Commands by donjuanica (2)

What's this? is the place to record those command-line gems that you return to again and again. That way others can gain from your CLI wisdom and you from theirs too. All commands can be commented on, discussed and voted up or down.

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Display IP : Count of failed login attempts
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.

beep when a server goes offline
pings a server once per second, and beeps when the server is unreachable. Basically the opposite of: $ ping -a which would beep when a server IS reachable. You could also substitute beep with any command, which makes this a powerful alternative to ping -a: $ while true; do [ "$(ping -c1W1w1 2>/dev/null | awk '/received/ {print $4}')" = 1 ] && date || echo 'server is down!'; sleep 1; done which would output the date and time every sec until the ping failed, in which case it would echo. Notes: Requires beep package. May need to run as root (beep uses the system speaker) Tested on Ubuntu which doesn't have beep out of the box... $ sudo apt-get install beep

Print all /etc/passwd lines with duplicated uid
Prints all the lines in /etc/passwd belonging to users with a duplicated uid. It also adds the hostname to the beginning of the line. It's been tested in AIX, Solaris and Linux.

Stop Flash from tracking everything you do.
Brute force way to block all LSO cookies on a Linux system with the non-free Flash browser plugin. Works just fine for my needs. Enjoy.

Rename files in batch

Convert CSV to JSON
Replace 'csv_file.csv' with your filename.

display a smiling smiley if the command succeeded and a sad smiley if the command failed
you could save the code between if and fi to a shell script named with the first argument as and then do a to see if the command succeeded. a bit needless but who cares ;)

create an emergency swapfile when the existing swap space is getting tight
Create a temporary file that acts as swap space. In this example it's a 1GB file at the root of the file system. This additional capacity is added to the existing swap space.

Unlock more space form your hard drive
This command changes the reserved space for privileged process on '/dev/sda' to 1 per cent.

Calculate the distance between two geographic coordinates points (latitude longitude)
The Haversine formula determines the great-circle distance between two points on a sphere given their longitudes and latitudes.

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