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 1.205 2015/02/20 22:17:21 djm Exp $ 37.Dd $Mdocdate: February 20 2015 $ 38.Dt SSH_CONFIG 5 39.Os 40.Sh NAME 41.Nm ssh_config 42.Nd OpenSSH SSH client configuration files 43.Sh SYNOPSIS 44.Nm ~/.ssh/config 45.Nm /etc/ssh/ssh_config 46.Sh DESCRIPTION 47.Xr ssh 1 48obtains configuration data from the following sources in 49the following order: 50.Pp 51.Bl -enum -offset indent -compact 52.It 53command-line options 54.It 55user's configuration file 56.Pq Pa ~/.ssh/config 57.It 58system-wide configuration file 59.Pq Pa /etc/ssh/ssh_config 60.El 61.Pp 62For each parameter, the first obtained value 63will be used. 64The configuration files contain sections separated by 65.Dq Host 66specifications, and that section is only applied for hosts that 67match one of the patterns given in the specification. 68The matched host name is usually the one given on the command line 69(see the 70.Cm CanonicalizeHostname 71option for exceptions.) 72.Pp 73Since the first obtained value for each parameter is used, more 74host-specific declarations should be given near the beginning of the 75file, and general defaults at the end. 76.Pp 77The configuration file has the following format: 78.Pp 79Empty lines and lines starting with 80.Ql # 81are comments. 82Otherwise a line is of the format 83.Dq keyword arguments . 84Configuration options may be separated by whitespace or 85optional whitespace and exactly one 86.Ql = ; 87the latter format is useful to avoid the need to quote whitespace 88when specifying configuration options using the 89.Nm ssh , 90.Nm scp , 91and 92.Nm sftp 93.Fl o 94option. 95Arguments may optionally be enclosed in double quotes 96.Pq \&" 97in order to represent arguments containing spaces. 98.Pp 99The possible 100keywords and their meanings are as follows (note that 101keywords are case-insensitive and arguments are case-sensitive): 102.Bl -tag -width Ds 103.It Cm Host 104Restricts the following declarations (up to the next 105.Cm Host 106or 107.Cm Match 108keyword) to be only for those hosts that match one of the patterns 109given after the keyword. 110If more than one pattern is provided, they should be separated by whitespace. 111A single 112.Ql * 113as a pattern can be used to provide global 114defaults for all hosts. 115The host is usually the 116.Ar hostname 117argument given on the command line 118(see the 119.Cm CanonicalizeHostname 120option for exceptions.) 121.Pp 122A pattern entry may be negated by prefixing it with an exclamation mark 123.Pq Sq !\& . 124If a negated entry is matched, then the 125.Cm Host 126entry is ignored, regardless of whether any other patterns on the line 127match. 128Negated matches are therefore useful to provide exceptions for wildcard 129matches. 130.Pp 131See 132.Sx PATTERNS 133for more information on patterns. 134.It Cm Match 135Restricts the following declarations (up to the next 136.Cm Host 137or 138.Cm Match 139keyword) to be used only when the conditions following the 140.Cm Match 141keyword are satisfied. 142Match conditions are specified using one or more critera 143or the single token 144.Cm all 145which always matches. 146The available criteria keywords are: 147.Cm canonical , 148.Cm exec , 149.Cm host , 150.Cm originalhost , 151.Cm user , 152and 153.Cm localuser . 154The 155.Cm all 156criteria must appear alone or immediately after 157.Cm canonical . 158Other criteria may be combined arbitrarily. 159All criteria but 160.Cm all 161and 162.Cm canonical 163require an argument. 164Criteria may be negated by prepending an exclamation mark 165.Pq Sq !\& . 166.Pp 167The 168.Cm canonical 169keywork matches only when the configuration file is being re-parsed 170after hostname canonicalization (see the 171.Cm CanonicalizeHostname 172option.) 173This may be useful to specify conditions that work with canonical host 174names only. 175The 176.Cm exec 177keyword executes the specified command under the user's shell. 178If the command returns a zero exit status then the condition is considered true. 179Commands containing whitespace characters must be quoted. 180The following character sequences in the command will be expanded prior to 181execution: 182.Ql %L 183will be substituted by the first component of the local host name, 184.Ql %l 185will be substituted by the local host name (including any domain name), 186.Ql %h 187will be substituted by the target host name, 188.Ql %n 189will be substituted by the original target host name 190specified on the command-line, 191.Ql %p 192the destination port, 193.Ql %r 194by the remote login username, and 195.Ql %u 196by the username of the user running 197.Xr ssh 1 . 198.Pp 199The other keywords' criteria must be single entries or comma-separated 200lists and may use the wildcard and negation operators described in the 201.Sx PATTERNS 202section. 203The criteria for the 204.Cm host 205keyword are matched against the target hostname, after any substitution 206by the 207.Cm Hostname 208or 209.Cm CanonicalizeHostname 210options. 211The 212.Cm originalhost 213keyword matches against the hostname as it was specified on the command-line. 214The 215.Cm user 216keyword matches against the target username on the remote host. 217The 218.Cm localuser 219keyword matches against the name of the local user running 220.Xr ssh 1 221(this keyword may be useful in system-wide 222.Nm 223files). 224.It Cm AddressFamily 225Specifies which address family to use when connecting. 226Valid arguments are 227.Dq any , 228.Dq inet 229(use IPv4 only), or 230.Dq inet6 231(use IPv6 only). 232.It Cm BatchMode 233If set to 234.Dq yes , 235passphrase/password querying will be disabled. 236This option is useful in scripts and other batch jobs where no user 237is present to supply the password. 238The argument must be 239.Dq yes 240or 241.Dq no . 242The default is 243.Dq no . 244.It Cm BindAddress 245Use the specified address on the local machine as the source address of 246the connection. 247Only useful on systems with more than one address. 248Note that this option does not work if 249.Cm UsePrivilegedPort 250is set to 251.Dq yes . 252.It Cm CanonicalDomains 253When 254.Cm CanonicalizeHostname 255is enabled, this option specifies the list of domain suffixes in which to 256search for the specified destination host. 257.It Cm CanonicalizeFallbackLocal 258Specifies whether to fail with an error when hostname canonicalization fails. 