~/.ssh/config
/etc/ssh/ssh_config
DESCRIPTION
ssh obtains configuration data from the following sources in
the follow-
ing order:
1. command-line options
2. user's configuration file (~/.ssh/config)
3. system-wide configuration file (/etc/ssh/ssh_con-
fig)
For each parameter, the first obtained value will be used.
The configu-
ration files contain sections separated by ``Host'' specifi-
cations, 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 white-
space and exactly
one `='; the latter format is useful to avoid the need to
quote whites-
pace 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-sensi-
tive):
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
IPv6 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 argu-
ment must be
``yes'' or ``no''. The default is ``no''.
BindAddress
Use the specified address on the local machine as
the source ad-
dress of the connection. Only useful on systems
with more than
one address. Note that this option does not work if
UsePrivilegedPort is set to ``yes''.
ChallengeResponseAuthentication
Specifies whether to use challenge response authen-
tication. The
argument to this keyword must be ``yes'' or ``no''.
The default
is ``yes''.
CheckHostIP
If this flag is set to ``yes'', ssh will additional-
ly check the
host IP address in the known_hosts file. This al-
lows ssh to de-
tect 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''.
Cipher Specifies the cipher to use for encrypting the ses-
sion in proto-
col version 1. Currently, ``blowfish'', ``3des'',
and ``des''
are supported. des is only supported in the ssh
client for in-
teroperability with legacy protocol 1 implementa-
tions that do not
support the 3des cipher. Its use is strongly dis-
couraged due to
cryptographic weaknesses. The default is ``3des''.
Ciphers
Specifies the ciphers allowed for protocol version 2
in order of
aes192-ctr,aes256-ctr''
ClearAllForwardings
Specifies that all local, remote and dynamic port
forwardings
specified in the configuration files or on the com-
mand line be
cleared. This option is primarily useful when used
from the ssh
command line to clear port forwardings set in con-
figuration
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 compres-
sion 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 ap-
plications. 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 ex-
iting. The argument must be an integer. This may
be useful in
scripts if the connection sometimes fails. The de-
fault is 1.
ConnectTimeout
Specifies the timeout (in seconds) used when con-
necting to the
ssh server, instead of using the default system TCP
timeout.
This value is used only when the target is down or
really un-
reachable, not when it refuses the connection.
ControlMaster
Enables the sharing of multiple sessions over a sin-
gle network
confirmation using the SSH_ASKPASS program before
they are ac-
cepted (see ssh-add(1) for details). If the Con-
trolPath can not
be opened, ssh will continue without connecting to a
master in-
stance.
X11 and ssh-agent(1) forwarding is supported over
these multi-
plexed connections, however the display and agent
fowarded will
be the one belonging to the master connection i.e.
it is not pos-
sible to forward multiple displays or agents.
Two additional options allow for opportunistic mul-
tiplexing: try
to use a master connection but fall back to creating
a new one if
one does not already exist. These options are:
``auto'' and
``autoask''. The latter requires confirmation like
the ``ask''
option.
ControlPath
Specify the path to the control socket used for con-
nection shar-
ing as described in the ControlMaster section above
or the string
``none'' to disable connection sharing. In the
path, `%h' will
be substituted by the target host name, `%p' the
port and `%r' by
the remote login username. It is recommended that
any
ControlPath used for opportunistic connection shar-
ing include all
three of these escape sequences. This ensures that
shared con-
nections are uniquely identified.
DynamicForward
Specifies that a TCP/IP port on the local machine be
forwarded
over the secure channel, and the application proto-
col is then
used to determine where to connect to from the re-
mote machine.
The argument must be a port number. Currently the
SOCKS4 and
argument must
be ``yes'' or ``no''. The default is ``no''. This
option should
be placed in the non-hostspecific section. See ssh-
keysign(8)
for more information.
EscapeChar
Sets the escape character (default: `~'). The es-
cape character
can also be set on the command line. The argument
should be a
single character, `^' followed by a letter, or
``none'' to dis-
able the escape character entirely (making the con-
nection trans-
parent for binary data).
ForwardAgent
Specifies whether the connection to the authentica-
tion agent (if
any) will be forwarded to the remote machine. The
argument must
be ``yes'' or ``no''. The default is ``no''.
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 identi-
ties loaded into
the agent.
ForwardX11
Specifies whether X11 connections will be automati-
cally redirect-
ed over the secure channel and DISPLAY set. The ar-
gument must be
``yes'' or ``no''. The default is ``no''.
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 dis-
tampering
with data belonging to trusted X11 clients. Fur-
thermore, 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 ``no''.
See the X11 SECURITY extension specification for
full details on
the restrictions imposed on untrusted clients.
GatewayPorts
Specifies whether remote hosts are allowed to con-
nect 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 ad-
dress, thus allowing remote hosts to connect to for-
warded 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.
GSSAPIAuthentication
Specifies whether user authentication based on GSS-
API is allowed.
The default is ``no''. Note that this option ap-
plies to protocol
version 2 only.
GSSAPIDelegateCredentials
Forward (delegate) credentials to the server. The
default is
``no''. Note that this option applies to protocol
version 2 on-
ly.
HashKnownHosts
Indicates that ssh should hash host names and ad-
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 on-
ly 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 de-
fault 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
database files. This option is useful for tunneling
ssh connec-
tions 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. De-
fault is the
name given on the command line. Numeric IP address-
es 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 ~/.ssh/identity
for protocol
version 1, and ~/.ssh/id_rsa and ~/.ssh/id_dsa for
protocol ver-
sion 2. Additionally, any identities represented by
the authen-
tication 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 speci-
fied in configu-
ration files; all these identities will be tried in
KbdInteractiveDevices
Specifies the list of methods to use in keyboard-in-
teractive au-
thentication. Multiple method names must be comma-
separated.
