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-Qdt Lists dependencies/packages which are no longer required by any packages
-q Output only package name (not the version number)
-R Remove package(s)
Rest is self-explanatory.
I just started out with Arch - so if there is any better/standard method to achieve the same - please suggest.
This, like the other commands listed here, displays installed arch packages. Unlike the other ones this also displays the short description so you can see what that package does without having to go to google. It also shows the largest packages on top. You can optionally pipe this through head to display an arbitrary number of the largest packages installed (e.g. ... | head -30 # for the largest 30 packages installed)
The lastb command presents you with the history of failed login attempts (stored in /var/log/btmp). The reference file is read/write by root only by default. This can be quite an exhaustive list with lots of bots hammering away at your machine. Sometimes it is more important to see the scale of things, or in this case the volume of failed logins tied to each source IP.
The awk statement determines if the 3rd element is an IP address, and if so increments the running count of failed login attempts associated with it. When done it prints the IP and count.
The sort statement sorts numerically (-n) by column 3 (-k 3), so you can see the most aggressive sources of login attempts. Note that the ':' character is the 2nd column, and that the -n and -k can be combined to -nk.
Please be aware that the btmp file will contain every instance of a failed login unless explicitly rolled over. It should be safe to delete/archive this file after you've processed it.
M is size in megabytes, man expac to see other sizes
%m is install size
%k is download size
An alternative to: python -m SimpleHTTPServer for Arch Linux
This one-liner will output installed packages sorted by size in Kilobytes.