259The default, 260.Dq yes , 261will attempt to look up the unqualified hostname using the system resolver's 262search rules. 263A value of 264.Dq no 265will cause 266.Xr ssh 1 267to fail instantly if 268.Cm CanonicalizeHostname 269is enabled and the target hostname cannot be found in any of the domains 270specified by 271.Cm CanonicalDomains . 272.It Cm CanonicalizeHostname 273Controls whether explicit hostname canonicalization is performed. 274The default, 275.Dq no , 276is not to perform any name rewriting and let the system resolver handle all 277hostname lookups. 278If set to 279.Dq yes 280then, for connections that do not use a 281.Cm ProxyCommand , 282.Xr ssh 1 283will attempt to canonicalize the hostname specified on the command line 284using the 285.Cm CanonicalDomains 286suffixes and 287.Cm CanonicalizePermittedCNAMEs 288rules. 289If 290.Cm CanonicalizeHostname 291is set to 292.Dq always , 293then canonicalization is applied to proxied connections too. 294.Pp 295If this option is enabled, then the configuration files are processed 296again using the new target name to pick up any new configuration in matching 297.Cm Host 298and 299.Cm Match 300stanzas. 301.It Cm CanonicalizeMaxDots 302Specifies the maximum number of dot characters in a hostname before 303canonicalization is disabled. 304The default, 305.Dq 1 , 306allows a single dot (i.e. hostname.subdomain). 307.It Cm CanonicalizePermittedCNAMEs 308Specifies rules to determine whether CNAMEs should be followed when 309canonicalizing hostnames. 310The rules consist of one or more arguments of 311.Ar source_domain_list : Ns Ar target_domain_list , 312where 313.Ar source_domain_list 314is a pattern-list of domains that may follow CNAMEs in canonicalization, 315and 316.Ar target_domain_list 317is a pattern-list of domains that they may resolve to. 318.Pp 319For example, 320.Dq *.a.example.com:*.b.example.com,*.c.example.com 321will allow hostnames matching 322.Dq *.a.example.com 323to be canonicalized to names in the 324.Dq *.b.example.com 325or 326.Dq *.c.example.com 327domains. 328.It Cm ChallengeResponseAuthentication 329Specifies whether to use challenge-response authentication. 330The argument to this keyword must be 331.Dq yes 332or 333.Dq no . 334The default is 335.Dq yes . 336.It Cm CheckHostIP 337If this flag is set to 338.Dq yes , 339.Xr ssh 1 340will additionally check the host IP address in the 341.Pa known_hosts 342file. 343This allows ssh to detect if a host key changed due to DNS spoofing. 344If the option is set to 345.Dq no , 346the check will not be executed. 347The default is 348.Dq yes . 349.It Cm Cipher 350Specifies the cipher to use for encrypting the session 351in protocol version 1. 352Currently, 353.Dq blowfish , 354.Dq 3des , 355and 356.Dq des 357are supported. 358.Ar des 359is only supported in the 360.Xr ssh 1 361client for interoperability with legacy protocol 1 implementations 362that do not support the 363.Ar 3des 364cipher. 365Its use is strongly discouraged due to cryptographic weaknesses. 366The default is 367.Dq 3des . 368.It Cm Ciphers 369Specifies the ciphers allowed for protocol version 2 370in order of preference. 371Multiple ciphers must be comma-separated. 372The supported ciphers are: 373.Pp 374.Bl -item -compact -offset indent 375.It 3763des-cbc 377.It 378aes128-cbc 379.It 380aes192-cbc 381.It 382aes256-cbc 383.It 384aes128-ctr 385.It 386aes192-ctr 387.It 388aes256-ctr 389.It 390aes128-gcm@openssh.com 391.It 392aes256-gcm@openssh.com 393.It 394arcfour 395.It 396arcfour128 397.It 398arcfour256 399.It 400blowfish-cbc 401.It 402cast128-cbc 403.It 404chacha20-poly1305@openssh.com 405.El 406.Pp 407The default is: 408.Bd -literal -offset indent 409aes128-ctr,aes192-ctr,aes256-ctr, 410aes128-gcm@openssh.com,aes256-gcm@openssh.com, 411chacha20-poly1305@openssh.com, 412arcfour256,arcfour128, 413aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc, 414aes192-cbc,aes256-cbc,arcfour 415.Ed 416.Pp 417The list of available ciphers may also be obtained using the 418.Fl Q 419option of 420.Xr ssh 1 421with an argument of 422.Dq cipher . 423.It Cm ClearAllForwardings 424Specifies that all local, remote, and dynamic port forwardings 425specified in the configuration files or on the command line be 426cleared. 427This option is primarily useful when used from the 428.Xr ssh 1 429command line to clear port forwardings set in 430configuration files, and is automatically set by 431.Xr scp 1 432and 433.Xr sftp 1 . 434The argument must be 435.Dq yes 436or 437.Dq no . 438The default is 439.Dq no . 440.It Cm Compression 441Specifies whether to use compression. 442The argument must be 443.Dq yes 444or 445.Dq no . 446The default is 447.Dq no . 448.It Cm CompressionLevel 449Specifies the compression level to use if compression is enabled. 450The argument must be an integer from 1 (fast) to 9 (slow, best). 451The default level is 6, which is good for most applications. 452The meaning of the values is the same as in 453.Xr gzip 1 . 454Note that this option applies to protocol version 1 only. 455.It Cm ConnectionAttempts 456Specifies the number of tries (one per second) to make before exiting. 457The argument must be an integer. 458This may be useful in scripts if the connection sometimes fails. 459The default is 1. 460.It Cm ConnectTimeout 461Specifies the timeout (in seconds) used when connecting to the 462SSH server, instead of using the default system TCP timeout. 463This value is used only when the target is down or really unreachable, 464not when it refuses the connection. 465.It Cm ControlMaster 466Enables the sharing of multiple sessions over a single network connection. 467When set to 468.Dq yes , 469.Xr ssh 1 470will listen for connections on a control socket specified using the 471.Cm ControlPath 472argument. 473Additional sessions can connect to this socket using the same 474.Cm ControlPath 475with 476.Cm ControlMaster 477set to 478.Dq no 479(the default). 480These sessions will try to reuse the master instance's network connection 481rather than initiating new ones, but will fall back to connecting normally 482if the control socket does not exist, or is not listening. 