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diff --git a/crypto/openssh/ssh_config.5 b/crypto/openssh/ssh_config.5 new file mode 100644 index 0000000..c7da553 --- /dev/null +++ b/crypto/openssh/ssh_config.5 @@ -0,0 +1,1313 @@ +.\" +.\" Author: Tatu Ylonen <ylo@cs.hut.fi> +.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland +.\" All rights reserved +.\" +.\" As far as I am concerned, the code I have written for this software +.\" can be used freely for any purpose. Any derived versions of this +.\" software must be clearly marked as such, and if the derived work is +.\" incompatible with the protocol description in the RFC file, it must be +.\" called by a name other than "ssh" or "Secure Shell". +.\" +.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. +.\" Copyright (c) 1999 Aaron Campbell. All rights reserved. +.\" Copyright (c) 1999 Theo de Raadt. All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR +.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES +.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. +.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, +.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT +.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, +.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY +.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT +.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF +.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. +.\" +.\" $OpenBSD: ssh_config.5,v 1.161 2013/01/08 18:49:04 markus Exp $ +.\" $FreeBSD$ +.Dd January 8, 2013 +.Dt SSH_CONFIG 5 +.Os +.Sh NAME +.Nm ssh_config +.Nd OpenSSH SSH client configuration files +.Sh SYNOPSIS +.Nm ~/.ssh/config +.Nm /etc/ssh/ssh_config +.Sh DESCRIPTION +.Xr ssh 1 +obtains configuration data from the following sources in +the following order: +.Pp +.Bl -enum -offset indent -compact +.It +command-line options +.It +user's configuration file +.Pq Pa ~/.ssh/config +.It +system-wide configuration file +.Pq Pa /etc/ssh/ssh_config +.El +.Pp +For each parameter, the first obtained value +will be used. +The configuration files contain sections separated by +.Dq Host +specifications, and that section is only applied for hosts that +match one of the patterns given in the specification. +The matched host name is the one given on the command line. +.Pp +Since the first obtained value for each parameter is used, more +host-specific declarations should be given near the beginning of the +file, and general defaults at the end. +.Pp +The configuration file has the following format: +.Pp +Empty lines and lines starting with +.Ql # +are comments. +Otherwise a line is of the format +.Dq keyword arguments . +Configuration options may be separated by whitespace or +optional whitespace and exactly one +.Ql = ; +the latter format is useful to avoid the need to quote whitespace +when specifying configuration options using the +.Nm ssh , +.Nm scp , +and +.Nm sftp +.Fl o +option. +Arguments may optionally be enclosed in double quotes +.Pq \&" +in order to represent arguments containing spaces. +.Pp +The possible +keywords and their meanings are as follows (note that +keywords are case-insensitive and arguments are case-sensitive): +.Bl -tag -width Ds +.It Cm Host +Restricts the following declarations (up to the next +.Cm Host +keyword) to be only for those hosts that match one of the patterns +given after the keyword. +If more than one pattern is provided, they should be separated by whitespace. +A single +.Ql * +as a pattern can be used to provide global +defaults for all hosts. +The host is the +.Ar hostname +argument given on the command line (i.e. the name is not converted to +a canonicalized host name before matching). +.Pp +A pattern entry may be negated by prefixing it with an exclamation mark +.Pq Sq !\& . +If a negated entry is matched, then the +.Cm Host +entry is ignored, regardless of whether any other patterns on the line +match. +Negated matches are therefore useful to provide exceptions for wildcard +matches. +.Pp +See +.Sx PATTERNS +for more information on patterns. +.It Cm AddressFamily +Specifies which address family to use when connecting. +Valid arguments are +.Dq any , +.Dq inet +(use IPv4 only), or +.Dq inet6 +(use IPv6 only). +.It Cm BatchMode +If set to +.Dq yes , +passphrase/password querying will be disabled. +This option is useful in scripts and other batch jobs where no user +is present to supply the password. +The argument must be +.Dq yes +or +.Dq no . +The default is +.Dq no . +.It Cm BindAddress +Use the specified address on the local machine as the source address of +the connection. +Only useful on systems with more than one address. +Note that this option does not work if +.Cm UsePrivilegedPort +is set to +.Dq yes . +.It Cm