diff options
Diffstat (limited to 'ssh.0')
| -rw-r--r-- | ssh.0 | 478 |
1 files changed, 243 insertions, 235 deletions
@@ -14,14 +14,14 @@ SYNOPSIS DESCRIPTION ssh (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 untrust- - ed hosts over an insecure network. X11 connections and arbitrary TCP - ports can also be forwarded over the secure channel. + and rsh, and provide secure encrypted communications between two + untrusted hosts over an insecure network. X11 connections and arbitrary + TCP ports can also be forwarded over the secure channel. ssh connects and logs into the specified hostname (with optional user name). The user must prove his/her identity to the remote machine using - one of several methods depending on the protocol version used (see be- - low). + one of several methods depending on the protocol version used (see + below). If command is specified, it is executed on the remote host instead of a login shell. @@ -52,8 +52,8 @@ DESCRIPTION -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 ad- - dress. + 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 @@ -69,17 +69,17 @@ DESCRIPTION Protocol version 1 allows specification of a single cipher. The supported values are ``3des'', ``blowfish'', and ``des''. 3des - (triple-des) is an encrypt-decrypt-encrypt triple with three dif- - ferent keys. It is believed to be secure. blowfish is a fast + (triple-des) is an encrypt-decrypt-encrypt triple with three + different keys. It is believed to be secure. blowfish is a fast block cipher; it appears very secure and is much faster than - 3des. des is only supported in the ssh client for interoperabil- - ity with legacy protocol 1 implementations that do not support - the 3des cipher. Its use is strongly discouraged due to crypto- - graphic weaknesses. The default is ``3des''. + 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. The default is ``3des''. For protocol version 2, cipher_spec is a comma-separated list of ciphers listed in order of preference. See the Ciphers keyword - for more information. + in ssh_config(5) for more information. -D [bind_address:]port Specifies a local ``dynamic'' application-level port forwarding. @@ -89,19 +89,18 @@ DESCRIPTION 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. Dy- - namic port forwardings can also be specified in the configuration - file. + 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 with an alternative syntax: - [bind_address/]port or by enclosing the address in square brack- - ets. Only the superuser can forward privileged ports. By de- - fault, 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 + 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 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 `*' indi- - cates that the port should be available from all interfaces. + be bound for local use only, while an empty address or `*' + indicates that the port should be available from all interfaces. -e escape_char Sets the escape character for sessions with a pty (default: `~'). @@ -113,21 +112,21 @@ DESCRIPTION fully transparent. -F configfile - Specifies an alternative per-user configuration file. If a con- - figuration file is given on the command line, the system-wide + 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 passphras- - es, 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. + 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 it- - self in the background. + port forwards to be successfully established before placing + itself in the background. -g Allows remote hosts to connect to local forwarded ports. @@ -138,13 +137,13 @@ DESCRIPTION -i identity_file Selects a file from which the identity (private key) for RSA or DSA authentication is read. The default is ~/.ssh/identity for - protocol version 1, and ~/.ssh/id_rsa and ~/.ssh/id_dsa for pro- - tocol version 2. Identity files may also be specified on a per- - host basis in the configuration file. It is possible to have - multiple -i options (and multiple identities specified in config- - uration files). ssh will also try to load certificate informa- - tion from the filename obtained by appending -cert.pub to identi- - ty filenames. + protocol version 1, and ~/.ssh/id_rsa and ~/.ssh/id_dsa for + protocol version 2. Identity files may also be specified on a + per-host basis in the configuration file. It is possible to have + multiple -i options (and multiple identities specified in + configuration files). 