.Cm ProxyJump 1646host and then establishing a 1647TCP forwarding to the ultimate target from there. 1648Setting the host to 1649.Cm none 1650disables this option entirely. 1651.Pp 1652Note that this option will compete with the 1653.Cm ProxyCommand 1654option - whichever is specified first will prevent later instances of the 1655other from taking effect. 1656.Pp 1657Note also that the configuration for the destination host (either supplied 1658via the command-line or the configuration file) is not generally applied 1659to jump hosts. 1660.Pa ~/.ssh/config 1661should be used if specific configuration is required for jump hosts. 1662.It Cm ProxyUseFdpass 1663Specifies that 1664.Cm ProxyCommand 1665will pass a connected file descriptor back to 1666.Xr ssh 1 1667instead of continuing to execute and pass data. 1668The default is 1669.Cm no . 1670.It Cm PubkeyAcceptedAlgorithms 1671Specifies the signature algorithms that will be used for public key 1672authentication as a comma-separated list of patterns. 1673If the specified list begins with a 1674.Sq + 1675character, then the algorithms after it will be appended to the default 1676instead of replacing it. 1677If the specified list begins with a 1678.Sq - 1679character, then the specified algorithms (including wildcards) will be removed 1680from the default set instead of replacing them. 1681If the specified list begins with a 1682.Sq ^ 1683character, then the specified algorithms will be placed at the head of the 1684default set. 1685The default for this option is: 1686.Bd -literal -offset 3n 1687ssh-ed25519-cert-v01@openssh.com, 1688ecdsa-sha2-nistp256-cert-v01@openssh.com, 1689ecdsa-sha2-nistp384-cert-v01@openssh.com, 1690ecdsa-sha2-nistp521-cert-v01@openssh.com, 1691sk-ssh-ed25519-cert-v01@openssh.com, 1692sk-ecdsa-sha2-nistp256-cert-v01@openssh.com, 1693rsa-sha2-512-cert-v01@openssh.com, 1694rsa-sha2-256-cert-v01@openssh.com, 1695ssh-ed25519, 1696ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521, 1697sk-ssh-ed25519@openssh.com, 1698sk-ecdsa-sha2-nistp256@openssh.com, 1699rsa-sha2-512,rsa-sha2-256 1700.Ed 1701.Pp 1702The list of available signature algorithms may also be obtained using 1703.Qq ssh -Q PubkeyAcceptedAlgorithms . 1704.It Cm PubkeyAuthentication 1705Specifies whether to try public key authentication. 1706The argument to this keyword must be 1707.Cm yes 1708(the default), 1709.Cm no , 1710.Cm unbound 1711or 1712.Cm host-bound . 1713The final two options enable public key authentication while respectively 1714disabling or enabling the OpenSSH host-bound authentication protocol 1715extension required for restricted 1716.Xr ssh-agent 1 1717forwarding. 1718.It Cm RekeyLimit 1719Specifies the maximum amount of data that may be transmitted or received 1720before the session key is renegotiated, optionally followed by a maximum 1721amount of time that may pass before the session key is renegotiated. 1722The first argument is specified in bytes and may have a suffix of 1723.Sq K , 1724.Sq M , 1725or 1726.Sq G 1727to indicate Kilobytes, Megabytes, or Gigabytes, respectively. 1728The default is between 1729.Sq 1G 1730and 1731.Sq 4G , 1732depending on the cipher. 1733The optional second value is specified in seconds and may use any of the 1734units documented in the TIME FORMATS section of 1735.Xr sshd_config 5 . 1736The default value for 1737.Cm RekeyLimit 1738is 1739.Cm default none , 1740which means that rekeying is performed after the cipher's default amount 1741of data has been sent or received and no time based rekeying is done. 1742.It Cm RemoteCommand 1743Specifies a command to execute on the remote machine after successfully 1744connecting to the server. 1745The command string extends to the end of the line, and is executed with 1746the user's shell. 1747Arguments to 1748.Cm RemoteCommand 1749accept the tokens described in the 1750.Sx TOKENS 1751section. 1752.It Cm RemoteForward 1753Specifies that a TCP port or Unix-domain socket on the remote machine 1754be forwarded over the secure channel. 1755The remote port may either be forwarded to a specified host and port 1756or Unix-domain socket 1757from the local machine, or may act as a SOCKS 4/5 proxy that allows a remote 1758client to connect to arbitrary destinations from the local machine. 