483.Pp 484Setting this to 485.Dq ask 486will cause ssh 487to listen for control connections, but require confirmation using the 488.Ev SSH_ASKPASS 489program before they are accepted (see 490.Xr ssh-add 1 491for details). 492If the 493.Cm ControlPath 494cannot be opened, 495ssh will continue without connecting to a master instance. 496.Pp 497X11 and 498.Xr ssh-agent 1 499forwarding is supported over these multiplexed connections, however the 500display and agent forwarded will be the one belonging to the master 501connection i.e. it is not possible to forward multiple displays or agents. 502.Pp 503Two additional options allow for opportunistic multiplexing: try to use a 504master connection but fall back to creating a new one if one does not already 505exist. 506These options are: 507.Dq auto 508and 509.Dq autoask . 510The latter requires confirmation like the 511.Dq ask 512option. 513.It Cm ControlPath 514Specify the path to the control socket used for connection sharing as described 515in the 516.Cm ControlMaster 517section above or the string 518.Dq none 519to disable connection sharing. 520In the path, 521.Ql %L 522will be substituted by the first component of the local host name, 523.Ql %l 524will be substituted by the local host name (including any domain name), 525.Ql %h 526will be substituted by the target host name, 527.Ql %n 528will be substituted by the original target host name 529specified on the command line, 530.Ql %p 531the destination port, 532.Ql %r 533by the remote login username, 534.Ql %u 535by the username of the user running 536.Xr ssh 1 , and 537.Ql \&%C 538by a hash of the concatenation: %l%h%p%r. 539It is recommended that any 540.Cm ControlPath 541used for opportunistic connection sharing include 542at least %h, %p, and %r (or alternatively %C) and be placed in a directory 543that is not writable by other users. 544This ensures that shared connections are uniquely identified. 545.It Cm ControlPersist 546When used in conjunction with 547.Cm ControlMaster , 548specifies that the master connection should remain open 549in the background (waiting for future client connections) 550after the initial client connection has been closed. 551If set to 552.Dq no , 553then the master connection will not be placed into the background, 554and will close as soon as the initial client connection is closed. 555If set to 556.Dq yes 557or 558.Dq 0 , 559then the master connection will remain in the background indefinitely 560(until killed or closed via a mechanism such as the 561.Xr ssh 1 562.Dq Fl O No exit 563option). 564If set to a time in seconds, or a time in any of the formats documented in 565.Xr sshd_config 5 , 566then the backgrounded master connection will automatically terminate 567after it has remained idle (with no client connections) for the 568specified time. 569.It Cm DynamicForward 570Specifies that a TCP port on the local machine be forwarded 571over the secure channel, and the application 572protocol is then used to determine where to connect to from the 573remote machine. 574.Pp 575The argument must be 576.Sm off 577.Oo Ar bind_address : Oc Ar port . 578.Sm on 579IPv6 addresses can be specified by enclosing addresses in square brackets. 580By default, the local port is bound in accordance with the 581.Cm GatewayPorts 582setting. 583However, an explicit 584.Ar bind_address 585may be used to bind the connection to a specific address. 586The 587.Ar bind_address 588of 589.Dq localhost 590indicates that the listening port be bound for local use only, while an 591empty address or 592.Sq * 593indicates that the port should be available from all interfaces. 594.Pp 595Currently the SOCKS4 and SOCKS5 protocols are supported, and 596.Xr ssh 1 597will act as a SOCKS server. 598Multiple forwardings may be specified, and 599additional forwardings can be given on the command line. 600Only the superuser can forward privileged ports. 601.It Cm EnableSSHKeysign 602Setting this option to 603.Dq yes 604in the global client configuration file 605.Pa /etc/ssh/ssh_config 606enables the use of the helper program 607.Xr ssh-keysign 8 608during 609.Cm HostbasedAuthentication . 610The argument must be 611.Dq yes 612or 613.Dq no . 614The default is 615.Dq no . 616This option should be placed in the non-hostspecific section. 617See 618.Xr ssh-keysign 8 619for more information. 620.It Cm EscapeChar 621Sets the escape character (default: 622.Ql ~ ) . 623The escape character can also 624be set on the command line. 625The argument should be a single character, 626.Ql ^ 627followed by a letter, or 628.Dq none 629to disable the escape 630character entirely (making the connection transparent for binary 631data). 632.It Cm ExitOnForwardFailure 633Specifies whether 634.Xr ssh 1 635should terminate the connection if it cannot set up all requested 636dynamic, tunnel, local, and remote port forwardings. 637The argument must be 638.Dq yes 639or 640.Dq no . 641The default is 642.Dq no . 643.It Cm FingerprintHash 644Specifies the hash algorithm used when displaying key fingerprints. 645Valid options are: 646.Dq md5 647and 648.Dq sha256 . 649The default is 650.Dq sha256 . 651.It Cm ForwardAgent 652Specifies whether the connection to the authentication agent (if any) 653will be forwarded to the remote machine. 654The argument must be 655.Dq yes 656or 657.Dq no . 658The default is 659.Dq no . 660.Pp 661Agent forwarding should be enabled with caution. 662Users with the ability to bypass file permissions on the remote host 663(for the agent's Unix-domain socket) 664can access the local agent through the forwarded connection. 665An attacker cannot obtain key material from the agent, 666however they can perform operations on the keys that enable them to 667authenticate using the identities loaded into the agent. 668.It Cm ForwardX11 669Specifies whether X11 connections will be automatically redirected 670over the secure channel and 671.Ev DISPLAY 672set. 673The argument must be 674.Dq yes 675or 676.Dq no . 677The default is 678.Dq no . 679.Pp 680X11 forwarding should be enabled with caution. 681Users with the ability to bypass file permissions on the remote host 682(for the user's X11 authorization database) 683can access the local X11 display through the forwarded connection. 