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Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.14

1.1       stevesk     1: .\"  -*- nroff -*-
                      2: .\"
                      3: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
                      4: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
                      5: .\"                    All rights reserved
                      6: .\"
                      7: .\" As far as I am concerned, the code I have written for this software
                      8: .\" can be used freely for any purpose.  Any derived versions of this
                      9: .\" software must be clearly marked as such, and if the derived work is
                     10: .\" incompatible with the protocol description in the RFC file, it must be
                     11: .\" called by a name other than "ssh" or "Secure Shell".
                     12: .\"
                     13: .\" Copyright (c) 1999,2000 Markus Friedl.  All rights reserved.
                     14: .\" Copyright (c) 1999 Aaron Campbell.  All rights reserved.
                     15: .\" Copyright (c) 1999 Theo de Raadt.  All rights reserved.
                     16: .\"
                     17: .\" Redistribution and use in source and binary forms, with or without
                     18: .\" modification, are permitted provided that the following conditions
                     19: .\" are met:
                     20: .\" 1. Redistributions of source code must retain the above copyright
                     21: .\"    notice, this list of conditions and the following disclaimer.
                     22: .\" 2. Redistributions in binary form must reproduce the above copyright
                     23: .\"    notice, this list of conditions and the following disclaimer in the
                     24: .\"    documentation and/or other materials provided with the distribution.
                     25: .\"
                     26: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
                     27: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
                     28: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
                     29: .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
                     30: .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
                     31: .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
                     32: .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
                     33: .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
                     34: .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
                     35: .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
                     36: .\"
1.14    ! markus     37: .\" $OpenBSD: ssh_config.5,v 1.13 2003/06/10 09:12:12 jmc Exp $
1.1       stevesk    38: .Dd September 25, 1999
                     39: .Dt SSH_CONFIG 5
                     40: .Os
                     41: .Sh NAME
                     42: .Nm ssh_config
                     43: .Nd OpenSSH SSH client configuration files
                     44: .Sh SYNOPSIS
                     45: .Bl -tag -width Ds -compact
                     46: .It Pa $HOME/.ssh/config
                     47: .It Pa /etc/ssh/ssh_config
                     48: .El
                     49: .Sh DESCRIPTION
                     50: .Nm ssh
                     51: obtains configuration data from the following sources in
                     52: the following order:
1.2       stevesk    53: .Bl -enum -offset indent -compact
                     54: .It
                     55: command-line options
                     56: .It
                     57: user's configuration file
                     58: .Pq Pa $HOME/.ssh/config
                     59: .It
                     60: system-wide configuration file
                     61: .Pq Pa /etc/ssh/ssh_config
                     62: .El
1.1       stevesk    63: .Pp
                     64: For each parameter, the first obtained value
                     65: will be used.
                     66: The configuration files contain sections bracketed by
                     67: .Dq Host
                     68: specifications, and that section is only applied for hosts that
                     69: match one of the patterns given in the specification.
                     70: The matched host name is the one given on the command line.
                     71: .Pp
                     72: Since the first obtained value for each parameter is used, more
                     73: host-specific declarations should be given near the beginning of the
                     74: file, and general defaults at the end.
                     75: .Pp
                     76: The configuration file has the following format:
                     77: .Pp
                     78: Empty lines and lines starting with
                     79: .Ql #
                     80: are comments.
                     81: .Pp
                     82: Otherwise a line is of the format
                     83: .Dq keyword arguments .
                     84: Configuration options may be separated by whitespace or
                     85: optional whitespace and exactly one
                     86: .Ql = ;
                     87: the latter format is useful to avoid the need to quote whitespace
                     88: when specifying configuration options using the
                     89: .Nm ssh ,
                     90: .Nm scp
                     91: and
                     92: .Nm sftp
                     93: .Fl o
                     94: option.
