Ubuntu Server Utilities

Linux DIG Command Examples for DNS Lookup

dig redhat.com - dns lookup

dig redhat.com  MX - mx records lookup

dig redhat.com NS

View ALL DNS Records Types Using dig -t ANY

dig -t ANY redhat.com

DNS Reverse Look-up Using dig -x

dig -x 209.132.183.81

Use a Specific DNS server Using dig @dnsserver

dig @ns1.redhat.com redhat.com

Extract Images from PDF Files With PDFimages

apt-get install poppler-utils

pdfimages --help for options

eg

pdfimages -j filename.pdf prefixforallfiles

if the image doesn't convert to jpg. then use the mogrify to convert them. mogrify is part of imagemagick

mogrify -format jpg *.pcm // this will convert all *.pcm files to jpg

Imagemagic

convert rose.jpg rose.png

convert rose.jpg -resize 64x64 thumb_rose.jpg

Only shrink larger images

convert rose.jpg -resize 64x64\> rose.jpg

Percentage Resize

convert rose.jpg -resize 50% rose.jpg

Rotate

convert rose.jpg -rotate 90 rose.jpg

Rotate and overite 

mogrify -rotate 90 img.jpg

Batch Convert from one format to another

mogrify -format jpg *.png 

this will convert all png files to jpg

Using Rsync

rsync options source destination

Rsync Local Dir to Amazon AWS servers
 rsync azvr --delete --progress -e "ssh -i /fordertopemfile/pemfile.pem" localfoldertosync ubuntu@ipaddress:/var/tmp/
Synchronize Two Directories in a Local Server: To sync two directories in a local computer, use the following rsync -zvr command.
$ rsync -azvr /var/opt/installation/inventory/ /root/temp
building file list ... done
sva.xml
svB.xml
.
sent 26385 bytes  received 1098 bytes  54966.00 bytes/sec
total size is 44867  speedup is 1.63
$
In the above rsync example: -a archive mode (which preserves timestamp) -z is to enable compression -v verbose -r indicates recursive
Synchronize Only One File: To copy only one file, specify the file name to rsync command, as shown below
$ rsync -v /var/lib/rpm/Pubkeys /root/temp/
Pubkeys

sent 42 bytes  received 12380 bytes  3549.14 bytes/sec
total size is 12288  speedup is 0.99 

Rsync Over SSH

With rsync, we can use SSH (Secure Shell) for data transfer, using SSH protocol while transferring our data you can be ensured that your data is being transferred in a secured connection with encryption so that nobody can read your data while it is being transferred over the wire on the internet. Also when we use rsync we need to provide the user/root password to accomplish that particular task, so using SSH option will send your logins in an encrypted manner so that your password will be safe.

=== Copy a File from a Remote Server to a Local Server with SSH ===
To specify a protocol with rsync you need to give “-e” option with protocol name you want to use. Here in this example, We will be using “ssh” with “-e” option and perform data transfer.
 rsync -avzhe ssh root@192.168.0.100:/root/install.log /tmp/

root@192.168.0.100's password:
receiving incremental file list
install.log
sent 30 bytes  received 8.12K bytes  1.48K bytes/sec
total size is 30.74K  speedup is 3.77>/dd>

Copy a File from a Local Server to a Remote Server with SSH

rsync -avzhe ssh backup.tar root@192.168.0.100:/backups/

root@192.168.0.100's password:
sending incremental file list
backup.tar
sent 14.71M bytes  received 31 bytes  1.28M bytes/sec
total size is 16.18M  speedup is 1.10 

Use of –include and –exclude Options

These two options allows us to include and exclude files by specifying parameters with these option helps us to specify those files or directories which you want to include in your sync and exclude files and folders with you don’t want to be transferred. Here in this example, rsync command will include those files and directory only which starts with ‘R’ and exclude all other files and directory.
 rsync -avze ssh --include 'R*' --exclude '*' root@192.168.0.101:/var/lib/rpm/ /root/rpm
root@192.168.0.101's password:
receiving incremental file list
created directory /root/rpm

Vi Text Editor

Main command mode commands

i puts you in insert mode where you can enter text.

