ssh [-1246AaCfgkMNnqsTtVvXxY] [user@]hostname [command]
[-b bind_address]
[-c cipher_spec]
[-D [bind_address:]port]
[-e escape_char]
[-F configfile]
[-i identity_file]
[-l login_name]
[-m mac_spec]
[-O ctl_cmd]
[-o option]
[-p port]
[-L [bind_address:]port:host:hostport]
[-R [bind_address:]port:host:hostport]
[-S ctl_path]
[-w local_tun[:remote_tun]]
used to logon to a remote host and for executing commands. Replaces rlogin
and rsh, and provide secure encrypted communications between two untrusted hosts over an insecure network. X11 connections and arbitrary TCP ports can be forwarded over the secure channel.
When the user's identity has been validated ssh executes command or logs on and presents a shell prompt. All communication is encrypted.
The session terminates when the command or shell on the remote machine exits and all X11 and TCP connections have been closed.
If a pseudo-terminal has been allocated (normal login session), the user may use the escape characters to control the connection.
If a pseudo-terminal has not been allocated(-T) , the session is transparent and can be used to reliably transfer binary data. On most systems, setting the escape character to none will also make the session transparent even if a tty is used.
~ .~-L and -R ,
the cancellation of existing remote port-forwardings using -KR[bind_address:]port. !command allows executetion of a
command at the local host if PermitLocalCommand is enabled in
ssh_config.
The escape character is only recognized at the beginning of a line and be follow a newline to be interpreted as special.
The escape character can be changed in configuration files with the EscapeChar or
on the command line with -e .
-e escape_char (default: ~).
Setting the character to none disables escapes and makes the session fully transparent.
-l login_name to use on the remote host, may be specified on a per-host basis in the configuration file.
-F configfile
Specifies an alternative per-user configuration file. If given on the command line, the system-wide
configuration file (/etc/ssh_config) will be ignored.
The default for the per-user configuration file is ~/.ssh/config.
-v Verbose mode. display debugging messages . Helpful in debugging connection, authentication, and configuration problems. Multiple -v options increase the verbosity. maximum is 3 i.e. ssh -v -v -v .
~R Request rekeying of the connection (only version 2 if the peer supports it).
-A Enables forwarding of the authentication agent connection.
can also be specified on a per-host basis in a configuration file.
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.
-a Disables forwarding of the authentication agent connection.
-b bind_address Use bind_address on the local machine as the source address of the connection. Only useful on systems with more than one address.
-C Requests compression of all data (including stdin, ,stdout,
stderr, and data for forwarded X11 and TCP connections). The
compression algorithm is the same used by gzip(1), and the
level can be controlled by the CompressionLevel option for protocol version 1. Compression is desirable on modem lines and
other slow connections, but will only slow down things on fast networks. The default value can be set on a host‑by‑host basis
in the configuration files; see the Compression option.
-c cipher_spec Selects the cipher specification for encrypting the session.
3des (triple-des) is an encrypt-decrypt-encrypt triple with three different keys believed to be secure. blowfish a fast block cipher; it appears very secure and is much faster than 3des. 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. 3des.
aes128‑cbc,3des‑cbc,blowfish‑cbc,cast128‑cbc,arcfour128,
arcfour256,arcfour,aes192‑cbc,aes256‑cbc,aes128‑ctr,aes192‑ctr,aes256‑ctr
-D [bind_address:]port
Specifies a local dynamic application-level port forwarding.
Only root can forward privileged ports.
This works by allocating a socket to listen to port on the local
side, optionally bound to the specified bind_address. Connections to this port are forwarded over
the secure channel, and the application protocol is then used to
determine where to connect to from the remote machine. Currently
the SOCKS4 and SOCKS5 protocols are supported, and ssh will act
as a SOCKS server.
Dynamic port forwardings can also be specified in the configuration file.
IPv6 addresses can be specified with an alternative syntax:
[bind_address/]port or by enclosing the address in square brackets.
Only the root can forward privileged ports.
By default, the local port is bound in accordance with the GatewayPorts setting. An explicit bind_address may be
used to bind the connection to a specific address. The
bind_address of localhost 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.
-g Allows remote hosts to connect to local forwarded ports.
-f Requests ssh to go to background just before command execution.
Useful if ssh is going to ask for passwords or
passphrases, but the user wants it in the background. implies -n. The recommended way to start X11 programs at a
remote site is with something like ssh -f host xterm.
-I smartcard_device used for storing the user's private RSA key.
Only available if support for smartcard devices is compiled in (default is no support).
-i identity_file
Selects a file from which the identity (private key) for RSA or
DSA authentication is read. default ~/.ssh/identity for
protocol version 1, and ~/.ssh/id_rsa and ~/.ssh/id_dsa for protocol version 2.
May be specified on a perhost basis in the configuration file.
