Redhat releases their flagship distro for every 3 years and patches for every 6 months. Here is a quick release dates of all the Versions of RHEL taken from Wikipedia.org

• Red Hat Enterprise Linux 2.1 AS (Pensacola), 2002-03-26
  • Update 1, 2003-02-14 (Release Notes)
  • Update 2, 2003-05-02 (Release Notes)
  • Update 3, 2003-12-19 (Release Notes)
  • Update 4, 2004-04-30 (Release Notes)
  • Update 5, 2004-08-18 (Release Notes)
  • Update 6, 2004-12-13 (Release Notes)
  • Update 7, 2005-04-28 (Release Notes, redhat-release-as-2.1AS-121.src.rpm)
• Red Hat Enterprise Linux 2.1 ES (Panama), May 2003

• Red Hat Enterprise Linux 3 (Taroon), 2003-10-22. Uses Linux 2.4.21 (Release notes also for updates)
  • Update 1, 2004-01-16 (Release Notes)
  • Update 2, 2004-05-18 (Release Notes)
  • Update 3, 2004-09-03 (Release Notes)
  • Update 4, 2004-12-21 (Release Notes)
  • Update 5, 2005-05-20 (Release Notes)
  • Update 6, 2005-09-28 (Release Notes)
  • Update 7, 2006-03-15 (Release Notes)
  • Update 8, 2006-07-20 (Release Notes)
  • Update 9, 2007-06-15 (Release Notes)
• Red Hat Enterprise Linux 4 (Nahant), 2005-02-15. Uses Linux kernel 2.6.9-5
  • 4.1, also termed Update 1, 2005-06-09 (kernel 2.6.9-11, Release Notes)
  • 4.2, also termed Update 2, 2005-10-05 (kernel 2.6.9-22, Release Notes)
  • 4.3, also termed Update 3, 2006-03-07 (kernel 2.6.9-34, Release Notes) (Release Notes on centos.org)
  • 4.4, also termed Update 4, 2006-08-11 (kernel 2.6.9-42, Release Notes)
  • 4.5, also termed Update 5, 2007-05-01 (kernel 2.6.9-55, Release Notes)
  • 4.6, also termed Update 6, 2007-11-15 (kernel 2.6.9-67, Release Notes)
  • 4.7, also termed Update 7, 2008-07-24 (kernel 2.6.9-78, Release Notes)
  • 4.8, also termed Update 8, 2009-05-18 (kernel 2.6.9-89, Release Notes)
  • 4.9, also termed Update 9, 2011-02-16 (kernel 2.6.9-100, Release Notes)
• Red Hat Enterprise Linux 5 (Tikanga), 2007-03-14. Uses Linux kernel 2.6.18-8 (Release notes)
  • 5.1, also termed Update 1, 2007-11-07 (kernel 2.6.18-53, Release Notes)
  • 5.2, also termed Update 2, 2008-05-21 (kernel 2.6.18-92, Release Notes, single file)
  • 5.3, also termed Update 3, 2009-01-20 (kernel 2.6.18-128, Release Notes)
  • 5.4, also termed Update 4, 2009-09-02 (kernel 2.6.18-164, Release Notes)
  • 5.5, also termed Update 5, 2010-03-30 (kernel 2.6.18-194, Release Notes)
  • 5.6, also termed Update 6, 2011-01-12 (kernel 2.6.18-238, Release Notes and Errata for release)
  • 5.7, also termed Update 7, 2011-07-21 (kernel 2.6.18-274, Release Notes and Errata for release)
  • 5.8, also termed Update 8, 2012-02-21 (kernel 2.6.18-308, Release Notes and Errata for release)
• Red Hat Enterprise Linux 6 (Santiago), 2010-11-10 Uses Linux kernel 2.6.32-71 (Release Notes).
  • 6.1 also termed Update 1, 2011-05-19 (kernel 2.6.32-131, Release Notes and Release Announcement)
  • 6.2 also termed Update 2, 2011-12-06 (kernel 2.6.32-220, Release Notes and Errata for release)

Please free to share your knowledge on this.