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. @@ -156,60 +155,62 @@ DESCRIPTION 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 port on the local side, - optionally bound to the specified bind_address. Whenever a con- - nection is made to this port, the connection is forwarded over + 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 spec- - ified with an alternative syntax: [bind_address/]port/host/host- - port or by enclosing the address in square brackets. Only the + 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 accordance with the GatewayPorts setting. How- - ever, an explicit bind_address may be used to bind the connection - to a specific address. The bind_address of ``localhost'' indi- - cates that the listening port be bound for local use only, while - an empty address or `*' indicates that the port should be avail- - able from all interfaces. + 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 shar- - ing. Multiple -M options places ssh into ``master'' mode with - confirmation required before slave connections are accepted. Re- - fer to the description of ControlMaster in ssh_config(5) for de- - tails. + -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 Additionally, 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. This is useful for just for- - warding ports (protocol version 2 only). + -N Do not execute a remote command. This is useful for just + forwarding ports (protocol version 2 only). -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 programs on a remote ma- - chine. For example, ssh -n shadows.cs.hut.fi emacs & will start - an emacs on shadows.cs.hut.fi, and the X11 connection will be au- - tomatically 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.) + common trick is to 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. (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 commands are: ``check'' - (check that the master process is running) and ``exit'' (request - the master to exit). + (check that the master process is running), ``forward'' (request + forwardings without command execution) and ``exit'' (request the + master to exit). -o option - Can be used to give options in the format used in the configura- - tion file. This is useful for specifying options for which there - is no separate command-line flag. For full details of the op- - tions listed below, and their possible values, see ssh_config(5). + 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). AddressFamily BatchMode @@ -287,61 +288,64 @@ DESCRIPTION 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 port on the remote - side, and whenever a connection is made to this port, the connec- - tion is forwarded over the secure channel, and a connection is - made to host port hostport from the local machine. + side, and 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 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. + the address in square braces. By default, the listening socket on the server will be bound to - the loopback interface only. This may be overridden by specify- - ing 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 serv- - er's GatewayPorts option is enabled (see sshd_config(5)). + 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 allocated 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. + 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 are a feature of the SSH2 protocol which fa- - cilitate the use of SSH as a secure transport for other applica- - tions (eg. sftp(1)). The subsystem is specified as the remote - command. + 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. This can be used to execute arbi- - trary screen-based programs on a remote machine, which can be + -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. 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, authentica- - tion, and configuration problems. Multiple -v options increase - the verbosity. The maximum is 3. + 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 forward- - ed to host on port over the secure channel. Implies -N, -T, - ExitOnForwardFailure and ClearAllForwardings and works with Pro- - tocol version 2 only. + 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 and works with + Protocol version 2 only. -w local_tun[:remote_tun] - Requests tunnel device forwarding with the specified tun(4) de- - vices between the client (local_tun) and the server (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 @@ -359,9 +363,9 @@ DESCRIPTION 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 ex- - tension restrictions by default. Please refer to the ssh -Y op- - tion and the ForwardX11Trusted directive in ssh_config(5) for + 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. -x Disables X11 forwarding. @@ -369,12 +373,12 @@ DESCRIPTION -Y Enables trusted X11 forwarding. Trusted X11 forwardings are not subjected to the X11 SECURITY extension controls. - -y Send log information using the syslog(3) system module. By de- - fault this information is sent to stderr. + -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 configura- - tion file and a system-wide configuration file. The file format and con- - figuration options are described in ssh_config(5). + 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). ssh exits with the exit status of the remote command or with 255 if an error occurred. @@ -385,15 +389,16 @@ AUTHENTICATION in ssh_config(5) or the -1 and -2 options (see above). Both protocols support similar authentication methods, but protocol 2 is the default since it provides additional mechanisms for confidentiality (the traffic - is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour) and integri- - ty (hmac-md5, hmac-sha1, umac-64, hmac-ripemd160). Protocol 1 lacks a - strong mechanism for ensuring the integrity of the connection. + is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour) and + integrity (hmac-md5, hmac-sha1, umac-64, hmac-ripemd160). Protocol 1 + lacks a strong mechanism for ensuring the integrity of the connection. - The methods available for authentication are: GSSAPI-based authentica- - tion, host-based authentication, public key authentication, challenge-re- - sponse authentication, and password authentication. Authentication meth- - ods are tried in the order specified above, though protocol 2 has a con- - figuration option to change the default order: PreferredAuthentications. + The methods available for authentication are: GSSAPI-based + authentication, host-based authentication, public key authentication, + challenge-response authentication, and password authentication. + Authentication methods are tried in the order specified above, though + protocol 2 has a configuration option to change the default order: + PreferredAuthentications. Host-based authentication works as follows: If the machine the user logs in from is listed in /etc/hosts.equiv or /etc/shosts.equiv on the remote @@ -403,22 +408,22 @@ AUTHENTICATION the name of the user on that machine, the user is considered for login. Additionally, the server must be able to verify the client's host key (see the description of /etc/ssh/ssh_known_hosts and ~/.ssh/known_hosts, - below) for login to be permitted. This authentication method closes se- - curity holes due to IP spoofing, DNS spoofing, and routing spoofing. + below) for login to be permitted. This authentication method closes + security holes due to IP spoofing, DNS spoofing, and routing spoofing. [Note to the administrator: /etc/hosts.equiv, ~/.rhosts, and the rlogin/rsh protocol in general, are inherently insecure and should be disabled if security is desired.] - Public key authentication works as follows: The scheme is based on pub- - lic-key cryptography, using cryptosystems where encryption and decryption - are done using separate keys, and it is unfeasible to derive the decryp- - tion key from the encryption key. 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. ssh implements - public key authentication protocol automatically, using either the RSA or - DSA algorithms. Protocol 1 is restricted to using only RSA keys, but - protocol 2 may use either. The HISTORY section of ssl(8) contains a - brief discussion of the two algorithms. + Public key authentication works as follows: The scheme is based on + public-key cryptography, using cryptosystems where encryption and + decryption are done using separate keys, and it is unfeasible to derive + the decryption key from the encryption key. 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. + ssh implements public key authentication protocol automatically, using + either the RSA or DSA algorithms. Protocol 1 is restricted to using only + RSA keys, but protocol 2 may use either. The HISTORY section of ssl(8) + contains a brief discussion of the two algorithms. The file ~/.ssh/authorized_keys lists the public keys that are permitted for logging in. When the user logs in, the ssh program tells the server @@ -430,48 +435,49 @@ AUTHENTICATION the private key in ~/.ssh/identity (protocol 1), ~/.ssh/id_dsa (protocol 2 DSA), or ~/.ssh/id_rsa (protocol 2 RSA) and stores the public key in ~/.ssh/identity.pub (protocol 1), ~/.ssh/id_dsa.pub (protocol 2 DSA), or - ~/.ssh/id_rsa.pub (protocol 2 RSA) in the user's home directory. The us- - er should then copy the public key to ~/.ssh/authorized_keys in his/her - home directory on the remote machine. The authorized_keys file corre- - sponds to the conventional ~/.rhosts file, and has one key per line, - though the lines can be very long. After this, the user can log in with- - out giving the password. + ~/.ssh/id_rsa.pub (protocol 2 RSA) in the user's home directory. The + user should then copy the public key to ~/.ssh/authorized_keys in his/her + home directory on the remote machine. The authorized_keys file + corresponds to the conventional ~/.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. - A variation on public key authentication is available in the form of cer- - tificate authentication: instead of a set of public/private keys, signed - certificates are used. This has the advantage that a single trusted cer- - tification authority can be used in place of many public/private keys. - See the CERTIFICATES section of ssh-keygen(1) for more information. + A variation on public key authentication is available in the form of + certificate authentication: instead of a set of public/private keys, + signed certificates are used. This has the advantage that a single + trusted certification authority can be used in place of many + public/private keys. See the CERTIFICATES section of ssh-keygen(1) for + more information. The most convenient way to use public key or certificate authentication - may be with an authentication agent. See ssh-agent(1) for