ssh_config
NAME
SYNOPSIS
DESCRIPTION
ssh(1)
obtains configuration data from the following sources in
the following order:
- t
command-line options
t
user's configuration file
t
system-wide configuration file
For each parameter, the first obtained value
will be used.
The configuration files contain sections separated by
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-specific 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
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
and
option.
Arguments may optionally be enclosed in double quotes
in order to represent arguments containing spaces.
The possible
keywords and their meanings are as follows (note that
keywords are case-insensitive and arguments are case-sensitive):
- Host Restricts the following declarations (up to the next keyword) to be only for those hosts that match one of the patterns given after the keyword. A single as a pattern can be used to provide global defaults for all hosts. The host is the argument given on the command line (i.e. the name is not converted to a canonicalized host name before matching).
See
for more information on patterns.
AddressFamily
Specifies which address family to use when connecting.
Valid arguments are
(use IPv4 only), or
(use IPv6 only).
BatchMode
If set to
passphrase/password querying will be disabled.
In addition, the
and
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
or
The default is
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
is set to
ChallengeResponseAuthentication
Specifies whether to use challenge-response authentication.
The argument to this keyword must be
or
The default is
CheckHostIP
If this flag is set to
ssh(1)
will additionally check the host IP address in the
file.
This allows ssh to detect if a host key changed due to DNS spoofing.
If the option is set to
the check will not be executed.
The default is
Cipher
Specifies the cipher to use for encrypting the session
in protocol version 1.
Currently,
and
are supported.
is only supported in the
ssh(1)
client for interoperability with legacy protocol 1 implementations
that do not support the
cipher.
Its use is strongly discouraged due to cryptographic weaknesses.
The default is
Ciphers
Specifies the ciphers allowed for protocol version 2
in order of preference.
Multiple ciphers must be comma-separated.
The supported ciphers are
and
The default is:
aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128, arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr, aes192-ctr,aes256-ctr
Setting this to
will cause ssh
to listen for control connections, but require confirmation using the
program before they are accepted (see
ssh-add(1)
for details).
If the
cannot be opened,
ssh will continue without connecting to a master instance.
X11 and
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.
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:
and
The latter requires confirmation like the
option.
ControlPath
Specify the path to the control socket used for connection sharing as described
in the
section above or the string
to disable connection sharing.
In the path,
will be substituted by the local host name,
will be substituted by the target host name,
the port, and
by the remote login username.
It is recommended that any
used for opportunistic connection sharing include
at least %h, %p, and %r.
This ensures that shared connections are uniquely identified.
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.
The argument must be
IPv6 addresses can be specified by enclosing addresses in square brackets or
by using an alternative syntax:
By default, the local port is bound in accordance with the
setting.
However, an explicit
may be used to bind the connection to a specific address.
The
of
indicates that the listening port be bound for local use only, while an
empty address or
indicates that the port should be available from all interfaces.
Currently the SOCKS4 and SOCKS5 protocols are supported, and
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.
EnableSSHKeysign
Setting this option to
in the global client configuration file
enables the use of the helper program
ssh-keysign(8)
during
The argument must be
or
The default is
This option should be placed in the non-hostspecific section.
See
ssh-keysign(8)
for more information.
EscapeChar
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
to disable the escape
character entirely (making the connection transparent for binary
data).
ExitOnForwardFailure
Specifies whether
ssh(1)
should terminate the connection if it cannot set up all requested
dynamic, local, and remote port forwardings.
The argument must be
or
The default is
ForwardAgent
Specifies whether the connection to the authentication agent (if any)
will be forwarded to the remote machine.
The argument must be
or
The default is
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.
ForwardX11
Specifies whether X11 connections will be automatically redirected
over the secure channel and
set.
The argument must be
or
The default is
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
option is also enabled.
ForwardX11Trusted
If this option is set to
remote X11 clients will have full access to the original X11 display.
If this option is set to
remote X11 clients will be considered untrusted and prevented
from stealing or tampering with data belonging to trusted X11
clients.
Furthermore, the
xauth(1)
token used for the session will be set to expire after 20 minutes.
Remote clients will be refused access after this time.
The default is
(Debian-specific).
See the X11 SECURITY extension specification for full details on
the restrictions imposed on untrusted clients.
GatewayPorts
Specifies whether remote hosts are allowed to connect to local
forwarded ports.
By default,
ssh(1)
binds local port forwardings to the loopback address.
This prevents other remote hosts from connecting to forwarded ports.
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
or
The default is
GlobalKnownHostsFile
Specifies a file to use for the global
host key database instead of
These hashed names may be used normally by
ssh(1)
and
sshd(8)
but they do not reveal identifying information should the file's contents
be disclosed.
The default is
Note that existing names and addresses in known hosts files
will not be converted automatically,
but may be manually hashed using
ssh-keygen(1)
Use of this option may break facilities such as tab-completion that rely
on being able to read unhashed host names from
for protocol version 1, and
and
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 or one of the following
escape characters:
(local user's home directory),
(local user name),
(local host name),
(remote host name) or
(remote user name).
It is possible to have
multiple identity files specified in configuration files; all these
identities will be tried in sequence.
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:
and
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
This directive is ignored unless
has been enabled.
