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Drop or block attackers IP with null routes
Someone might attack on your system. You can drop attacker IP using IPtables. However, you can use route command to null route unwanted traffic. A null route (also called as blackhole route) is a network route or kernel routing table entry that goes nowhere. Matching packets are dropped (ignored) rather than forwarded, acting as a kind of very limited firewall. The act of using null routes is often called blackhole filtering.

Show me just the ip address
Sometimes it's useful to output just the ip address. Or some other information, changing the "ipv4.addresses" in command. The power of awk! Show all possible "greps" with $ nmcli connection show [yourInterfaceNameHere]

Quick calculator at the terminal
Useful for quick calculations at the command line. $math_expr is any arithmetic expression (see sample output): 4.5*16+3^2 s(3.1415926/2) More options in the bc man page.

diff files while disregarding indentation and trailing white space

GREP a PDF file.
This is a good alternative to pdf2text for Ubuntu. To install it: sudo apt-get install python-pdfminer

simple du command to give size of next level of subfolder in MB
If you're only using -m or -k, you will need to remember they are either in Megabyte or kilobyte forms. So by using -B, it gives you the unit of the size measurement, which helps you from reading the result faster. You can try with -B K as well.

Start a command on only one CPU core
This is useful if you have a program which doesn't work well with multicore CPUs. With taskset you can set its CPU affinity to run on only one core.

Get all possible problems from any log files
Using the grep command, retrieve all lines from any log files in /var/log/ that have one of the problem states

Convert seconds to [DD:][HH:]MM:SS
Converts any number of seconds into days, hours, minutes and seconds. sec2dhms() { declare -i SS="$1" D=$(( SS / 86400 )) H=$(( SS % 86400 / 3600 )) M=$(( SS % 3600 / 60 )) S=$(( SS % 60 )) [ "$D" -gt 0 ] && echo -n "${D}:" [ "$H" -gt 0 ] && printf "%02g:" "$H" printf "%02g:%02g\n" "$M" "$S" }

Send a local file via email
Another way of sending an attachment. -s : subject file : file to be sent


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