This is a small post on how to crate multiple files/folders, sequence generation with flower brackets in-order to save valuable time.

Creating empty files can be done with touch command. We will see how to create multiple files using this command in one shot

Example1: Create a file with name abc.txt

touch abc.txt

Example2: Create multiple files abc, cde, efg, hij, klm

touch  abc cde efg hij klm

Example3: How about creating 1 to 20 files, ie creating multiple files with one command. Its bit tedious job for an admin. Don’t worry Linux provide us with some useful option with “Flower braces” to do expansion. Instead of writing below command

touch 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

We can create 20 files using flower brace {} exapantion as shown below..

touch {1..20}

Your shell tries to expand this brace and generate 1 to 20 numbers. The above command will create total 20 files in one shot.

Example4: How about creating files as 1.txt, 2.txt, 3.txt up to 1000.txt. This can be achieved suffixing it after brackets as shown below.

touch {1..1000}.txt

Example5: how about creating a1, a2, a3 so on up to a1000 files?

touch a{1..1000}

Example6:How about generating numbers?. We can generate numbers using flower braces with echo command. The other way to generate numbers is seq command.

echo {1..10}

Example7: Even we can do sequence for alphabets as shown below

touch {a..z}

Example8: Generate files from A to Z

touch {A..Z}

Note: The above alphabets generation is done using asci values

Example9: How about creating 1 to 1000000 files in one shot, by using multiplication/matrix of numbers?. We can achieve this one with multiplying two sequences.

touch {0..1000}{0..1000}

Example10: How about creating files as multiples of 2.

touch {1..100..2}

this will create files as 1, 3, 5, 7, 9, 11 etc.

Note: This interval will work only bash version 4.0 and above, make a note about this.

Example11: How about creating files as multiples of 7?

touch {1..100..7}

Note: This interval option will work only bash version 4 and above.

Practical usage of this brackets

1)In bash for loop.

2)Generating sequence of numbers.

As mention in above examples we can create folders similarly in one shot. use -p option if you want to create folders in sub folders too.

Example12: Create a folder structure as 2012, under this i want to create 12 folders for each month and under each month create 30 folders which corresponding to 30 days.

mkdir -p 2012/{1..12}/{1..30}

read command is useful in scripts when reading an input from user. This read command is used when the script want to interact with user for his inputs.

read command syntax
 read VARIABLE

Example1:Read a value from user input.

read VAR1

To display this value we have to use echo command.

echo $VAR1

Example2: Reading two words/variable/values at a time.

read VAR1 VAR2

Example3: Reading multiple values at a time.

read VAR1 VAR2 VAR3 VAR4

Example4: Read values in to an Array

read VAR1

ARR1=(VAR1)

to display first value in array use below command

echo ${ARR1[0]}

Example5: Read values from a command

read VAR1 VAR2 VAR3 << ( echo surendra kumar anne )

 echo "Enter values are $VAR1 $VAR2 $VAR3"

Example6: Read user input and give some info to user what he have to give. For this use -p option to display some info when reading value.

read -p "Please enter 1 to 10 numbers: " VAL1

Note: You no need to echo command to display information to user, you can achieve that one using read -p option.

Example7: Read have inbuilt variable called REPLY. this is system variable which stores read value in to $REPLY.

read -p "Please enter a value"

echo "Enter value is $REPLY"
 Please share your thoughts on this.

This is a small tutorial on how to use sort command to soft a file. Sorting is very much useful when dealing with DB files, CSV, xls, log files in fact a text file to. By default sort command will sort according to alpha-bates. First sort tries to sort according to single character, if it finds the first character same in two lines, then it move on to sort second character. Suppose I have a following word list in a file

cat filename.txt

abc
cde
hij
klm
kle
ble

This will be sorted first with first char. When it finds both the char same in this example klm and kle start with same characters, so it tries to sort with third character which is different in them. The output of sort  as below

sort filename.txt

abc

ble
cde
hij
kle
klm

Sort command syntax

sort filename.txt

Example1: Sort a given file according to alpha-bates

 sort filename.txt

Example2: I have a file with host names in third column, how can i sort them according to this column?. Use -k for sorting according to column

sort -k3 filename.txt

The above command will sort according to third column.

