| .\" -*- nroff -*- |
| .\" |
| .\" 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 1.3 2002/08/27 17:18:40 stevesk Exp $ |
| .Dd September 25, 1999 |
| .Dt SSH_CONFIG 5 |
| .Os |
| .Sh NAME |
| .Nm ssh_config |
| .Nd OpenSSH SSH client configuration files |
| .Sh SYNOPSIS |
| .Bl -tag -width Ds -compact |
| .It Pa $HOME/.ssh/config |
| .It Pa /etc/ssh/ssh_config |
| .El |
| .Sh DESCRIPTION |
| .Nm ssh |
| obtains configuration data from the following sources in |
| the following order: |
| .Bl -enum -offset indent -compact |
| .It |
| command-line options |
| .It |
| user's configuration file |
| .Pq Pa $HOME/.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 bracketed 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. |
| .Pp |
| 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. |
| .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. |
| .Ql \&* |
| and |
| .Ql ? |
| can be used as wildcards in the |
| patterns. |
| 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). |
| .It Cm AFSTokenPassing |
| Specifies whether to pass AFS tokens to remote host. |
| The argument to this keyword must be |
| .Dq yes |
| or |
| .Dq no . |
| This option applies to protocol version 1 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 |
| Specify the interface to transmit from on machines with multiple |
| interfaces or aliased addresses. |
| 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 , |
| ssh 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 yes . |
| .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 |
| .Nm ssh |
| 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 default is |
| .Pp |
| .Bd -literal |
| ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour, |
| aes192-cbc,aes256-cbc'' |
| .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 |
| .Nm ssh |
| 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 DynamicForward |
| Specifies that a TCP/IP 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. The argument must be a port number. |
| Currently the SOCKS4 protocol is supported, and |
| .Nm ssh |
| will act as a SOCKS4 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 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 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 X |
| 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. |
| .It Cm GatewayPorts |
| Specifies whether remote hosts are allowed to connect to local |
| forwarded ports. |
| By default, |
| .Nm ssh |
| 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 |
| .Nm 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 a file to use for the global |
| host key database instead of |
| .Pa /etc/ssh/ssh_known_hosts . |
| .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: |
| .Dq ssh-rsa,ssh-dss . |
| .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. |
| 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 IdentityFile |
| Specifies a file from which the user's RSA or DSA authentication identity |
| is read. The default is |
| .Pa $HOME/.ssh/identity |
| for protocol version 1, and |
| .Pa $HOME/.ssh/id_rsa |
| and |
| .Pa $HOME/.ssh/id_dsa |
| for protocol version 2. |
| Additionally, any identities represented by the authentication agent |
| will be used for authentication. |
| The file name may use the tilde |
| syntax to refer to a user's home directory. |
| It is possible to have |
| multiple identity files specified in configuration files; all these |
| identities will be tried in sequence. |
| .It Cm KeepAlive |
| 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 keepalives), 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 keepalives, the value should be set to |
| .Dq no . |
| .It Cm KerberosAuthentication |
| Specifies whether Kerberos authentication will be used. |
| The argument to this keyword must be |
| .Dq yes |
| or |
| .Dq no . |
| .It Cm KerberosTgtPassing |
| Specifies whether a Kerberos TGT will be forwarded to the server. |
| This will only work if the Kerberos server is actually an AFS kaserver. |
| The argument to this keyword must be |
| .Dq yes |
| or |
| .Dq no . |
| .It Cm LocalForward |
| Specifies that a TCP/IP 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 a port number, and the second must be |
| .Ar host:port . |
| IPv6 addresses can be specified with an alternative syntax: |
| .Ar host/port . |
| Multiple forwardings may be specified, and additional |
| forwardings can be given on the command line. |
| Only the superuser can forward privileged ports. |
| .It Cm LogLevel |
| Gives the verbosity level that is used when logging messages from |
| .Nm ssh . |
| 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 default is |
| .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 . |
| .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. |
| 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 Port |
| Specifies the port number to connect on the remote host. |
| 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 for this option is: |
| .Dq hostbased,publickey,keyboard-interactive,password . |
| .It Cm Protocol |
| Specifies the protocol versions |
| .Nm ssh |
| should support in order of preference. |
| The possible values are |
| .Dq 1 |
| and |
| .Dq 2 . |
| Multiple versions must be comma-separated. |
| The default is |
| .Dq 2,1 . |
| This means that |
| .Nm ssh |
| tries version 2 and falls back to version 1 |
| if version 2 is not available. |
| .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 |
| .Pa /bin/sh . |
| In the command string, |
| .Ql %h |
| will be substituted by the host name to |
| connect and |
| .Ql %p |
| by the port. |
| 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). |
| Note that |
| .Cm CheckHostIP |
| is not available for connects with a proxy command. |
| .Pp |
| .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 RemoteForward |
| Specifies that a TCP/IP 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 a port number, and the second must be |
| .Ar host:port . |
| IPv6 addresses can be specified with an alternative syntax: |
| .Ar host/port . |
| Multiple forwardings may be specified, and additional |
| forwardings can be given on the command line. |
| Only the superuser can forward privileged ports. |
| .It Cm RhostsAuthentication |
| Specifies whether to try rhosts based authentication. |
| Note that this |
| declaration only affects the client side and has no effect whatsoever |
| on security. |
| Most servers do not permit RhostsAuthentication because it |
| is not secure (see |
| .Cm RhostsRSAAuthentication ) . |
| The argument to this keyword must be |
| .Dq yes |
| or |
| .Dq no . |
| The default is |
| .Dq no . |
| This option applies to protocol version 1 only. |
| .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 |
| .Nm ssh |
| 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 SmartcardDevice |
| Specifies which smartcard device to use. The argument to this keyword is |
| the device |
| .Nm ssh |
| should use to communicate with a smartcard used for storing the user's |
| private RSA key. By default, no device is specified and smartcard support |
| is not activated. |
| .It Cm StrictHostKeyChecking |
| If this flag is set to |
| .Dq yes , |
| .Nm ssh |
| will never automatically add host keys to the |
| .Pa $HOME/.ssh/known_hosts |
| file, and refuses to connect to hosts whose host key has changed. |
| This provides maximum protection against trojan horse attacks, |
| however, can be annoying when the |
| .Pa /etc/ssh/ssh_known_hosts |
| file is poorly maintained, or 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 , |
| .Nm 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 |
| .Nm 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 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 . |
| Note that this option must be set to |
| .Dq yes |
| if |
| .Cm RhostsAuthentication |
| and |
| .Cm RhostsRSAAuthentication |
| authentications are needed 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 a file to use for the user |
| host key database instead of |
| .Pa $HOME/.ssh/known_hosts . |
| .It Cm XAuthLocation |
| Specifies the location of the |
| .Xr xauth 1 |
| program. |
| The default is |
| .Pa /usr/X11R6/bin/xauth . |
| .El |
| .Sh FILES |
| .Bl -tag -width Ds |
| .It Pa $HOME/.ssh/config |
| This is the per-user configuration file. |
| The format of this file is described above. |
| This file is used by the |
| .Nm ssh |
| client. |
| This file does not usually contain any sensitive information, |
| but the recommended permissions are 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 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. |
| .Sh SEE ALSO |
| .Xr ssh 1 |