1759The first argument is the listening specification and may be 1760.Sm off 1761.Oo Ar bind_address : Oc Ar port 1762.Sm on 1763or, if the remote host supports it, a Unix domain socket path. 1764If forwarding to a specific destination then the second argument must be 1765.Ar host : Ns Ar hostport 1766or a Unix domain socket path, 1767otherwise if no destination argument is specified then the remote forwarding 1768will be established as a SOCKS proxy. 1769When acting as a SOCKS proxy, the destination of the connection can be 1770restricted by 1771.Cm PermitRemoteOpen . 1772.Pp 1773IPv6 addresses can be specified by enclosing addresses in square brackets. 1774.Pp 1775If either argument contains a '/' in it, that argument will be 1776interpreted as a Unix-domain socket (on the corresponding host) rather 1777than a TCP port. 1778.Pp 1779Multiple forwardings may be specified, and additional 1780forwardings can be given on the command line. 1781Privileged ports can be forwarded only when 1782logging in as root on the remote machine. 1783Unix domain socket paths may use the tokens described in the 1784.Sx TOKENS 1785section and environment variables as described in the 1786.Sx ENVIRONMENT VARIABLES 1787section. 1788.Pp 1789If the 1790.Ar port 1791argument is 0, 1792the listen port will be dynamically allocated on the server and reported 1793to the client at run time. 1794.Pp 1795If the 1796.Ar bind_address 1797is not specified, the default is to only bind to loopback addresses. 1798If the 1799.Ar bind_address 1800is 1801.Ql * 1802or an empty string, then the forwarding is requested to listen on all 1803interfaces. 1804Specifying a remote 1805.Ar bind_address 1806will only succeed if the server's 1807.Cm GatewayPorts 1808option is enabled (see 1809.Xr sshd_config 5 ) . 1810.It Cm RequestTTY 1811Specifies whether to request a pseudo-tty for the session. 1812The argument may be one of: 1813.Cm no 1814(never request a TTY), 1815.Cm yes 1816(always request a TTY when standard input is a TTY), 1817.Cm force 1818(always request a TTY) or 1819.Cm auto 1820(request a TTY when opening a login session). 1821This option mirrors the 1822.Fl t 1823and 1824.Fl T 1825flags for 1826.Xr ssh 1 . 1827.It Cm RequiredRSASize 1828Specifies the minimum RSA key size (in bits) that 1829.Xr ssh 1 1830will accept. 1831User authentication keys smaller than this limit will be ignored. 1832Servers that present host keys smaller than this limit will cause the 1833connection to be terminated. 1834The default is 1835.Cm 1024 1836bits. 1837Note that this limit may only be raised from the default. 1838.It Cm RevokedHostKeys 1839Specifies revoked host public keys. 1840Keys listed in this file will be refused for host authentication. 1841Note that if this file does not exist or is not readable, 1842then host authentication will be refused for all hosts. 1843Keys may be specified as a text file, listing one public key per line, or as 1844an OpenSSH Key Revocation List (KRL) as generated by 1845.Xr ssh-keygen 1 . 1846For more information on KRLs, see the KEY REVOCATION LISTS section in 1847.Xr ssh-keygen 1 . 1848Arguments to 1849.Cm RevokedHostKeys 1850may use the tilde syntax to refer to a user's home directory, 1851the tokens described in the 1852.Sx TOKENS 1853section and environment variables as described in the 1854.Sx ENVIRONMENT VARIABLES 1855section. 1856.It Cm SecurityKeyProvider 1857Specifies a path to a library that will be used when loading any 1858FIDO authenticator-hosted keys, overriding the default of using 1859the built-in USB HID support. 1860.Pp 1861If the specified value begins with a 1862.Sq $ 1863character, then it will be treated as an environment variable containing 1864the path to the library. 1865.It Cm SendEnv 1866Specifies what variables from the local 1867.Xr environ 7 1868should be sent to the server. 1869The server must also support it, and the server must be configured to 1870accept these environment variables. 1871Note that the 1872.Ev TERM 1873environment variable is always sent whenever a 1874pseudo-terminal is requested as it is required by the protocol. 1875Refer to 1876.Cm AcceptEnv 1877in 1878.Xr sshd_config 5 1879for how to configure the server. 1880Variables are specified by name, which may contain wildcard characters. 