                     95: .Pp
                     96: The possible
                     97: keywords and their meanings are as follows (note that
                     98: keywords are case-insensitive and arguments are case-sensitive):
                     99: .Bl -tag -width Ds
                    100: .It Cm Host
                    101: Restricts the following declarations (up to the next
                    102: .Cm Host
                    103: keyword) to be only for those hosts that match one of the patterns
                    104: given after the keyword.
                    105: .Ql \&*
                    106: and
                    107: .Ql ?
                    108: can be used as wildcards in the
                    109: patterns.
                    110: A single
                    111: .Ql \&*
                    112: as a pattern can be used to provide global
                    113: defaults for all hosts.
                    114: The host is the
                    115: .Ar hostname
                    116: argument given on the command line (i.e., the name is not converted to
                    117: a canonicalized host name before matching).
1.10      djm       118: .It Cm AddressFamily
1.11      jmc       119: Specifies which address family to use when connecting.
                    120: Valid arguments are
1.10      djm       121: .Dq any ,
                    122: .Dq inet
                    123: (Use IPv4 only) or
                    124: .Dq inet6
                    125: (Use IPv6 only.)
1.1       stevesk   126: .It Cm AFSTokenPassing
                    127: Specifies whether to pass AFS tokens to remote host.
                    128: The argument to this keyword must be
                    129: .Dq yes
                    130: or
                    131: .Dq no .
                    132: This option applies to protocol version 1 only.
                    133: .It Cm BatchMode
                    134: If set to
                    135: .Dq yes ,
                    136: passphrase/password querying will be disabled.
                    137: This option is useful in scripts and other batch jobs where no user
                    138: is present to supply the password.
                    139: The argument must be
                    140: .Dq yes
                    141: or
                    142: .Dq no .
                    143: The default is
                    144: .Dq no .
                    145: .It Cm BindAddress
                    146: Specify the interface to transmit from on machines with multiple
                    147: interfaces or aliased addresses.
                    148: Note that this option does not work if
                    149: .Cm UsePrivilegedPort
                    150: is set to
                    151: .Dq yes .
                    152: .It Cm ChallengeResponseAuthentication
                    153: Specifies whether to use challenge response authentication.
                    154: The argument to this keyword must be
                    155: .Dq yes
                    156: or
                    157: .Dq no .
                    158: The default is
                    159: .Dq yes .
                    160: .It Cm CheckHostIP
                    161: If this flag is set to
                    162: .Dq yes ,
                    163: ssh will additionally check the host IP address in the
                    164: .Pa known_hosts
                    165: file.
                    166: This allows ssh to detect if a host key changed due to DNS spoofing.
                    167: If the option is set to
                    168: .Dq no ,
                    169: the check will not be executed.
                    170: The default is
                    171: .Dq yes .
                    172: .It Cm Cipher
                    173: Specifies the cipher to use for encrypting the session
                    174: in protocol version 1.
                    175: Currently,
                    176: .Dq blowfish ,
                    177: .Dq 3des ,
                    178: and
                    179: .Dq des
                    180: are supported.
                    181: .Ar des
                    182: is only supported in the
                    183: .Nm ssh
                    184: client for interoperability with legacy protocol 1 implementations
                    185: that do not support the
                    186: .Ar 3des
1.7       jmc       187: cipher.
                    188: Its use is strongly discouraged due to cryptographic weaknesses.
1.1       stevesk   189: The default is
                    190: .Dq 3des .
                    191: .It Cm Ciphers
                    192: Specifies the ciphers allowed for protocol version 2
                    193: in order of preference.
                    194: Multiple ciphers must be comma-separated.
                    195: The default is
                    196: .Pp
                    197: .Bd -literal
                    198:   ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
                    199:     aes192-cbc,aes256-cbc''
                    200: .Ed
                    201: .It Cm ClearAllForwardings
                    202: Specifies that all local, remote and dynamic port forwardings
                    203: specified in the configuration files or on the command line be
1.7       jmc       204: cleared.