684An attacker may then be able to perform activities such as keystroke monitoring 685if the 686.Cm ForwardX11Trusted 687option is also enabled. 688.It Cm ForwardX11Timeout 689Specify a timeout for untrusted X11 forwarding 690using the format described in the 691TIME FORMATS section of 692.Xr sshd_config 5 . 693X11 connections received by 694.Xr ssh 1 695after this time will be refused. 696The default is to disable untrusted X11 forwarding after twenty minutes has 697elapsed. 698.It Cm ForwardX11Trusted 699If this option is set to 700.Dq yes , 701remote X11 clients will have full access to the original X11 display. 702.Pp 703If this option is set to 704.Dq no , 705remote X11 clients will be considered untrusted and prevented 706from stealing or tampering with data belonging to trusted X11 707clients. 708Furthermore, the 709.Xr xauth 1 710token used for the session will be set to expire after 20 minutes. 711Remote clients will be refused access after this time. 712.Pp 713The default is 714.Dq no . 715.Pp 716See the X11 SECURITY extension specification for full details on 717the restrictions imposed on untrusted clients. 718.It Cm GatewayPorts 719Specifies whether remote hosts are allowed to connect to local 720forwarded ports. 721By default, 722.Xr ssh 1 723binds local port forwardings to the loopback address. 724This prevents other remote hosts from connecting to forwarded ports. 725.Cm GatewayPorts 726can be used to specify that ssh 727should bind local port forwardings to the wildcard address, 728thus allowing remote hosts to connect to forwarded ports. 729The argument must be 730.Dq yes 731or 732.Dq no . 733The default is 734.Dq no . 735.It Cm GlobalKnownHostsFile 736Specifies one or more files to use for the global 737host key database, separated by whitespace. 738The default is 739.Pa /etc/ssh/ssh_known_hosts , 740.Pa /etc/ssh/ssh_known_hosts2 . 741.It Cm GSSAPIAuthentication 742Specifies whether user authentication based on GSSAPI is allowed. 743The default is 744.Dq no . 745Note that this option applies to protocol version 2 only. 746.It Cm GSSAPIDelegateCredentials 747Forward (delegate) credentials to the server. 748The default is 749.Dq no . 750Note that this option applies to protocol version 2 only. 751.It Cm HashKnownHosts 752Indicates that 753.Xr ssh 1 754should hash host names and addresses when they are added to 755.Pa ~/.ssh/known_hosts . 756These hashed names may be used normally by 757.Xr ssh 1 758and 759.Xr sshd 8 , 760but they do not reveal identifying information should the file's contents 761be disclosed. 762The default is 763.Dq no . 764Note that existing names and addresses in known hosts files 765will not be converted automatically, 766but may be manually hashed using 767.Xr ssh-keygen 1 . 768.It Cm HostbasedAuthentication 769Specifies whether to try rhosts based authentication with public key 770authentication. 771The argument must be 772.Dq yes 773or 774.Dq no . 775The default is 776.Dq no . 777This option applies to protocol version 2 only and 778is similar to 779.Cm RhostsRSAAuthentication . 780.It Cm HostbasedKeyTypes 781Specifies the key types that will be used for hostbased authentication 782as a comma-separated pattern list. 783The default 784.Dq * 785will allow all key types. 786The 787.Fl Q 788option of 789.Xr ssh 1 790may be used to list supported key types. 791.It Cm HostKeyAlgorithms 792Specifies the protocol version 2 host key algorithms 793that the client wants to use in order of preference. 794The default for this option is: 795.Bd -literal -offset 3n 796ecdsa-sha2-nistp256-cert-v01@openssh.com, 797ecdsa-sha2-nistp384-cert-v01@openssh.com, 798ecdsa-sha2-nistp521-cert-v01@openssh.com, 799ssh-ed25519-cert-v01@openssh.com, 800ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com, 801ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com, 802ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521, 803ssh-ed25519,ssh-rsa,ssh-dss 804.Ed 805.Pp 806If hostkeys are known for the destination host then this default is modified 807to prefer their algorithms. 808.Pp 809The list of available key types may also be obtained using the 810.Fl Q 811option of 812.Xr ssh 1 813with an argument of 814.Dq key . 815.It Cm HostKeyAlias 816Specifies an alias that should be used instead of the 817real host name when looking up or saving the host key 818in the host key database files. 819This option is useful for tunneling SSH connections 820or for multiple servers running on a single host. 821.It Cm HostName 822Specifies the real host name to log into. 823This can be used to specify nicknames or abbreviations for hosts. 824If the hostname contains the character sequence 825.Ql %h , 826then this will be replaced with the host name specified on the command line 827(this is useful for manipulating unqualified names). 828The character sequence 829.Ql %% 830will be replaced by a single 831.Ql % 832character, which may be used when specifying IPv6 link-local addresses. 833.Pp 834The default is the name given on the command line. 835Numeric IP addresses are also permitted (both on the command line and in 836.Cm HostName 837specifications). 838.It Cm IdentitiesOnly 839Specifies that 840.Xr ssh 1 841should only use the authentication identity files configured in the 842.Nm 843files, 844even if 845.Xr ssh-agent 1 846or a 847.Cm PKCS11Provider 848offers more identities. 849The argument to this keyword must be 850.Dq yes 851or 852.Dq no . 853This option is intended for situations where ssh-agent 854offers many different identities. 855The default is 856.Dq no . 857.It Cm IdentityFile 858Specifies a file from which the user's DSA, ECDSA, Ed25519 or RSA authentication 859identity is read. 860The default is 861.Pa ~/.ssh/identity 862for protocol version 1, and 863.Pa ~/.ssh/id_dsa , 864.Pa ~/.ssh/id_ecdsa , 865.Pa ~/.ssh/id_ed25519 866and 867.Pa ~/.ssh/id_rsa 868for protocol version 2. 869Additionally, any identities represented by the authentication agent 870will be used for authentication unless 871.Cm IdentitiesOnly 872is set. 873.Xr ssh 1 874will try to load certificate information from the filename obtained by 875appending 876.Pa -cert.pub 877to the path of a specified 878.Cm IdentityFile . 