1881Multiple environment variables may be separated by whitespace or spread 1882across multiple 1883.Cm SendEnv 1884directives. 1885.Pp 1886See 1887.Sx PATTERNS 1888for more information on patterns. 1889.Pp 1890It is possible to clear previously set 1891.Cm SendEnv 1892variable names by prefixing patterns with 1893.Pa - . 1894The default is not to send any environment variables. 1895.It Cm ServerAliveCountMax 1896Sets the number of server alive messages (see below) which may be 1897sent without 1898.Xr ssh 1 1899receiving any messages back from the server. 1900If this threshold is reached while server alive messages are being sent, 1901ssh will disconnect from the server, terminating the session. 1902It is important to note that the use of server alive messages is very 1903different from 1904.Cm TCPKeepAlive 1905(below). 1906The server alive messages are sent through the encrypted channel 1907and therefore will not be spoofable. 1908The TCP keepalive option enabled by 1909.Cm TCPKeepAlive 1910is spoofable. 1911The server alive mechanism is valuable when the client or 1912server depend on knowing when a connection has become unresponsive. 1913.Pp 1914The default value is 3. 1915If, for example, 1916.Cm ServerAliveInterval 1917(see below) is set to 15 and 1918.Cm ServerAliveCountMax 1919is left at the default, if the server becomes unresponsive, 1920ssh will disconnect after approximately 45 seconds. 1921.It Cm ServerAliveInterval 1922Sets a timeout interval in seconds after which if no data has been received 1923from the server, 1924.Xr ssh 1 1925will send a message through the encrypted 1926channel to request a response from the server. 1927The default 1928is 0, indicating that these messages will not be sent to the server. 1929.It Cm SessionType 1930May be used to either request invocation of a subsystem on the remote system, 1931or to prevent the execution of a remote command at all. 1932The latter is useful for just forwarding ports. 1933The argument to this keyword must be 1934.Cm none 1935(same as the 1936.Fl N 1937option), 1938.Cm subsystem 1939(same as the 1940.Fl s 1941option) or 1942.Cm default 1943(shell or command execution). 1944.It Cm SetEnv 1945Directly specify one or more environment variables and their contents to 1946be sent to the server in the form 1947.Dq NAME=VALUE . 1948Similarly to 1949.Cm SendEnv , 1950with the exception of the 1951.Ev TERM 1952variable, the server must be prepared to accept the environment variable. 1953.Pp 1954The 1955.Dq VALUE 1956may use the tokens described in the 1957.Sx TOKENS 1958section and environment variables as described in the 1959.Sx ENVIRONMENT VARIABLES 1960section. 1961.It Cm StdinNull 1962Redirects stdin from 1963.Pa /dev/null 1964(actually, prevents reading from stdin). 1965Either this or the equivalent 1966.Fl n 1967option must be used when 1968.Nm ssh 1969is run in the background. 1970The argument to this keyword must be 1971.Cm yes 1972(same as the 1973.Fl n 1974option) or 1975.Cm no 1976(the default). 1977.It Cm StreamLocalBindMask 1978Sets the octal file creation mode mask 1979.Pq umask 1980used when creating a Unix-domain socket file for local or remote 1981port forwarding. 1982This option is only used for port forwarding to a Unix-domain socket file. 1983.Pp 1984The default value is 0177, which creates a Unix-domain socket file that is 1985readable and writable only by the owner. 1986Note that not all operating systems honor the file mode on Unix-domain 1987socket files. 1988.It Cm StreamLocalBindUnlink 1989Specifies whether to remove an existing Unix-domain socket file for local 1990or remote port forwarding before creating a new one. 1991If the socket file already exists and 1992.Cm StreamLocalBindUnlink 1993is not enabled, 1994.Nm ssh 1995will be unable to forward the port to the Unix-domain socket file. 1996This option is only used for port forwarding to a Unix-domain socket file. 1997.Pp 1998The argument must be 1999.Cm yes 2000or 2001.Cm no 2002(the default). 2003.It Cm StrictHostKeyChecking 2004If this flag is set to 2005.Cm yes , 2006.Xr ssh 1 2007will never automatically add host keys to the 2008.Pa ~/.ssh/known_hosts 2009file, and refuses to connect to hosts whose host key has changed. 