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1 MattBrown 1 ssh_config - OpenSSH SSH client configuration
2
3 !!files
4
5 $HOME/.ssh/config
6
7 /etc/ssh/ssh_config
8
9 !!DESCRIPTION
10
11 !Synopsis
12 ssh obtains configuration data from the following sources in the following order: command line options, user's configuration file ($HOME/.ssh/config), and system-wide
13 configuration file (/etc/ssh/ssh_config).
14
15 For each parameter, the first obtained value will be used. The configuration files contain sections bracketed by `Host' specifications, and that section is only applied
16 for hosts that match one of the patterns given in the specification. The matched host name is the one given on the command line.
17
18 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
19 end.
20
21 The configuration file has the following format:
22
23 Empty lines and lines starting with # are comments.
24
25 Otherwise a line is of the format `keyword arguments'. Configuration options may be separated by whitespace or optional whitespace and exactly one =; the latter format is useful to avoid the need to quote whitespace when specifying configuration options using the ssh, scp and sftp -o option.
26
27 The possible keywords and their meanings are as follows (note that keywords are case-insensitive and arguments are case-sensitive):
28
29 !Host
30 Restricts the following declarations (up to the next Host keyword) to be only for those hosts that match one of the patterns given after the keyword. * and ? can be used as wildcards in the patterns. A single * as a pattern can be used to provide global defaults for all hosts. The host is the hostname argument given on the command line (i.e., the name is not con-verted to a canonicalized host name before matching).
31
32 !AFSTokenPassing
33 Specifies whether to pass AFS tokens to remote host. The argument to this keyword must be `yes' or `no'. This option applies to protocol version 1 only.
34
35 !!BatchMode
36 If set to `yes', passphrase/password querying will be disabled. In addition, the !ProtocolKeepAlives and !SetupTimeOut options will both be set to 300 seconds by default. This option is useful in scripts and other batch jobs where no user is present to supply the password, and where it is desirable to detect a broken network swiftly. The argument must be `yes'or `no'. The default is `no'.
37
38 !!BindAddress
39 Specify the interface to transmit from on machines with multiple interfaces or aliased addresses. Note that this option does not work of !UsePrivilegedPort is set to `yes'.
40
41 !!ChallengeResponseAuthentication
42 Specifies whether to use challenge response authentication. The argument to this keyword must be `yes' or `no'. The default is `yes'.
43
44 !CheckHostIP
45 If this flag is set to `yes', ssh will additionally check the host IP address in the known_hosts file. This allows ssh to detect if a host key changed due to DNS spoofing. If the option is set to `no', the check will not be executed. The default is `yes'.
46
47
48 !Cipher
49 Specifies the cipher to use for encrypting the session in protocol version 1. Currently, `blowfish', `3des', and `des' are supported. des is only supported in the ssh
50 client for interoperability with legacy protocol 1 implementations that do not support the 3des cipher. Its use is strongly discouraged due to cryptographic weaknesses. The default is `3des'.
51
52
53 !Ciphers
54 Specifies the ciphers allowed for protocol version 2 in order of preference. Multiple ciphers must be comma-separated. The default is `aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,aes192-cbc,aes256-cbc'
55
56 !!ClearAllForwardings
57 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
58 when used from the ssh command line to clear port forwardings set in configuration files, and is automatically set by scp(1) and sftp(1). The argument must be `yes' or `no'. The default is `no'.
59
60
61 !Compression
62 Specifies whether to use compression. The argument must be `yes' or `no'. The default is `no'.
63
64 !!CompressionLevel
65 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 gzip(1). Note that this option applies to protocol version 1 only.
66
67 !!ConnectionAttempts
68 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.
69
70 !!DynamicForward
71 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 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.
72
73 !!EscapeChar
74 Sets the escape character (default: ~). The escape character can also be set on the command line. The argument should be a single character, ^ followed by a letter, or `none' to disable the escape character entirely (making the connection transparent for binary data).
75
76 !!ForwardAgent
77 Specifies whether the connection to the authentication agent (if any) will be forwarded to the remote machine. The argument must be `yes' or `no'. The default is `no'.
78
79 !ForwardX11
80 Specifies whether X11 connections will be automatically redirected over the secure channel and DISPLAY set. The argument must be `yes' or `no'. The default is `no'.
81
82
83 !!GatewayPorts
84 Specifies whether remote hosts are allowed to connect to local forwarded ports. By default, ssh binds local port forwardings to the loopback address. This prevents other
85 remote hosts from connecting to forwarded ports. !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 `yes' or `no'. The default is `no'.
86
87 !!GlobalKnownHostsFile
88 Specifies a file to use for the global host key database instead of /etc/ssh/ssh_known_hosts.
89
90 !!HostbasedAuthentication
91 Specifies whether to try rhosts based authentication with public key authentication. The argument must be `yes' or `no'. The default is `no'. This option applies to
92 protocol version 2 only and is similar to RhostsRSAAuthentication.
93
94 !!HostKeyAlgorithms
95 Specifies the protocol version 2 host key algorithms that the client wants to use in order of preference. The default for this option is: `ssh-rsa,ssh-dss'.
96
97 !!HostKeyAlias
98 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.
99
100 !!HostName
101 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 !HostName specifications).
102
103
104 !!IdentityFile
105 Specifies a file from which the user's RSA or DSA authentication identity is read. The default is $HOME/.ssh/identity for protocol version 1, and $HOME/.ssh/id_rsa and $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.
