4 replies
by cpfeiffe
Unix Shutdown and Reboot
It is critical for system administrators to have a firm understanding of how the machine is being used and actively involve the users in scheduling downtime. For example, on most systems (except Cray to my knowledge), a shutdown will cause all user processes to be killed. If users on a system are running jobs that take days or weeks to complete then shutting the system down and cause all processes to be killed could severly impact the productivity of users. Whenever possible, users should be given as much lead time as possible when scheduling a shutdown. Once brought up to multi-user mode it is not uncommon for the system to run for many days, possibly even months, without being shutdown or rebooted. There are valid reasons for shutting down the system, these include:
Many systems now have a graphics dispaly and use an assortment of X11 based applications. Also, it is not uncommon for a server machine to support remote X11 applications. Under many vendors version of X11 there are known memory leaks. These memory leaks result in the X11 server or application allocating memory and never releasing it. Over time you may find that free memory becomes tight. Rebooting will elliminate that.
Installation of system software or changes in hardware often require a system reboot to take affect.
Devices can get in a state where they don't function properly. The only fix is to shutdown the system and power off the component. Likewise, system software may get in a confused state and require a reboot to be corrected.
Often, system administrators bring the system down to single-user mode to perform full backups of file systems. Performing a full backup on a quiescent is one way of gaurenteeing a complete backup.
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