we are trying to set up cron for magento site running in ubuntu server

we are trying following command :

*/5 * * * * php -f /var/www/html/sitename/cron.php

but we are getting error as below :

-bash: */5: No such file or directory

Update 1

Update 2 - Error

PHP Warning:  require(app/bootstrap.php): failed to open stream: No such file or directory in /var/www/html/sitename/cron.php on line 30



PHP Fatal error:  require(): Failed opening required 'app/bootstrap.php' (include_path='.:/usr/share/php:/usr/share/pear') in /var/www/html/sitename/cron.php on line 30

cron.php

<?php





// Change current directory to the directory of current script

chdir(dirname(__FILE__));



require 'app/bootstrap.php';

require 'app/Mage.php';



if (!Mage::isInstalled()) {

    echo "Application is not installed yet, please complete install wizard first.";

    exit;

}



// Only for urls

// Don't remove this

$_SERVER['SCRIPT_NAME'] = str_replace(basename(__FILE__), 'index.php', $_SERVER['SCRIPT_NAME']);

$_SERVER['SCRIPT_FILENAME'] = str_replace(basename(__FILE__), 'index.php', $_SERVER['SCRIPT_FILENAME']);



Mage::app('admin')->setUseSessionInUrl(false);



umask(0);



$disabledFuncs = explode(',', ini_get('disable_functions'));

$isShellDisabled = is_array($disabledFuncs) ? in_array('shell_exec', $disabledFuncs) : true;

$isShellDisabled = (stripos(PHP_OS, 'win') === false) ? $isShellDisabled : true;

$isShellDisabled = true;



try {

    if (stripos(PHP_OS, 'win') === false) {

        $options = getopt('m::');

        if (isset($options['m'])) {

            if ($options['m'] == 'always') {

                $cronMode = 'always';

            } elseif ($options['m'] == 'default') {

                $cronMode = 'default';

            } else {

                Mage::throwException('Unrecognized cron mode was defined');

            }

        } else if (!$isShellDisabled) {

            $fileName = basename(__FILE__);

            $baseDir = dirname(__FILE__);

            shell_exec("/bin/sh $baseDir/cron.sh $fileName -mdefault 1 > /dev/null 2>&1 &");

            shell_exec("/bin/sh $baseDir/cron.sh $fileName -malways 1 > /dev/null 2>&1 &");

            exit;

        }

    }



    Mage::getConfig()->init()->loadEventObservers('crontab');

    Mage::app()->addEventArea('crontab');

    if ($isShellDisabled) {

        Mage::dispatchEvent('always');

        Mage::dispatchEvent('default');

    } else {

        Mage::dispatchEvent($cronMode);

    }

} catch (Exception $e) {

    Mage::printException($e);

    exit(1);

}