ChallengeResponseAuthentication +Specifies whether to use challenge-response authentication. +The argument to this keyword must be +.Dq yes +or +.Dq no . +The default is +.Dq yes . +.It Cm CheckHostIP +If this flag is set to +.Dq yes , +.Xr ssh 1 +will additionally check the host IP address in the +.Pa known_hosts +file. +This allows ssh to detect if a host key changed due to DNS spoofing. +If the option is set to +.Dq no , +the check will not be executed. +The default is +.Dq no . +.It Cm Cipher +Specifies the cipher to use for encrypting the session +in protocol version 1. +Currently, +.Dq blowfish , +.Dq 3des , +and +.Dq des +are supported. +.Ar des +is only supported in the +.Xr ssh 1 +client for interoperability with legacy protocol 1 implementations +that do not support the +.Ar 3des +cipher. +Its use is strongly discouraged due to cryptographic weaknesses. +The default is +.Dq 3des . +.It Cm Ciphers +Specifies the ciphers allowed for protocol version 2 +in order of preference. +Multiple ciphers must be comma-separated. +The supported ciphers are +.Dq 3des-cbc , +.Dq aes128-cbc , +.Dq aes192-cbc , +.Dq aes256-cbc , +.Dq aes128-ctr , +.Dq aes192-ctr , +.Dq aes256-ctr , +.Dq aes128-gcm@openssh.com , +.Dq aes256-gcm@openssh.com , +.Dq arcfour128 , +.Dq arcfour256 , +.Dq arcfour , +.Dq blowfish-cbc , +and +.Dq cast128-cbc . +The default is: +.Bd -literal -offset 3n +aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128, +aes128-gcm@openssh.com,aes256-gcm@openssh.com, +aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc, +aes256-cbc,arcfour +.Ed +.It Cm ClearAllForwardings +Specifies that all local, remote, and dynamic port forwardings +specified in the configuration files or on the command line be +cleared. +This option is primarily useful when used from the +.Xr ssh 1 +command line to clear port forwardings set in +configuration files, and is automatically set by +.Xr scp 1 +and +.Xr sftp 1 . +The argument must be +.Dq yes +or +.Dq no . +The default is +.Dq no . +.It Cm Compression +Specifies whether to use compression. +The argument must be +.Dq yes +or +.Dq no . +The default is +.Dq no . +.It Cm CompressionLevel +Specifies the compression level to use if compression is enabled. +The argument must be an integer from 1 (fast) to 9 (slow, best). +The default level is 6, which is good for most applications. +The meaning of the values is the same as in +.Xr gzip 1 . +Note that this option applies to protocol version 1 only. +.It Cm ConnectionAttempts +Specifies the number of tries (one per second) to make before exiting. +The argument must be an integer. +This may be useful in scripts if the connection sometimes fails. +The default is 1. +.It Cm ConnectTimeout +Specifies the timeout (in seconds) used when connecting to the +SSH server, instead of using the default system TCP timeout. +This value is used only when the target is down or really unreachable, +not when it refuses the connection. +.It Cm ControlMaster +Enables the sharing of multiple sessions over a single network connection. +When set to +.Dq yes , +.Xr ssh 1 +will listen for connections on a control socket specified using the +.Cm ControlPath +argument. +Additional sessions can connect to this socket using the same +.Cm ControlPath +with +.Cm ControlMaster +set to +.Dq no +(the default). +These sessions will try to reuse the master instance's network connection +rather than initiating new ones, but will fall back to connecting normally +if the control socket does not exist, or is not listening. +.Pp +Setting this to +.Dq ask +will cause ssh +to listen for control connections, but require confirmation using the +.Ev SSH_ASKPASS +program before they are accepted (see +.Xr ssh-add 1 +for details). +If the +.Cm ControlPath +cannot be opened, +ssh will continue without connecting to a master instance. +.Pp +X11 and +.Xr ssh-agent 1 +forwarding is supported over these multiplexed connections, however the +display and agent forwarded will be the one belonging to the master +connection i.e. it is not possible to forward multiple displays or agents. +.Pp +Two additional options allow for opportunistic multiplexing: try to use a +master connection but fall back to creating a new one if one does not already +exist. +These options are: +.Dq auto +and +.Dq autoask . +The latter requires confirmation like the +.Dq ask +option. +.It Cm ControlPath +Specify the path to the control socket used for connection sharing as described +in the +.Cm ControlMaster +section above or the string +.Dq none +to disable connection sharing. +In the path, +.Ql %L +will be substituted by the first component of the local host name, +.Ql %l +will be substituted by the local host name (including any domain name), +.Ql %h +will be substituted by the target