How to use shutdown command under Ubuntu Linux

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Q. I’ve just installed Ubuntu Linux on my computer. I’d like to know – how to shutdown Ubuntu box over ssh session?

A. If you are not using GUI, you can run halt or shutdown command to powerdown box.

shutdown command

shutdown arranges for the system to be brought down in a safe way. All logged-in users are notified that the system is going down and, within the last five minutes of TIME, new logins are prevented. The shutdown utility provides an automated shutdown procedure for supersers to nicely notify users when the system is shutting down, saving them from system administrators, hackers, and gurus, who would otherwise not bother with such niceties.

How do I use shutdown command?

The shutdown command can be used to turn off or reboot a computer. Type the command as follows to shutdown server / computer immediately:
$ sudo shutdown -h now
$ sudo shutdown -h 0

How do I shutdown compute at specific time?

To shutdown computer at 6:45pm, enter:
$ sudo shutdown -h 18:45 "Server is going down for maintenance"
At 6:30pm message will go out to all user and 6:45 system will shutdown.

Please note that you can also use halt or poweroff or reboot command for stopping and restarting the system:
$ sudo halt
$ sudo poweroff

How do I reboot computer?

Simply use reboot command:
$ sudo reboot
$ sudo shutdown -r 0

Howto rebuilding a RAID array after a disk fails

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Q. I have two disk-mirrored array, suppose if one of my disk in mirrored RAID array fails, then I will replace that disk with new one (I have hot swapping SCSI drives). Now question is how I rebuild a RAID array after a disk fails.

A. A redundant array of inexpensive disks, (redundant array of independent disks) is a system, which uses multiple hard drives to share or replicate data among the drives. You can use both IDE and SCSI disk for mirroring.

If you are not using hot swapping drives then you need to shutdown server. Once hard disk has been replaced to system, you need to use used raidhotadd to add disks from RAID-1, -4 and -5 arrays, while they are active.

Assuming that new SCSI disk is /dev/sdb, type the following command:# raidhotadd /dev/mdX /dev/sdbReplace /dev/mdX with actual raid device name (e.g. /dev/md0). While array is under construction, you can see progress and other information by typing following command:# cat /proc/mdstat

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