2010This provides maximum protection against man-in-the-middle (MITM) attacks, 2011though it can be annoying when the 2012.Pa /etc/ssh/ssh_known_hosts 2013file is poorly maintained or when connections to new hosts are 2014frequently made. 2015This option forces the user to manually 2016add all new hosts. 2017.Pp 2018If this flag is set to 2019.Cm accept-new 2020then ssh will automatically add new host keys to the user's 2021.Pa known_hosts 2022file, but will not permit connections to hosts with 2023changed host keys. 2024If this flag is set to 2025.Cm no 2026or 2027.Cm off , 2028ssh will automatically add new host keys to the user known hosts files 2029and allow connections to hosts with changed hostkeys to proceed, 2030subject to some restrictions. 2031If this flag is set to 2032.Cm ask 2033(the default), 2034new host keys 2035will be added to the user known host files only after the user 2036has confirmed that is what they really want to do, and 2037ssh will refuse to connect to hosts whose host key has changed. 2038The host keys of 2039known hosts will be verified automatically in all cases. 2040.It Cm SyslogFacility 2041Gives the facility code that is used when logging messages from 2042.Xr ssh 1 . 2043The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, 2044LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. 2045The default is USER. 2046.It Cm TCPKeepAlive 2047Specifies whether the system should send TCP keepalive messages to the 2048other side. 2049If they are sent, death of the connection or crash of one 2050of the machines will be properly noticed. 2051However, this means that 2052connections will die if the route is down temporarily, and some people 2053find it annoying. 2054.Pp 2055The default is 2056.Cm yes 2057(to send TCP keepalive messages), and the client will notice 2058if the network goes down or the remote host dies. 2059This is important in scripts, and many users want it too. 2060.Pp 2061To disable TCP keepalive messages, the value should be set to 2062.Cm no . 2063See also 2064.Cm ServerAliveInterval 2065for protocol-level keepalives. 2066.It Cm Tag 2067Specify a configuration tag name that may be later used by a 2068.Cm Match 2069directive to select a block of configuration. 2070.It Cm Tunnel 2071Request 2072.Xr tun 4 2073device forwarding between the client and the server. 2074The argument must be 2075.Cm yes , 2076.Cm point-to-point 2077(layer 3), 2078.Cm ethernet 2079(layer 2), 2080or 2081.Cm no 2082(the default). 2083Specifying 2084.Cm yes 2085requests the default tunnel mode, which is 2086.Cm point-to-point . 2087.It Cm TunnelDevice 2088Specifies the 2089.Xr tun 4 2090devices to open on the client 2091.Pq Ar local_tun 2092and the server 2093.Pq Ar remote_tun . 2094.Pp 2095The argument must be 2096.Sm off 2097.Ar local_tun Op : Ar remote_tun . 2098.Sm on 2099The devices may be specified by numerical ID or the keyword 2100.Cm any , 2101which uses the next available tunnel device. 2102If 2103.Ar remote_tun 2104is not specified, it defaults to 2105.Cm any . 2106The default is 2107.Cm any:any . 2108.It Cm UpdateHostKeys 2109Specifies whether 2110.Xr ssh 1 2111should accept notifications of additional hostkeys from the server sent 2112after authentication has completed and add them to 2113.Cm UserKnownHostsFile . 2114The argument must be 2115.Cm yes , 2116.Cm no 2117or 2118.Cm ask . 2119This option allows learning alternate hostkeys for a server 2120and supports graceful key rotation by allowing a server to send replacement 2121public keys before old ones are removed. 2122.Pp 2123Additional hostkeys are only accepted if the key used to authenticate the 2124host was already trusted or explicitly accepted by the user, the host was 2125authenticated via 2126.Cm UserKnownHostsFile 2127(i.e. not 2128.Cm GlobalKnownHostsFile ) 2129and the host was authenticated using a plain key and not a certificate. 2130.Pp 2131.Cm UpdateHostKeys 2132is enabled by default if the user has not overridden the default 2133.Cm UserKnownHostsFile 2134setting and has not enabled 2135.Cm VerifyHostKeyDNS , 2136otherwise 2137.Cm UpdateHostKeys 2138will be set to 2139.Cm no . 2140.Pp 2141If 2142.Cm UpdateHostKeys 2143is set to 2144.Cm ask , 2145then the user is asked to confirm the modifications to the known_hosts file. 2146Confirmation is currently incompatible with 2147.Cm ControlPersist , 2148and will be disabled if it is enabled. 