more informa- - tion. + may be with an authentication agent. See ssh-agent(1) for more + information. Challenge-response authentication works as follows: The server sends an - arbitrary "challenge" text, and prompts for a response. Protocol 2 al- - lows multiple challenges and responses; protocol 1 is restricted to just - one challenge/response. Examples of challenge-response authentication - include BSD Authentication (see login.conf(5)) and PAM (some non-OpenBSD - systems). + arbitrary "challenge" text, and prompts for a response. Protocol 2 + allows multiple challenges and responses; protocol 1 is restricted to + just one challenge/response. Examples of challenge-response + authentication include BSD Authentication (see login.conf(5)) and PAM + (some non-OpenBSD systems). Finally, if other authentication methods fail, ssh 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. - ssh automatically maintains and checks a database containing identifica- - tion for all hosts it has ever been used with. Host keys are stored in - ~/.ssh/known_hosts in the user's home directory. Additionally, the file - /etc/ssh/ssh_known_hosts is automatically checked for known hosts. Any - new hosts are automatically added to the user's file. If a host's iden- - tification ever changes, ssh warns about this and disables password au- - thentication to prevent server spoofing or man-in-the-middle attacks, - which could otherwise be used to circumvent the encryption. The + ssh automatically maintains and checks a database containing + identification for all hosts it has ever been used with. Host keys are + stored in ~/.ssh/known_hosts in the user's home directory. Additionally, + the file /etc/ssh/ssh_known_hosts is automatically checked for known + hosts. Any new hosts are automatically added to the user's file. If a + host's identification ever changes, ssh warns about this and disables + password authentication to prevent server spoofing or man-in-the-middle + attacks, which could otherwise be used to circumvent the encryption. The StrictHostKeyChecking option can be used to control logins to machines whose host key is not known or has changed. - When the user's identity has been accepted by the server, the server ei- - ther executes the given command, or logs into the machine and gives the + 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. @@ -487,14 +493,14 @@ AUTHENTICATION exits and all X11 and TCP connections have been closed. ESCAPE CHARACTERS - When a pseudo-terminal has been requested, ssh supports a number of func- - tions through the use of an escape character. + When a pseudo-terminal has been requested, ssh supports a number of + functions through the use of an escape character. A single tilde character can be sent as ~~ or 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 charac- - ter can be changed in configuration files using the EscapeChar configura- - tion directive or on the command line by the -e option. + always follow a newline to be interpreted as special. The escape + character can be changed in configuration files using the EscapeChar + configuration directive or on the command line by the -e option. The supported escapes (assuming the default `~') are: @@ -531,8 +537,8 @@ TCP FORWARDING In the example below, we look at encrypting communication between an IRC client and server, even though the IRC server does not directly support encrypted communications. This works as follows: the user connects to - the remote host using ssh, specifying a port to be used to forward con- - nections to the remote server. After that it is possible to start the + the remote host using ssh, specifying a port to be used to forward + connections to the remote server. After that it is possible to start the service which is to be encrypted on the client machine, connecting to the same local port, and ssh will encrypt and forward the connection. @@ -543,11 +549,11 @@ TCP FORWARDING $ irc -c '#users' -p 1234 pinky 127.0.0.1 This tunnels a connection to IRC server ``server.example.com'', joining - channel ``#users'', nickname ``pinky'', using port 1234. It doesn't mat- - ter which port is used, as long as it's greater than 1023 (remember, only - root can open sockets on privileged ports) and doesn't conflict with any - ports already in use. The connection is forwarded to port 6667 on the - remote server, since that's the standard port for IRC services. + channel ``#users'', nickname ``pinky'', using port 1234. It doesn't + matter which port is used, as long as it's greater than 1023 (remember, + only root can open sockets on privileged ports) and doesn't conflict with + any ports already in use. The connection is forwarded to port 6667 on + the remote server, since that's the standard port for IRC services. The -f option backgrounds ssh and the remote command ``sleep 10'' is specified to allow an amount of time (10 seconds, in the example) to @@ -557,13 +563,13 @@ TCP FORWARDING X11 FORWARDING If the ForwardX11 variable is set to ``yes'' (or see the description of the -X, -x, and -Y options