A Few Power Supply Wattage Calculators

When building your computer from components, these can help you size the power supply for the machine. This is especially useful if you want to build a solar powered computer.

Backups: Sorting Through a Restore

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Linux Backups

When you need to be rough with your data–change a bunch of files at once…and you might not do it right the first time. Or you need to recover something that grew a few bad sectors and you only have a bits of your file left. Do you have to restore ALL your work? How do you see where the changes are?

Let’s step thru a partial restore using tar and diff. For example, say I have a code directory that I’ve damaged with a regular expression. My work is in /home/work, my backups are in /home/backups.

I “untar” the backup in a temporary directory next to the work directory like so:

$ cd /home/
$ mkdir restore
$ cd restore
$ tar xzf /home/backup/monday.tgz
$ cd /home

With the two directory trees next to each other, finding the differences is easy. The -r switch for diff tell us to search an entire directory tree, and the -q switch tells diff to display a brief description of just file names. (Diff will work on binary files, so this command will also work on graphics and audio files, just don’t forget the -q).

$ diff -qr /home/work /home/restore
Files /home/work/lib/BugCatcherHelper.java and /home/restore/lib/BugCatcherHelper.java differ
Files /home/work/lib/BugCatcher.java and /home/restore/lib/BugCatcher.java differ

This example is obviously contrived, and often what source control should be used for, but not everyone uses source control.