                    205: This option is primarily useful when used from the
1.1       stevesk   206: .Nm ssh
                    207: command line to clear port forwardings set in
                    208: configuration files, and is automatically set by
                    209: .Xr scp 1
                    210: and
                    211: .Xr sftp 1 .
                    212: The argument must be
                    213: .Dq yes
                    214: or
                    215: .Dq no .
                    216: The default is
                    217: .Dq no .
                    218: .It Cm Compression
                    219: Specifies whether to use compression.
                    220: The argument must be
                    221: .Dq yes
                    222: or
                    223: .Dq no .
                    224: The default is
                    225: .Dq no .
                    226: .It Cm CompressionLevel
                    227: Specifies the compression level to use if compression is enabled.
                    228: The argument must be an integer from 1 (fast) to 9 (slow, best).
                    229: The default level is 6, which is good for most applications.
                    230: The meaning of the values is the same as in
                    231: .Xr gzip 1 .
                    232: Note that this option applies to protocol version 1 only.
                    233: .It Cm ConnectionAttempts
                    234: Specifies the number of tries (one per second) to make before exiting.
                    235: The argument must be an integer.
                    236: This may be useful in scripts if the connection sometimes fails.
                    237: The default is 1.
1.9       djm       238: .It Cm ConnectTimeout
                    239: Specifies the timeout (in seconds) used when connecting to the ssh
1.11      jmc       240: server, instead of using the default system TCP timeout.
                    241: This value is used only when the target is down or really unreachable,
                    242: not when it refuses the connection.
1.1       stevesk   243: .It Cm DynamicForward
                    244: Specifies that a TCP/IP port on the local machine be forwarded
                    245: over the secure channel, and the application
                    246: protocol is then used to determine where to connect to from the
1.7       jmc       247: remote machine.
                    248: The argument must be a port number.
1.1       stevesk   249: Currently the SOCKS4 protocol is supported, and
                    250: .Nm ssh
                    251: will act as a SOCKS4 server.
                    252: Multiple forwardings may be specified, and
1.7       jmc       253: additional forwardings can be given on the command line.
                    254: Only the superuser can forward privileged ports.
1.14    ! markus    255: .It Cm EnableSSHKeysign
        !           256: Setting this option to
        !           257: .Dq yes
        !           258: in the global client configuration file
        !           259: .Pa /etc/ssh/ssh_config
        !           260: enables the use of the helper program
        !           261: .Xr ssh-keysign 8
        !           262: during
        !           263: .Cm HostbasedAuthentication .
        !           264: The argument must be
        !           265: .Dq yes
        !           266: or
        !           267: .Dq no .
        !           268: The default is
        !           269: .Dq no .
        !           270: See
        !           271: .Xr ssh-keysign 8
        !           272: for more information.
1.1       stevesk   273: .It Cm EscapeChar
                    274: Sets the escape character (default:
                    275: .Ql ~ ) .
                    276: The escape character can also
                    277: be set on the command line.
                    278: The argument should be a single character,
                    279: .Ql ^
                    280: followed by a letter, or
                    281: .Dq none
                    282: to disable the escape
                    283: character entirely (making the connection transparent for binary
                    284: data).
                    285: .It Cm ForwardAgent
                    286: Specifies whether the connection to the authentication agent (if any)
                    287: will be forwarded to the remote machine.
                    288: The argument must be
                    289: .Dq yes
                    290: or
                    291: .Dq no .
                    292: The default is
                    293: .Dq no .
1.3       stevesk   294: .Pp
1.7       jmc       295: Agent forwarding should be enabled with caution.
                    296: Users with the ability to bypass file permissions on the remote host
                    297: (for the agent's Unix-domain socket)
                    298: can access the local agent through the forwarded connection.
                    299: An attacker cannot obtain key material from the agent,
1.3       stevesk   300: however they can perform operations on the keys that enable them to
                    301: authenticate using the identities loaded into the agent.
