Linux Command – ssh เป็นคำสั่งเชื่อมต่อจาก Client ไปยัง Server เพื่อเข้าสู่ Shell พร้อมทั้งมีการเข้ารหัสความปลอดภัย หรือ secure shell
$ ssh firstname.lastname@example.org
Last login: Mon May 15 14:42:35 2017 from 172.16.12.16
ssh [-1246AaCfGgKkMNnqsTtVvXxYy] [-b bind_address] [-c cipher_spec] [-D [bind_address:]port] [-E log_file] [-e escape_char] [-F configfile] [-I pkcs11] [-i identity_file] [-L address] [-l login_name] [-m mac_spec] [-O ctl_cmd] [-o option] [-p port] [-Q query_option] [-R address] [-S ctl_path] [-W host:port] [-w local_tun[:remote_tun]] [user@]hostname [command]
เป็นคำสั่งเชื่อมต่อจาก Client ไปยัง Server เพื่อเข้าสู่ Shell พร้อมทั้งมีการเข้ารหัสความปลอดภัย หรือ secure shell โดยอาศัย public-key cryptography ในการขอเข้าสู่เครื่อง remote ปัจจุบันมีการใช้งาน ssh หลายรูปแบบ แต่วิธีที่นิยมกันคือการใช้ public-private key ในการเข้ารหัส network connection และใช้ user/password ในการ login เข้าสู่ server
-1 Forces ssh to try protocol version 1 only. -2 Forces ssh to try protocol version 2 only. -4 Forces ssh to use IPv4 addresses only. -6 Forces ssh to use IPv6 addresses only. -A Enables forwarding of the authentication agent connection. This 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, TCP and UNIX-domain 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. Protocol version 1 allows specification of a single cipher. The supported values are “3des”, “blowfish”, and “des”. For protocol version 2, cipher_spec is a comma-separated list of ciphers listed in order of preference. See the Ciphers keyword in ssh_config(5) for more information. -D [bind_address:]port Specifies a local “dynamic” application-level port forwarding. 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 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. Only root can forward privileged ports. Dynamic port forwardings can also be specified in the configuration file. IPv6 addresses can be specified by enclosing the address in square brackets. Only the superuser can forward privileged ports. By default, the local port is bound in accor‐ dance 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. -E log_file Append debug logs to log_file instead of standard error. -e escape_char Sets the escape character for sessions with a pty (default: ‘~’). The escape character is only recognized at the beginning of a line. The escape character followed by a dot (‘.’) closes the connection; followed by control-Z suspends the connection; and followed by itself sends the escape character once. Setting the character to “none” disables any escapes and makes the session fully transparent. -F configfile Specifies an alternative per-user configuration file. If a configuration file is given on the command line, the system-wide configuration file (/etc/ssh/ssh_config) will be ignored. The default for the per-user configuration file is ~/.ssh/config. -f Requests ssh to go to background just before command execution. This is useful if ssh is going to ask for passwords or passphrases, but the user wants it in the background. This implies -n. The recommended way to start X11 programs at a remote site is with something like ssh -f host xterm. If the ExitOnForwardFailure configuration option is set to “yes”, then a client started with -f will wait for all remote port forwards to be successfully established before placing itself in the background. -G Causes ssh to print its configuration after evaluating Host and Match blocks and exit. -g Allows remote hosts to connect to local forwarded ports. If used on a multiplexed connection, then this option must be specified on the master process. -I pkcs11 Specify the PKCS#11 shared library ssh should use to communicate with a PKCS#11 token providing the user's private RSA key. -i identity_file Selects a file from which the identity (private key) for public key authentication is read. The default is ~/.ssh/identity for protocol version 1, and ~/.ssh/id_dsa, ~/.ssh/id_ecdsa, ~/.ssh/id_ed25519 and ~/.ssh/id_rsa for protocol version 2. Identity files may also be specified on a per-host basis in the configuration file. It is pos‐ sible to have multiple -i options (and multiple identities specified in configuration files). If no certificates have been explicitly specified by the CertificateFile direc‐ tive, ssh will also try to load certificate information from the filename obtained by appending -cert.pub to identity filenames. -K Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI credentials to the server. -k Disables forwarding (delegation) of GSSAPI credentials to the server. -L [bind_address:]port:host:hostport -L [bind_address:]port:remote_socket -L local_socket:host:hostport -L local_socket:remote_socket Specifies that connections to the given TCP port or Unix socket on the local (client) host are to be forwarded to the given host and port, or Unix socket, on the remote side. This works by allocating a socket to listen to either a TCP port on the local side, optionally bound to the specified bind_address, or to a Unix socket. Whenever a connec‐ tion is made to the local port or socket, the connection is forwarded over the secure channel, and a connection is made to either host port hostport, or the Unix socket remote_socket, from the remote machine. Port forwardings can also be specified in the configuration file. Only the superuser can forward privileged ports. IPv6 addresses can be specified by enclosing the address in square brackets. 