Useful Unix OS Commands

I have listed some useful unix operating system level commands, if you are new and looking for the tutorials and stuff hope these commands will help in performing difference operations. Cheers and Good Luck!

grep
----
used to find a specific word

head
----
this command is used to read starting lines of a file

tail
----
this command is used to read the last lines of a file

nohup
-----
Command is used to run processes in background

gzip
----
this command zip files in unix

gzcat
-----
this command is used to view the zipped file

for
---
we use loops in a console or shell sctipts to execute any command more than once

cp
--
copy command

mv
--
move command

rm
--
it deletes file

rmdir
-----
remove directory

mkdir
------
creates directory

awk
-----
this command is string manupulation, and is major use is to print columns from a file and other sources

sed
----
stread line editor is also a string manupulation command used for manupulation data as per requirement

>
---
this is very important symbol which redirects an output to a file rather than displaying on consoele

>>
---
this redirection sign append data content in a file that alresdy contain data

find
-----
to locate or find a command from various directories or same directory we use this command

cat
----
to read only a file we use this command

ps -ef
-------
this command is used to find the running processes on the server

bash
-----
shell mostly used for shell scripting and on console as well

chmod
--------
to change the permisions

crontab
--------
this is a scheduler in unix where we schedule our jobs for execution on specified time, read it from internet also

Crontab syntax :
A crontab file has five fields for specifying day , date and time followed by the command to be run at that interval.

*     *     *   *    *        command to be executed
-     -     -   -    -
|     |     |   |    |
|     |     |   |    +----- day of week (0 - 6) (Sunday=0)
|     |          |   |
|     |     |   +------- month (1 - 12)
|     |          |
|     |     +--------- day of month (1 - 31)
|     |     
|     +----------- hour (0 - 23)
|
+------------- min (0 - 59)

df
---
shows free disk space

du
---
shows disk usage

prstat -a
----------
shows systems current status

vi
---
editor used in unix to create/update files

--
Author:
Waqas Rafi

Generate Keys for copying files in Unix/Linux

In order to copy files to a remote machine without being asked for a password we can perform this task to complete this process.

Generate keys on a source system at (/home/user/.ssh/) and place its public key on the destination system on (home/user/.ssh/) with a file named authorized_keys that will be used while file transfer without asking for a password.

Commands

1. Go to Source Machine /home/user/.ssh/
2. Give command
>ssh-keygen -t rsa

i-  it will ask u for a file name,
ii- it will ask for a paraphrase
iii- it will ask for a paraphrase again 

or just enter thrice to create public and private keys.

3. Now copy the content of public key with extension .pub into the destination machine by creating a file name authorized_keys in directory /home/user/.ssh/

4. Now secure copy a file to the remote machine by using scp command and u will not prompt with password any more.

scp file_to_be_copied.txt user@ip-address:/destination_path_on_remote machine

Good Luck!

Author:
Waqas Rafi

Steve Jobs Died 'Peacefully,' Family Says

 The family of former Apple chief executive Steve Jobs said that he died "peacefully" on Wednesday, surrounded by his family. A memorial Web site will be posted.

Jobs passed away at the age of 56. Jobs is survived by his wife Laurene and two children, as well as a daughter from a previous relationship.

On August 24, Jobs stepped down, stating that he could no longer meet his duties and expectations as Apple's chief executive. Jobs was diagnosed with and treated for a rare type of pancreatic cancer in 2004, but he said the 2009 absence was not a resurgence of that cancer. He took a medical leave of absence in January.

In a statement, Jobs' family said he died peacefully.

"Steve died peacefully today surrounded by his family.

"In his public life, Steve was known as a visionary; in his private life, he cherished his family. We are thankful to the many people who have shared their wishes and prayers during the last year of Steve's illness; a website will be provided for those who wish to offer tributes and memories. 

"We are grateful for the support and kindness of those who share our feelings for Steve. We know many of you will mourn with us, and we ask that you respect our privacy during our time of grief."

Numerous members of the tech world chimed in with their own tributes, and Twitter was filled with condolences attached to the #RIPSteveJobs hashtag. Online, mourners began leaving notes on Facebook tribute pages as well as the Steve Jobs Day Facebook page.

Apple's board also released its own statement. 

"We are deeply saddened to announce that Steve Jobs passed away today," the board said.
"Steve's brilliance, passion and energy were the source of countless innovations that enrich and improve all of our lives. The world is immeasurably better because of Steve.
"His greatest love was for his wife, Laurene, and his family. Our hearts go out to them and to all who were touched by his extraordinary gifts.
John Lasseter, chief creative officer and Ed Catmull, president of Walt Disney and Pixar Animation Studios, released their own joint statement. Jobs was chief executive at Pixar, the digital anaimation house that gave the world Cars, The Incredibles and Toy Story, before it was acquired by Disney in 2006.
"Steve Jobs was an extraordinary visionary, our very dear friend and the guiding light of the Pixar family," Lasseter and Catmull said. "He saw the potential of what Pixar could be before the rest of us, and beyond what anyone ever imagined. Steve took a chance on us and believed in our crazy dream of making computer animated films; the one thing he always said was to simply 'make it great.' He is why Pixar turned out the way we did and his strength, integrity and love of life has made us all better people. He will forever be a part of Pixar's DNA. Our hearts go out to his wife Laurene and their children during this incredibly difficult time." 

Source: http://www.pcmag.com/article2/0,2817,2394212,00.asp#fbid=NwMGyfuEQvV

Kill multiple processes using awk command

If you wish to kill multiple instances manually executed in background or the running processes of crontab then you can kill them all without taking the headache of selecting process id of each process and giving command "kill -9 process id", so this command can do magic for you

ps -ef | grep "username or process name" | grep -v grep | awk '{ print $2 }' | xargs kill -9

This command will first check running process with specific username or process name than "grep -v grep" will exclude the row which contain the word grep in it after that awk command prints the second column of process id's and "xargs kill -9" will kill all the returned process id's associated with it.

Author:
Waqas Rafi

Unix Command Symbols

> Sign
The symbol > is used to redirect the output of a command.
#cat >list1
cat command read standard input(keyboard) and > redirect the output, which normally goes to screen but in this case is moved into a file called list1

>> Sign

#cat >>list1
>> (symbol) will add more items to the existing file list1

Merging two files
If we have two files list1 and list2 and merging these files in one file.
#cat list1 list2 > biglist
#cat biglist (to read contents of file and verify changes)

(pipe sign)
We use sign to concatenate more than than one commands together.

#crontab -l grep hello.sh

Waqas Rafi

Sed Command VS Head Tail

Well for past few months i was using the head and tail command to look into desired line inside a file... which works like this

If i want to see line number 45 from filename.txt than,

$head -45 filename.txt | tail -1

which is bit complex, but we can also use sed command(stream editor) for it, which goes like this,

$sed -45 filename.txt

Author
Waqas Rafi