106
107 !!KeepAlive
108 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. of the machines will be properly noticed. This option only uses TCP keepalives (as opposed to using ssh level keepalives), so takes a long time to notice when the connection dies. As such, you probably want the !ProtocolKeepAlives option as well. However, this means that connections will die if the route is down temporarily, and some people find it annoying. The default is `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. To disable keepalives, the value should be set to `no'.
109
110 !!KerberosAuthentication
111 Specifies whether Kerberos authentication will be used. The argument to this keyword must be `yes' or `no'.
112
113 !!KerberosTgtPassing
114 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 `yes' or `no'.
115
116 !!LocalForward
117 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 host:port. IPv6 addresses can be specified with an alternative syntax: host/port. Multiple forward- ings may be specified, and additional forwardings can be given on the command line. Only the superuser can forward privileged ports.
118
119
120 !!LogLevel
121 Gives the verbosity level that is used when logging messages from 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.
122
123 !MACs
124 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 `hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96'.
125
126 !!NoHostAuthenticationForLocalhost
127 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 `yes' or `no'. The
128 default is to check the host key for localhost.
129
130 !!NumberOfPasswordPrompts
131 Specifies the number of password prompts before giving up. The argument to this keyword must be an integer. Default is 3.
132
133 !!PasswordAuthentication
134 Specifies whether to use password authentication. The default is `yes'.
135
136 !Port
137 Specifies the port number to connect on the remote host. Default is 22.
138
139 !!PreferredAuthentications
140 Specifies the order in which the client should try protocol 2 authentication methods. This allows a client to prefer one method (e.g. keyboard-interactive) over another method (e.g.password) The default for this option is: `hostbased,publickey,keyboard-interactive,password'.
141
142 !Protocol
143 Specifies the protocol versions ssh should support in order of preference. The possible values are `1' and `2'. Multiple versions must be comma-separated. The default is
144 `2,1'. This means that ssh tries version 2 and falls back to version 1 if version 2 is not available.
145
146 !!ProtocolKeepAlives
2 NeilHoughton 147 Specifies the interval at which IGNORE packets will be sent to the server during dile periods. Use this option in scripts to detect when the network fails. The argument must be an integer. The default is 0 (disabled), or 300 if the !BatchMode option is set. The value is the time in seconds.
1 MattBrown 148
149 !!ProxyCommand
150 Specifies the command to use to connect to the server. The command string extends to the end of the line, and is executed with /bin/sh. In the command string, %h will be substituted by the host name to connect and %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 sshd(8) server running on some machine, or execute 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 !CheckHostIP is not available for connects with a proxy command.
151
152 !!PubkeyAuthentication
153 Specifies whether to try public key authentication. The argument to this keyword must be `yes' or `no'. The default is `yes'. This option applies to protocol version 2 only.
154
155 !!RemoteForward
156 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 host:port. IPv6 addresses can be specified with an alternative syntax: host/port. Multiple forwardings may be specified, and additional forwardings can be given on the command line. Only the superuser can forward privileged ports.
157
158 !!RhostsAuthentication
159 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 RhostsRSAAuthentication). The argument to this keyword must be `yes' or `no'. The default is `no'. This option applies to protocol version 1 only.
160
161 !RhostsRSAAuthentication
162 Specifies whether to try rhosts based authentication with RSA host authentication. The argument must be `yes' or `no'. The default is `no'. This option applies to protocol version 1 only and requires ssh to be setuid root.
163
164 !RSAAuthentication
165 Specifies whether to try RSA authentication. The argument to this keyword must be `yes' or `no'. RSA authentication will only be attempted if the identity file exists, or an authentication agent is running. The default is `yes'. Note that this option applies to protocol version 1 only.
166
167 !!SetupTimeOut
168 Normally, ssh blocks indefinitly whilst waiting to receive the ssh banner and other setup protocol from the server, during the session setup. This can cause ssh to hang under certain circumstances. If this option is set, ssh will give up if no data from the server is received for the specified number of seconds. The argument must be an integer. The default is 0 (disabled), or 300 if !BatchMode is set.
169
170 !!SmartcardDevice
171 Specifies which smartcard device to use. The argument to this keyword is the device ssh should use to communicate with a smartcard used for storing the user's private RSA
172 key. By default, no device is specified and smartcard support is not activated.
173
174 !!StrictHostKeyChecking
175 If this flag is set to `yes', ssh will never automatically add host keys to the $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 /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 `no', ssh will automatically add new host keys to the user known hosts files. If this flag is set to `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 veri- fied automatically in all cases. The argument must be `yes', `no' or `ask'. The default is `ask'.
176
177 !!UsePrivilegedPort
178 Specifies whether to use a privileged port for outgoing connections. The argument must be `yes' or `no'. The default is `no'. Note that this option must be set to `yes' if !RhostsAuthentication and RhostsRSAAuthentication authentications are needed with older servers.
179
180 !User
181 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.
182
183 !!UserKnownHostsFile
184 Specifies a file to use for the user host key database
185 instead of $HOME/.ssh/known_hosts.
186
187 !!XAuthLocation
188 Specifies the location of the xauth(1) program. The default is /usr/bin/X11/xauth.
189
190 !!FILES
191
192 $HOME/.ssh/config
193
194 This is the per-user configuration file. The format of this file is described above. This file is used by the ssh client. This file does not usually contain any sensitive
195 information, but the recommended permissions are read/write for the user, and not accessible by others.
196
197 /etc/ssh/ssh_config
198 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
199 configuration file. This file must be world-readable.
200
201
202 !!AUTHORS
203
204 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.
205
206 !!SEE ALSO
207
208 ssh(1)
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