1.1       stevesk   302: .It Cm ForwardX11
                    303: Specifies whether X11 connections will be automatically redirected
                    304: over the secure channel and
                    305: .Ev DISPLAY
                    306: set.
                    307: The argument must be
                    308: .Dq yes
                    309: or
                    310: .Dq no .
                    311: The default is
                    312: .Dq no .
1.3       stevesk   313: .Pp
1.7       jmc       314: X11 forwarding should be enabled with caution.
                    315: Users with the ability to bypass file permissions on the remote host
                    316: (for the user's X authorization database)
                    317: can access the local X11 display through the forwarded connection.
                    318: An attacker may then be able to perform activities such as keystroke monitoring.
1.1       stevesk   319: .It Cm GatewayPorts
                    320: Specifies whether remote hosts are allowed to connect to local
                    321: forwarded ports.
                    322: By default,
                    323: .Nm ssh
1.7       jmc       324: binds local port forwardings to the loopback address.
                    325: This prevents other remote hosts from connecting to forwarded ports.
1.1       stevesk   326: .Cm GatewayPorts
                    327: can be used to specify that
                    328: .Nm ssh
                    329: should bind local port forwardings to the wildcard address,
                    330: thus allowing remote hosts to connect to forwarded ports.
                    331: The argument must be
                    332: .Dq yes
                    333: or
                    334: .Dq no .
                    335: The default is
                    336: .Dq no .
                    337: .It Cm GlobalKnownHostsFile
                    338: Specifies a file to use for the global
                    339: host key database instead of
                    340: .Pa /etc/ssh/ssh_known_hosts .
                    341: .It Cm HostbasedAuthentication
                    342: Specifies whether to try rhosts based authentication with public key
                    343: authentication.
                    344: The argument must be
                    345: .Dq yes
                    346: or
                    347: .Dq no .
                    348: The default is
                    349: .Dq no .
                    350: This option applies to protocol version 2 only and
                    351: is similar to
                    352: .Cm RhostsRSAAuthentication .
                    353: .It Cm HostKeyAlgorithms
                    354: Specifies the protocol version 2 host key algorithms
                    355: that the client wants to use in order of preference.
                    356: The default for this option is:
                    357: .Dq ssh-rsa,ssh-dss .
                    358: .It Cm HostKeyAlias
                    359: Specifies an alias that should be used instead of the
                    360: real host name when looking up or saving the host key
                    361: in the host key database files.
                    362: This option is useful for tunneling ssh connections
                    363: or for multiple servers running on a single host.
                    364: .It Cm HostName
                    365: Specifies the real host name to log into.
                    366: This can be used to specify nicknames or abbreviations for hosts.
                    367: Default is the name given on the command line.
                    368: Numeric IP addresses are also permitted (both on the command line and in
                    369: .Cm HostName
                    370: specifications).
                    371: .It Cm IdentityFile
                    372: Specifies a file from which the user's RSA or DSA authentication identity
1.11      jmc       373: is read.
                    374: The default is
1.1       stevesk   375: .Pa $HOME/.ssh/identity
                    376: for protocol version 1, and
                    377: .Pa $HOME/.ssh/id_rsa
                    378: and
                    379: .Pa $HOME/.ssh/id_dsa
                    380: for protocol version 2.
                    381: Additionally, any identities represented by the authentication agent
                    382: will be used for authentication.
                    383: The file name may use the tilde
                    384: syntax to refer to a user's home directory.
                    385: It is possible to have
                    386: multiple identity files specified in configuration files; all these
                    387: identities will be tried in sequence.
                    388: .It Cm KeepAlive
                    389: Specifies whether the system should send TCP keepalive messages to the
                    390: other side.
                    391: If they are sent, death of the connection or crash of one
                    392: of the machines will be properly noticed.
                    393: However, this means that
                    394: connections will die if the route is down temporarily, and some people
                    395: find it annoying.
