( . 1 ) Sync (Function Description: The data from the synchronous memory to the hard disk)
( 2 ) HALT (Function Description: shut down the system, it is equivalent to the shutdown -h now and the poweroff )
( . 3 ) reboot (Function Description: is restarted, equivalent to the shutdown -R & lt now )
( 4 ) the shutdown [ options ] time
Table 1-4
| Options |
Features |
| -h |
-h = halt shutdown |
| -r |
-r = reboot reboot |
Table 1-5
| parameter |
Features |
| now |
Immediately shut down |
| time |
How long to wait after shutdown (time unit is minutes ). |
Linux systems in order to improve the efficiency of disk read and write, the disk has taken " pre-read write-behind " operation.
When a user saves a file, Linux kernel does not necessarily immediately save the data written to the physical disk, but the data stored in the buffer, such as when the buffer is full and then written to disk in this way can greatly improve disk writing efficiency data.
However, it also brings security risks, if the data is not written to disk, power failure or other serious system problems, it will cause data loss. Use sync instruction buffer data can be immediately written to disk.
Case practical operation
( 1 ) the sync data from the memory to the hard disk
[root @ hadoop100 Desktop ] #sync
( 2 ) Restart
[root @ hadoop100 Desktop ] # reboot
( 3 ) Off
[root @ hadoop100 Desktop ] #halt
( 4 ) in a computer . 1 minute off, and will appear on the user's current login screen
[root@hadoop100桌面]#shutdown -h 1 ‘This server will shutdown after 1 mins’
( 5 ) immediately off (equivalent to HALT )
[root @ hadoop100 Desktop ] # shutdown -h now
( 6 ) immediately restart the system (equivalent to reboot )
[root@hadoop100桌面]# shutdown -r now
Retrieve root password
See root password cracking [1.0 version ] .pdf file
Not when you enter a password, pay attention