如何解决vSphere4上RHEL5 Starting udev时间过长问题

    今天发现vSphere4上linux服务器重启至Starting udev后不再继续，网上查找相关资料后有以下几种方法解决此问题：

一、修改"/etc/udev/rules.d/99-vmware-scsi-udev.rules" 文件，优化系统启动设备搜寻和生成虚拟设备时间。

二、但上一种方法并不是问题本质，真正的原因是：

       Clocksource is the name of the new timekeeping subsystem introduced in the Linux 2.6.18 kernel. In this subsystem there are several clocksources that can be used to read the time. One of them is the tsc clocksource which uses the Time Stamp Counter that is present on each processor and can be used to track how much time has elapsed. The TSCs on the different processors are not necessarily perfectly in sync with each other, so time can appear to go backward if the TSC is read on one processor and then another processor. Early versions of the tsc clocksource did not handle this case, which can lead to the guest operating system not responding. Due to the different timing behavior of running in a virtual machine, this can be observed more frequently in a virtual machine.

经验证确实如此：如果是单个vCPU,则Starting udev很快就能过去。

具体解决方法：

1、把虚拟机的电源关闭

2、然后编辑配置,改为1个vCPU 

3、启动系统

4、编辑/etc/grub.conf，在kernel一行最后加上clocksource=acpi_pm

5、重启虚拟机

此方法为vmware官方说明：