                    396: .Pp
                    397: The default is
                    398: .Dq yes
                    399: (to send keepalives), and the client will notice
                    400: if the network goes down or the remote host dies.
                    401: This is important in scripts, and many users want it too.
                    402: .Pp
                    403: To disable keepalives, the value should be set to
                    404: .Dq no .
                    405: .It Cm KerberosAuthentication
                    406: Specifies whether Kerberos authentication will be used.
                    407: The argument to this keyword must be
                    408: .Dq yes
                    409: or
                    410: .Dq no .
                    411: .It Cm KerberosTgtPassing
                    412: Specifies whether a Kerberos TGT will be forwarded to the server.
                    413: This will only work if the Kerberos server is actually an AFS kaserver.
                    414: The argument to this keyword must be
                    415: .Dq yes
                    416: or
                    417: .Dq no .
                    418: .It Cm LocalForward
                    419: Specifies that a TCP/IP port on the local machine be forwarded over
                    420: the secure channel to the specified host and port from the remote machine.
                    421: The first argument must be a port number, and the second must be
                    422: .Ar host:port .
                    423: IPv6 addresses can be specified with an alternative syntax:
                    424: .Ar host/port .
                    425: Multiple forwardings may be specified, and additional
                    426: forwardings can be given on the command line.
                    427: Only the superuser can forward privileged ports.
                    428: .It Cm LogLevel
                    429: Gives the verbosity level that is used when logging messages from
                    430: .Nm ssh .
                    431: The possible values are:
                    432: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3.
1.7       jmc       433: The default is INFO.
                    434: DEBUG and DEBUG1 are equivalent.
                    435: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1       stevesk   436: .It Cm MACs
                    437: Specifies the MAC (message authentication code) algorithms
                    438: in order of preference.
                    439: The MAC algorithm is used in protocol version 2
                    440: for data integrity protection.
                    441: Multiple algorithms must be comma-separated.
                    442: The default is
                    443: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
                    444: .It Cm NoHostAuthenticationForLocalhost
                    445: This option can be used if the home directory is shared across machines.
                    446: In this case localhost will refer to a different machine on each of
                    447: the machines and the user will get many warnings about changed host keys.
                    448: However, this option disables host authentication for localhost.
                    449: The argument to this keyword must be
                    450: .Dq yes
                    451: or
                    452: .Dq no .
                    453: The default is to check the host key for localhost.
                    454: .It Cm NumberOfPasswordPrompts
                    455: Specifies the number of password prompts before giving up.
                    456: The argument to this keyword must be an integer.
                    457: Default is 3.
                    458: .It Cm PasswordAuthentication
                    459: Specifies whether to use password authentication.
                    460: The argument to this keyword must be
                    461: .Dq yes
                    462: or
                    463: .Dq no .
                    464: The default is
                    465: .Dq yes .
                    466: .It Cm Port
                    467: Specifies the port number to connect on the remote host.
                    468: Default is 22.
                    469: .It Cm PreferredAuthentications
                    470: Specifies the order in which the client should try protocol 2
1.11      jmc       471: authentication methods.
                    472: This allows a client to prefer one method (e.g.
1.1       stevesk   473: .Cm keyboard-interactive )
                    474: over another method (e.g.
                    475: .Cm password )
                    476: The default for this option is:
                    477: .Dq hostbased,publickey,keyboard-interactive,password .
                    478: .It Cm Protocol
                    479: Specifies the protocol versions
                    480: .Nm ssh
                    481: should support in order of preference.
                    482: The possible values are
                    483: .Dq 1
                    484: and
                    485: .Dq 2 .
                    486: Multiple versions must be comma-separated.
                    487: The default is
                    488: .Dq 2,1 .
                    489: This means that
                    490: .Nm ssh
                    491: tries version 2 and falls back to version 1
                    492: if version 2 is not available.
                    493: .It Cm ProxyCommand
                    494: Specifies the command to use to connect to the server.