Example3:I want to sort /etc/passwd file according to home directories but my sort is not working how can i sort them?. by default sort will take space/tabs as field separators. But in /etc/passwd file the field separator is : so we have to mention this one when sorting a file. This can be done with -t option

sort -t: -k6 /etc/passwd

Example4: I want to sort according to number, suppose i want to sort /etc/passwd file according to UID, use -n option to do that.

sort -n -t: -k3 /etc/passwd

Note: For example with out -n option sort will put 10 before 3 when it find this values, by default it will sort only first numerical char.

Example5: Sort the file and reverse the order

sort -r filename.txt

Example6: Some times its required to sort the file and display only uniq values.

sort -u filename

Note: though the values on other field are different this will not consider by -u option.

Example7: I want to sort a file according to my requirement and save it to a different file. Use -o option to save the sorted output to a file.

sort -o temp.txt filename.txt

You can now mix above options to get your sorting work done.

This is a small how to on finding your command location. Some times its required to find command location to use it as path is not set properly to /bin or /sbin or some other folder. And some times we install packages through scripts where the commands will be installed in a defined path other than /usr/bin or /usr/sbin etc.

command to check where the particular command is installed?

which command-name

Example:

which ls

Output:

root@surendra:/home/surendra# which ls
/bin/ls
root@surendra:/home/surendra#

How about getting with other command along with manual pages?

whereis command-name

Example:

whereis ls

Output:

root@surendra:/home/surendra# whereis ls
ls: /bin/ls /usr/share/man/man1/ls.1.gz
root@surendra:/home/surendra#

some times we don’t know where the command is located but still we want to use it, at these times you can use which command to give entire path

`which ls`

or

$(which ls)

the above two are very much handy when writing shell scripts when you are not aware/sure where the command located. Please share your thoughts on how you avoid this situation.

This is a small how-to to set up two are more IP address on single LAN card. There are some times which require two IP address to set up so that we can make a Linux box as a router. This can be possible without even having two NIC cards. We can configure two different IP address on single Network Card as shown below.

Setting up 2 IP address on “One” NIC. This example is on ethernet.

STEP 1:Setting up first IP address. Edit /etc/sysconfig/network-scripts/ifcfg-eth0 on Redhat Linux box and give the following entries as shown.

vi /etc/sysconfig/network-scripts/ifcfg-eth0

DEVICE=eth0
BOOTPROTO=static
IPADDR=192.168.1.10
NETMASK=255.255.255.0
NETWORK=192.168.1.0
ONBOOT=yes

STEP 2: Setting up second IP address. Create one file as /etc/sysconfig/network-scripts/ifcfg-eth0:1 and give the entries as below in to this file.

vi /etc/sysconfig/network-scripts/ifcfg-eth0:1

DEVICE=eth0:1
BOOTPROTO=static
IPADDR=192.168.1.11
NETMASK=255.255.255.0
NETWORK=192.168.1.0
ONBOOT=yes

STEP 3: Once you configure above files and save them. Now reload the network service on your machine.

service network reload

STEP 4: Check if you get the IP address assigned to the eth0 and eth0:1 interfaces respectively.

ifconfig

Note1: We can assign virtual IP to the same interface with ifconfig but that one is not permanent so not giving info on that.

Note2: We can assign up to 16 virtual IP address to a single NIC card.

This is a small Shell tutorial on how to convert different bases to other bases.
Some times when working as system admin you require to convert different number systems to others. In this post we will see how to convert different number systems to others.

Decimal to Binary

echo "obase=2; 23" | bc

Output:
10111
Let me explain above command. obase is a special variable in bc command which defines the output base value for a given number. There is one more special variable for bc command called ibase which defines input base value. In our example we did not mention ibase so by default it will take my input value as decimal value. So we feed obase=2 and decimal number 23 to bc command to convert decimal 23 in to binary number.