host name, +.Ql %n +will be substituted by the original target host name +specified on the command line, +.Ql %p +the port, +.Ql %r +by the remote login username, and +.Ql %u +by the username of the user running +.Xr ssh 1 . +It is recommended that any +.Cm ControlPath +used for opportunistic connection sharing include +at least %h, %p, and %r. +This ensures that shared connections are uniquely identified. +.It Cm ControlPersist +When used in conjunction with +.Cm ControlMaster , +specifies that the master connection should remain open +in the background (waiting for future client connections) +after the initial client connection has been closed. +If set to +.Dq no , +then the master connection will not be placed into the background, +and will close as soon as the initial client connection is closed. +If set to +.Dq yes , +then the master connection will remain in the background indefinitely +(until killed or closed via a mechanism such as the +.Xr ssh 1 +.Dq Fl O No exit +option). +If set to a time in seconds, or a time in any of the formats documented in +.Xr sshd_config 5 , +then the backgrounded master connection will automatically terminate +after it has remained idle (with no client connections) for the +specified time. +.It Cm DynamicForward +Specifies that a TCP port on the local machine be forwarded +over the secure channel, and the application +protocol is then used to determine where to connect to from the +remote machine. +.Pp +The argument must be +.Sm off +.Oo Ar bind_address : Oc Ar port . +.Sm on +IPv6 addresses can be specified by enclosing addresses in square brackets. +By default, the local port is bound in accordance with the +.Cm GatewayPorts +setting. +However, an explicit +.Ar bind_address +may be used to bind the connection to a specific address. +The +.Ar bind_address +of +.Dq localhost +indicates that the listening port be bound for local use only, while an +empty address or +.Sq * +indicates that the port should be available from all interfaces. +.Pp +Currently the SOCKS4 and SOCKS5 protocols are supported, and +.Xr ssh 1 +will act as a SOCKS server. +Multiple forwardings may be specified, and +additional forwardings can be given on the command line. +Only the superuser can forward privileged ports. +.It Cm EnableSSHKeysign +Setting this option to +.Dq yes +in the global client configuration file +.Pa /etc/ssh/ssh_config +enables the use of the helper program +.Xr ssh-keysign 8 +during +.Cm HostbasedAuthentication . +The argument must be +.Dq yes +or +.Dq no . +The default is +.Dq no . +This option should be placed in the non-hostspecific section. +See +.Xr ssh-keysign 8 +for more information. +.It Cm EscapeChar +Sets the escape character (default: +.Ql ~ ) . +The escape character can also +be set on the command line. +The argument should be a single character, +.Ql ^ +followed by a letter, or +.Dq none +to disable the escape +character entirely (making the connection transparent for binary +data). +.It Cm ExitOnForwardFailure +Specifies whether +.Xr ssh 1 +should terminate the connection if it cannot set up all requested +dynamic, tunnel, local, and remote port forwardings. +The argument must be +.Dq yes +or +.Dq no . +The default is +.Dq no . +.It Cm ForwardAgent +Specifies whether the connection to the authentication agent (if any) +will be forwarded to the remote machine. +The argument must be +.Dq yes +or +.Dq no . +The default is +.Dq no . +.Pp +Agent forwarding should be enabled with caution. +Users with the ability to bypass file permissions on the remote host +(for the agent's Unix-domain socket) +can access the local agent through the forwarded connection. +An attacker cannot obtain key material from the agent, +however they can perform operations on the keys that enable them to +authenticate using the identities loaded into the agent. +.It Cm ForwardX11 +Specifies whether X11 connections will be automatically redirected +over the secure channel and +.Ev DISPLAY +set. +The argument must be +.Dq yes +or +.Dq no . +The default is +.Dq no . +.Pp +X11 forwarding should be enabled with caution. +Users with the ability to bypass file permissions on the remote host +(for the user's X11 authorization database) +can access the local X11 display through the forwarded connection. +An attacker may then be able to perform activities such as keystroke monitoring +if the +.Cm ForwardX11Trusted +option is also enabled. +.It Cm ForwardX11Timeout +Specify a timeout for untrusted X11 forwarding +using the format described in the +.Sx TIME FORMATS +section of +.Xr sshd_config 5 . +X11 connections received by +.Xr ssh 1 +after this time will be refused. +The default is to disable untrusted X11 forwarding after twenty minutes has +elapsed. +.It Cm ForwardX11Trusted +If this