879.Pp 880The file name may use the tilde 881syntax to refer to a user's home directory or one of the following 882escape characters: 883.Ql %d 884(local user's home directory), 885.Ql %u 886(local user name), 887.Ql %l 888(local host name), 889.Ql %h 890(remote host name) or 891.Ql %r 892(remote user name). 893.Pp 894It is possible to have 895multiple identity files specified in configuration files; all these 896identities will be tried in sequence. 897Multiple 898.Cm IdentityFile 899directives will add to the list of identities tried (this behaviour 900differs from that of other configuration directives). 901.Pp 902.Cm IdentityFile 903may be used in conjunction with 904.Cm IdentitiesOnly 905to select which identities in an agent are offered during authentication. 906.It Cm IgnoreUnknown 907Specifies a pattern-list of unknown options to be ignored if they are 908encountered in configuration parsing. 909This may be used to suppress errors if 910.Nm 911contains options that are unrecognised by 912.Xr ssh 1 . 913It is recommended that 914.Cm IgnoreUnknown 915be listed early in the configuration file as it will not be applied 916to unknown options that appear before it. 917.It Cm IPQoS 918Specifies the IPv4 type-of-service or DSCP class for connections. 919Accepted values are 920.Dq af11 , 921.Dq af12 , 922.Dq af13 , 923.Dq af21 , 924.Dq af22 , 925.Dq af23 , 926.Dq af31 , 927.Dq af32 , 928.Dq af33 , 929.Dq af41 , 930.Dq af42 , 931.Dq af43 , 932.Dq cs0 , 933.Dq cs1 , 934.Dq cs2 , 935.Dq cs3 , 936.Dq cs4 , 937.Dq cs5 , 938.Dq cs6 , 939.Dq cs7 , 940.Dq ef , 941.Dq lowdelay , 942.Dq throughput , 943.Dq reliability , 944or a numeric value. 945This option may take one or two arguments, separated by whitespace. 946If one argument is specified, it is used as the packet class unconditionally. 947If two values are specified, the first is automatically selected for 948interactive sessions and the second for non-interactive sessions. 949The default is 950.Dq lowdelay 951for interactive sessions and 952.Dq throughput 953for non-interactive sessions. 954.It Cm KbdInteractiveAuthentication 955Specifies whether to use keyboard-interactive authentication. 956The argument to this keyword must be 957.Dq yes 958or 959.Dq no . 960The default is 961.Dq yes . 962.It Cm KbdInteractiveDevices 963Specifies the list of methods to use in keyboard-interactive authentication. 964Multiple method names must be comma-separated. 965The default is to use the server specified list. 966The methods available vary depending on what the server supports. 967For an OpenSSH server, 968it may be zero or more of: 969.Dq bsdauth , 970.Dq pam , 971and 972.Dq skey . 973.It Cm KexAlgorithms 974Specifies the available KEX (Key Exchange) algorithms. 975Multiple algorithms must be comma-separated. 976The default is: 977.Bd -literal -offset indent 978curve25519-sha256@libssh.org, 979ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521, 980diffie-hellman-group-exchange-sha256, 981diffie-hellman-group14-sha1, 982diffie-hellman-group-exchange-sha1, 983diffie-hellman-group1-sha1 984.Ed 985.Pp 986The list of available key exchange algorithms may also be obtained using the 987.Fl Q 988option of 989.Xr ssh 1 990with an argument of 991.Dq kex . 992.It Cm LocalCommand 993Specifies a command to execute on the local machine after successfully 994connecting to the server. 995The command string extends to the end of the line, and is executed with 996the user's shell. 997The following escape character substitutions will be performed: 998.Ql %d 999(local user's home directory), 1000.Ql %h 1001(remote host name), 1002.Ql %l 1003(local host name), 1004.Ql %n 1005(host name as provided on the command line), 1006.Ql %p 1007(remote port), 1008.Ql %r 1009(remote user name) or 1010.Ql %u 1011(local user name) or 1012.Ql \&%C 1013by a hash of the concatenation: %l%h%p%r. 1014.Pp 1015The command is run synchronously and does not have access to the 1016session of the 1017.Xr ssh 1 1018that spawned it. 1019It should not be used for interactive commands. 1020.Pp 1021This directive is ignored unless 1022.Cm PermitLocalCommand 1023has been enabled. 1024.It Cm LocalForward 1025Specifies that a TCP port on the local machine be forwarded over 1026the secure channel to the specified host and port from the remote machine. 1027The first argument must be 1028.Sm off 1029.Oo Ar bind_address : Oc Ar port 1030.Sm on 1031and the second argument must be 1032.Ar host : Ns Ar hostport . 1033IPv6 addresses can be specified by enclosing addresses in square brackets. 1034Multiple forwardings may be specified, and additional forwardings can be 1035given on the command line. 1036Only the superuser can forward privileged ports. 1037By default, the local port is bound in accordance with the 1038.Cm GatewayPorts 1039setting. 1040However, an explicit 1041.Ar bind_address 1042may be used to bind the connection to a specific address. 1043The 1044.Ar bind_address 1045of 1046.Dq localhost 1047indicates that the listening port be bound for local use only, while an 1048empty address or 1049.Sq * 1050indicates that the port should be available from all interfaces. 1051.It Cm LogLevel 1052Gives the verbosity level that is used when logging messages from 1053.Xr ssh 1 . 1054The possible values are: 1055QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. 1056The default is INFO. 1057DEBUG and DEBUG1 are equivalent. 1058DEBUG2 and DEBUG3 each specify higher levels of verbose output. 1059.It Cm MACs 1060Specifies the MAC (message authentication code) algorithms 1061in order of preference. 1062The MAC algorithm is used in protocol version 2 1063for data integrity protection. 1064Multiple algorithms must be comma-separated. 1065The algorithms that contain 1066.Dq -etm 1067calculate the MAC after encryption (encrypt-then-mac). 1068These are considered safer and their use recommended. 1069The default is: 1070.Bd -literal -offset indent 1071umac-64-etm@openssh.com,umac-128-etm@openssh.com, 1072hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com, 1073umac-64@openssh.com,umac-128@openssh.com, 1074hmac-sha2-256,hmac-sha2-512, 1075hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com, 1076hmac-ripemd160-etm@openssh.com, 1077hmac-sha1-96-etm@openssh.com,hmac-md5-96-etm@openssh.com, 1078hmac-md5,hmac-sha1,hmac-ripemd160, 1079hmac-sha1-96,hmac-md5-96 1080.Ed 1081.Pp 1082The list of available MAC algorithms may also be obtained using the 1083.Fl Q 1084option of 1085.Xr ssh 1 1086with an argument of 1087.Dq mac . 