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
and the second argument must be
IPv6 addresses can be specified by enclosing addresses in square brackets or
by using an alternative syntax:
and
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
setting.
However, an explicit
may be used to bind the connection to a specific address.
The
of
indicates that the listening port be bound for local use only, while an
empty address or
indicates that the port should be available from all interfaces.
LogLevel
Gives the verbosity level that is used when logging messages from
ssh(1)
The possible values are:
SILENT, 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.
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:
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
or
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.
The default is 3.
PasswordAuthentication
Specifies whether to use password authentication.
The argument to this keyword must be
or
The default is
PermitLocalCommand
Allow local command execution via the
c LocalCommand
option or using the
c ! Ns Ar command
escape sequence in
ssh(1)
The argument must be
or
The default is
Port
Specifies the port number to connect on the remote host.
The default is 22.
PreferredAuthentications
Specifies the order in which the client should try protocol 2
authentication methods.
This allows a client to prefer one method (e.g.
over another method (e.g.
The default for this option is:
hostbased,
publickey,
keyboard-interactive,
password
Protocol
Specifies the protocol versions
ssh(1)
should support in order of preference.
The possible values are
and
Multiple versions must be comma-separated.
The default is
This means that ssh
tries version 2 and falls back to version 1
if version 2 is not available.
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
In the command string,
will be substituted by the host name to
connect and
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
c 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
disables this option entirely.
Note that
is not available for connects with a proxy command.
This directive is useful in conjunction with
nc(1)
and its proxy support.
For example, the following directive would connect via an HTTP proxy at
192.0.2.0:
ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
If the
is not specified, the default is to only bind to loopback addresses.
If the
is
or an empty string, then the forwarding is requested to listen on all
interfaces.
Specifying a remote
will only succeed if the server's
option is enabled (see
sshd_config(5)
RhostsRSAAuthentication
Specifies whether to try rhosts based authentication with RSA host
authentication.
The argument must be
or
The default is
This option applies to protocol version 1 only and requires
ssh(1)
to be setuid root.
RSAAuthentication
Specifies whether to try RSA authentication.
The argument to this keyword must be
or
RSA authentication will only be
attempted if the identity file exists, or an authentication agent is
running.
The default is
Note that this option applies to protocol version 1 only.
SendEnv
Specifies what variables from the local
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
in
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
directives.
The default is not to send any environment variables.
See
for more information on patterns.
ServerAliveCountMax
Sets the number of server alive messages (see below) which may be
sent without
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
(below).
The server alive messages are sent through the encrypted channel
and therefore will not be spoofable.
The TCP keepalive option enabled by
is spoofable.
The server alive mechanism is valuable when the client or
server depend on knowing when a connection has become inactive.
The default value is 3.
If, for example,
(see below) is set to 15 and
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; in protocol version
1 there is no mechanism to request a response from the server to the
server alive messages, so disconnection is the responsibility of the TCP
stack.
ServerAliveInterval
Sets a timeout interval in seconds after which if no data has been received
from the server,
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,
or 300 if the
option is set.
This option applies to protocol version 2 only.
is a Debian-specific compatibility alias for this option.
SetupTimeOut
Normally,
blocks indefinitely whilst waiting to receive the ssh banner and other
setup protocol from the server, during the session setup.
This can cause
to hang under certain circumstances.
If this option is set,
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
is set.
This is a Debian-specific option.
SmartcardDevice
Specifies which smartcard device to use.
The argument to this keyword is the device
ssh(1)
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.
StrictHostKeyChecking
If this flag is set to
ssh(1)
will never automatically add host keys to the
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
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
ssh will automatically add new host keys to the
user known hosts files.
If this flag is set to
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
or
The default is
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.
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
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
(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.
To disable TCP keepalive messages, the value should be set to
Tunnel
Request
tun(4)
device forwarding between the client and the server.
The argument must be
(layer 3),
(layer 2),
or
Specifying
requests the default tunnel mode, which is
The default is
TunnelDevice
Specifies the
tun(4)
devices to open on the client
and the server
The argument must be
The devices may be specified by numerical ID or the keyword
which uses the next available tunnel device.
If
is not specified, it defaults to
The default is
UsePrivilegedPort
Specifies whether to use a privileged port for outgoing connections.
The argument must be
or
The default is
If set to
ssh(1)
must be setuid root.
Note that this option must be set to
for
with older servers.
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.
UserKnownHostsFile
Specifies a file to use for the user
host key database instead of
See also
in
ssh(1)
XAuthLocation
Specifies the full pathname of the
xauth(1)
program.
The default is
PATTERNS
A
consists of zero or more non-whitespace characters,
(a wildcard that matches zero or more characters),
or
(a wildcard that matches exactly one character).
For example, to specify a set of declarations for any host in the
set of domains,
the following pattern could be used:
The following pattern
would match any host in the 192.168.0.[0-9] network range:
A
is a comma-separated list of patterns.
Patterns within pattern-lists may be negated
by preceding them with an exclamation mark
For example,
to allow a key to be used from anywhere within an organisation
except from the
pool,
the following entry (in authorized_keys) could be used:
FILES
- ~/.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 may be group-writable provided that the group in question contains only the user.
- /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.
SEE ALSO
ssh(1)
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.
ČLÁNKY DO MAILU