Decimal to Octal number

echo "obase=8; 23" | bc

Decimal to Hex number

echo "obase=16; 23" | bc

Decimal to any base number

convert decimal number to base 4 number system

echo "obase=4; 23" | bc

How about convert to base 7?

echo "obase=7; 23" | bc

Binary to decimal

echo "ibase=2; 11010101" | bc

Oct to decimal

echo "ibase=8; 723" | bc

Hex to decimal

echo "ibase=16; 23" | bc

How about converting binary to Oct?

echo "ibase=2;obase=8 1010101" | bc

As given above we can convert any number system to any number systems

Other ways to do base convertions

bc will convert from any base to any other base. There are some other tools which can do partially these conventions.
$(()) –can convert hex to decimal
example:

echo $((0x123))

printf command can convert hex and oct to decimal

decimal to Octal

printf "%o\n" 123

decimal to Hex

printf "%x\n" 123

This is a small post for Linux new babies. Viewing folders can be achieved by two ways in linux/unix

1. Through ls command
2. Through find command

With ls we have to use grep to get the directory listings..

Ls –l | grep ^d

Example

[root@test surendra_a]# ls -l | grep ^d

d——— 2 surendra_a surendra_a 4096 Sep 8 09:54 HTWFAIP

drwxrwxr-x 2 surendra_a root 4096 Nov 27 12:30 LinuxCBT – RHEL5

drwxrwxr-x 2 surendra_a root 4096 Oct 12 16:40 Software

Through find command

find . -type d

The above command will show you all the file types which are directories in present working directory.

Playing with basics find command options

For basic Linux Find command usage please click here Example31:find all the files which are with more than size 100MB and less than 1GB and the owner of the file is xyz and the file name is Adda.txt in /red folder

find /red –size +100M –size -1G –user xyz –iname adda.txt

Example32:find all the files with SGID for the group sales and with size exactly 100MB with file name as pass.txt under /opt

find /opt –size 100M –group sales –perm g+s –name pass.txt

Linux find command AND Operator

By default find command will use AND option between two options. No need of mentioning any option. For example see below examples.

Example33: find all the files which are more than 100MB and less than 1GB in size.

find / -size +100M –size -1G

or

find / -size +100M -a -size -1G

Like above we can combine many options and your find command use AND operator by default no need of mentioning -a option.

Search for files and execute commands on Found files

Caution: Be careful when using -exec option which you are going to learn below. This is very dangerous option which can change/remove anything if don’t use wisely. There are some instances when you want to execute commands on the found files with find command. -exec is the option used in find command to execute shell commands directly on found files. Let’s discuss this with a basic example.

Example34:find a file with passwd.txt in /var folder and long list this file for checking file properties.

find /var –iname passwd.txt –exec ls –l {} \;

Let me explain above command. Up to find /var –iname passwd.txt, this command you are aware. This command will search for passwd.txt file in /var folder and give the paths and file names where this file is located.

-exec: with this option we are saying to find command to execute a command(here its ls -l) followed by this option

{} –This is used as input to the command which we get as files/folders from find command output.

\; –This indicates that find command is completed.

Actually ; is a command chaining capability and it’s a special character. In order to negate this special character we are using \ before;.

Example35: Find all the files with name test.txt in /mnt and change the ownership of the files from Surendra to Narendra

find /mnt –user surendra –name test.txt –exec chown narendra: {} \;

-exec command {} \; –for executing a command on find files -inum -For finding a file with inode number

Example36:Find all the files with name test.sh in /abc folder and then grep if for word is there in that file or not

find /abc –name test.sh –exec grep ‘for’ {} \;

chmod, grep, ls, rm, mv, cp,md5sum

Example37: Find all the files with name xyz.txt owned by Surendra in /var/ftp/pub and change the permissions to 775 to them.

find /var/ftp –user surendra –name xyz.txt –exec chmod 775 {} \;

Example 38:Find all the files with name temp.txt in /xyz folder and backup then compress them to send it for saving

Find /xyz –name xyz.txt –exec tar xvfz temp.tar.gz {} \;

Example39:Find files with name abc.txt in /home directory and take backup of each file before modifying it.

find /home –name abc.txt –exec cp {} {}.bkf \;

This above command will create files with .bkf extension whenever it finds abc.txt file.