                    495: The command
                    496: string extends to the end of the line, and is executed with
                    497: .Pa /bin/sh .
                    498: In the command string,
                    499: .Ql %h
                    500: will be substituted by the host name to
                    501: connect and
                    502: .Ql %p
                    503: by the port.
                    504: The command can be basically anything,
                    505: and should read from its standard input and write to its standard output.
                    506: It should eventually connect an
                    507: .Xr sshd 8
                    508: server running on some machine, or execute
                    509: .Ic sshd -i
                    510: somewhere.
                    511: Host key management will be done using the
                    512: HostName of the host being connected (defaulting to the name typed by
                    513: the user).
1.7       jmc       514: Setting the command to
                    515: .Dq none
1.6       markus    516: disables this option entirely.
1.1       stevesk   517: Note that
                    518: .Cm CheckHostIP
                    519: is not available for connects with a proxy command.
                    520: .Pp
                    521: .It Cm PubkeyAuthentication
                    522: Specifies whether to try public key authentication.
                    523: The argument to this keyword must be
                    524: .Dq yes
                    525: or
                    526: .Dq no .
                    527: The default is
                    528: .Dq yes .
                    529: This option applies to protocol version 2 only.
                    530: .It Cm RemoteForward
                    531: Specifies that a TCP/IP port on the remote machine be forwarded over
                    532: the secure channel to the specified host and port from the local machine.
                    533: The first argument must be a port number, and the second must be
                    534: .Ar host:port .
                    535: IPv6 addresses can be specified with an alternative syntax:
                    536: .Ar host/port .
                    537: Multiple forwardings may be specified, and additional
                    538: forwardings can be given on the command line.
                    539: Only the superuser can forward privileged ports.
                    540: .It Cm RhostsAuthentication
                    541: Specifies whether to try rhosts based authentication.
                    542: Note that this
                    543: declaration only affects the client side and has no effect whatsoever
                    544: on security.
                    545: Most servers do not permit RhostsAuthentication because it
                    546: is not secure (see
                    547: .Cm RhostsRSAAuthentication ) .
                    548: The argument to this keyword must be
                    549: .Dq yes
                    550: or
                    551: .Dq no .
                    552: The default is
                    553: .Dq no .
1.4       stevesk   554: This option applies to protocol version 1 only and requires
                    555: .Nm ssh
                    556: to be setuid root and
                    557: .Cm UsePrivilegedPort
                    558: to be set to
                    559: .Dq yes .
1.1       stevesk   560: .It Cm RhostsRSAAuthentication
                    561: Specifies whether to try rhosts based authentication with RSA host
                    562: authentication.
                    563: The argument must be
                    564: .Dq yes
                    565: or
                    566: .Dq no .
                    567: The default is
                    568: .Dq no .
                    569: This option applies to protocol version 1 only and requires
                    570: .Nm ssh
                    571: to be setuid root.
                    572: .It Cm RSAAuthentication
                    573: Specifies whether to try RSA authentication.
                    574: The argument to this keyword must be
                    575: .Dq yes
                    576: or
                    577: .Dq no .
                    578: RSA authentication will only be
                    579: attempted if the identity file exists, or an authentication agent is
                    580: running.
                    581: The default is
                    582: .Dq yes .
                    583: Note that this option applies to protocol version 1 only.
                    584: .It Cm SmartcardDevice
1.11      jmc       585: Specifies which smartcard device to use.
                    586: The argument to this keyword is the device
1.1       stevesk   587: .Nm ssh
                    588: should use to communicate with a smartcard used for storing the user's
1.11      jmc       589: private RSA key.
                    590: By default, no device is specified and smartcard support is not activated.
1.1       stevesk   591: .It Cm StrictHostKeyChecking
                    592: If this flag is set to
                    593: .Dq yes ,
                    594: .Nm ssh
                    595: will never automatically add host keys to the
                    596: .Pa $HOME/.ssh/known_hosts
                    597: file, and refuses to connect to hosts whose host key has changed.