2149.Pp 2150Presently, only 2151.Xr sshd 8 2152from OpenSSH 6.8 and greater support the 2153.Qq hostkeys@openssh.com 2154protocol extension used to inform the client of all the server's hostkeys. 2155.It Cm User 2156Specifies the user to log in as. 2157This can be useful when a different user name is used on different machines. 2158This saves the trouble of 2159having to remember to give the user name on the command line. 2160Arguments to 2161.Cm User 2162may use the tokens described in the 2163.Sx TOKENS 2164section 2165(with the exception of %r and %C) 2166and environment variables as described in the 2167.Sx ENVIRONMENT VARIABLES 2168section. 2169.It Cm UserKnownHostsFile 2170Specifies one or more files to use for the user 2171host key database, separated by whitespace. 2172Each filename may use tilde notation to refer to the user's home directory, 2173the tokens described in the 2174.Sx TOKENS 2175section and environment variables as described in the 2176.Sx ENVIRONMENT VARIABLES 2177section. 2178A value of 2179.Cm none 2180causes 2181.Xr ssh 1 2182to ignore any user-specific known hosts files. 2183The default is 2184.Pa ~/.ssh/known_hosts , 2185.Pa ~/.ssh/known_hosts2 . 2186.It Cm VerifyHostKeyDNS 2187Specifies whether to verify the remote key using DNS and SSHFP resource 2188records. 2189If this option is set to 2190.Cm yes , 2191the client will implicitly trust keys that match a secure fingerprint 2192from DNS. 2193Insecure fingerprints will be handled as if this option was set to 2194.Cm ask . 2195If this option is set to 2196.Cm ask , 2197information on fingerprint match will be displayed, but the user will still 2198need to confirm new host keys according to the 2199.Cm StrictHostKeyChecking 2200option. 2201The default is 2202.Cm no . 2203.Pp 2204See also 2205.Sx VERIFYING HOST KEYS 2206in 2207.Xr ssh 1 . 2208.It Cm VersionAddendum 2209Optionally specifies additional text to append to the SSH protocol banner 2210sent by the client upon connection. 2211The default is 2212.Cm none . 2213.It Cm VisualHostKey 2214If this flag is set to 2215.Cm yes , 2216an ASCII art representation of the remote host key fingerprint is 2217printed in addition to the fingerprint string at login and 2218for unknown host keys. 2219If this flag is set to 2220.Cm no 2221(the default), 2222no fingerprint strings are printed at login and 2223only the fingerprint string will be printed for unknown host keys. 2224.It Cm XAuthLocation 2225Specifies the full pathname of the 2226.Xr xauth 1 2227program. 2228The default is 2229.Pa /usr/local/bin/xauth . 2230.El 2231.Sh PATTERNS 2232A 2233.Em pattern 2234consists of zero or more non-whitespace characters, 2235.Sq * 2236(a wildcard that matches zero or more characters), 2237or 2238.Sq ?\& 2239(a wildcard that matches exactly one character). 2240For example, to specify a set of declarations for any host in the 2241.Qq .co.uk 2242set of domains, 2243the following pattern could be used: 2244.Pp 2245.Dl Host *.co.uk 2246.Pp 2247The following pattern 2248would match any host in the 192.168.0.[0-9] network range: 2249.Pp 2250.Dl Host 192.168.0.? 2251.Pp 2252A 2253.Em pattern-list 2254is a comma-separated list of patterns. 2255Patterns within pattern-lists may be negated 2256by preceding them with an exclamation mark 2257.Pq Sq !\& . 2258For example, 2259to allow a key to be used from anywhere within an organization 2260except from the 2261.Qq dialup 2262pool, 2263the following entry (in authorized_keys) could be used: 2264.Pp 2265.Dl from=\&"!*.dialup.example.com,*.example.com\&" 2266.Pp 2267Note that a negated match will never produce a positive result by itself. 2268For example, attempting to match 2269.Qq host3 2270against the following pattern-list will fail: 2271.Pp 2272.Dl from=\&"!host1,!host2\&" 2273.Pp 2274The solution here is to include a term that will yield a positive match, 2275such as a wildcard: 2276.Pp 2277.Dl from=\&"!host1,!host2,*\&" 2278.Sh TOKENS 2279Arguments to some keywords can make use of tokens, 2280which are expanded at runtime: 2281.Pp 2282.Bl -tag -width XXXX -offset indent -compact 2283.It %% 2284A literal 2285.Sq % . 2286.It \&%C 2287Hash of %l%h%p%r%j. 2288.It %d 2289Local user's home directory. 