ESC key takes you out of insert mode.

w -> go to the beginning of the next word
b -> go to the beginning of the previous word
e -> go to the end of the next word
n| -> go to the 'n' columns of the current row
$ -> go to the end of the current row
^ -> go to the first character of the current row
G -> go to the end of the file
gg -> go to the beginning of the file
Gn -> go to 'n' row of the file
i -> insert mode (before the cursor)
a -> insert mode (after the cursor)
o -> insert mode (under the current row)
x -> delete one character
nx -> delete 'n' characters
dd -> delete the whole row
ndd -> delete 'n' rows
yy -> copy the current row
p -> paste the copied row
Rmystring -> replace next characters with the string 'mystring'
/string -> find the next string 'string'
?string -> find the string 'string' backwards
n -> repeat the search again
u -> undo the last command

Main row editing mode commands

:w -> write the file
:w myfile -> write the file as 'myfile'
:q -> quit the file
:wq -> write and quit the file
:q! -> quit without saving the file
:help -> open the help file (:q to return editing the file)
:help topic -> open the help file showing the subject 'topic' (:q to return editing the file)
:rs/string1/string2/options -> replace string1 with string2 withing the 'r' range; options may be: g (replace all), c (ask before any replacement)
:set number -> set rows numbering


* to move down:press j
* to move up:press k
* to move to the left:press h
* to move to the right:press l
 

You will have to tap each key for the number of lines or characters you want the cursor to move. In this case, I want to move down seven lines and then to the right. So I would hit j seven times, and hold down the l key until I got to the word “friend.”

Not every file you’re going to work in will be so small; some will be a couple hundred lines long. If you look at the last line of our file, you’ll see that the editor tells you how many lines there are in the file. If you want to jump down, you can type :(line number), where the line number is the actual numeral. So if I wanted to jump down to line 16 (the line beginning with “q”), I’d type:

:16

hit Enter, and there I’d be.
 

Deleting Text

You can delete text one character at a time simply by pressing x. The character that gets deleted will be the one the cursor highlights.

If that seems too tedious, you can type dw, and delete the text a word at a time. Note that vi counts the spaces in between words as words too, so I’d have to type dw nine times to delete the line.

Or you can just wipe out the entire line of text. To do that, just type dd. Since this is the fastest way to do it, I’m going to type:

dd

and the line that my cursor sits in is gone.

Replacing text

type r (this tells the editor I want to replace the highlighted character). If I wanted to change the letter c to s, I’d type r, then s. If I wanted to change it to – well, you get the picture:Type r and then the replacing character.

Adding Text

So far, we’ve been working in edit mode. In this mode, we can move around the file with impunity, deleting or replacing existing text without worry. To add text, we have to switch to the insert mode.Fortunately, this isn’t hard:Just move the cursor to the spot in the document you want to edit, hit i, and begin typing.

The first thing you should know is that vi takes the insert command rather literally. Wherever your cursor is when you hit i will be the first point at which you can begin typing. So if you’re looking at a sentence like this:

w means to overwrite the last version

and the cursor is on the v in ” overwrite,” you’re going to start inserting text where the v used to be. So if you try to type the words “saved file” you’ll end up with a sentence that looks like this:

w means to osaved fileverwrite the last version

The easiest way around it is to position the cursor where you want it before you start typing. So, if I wanted to insert the phrase “saved file” after the word last, I would hit Escape to make sure I’m out of insert mode, move the cursor to the space between “last” and “version,” hit i for insert, and type in a space and then ” saved file.”

Note:You cannot move around using the h, j, k, and l keys, or edit anything, while you’re in insert mode! To snap out of insert mode and back into edit mode, hit the Escape key. Any time I’m in vi and forget which mode I’m in (it can happen), I hit Escape before I do anything else.

Undoing Mistakes

So let’s say you haven’t quite got the hang of inserting text and you’ve just typed something very wrong. Will you have to delete all the text and start over?

Nope – if you catch your errors quickly (like, right after you make them), you can always undo them. To undo any inserted text, hit the Escape key, then type u. It will undo the last action you did.

If you’re already in edit mode, just type u to undo your last action.