Answer:

Use the command `dig`, e.g.

dig +trace mit.edu

;; global options: +cmd
.			19927	IN	NS	d.root-servers.net.
.			19927	IN	NS	e.root-servers.net.
.			19927	IN	NS	m.root-servers.net.
.			19927	IN	NS	l.root-servers.net.
.			19927	IN	NS	a.root-servers.net.
.			19927	IN	NS	k.root-servers.net.
.			19927	IN	NS	f.root-servers.net.
.			19927	IN	NS	j.root-servers.net.
.			19927	IN	NS	b.root-servers.net.
.			19927	IN	NS	h.root-servers.net.
.			19927	IN	NS	g.root-servers.net.
.			19927	IN	NS	i.root-servers.net.
.			19927	IN	NS	c.root-servers.net.
;; Received 228 bytes from 8.8.8.8#53(8.8.8.8) in 12 ms

edu.			172800	IN	NS	a.edu-servers.net.
edu.			172800	IN	NS	c.edu-servers.net.
edu.			172800	IN	NS	d.edu-servers.net.
edu.			172800	IN	NS	f.edu-servers.net.
edu.			172800	IN	NS	g.edu-servers.net.
edu.			172800	IN	NS	l.edu-servers.net.
;; Received 260 bytes from 199.7.83.42#53(199.7.83.42) in 223 ms

mit.edu.		172800	IN	NS	usw2.akam.net.
mit.edu.		172800	IN	NS	asia1.akam.net.
mit.edu.		172800	IN	NS	asia2.akam.net.
mit.edu.		172800	IN	NS	use2.akam.net.
mit.edu.		172800	IN	NS	ns1-37.akam.net.
mit.edu.		172800	IN	NS	ns1-173.akam.net.
mit.edu.		172800	IN	NS	eur5.akam.net.
mit.edu.		172800	IN	NS	use5.akam.net.
;; Received 404 bytes from 192.31.80.30#53(192.31.80.30) in 548 ms

mit.edu.		20	IN	A	23.46.134.151
;; Received 41 bytes from 63.150.131.81#53(63.150.131.81) in 4 ms

Answer:

When you want to comment out multiple lines in a configuration file or a program script, it is easy with the help of vim.

Steps:

1. Change to command mode
2. Enable visual block editing by pressing Ctrl + V
3. Select the line(s)
4. Press "I", enter the character you needed, e.g. "#"
5. Press "Esc", then "Enter"

Answer:

When you in the command mode, you have two options to delete the word under the cursor

daw: Delete the word under the cursor    
caw: Delete the word under the cursor and change to insert mode

Answer:

A newer version of MySQL use upstart to autostart when system bootup, to disable it

# sudo mkdir /etc/init.disabled
# sudo mv /etc/init/mysql.conf /etc/init.disabled/

Answer:

You can use the following method to generate random string into a collection in MongoDB:

function randomString() { 
        var chars = 
"0123456789ABCDEFGHIJKLMNOPQRSTUVWXTZabcdefghiklmnopqrstuvwxyz"; 
        var randomstring = ''; 
        var string_length = 100;
        for (var i=0; i<string_length; i++) { 
                var rnum = Math.floor(Math.random() * chars.length); 
                randomstring += chars.substring(rnum,rnum+1); 
        } 
        return randomstring; 
} 

for(var i=0; i<2000000; i++){db.test.save({x:i, data:randomString()});} 

Answer:

In you mongo shell, execute the following command:

var sum = 0; db.getMongo().getDBs()["databases"].forEach(function(x) { sum += db.getMongo().getDB(x.name).stats().indexSize }); print(sum)

Answer:

Edit the file "/etc/default/locale" to the locale you want.

Answer:

Use the -L or --copy-links option, e.g.

rsync -avuz --copy-links -e ssh /home/john 192.168.1.5:/data/backup/

Answer:

To move more efficiently in bash shell, you can use the following short cuts

Meta + f (move forward by a word)
Meta + b (move backward by a word)

The Meta key is the Alt key under most systems, on Mac, you would need to enable "use option as meta key" in the Terminal's Preference.

Answer:

The answer is no, you can't.

You need to use other alternative like rsync.

Reference: https://bugzilla.mindrot.org/show_bug.cgi?id=485