2290.It %f 2291The fingerprint of the server's host key. 2292.It %H 2293The 2294.Pa known_hosts 2295hostname or address that is being searched for. 2296.It %h 2297The remote hostname. 2298.It \%%I 2299A string describing the reason for a 2300.Cm KnownHostsCommand 2301execution: either 2302.Cm ADDRESS 2303when looking up a host by address (only when 2304.Cm CheckHostIP 2305is enabled), 2306.Cm HOSTNAME 2307when searching by hostname, or 2308.Cm ORDER 2309when preparing the host key algorithm preference list to use for the 2310destination host. 2311.It %i 2312The local user ID. 2313.It %j 2314The contents of the ProxyJump option, or the empty string if this 2315option is unset. 2316.It %K 2317The base64 encoded host key. 2318.It %k 2319The host key alias if specified, otherwise the original remote hostname given 2320on the command line. 2321.It %L 2322The local hostname. 2323.It %l 2324The local hostname, including the domain name. 2325.It %n 2326The original remote hostname, as given on the command line. 2327.It %p 2328The remote port. 2329.It %r 2330The remote username. 2331.It \&%T 2332The local 2333.Xr tun 4 2334or 2335.Xr tap 4 2336network interface assigned if 2337tunnel forwarding was requested, or 2338.Qq NONE 2339otherwise. 2340.It %t 2341The type of the server host key, e.g. 2342.Cm ssh-ed25519 . 2343.It %u 2344The local username. 2345.El 2346.Pp 2347.Cm CertificateFile , 2348.Cm ControlPath , 2349.Cm IdentityAgent , 2350.Cm IdentityFile , 2351.Cm Include , 2352.Cm KnownHostsCommand , 2353.Cm LocalForward , 2354.Cm Match exec , 2355.Cm RemoteCommand , 2356.Cm RemoteForward , 2357.Cm RevokedHostKeys , 2358.Cm UserKnownHostsFile 2359and 2360.Cm VersionAddendum 2361accept the tokens %%, %C, %d, %h, %i, %j, %k, %L, %l, %n, %p, %r, and %u. 2362.Pp 2363.Cm KnownHostsCommand 2364additionally accepts the tokens %f, %H, %I, %K and %t. 2365.Pp 2366.Cm Hostname 2367accepts the tokens %% and %h. 2368.Pp 2369.Cm LocalCommand 2370accepts all tokens. 2371.Pp 2372.Cm ProxyCommand 2373and 2374.Cm ProxyJump 2375accept the tokens %%, %h, %n, %p, and %r. 2376.Pp 2377Note that some of these directives build commands for execution via the shell. 2378Because 2379.Xr ssh 1 2380performs no filtering or escaping of characters that have special meaning in 2381shell commands (e.g. quotes), it is the user's responsibility to ensure that 2382the arguments passed to 2383.Xr ssh 1 2384do not contain such characters and that tokens are appropriately quoted 2385when used. 2386.Sh ENVIRONMENT VARIABLES 2387Arguments to some keywords can be expanded at runtime from environment 2388variables on the client by enclosing them in 2389.Ic ${} , 2390for example 2391.Ic ${HOME}/.ssh 2392would refer to the user's .ssh directory. 2393If a specified environment variable does not exist then an error will be 2394returned and the setting for that keyword will be ignored. 2395.Pp 2396The keywords 2397.Cm CertificateFile , 2398.Cm ControlPath , 2399.Cm IdentityAgent , 2400.Cm IdentityFile , 2401.Cm Include , 2402.Cm KnownHostsCommand , 2403and 2404.Cm UserKnownHostsFile 2405support environment variables. 2406The keywords 2407.Cm LocalForward 2408and 2409.Cm RemoteForward 2410support environment variables only for Unix domain socket paths. 2411.Sh FILES 2412.Bl -tag -width Ds 2413.It Pa ~/.ssh/config 2414This is the per-user configuration file. 2415The format of this file is described above. 2416This file is used by the SSH client. 2417Because of the potential for abuse, this file must have strict permissions: 2418read/write for the user, and not writable by others. 2419.It Pa /etc/ssh/ssh_config 2420Systemwide configuration file. 2421This file provides defaults for those 2422values that are not specified in the user's configuration file, and 2423for those users who do not have a configuration file. 2424This file must be world-readable. 2425.El 2426.Sh SEE ALSO 2427.Xr ssh 1 2428.Sh AUTHORS 2429.An -nosplit 2430OpenSSH is a derivative of the original and free 2431ssh 1.2.12 release by 2432.An Tatu Ylonen . 2433.An Aaron Campbell , Bob Beck , Markus Friedl , 2434.An Niels Provos , Theo de Raadt 2435and 2436.An Dug Song 2437removed many bugs, re-added newer features and 2438created OpenSSH. 2439.An Markus Friedl 2440contributed the support for SSH protocol versions 1.5 and 2.0. 2441