Hey, here are some simple steps to run shell commands under cgi-bin using Apache web server (/var/www/cgi-bin), which is configured with cgi access.
Apache CGI allows files with executable permission in cgi-bin directory treated as application and run on web browsers.
We have to send the MIME type before outputting data to the web from shell script.
echo “Content-type: text/plain”
Create a shell script to display linux manual pages on web clients:
#!/bin/sh echo Content-type: text/plain echo "" man $1 | col -b > /tmp/svman.txt cat /tmp/svman.txt
# chmod ugo+x svman.sh
Test: here “ssh” is secure shell client (remote login program)
NAME ssh - secure shell client (remote login program) SYNOPSIS ssh [-l login_name] hostname [command] ssh [-a] [-c idea|blowfish|des|3des|arcfour|none] [-e escape_char] [-i identity_file] [-l login_name] [-n] [-k] [-V] [-o option] [-p port] [-q] [-P] [-t] [-v] [-x] [-C] [-g] [-L port:host:hostport] [-R port:host:hostport] hostname [command] DESCRIPTION Ssh (Secure Shell) a program for logging into a remote machine and for exe- cuting commands in 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. Ssh connects and logs into the specified hostname. The user must prove his/her identity to the remote machine using one of several methods. First, if the machine the user logs in from is listed in /etc/hosts.equiv or /etc/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 .rhosts or .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. The second (and primary) authentication method is the rhosts or hosts.equiv method combined with RSA-based host authentication. It means that if the login would be permitted by .rhosts, .shosts, /etc/hosts.equiv, or /etc/shosts.equiv, and additionally it can verify the client's host key (see $HOME/.ssh/known_hosts and /etc/ssh_known_hosts in the 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: /etc/hosts.equiv, .rhosts, and the rlogin/rsh protocol in general, are inherently insecure and should be disabled if security is desired.] As a third authentication method, ssh 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 $HOME/.ssh/authorized_keys lists 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. RSA authentication is much more secure than rhosts authentication. The most convenient way to use RSA authentication may be with an authenti- cation agent. See ssh-agent(1) for more information. As a fourth authentication method, ssh supports authentication through TIS authentication server. The idea is that ssh asks TIS authsrv(8) to authen- ticate the user. Sometime, usernames in the TIS database cannot be the same as the local users. This can be the case if the user authenticates itself with a smartcard or a Digipass. In that case, the username in the database is usually known as the serial number of the authentification device. The file /etc/sshd_tis.map contains the mapping between local users and their corresponding name in the TIS database. If the file does not exist or the user is not found, the corresponding name in the TIS database is supposed to be the same. 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. 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 com- mand or shell will be automatically encrypted. If a pseudo-terminal has been allocated (normal login session), the user can disconnect with "~.", and suspend ssh with "~^Z". All forwarded con- nections can be listed with "~#", and if the session blocks waiting for forwarded X11 or TCP/IP connections to terminate, it can be backgrounded with "~&" (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 "~?". A single tilde character can be sent as "~~" (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. 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 ``none'' will also make the session transparent even if a tty is used. 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 ssh. If the user is using X11 (the DISPLAY environment variable is set), the 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 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. 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. Ssh automatically maintains and checks a database containing RSA-based identifications for all hosts it has ever been used with. The database is stored in .ssh/known_hosts in the user's home directory. Additionally, the file /etc/ssh_known_hosts is automatically checked for known hosts. Any new hosts are automatically added to the user's file. If a host's identif- ication ever changes, ssh warns about this and disables password authenti- cation 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 StrictHostKey- Checking option (see below) can be used to prevent logins to machines whose host key is not known or has changed. OPTIONS -a Disables forwarding of the authentication agent connection. This may also be specified on a per-host basis in the configuration file. -c idea|des|3des|blowfish|arcfour|none Selects the cipher to use for encrypting the session. idea is used by default. It is believed to be secure. des is the data encryption standard, but is breakable by governments, large corporations, and major criminal organizations. 3des (triple-des) is encrypt-decrypt- encrypt triple with three different keys. It is presumably more secure than DES. It is used as default if both sites do not support IDEA. blowfish is an encryption algorithm invented by Bruce Schneier. It uses 128 bit keys. arcfour is an algorithm published in the Usenet News in 1995. This algorithm is believed to be equivalent with the RC4 cipher from RSA Data Security (RC4 is a trademark of RSA Data Security). This is the fastest algorithm currently supported. none disables encryption entirely; it is only intended for debugging, and it renders the connection insecure. -e ch|^ch|none Sets the escape character for sessions with a pty (default: ~). The escape character is only recognized at the beginning of a line. The escape character followed by a dot (.) closes the connection, followed tory. 