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Verify if user account exists in Linux / Unix

Sysadmin day date of any given year
Calculate the date of Sysadmin day (last Friday of July) of any given year

An alias to re-run last command with sudo. Similar to "sudo !!"
I didn't come up with this myself, but I always add this to my .bash_aliases file. It's essentially the same idea as running "sudo !!" except it's much easier to type. (You can't just alias "sudo !!", it doesn't really work for reasons I don't understand.) "fc" is a shell built-in for editing and re-running previous commands. The -l flag tells it to display the line rather than edit it, and the -n command tells it to omit the line number. -1 tells it to print the previous line. For more detail: $help fc

Convert seconds into minutes and seconds
This is a very simple way to input a large number of seconds and get a more useful value in minutes and seconds. Avoids useless use of echo.

Watch RX/TX rate of an interface in kb/s
Just a simple way without the need of additional tools. Of course, replace eth0 with your IF.

Edit all files found having a specific string found by grep
The grep switches eliminate the need for awk and sed. Modifying vim with -p will show all files in separate tabs, -o in separate vim windows. Just wish it didn't hose my terminal once I exit vim!!

Get AWS temporary credentials ready to export based on a MFA virtual appliance
You might want to secure your AWS operations requiring to use a MFA token. But then to use API or tools, you need to pass credentials generated with a MFA token. This commands asks you for the MFA code and retrieves these credentials using AWS Cli. To print the exports, you can use: `awk '{ print "export AWS_ACCESS_KEY_ID=\"" $1 "\"\n" "export AWS_SECRET_ACCESS_KEY=\"" $2 "\"\n" "export AWS_SESSION_TOKEN=\"" $3 "\"" }'` You must adapt the command line to include: * $MFA_IDis ARN of the virtual MFA or serial number of the physical one * TTL for the credentials

Look for English words in /dev/urandom
* to get the English dictionary: wget http://www.mavi1.org/web_security/wordlists/webster-dictionary.txt

Find usb device in realtime
Using this command you can track a moment when usb device was attached.

small CPU benchmark with PI, bc and time.
$ # 4 cores with 2500 pi digits $ CPUBENCH 4 2500 $. $ every core will use 100% cpu and you can see how fast they calculate it. $ if you do 50000 digitits and more it can take hours or days


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