Modify system time and CMOS time in Centos

1. Set the system time

 
 

  
  
Date-s // set the current time. Only the root permission can be set. Others can only be viewed.
  
  
Date-s 20080523 // set to 20080523, so that the specific time is set to null 00:00:00
  
  
Date-s 01:01:01 // set the specific time and do not change the date
  
  
Date-s "01:01:01" // you can set all the time
  
  
Date-s "01:01:01 20080523" // you can set all the time
  
  
Date-s "01:01:01" // you can set all the time
  
  
Date-s "20080523 01:01:01" // you can set all the time
 
 

2. View hardware time

   
   

    
    
# hwclock 
   
   

Set hardware time

   
   

    
    
# Hwclock -- set -- date = "07/07/06" (month/day/year hour: minute: second)
   
   

3. When the hardware time and system time are synced and restarted, the hardware time reads the system time for synchronization. However, when the system time is not restarted, you need to use the hwclock command for synchronization. Hardware clock and system clock synchronization:

    
    

     
     
# Hwclock -- hctosys (hc indicates the hardware time, sys indicates the system time)
    
    

System clock and hardware clock synchronization: (synchronize the system time to the hardware clock)

    
    

     
     
# hwclock –-systohc 
    
    

4. If you do not have the command to use ntpdate to synchronize time, install the following package:

     
     

      
      
rpm -ivh ntp-4.2.2p1-9.el5.centos.2.1.i386.rpm 
     
     

National Time Service Center address: 210.72.145.44 use ntpdate 210.72.145.44 to synchronize time. After the synchronization is complete, clock-w writes to CMOS. If iptables is used as the firewall, add the following statement to update

     
     

      
      
iptables -A INPUT -p tcp --sport 123 -s 210.72.145.44 -j ACCEPT 
      
      
iptables -A OUTPUT -p tcp --dport 123 -d 210.72.145.44 -j ACCEPT 
      
      

      
      
iptables -A OUTPUT -p udp --dport 123 -d 210.72.145.44 -j ACCEPT 
      
      
iptables -A INPUT -p udp --sport 123 -s 210.72.145.44 -j ACCEPT 
     
     

5. Run the following script by running the script on crontab at the scheduled synchronization time. The synchronization time is 30 23 ** 5/root/ntpdate. sh at every week.

      
      

       
       
#!/bin/bash 
       
       


       
       
export PATH=/usr/kerberos/sbin:/usr/kerberos/bin:/usr/local/java/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/usr/loc 
       
       
al/mysql5/bin:/root/bin 
       
       

       
       
LOG="/tmp/ntpdate.log"
       
       
for((i=0; i<5; i++)) 
       
       
do
       
       
 ntpdate 210.72.145.44 &>/dev/null 
       
       
if [ $? == 0 ];then 
       
       
 clock -w 
       
       
echo"$(date +%Y-%m-%d_%T) ==>update time successful!" >>$LOG
       
       
echo"" >>$LOG
       
       
exit 0 
       
       
else
       
       
echo"$(date +%Y-%m-%d_%T) ==>update time occur error!" >>$LOG
       
       
echo"" >>$LOG
       
       
 fi 
       
       
done