/etc/ssh/ssh_config
DESCRIPTION
ssh obtains configuration data from the following sources in the follow-
ing order: command line options, user's configuration file
($HOME/.ssh/config), and system-wide configuration file
(/etc/ssh/ssh_config).
For each parameter, the first obtained value will be used. The configu-
ration files contain sections bracketed by ``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.
Since the first obtained value for each parameter is used, more host-spe-
cific declarations should be given near the beginning of the file, and
general defaults at the end.
The configuration file has the following format:
Empty lines and lines starting with `#' are comments.
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 white-
space when specifying configuration options using the ssh, scp and sftp
-o option.
The possible keywords and their meanings are as follows (note that key-
words are case-insensitive and arguments are case-sensitive):
Host Restricts the following declarations (up to the next Host key-
word) 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 pro-
vide 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).
AFSTokenPassing
Specifies whether to pass AFS tokens to remote host. The argu-
ment to this keyword must be ``yes'' or ``no''. This option
applies to protocol version 1 only.
BatchMode
If set to ``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
``yes'' or ``no''. The default is ``no''.
BindAddress
Specify the interface to transmit from on machines with multiple
Cipher Specifies the cipher to use for encrypting the session in proto-
col version 1. Currently, ``blowfish'', ``3des'', and ``des''
are supported. des is only supported in the ssh 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''.
Ciphers
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''
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 ssh
command line to clear port forwardings set in configuration
files, and is automatically set by scp(1) and sftp(1). The argu-
ment must be ``yes'' or ``no''. The default is ``no''.
Compression
Specifies whether to use compression. The argument must be
``yes'' or ``no''. The default is ``no''.
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 gzip(1). Note that this
option applies to protocol version 1 only.
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.
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 proto-
col 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 privi-
leged ports.
EscapeChar
Sets the escape character (default: `~'). The escape character
GatewayPorts
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 remote hosts from con-
necting 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''.
GlobalKnownHostsFile
Specifies a file to use for the global host key database instead
of /etc/ssh/ssh_known_hosts.
HostbasedAuthentication
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 protocol version 2
only and is similar to RhostsRSAAuthentication.
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: ``ssh-rsa,ssh-dss''.
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 data-
base files. This option is useful for tunneling ssh connections
or for multiple servers running on a single host.
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 HostName specifica-
tions).
IdentityFile
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 proto-
col 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 direc-
tory. It is possible to have multiple identity files specified
in configuration files; all these identities will be tried in
sequence.
KeepAlive
Specifies whether the system should send TCP keepalive messages
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 ``yes'' or
``no''.
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 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 com-
mand line. Only the superuser can forward privileged ports.
LogLevel
Gives the verbosity level that is used when logging messages from
ssh. The possible values are: QUIET, FATAL, ERROR, INFO, VER-
BOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3. The default is INFO.
DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify
higher levels of verbose output.
MACs Specifies the MAC (message authentication code) algorithms in
order of preference. The MAC algorithm is used in protocol ver-
sion 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''.
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 warn-
ings about changed host keys. However, this option disables host
authentication for localhost. The argument to this keyword must
be ``yes'' or ``no''. The default is to check the host key for
localhost.
NumberOfPasswordPrompts
Specifies the number of password prompts before giving up. The
argument to this keyword must be an integer. Default is 3.
PasswordAuthentication
Specifies whether to use password authentication. The argument
to this keyword must be ``yes'' or ``no''. The default is
``yes''.
Port Specifies the port number to connect on the remote host. Default
is 22.
PreferredAuthentications
Specifies the order in which the client should try protocol 2
mand 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 some-
where. 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.
PubkeyAuthentication
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.
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 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.
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 RhostsAuthen-
tication 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.
RhostsRSAAuthentication
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.
RSAAuthentication
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 authentica-
tion agent is running. The default is ``yes''. Note that this
option applies to protocol version 1 only.
SmartcardDevice
Specifies which smartcard device to use. The argument to this
keyword is the device ssh should use to communicate with a smart-
card used for storing the user's private RSA key. By default, no
device is specified and smartcard support is not activated.
keys of known hosts will be verified automatically in all cases.
The argument must be ``yes'', ``no'' or ``ask''. The default is
``ask''.
UsePrivilegedPort
Specifies whether to use a privileged port for outgoing connec-
tions. 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.
User Specifies the user to log in as. This can be useful when a dif-
ferent user name is used on different machines. This saves the
trouble of having to remember to give the user name on the com-
mand line.
UserKnownHostsFile
Specifies a file to use for the user host key database instead of
$HOME/.ssh/known_hosts.
XAuthLocation
Specifies the location of the xauth(1) program. The default is
/usr/X11R6/bin/xauth.
FILES
$HOME/.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. This
file does not usually contain any sensitive information, but the
recommended permissions are read/write for the user, and not
accessible by others.
/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.
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 cre-
ated OpenSSH. Markus Friedl contributed the support for SSH protocol
versions 1.5 and 2.0.
SEE ALSO
ssh(1)
BSD September 25, 1999 BSD
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