option is set to +.Dq yes , +remote X11 clients will have full access to the original X11 display. +.Pp +If this option is set to +.Dq no , +remote X11 clients will be considered untrusted and prevented +from stealing or tampering with data belonging to trusted X11 +clients. +Furthermore, the +.Xr xauth 1 +token used for the session will be set to expire after 20 minutes. +Remote clients will be refused access after this time. +.Pp +The default is +.Dq no . +.Pp +See the X11 SECURITY extension specification for full details on +the restrictions imposed on untrusted clients. +.It Cm GatewayPorts +Specifies whether remote hosts are allowed to connect to local +forwarded ports. +By default, +.Xr ssh 1 +binds local port forwardings to the loopback address. +This prevents other remote hosts from connecting to forwarded ports. +.Cm GatewayPorts +can be used to specify that ssh +should bind local port forwardings to the wildcard address, +thus allowing remote hosts to connect to forwarded ports. +The argument must be +.Dq yes +or +.Dq no . +The default is +.Dq no . +.It Cm GlobalKnownHostsFile +Specifies one or more files to use for the global +host key database, separated by whitespace. +The default is +.Pa /etc/ssh/ssh_known_hosts , +.Pa /etc/ssh/ssh_known_hosts2 . +.It Cm GSSAPIAuthentication +Specifies whether user authentication based on GSSAPI is allowed. +The default is +.Dq no . +Note that this option applies to protocol version 2 only. +.It Cm GSSAPIDelegateCredentials +Forward (delegate) credentials to the server. +The default is +.Dq no . +Note that this option applies to protocol version 2 only. +.It Cm HashKnownHosts +Indicates that +.Xr ssh 1 +should hash host names and addresses when they are added to +.Pa ~/.ssh/known_hosts . +These hashed names may be used normally by +.Xr ssh 1 +and +.Xr sshd 8 , +but they do not reveal identifying information should the file's contents +be disclosed. +The default is +.Dq no . +Note that existing names and addresses in known hosts files +will not be converted automatically, +but may be manually hashed using +.Xr ssh-keygen 1 . +.It Cm HostbasedAuthentication +Specifies whether to try rhosts based authentication with public key +authentication. +The argument must be +.Dq yes +or +.Dq no . +The default is +.Dq no . +This option applies to protocol version 2 only and +is similar to +.Cm RhostsRSAAuthentication . +.It Cm HostKeyAlgorithms +Specifies the protocol version 2 host key algorithms +that the client wants to use in order of preference. +The default for this option is: +.Bd -literal -offset 3n +ecdsa-sha2-nistp256-cert-v01@openssh.com, +ecdsa-sha2-nistp384-cert-v01@openssh.com, +ecdsa-sha2-nistp521-cert-v01@openssh.com, +ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com, +ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com, +ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521, +ssh-rsa,ssh-dss +.Ed +.Pp +If hostkeys are known for the destination host then this default is modified +to prefer their algorithms. +.It Cm HostKeyAlias +Specifies an alias that should be used instead of the +real host name when looking up or saving the host key +in the host key database files. +This option is useful for tunneling SSH connections +or for multiple servers running on a single host. +.It Cm HostName +Specifies the real host name to log into. +This can be used to specify nicknames or abbreviations for hosts. +If the hostname contains the character sequence +.Ql %h , +then this will be replaced with the host name specified on the command line +(this is useful for manipulating unqualified names). +The default is the name given on the command line. +Numeric IP addresses are also permitted (both on the command line and in +.Cm HostName +specifications). +.It Cm IdentitiesOnly +Specifies that +.Xr ssh 1 +should only use the authentication identity files configured in the +.Nm +files, +even if +.Xr ssh-agent 1 +or a +.Cm PKCS11Provider +offers more identities. +The argument to this keyword must be +.Dq yes +or +.Dq no . +This option is intended for situations where ssh-agent +offers many different identities. +The default is +.Dq no . +.It Cm IdentityFile +Specifies a file from which the user's DSA, ECDSA or RSA authentication +identity is read. +The default is +.Pa ~/.ssh/identity +for protocol version 1, and +.Pa ~/.ssh/id_dsa , +.Pa ~/.ssh/id_ecdsa +and +.Pa ~/.ssh/id_rsa +for protocol version 2. +Additionally, any identities represented by the authentication agent +will be used for authentication. +.Xr ssh 1 +will try to load certificate information from the filename obtained by +appending +.Pa -cert.pub +to the path of a specified +.Cm IdentityFile . +.Pp +The file name may use the tilde +syntax to refer to a user's home directory or