Multiple -i options (and multiple identities specified in configuration files) is permitted.
-k Disables forwarding (delegation) of GSSAPI credentials to the
server.
-L [bind_address:]port:host:hostport
Port on the local (client) host is to be
forwarded to the given host and port on the remote side. This
works by allocating a socket to listen to port on the local side,
optionally bound to the specified bind_address. Whenever a connection is made to this port, the connection is forwarded over
the secure channel, and a connection is made to host port
hostport from the remote machine. Port forwardings can also be
specified in the configuration file. IPv6 addresses can be specified with an alternative syntax:
[bind_address/]port/host/hostport or by enclosing the address in
square brackets. Only the superuser can forward privileged
ports. By default, the local port is bound in accordance with
the GatewayPorts setting. However, an explicit bind_address may
be used to bind the connection to a specific address. The
bind_address of localhost 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.
-M Places the ssh client into master mode for connection sharing.
Multiple -M options places ssh into master mode with
confirmation required before slave connections are accepted.
Refer to ControlMaster in ssh_config(5)
-m mac_spec for protocol version 2 a comma-separated list of
MAC (message authentication code) algorithms can be specified in
order of preference. See the MACs keyword for more information.
-N Do not execute a remote command. for just forwarding ports (protocol version 2 only).
-n Redirects stdin from /dev/null (i.e., prevents reading from
stdin). must be used when ssh is run in the background.
Use this to run X11 programs on a remote
machine. For example, ssh -n shadows.cs.hut.fi emacs & will
start an emacs on shadows.cs.hut.fi, and the X11 connection will
be automatically forwarded over an encrypted channel. The ssh
program will be put in the background. Does not work if password is needed; see -f
-O ctl_cmd
Control an active connection multiplexing master process. When
the -O option is specified, the ctl_cmd argument is interpreted
and passed to the master process. Valid commands are: check
(check that the master process is running) and exit (request the master to exit).
-o option
provide options in the format used in the configuration file. useful for specifying options for which there
is no command-line flag, see ssh_config(5).
AddressFamily BatchMode BindAddress ChallengeResponseAuthentication CheckHostIP Cipher Ciphers ClearAllForwardings Compression CompressionLevel ConnectionAttempts ConnectTimeout ControlMaster ControlPath DynamicForward EscapeChar ExitOnForwardFailure ForwardAgent ForwardX11 ForwardX11Trusted |
-p port
Can be specified on a per-host basis in the configuration file.
-1 tries protocol version 1 only.
-2 version 2 only.
-4 use IPv4 addresses only.
-6 use IPv6 addresses only.
-q Quiet (IMHO not a good idea). Warnings and diagnostics are suppressed.
-R [bind_address:]port:host:hostport
Specifies that the given port on the remote (server) host is to
be forwarded to the given host and port on the local side.
Works by allocating a socket to listen to port on the remote
side, and whenever a connection is made to this port, it is forwarded over the secure channel, and a connection is
made to host port hostport from the local machine.
Port forwardings can also be specified in the configuration file.
Privileged ports can be forwarded only when logging in as root on
the remote machine.
IPv6 addresses can be specified by enclosing
the address in square braces or using an alternative syntax:
[bind_address/]host/port/hostport.
By default, the listening socket on the server will be bound to the loopback interface only. This may be overriden by specifying a bind_address. An empty bind_address, or the address `*', indicates that the remote socket should listen on all interfaces. Specifying a remote bind_address will only succeed if the server's GatewayPorts option is enabled (see sshd_config(5)).
-S ctl_path
location of a control socket for connection sharing. Refer to ControlPath and ControlMaster
in ssh_config(5)
-s requests invocation of a subsystem on the remote
system. Subsystems are a feature of the SSH2 protocol which
facilitate the use of SSH as a secure transport for other applications (eg. sftp(1)).
The subsystem is specified as the remote command.
-T Disable pseudo-tty allocation.
-t Force pseudo-tty allocation, allows execution of screen-based programs on a remote host, which can be
, e.g. when implementing menu services. Multiple -t options force tty allocation, even if ssh has no local tty.
-V Display the version number and exit.
-w local_tun[:remote_tun ] Requests tunnel device forwarding with the specified tun(4)
devices between the client (local_tun) and the server (remote_tun).
The devices may be specified by numerical ID or the keyword any, which uses the next available tunnel device. If
remote_tun is not specified, it defaults to any. See also the Tunnel and TunnelDevice directives in ssh_config(5).
If the Tunnel directive is unset, it is set to the default tunnel mode, which is point-to-point.
-X Enables X11 forwarding. can be specified on a per-host basis in a configuration file.
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.
For this reason, X11 forwarding is subjected to X11 SECURITY
extension restrictions by default. refer to -Y and the ForwardX11Trusted directive in ssh_config(5) for more information.
-x Disables X11 forwarding.