diff options
author | Colin Watson <cjwatson@debian.org> | 2003-09-01 18:33:32 +0000 |
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committer | Colin Watson <cjwatson@debian.org> | 2003-09-01 18:33:32 +0000 |
commit | 58bfa257481a1c6938ada9bbd38801cc45633fb0 (patch) | |
tree | 385160ff5c19376a1e1bfd34fcf5c91cff42908e /ssh.0 | |
parent | ae225aa5594655e3fa5685b4dd7f2ae0e1a5e2d7 (diff) | |
parent | 58657d96514cd6f16d82add8d6f4adbb36765758 (diff) |
Import OpenSSH 3.6p1.
Diffstat (limited to 'ssh.0')
-rw-r--r-- | ssh.0 | 614 |
1 files changed, 614 insertions, 0 deletions
@@ -0,0 +1,614 @@ +SSH(1) BSD General Commands Manual SSH(1) + +^[[1mNAME^[[0m + ^[[1mssh ^[[22mM-bMM-^R OpenSSH SSH client (remote login program) + +^[[1mSYNOPSIS^[[0m + ^[[1mssh ^[[22m[^[[1mM-bMM-^Rl ^[[4m^[[22mlogin_name^[[24m] ^[[4mhostname^[[24m | ^[[4muser@hostname^[[24m [^[[4mcommand^[[24m] + + ^[[1mssh ^[[22m[^[[1mM-bMM-^RafgknqstvxACNTX1246^[[22m] [^[[1mM-bMM-^Rb ^[[4m^[[22mbind_address^[[24m] [^[[1mM-bMM-^Rc ^[[4m^[[22mcipher_spec^[[24m] + [^[[1mM-bMM-^Re ^[[4m^[[22mescape_char^[[24m] [^[[1mM-bMM-^Ri ^[[4m^[[22midentity_file^[[24m] [^[[1mM-bMM-^Rl ^[[4m^[[22mlogin_name^[[24m] [^[[1mM-bMM-^Rm ^[[4m^[[22mmac_spec^[[24m] + [^[[1mM-bMM-^Ro ^[[4m^[[22moption^[[24m] [^[[1mM-bMM-^Rp ^[[4m^[[22mport^[[24m] [^[[1mM-bMM-^RF ^[[4m^[[22mconfigfile^[[24m] [^[[1mM-bMM-^RL ^[[4m^[[22mport^[[24m:^[[4mhost^[[24m:^[[4mhostport^[[24m] [^[[1mM-bMM-^RR^[[0m + ^[[4mport^[[24m:^[[4mhost^[[24m:^[[4mhostport^[[24m] [^[[1mM-bMM-^RD ^[[4m^[[22mport^[[24m] ^[[4mhostname^[[24m | ^[[4muser@hostname^[[24m [^[[4mcommand^[[24m] + +^[[1mDESCRIPTION^[[0m + ^[[1mssh ^[[22m(SSH client) is a program for logging into a remote machine and for + executing commands on a remote machine. It is intended to replace rlogin + and rsh, and provide secure encrypted communications between two + untrusted hosts over an insecure network. X11 connections and arbitrary + TCP/IP ports can also be forwarded over the secure channel. + + ^[[1mssh ^[[22mconnects and logs into the specified ^[[4mhostname^[[24m. The user must prove + his/her identity to the remote machine using one of several methods + depending on the protocol version used: + + ^[[1mSSH protocol version 1^[[0m + + First, if the machine the user logs in from is listed in ^[[4m/etc/hosts.equiv^[[0m + or ^[[4m/etc/shosts.equiv^[[24m on the remote machine, and the user names are the + same on both sides, the user is immediately permitted to log in. Second, + if ^[[4m.rhosts^[[24m or ^[[4m.shosts^[[24m exists in the userM-bM-^@M-^Ys home directory on the remote + machine and contains a line containing the name of the client machine and + the name of the user on that machine, the user is permitted to log in. + This form of authentication alone is normally not allowed by the server + because it is not secure. + + The second authentication method is the ^[[4mrhosts^[[24m or ^[[4mhosts.equiv^[[24m method comM-bM-^@M-^P + bined with RSAM-bM-^@M-^Pbased host authentication. It means that if the login + would be permitted by ^[[4m$HOME/.rhosts^[[24m, ^[[4m$HOME/.shosts^[[24m, ^[[4m/etc/hosts.equiv^[[24m, or + ^[[4m/etc/shosts.equiv^[[24m, and if additionally the server can verify the clientM-bM-^@M-^Ys + host key (see ^[[4m/etc/ssh/ssh_known_hosts^[[24m and ^[[4m$HOME/.ssh/known_hosts^[[24m in the + ^[[4mFILES^[[24m section), only then login is permitted. This authentication method + closes security holes due to IP spoofing, DNS spoofing and routing spoofM-bM-^@M-^P + ing. [Note to the administrator: ^[[4m/etc/hosts.equiv^[[24m, ^[[4m$HOME/.rhosts^[[24m, and + the rlogin/rsh protocol in general, are inherently insecure and should be + disabled if security is desired.] + + As a third authentication method, ^[[1mssh ^[[22msupports RSA based authentication. + The scheme is based on publicM-bM-^@M-^Pkey cryptography: there are cryptosystems + where encryption and decryption are done using separate keys, and it is + not possible to derive the decryption key from the encryption key. RSA + is one such system. The idea is that each user creates a