above) and the user is using X11 (the DISPLAY - environment variable is set), the connection to the X11 display is auto- - matically forwarded to the remote side in such a way that any X11 pro- - grams 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. Forwarding of - X11 connections can be configured on the command line or in configuration - files. + 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. + Forwarding of X11 connections can be configured on the command line or in + configuration files. The DISPLAY value set by ssh will point to the server machine, but with a display number greater than zero. This is normal, and happens because @@ -579,8 +585,8 @@ X11 FORWARDING If the ForwardAgent variable is set to ``yes'' (or see the description of the -A and -a options above) and the user is using an authentication - agent, the connection to the agent is automatically forwarded to the re- - mote side. + agent, the connection to the agent is automatically forwarded to the + remote side. VERIFYING HOST KEYS When connecting to a server for the first time, a fingerprint of the @@ -597,8 +603,8 @@ VERIFYING HOST KEYS ``yes'', a small ASCII graphic gets displayed on every login to a server, no matter if the session itself is interactive or not. By learning the pattern a known server produces, a user can easily find out that the host - key has changed when a completely different pattern is displayed. Be- - cause these patterns are not unambiguous however, a pattern that looks + key has changed when a completely different pattern is displayed. + Because these patterns are not unambiguous however, a pattern that looks similar to the pattern remembered only gives a good probability that the host key is the same, not guaranteed proof. @@ -634,15 +640,15 @@ VERIFYING HOST KEYS SSH-BASED VIRTUAL PRIVATE NETWORKS ssh contains support for Virtual Private Network (VPN) tunnelling using - the tun(4) network pseudo-device, allowing two networks to be joined se- - curely. The sshd_config(5) configuration option PermitTunnel controls - whether the server supports this, and at what level (layer 2 or 3 traf- - fic). + the tun(4) network pseudo-device, allowing two networks to be joined + securely. The sshd_config(5) configuration option PermitTunnel controls + whether the server supports this, and at what level (layer 2 or 3 + traffic). - The following example would connect client network 10.0.50.0/24 with re- - mote network 10.0.99.0/24 using a point-to-point connection from 10.1.1.1 - to 10.1.1.2, provided that the SSH server running on the gateway to the - remote network, at 192.168.1.15, allows it. + The following example would connect client network 10.0.50.0/24 with + remote network 10.0.99.0/24 using a point-to-point connection from + 10.1.1.1 to 10.1.1.2, provided that the SSH server running on the gateway + to the remote network, at 192.168.1.15, allows it. On the client: @@ -665,8 +671,8 @@ SSH-BASED VIRTUAL PRIVATE NETWORKS tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john Since an SSH-based setup entails a fair amount of overhead, it may be - more suited to temporary setups, such as for wireless VPNs. More perma- - nent VPNs are better provided by tools such as ipsecctl(8) and + more suited to temporary setups, such as for wireless VPNs. More + permanent VPNs are better provided by tools such as ipsecctl(8) and isakmpd(8). ENVIRONMENT @@ -685,13 +691,13 @@ ENVIRONMENT HOME Set to the path of the user's home directory. - LOGNAME Synonym for USER; set for compatibility with sys- - tems that use this variable. + LOGNAME Synonym for USER; set for compatibility with + systems that use this variable. MAIL Set to the path of the user's mailbox. - PATH Set to the default PATH, as specified when compil- - ing ssh. + PATH Set to the default PATH, as specified when + compiling ssh. SSH_ASKPASS If ssh needs a passphrase, it will read the passphrase from the current terminal if it was run @@ -699,49 +705,50 @@ ENVIRONMENT 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 call- - ing ssh from a .xsession or related script. (Note - that on some machines it may be necessary to redi- - rect the input from /dev/null to make this work.) + passphrase. This is particularly useful when + calling ssh from a .xsession or related script. + (Note that on some machines it may be necessary to + redirect the input from /dev/null to make this + work.) SSH_AUTH_SOCK Identifies the path of a UNIX-domain socket used to communicate with the agent. - SSH_CONNECTION Identifies the client and server ends of the con- - nection. The variable contains four space-separat- - ed values: client IP address, client port number, - server IP address, and server port number. + SSH_CONNECTION Identifies the client and server ends of the + connection. The variable contains four space- + separated values: client IP address, client port + number, server IP address, and server port number. SSH_ORIGINAL_COMMAND This variable contains the original command line if a forced command is executed. It can be used to extract the original