1088.It Cm NoHostAuthenticationForLocalhost 1089This option can be used if the home directory is shared across machines. 1090In this case localhost will refer to a different machine on each of 1091the machines and the user will get many warnings about changed host keys. 1092However, this option disables host authentication for localhost. 1093The argument to this keyword must be 1094.Dq yes 1095or 1096.Dq no . 1097The default is to check the host key for localhost. 1098.It Cm NumberOfPasswordPrompts 1099Specifies the number of password prompts before giving up. 1100The argument to this keyword must be an integer. 1101The default is 3. 1102.It Cm PasswordAuthentication 1103Specifies whether to use password authentication. 1104The argument to this keyword must be 1105.Dq yes 1106or 1107.Dq no . 1108The default is 1109.Dq yes . 1110.It Cm PermitLocalCommand 1111Allow local command execution via the 1112.Ic LocalCommand 1113option or using the 1114.Ic !\& Ns Ar command 1115escape sequence in 1116.Xr ssh 1 . 1117The argument must be 1118.Dq yes 1119or 1120.Dq no . 1121The default is 1122.Dq no . 1123.It Cm PKCS11Provider 1124Specifies which PKCS#11 provider to use. 1125The argument to this keyword is the PKCS#11 shared library 1126.Xr ssh 1 1127should use to communicate with a PKCS#11 token providing the user's 1128private RSA key. 1129.It Cm Port 1130Specifies the port number to connect on the remote host. 1131The default is 22. 1132.It Cm PreferredAuthentications 1133Specifies the order in which the client should try protocol 2 1134authentication methods. 1135This allows a client to prefer one method (e.g.\& 1136.Cm keyboard-interactive ) 1137over another method (e.g.\& 1138.Cm password ) . 1139The default is: 1140.Bd -literal -offset indent 1141gssapi-with-mic,hostbased,publickey, 1142keyboard-interactive,password 1143.Ed 1144.It Cm Protocol 1145Specifies the protocol versions 1146.Xr ssh 1 1147should support in order of preference. 1148The possible values are 1149.Sq 1 1150and 1151.Sq 2 . 1152Multiple versions must be comma-separated. 1153When this option is set to 1154.Dq 2,1 1155.Nm ssh 1156will try version 2 and fall back to version 1 1157if version 2 is not available. 1158The default is 1159.Sq 2 . 1160.It Cm ProxyCommand 1161Specifies the command to use to connect to the server. 1162The command 1163string extends to the end of the line, and is executed 1164using the user's shell 1165.Ql exec 1166directive to avoid a lingering shell process. 1167.Pp 1168In the command string, any occurrence of 1169.Ql %h 1170will be substituted by the host name to 1171connect, 1172.Ql %p 1173by the port, and 1174.Ql %r 1175by the remote user name. 1176The command can be basically anything, 1177and should read from its standard input and write to its standard output. 1178It should eventually connect an 1179.Xr sshd 8 1180server running on some machine, or execute 1181.Ic sshd -i 1182somewhere. 1183Host key management will be done using the 1184HostName of the host being connected (defaulting to the name typed by 1185the user). 1186Setting the command to 1187.Dq none 1188disables this option entirely. 1189Note that 1190.Cm CheckHostIP 1191is not available for connects with a proxy command. 1192.Pp 1193This directive is useful in conjunction with 1194.Xr nc 1 1195and its proxy support. 1196For example, the following directive would connect via an HTTP proxy at 1197192.0.2.0: 1198.Bd -literal -offset 3n 1199ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p 1200.Ed 1201.It Cm ProxyUseFdpass 1202Specifies that 1203.Cm ProxyCommand 1204will pass a connected file descriptor back to 1205.Xr ssh 1 1206instead of continuing to execute and pass data. 1207The default is 1208.Dq no . 1209.It Cm PubkeyAuthentication 1210Specifies whether to try public key authentication. 1211The argument to this keyword must be 1212.Dq yes 1213or 1214.Dq no . 1215The default is 1216.Dq yes . 1217This option applies to protocol version 2 only. 1218.It Cm RekeyLimit 1219Specifies the maximum amount of data that may be transmitted before the 1220session key is renegotiated, optionally followed a maximum amount of 1221time that may pass before the session key is renegotiated. 1222The first argument is specified in bytes and may have a suffix of 1223.Sq K , 1224.Sq M , 1225or 1226.Sq G 1227to indicate Kilobytes, Megabytes, or Gigabytes, respectively. 1228The default is between 1229.Sq 1G 1230and 1231.Sq 4G , 1232depending on the cipher. 1233The optional second value is specified in seconds and may use any of the 1234units documented in the 1235TIME FORMATS section of 1236.Xr sshd_config 5 . 1237The default value for 1238.Cm RekeyLimit 1239is 1240.Dq default none , 1241which means that rekeying is performed after the cipher's default amount 1242of data has been sent or received and no time based rekeying is done. 1243This option applies to protocol version 2 only. 1244.It Cm RemoteForward 1245Specifies that a TCP port on the remote machine be forwarded over 1246the secure channel to the specified host and port from the local machine. 1247The first argument must be 1248.Sm off 1249.Oo Ar bind_address : Oc Ar port 1250.Sm on 1251and the second argument must be 1252.Ar host : Ns Ar hostport . 1253IPv6 addresses can be specified by enclosing addresses in square brackets. 1254Multiple forwardings may be specified, and additional 1255forwardings can be given on the command line. 1256Privileged ports can be forwarded only when 1257logging in as root on the remote machine. 1258.Pp 1259If the 1260.Ar port 1261argument is 1262.Ql 0 , 1263the listen port will be dynamically allocated on the server and reported 1264to the client at run time. 1265.Pp 1266If the 1267.Ar bind_address 1268is not specified, the default is to only bind to loopback addresses. 1269If the 1270.Ar bind_address 1271is 1272.Ql * 1273or an empty string, then the forwarding is requested to listen on all 1274interfaces. 1275Specifying a remote 1276.Ar bind_address 1277will only succeed if the server's 1278.Cm GatewayPorts 1279option is enabled (see 1280.Xr sshd_config 5 ) . 1281.It Cm RequestTTY 1282Specifies whether to request a pseudo-tty for the session. 