one of the following +escape characters: +.Ql %d +(local user's home directory), +.Ql %u +(local user name), +.Ql %l +(local host name), +.Ql %h +(remote host name) or +.Ql %r +(remote user name). +.Pp +It is possible to have +multiple identity files specified in configuration files; all these +identities will be tried in sequence. +Multiple +.Cm IdentityFile +directives will add to the list of identities tried (this behaviour +differs from that of other configuration directives). +.It Cm IPQoS +Specifies the IPv4 type-of-service or DSCP class for connections. +Accepted values are +.Dq af11 , +.Dq af12 , +.Dq af13 , +.Dq af21 , +.Dq af22 , +.Dq af23 , +.Dq af31 , +.Dq af32 , +.Dq af33 , +.Dq af41 , +.Dq af42 , +.Dq af43 , +.Dq cs0 , +.Dq cs1 , +.Dq cs2 , +.Dq cs3 , +.Dq cs4 , +.Dq cs5 , +.Dq cs6 , +.Dq cs7 , +.Dq ef , +.Dq lowdelay , +.Dq throughput , +.Dq reliability , +or a numeric value. +This option may take one or two arguments, separated by whitespace. +If one argument is specified, it is used as the packet class unconditionally. +If two values are specified, the first is automatically selected for +interactive sessions and the second for non-interactive sessions. +The default is +.Dq lowdelay +for interactive sessions and +.Dq throughput +for non-interactive sessions. +.It Cm KbdInteractiveAuthentication +Specifies whether to use keyboard-interactive authentication. +The argument to this keyword must be +.Dq yes +or +.Dq no . +The default is +.Dq yes . +.It Cm KbdInteractiveDevices +Specifies the list of methods to use in keyboard-interactive authentication. +Multiple method names must be comma-separated. +The default is to use the server specified list. +The methods available vary depending on what the server supports. +For an OpenSSH server, +it may be zero or more of: +.Dq bsdauth , +.Dq pam , +and +.Dq skey . +.It Cm KexAlgorithms +Specifies the available KEX (Key Exchange) algorithms. +Multiple algorithms must be comma-separated. +The default is: +.Bd -literal -offset indent +ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521, +diffie-hellman-group-exchange-sha256, +diffie-hellman-group-exchange-sha1, +diffie-hellman-group14-sha1, +diffie-hellman-group1-sha1 +.Ed +.It Cm LocalCommand +Specifies a command to execute on the local machine after successfully +connecting to the server. +The command string extends to the end of the line, and is executed with +the user's shell. +The following escape character substitutions will be performed: +.Ql %d +(local user's home directory), +.Ql %h +(remote host name), +.Ql %l +(local host name), +.Ql %n +(host name as provided on the command line), +.Ql %p +(remote port), +.Ql %r +(remote user name) or +.Ql %u +(local user name). +.Pp +The command is run synchronously and does not have access to the +session of the +.Xr ssh 1 +that spawned it. +It should not be used for interactive commands. +.Pp +This directive is ignored unless +.Cm PermitLocalCommand +has been enabled. +.It Cm LocalForward +Specifies that a TCP port on the local machine be forwarded over +the secure channel to the specified host and port from the remote machine. +The first argument must be +.Sm off +.Oo Ar bind_address : Oc Ar port +.Sm on +and the second argument must be +.Ar host : Ns Ar hostport . +IPv6 addresses can be specified by enclosing addresses in square brackets. +Multiple forwardings may be specified, and additional forwardings can be +given on the command line. +Only the superuser can forward privileged ports. +By default, the local port is bound in accordance with the +.Cm GatewayPorts +setting. +However, an explicit +.Ar bind_address +may be used to bind the connection to a specific address. +The +.Ar bind_address +of +.Dq localhost +indicates that the listening port be bound for local use only, while an +empty address or +.Sq * +indicates that the port should be available from all interfaces. +.It Cm LogLevel +Gives the verbosity level that is used when logging messages from +.Xr ssh 1 . +The possible values are: +QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. +The default is INFO. +DEBUG and DEBUG1 are equivalent. +DEBUG2 and DEBUG3 each specify higher levels of verbose output. +.It Cm MACs +Specifies the MAC (message authentication code) algorithms +in order of preference. +The MAC algorithm is used in protocol version 2 +for data integrity protection. +Multiple algorithms must be comma-separated. +The algorithms that contain +.Dq -etm +calculate the MAC after encryption (encrypt-then-mac). +These are considered safer and their use recommended. +The default is: +.Bd -literal -offset indent +hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com, +umac-64-etm@openssh.com,umac-128-etm@openssh.com, +hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com, +hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com, +hmac-md5-96-etm@openssh.com, +hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com, +hmac-sha2-256,hmac-sha2-512,hmac-ripemd160, +hmac-sha1-96,hmac-md5-96 +.Ed +.It Cm NoHostAuthenticationForLocalhost +This option can be used if the home directory is shared across machines. +In this case localhost will refer to a different machine on each of +the machines and the user will get many warnings about changed host keys. +However, this option disables host authentication for localhost. +The argument to this keyword must be +.Dq yes +or +.Dq no . +The default is to check the host key for localhost. +.It Cm NumberOfPasswordPrompts +Specifies the number of password prompts before giving up. +The argument to this keyword must be an integer. +The default is 3. +.It Cm PasswordAuthentication +Specifies whether to use password authentication. +The argument to this keyword must be +.Dq yes +or +.Dq no . +The default is +.Dq yes . +.It Cm PermitLocalCommand +Allow local command execution via the +.Ic LocalCommand +option or using the +.Ic !\& Ns Ar command +escape sequence in +.Xr ssh 1 . +The argument must be +.Dq yes +or +.Dq no . +The default is +.Dq no . +.It Cm PKCS11Provider +Specifies which PKCS#11 provider to use. +The argument to this keyword is the PKCS#11 shared library +.Xr ssh 1 +should use to communicate with a PKCS#11 token providing the user's +private RSA key. +.It Cm Port +Specifies the port number to connect on the remote host. +The default is 22. +.It Cm PreferredAuthentications +Specifies the order in which the client should try protocol 2 +authentication methods. +This allows a client to prefer one method (e.g.\& +.Cm keyboard-interactive ) +over another method (e.g.\& +.Cm password ) . +The default is: +.Bd -literal -offset indent +gssapi-with-mic,hostbased,publickey, +keyboard-interactive,password +.Ed +.It Cm Protocol +Specifies the protocol versions +.Xr ssh 1 +should support in order of preference. +The possible values are +.Sq 1 +and +.Sq 2 . +Multiple versions must be comma-separated. +When this option is set to +.Dq 2,1 +.Nm ssh +will try version 2 and fall back to version 1 +if version 2 is not available. +The default is +.Sq 2 . +.It Cm ProxyCommand +Specifies the command to use to connect to the server. +The command +string extends to the end of the line, and is executed with +the user's shell. +In the command string, any occurrence of +.Ql %h +will be substituted by the host name to +connect, +.Ql %p +by the port, and +.Ql %r +by the remote user name. +The command can be basically anything, +and should read from its standard input and write to its standard output. +It should eventually connect an +.Xr sshd 8 +server running on some machine, or execute +.Ic sshd -i +somewhere. +Host key management will be done using the +HostName of the host being connected (defaulting to the name typed by +the user). +Setting the command to +.Dq none +disables this option entirely. +Note that +.Cm CheckHostIP +is not available for connects with a proxy command. +.Pp +This directive is useful in conjunction with +.Xr nc 1 +and its proxy support. +For example, the following directive would connect via an HTTP proxy at +192.0.2.0: +.Bd -literal -offset 3n +ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p +.Ed +.It Cm PubkeyAuthentication +Specifies whether to try public key authentication. +The argument to this keyword must be +.Dq yes +or +.Dq no . +The default is +.Dq yes . +This option applies to protocol version 2 only. +.It Cm RekeyLimit +Specifies the maximum amount of data that may be transmitted before the +session key is renegotiated. +The argument is the number of bytes, with an optional suffix of +.Sq K , +.Sq M , +or +.Sq G +to indicate Kilobytes, Megabytes, or Gigabytes, respectively. +The default is between +.Sq 1G +and +.Sq 4G , +depending on the cipher. +This option applies to protocol version 2 only. +.It Cm RemoteForward +Specifies that a TCP port on the remote machine be forwarded over +the secure channel to the specified host and port from the local machine. +The first argument must be +.Sm off +.Oo Ar bind_address : Oc Ar port +.Sm on +and the second argument must be +.Ar host : Ns Ar hostport . +IPv6 addresses can be specified by enclosing addresses in square brackets. +Multiple forwardings may be specified, and additional +forwardings can be given on the command line. +Privileged ports can be forwarded only when +logging in as root on the remote machine. +.Pp +If the +.Ar port +argument is +.Ql 0 , +the listen port will be dynamically allocated on the server and reported +to the client at run time. +.Pp +If the +.Ar bind_address +is not specified, the default is to only bind