Most server systems, regardless of what OS they are running,
are connected to a UPS to ensure uptime in the event of power fluctuations,
brief power outages, brown-outs, etc. Using a UPS is a great way to ensure data
safety by preventing the machine from turning off immediately if the power goes
out. However, in an extended power outage—when the downtime exceeds the
capacity of the UPS battery—unless you have a system in place to monitor the
status of the UPS, all that is being done is delaying the amount of time it
takes for the system to halt.

A tool such as apcupsd,
can be used to monitor the status of the UPS and trigger a shutdown event prior
to the battery being drained. This allows the system to shut down clean in the
event of an extended power loss.

Most Linux distributions come with apcupsd and if not, building it from source is as trivial as
building most other software from source. Keep in mind that apcupsd only works with APC-brand UPS
devices—both serial- and USB-based. To determine if the system recognizes your
USB-based UPS, you can check the USB device table by executing:

# cat /proc/bus/usb/devices

By examining this list, you should see the APC USB listed when
it is connected. You will also need to modify the configuration file, /etc/apcupsd/apcupsd.conf in most cases,
and tell it the type of UPS you have with the UPSNAME, UPSCABLE, and UPSTYPE
directives. The configuration file is well commented and you can define how
much battery power must remain before initiating the shutdown, etc. A number of
scripts are included in the /etc/apcupsd/
directory that control various aspects of what apcupsd does when it detects power loss, power return, etc.

Having a UPS is a good idea no matter what type of system you
are running, but setting up the UPS for automated shutdowns will go a long way
in preventing data loss or corruption due to unexpected power loss.

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