1283The argument may be one of: 1284.Dq no 1285(never request a TTY), 1286.Dq yes 1287(always request a TTY when standard input is a TTY), 1288.Dq force 1289(always request a TTY) or 1290.Dq auto 1291(request a TTY when opening a login session). 1292This option mirrors the 1293.Fl t 1294and 1295.Fl T 1296flags for 1297.Xr ssh 1 . 1298.It Cm RevokedHostKeys 1299Specifies revoked host public keys. 1300Keys listed in this file will be refused for host authentication. 1301Note that if this file does not exist or is not readable, 1302then host authentication will be refused for all hosts. 1303Keys may be specified as a text file, listing one public key per line, or as 1304an OpenSSH Key Revocation List (KRL) as generated by 1305.Xr ssh-keygen 1 . 1306For more information on KRLs, see the KEY REVOCATION LISTS section in 1307.Xr ssh-keygen 1 . 1308.It Cm RhostsRSAAuthentication 1309Specifies whether to try rhosts based authentication with RSA host 1310authentication. 1311The argument must be 1312.Dq yes 1313or 1314.Dq no . 1315The default is 1316.Dq no . 1317This option applies to protocol version 1 only and requires 1318.Xr ssh 1 1319to be setuid root. 1320.It Cm RSAAuthentication 1321Specifies whether to try RSA authentication. 1322The argument to this keyword must be 1323.Dq yes 1324or 1325.Dq no . 1326RSA authentication will only be 1327attempted if the identity file exists, or an authentication agent is 1328running. 1329The default is 1330.Dq yes . 1331Note that this option applies to protocol version 1 only. 1332.It Cm SendEnv 1333Specifies what variables from the local 1334.Xr environ 7 1335should be sent to the server. 1336Note that environment passing is only supported for protocol 2. 1337The server must also support it, and the server must be configured to 1338accept these environment variables. 1339Refer to 1340.Cm AcceptEnv 1341in 1342.Xr sshd_config 5 1343for how to configure the server. 1344Variables are specified by name, which may contain wildcard characters. 1345Multiple environment variables may be separated by whitespace or spread 1346across multiple 1347.Cm SendEnv 1348directives. 1349The default is not to send any environment variables. 1350.Pp 1351See 1352.Sx PATTERNS 1353for more information on patterns. 1354.It Cm ServerAliveCountMax 1355Sets the number of server alive messages (see below) which may be 1356sent without 1357.Xr ssh 1 1358receiving any messages back from the server. 1359If this threshold is reached while server alive messages are being sent, 1360ssh will disconnect from the server, terminating the session. 1361It is important to note that the use of server alive messages is very 1362different from 1363.Cm TCPKeepAlive 1364(below). 1365The server alive messages are sent through the encrypted channel 1366and therefore will not be spoofable. 1367The TCP keepalive option enabled by 1368.Cm TCPKeepAlive 1369is spoofable. 1370The server alive mechanism is valuable when the client or 1371server depend on knowing when a connection has become inactive. 1372.Pp 1373The default value is 3. 1374If, for example, 1375.Cm ServerAliveInterval 1376(see below) is set to 15 and 1377.Cm ServerAliveCountMax 1378is left at the default, if the server becomes unresponsive, 1379ssh will disconnect after approximately 45 seconds. 1380This option applies to protocol version 2 only. 1381.It Cm ServerAliveInterval 1382Sets a timeout interval in seconds after which if no data has been received 1383from the server, 1384.Xr ssh 1 1385will send a message through the encrypted 1386channel to request a response from the server. 1387The default 1388is 0, indicating that these messages will not be sent to the server. 1389This option applies to protocol version 2 only. 1390.It Cm StreamLocalBindMask 1391Sets the octal file creation mode mask 1392.Pq umask 1393used when creating a Unix-domain socket file for local or remote 1394port forwarding. 1395This option is only used for port forwarding to a Unix-domain socket file. 1396.Pp 1397The default value is 0177, which creates a Unix-domain socket file that is 1398readable and writable only by the owner. 1399Note that not all operating systems honor the file mode on Unix-domain 1400socket files. 1401.It Cm StreamLocalBindUnlink 1402Specifies whether to remove an existing Unix-domain socket file for local 1403or remote port forwarding before creating a new one. 1404If the socket file already exists and 1405.Cm StreamLocalBindUnlink 1406is not enabled, 1407.Nm ssh 1408will be unable to forward the port to the Unix-domain socket file. 1409This option is only used for port forwarding to a Unix-domain socket file. 1410.Pp 1411The argument must be 1412.Dq yes 1413or 1414.Dq no . 1415The default is 1416.Dq no . 1417.It Cm StrictHostKeyChecking 1418If this flag is set to 1419.Dq yes , 1420.Xr ssh 1 1421will never automatically add host keys to the 1422.Pa ~/.ssh/known_hosts 1423file, and refuses to connect to hosts whose host key has changed. 1424This provides maximum protection against trojan horse attacks, 1425though it can be annoying when the 1426.Pa /etc/ssh/ssh_known_hosts 1427file is poorly maintained or when connections to new hosts are 1428frequently made. 1429This option forces the user to manually 1430add all new hosts. 1431If this flag is set to 1432.Dq no , 1433ssh will automatically add new host keys to the 1434user known hosts files. 1435If this flag is set to 1436.Dq ask , 1437new host keys 1438will be added to the user known host files only after the user 1439has confirmed that is what they really want to do, and 1440ssh will refuse to connect to hosts whose host key has changed. 1441The host keys of 1442known hosts will be verified automatically in all cases. 1443The argument must be 1444.Dq yes , 1445.Dq no , 1446or 1447.Dq ask . 1448The default is 1449.Dq ask . 1450.It Cm TCPKeepAlive 1451Specifies whether the system should send TCP keepalive messages to the 1452other side. 1453If they are sent, death of the connection or crash of one 1454of the machines will be properly noticed. 1455However, this means that 1456connections will die if the route is down temporarily, and some people 1457find it annoying. 