方法一：

<?php
if ( !function_exists( 'sys_uptime' ) ) {
    function sys_uptime() {
        $output='';
        if (false === ($str = @file("/proc/uptime"))) return false;
        $str = explode(" ", implode("", $str));
        $str = trim($str[0]);
        $min = $str / 60;
        $hours = $min / 60;
        $days = floor($hours / 24);
        $hours = floor($hours - ($days * 24));
        $min = floor($min - ($days * 60 * 24) - ($hours * 60));
        if ($days !== 0) $output .= $days."天";
        if ($hours !== 0) $output .= $hours."小时";
        if ($min !== 0) $output .= $min."分钟";
        return $output;
    }
}
$starttime = sys_uptime();
echo $starttime;
?>

或者

<?php
function sys_linux()
{
if (false === ($str = @file("/proc/uptime"))) return false;
$str = explode(" ", implode("", $str));
$str = trim($str[0]);
$min = $str / 60;
$hours = $min / 60;
$days = floor($hours / 24);
$hours = floor($hours - ($days * 24));
$min = floor($min - ($days * 60 * 24) - ($hours * 60));
if ($days !== 0) $res['uptime'] = $days."天";
if ($hours !== 0) $res['uptime'] .= $hours."小时";
$res['uptime'] .= $min."分钟";
return $res;
}
$sysInfo = sys_linux();
$uptime = $sysInfo['uptime'];
echo $uptime;
?>

方法二：

<?php
function Uptime() {

    $uptime = @file_get_contents( "/proc/uptime");
    $uptime = explode(" ",$uptime);
    $uptime = $uptime[0];
    $days = explode(".",(($uptime % 31556926) / 86400));
    $hours = explode(".",((($uptime % 31556926) % 86400) / 3600));
    $minutes = explode(".",(((($uptime % 31556926) % 86400) % 3600) / 60));
    $seconds = explode(".",((((($uptime % 31556926) % 86400) % 3600) / 60) / 60));
    $time = $days[0].":".$hours[0].":".$minutes[0].":".$seconds[0];
    return $time;

}
?>

方法三：

<?php
function Uptime() {
        $str   = @file_get_contents('/proc/uptime');
        $num   = floatval($str);
        $secs  = $num % 60;
        $num   = (int)($num / 60);
        $mins  = $num % 60;
        $num   = (int)($num / 60);
        $hours = $num % 24;
        $num   = (int)($num / 24);
        $days  = $num;
        return array(
            "days"  => $days,
            "hours" => $hours,
            "mins"  => $mins,
            "secs"  => $secs
        );
    }
?>