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). -k Disables forwarding of the kerberos tickets. This may also be speci- fied on a per-host basis in the configuration file. -l login_name Specifies the user to log in as on the remote machine. This may also be specified on a per-host basis in the configuration file. -n Redirects stdin from /dev/null (actually, prevents reading from stdin). This must be used when ssh is run in the background. A com- mon trick is to use this to run X11 programs in 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 for- warded 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 '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. -p port Port to connect to on the remote host. This can be specified on a per-host basis in the configuration file. -q Quiet mode. Causes all warning and diagnostic messages to be suppressed. Only fatal errors are displayed. -P Use non privileged port. With this you cannot use rhosts or rsarhosts authentications, but it can be used to bypass some firewalls that dont allow privileged source ports to pass. -t Force pseudo-tty allocation. This can be used to execute arbitary screen-based programs on a remote machine, which can be very useful e.g. when implementing menu services. -v Verbose mode. Causes ssh to print debugging messages about its pro- gress. This is helpful in debugging connection, authentication, and configuration problems. -V Print only version number and exit. -g Allows remote hosts to connect local port forwarding ports. The default is that only localhost may connect to locally binded ports. -x Disables X11 forwarding. This can also be specified on a per-host allocating a socket to listen to 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 host:hostport from the remote machine. Port forwardings can also be specified in the confi- guration file. Only root can forward privileged ports. -R 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 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 host:hostport from the local machine. Port forwardings can also be specified in the confi- guration file. Privileged ports can be forwarded only when logging in as root on the remote machine. CONFIGURATION FILES Ssh obtains configuration data from the following sources (in this order): command line options, user's configuration file ($HOME/.ssh/config), and system-wide configuration file (/etc/ssh_config). For each parameter, the first obtained value will be used. The configuration files contain sec- tions bracketed by "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. 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. The configuration file has the following format: Empty lines and lines starting with '#' are comments. Otherwise a line is of the format "keyword arguments" or "keyword = arguments". The possible keywords and their meanings are as follows (note that the configuration files are case-sensitive, but keywords are case-insensitive):
Restricts the following declarations (up to the next Host keyword) to be only for those hosts that match one of the patterns given after the keyword. '*' and '?' can be as wildcards in the patterns. A single '*' as a pattern can be used to provide global defaults for all hosts. The host is the hostname argument given on the command line (i.e., the name is not converted to a canonicalized host name before matching). BatchMode If set to "yes", passphrase/password querying will be disabled. This option is useful in scripts and other batch jobs where you have no mand line. This is usefull to disable forwardings in config file when you want to make second connection to host having forwardings in con- fig file. Scp sets this on by default so it will not fail even if you have some forwardings set in config file. Compression Specifies whether to use compression. The argument must be "yes" or "no". 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 GNU GZIP. 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. EscapeChar Sets the escape character (default: ~). The escape character can also be set on the command line. The argument should be a single charac- ter, '^' followed by a letter, or ``none'' to disable the escape char- acter entirely (making the connection transparent for binary data). FallBackToRsh Specifies that if connecting via ssh fails due to a connection refused error (there is no sshd listening on the remote host), rsh should automatically be used instead (after a suitable warning about the ses- sion being unencrypted). The argument must be "yes" or "no". ForwardAgent Specifies whether the connection to the authentication agent (if any) will be forwarded to the remote machine. The argument must be "yes" or "no". ForwardX11 Specifies whether X11 connections will be automatically redirected over the secure channel and DISPLAY set. The argument must be "yes" or "no". GatewayPorts Specifies that also remote hosts may connect to locally forwarded command line and in HostName specifications). IdentityFile Specifies the file from which the user's RSA authentication identity is read (default .ssh/identity in the user's home directory). Addi- tionally, 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. 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. The default is "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. To disable keepalives, the value should be set to "no" in both the server and the client configuration files. KerberosAuthentication Specifies whether Kerberos V5 authentication will be used. KerberosTgtPassing Specifies whether a Kerberos V5 TGT will be forwarded to the server. 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 for- wardings can be given on the command line. Only the root can forward privileged ports. NumberOfPasswordPrompts Specifies number of password prompts before giving up. The argument to must be integer. Note that server also limits number of attempts (currently 5), so setting this larger doesn't have any effect. Default value is one. Port Specifies the port number to connect on the remote host. Default is 22. 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 /bin/sh. In the command string, %h will be substituted by the host name to con- nect and %p by the port. The command can be basically anything, and should read from its stdin and write to its stdout. It should eventu- ally connect an sshd server running on some machine, or execute "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 ssh can also be configured to support the SOCKS system using the --with-socks4 or --with-socks5 compile-time configuration option. 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 for- wardings can be given on the command line. Only the root can forward privileged ports. 