1458.Pp 1459The default is 1460.Dq yes 1461(to send TCP keepalive messages), and the client will notice 1462if the network goes down or the remote host dies. 1463This is important in scripts, and many users want it too. 1464.Pp 1465To disable TCP keepalive messages, the value should be set to 1466.Dq no . 1467.It Cm Tunnel 1468Request 1469.Xr tun 4 1470device forwarding between the client and the server. 1471The argument must be 1472.Dq yes , 1473.Dq point-to-point 1474(layer 3), 1475.Dq ethernet 1476(layer 2), 1477or 1478.Dq no . 1479Specifying 1480.Dq yes 1481requests the default tunnel mode, which is 1482.Dq point-to-point . 1483The default is 1484.Dq no . 1485.It Cm TunnelDevice 1486Specifies the 1487.Xr tun 4 1488devices to open on the client 1489.Pq Ar local_tun 1490and the server 1491.Pq Ar remote_tun . 1492.Pp 1493The argument must be 1494.Sm off 1495.Ar local_tun Op : Ar remote_tun . 1496.Sm on 1497The devices may be specified by numerical ID or the keyword 1498.Dq any , 1499which uses the next available tunnel device. 1500If 1501.Ar remote_tun 1502is not specified, it defaults to 1503.Dq any . 1504The default is 1505.Dq any:any . 1506.It Cm UpdateHostKeys 1507Specifies whether 1508.Xr ssh 1 1509should accept notifications of additional hostkeys from the server sent 1510after authentication has completed and add them to 1511.Cm UserKnownHostsFile . 1512The argument must be 1513.Dq yes , 1514.Dq no 1515(the default) or 1516.Dq ask . 1517Enabling this option allows learning alternate hostkeys for a server 1518and supports graceful key rotation by allowing a server to send replacement 1519public keys before old ones are removed. 1520Additional hostkeys are only accepted if the key used to authenticate the 1521host was already trusted or explicity accepted by the user. 1522If 1523.Cm UpdateHostKeys 1524is set to 1525.Dq ask , 1526then the user is asked to confirm the modifications to the known_hosts file. 1527Confirmation is currently incompatible with 1528.Cm ControlPersist , 1529and will be disabled if it is enabled. 1530.Pp 1531Presently, only 1532.Xr sshd 8 1533from OpenSSH 6.8 and greater support the 1534.Dq hostkeys@openssh.com 1535protocol extension used to inform the client of all the server's hostkeys. 1536.It Cm UsePrivilegedPort 1537Specifies whether to use a privileged port for outgoing connections. 1538The argument must be 1539.Dq yes 1540or 1541.Dq no . 1542The default is 1543.Dq no . 1544If set to 1545.Dq yes , 1546.Xr ssh 1 1547must be setuid root. 1548Note that this option must be set to 1549.Dq yes 1550for 1551.Cm RhostsRSAAuthentication 1552with older servers. 1553.It Cm User 1554Specifies the user to log in as. 1555This can be useful when a different user name is used on different machines. 1556This saves the trouble of 1557having to remember to give the user name on the command line. 1558.It Cm UserKnownHostsFile 1559Specifies one or more files to use for the user 1560host key database, separated by whitespace. 1561The default is 1562.Pa ~/.ssh/known_hosts , 1563.Pa ~/.ssh/known_hosts2 . 1564.It Cm VerifyHostKeyDNS 1565Specifies whether to verify the remote key using DNS and SSHFP resource 1566records. 1567If this option is set to 1568.Dq yes , 1569the client will implicitly trust keys that match a secure fingerprint 1570from DNS. 1571Insecure fingerprints will be handled as if this option was set to 1572.Dq ask . 1573If this option is set to 1574.Dq ask , 1575information on fingerprint match will be displayed, but the user will still 1576need to confirm new host keys according to the 1577.Cm StrictHostKeyChecking 1578option. 1579The argument must be 1580.Dq yes , 1581.Dq no , 1582or 1583.Dq ask . 1584The default is 1585.Dq no . 1586Note that this option applies to protocol version 2 only. 1587.Pp 1588See also VERIFYING HOST KEYS in 1589.Xr ssh 1 . 1590.It Cm VisualHostKey 1591If this flag is set to 1592.Dq yes , 1593an ASCII art representation of the remote host key fingerprint is 1594printed in addition to the fingerprint string at login and 1595for unknown host keys. 1596If this flag is set to 1597.Dq no , 1598no fingerprint strings are printed at login and 1599only the fingerprint string will be printed for unknown host keys. 1600The default is 1601.Dq no . 1602.It Cm XAuthLocation 1603Specifies the full pathname of the 1604.Xr xauth 1 1605program. 1606The default is 1607.Pa /usr/X11R6/bin/xauth . 1608.El 1609.Sh PATTERNS 1610A 1611.Em pattern 1612consists of zero or more non-whitespace characters, 1613.Sq * 1614(a wildcard that matches zero or more characters), 1615or 1616.Sq ?\& 1617(a wildcard that matches exactly one character). 1618For example, to specify a set of declarations for any host in the 1619.Dq .co.uk 1620set of domains, 1621the following pattern could be used: 1622.Pp 1623.Dl Host *.co.uk 1624.Pp 1625The following pattern 1626would match any host in the 192.168.0.[0-9] network range: 1627.Pp 1628.Dl Host 192.168.0.? 1629.Pp 1630A 1631.Em pattern-list 1632is a comma-separated list of patterns. 1633Patterns within pattern-lists may be negated 1634by preceding them with an exclamation mark 1635.Pq Sq !\& . 1636For example, 1637to allow a key to be used from anywhere within an organization 1638except from the 1639.Dq dialup 1640pool, 1641the following entry (in authorized_keys) could be used: 1642.Pp 1643.Dl from=\&"!*.dialup.example.com,*.example.com\&" 1644.Sh FILES 1645.Bl -tag -width Ds 1646.It Pa ~/.ssh/config 1647This is the per-user configuration file. 1648The format of this file is described above. 1649This file is used by the SSH client. 1650Because of the potential for abuse, this file must have strict permissions: 1651read/write for the user, and not accessible by others. 1652.It Pa /etc/ssh/ssh_config 1653Systemwide configuration file. 1654This file provides defaults for those 1655values that are not specified in the user's configuration file, and 1656for those users who do not have a configuration file. 1657This file must be world-readable. 1658.El 1659.Sh SEE ALSO 1660.Xr ssh 1 1661.Sh AUTHORS 1662OpenSSH is a derivative of the original and free 1663ssh 1.2.12 release by Tatu Ylonen. 1664Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, 1665Theo de Raadt and Dug Song 1666removed many bugs, re-added newer features and 1667created OpenSSH. 1668Markus Friedl contributed the support for SSH 1669protocol versions 1.5 and 2.0. 1670