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. -l login_name Specifies the user to log in as on the remote machine. This also may be specified on a per-host basis in the configuration file. -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 the description of ControlMaster in ssh_config(5) for details. -m mac_spec A comma-separated list of MAC (message authentication code) algorithms, specified in order of preference. See the MACs keyword for more information. -N Do not execute a remote command. This is useful for just forwarding ports. -n Redirects stdin from /dev/null (actually, prevents reading from stdin). This must be used when ssh is run in the background. A common trick is to use this to run X11 pro‐ grams 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. (This does not work if ssh needs to ask for a password or passphrase; see also the -f option.) -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 com‐ mands are: “check” (check that the master process is running), “forward” (request forwardings without command execution), “cancel” (cancel forwardings), “exit” (request the master to exit), and “stop” (request the master to stop accepting further multiplexing requests). -o option Can be used to give options in the format used in the configuration file. This is useful for specifying options for which there is no separate command-line flag. For full details of the options listed below, and their possible values, see ssh_config(5). AddKeysToAgent AddressFamily BatchMode BindAddress CanonicalDomains CanonicalizeFallbackLocal CanonicalizeHostname CanonicalizeMaxDots CanonicalizePermittedCNAMEs CertificateFile ChallengeResponseAuthentication CheckHostIP Cipher Ciphers ClearAllForwardings Compression CompressionLevel ConnectionAttempts ConnectTimeout ControlMaster ControlPath ControlPersist DynamicForward EscapeChar ExitOnForwardFailure FingerprintHash ForwardAgent ForwardX11 ForwardX11Timeout ForwardX11Trusted GatewayPorts GlobalKnownHostsFile GSSAPIAuthentication GSSAPIDelegateCredentials HashKnownHosts Host HostbasedAuthentication HostbasedKeyTypes HostKeyAlgorithms HostKeyAlias HostName IdentityFile IdentitiesOnly IPQoS KbdInteractiveAuthentication KbdInteractiveDevices KexAlgorithms LocalCommand LocalForward LogLevel MACs Match NoHostAuthenticationForLocalhost NumberOfPasswordPrompts PasswordAuthentication PermitLocalCommand PKCS11Provider Port PreferredAuthentications Protocol ProxyCommand ProxyUseFdpass PubkeyAcceptedKeyTypes PubkeyAuthentication RekeyLimit RemoteForward RequestTTY RhostsRSAAuthentication RSAAuthentication SendEnv ServerAliveInterval ServerAliveCountMax StreamLocalBindMask StreamLocalBindUnlink StrictHostKeyChecking TCPKeepAlive Tunnel TunnelDevice UpdateHostKeys UsePrivilegedPort User UserKnownHostsFile VerifyHostKeyDNS VisualHostKey XAuthLocation -p port Port to connect to on the remote host. This can be specified on a per-host basis in the configuration file. -Q query_option Queries ssh for the algorithms supported for the specified version 2. The available features are: cipher (supported symmetric ciphers), cipher-auth (supported symmetric ciphers that support authenticated encryption), mac (supported message integrity codes), kex (key exchange algorithms), key (key types), key-cert (certificate key types), key-plain (non-certificate key types), and protocol-version (supported SSH protocol versions). -q Quiet mode. Causes most warning and diagnostic messages to be suppressed. -R [bind_address:]port:host:hostport -R [bind_address:]port:local_socket -R remote_socket:host:hostport -R remote_socket:local_socket Specifies that connections to the given TCP port or Unix socket on the remote (server) host are to be forwarded to the given host and port, or Unix socket, on the local side. This works by allocating a socket to listen to either a TCP port or to a Unix socket on the remote side. Whenever a connection is made to this port or Unix socket, the con‐ nection is forwarded over the secure channel, and a connection is made to either host port hostport, or local_socket, 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 brackets. By default, TCP listening sockets on the server will be bound to the loopback interface only. This may be overridden 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)). If the port argument is ‘0’, the listen port will be dynamically allocated on the server and reported to the client at run time. When used together with -O forward the allo‐ cated port will be printed to the standard output. -S ctl_path Specifies the location of a control socket for connection sharing, or the string “none” to disable connection sharing. Refer to the description of ControlPath and ControlMaster in ssh_config(5) for details. -s May be used to request invocation of a subsystem on the remote system. Subsystems facilitate the use of SSH as a secure transport for other applications (e.g. sftp(1)). The subsystem is specified as the remote command. -T Disable pseudo-terminal allocation. -t Force pseudo-terminal allocation. This can be used to execute arbitrary screen-based programs on a remote machine, which can be very useful, e.g. when implementing menu ser‐ vices. Multiple -t options force tty allocation, even if ssh has no local tty. -V Display the version number and exit. -v Verbose mode. Causes ssh to print debugging messages about its progress. This is helpful in debugging connection, authentication, and configuration problems. Multiple -v options increase the verbosity. The maximum is 3. -W host:port Requests that standard input and output on the client be forwarded to host on port over the secure channel. Implies -N, -T, ExitOnForwardFailure and ClearAllForwardings. -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. This can also 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. Please refer to the ssh -Y option and the ForwardX11Trusted directive in ssh_config(5) for more information. (Debian-specific: X11 forwarding is not subjected to X11 SECURITY extension restrictions by default, because too many programs currently crash in this mode. Set the ForwardX11Trusted option to “no” to restore the upstream behaviour. This may change in future depending on client-side improvements.) -x Disables X11 forwarding. -Y Enables trusted X11 forwarding. Trusted X11 forwardings are not subjected to the X11 SECURITY extension controls. (Debian-specific: This option does nothing in the default configuration: it is equivalent to “ForwardX11Trusted yes”, which is the default as described above. Set the ForwardX11Trusted option to “no” to restore the upstream behaviour. This may change in future depending on client-side improvements.) -y Send log information using the syslog(3) system module. By default this information is sent to stderr. ssh may additionally obtain configuration data from a per-user configuration file and a system-wide configuration file. The file format and configuration options are described in ssh_config(5).
Author: Suphakit Annoppornchai