public/private + key pair for authentication purposes. The server knows the public key, + and only the user knows the private key. The file + ^[[4m$HOME/.ssh/authorized_keys^[[24m lists the public keys that are permitted for + logging in. When the user logs in, the ^[[1mssh ^[[22mprogram tells the server + which key pair it would like to use for authentication. The server + checks if this key is permitted, and if so, sends the user (actually the + ^[[1mssh ^[[22mprogram running on behalf of the user) a challenge, a random number, + encrypted by the userM-bM-^@M-^Ys public key. The challenge can only be decrypted + using the proper private key. The userM-bM-^@M-^Ys client then decrypts the chalM-bM-^@M-^P + lenge using the private key, proving that he/she knows the private key + but without disclosing it to the server. + + ^[[1mssh ^[[22mimplements the RSA authentication protocol automatically. The user + creates his/her RSA key pair by running sshM-bM-^@M-^Pkeygen(1). This stores the + private key in ^[[4m$HOME/.ssh/identity^[[24m and the public key in + ^[[4m$HOME/.ssh/identity.pub^[[24m in the userM-bM-^@M-^Ys home directory. The user should + then copy the ^[[4midentity.pub^[[24m to ^[[4m$HOME/.ssh/authorized_keys^[[24m in his/her home + directory on the remote machine (the ^[[4mauthorized_keys^[[24m file corresponds to + the conventional ^[[4m$HOME/.rhosts^[[24m file, and has one key per line, though the + lines can be very long). After this, the user can log in without giving + the password. RSA authentication is much more secure than rhosts authenM-bM-^@M-^P + tication. + + The most convenient way to use RSA authentication may be with an authenM-bM-^@M-^P + tication agent. See sshM-bM-^@M-^Pagent(1) for more information. + + If other authentication methods fail, ^[[1mssh ^[[22mprompts the user for a passM-bM-^@M-^P + word. The password is sent to the remote host for checking; however, + since all communications are encrypted, the password cannot be seen by + someone listening on the network. + + ^[[1mSSH protocol version 2^[[0m + + When a user connects using protocol version 2 similar authentication + methods are available. Using the default values for + ^[[1mPreferredAuthentications^[[22m, the client will try to authenticate first using + the hostbased method; if this method fails public key authentication is + attempted, and finally if this method fails keyboardM-bM-^@M-^Pinteractive and + password authentication are tried. + + The public key method is similar to RSA authentication described in the + previous section and allows the RSA or DSA algorithm to be used: The + client uses his private key, ^[[4m$HOME/.ssh/id_dsa^[[24m or ^[[4m$HOME/.ssh/id_rsa^[[24m, to + sign the session identifier and sends the result to the server. The + server checks whether the matching public key is listed in + ^[[4m$HOME/.ssh/authorized_keys^[[24m and grants access if both the key is found and + the signature is correct. The session identifier is derived from a + shared DiffieM-bM-^@M-^PHellman value and is only known to the client and the + server. + + If public key authentication fails or is not available a password can be + sent encrypted to the remote host for proving the userM-bM-^@M-^Ys identity. + + Additionally, ^[[1mssh ^[[22msupports hostbased or challenge response authenticaM-bM-^@M-^P + tion. + + Protocol 2 provides additional mechanisms for confidentiality (the trafM-bM-^@M-^P + fic is encrypted using 3DES, Blowfish, CAST128 or Arcfour) and integrity + (hmacM-bM-^@M-^Pmd5, hmacM-bM-^@M-^Psha1). Note that protocol 1 lacks a strong mechanism for + ensuring the integrity of the connection. + + ^[[1mLogin session and remote execution^[[0m + + When the userM-bM-^@M-^Ys identity has been accepted by the server, the server + either executes the given command, or logs into the machine and gives the + user a normal shell on the remote machine. All communication with the + remote command or shell will be automatically encrypted. + + If a pseudoM-bM-^@M-^Pterminal has been allocated (normal login session), the user + may use the escape characters noted below. + + If no pseudo tty has been allocated, the session is transparent and can + be used to reliably transfer binary data. On most systems, setting the + escape character to M-bM-^@M-^\noneM-bM-^@M-^] will also make the session transparent even if + a tty is used. + + The session terminates when the command or shell on the remote machine + exits and all X11 and TCP/IP connections have been closed. The exit staM-bM-^@M-^P + tus of the remote program is returned as the exit status of ^[[1mssh^[[22m. + + ^[[1mEscape Characters^[[0m + + When a pseudo terminal has been requested, ssh supports a number of funcM-bM-^@M-^P + tions through the use of an escape character. + + A single tilde character can be sent as ^[[1m~~ ^[[22mor by following the tilde by a + character other than those described below. The escape character must + always follow a newline to be interpreted as special. The escape characM-bM-^@M-^P + ter can be changed in configuration files using the ^[[1mEscapeChar ^[[22mconfiguraM-bM-^@M-^P + tion directive or on the command line by the ^[[1mM-bMM-^Re ^[[22moption. + + The supported escapes (assuming the default M-bM-^@M-^X~M-bM-^@M-^Y) are: + + ^[[1m~. ^[[22mDisconnect + + ^[[1m~^Z ^[[22mBackground ssh + + ^[[1m~# ^[[22mList forwarded connections + + ^[[1m~& ^[[22mBackground ssh at logout when waiting for forwarded connection / + X11 sessions to terminate + + ^[[1m~? ^[[22mDisplay a list of escape characters + + ^[[1m~C ^[[22mOpen command line (only useful for adding port forwardings using + the ^[[1mM-bMM-^RL ^[[22mand ^[[1mM-bMM-^RR ^[[22moptions) + + ^[[1m~R ^[[22mRequest rekeying of the connection (only useful for SSH protocol + version 2 and if the peer supports it) + + ^[[1mX11 and TCP forwarding^[[0m + + If the ^[[1mForwardX11 ^[[22mvariable is set to M-bM-^@M-^\yesM-bM-^@M-^] (or, see the description of + the ^[[1mM-bMM-^RX ^[[22mand ^[[1mM-bMM-^Rx ^[[22moptions described later) and the user is using X11 (the + DISPLAY environment variable is set), the connection to the X11 display + is automatically forwarded to the remote side in such a way that any X11 + programs started from the shell (or command) will go through the + encrypted channel, and the connection to the real X server will be made + from the local machine. The user should not manually set DISPLAY. ForM-bM-^@M-^P + warding of X11 connections can be configured on the command line or in + configuration files. + + The DISPLAY value set by ^[[1mssh ^[[22mwill point to the server machine, but with a + display number greater than zero. This is normal, and happens because + ^[[1mssh ^[[22mcreates a M-bM-^@M-^\proxyM-bM-^@M-^] X server on the server machine for forwarding the + connections over the encrypted channel. + + ^[[1mssh ^[[22mwill also automatically set up Xauthority data on the server machine. + For this purpose, it will generate a random authorization cookie, store + it in Xauthority on the server, and verify that any forwarded connections + carry this cookie and replace it by the real cookie when the connection + is opened. The real authentication cookie is never sent to the server + machine (and no cookies are sent in the plain). + + If the ^[[1mForwardAgent ^[[22mvariable is set to M-bM-^@M-^\yesM-bM-^@M-^] (or, see the description of + the ^[[1mM-bMM-^RA ^[[22mand ^[[1mM-bMM-^Ra ^[[22moptions described later) and the user is using an authentiM-bM-^@M-^P + cation agent, the connection to the agent is automatically forwarded to + the remote side. + + Forwarding of arbitrary TCP/IP connections over the secure channel can be + specified either on the command line or in a configuration file. One + possible application of TCP/IP forwarding is a secure connection to an + electronic purse; another is going through firewalls. + + ^[[1mServer authentication^[[0m + + ^[[1mssh ^[[22mautomatically maintains and checks a database containing identificaM-bM-^@M-^P + tions for all hosts it has ever been used with. Host keys are stored in + ^[[4m$HOME/.ssh/known_hosts^[[24m in the userM-bM-^@M-^Ys home directory. Additionally, the + file ^[[4m/etc/ssh/ssh_known_hosts^[[24m is automatically checked for known hosts. + Any new hosts are automatically added to the userM-bM-^@M-^Ys file. If a hostM-bM-^@M-^Ys + identification ever changes, ^[[1mssh ^[[22mwarns about this and disables password + authentication to prevent a trojan horse from getting the userM-bM-^@M-^Ys passM-bM-^@M-^P + word. Another purpose of this mechanism is to prevent manM-bM-^@M-^PinM-bM-^@M-^PtheM-bM-^@M-^Pmiddle + attacks which could otherwise be used to circumvent the encryption. The + ^[[1mStrictHostKeyChecking ^[[22moption can be used to prevent logins to machines + whose host key is not known or has changed. + + The options are as follows: + + ^[[1mM-bMM-^Ra ^[[22mDisables forwarding of the authentication agent connection. + + ^[[1mM-bMM-^RA ^[[22mEnables forwarding of the authentication agent connection. This + can also be specified on a perM-bM-^@M-^Phost 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 + agentM-bM-^@M-^Ys UnixM-bM-^@M-^Pdomain 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. + + ^[[1mM-bMM-^Rb ^[[4m^[[22mbind_address^[[0m + Specify the interface to transmit from on machines with multiple + interfaces or aliased addresses. + + ^[[1mM-bMM-^Rc ^[[4m^[[22mblowfish|3des|des^[[0m + Selects the cipher to use for encrypting the session. ^[[4m3des^[[24m is + used by default. It is believed to be secure. ^[[4m3des^[[24m (tripleM-bM-^@M-^Pdes) + is an encryptM-bM-^@M-^PdecryptM-bM-^@M-^Pencrypt triple with three different keys. + ^[[4mblowfish^[[24m is a fast block cipher, it appears very secure and is + much faster than ^[[4m3des^[[24m. ^[[4mdes^[[24m is only supported in the ^[[1mssh ^[[22mclient + for interoperability with legacy protocol 1 implementations that + do not support the ^[[4m3des^[[24m cipher. Its use is strongly discouraged + due to cryptographic weaknesses. + + ^[[1mM-bMM-^Rc ^[[4m^[[22mcipher_spec^[[0m + Additionally, for protocol version 2 a commaM-bM-^@M-^Pseparated list of + ciphers can be specified in order of preference. See ^[[1mCiphers ^[[22mfor + more information. + + ^[[1mM-bMM-^Re ^[[4m^[[22mch|^ch|none^[[0m + Sets the escape character for sessions with a pty (default: M-bM-^@M-^X~M-bM-^@M-^Y). + The escape character is only recognized at the beginning of a + line. The escape character followed by a dot (M-bM-^@M-^X.M-bM-^@M-^Y) closes the + connection, followed by controlM-bM-^@M-^PZ suspends the connection, and + followed by itself sends the escape character once. Setting the + character to M-bM-^@M-^\noneM-bM-^@M-^] disables any escapes and makes the session + fully transparent. + + ^[[1mM-bMM-^Rf ^[[22mRequests ^[[1mssh ^[[22mto go to background just before command execution. + This is useful if ^[[1mssh ^[[22mis going to ask for passwords or + passphrases, but the user wants it in the background. This + implies ^[[1mM-bMM-^Rn^[[22m. The recommended way to start X11 programs at a + remote site is with something like ^[[1mssh M-bM-^@M-^Pf host xterm^[[22m. + + ^[[1mM-bMM-^Rg ^[[22mAllows remote hosts to connect to local forwarded ports. + + ^[[1mM-bMM-^Ri ^[[4m^[[22midentity_file^[[0m + Selects a file from which the identity (private key) for RSA or + DSA authentication is read. The default is ^[[4m$HOME/.ssh/identity^[[0m + for protocol version 1, and ^[[4m$HOME/.ssh/id_rsa^[[24m and + ^[[4m$HOME/.ssh/id_dsa^[[24m for protocol version 2. Identity files may + also be specified on a perM-bM-^@M-^Phost basis in the configuration file. + It is possible to have multiple ^[[1mM-bMM-^Ri ^[[22moptions (and multiple identiM-bM-^@M-^P + ties specified in configuration files). + + ^[[1mM-bMM-^RI ^[[4m^[[22msmartcard_device^[[0m + Specifies which smartcard device to use. The argument is the + device ^[[1mssh ^[[22mshould use to communicate with a smartcard used for + storing the userM-bM-^@M-^Ys private RSA key. + + ^[[1mM-bMM-^Rk ^[[22mDisables forwarding of Kerberos tickets and AFS tokens. This may + also be specified on a perM-bM-^@M-^Phost basis in the configuration file. + + ^[[1mM-bMM-^Rl ^[[4m^[[22mlogin_name^[[0m + Specifies the user to log in as on the remote machine. This also + may be specified on a perM-bM-^@M-^Phost basis in the configuration file. + + ^[[1mM-bMM-^Rm ^[[4m^[[22mmac_spec^[[0m + Additionally, for protocol version 2 a commaM-bM-^@M-^Pseparated list of + MAC (message authentication code) algorithms can be specified in + order of preference. See the ^[[1mMACs ^[[22mkeyword for more information. + + ^[[1mM-bMM-^Rn ^[[22mRedirects stdin from ^[[4m/dev/null^[[24m (actually, prevents reading from + stdin). This must be used when ^[[1mssh ^[[22mis run in the background. A + common trick is to use this to run X11 programs on a remote + machine. For example, ^[[1mssh M-bM-^@M-^Pn shadows.cs.hut.fi emacs & ^[[22mwill + start an emacs on shadows.cs.hut.fi, and the X11 connection will + be automatically forwarded over an encrypted channel. The ^[[1mssh^[[0m + program will be put in the background. (This does not work if + ^[[1mssh ^[[22mneeds to ask for a password or passphrase; see also the ^[[1mM-bMM-^Rf^[[0m + option.) + + ^[[1mM-bMM-^RN ^[[22mDo not execute a remote command. This is useful for just forM-bM-^@M-^P + warding ports (protocol version 2 only). + + ^[[1mM-bMM-^Ro ^[[4m^[[22moption^[[0m + Can be used to give options in the format used in the configuraM-bM-^@M-^P + tion file. This is useful for specifying options for which there + is no separate commandM-bM-^@M-^Pline flag. + + ^[[1mM-bMM-^Rp ^[[4m^[[22mport^[[0m + Port to connect to on the remote host. This can be specified on + a perM-bM-^@M-^Phost basis in the configuration file. + + ^[[1mM-bMM-^Rq ^[[22mQuiet mode. Causes all warning and diagnostic messages to be + suppressed. + + ^[[1mM-bMM-^Rs ^[[22mMay be used to request 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 appliM-bM-^@M-^P + cations (eg. sftp). The subsystem is specified as the remote comM-bM-^@M-^P + mand. + + ^[[1mM-bMM-^Rt ^[[22mForce pseudoM-bM-^@M-^Ptty allocation. This can be used to execute arbiM-bM-^@M-^P + trary screenM-bM-^@M-^Pbased programs on a remote machine, which can be + very useful, e.g., when implementing menu services. Multiple ^[[1mM-bMM-^Rt^[[0m + options force tty allocation, even if ^[[1mssh ^[[22mhas no local tty. + + ^[[1mM-bMM-^RT ^[[22mDisable pseudoM-bM-^@M-^Ptty allocation. + + ^[[1mM-bMM-^Rv ^[[22mVerbose mode. Causes ^[[1mssh ^[[22mto print debugging messages about its + progress. This is helpful in debugging connection, authenticaM-bM-^@M-^P + tion, and configuration problems. Multiple ^[[1mM-bMM-^Rv ^[[22moptions increases + the verbosity. Maximum is 3. + + ^[[1mM-bMM-^Rx ^[[22mDisables X11 forwarding. + + ^[[1mM-bMM-^RX ^[[22mEnables X11 forwarding. This can also be specified on a perM-bM-^@M-^Phost + 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 + userM-bM-^@M-^Ys 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. + + ^[[1mM-bMM-^RC ^[[22mRequests compression of all data (including stdin, stdout, + stderr, and data for forwarded X11 and TCP/IP connections). The + compression algorithm is the same used by gzip(1), and the + M-bM-^@M-^\levelM-bM-^@M-^] can be controlled by the ^[[1mCompressionLevel ^[[22moption for proM-bM-^@M-^P + tocol 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 hostM-bM-^@M-^PbyM-bM-^@M-^Phost basis + in the configuration files; see the ^[[1mCompression ^[[22moption. + + ^[[1mM-bMM-^RF ^[[4m^[[22mconfigfile^[[0m + Specifies an alternative perM-bM-^@M-^Puser configuration file. If a conM-bM-^@M-^P + figuration file is given on the command line, the systemM-bM-^@M-^Pwide + configuration file (^[[4m/etc/ssh/ssh_config^[[24m) will be ignored. The + default for the perM-bM-^@M-^Puser configuration file is ^[[4m$HOME/.ssh/config^[[24m. + + ^[[1mM-bMM-^RL ^[[4m^[[22mport:host:hostport^[[0m + Specifies that the given 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 ^[[4mport^[[24m on the local side, + and whenever a connection is made to this port, the connection is + forwarded over the secure channel, and a connection is made to + ^[[4mhost^[[24m port ^[[4mhostport^[[24m from the remote machine. Port forwardings can + also be specified in the configuration file. Only root can forM-bM-^@M-^P + ward privileged ports. IPv6 addresses can be specified with an + alternative syntax: ^[[4mport/host/hostport^[[0m + + ^[[1mM-bMM-^RR ^[[4m^[[22mport:host:hostport^[[0m + Specifies that the given port on the remote (server) host is to + be forwarded to the given host and port on the local side. This + works by allocating a socket to listen to ^[[4mport^[[24m on the remote + side, and whenever a connection is made to this port, the connecM-bM-^@M-^P + tion is forwarded over the secure channel, and a connection is + made to ^[[4mhost^[[24m port ^[[4mhostport^[[24m from the local machine. Port forwardM-bM-^@M-^P + ings 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 with an alternative + syntax: ^[[4mport/host/hostport^[[0m + + ^[[1mM-bMM-^RD ^[[4m^[[22mport^[[0m + Specifies a local M-bM-^@M-^\dynamicM-bM-^@M-^] applicationM-bM-^@M-^Plevel port forwarding. + This works by allocating a socket to listen to ^[[4mport^[[24m on the local + side, and whenever a connection is made to this port, the connecM-bM-^@M-^P + tion 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 protocol is supported, and + ^[[1mssh ^[[22mwill act as a SOCKS4 server. Only root can forward priviM-bM-^@M-^P + leged ports. Dynamic port forwardings can also be specified in + the configuration file. + + ^[[1mM-bMM-^R1 ^[[22mForces ^[[1mssh ^[[22mto try protocol version 1 only. + + ^[[1mM-bMM-^R2 ^[[22mForces ^[[1mssh ^[[22mto try protocol version 2 only. + + ^[[1mM-bMM-^R4 ^[[22mForces ^[[1mssh ^[[22mto use IPv4 addresses only. + + ^[[1mM-bMM-^R6 ^[[22mForces ^[[1mssh ^[[22mto use IPv6 addresses only. + +^[[1mCONFIGURATION FILES^[[0m + ^[[1mssh ^[[22mmay additionally obtain configuration data from a perM-bM-^@M-^Puser configuraM-bM-^@M-^P + tion file and a systemM-bM-^@M-^Pwide configuration file. The file format and conM-bM-^@M-^P + figuration options are described in ssh_config(5). + +^[[1mENVIRONMENT^[[0m + ^[[1mssh ^[[22mwill normally set the following environment variables: + + DISPLAY + The DISPLAY variable indicates the location of the X11 server. + It is automatically set by ^[[1mssh ^[[22mto point to a value of the form + M-bM-^@M-^\hostname:nM-bM-^@M-^] where hostname indicates the host where the shell + runs, and n is an integer >= 1. ^[[1mssh ^[[22muses this special value to + forward X11 connections over the secure channel. The user should + normally not set DISPLAY explicitly, as that will render the X11 + connection insecure (and will require the user to manually copy + any required authorization cookies). + + HOME Set to the path of the userM-bM-^@M-^Ys home directory. + + LOGNAME + Synonym for USER; set for compatibility with systems that use + this variable. + + MAIL Set to the path of the userM-bM-^@M-^Ys mailbox. + + PATH Set to the default PATH, as specified when compiling ^[[1mssh^[[22m. + + SSH_ASKPASS + If ^[[1mssh ^[[22mneeds a passphrase, it will read the passphrase from the + current terminal if it was run from a terminal. If ^[[1mssh ^[[22mdoes not + have a terminal associated with it but DISPLAY and SSH_ASKPASS + are set, it will execute the program specified by SSH_ASKPASS and + open an X11 window to read the passphrase. This is particularly + useful when calling ^[[1mssh ^[[22mfrom a ^[[4m.Xsession^[[24m or related script. + (Note that on some machines it may be necessary to redirect the + input from ^[[4m/dev/null^[[24m to make this work.) + + SSH_AUTH_SOCK + Identifies the path of a unixM-bM-^@M-^Pdomain socket used to communicate + with the agent. + + SSH_CONNECTION + Identifies the client and server ends of the connection. The + variable contains four spaceM-bM-^@M-^Pseparated values: client ipM-bM-^@M-^Paddress, + client port number, server ipM-bM-^@M-^Paddress and server port number. + + SSH_ORIGINAL_COMMAND + The variable contains the original command line if a forced comM-bM-^@M-^P + mand is executed. It can be used to extract the original arguM-bM-^@M-^P + ments. + + SSH_TTY + This is set to the name of the tty (path to the device) associM-bM-^@M-^P + ated with the current shell or command. If the current session + has no tty, this variable is not set. + + TZ The timezone variable is set to indicate the present timezone if + it was set when the daemon was started (i.e., the daemon passes + the value on to new connections). + + USER Set to the name of the user logging in. + + Additionally, ^[[1mssh ^[[22mreads ^[[4m$HOME/.ssh/environment^[[24m, and adds lines of the + format M-bM-^@M-^\VARNAME=valueM-bM-^@M-^] to the environment if the file exists and if users + are allowed to change their environment. See the ^[[1mPermitUserEnvironment^[[0m + option in sshd_config(5). + +^[[1mFILES^[[0m + $HOME/.ssh/known_hosts + Records host keys for all hosts the user has logged into that are + not in ^[[4m/etc/ssh/ssh_known_hosts^[[24m. See sshd(8). + + $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa + Contains the authentication identity of the user. They are for + protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively. + These files contain sensitive data and should be readable by the + user but not accessible by others (read/write/execute). Note + that ^[[1mssh ^[[22mignores a private key file if it is accessible by othM-bM-^@M-^P + ers. It is possible to specify a passphrase when generating the + key; the passphrase will be used to encrypt the sensitive part of + this file using 3DES. + + $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub, $HOME/.ssh/id_rsa.pub + Contains the public key for authentication (public part of the + identity file in humanM-bM-^@M-^Preadable form). The contents of the + ^[[4m$HOME/.ssh/identity.pub^[[24m file should be added to + ^[[4m$HOME/.ssh/authorized_keys^[[24m on all machines where the user wishes + to log in using protocol version 1 RSA authentication. The conM-bM-^@M-^P + tents of the ^[[4m$HOME/.ssh/id_dsa.pub^[[24m and ^[[4m$HOME/.ssh/id_rsa.pub^[[24m file + should be added to ^[[4m$HOME/.ssh/authorized_keys^[[24m on all machines + where the user wishes to log in using protocol version 2 DSA/RSA + authentication. These files are not sensitive and can (but need + not) be readable by anyone. These files are never used automatiM-bM-^@M-^P + cally and are not necessary; they are only provided for the conM-bM-^@M-^P + venience of the user. + + $HOME/.ssh/config + This is the perM-bM-^@M-^Puser configuration file. The file format and + configuration options are described in ssh_config(5). + + $HOME/.ssh/authorized_keys + Lists the public keys (RSA/DSA) that can be used for logging in + as this user. The format of this file is described in the + sshd(8) manual page. In the simplest form the format is the same + as the .pub identity files. This file is not highly sensitive, + but the recommended permissions are read/write for the user, and + not accessible by others. + + /etc/ssh/ssh_known_hosts + Systemwide list of known host keys. This file should be prepared + by the system administrator to contain the public host keys of + all machines in the organization. This file should be worldM-bM-^@M-^P + readable. This file contains public keys, one per line, in the + following format (fields separated by spaces): system name, pubM-bM-^@M-^P + lic key and optional comment field. When different names are + used for the same machine, all such names should be listed, sepaM-bM-^@M-^P + rated by commas. The format is described on the sshd(8) manual + page. + + The canonical system name (as returned by name servers) is used + by sshd(8) to verify the client host when logging in; other names + are needed because ^[[1mssh ^[[22mdoes not convert the userM-bM-^@M-^Psupplied name to + a canonical name before checking the key, because someone with + access to the name servers would then be able to fool host + authentication. + + /etc/ssh/ssh_config + Systemwide configuration file. The file format and configuration + options are described in ssh_config(5). + + /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, + /etc/ssh/ssh_host_rsa_key + These three files contain the private parts of the host keys and + are used for ^[[1mRhostsRSAAuthentication ^[[22mand ^[[1mHostbasedAuthentication^[[22m. + If the protocol version 1 ^[[1mRhostsRSAAuthentication ^[[22mmethod is used, + ^[[1mssh ^[[22mmust be setuid root, since the host key is readable only by + root. For protocol version 2, ^[[1mssh ^[[22muses sshM-bM-^@M-^Pkeysign(8) to access + the host keys for ^[[1mHostbasedAuthentication^[[22m. This eliminates the + requirement that ^[[1mssh ^[[22mbe setuid root when that authentication + method is used. By default ^[[1mssh ^[[22mis not setuid root. + + $HOME/.rhosts + This file is used in ^[[4m.rhosts^[[24m authentication to list the host/user + pairs that are permitted to log in. (Note that this file is also + used by rlogin and rsh, which makes using this file insecure.) + Each line of the file contains a host name (in the canonical form + returned by name servers), and then a user name on that host, + separated by a space. On some machines this file may need to be + worldM-bM-^@M-^Preadable if the userM-bM-^@M-^Ys home directory is on a NFS partiM-bM-^@M-^P + tion, because sshd(8) reads it as root. Additionally, this file + must be owned by the user, and must not have write permissions + for anyone else. The recommended permission for most machines is + read/write for the user, and not accessible by others. + + Note that by default sshd(8) will be installed so that it + requires successful RSA host authentication before permitting + .rhosts authentication. If the server machine does not have the + clientM-bM-^@M-^Ys host key in ^[[4m/etc/ssh/ssh_known_hosts^[[24m, it can be stored + in ^[[4m$HOME/.ssh/known_hosts^[[24m. The easiest way to do this is to conM-bM-^@M-^P + nect back to the client from the server machine using ssh; this + will automatically add the host key to ^[[4m$HOME/.ssh/known_hosts^[[24m. + + $HOME/.shosts + This file is used exactly the same way as ^[[4m.rhosts^[[24m. The purpose + for having this file is to be able to use rhosts authentication + with ^[[1mssh ^[[22mwithout permitting login with ^[[1mrlogin ^[[22mor rsh(1). + + /etc/hosts.equiv + This file is used during ^[[4m.rhosts^[[24m ^[[4mauthentication.^[[24m It contains + canonical hosts names, one per line (the full format is described + on the sshd(8) manual page). If the client host is found in this + file, login is automatically permitted provided client and server + user names are the same. Additionally, successful RSA host + authentication is normally required. This file should only be + writable by root. + + /etc/shosts.equiv + This file is processed exactly as ^[[4m/etc/hosts.equiv^[[24m. This file + may be useful to permit logins using ^[[1mssh ^[[22mbut not using + rsh/rlogin. + + /etc/ssh/sshrc + Commands in this file are executed by ^[[1mssh ^[[22mwhen the user logs in + just before the userM-bM-^@M-^Ys shell (or command) is started. See the + sshd(8) manual page for more information. + + $HOME/.ssh/rc + Commands in this file are executed by ^[[1mssh ^[[22mwhen the user logs in + just before the userM-bM-^@M-^Ys shell (or command) is started. See the + sshd(8) manual page for more information. + + $HOME/.ssh/environment + Contains additional definitions for environment variables, see + section ^[[4mENVIRONMENT^[[24m above. + +^[[1mDIAGNOSTICS^[[0m + ^[[1mssh ^[[22mexits with the exit status of the remote command or with 255 if an + error occurred. + +^[[1mAUTHORS^[[0m + 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, reM-bM-^@M-^Padded newer features and creM-bM-^@M-^P + ated OpenSSH. Markus Friedl contributed the support for SSH protocol + versions 1.5 and 2.0. + +^[[1mSEE ALSO^[[0m + rsh(1), scp(1), sftp(1), sshM-bM-^@M-^Padd(1), sshM-bM-^@M-^Pagent(1), sshM-bM-^@M-^Pkeygen(1), + telnet(1), ssh_config(5), sshM-bM-^@M-^Pkeysign(8), sshd(8) + + T. Ylonen, T. Kivinen, M. Saarinen, T. Rinne, and S. Lehtinen, ^[[4mSSH^[[0m + ^[[4mProtocol^[[24m ^[[4mArchitecture^[[24m, draftM-bM-^@M-^PietfM-bM-^@M-^PsecshM-bM-^@M-^ParchitectureM-bM-^@M-^P12.txt, January + 2002, work in progress material. + +BSD September 25, 1999 BSD |