to loopback addresses. +If the +.Ar bind_address +is +.Ql * +or an empty string, then the forwarding is requested to listen on all +interfaces. +Specifying a remote +.Ar bind_address +will only succeed if the server's +.Cm GatewayPorts +option is enabled (see +.Xr sshd_config 5 ) . +.It Cm RequestTTY +Specifies whether to request a pseudo-tty for the session. +The argument may be one of: +.Dq no +(never request a TTY), +.Dq yes +(always request a TTY when standard input is a TTY), +.Dq force +(always request a TTY) or +.Dq auto +(request a TTY when opening a login session). +This option mirrors the +.Fl t +and +.Fl T +flags for +.Xr ssh 1 . +.It Cm RhostsRSAAuthentication +Specifies whether to try rhosts based authentication with RSA host +authentication. +The argument must be +.Dq yes +or +.Dq no . +The default is +.Dq no . +This option applies to protocol version 1 only and requires +.Xr ssh 1 +to be setuid root. +.It Cm RSAAuthentication +Specifies whether to try RSA authentication. +The argument to this keyword must be +.Dq yes +or +.Dq no . +RSA authentication will only be +attempted if the identity file exists, or an authentication agent is +running. +The default is +.Dq yes . +Note that this option applies to protocol version 1 only. +.It Cm SendEnv +Specifies what variables from the local +.Xr environ 7 +should be sent to the server. +Note that environment passing is only supported for protocol 2. +The server must also support it, and the server must be configured to +accept these environment variables. +Refer to +.Cm AcceptEnv +in +.Xr sshd_config 5 +for how to configure the server. +Variables are specified by name, which may contain wildcard characters. +Multiple environment variables may be separated by whitespace or spread +across multiple +.Cm SendEnv +directives. +The default is not to send any environment variables. +.Pp +See +.Sx PATTERNS +for more information on patterns. +.It Cm ServerAliveCountMax +Sets the number of server alive messages (see below) which may be +sent without +.Xr ssh 1 +receiving any messages back from the server. +If this threshold is reached while server alive messages are being sent, +ssh will disconnect from the server, terminating the session. +It is important to note that the use of server alive messages is very +different from +.Cm TCPKeepAlive +(below). +The server alive messages are sent through the encrypted channel +and therefore will not be spoofable. +The TCP keepalive option enabled by +.Cm TCPKeepAlive +is spoofable. +The server alive mechanism is valuable when the client or +server depend on knowing when a connection has become inactive. +.Pp +The default value is 3. +If, for example, +.Cm ServerAliveInterval +(see below) is set to 15 and +.Cm ServerAliveCountMax +is left at the default, if the server becomes unresponsive, +ssh will disconnect after approximately 45 seconds. +This option applies to protocol version 2 only. +.It Cm ServerAliveInterval +Sets a timeout interval in seconds after which if no data has been received +from the server, +.Xr ssh 1 +will send a message through the encrypted +channel to request a response from the server. +The default +is 0, indicating that these messages will not be sent to the server. +This option applies to protocol version 2 only. +.It Cm StrictHostKeyChecking +If this flag is set to +.Dq yes , +.Xr ssh 1 +will never automatically add host keys to the +.Pa ~/.ssh/known_hosts +file, and refuses to connect to hosts whose host key has changed. +This provides maximum protection against trojan horse attacks, +though it can be annoying when the +.Pa /etc/ssh/ssh_known_hosts +file is poorly maintained or when connections to new hosts are +frequently made. +This option forces the user to manually +add all new hosts. +If this flag is set to +.Dq no , +ssh will automatically add new host keys to the +user known hosts files. +If this flag is set to +.Dq ask , +new host keys +will be added to the user known host files only after the user +has confirmed that is what they really want to do, and +ssh will refuse to connect to hosts whose host key has changed. +The host keys of +known hosts will be verified automatically in all cases. +The argument must be +.Dq yes , +.Dq no , +or +.Dq ask . +The default is +.Dq ask . +.It Cm TCPKeepAlive +Specifies whether the system should send TCP keepalive messages to the +other side. +If they are sent, death of the connection or crash of one +of the machines will be properly noticed. +However, this means that +connections will die if the route is down temporarily, and some people +find it annoying. +.Pp +The default is +.Dq yes +(to send TCP keepalive messages), and the client will notice +if the network goes down or the remote host dies. +This is important in