Example40:Find files which are more than 1GB and not accessed for the past 6 months and delete them.

find / -size +1G -mtime +180 –exec rm –rf {} \;

Example41:Find all the files with executable permissions and display their checksum value

find / -perm /a=x -exec md5sum {} \;

Example42:find all the files with name abc.txt and owner as surendra then move them to /opt folder

find / -user surendra -name abc.txt -exec mv {} /opt/ \;

There are many other commands you can try your own. Some other commands which can work with –exec option is mv, md5sum etc.

Find command with multiple -exec option

Find command is capable of using multiple times using the same option(We seen it for finding files which are more than 200M and less then 1GB). In our previous examples we used –size to mention the size between two sizes. Similarly we can use –exec command multiple times.

Example43:Find files with abc.txt name in /opt directory change the owner permissions from Surendra to Narendra and change the permissions to 775

find /opt –user Surendra –name abc.txt –exec chown Narendra: {} \; -exec chmod 775 {} \;

Note: We can use this multiple –exec option more than two times.

Search for multiple files

Till this point if you observe we just search for single file. But sometimes there is a requirement to search for multiple files with single find command to save some valuable time. The following two examples we will see how to do that. Example44: Find all the commands which ends with .sh file extension in /opt folder

find /opt –name *.sh

Note: Sometimes the above command will not work properly because your shell will try to parse the * before find command is executed. So you have made * as not a special character or wild character. In order to understand more about this type of characters you have to learn RegExp. Please find our other posts on Basic RegExp and Advanced RegExp.

Example45:

find /opt –name \*.sh

Or

find /opt –name “*.sh”

Note: These two will work, because you negated your shell parsing * wild character.

Example46:Search for all the files which start with abc and ends with different extension in /opt folder

find /opt –name abc.\*

Example47:Search for files which start with red and ends with many names such as redhat, redtop, redsoap etc.

find / -name red\*

Example 48:How about search for files which always end with dump.

find / -name \*dump

Search for files in multiple locations

Search multiple locations using single find command We can accomplish searching multiple folders with single command without any options. Lets see below command.

Example49: Find abc.txt file in /opt and /var folder at a time

find /opt /var –name abc.txt

The above command will search in only two locations i.e. in /opt and /var Search multiple locations but not in particular location. Example50:Search in entire system expect /proc folder

find / -path /proc -prune -name cpuinfo

Let me explain above command. The -path variable to define the path of a location. And -prune combined with -path will say not to descend in to the mention path /proc

Example51:Search for abc.txt in /opt and /var expect in /var/tmp folder

find /opt /var -path /var/tmp -prune -name abc.txt

Find command OR –o operator

Find have OR operator to do multiple file searches at a time.

Example52:I want to search for abc.txt and hash.c file at a time. This can be achieved by using -o operator

find / -name abc.txt -o -name hash.c

Here when ever find command sees -o it just or the options on its left and right hand side.

Example53:How about i want to find two directories say opt and var how can i find them?

find / -type d - name opt -o -type d -name var 

This above command may trow error. Try below syntax

find / -type d \( -name opt -o -name var \)

let me explain above command. () are used to combine two or more options in to one. So \( -name opt -o -name var \) are combined in to single option and are treated as directories as we given -type is d. We will see more about this operator in our coming post on find command advanced usage.

Linux find command ! Negation operator

find . -type f ! -perm 755 -name abc.txt

find command is very much powerful command which can do good work when its needed to find files with conditions. Find command  is useful when finding files with complex requirement such as size, permissions etc. Suppose we want to find a file which is a regular file and its size is more than 1GB and its accessed more than 90 days back and its owner is none and then delete it. This entire requirement is done with single command without even writing a shell script. Let’s see how we can use find command from basics to advanced in this post.

find command can find files according to

1) File names

2) File types

3) Permissions

4) Owners

5) Modified date and time

6) Size 

Advanced finds command usages

1) Mix of all the above things
2) AND operator
3) Search for files and execute commands on them
           a) chown, chmod, grep, ls, rm, mv, cp,md5sum

4) Multiple execute commands

5) Search for multiple files
            a) With different files with same extension
            b) Same file With different extensions
6) Search in multiple locations
            a) Exclude one location
            b) Search in multiple locations
         
7) OR( –o ) operator

  ! Negation operator

9) Linux find command with Regular Expressions

10) Linux find commnd practical examples

Basics of file/folders search using find command

 find files with name

Syntax:

find path options filename

Example1: find all the files in /home with name test.txt. Here –name is used to specify the filename.

find /home –name test.txt

Example2: find the files whose name is test.txt and in present working directory

find . –name test.txt

Or

find –name test.txt

Example3: find all the files whose name contains both capital letters and small letters in it.

find /home –iname test.txt

-iname option is used to mention ignore the case sensitivity of a file.

Search for files depending on their File types:

Example4: Search for only directories whose name is var in / directory

find / -type d –name var

Example5: Search for an mp3 files whose name is temp.mp3

find / -type f –name temp.mp3

Below are the file types supported by find command, to know more about file types in Linux/Unix please have a look at our other post on File types.

Search for files depending on their Permissions

Example6:Search for a file name test.txt and its permissions are 775 in a given box

find / -perm 775 –name test.txt

Example7: How about searcing files with SUID bit set and file permissions are 755?

find / -perm 4755

Example8:How can i find SGID bit set files with 644 permissions?

find / -perm 2644

Example9: How can i find Sticky bit set files in my system with permissions 551?

find / -perm 1551

Example10:Search for all the files whose SUID bit is set

find / -perm /u=s

Example11: Search for all the files whose SGID bit is set

find / -perm /g+s

Note: We can use = or + interchangeably to check if a permissions is set or not as shown in above two examples.

Example12: Search for all the files  whose StickyBit is set

find / -perm /o=t

Example13: Search for all the files whose owener permissions is read only.

find / -perm /u=r

Example14:Search for all the files which have user, group and others with executable permissions

find / -perm /a=x

To know about more on the permissions you have look at our other posts on chmod command.

Search according to Owners and group owners.

Example15: Search for all the files with name test.txt and the owner of this file is Surendra

find / -user Surendra –name test.txt

Example16: find all the files whos name is test.txt and owned by a group called redcluster

find / -group redcluster –name test.txt

to know more about owners and groups you have to look at our previous post on chown command.

Search according to Modified date and time.

Below is the matrix which give you brief idea on how to search according to modified date, accessed date etc.

Example17: Search for a file: test.txt whose file status is changed more than 90 days back

find / -ctime +90 –name test.txt

Example18: Search for all the files which are modified exactly 90 days back

find / -mtime 90

Example19: Search for all the files with name test.txt which is accessed less than 90 days

find / -atime -90

Example20: find all the files which are modified more than 90 days back and less than 180 days

find / -mtime +90 –mtime -180

Below is the matrix which gives you brief idea on how to search according to modified time, accessed time in minutes etc.

Example21: find all the files changed less than 30mins

find / -cmin -30

Example22: find all the files modified exactly 30 mins back

find / -mmin 30

Example23: find all the files accessed more than 30 mins back

find / -amin +30

Example24: find all the files which are modified more than 5mins back and less than 25mins

find / -mmin +5 –mmin -25

Example25: I have new file called test.txt which is just created, now I want to get all the files which are created later this file creation.

find / -newer test.txt

Search for files/folders depending on the size with –size option

Example26: Search for files whose size is more than 10bytes

find / -size +10c

Example27: Search for files which are exactly 10kb in /opt folder

find /opt –size 10k

Example28: Search for files which are less than 10MB in /var folder

find /var –size -10M

Example29: Search for files which are more than 1GB size in /usr folder

find /usr –size +1G

Example30: find all the empty files in my system

find / -size 0k

In next post on find command we will see more depth in to this find command. