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diff --git a/crypto/openssh/ssh.1 b/crypto/openssh/ssh.1 new file mode 100644 index 0000000..122431d2 --- /dev/null +++ b/crypto/openssh/ssh.1 @@ -0,0 +1,1266 @@ +.\" -*- nroff -*- +.\" +.\" Author: Tatu Ylonen <ylo@cs.hut.fi> +.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland +.\" All rights reserved +.\" +.\" As far as I am concerned, the code I have written for this software +.\" can be used freely for any purpose. Any derived versions of this +.\" software must be clearly marked as such, and if the derived work is +.\" incompatible with the protocol description in the RFC file, it must be +.\" called by a name other than "ssh" or "Secure Shell". +.\" +.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. +.\" Copyright (c) 1999 Aaron Campbell. All rights reserved. +.\" Copyright (c) 1999 Theo de Raadt. All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR +.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES +.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. +.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, +.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT +.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, +.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY +.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT +.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF +.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. +.\" +.\" $FreeBSD$ +.\" +.Dd September 25, 1999 +.Dt SSH 1 +.Os +.Sh NAME +.Nm ssh +.Nd OpenSSH secure shell client (remote login program) +.Sh SYNOPSIS +.Nm ssh +.Op Fl l Ar login_name +.Op Ar hostname | user@hostname +.Op Ar command +.Pp +.Nm ssh +.Op Fl afgknqtvxACNPTX246 +.Op Fl c Ar cipher_spec +.Op Fl e Ar escape_char +.Op Fl i Ar identity_file +.Op Fl l Ar login_name +.Op Fl o Ar option +.Op Fl p Ar port +.Oo Fl L Xo +.Sm off +.Ar port : +.Ar host : +.Ar hostport +.Sm on +.Xc +.Oc +.Oo Fl R Xo +.Sm off +.Ar port : +.Ar host : +.Ar hostport +.Sm on +.Xc +.Oc +.Op Ar hostname | user@hostname +.Op Ar command +.Sh DESCRIPTION +.Nm +(Secure Shell) 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. +.Pp +.Nm +connects and logs into the specified +.Ar hostname . +The user must prove +his/her identity to the remote machine using one of several methods +depending on the protocol version used: +.Pp +.Ss SSH protocol version 1 +.Pp +First, if the machine the user logs in from is listed in +.Pa /etc/hosts.equiv +or +.Pa /etc/ssh/shosts.equiv +on the remote machine, and the user names are +the same on both sides, the user is immediately permitted to log in. +Second, if +.Pa \&.rhosts +or +.Pa \&.shosts +exists in the user's 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. +.Pp +The second (and primary) authentication method is the +.Pa rhosts +or +.Pa hosts.equiv +method combined with RSA-based host authentication. +It means that if the login would be permitted by +.Pa $HOME/.rhosts , +.Pa $HOME/.shosts , +.Pa /etc/hosts.equiv , +or +.Pa /etc/ssh/shosts.equiv , +and if additionally the server can verify the client's +host key (see +.Pa /etc/ssh/ssh_known_hosts +and +.Pa $HOME/.ssh/known_hosts +in the +.Sx FILES +section), only then login is permitted. +This authentication method closes security holes due to IP +spoofing, DNS spoofing and routing spoofing. +[Note to the administrator: +.Pa /etc/hosts.equiv , +.Pa $HOME/.rhosts , +and the rlogin/rsh protocol in general, are inherently insecure and should be +disabled if security is desired.] +.Pp +As a third authentication method, +.Nm +supports RSA based authentication. +The scheme is based on public-key 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 +.Pa $HOME/.ssh/authorized_keys +lists the public keys that are permitted for logging +in. +When the user logs in, the +.Nm +program 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 +.Nm +program running on behalf of the user) a challenge, a random number, +encrypted by the user's public key. +The challenge can only be +decrypted using the proper private key. +The user's client then decrypts the +challenge using the private key, proving that he/she knows the private +key but without disclosing it to the server. +.Pp +.Nm +implements the RSA authentication protocol automatically. +The user creates his/her RSA key pair by running +.Xr ssh-keygen 1 . +This stores the private key in +.Pa $HOME/.ssh/identity +and the public key in +.Pa $HOME/.ssh/identity.pub +in the user's home directory. +The user should then copy the +.Pa identity.pub +to +.Pa $HOME/.ssh/authorized_keys +in his/her home directory on the remote machine (the +.Pa authorized_keys +file corresponds to the conventional +.Pa $HOME/.rhosts +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 authentication. +.Pp +The most convenient way to use RSA authentication may be with an +authentication agent. +See +.Xr ssh-agent 1 +for more information. +.Pp +If other authentication methods fail, +.Nm +prompts the user for a password. +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. +.Pp +.Ss SSH protocol version 2 +.Pp +When a user connects using the protocol version 2 +different authentication methods are available: +At first, the client attempts to authenticate using the public key method. +If this method fails password authentication is tried. +.Pp +The public key method is similar to RSA authentication described +in the previous section except that the DSA algorithm is used +instead of the patented RSA algorithm. +The client uses his private DSA key +.Pa $HOME/.ssh/id_dsa +to sign the session identifier and sends the result to the server. +The server checks whether the matching public key is listed in +.Pa $HOME/.ssh/authorized_keys2 +and grants access if both the key is found and the signature is correct. +The session identifier is derived from a shared Diffie-Hellman value +and is only known to the client and the server. +.Pp +If public key authentication fails or is not available a password +can be sent encrypted to the remote host for proving the user's identity. +This protocol 2 implementation does not yet support Kerberos or +OPIE authentication. +.Pp +Protocol 2 provides additional mechanisms for confidentiality +(the traffic is encrypted using 3DES, Blowfish, CAST128 or Arcfour) +and integrity (hmac-sha1, hmac-md5). +Note that protocol 1 lacks a strong mechanism for ensuring the +integrity of the connection. +.Pp +.Ss Login session and remote execution +.Pp +When the user's 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. +.Pp +If a pseudo-terminal has been allocated (normal login session), the +user can disconnect with +.Ic ~. , +and suspend +.Nm +with +.Ic ~^Z . +All forwarded connections can be listed with +.Ic ~# +and if +the session blocks waiting for forwarded X11 or TCP/IP +connections to terminate, it can be backgrounded with +.Ic ~& +(this should not be used while the user shell is active, as it can cause the +shell to hang). +All available escapes can be listed with +.Ic ~? . +.Pp +A single tilde character can be sent as +.Ic ~~ +(or by following the tilde by a character other than those described above). +The escape character must always follow a newline to be interpreted as +special. +The escape character can be changed in configuration files +or on the command line. +.Pp +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 +.Dq none +will also make the session transparent even if a tty is used. +.Pp +The session terminates when the command or shell in on the remote +machine exists and all X11 and TCP/IP connections have been closed. +The exit status of the remote program is returned as the exit status +of +.Nm ssh . +.Pp +.Ss X11 and TCP forwarding +.Pp +If the user is using X11 (the +.Ev DISPLAY +environment variable is set), the connection to the X11 display can +be 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 +.Ev DISPLAY . +Forwarding of X11 connections weakens the security of ssh and is +disabled by default. X11 forwarding can be enabled on the command line +or in configuration files. +.Pp +The +.Ev DISPLAY +value set by +.Nm +will point to the server machine, but with a display number greater +than zero. +This is normal, and happens because +.Nm +creates a +.Dq proxy +X server on the server machine for forwarding the +connections over the encrypted channel. +.Pp +.Nm +will 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). +.Pp +If the user is using an authentication agent, the connection to the agent +is automatically forwarded to the remote side unless disabled on +command line or in a configuration file. +.Pp +Forwarding of arbitrary TCP/IP connections over the secure channel can +be specified either on 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 trough firewalls. +.Pp +.Ss Server authentication +.Pp +.Nm +automatically maintains and checks a database containing +identifications for all hosts it has ever been used with. +RSA host keys are stored in +.Pa $HOME/.ssh/known_hosts +and +DSA host keys are stored in +.Pa $HOME/.ssh/known_hosts2 +in the user's home directory. +Additionally, the files +.Pa /etc/ssh/ssh_known_hosts +and +.Pa /etc/ssh/ssh_known_hosts2 +are automatically checked for known hosts. +Any new hosts are automatically added to the user's file. +If a host's identification +ever changes, +.Nm +warns about this and disables password authentication to prevent a +trojan horse from getting the user's password. +Another purpose of +this mechanism is to prevent man-in-the-middle attacks which could +otherwise be used to circumvent the encryption. +The +.Cm StrictHostKeyChecking +option (see below) can be used to prevent logins to machines whose +host key is not known or has changed. +.Sh OPTIONS +.Bl -tag -width Ds +.It Fl a +Disables forwarding of the authentication agent connection. +.It Fl A +Enables forwarding of the authentication agent connection. +This can also be specified on a per-host basis in a configuration file. +.It Fl c Ar blowfish|3des +Selects the cipher to use for encrypting the session. +.Ar 3des +is used by default. +It is believed to be secure. +.Ar 3des +(triple-des) is an encrypt-decrypt-encrypt triple with three different keys. +It is presumably more secure than the +.Ar des +cipher which is no longer fully supported in +.Nm ssh . +.Ar blowfish +is a fast block cipher, it appears very secure and is much faster than +.Ar 3des . +.It Fl c Ar "3des-cbc,blowfish-cbc,arcfour,cast128-cbc" +Additionally, for protocol version 2 a comma-separated list of ciphers can +be specified in order of preference. +Protocol version 2 supports 3DES, Blowfish, and CAST128 in CBC mode +and Arcfour. +.It Fl e Ar ch|^ch|none +Sets the escape character for sessions with a pty (default: +.Ql ~ ) . +The escape character is only recognized at the beginning of a line. +The escape character followed by a dot +.Pq Ql \&. +closes the connection, followed +by control-Z suspends the connection, and followed by itself sends the +escape character once. +Setting the character to +.Dq none +disables any escapes and makes the session fully transparent. +.It Fl f +Requests +.Nm +to go to background just before command execution. +This is useful if +.Nm +is going to ask for passwords or passphrases, but the user +wants it in the background. +This implies +.Fl n . +The recommended way to start X11 programs at a remote site is with +something like +.Ic ssh -f host xterm . +.It Fl g +Allows remote hosts to connect to local forwarded ports. +.It Fl i Ar identity_file +Selects the file from which the identity (private key) for +RSA authentication is read. +Default is +.Pa $HOME/.ssh/identity +in the user's home directory. +Identity files may also be specified on +a per-host basis in the configuration file. +It is possible to have multiple +.Fl i +options (and multiple identities specified in +configuration files). +.It Fl k +Disables forwarding of Kerberos tickets and AFS tokens. +This may also be specified on a per-host basis in the configuration file. +.It Fl l Ar 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. +.It Fl n +Redirects stdin from +.Pa /dev/null +(actually, prevents reading from stdin). +This must be used when +.Nm +is run in the background. +A common trick is to use this to run X11 programs on a remote machine. +For example, +.Ic 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 +.Nm +program will be put in the background. +(This does not work if +.Nm +needs to ask for a password or passphrase; see also the +.Fl f +option.) +.It Fl N +Do not execute a remote command. +This is usefull if you just want to forward ports +(protocol version 2 only). +.It Fl o Ar option +Can be used to give options in the format used in the config file. +This is useful for specifying options for which there is no separate +command-line flag. +The option has the same format as a line in the configuration file. +.It Fl p Ar port +Port to connect to on the remote host. +This can be specified on a +per-host basis in the configuration file. +.It Fl P +Use a non-privileged port for outgoing connections. +This can be used if your firewall does +not permit connections from privileged ports. +Note that this option turns off +.Cm RhostsAuthentication +and +.Cm RhostsRSAAuthentication . +.It Fl q +Quiet mode. +Causes all warning and diagnostic messages to be suppressed. +Only fatal errors are displayed. +.It Fl t +Force pseudo-tty 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 services. +.It Fl T +Disable pseudo-tty allocation (protocol version 2 only). +.It Fl v +Verbose mode. +Causes +.Nm +to print debugging messages about its progress. +This is helpful in +debugging connection, authentication, and configuration problems. +The verbose mode is also used to display +.Xr skey 1 +challenges, if the user entered "s/key" as password. +Multiple -v options increases the verbosity. +Maximum is 3. +.It Fl x +Disables X11 forwarding. +.It Fl X +Enables X11 forwarding. +This can also be specified on a per-host basis in a configuration file. +.It Fl C +Requests 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 +.Xr gzip 1 , +and the +.Dq level +can be controlled by the +.Cm CompressionLevel +option (see below). +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 +.Cm Compress +option below. +.It Fl L Ar port:host:hostport +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 +.Ar port +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 +.Ar host +port +.Ar hostport +from the remote machine. +Port forwardings can also be specified in the configuration file. +Only root can forward privileged ports. +IPv6 addresses can be specified with an alternative syntax: +.Ar port/host/hostport +.It Fl R Ar 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. +This works by allocating a socket to listen to +.Ar port +on the remote side, and whenever a connection is made to this port, the +connection is forwarded over the secure channel, and a connection is +made to +.Ar host +port +.Ar 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. +.It Fl 2 +Forces +.Nm +to try protocol version 2 only. +.It Fl 4 +Forces +.Nm +to use IPv4 addresses only. +.It Fl 6 +Forces +.Nm +to use IPv6 addresses only. +.El +.Sh CONFIGURATION FILES +.Nm +obtains configuration data from the following sources (in this order): +command line options, user's configuration file +.Pq Pa $HOME/.ssh/config , +and system-wide configuration file +.Pq Pa /etc/ssh/ssh_config . +For each parameter, the first obtained value +will be used. +The configuration files contain sections bracketed by +.Dq Host +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. +.Pp +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. +.Pp +The configuration file has the following format: +.Pp +Empty lines and lines starting with +.Ql # +are comments. +.Pp +Otherwise a line is of the format +.Dq keyword arguments . +The possible +keywords and their meanings are as follows (note that the +configuration files are case-sensitive): +.Bl -tag -width Ds +.It Cm Host +Restricts the following declarations (up to the next +.Cm Host +keyword) to be only for those hosts that match one of the patterns +given after the keyword. +.Ql \&* +and +.Ql ? +can be used as wildcards in the +patterns. +A single +.Ql \&* +as a pattern can be used to provide global +defaults for all hosts. +The host is the +.Ar hostname +argument given on the command line (i.e., the name is not converted to +a canonicalized host name before matching). +.It Cm AFSTokenPassing +Specifies whether to pass AFS tokens to remote host. +The argument to this keyword must be +.Dq yes +or +.Dq no . +.It Cm BatchMode +If set to +.Dq yes , +passphrase/password querying will be disabled. +This option is useful in scripts and other batch jobs where you have no +user to supply the password. +The argument must be +.Dq yes +or +.Dq no . +.It Cm CheckHostIP +If this flag is set to +.Dq yes , +ssh will additionally check the host ip address in the +.Pa known_hosts +file. +This allows ssh to detect if a host key changed due to DNS spoofing. +If the option is set to +.Dq no , +the check will not be executed. +.It Cm Cipher +Specifies the cipher to use for encrypting the session +in protocol version 1. +Currently, +.Dq blowfish +and +.Dq 3des +are supported. +The default is +.Dq 3des . +.It Cm Ciphers +Specifies the ciphers allowed for protocol version 2 +in order of preference. +Multiple ciphers must be comma-separated. +The default is +.Dq 3des-cbc,blowfish-cbc,cast128-cbc,arcfour . +.It Cm Compression +Specifies whether to use compression. +The argument must be +.Dq yes +or +.Dq no . +.It Cm CompressionLevel +Specifies the compression level to use if compression is enable. +The argument must be an integer from 1 (fast) to 9 (slow, best). +The default level is 6, which is good for most applications. +The meaning of the values is the same as in +.Xr gzip 1 . +.It Cm ConnectionAttempts +Specifies the number of tries (one per second) to make before falling +back to rsh or exiting. +The argument must be an integer. +This may be useful in scripts if the connection sometimes fails. +.It Cm DSAAuthentication +Specifies whether to try DSA authentication. +The argument to this keyword must be +.Dq yes +or +.Dq no . +DSA authentication will only be +attempted if a DSA identity file exists. +Note that this option applies to protocol version 2 only. +.It Cm EscapeChar +Sets the escape character (default: +.Ql ~ ) . +The escape character can also +be set on the command line. +The argument should be a single character, +.Ql ^ +followed by a letter, or +.Dq none +to disable the escape +character entirely (making the connection transparent for binary +data). +.It Cm FallBackToRsh +Specifies that if connecting via +.Nm +fails due to a connection refused error (there is no +.Xr sshd 8 +listening on the remote host), +.Xr rsh 1 +should automatically be used instead (after a suitable warning about +the session being unencrypted). +The argument must be +.Dq yes +or +.Dq no . +.It Cm ForwardAgent +Specifies whether the connection to the authentication agent (if any) +will be forwarded to the remote machine. +The argument must be +.Dq yes +or +.Dq no . +The default is +.Dq no . +.It Cm ForwardX11 +Specifies whether X11 connections will be automatically redirected +over the secure channel and +.Ev DISPLAY +set. +The argument must be +.Dq yes +or +.Dq no . +The default is +.Dq no . +.It Cm GatewayPorts +Specifies whether remote hosts are allowed to connect to local +forwarded ports. +The argument must be +.Dq yes +or +.Dq no . +The default is +.Dq no . +.It Cm GlobalKnownHostsFile +Specifies a file to use instead of +.Pa /etc/ssh/ssh_known_hosts . +.It Cm HostName +Specifies the real host name to log into. +This can be used to specify nicknames or abbreviations for hosts. +Default is the name given on the command line. +Numeric IP addresses are also permitted (both on the command line and in +.Cm HostName +specifications). +.It Cm IdentityFile +Specifies the file from which the user's RSA authentication identity +is read (default +.Pa $HOME/.ssh/identity +in the user's home directory). +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. +It is possible to have +multiple identity files specified in configuration files; all these +identities will be tried in sequence. +.It Cm IdentityFile2 +Specifies the file from which the user's DSA authentication identity +is read (default +.Pa $HOME/.ssh/id_dsa +in the user's home directory). +The file name may use the tilde +syntax to refer to a user's home directory. +It is possible to have +multiple identity files specified in configuration files; all these +identities will be tried in sequence. +.It Cm KeepAlive +Specifies whether the system should send 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. +However, this means that +connections will die if the route is down temporarily, and some people +find it annoying. +.Pp +The default is +.Dq yes +(to send keepalives), 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. +.Pp +To disable keepalives, the value should be set to +.Dq no +in both the server and the client configuration files. +.It Cm KerberosAuthentication +Specifies whether Kerberos authentication will be used. +The argument to this keyword must be +.Dq yes +or +.Dq no . +.It Cm KerberosTgtPassing +Specifies whether a Kerberos TGT will be forwarded to the server. +This will only work if the Kerberos server is actually an AFS kaserver. +The argument to this keyword must be +.Dq yes +or +.Dq no . +.It Cm LocalForward +Specifies that a TCP/IP port on the local machine be forwarded over +the secure channel to given host:port from the remote machine. +The first argument must be a port number, and the second must be +host:port. +Multiple forwardings may be specified, and additional +forwardings can be given on the command line. +Only the superuser can forward privileged ports. +.It Cm LogLevel +Gives the verbosity level that is used when logging messages from +.Nm ssh . +The possible values are: +QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. +The default is INFO. +.It Cm NumberOfPasswordPrompts +Specifies the number of password prompts before giving up. +The argument to this keyword must be an integer. +Default is 3. +.It Cm PasswordAuthentication +Specifies whether to use password authentication. +The argument to this keyword must be +.Dq yes +or +.Dq no . +Note that this option applies to both protocol version 1 and 2. +.It Cm Port +Specifies the port number to connect on the remote host. +Default is 22. +.It Cm Protocol +Specifies the protocol versions +.Nm +should support in order of preference. +The possible values are +.Dq 1 +and +.Dq 2 . +Multiple versions must be comma-separated. +The default is +.Dq 1,2 . +This means that +.Nm +tries version 1 and falls back to version 2 +if version 1 is not available. +.It Cm 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 +.Pa /bin/sh . +In the command string, +.Ql %h +will be substituted by the host name to +connect and +.Ql %p +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 +.Xr sshd 8 +server running on some machine, or execute +.Ic 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). +Note that +.Cm CheckHostIP +is not available for connects with a proxy command. +.Pp +.It Cm RemoteForward +Specifies that a TCP/IP port on the remote machine be forwarded over +the secure channel to given host:port from the local machine. +The first argument must be a port number, and the second must be +host:port. +Multiple forwardings may be specified, and additional +forwardings can be given on the command line. +Only the superuser can forward privileged ports. +.It Cm RhostsAuthentication +Specifies whether to try rhosts based authentication. +Note that this +declaration only affects the client side and has no effect whatsoever +on security. +Disabling rhosts authentication may reduce +authentication time on slow connections when rhosts authentication is +not used. +Most servers do not permit RhostsAuthentication because it +is not secure (see RhostsRSAAuthentication). +The argument to this keyword must be +.Dq yes +or +.Dq no . +.It Cm RhostsRSAAuthentication +Specifies whether to try rhosts based authentication with RSA host +authentication. +This is the primary authentication method for most sites. +The argument must be +.Dq yes +or +.Dq no . +.It Cm RSAAuthentication +Specifies whether to try RSA authentication. +The argument to this keyword must be +.Dq yes +or +.Dq no . +RSA authentication will only be +attempted if the identity file exists, or an authentication agent is +running. +Note that this option applies to protocol version 1 only. +.It Cm SkeyAuthentication +Specifies whether to use +.Xr skey 1 +authentication. +The argument to this keyword must be +.Dq yes +or +.Dq no . +The default is +.Dq no . +.It Cm StrictHostKeyChecking +If this flag is set to +.Dq yes , +.Nm +ssh will never automatically add host keys to the +.Pa $HOME/.ssh/known_hosts +and +.Pa $HOME/.ssh/known_hosts2 +files, and refuses to connect hosts whose host key has changed. +This provides maximum protection against trojan horse attacks. +However, it can be somewhat annoying if you don't have good +.Pa /etc/ssh/ssh_known_hosts +and +.Pa /etc/ssh/ssh_known_hosts2 +files installed and frequently +connect new hosts. +Basically this option forces the user to manually +add any new hosts. +Normally this option is disabled, and new hosts +will automatically be added to the known host files. +The host keys of +known hosts will be verified automatically in either case. +The argument must be +.Dq yes +or +.Dq no . +.It Cm UsePrivilegedPort +Specifies whether to use a privileged port for outgoing connections. +The argument must be +.Dq yes +or +.Dq no . +The default is +.Dq yes . +Note that setting this option to +.Dq no +turns off +.Cm RhostsAuthentication +and +.Cm RhostsRSAAuthentication . +.It Cm User +Specifies the user to log in as. +This can be useful if you have a different user name on different machines. +This saves the trouble of +having to remember to give the user name on the command line. +.It Cm UserKnownHostsFile +Specifies a file to use instead of +.Pa $HOME/.ssh/known_hosts . +.It Cm UseRsh +Specifies that rlogin/rsh should be used for this host. +It is possible that the host does not at all support the +.Nm +protocol. +This causes +.Nm +to immediately execute +.Xr rsh 1 . +All other options (except +.Cm HostName ) +are ignored if this has been specified. +The argument must be +.Dq yes +or +.Dq no . +.It Cm XAuthLocation +Specifies the location of the +.Xr xauth 1 +program. +The default is +.Pa /usr/X11R6/bin/xauth . +.El +.Sh ENVIRONMENT +.Nm +will normally set the following environment variables: +.Bl -tag -width Ds +.It Ev DISPLAY +The +.Ev DISPLAY +variable indicates the location of the X11 server. +It is automatically set by +.Nm +to point to a value of the form +.Dq hostname:n +where hostname indicates +the host where the shell runs, and n is an integer \*(>= 1. +.Nm +uses 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). +.It Ev HOME +Set to the path of the user's home directory. +.It Ev LOGNAME +Synonym for +.Ev USER ; +set for compatibility with systems that use this variable. +.It Ev MAIL +Set to point the user's mailbox. +.It Ev PATH +Set to the default +.Ev PATH , +as specified when compiling +.Nm ssh . +.It Ev SSH_AUTH_SOCK +indicates the path of a unix-domain socket used to communicate with the +agent. +.It Ev SSH_CLIENT +Identifies the client end of the connection. +The variable contains +three space-separated values: client ip-address, client port number, +and server port number. +.It Ev SSH_TTY +This is set to the name of the tty (path to the device) associated +with the current shell or command. +If the current session has no tty, +this variable is not set. +.It Ev 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). +.It Ev USER +Set to the name of the user logging in. +.El +.Pp +Additionally, +.Nm +reads +.Pa $HOME/.ssh/environment , +and adds lines of the format +.Dq VARNAME=value +to the environment. +.Sh FILES +.Bl -tag -width Ds +.It Pa $HOME/.ssh/known_hosts +Records host keys for all hosts the user has logged into (that are not +in +.Pa /etc/ssh/ssh_known_hosts ) . +See +.Xr sshd 8 . +.It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa +Contains the RSA and the DSA authentication identity of the user. +These files +contain sensitive data and should be readable by the user but not +accessible by others (read/write/execute). +Note that +.Nm +ignores a private key file if it is accessible by others. +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. +.It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub +Contains the public key for authentication (public part of the +identity file in human-readable form). +The contents of the +.Pa $HOME/.ssh/identity.pub +file should be added to +.Pa $HOME/.ssh/authorized_keys +on all machines +where you wish to log in using RSA authentication. +The contents of the +.Pa $HOME/.ssh/id_dsa.pub +file should be added to +.Pa $HOME/.ssh/authorized_keys2 +on all machines +where you wish to log in using DSA authentication. +These files are not +sensitive and can (but need not) be readable by anyone. +These files are +never used automatically and are not necessary; they are only provided for +the convenience of the user. +.It Pa $HOME/.ssh/config +This is the per-user configuration file. +The format of this file is described above. +This file is used by the +.Nm +client. +This file does not usually contain any sensitive information, +but the recommended permissions are read/write for the user, and not +accessible by others. +.It Pa $HOME/.ssh/authorized_keys +Lists the RSA keys that can be used for logging in as this user. +The format of this file is described in the +.Xr sshd 8 +manual page. +In the simplest form the format is the same as the .pub +identity files (that is, each line contains the number of bits in +modulus, public exponent, modulus, and comment fields, separated by +spaces). +This file is not highly sensitive, but the recommended +permissions are read/write for the user, and not accessible by others. +.It Pa $HOME/.ssh/authorized_keys2 +Lists the DSA keys that can be used for logging in as this user. +This file is not highly sensitive, but the recommended +permissions are read/write for the user, and not accessible by others. +.It Pa /etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2 +Systemwide list of known host keys. +.Pa /etc/ssh_known_hosts +contains RSA and +.Pa /etc/ssh_known_hosts2 +contains DSA keys. +These files should be prepared by the +system administrator to contain the public host keys of all machines in the +organization. +This file should be world-readable. +This file contains +public keys, one per line, in the following format (fields separated +by spaces): system name, number of bits in modulus, public exponent, +modulus, and optional comment field. +When different names are used +for the same machine, all such names should be listed, separated by +commas. +The format is described on the +.Xr sshd 8 +manual page. +.Pp +The canonical system name (as returned by name servers) is used by +.Xr sshd 8 +to verify the client host when logging in; other names are needed because +.Nm +does not convert the user-supplied 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. +.It Pa /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. +.It Pa $HOME/.rhosts +This file is used in +.Pa \&.rhosts +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. +One some machines this file may need to be +world-readable if the user's home directory is on a NFS partition, +because +.Xr 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. +.Pp +Note that by default +.Xr sshd 8 +will be installed so that it requires successful RSA host +authentication before permitting \s+2.\s0rhosts authentication. +If your server machine does not have the client's host key in +.Pa /etc/ssh/ssh_known_hosts , +you can store it in +.Pa $HOME/.ssh/known_hosts . +The easiest way to do this is to +connect back to the client from the server machine using ssh; this +will automatically add the host key to +.Pa $HOME/.ssh/known_hosts . +.It Pa $HOME/.shosts +This file is used exactly the same way as +.Pa \&.rhosts . +The purpose for +having this file is to be able to use rhosts authentication with +.Nm +without permitting login with +.Xr rlogin 1 +or +.Xr rsh 1 . +.It Pa /etc/hosts.equiv +This file is used during +.Pa \&.rhosts +authentication. +It contains +canonical hosts names, one per line (the full format is described on +the +.Xr 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. +.It Pa /etc/ssh/shosts.equiv +This file is processed exactly as +.Pa /etc/hosts.equiv . +This file may be useful to permit logins using +.Nm +but not using rsh/rlogin. +.It Pa /etc/ssh/sshrc +Commands in this file are executed by +.Nm +when the user logs in just before the user's shell (or command) is started. +See the +.Xr sshd 8 +manual page for more information. +.It Pa $HOME/.ssh/rc +Commands in this file are executed by +.Nm +when the user logs in just before the user's shell (or command) is +started. +See the +.Xr sshd 8 +manual page for more information. +.It Pa $HOME/.ssh/environment +Contains additional definitions for environment variables, see section +.Sx ENVIRONMENT +above. +.It Pa libcrypto.so.X.1 +A version of this library which includes support for the RSA algorithm +is required for proper operation. +.El +.Sh AUTHOR +OpenSSH +is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen, +but with bugs removed and newer features re-added. +Rapidly after the +1.2.12 release, newer versions of the original ssh bore successively +more restrictive licenses, and thus demand for a free version was born. +.Pp +This version of OpenSSH +.Bl -bullet +.It +has all components of a restrictive nature (i.e., patents, see +.Xr ssl 8 ) +directly removed from the source code; any licensed or patented components +are chosen from +external libraries. +.It +has been updated to support SSH protocol 1.5 and 2, making it compatible with +all other SSH clients and servers. +.It +contains added support for +.Xr kerberos 8 +authentication and ticket passing. +.It +supports one-time password authentication with +.Xr skey 1 . +.El +.Pp +OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl, +Niels Provos, Theo de Raadt, and Dug Song. +.Pp +The support for SSH protocol 2 was written by Markus Friedl. +.Sh SEE ALSO +.Xr rlogin 1 , +.Xr rsh 1 , +.Xr scp 1 , +.Xr ssh-add 1 , +.Xr ssh-agent 1 , +.Xr ssh-keygen 1 , +.Xr telnet 1 , +.Xr sshd 8 , +.Xr ssl 8 |