                    598: This provides maximum protection against trojan horse attacks,
                    599: however, can be annoying when the
                    600: .Pa /etc/ssh/ssh_known_hosts
                    601: file is poorly maintained, or connections to new hosts are
                    602: frequently made.
                    603: This option forces the user to manually
                    604: add all new hosts.
                    605: If this flag is set to
                    606: .Dq no ,
                    607: .Nm ssh
                    608: will automatically add new host keys to the
                    609: user known hosts files.
                    610: If this flag is set to
                    611: .Dq ask ,
                    612: new host keys
                    613: will be added to the user known host files only after the user
                    614: has confirmed that is what they really want to do, and
                    615: .Nm ssh
                    616: will refuse to connect to hosts whose host key has changed.
                    617: The host keys of
                    618: known hosts will be verified automatically in all cases.
                    619: The argument must be
                    620: .Dq yes ,
                    621: .Dq no
                    622: or
                    623: .Dq ask .
                    624: The default is
                    625: .Dq ask .
                    626: .It Cm UsePrivilegedPort
                    627: Specifies whether to use a privileged port for outgoing connections.
                    628: The argument must be
                    629: .Dq yes
                    630: or
                    631: .Dq no .
                    632: The default is
                    633: .Dq no .
1.4       stevesk   634: If set to
                    635: .Dq yes
                    636: .Nm ssh
                    637: must be setuid root.
1.1       stevesk   638: Note that this option must be set to
                    639: .Dq yes
                    640: if
                    641: .Cm RhostsAuthentication
                    642: and
                    643: .Cm RhostsRSAAuthentication
                    644: authentications are needed with older servers.
                    645: .It Cm User
                    646: Specifies the user to log in as.
                    647: This can be useful when a different user name is used on different machines.
                    648: This saves the trouble of
                    649: having to remember to give the user name on the command line.
                    650: .It Cm UserKnownHostsFile
                    651: Specifies a file to use for the user
                    652: host key database instead of
                    653: .Pa $HOME/.ssh/known_hosts .
1.8       jakob     654: .It Cm VerifyHostKeyDNS
                    655: Specifies whether to verify the remote key using DNS and SSHFP resource
                    656: records.
                    657: The default is
                    658: .Dq no .
1.12      jakob     659: Note that this option applies to protocol version 2 only.
1.1       stevesk   660: .It Cm XAuthLocation
1.5       stevesk   661: Specifies the full pathname of the
1.1       stevesk   662: .Xr xauth 1
                    663: program.
                    664: The default is
                    665: .Pa /usr/X11R6/bin/xauth .
                    666: .El
                    667: .Sh FILES
                    668: .Bl -tag -width Ds
                    669: .It Pa $HOME/.ssh/config
                    670: This is the per-user configuration file.
                    671: The format of this file is described above.
                    672: This file is used by the
                    673: .Nm ssh
                    674: client.
                    675: This file does not usually contain any sensitive information,
                    676: but the recommended permissions are read/write for the user, and not
                    677: accessible by others.
                    678: .It Pa /etc/ssh/ssh_config
                    679: Systemwide configuration file.
                    680: This file provides defaults for those
                    681: values that are not specified in the user's configuration file, and
                    682: for those users who do not have a configuration file.
                    683: This file must be world-readable.
                    684: .El
1.13      jmc       685: .Sh SEE ALSO
                    686: .Xr ssh 1
1.1       stevesk   687: .Sh AUTHORS
                    688: OpenSSH is a derivative of the original and free
                    689: ssh 1.2.12 release by Tatu Ylonen.
                    690: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
                    691: Theo de Raadt and Dug Song
                    692: removed many bugs, re-added newer features and
                    693: created OpenSSH.
                    694: Markus Friedl contributed the support for SSH
                    695: protocol versions 1.5 and 2.0.