arguments. - SSH_TTY This is set to the name of the tty (path to the de- - vice) associated with the current shell or command. - If the current session has no tty, this variable is - not set. + 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. TZ This variable is set to indicate the present time zone if it was set when the daemon was started - (i.e. the daemon passes the value on to new connec- - tions). + (i.e. the daemon passes the value on to new + connections). USER Set to the name of the user logging in. Additionally, ssh reads ~/.ssh/environment, and adds lines of the format - ``VARNAME=value'' to the environment if the file exists and users are al- - lowed to change their environment. For more information, see the + ``VARNAME=value'' to the environment if the file exists and users are + allowed to change their environment. For more information, see the PermitUserEnvironment option in sshd_config(5). FILES ~/.rhosts This file is used for host-based authentication (see above). On - some machines this file may need to be world-readable if the us- - er's home directory is on an NFS partition, 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 recom- - mended permission for most machines is read/write for the user, - and not accessible by others. + some machines this file may need to be world-readable if the + user's home directory is on an NFS partition, 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. ~/.shosts This file is used in exactly the same way as .rhosts, but allows @@ -749,18 +756,18 @@ FILES rlogin/rsh. ~/.ssh/ - This directory is the default location for all user-specific con- - figuration and authentication information. There is no general - requirement to keep the entire contents of this directory secret, - but the recommended permissions are read/write/execute for the - user, and not accessible by others. + This directory is the default location for all user-specific + configuration and authentication information. There is no + general requirement to keep the entire contents of this directory + secret, but the recommended permissions are read/write/execute + for the user, and not accessible by others. ~/.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. This file is not highly sensitive, but the - recommended permissions are read/write for the user, and not ac- - cessible by others. + recommended permissions are read/write for the user, and not + accessible by others. ~/.ssh/config This is the per-user configuration file. The file format and @@ -776,11 +783,12 @@ FILES ~/.ssh/id_dsa ~/.ssh/id_rsa Contains the private key for authentication. These files contain - sensitive data and should be readable by the user but not acces- - sible by others (read/write/execute). ssh will simply ignore a - private key file if it is accessible by others. It is possible - to specify a passphrase when generating the key which will be - used to encrypt the sensitive part of this file using 3DES. + sensitive data and should be readable by the user but not + accessible by others (read/write/execute). ssh will simply + ignore a private key file if it is accessible by others. It is + possible to specify a passphrase when generating the key which + will be used to encrypt the sensitive part of this file using + 3DES. ~/.ssh/identity.pub ~/.ssh/id_dsa.pub @@ -804,8 +812,8 @@ FILES should only be writable by root. /etc/shosts.equiv - This file is used in exactly the same way as hosts.equiv, but al- - lows host-based authentication without permitting login with + This file is used in exactly the same way as hosts.equiv, but + allows host-based authentication without permitting login with rlogin/rsh. /etc/ssh/ssh_config @@ -817,11 +825,11 @@ FILES /etc/ssh/ssh_host_rsa_key These three files contain the private parts of the host keys and are used for host-based authentication. If protocol version 1 is - used, ssh must be setuid root, since the host key is readable on- - ly by root. For protocol version 2, ssh uses ssh-keysign(8) to - access the host keys, eliminating the requirement that ssh be se- - tuid root when host-based authentication is used. By default ssh - is not setuid root. + used, ssh must be setuid root, since the host key is readable + only by root. For protocol version 2, ssh uses ssh-keysign(8) to + access the host keys, eliminating the requirement that ssh be + setuid root when host-based authentication is used. By default + ssh is not setuid root. /etc/ssh/ssh_known_hosts Systemwide list of known host keys. This file should be prepared @@ -866,7 +874,7 @@ SEE ALSO The Secure Shell (SSH) Public Key File Format, RFC 4716, 2006. - A. Perrig and D. Song, Hash Visualization: a New Technique to improve + A. Perrig, D. Song, Hash Visualization: a New Technique to improve Real-World Security, 1999, International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99). @@ -877,4 +885,4 @@ AUTHORS created OpenSSH. Markus Friedl contributed the support for SSH protocol versions 1.5 and 2.0. -OpenBSD 4.7 March 26, 2010 14 +OpenBSD 4.8 August 4, 2010 OpenBSD 4.8 |