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 authentica- tion 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 "yes" or "no". 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 "yes" or "no". RSAAuthentication Specifies whether to try RSA authentication. The argument to this keyword must be "yes" or "no". RSA authentication will only be attempted if the identity file exists, or an authentication agent is running. StrictHostKeyChecking TISAuthentication Specifies whether to try TIS authentication. The argument to this keyword must be "yes" or "no". UsePrivilegedPort Specifies whether to use privileged port when connecting to other end. The default is yes if rhosts or rsarhosts authentications are enabled. User Specifies the user to log in as. This can be useful if you have a different user name in different machines. This saves the trouble of having to remember to give the user name on the command line. UserKnownHostsFile Specifies a file to use instead of $HOME/.ssh/known_hosts. UseRsh Specifies that rlogin/rsh should be used for this host. It is possi- ble that the host does not at all support the ssh protocol. This causes ssh to immediately exec rsh. All other options (except Host- Name) are ignored if this has been specified. The argument must be "yes" or "no". XAuthLocation Specifies the path to xauth program. ENVIRONMENT Ssh will normally set the following environment variables: DISPLAY The DISPLAY variable indicates the location of the X11 server. It is automatically set by ssh to point to a value of the form "hostname:n" where hostname indicates the host where the shell runs, and n is an integer >= 1. Ssh 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). HOME Set to the path of the user's home directory. LOGNAME Synonym for USER; set for compatibility with systems that use this variable. and server port number. SSH_ORIGINAL_COMMAND This will be the original command line of given by protocol if forced command is run. It can be used to fetch arguments etc from the other end. 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 The timezone variable is set to indicate the present timezone if it was set when the daemon was started (e.i., the daemon passes the value on to new connections). USER Set to the name of the user logging in. Additionally, ssh reads /etc/environment and $HOME/.ssh/environment, and adds lines of the format VARNAME=value to the environment. Some systems may have still additional mechanisms for setting up the environment, such as /etc/default/login on Solaris. FILES $HOME/.ssh/known_hosts Records host keys for all hosts the user has logged into (that are not in /etc/ssh_known_hosts). See sshd manual page. $HOME/.ssh/random_seed Used for seeding the random number generator. This file contains sen- sitive data and should read/write for the user and not accessible for others. This file is created the first time the program is run and updated automatically. The user should never need to read or modify this file. $HOME/.ssh/identity Contains the RSA authentication identity of the user. This file con- tains sensitive data and should be readable by the user but not acces- sible by others. It is possible to specify a passphrase when generat- ing the key; the passphrase will be used to encrypt the sensitive part of this file using IDEA. $HOME/.ssh/identity.pub Contains the public key for authentication (public part of the iden- tity file in human-readable form). The contents of this file should be added to $HOME/.ssh/authorized_keys on all machines where you wish to log in using RSA authentication. This file is not sensitive and can (but need not) be readable by anyone. This file is never used automatically and is not necessary; it is only provided for the con- 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. /etc/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 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 sshd manual page. The canonical system name (as returned by name servers) is used by sshd to verify the client host when logging in; other names are needed because ssh 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. /etc/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. $HOME/.rhosts This file is used in .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. This file must be owned by the user, and must not have write permis- sions for anyone else. The recommended permission is read/write for the user, and not accessible by others. Note that by default sshd will be installed so that it requires suc- cessful RSA host authentication before permitting .rhosts authentica- tion. If your server machine does not have the client's host key in /etc/ssh_known_hosts, you can store it in $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 in $HOME/.ssh/known_hosts. $HOME/.shosts This file is used exactly the same way as .rhosts. The purpose for having this file is to be able to use rhosts authentication with ssh without permitting login with rlogin or rsh. /etc/hosts.equiv This file is used during .rhosts authentication. It contains canoni- cal hosts names, one per line (the full format is described on the $HOME/.ssh/rc Commands in this file are executed by ssh when the user logs in just before the user's shell (or command) is started. See the sshd manual page for more information. INSTALLATION Ssh is normally installed as suid root. It needs root privileges only for rhosts authentication (rhosts authentication requires that the connection must come from a privileged port, and allocating such a port requires root privileges). It also needs to be able to read /etc/ssh_host_key to perform RSA host authentication. It is possible to use ssh without root privileges, but rhosts authentication will then be disabled. Ssh drops any extra privileges immediately after the connection to the remote host has been made. Considerable work has been put into making ssh secure. However, if you find a security problem, please report it immediately to <ssh- firstname.lastname@example.org>. AUTHOR Tatu Ylonen <email@example.com> Information about new releases, mailing lists, and other related issues can be found from the ssh WWW home page at http://www.cs.hut.fi/ssh. SEE ALSO sshd(8), ssh-keygen(1), ssh-agent(1), ssh-add(1), scp(1), make-ssh-known- hosts(1), rlogin(1), rsh(1), telnet(1)