The default is to use the server specified list.
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
[bind_address:]port
and the second argument must be host:hostport. IPv6
addresses
can be specified by enclosing addresses in square
brackets or by
using an alternative syntax: [bind_address/]port and
host/hostport. Multiple forwardings may be speci-
fied, and addi-
tional 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 GatewayPorts
setting. How-
ever, an explicit bind_address may be used to bind
the connection
to a specific address. The bind_address of ``local-
host'' indi-
cates that the listening port be bound for local use
only, while
an empty address or `*' indicates that the port
should be avail-
able from all interfaces.
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) al-
gorithms in or-
der of preference. The MAC algorithm is used in
about changed host keys. However, this option dis-
ables host au-
thentication for localhost. The argument to this
keyword must be
``yes'' or ``no''. The default is to check the host
key for lo-
calhost.
NumberOfPasswordPrompts
Specifies the number of password prompts before giv-
ing up. The
argument to this keyword must be an integer. De-
fault is 3.
PasswordAuthentication
Specifies whether to use password authentication.
The argument
to this keyword must be ``yes'' or ``no''. The de-
fault 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 au-
thentication methods. This allows a client to pre-
fer one method
(e.g. keyboard-interactive) over another method
(e.g. password)
The default for this option is: ``hostbased,publick-
ey,keyboard-
interactive,password''.
Protocol
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
``2,1''. 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 serv-
er. The com-
mand string extends to the end of the line, and is
executed with
er). Setting the command to ``none'' disables this
option en-
tirely. Note that CheckHostIP 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
PubkeyAuthentication
Specifies whether to try public key authentication.
The argument
to this keyword must be ``yes'' or ``no''. The de-
fault 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 [bind_ad-
dress:]port
and the second argument must be host:hostport. IPv6
addresses
can be specified by enclosing addresses in square
brackets or by
using an alternative syntax: [bind_address/]port and
host/hostport. Multiple forwardings may be speci-
fied, and addi-
tional forwardings can be given on the command line.
Only the
superuser can forward privileged ports.
If the bind_address is not specified, the default is
to only bind
to loopback addresses. If the bind_address is `*'
or an empty
string, then the forwarding is requested to listen
on all inter-
faces. Specifying a remote bind_address will only
succeed if the
server's GatewayPorts option is enabled (see
sshd_config(5)).
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.
SendEnv
Specifies what variables from the local environ(7)
should be sent
to the server. Note that environment passing is on-
ly supported
for protocol 2, the server must also support it, and
the server
must be configured to accept these environment vari-
ables. Refer
to AcceptEnv in sshd_config(5) for how to configure
the server.
Variables are specified by name, which may contain
the wildcard
characters `*' and `?'. Multiple environment vari-
ables may be
separated by whitespace or spread across multiple
SendEnv direc-
tives. The default is not to send any environment
variables.
ServerAliveInterval
Sets a timeout interval in seconds after which if no
data has
been received from the server, ssh will send a mes-
sage 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.
ServerAliveCountMax
Sets the number of server alive messages (see above)
which may be
sent without ssh receiving any messages back from
the server. If
this threshold is reached while server alive mes-
sages are being
sent, ssh will disconnect from the server, terminat-
ing the ses-
sion. It is important to note that the use of serv-
er alive mes-
sages is very different from TCPKeepAlive (below).
The server
alive messages are sent through the encrypted chan-
disconnect af-
ter approximately 45 seconds.
SmartcardDevice
Specifies which smartcard device to use. The argu-
ment 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 ac-
tivated.
StrictHostKeyChecking
If this flag is set to ``yes'', ssh will never auto-
matically add
host keys to the ~/.ssh/known_hosts file, and refus-
es to connect
to hosts whose host key has changed. This provides
maximum pro-
tection 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 af-
ter 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 ``yes'', ``no'' or ``ask''.
The default is
``ask''.
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 no-
ticed. However,
this means that connections will die if the route is
UsePrivilegedPort
Specifies whether to use a privileged port for out-
going connec-
tions. The argument must be ``yes'' or ``no''. The
default is
``no''. If set to ``yes'' ssh must be setuid root.
Note that
this option must be set to ``yes'' for RhostsRSAAu-
thentication
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 data-
base instead of
~/.ssh/known_hosts.
VerifyHostKeyDNS
Specifies whether to verify the remote key using DNS
and SSHFP
resource records. If this option is set to ``yes'',
the client
will implicitly trust keys that match a secure fin-
gerprint from
DNS. Insecure fingerprints will be handled as if
this option was
set to ``ask''. If this option is set to ``ask'',
information on
fingerprint match will be displayed, but the user
will still need
to confirm new host keys according to the Stric-
tHostKeyChecking
option. The argument must be ``yes'', ``no'' or
``ask''. The
default is ``no''. Note that this option applies to
protocol
version 2 only.
XAuthLocation
Specifies the full pathname of the xauth(1) program.
The default
is /usr/X11R6/bin/xauth.
FILES
~/.ssh/config
file, and for those users who do not have a configu-
ration 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 fea-
tures and cre-
ated OpenSSH. Markus Friedl contributed the support for SSH
protocol
versions 1.5 and 2.0.
OpenBSD 3.8 September 25, 1999
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