scripts, and many users want it too. +.Pp +To disable TCP keepalive messages, the value should be set to +.Dq no . +.It Cm Tunnel +Request +.Xr tun 4 +device forwarding between the client and the server. +The argument must be +.Dq yes , +.Dq point-to-point +(layer 3), +.Dq ethernet +(layer 2), +or +.Dq no . +Specifying +.Dq yes +requests the default tunnel mode, which is +.Dq point-to-point . +The default is +.Dq no . +.It Cm TunnelDevice +Specifies the +.Xr tun 4 +devices to open on the client +.Pq Ar local_tun +and the server +.Pq Ar remote_tun . +.Pp +The argument must be +.Sm off +.Ar local_tun Op : Ar remote_tun . +.Sm on +The devices may be specified by numerical ID or the keyword +.Dq any , +which uses the next available tunnel device. +If +.Ar remote_tun +is not specified, it defaults to +.Dq any . +The default is +.Dq any:any . +.It Cm UsePrivilegedPort +Specifies whether to use a privileged port for outgoing connections. +The argument must be +.Dq yes +or +.Dq no . +The default is +.Dq no . +If set to +.Dq yes , +.Xr ssh 1 +must be setuid root. +Note that this option must be set to +.Dq yes +for +.Cm RhostsRSAAuthentication +with older servers. +.It Cm User +Specifies the user to log in as. +This can be useful when a different user name is used on different machines. +This saves the trouble of +having to remember to give the user name on the command line. +.It Cm UserKnownHostsFile +Specifies one or more files to use for the user +host key database, separated by whitespace. +The default is +.Pa ~/.ssh/known_hosts , +.Pa ~/.ssh/known_hosts2 . +.It Cm VerifyHostKeyDNS +Specifies whether to verify the remote key using DNS and SSHFP resource +records. +If this option is set to +.Dq yes , +the client will implicitly trust keys that match a secure fingerprint +from DNS. +Insecure fingerprints will be handled as if this option was set to +.Dq ask . +If this option is set to +.Dq ask , +information on fingerprint match will be displayed, but the user will still +need to confirm new host keys according to the +.Cm StrictHostKeyChecking +option. +The argument must be +.Dq yes , +.Dq no , +or +.Dq ask . +The default is +.Dq no . +Note that this option applies to protocol version 2 only. +.Pp +See also +.Sx VERIFYING HOST KEYS +in +.Xr ssh 1 . +.It Cm VersionAddendum +Specifies a string to append to the regular version string to identify +OS- or site-specific modifications. +The default is +.Dq FreeBSD-20130322 . +.It Cm VisualHostKey +If this flag is set to +.Dq yes , +an ASCII art representation of the remote host key fingerprint is +printed in addition to the hex fingerprint string at login and +for unknown host keys. +If this flag is set to +.Dq no , +no fingerprint strings are printed at login and +only the hex fingerprint string will be printed for unknown host keys. +The default is +.Dq no . +.It Cm XAuthLocation +Specifies the full pathname of the +.Xr xauth 1 +program. +The default is +.Pa /usr/local/bin/xauth . +.El +.Sh PATTERNS +A +.Em pattern +consists of zero or more non-whitespace characters, +.Sq * +(a wildcard that matches zero or more characters), +or +.Sq ?\& +(a wildcard that matches exactly one character). +For example, to specify a set of declarations for any host in the +.Dq .co.uk +set of domains, +the following pattern could be used: +.Pp +.Dl Host *.co.uk +.Pp +The following pattern +would match any host in the 192.168.0.[0-9] network range: +.Pp +.Dl Host 192.168.0.? +.Pp +A +.Em pattern-list +is a comma-separated list of patterns. +Patterns within pattern-lists may be negated +by preceding them with an exclamation mark +.Pq Sq !\& . +For example, +to allow a key to be used from anywhere within an organisation +except from the +.Dq dialup +pool, +the following entry (in authorized_keys) could be used: +.Pp +.Dl from=\&"!*.dialup.example.com,*.example.com\&" +.Sh FILES +.Bl -tag -width Ds +.It Pa ~/.ssh/config +This is the per-user configuration file. +The format of this file is described above. +This file is used by the SSH client. +Because of the potential for abuse, this file must have strict permissions: +read/write for the user, and not accessible by others. +.It Pa /etc/ssh/ssh_config +Systemwide configuration file. +This file provides defaults for those +values that are not specified in the user's configuration file, and +for those users who do not have a configuration file. +This file must be world-readable. +.El +.Sh SEE ALSO +.Xr ssh 1 +.Sh AUTHORS +OpenSSH is a derivative of the original and free +ssh 1.2.12 release by Tatu Ylonen. +Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, +Theo de Raadt and Dug Song +removed many bugs, re-added newer features and +created OpenSSH. +Markus Friedl contributed the support for SSH +protocol versions 1.5 and 2.0. |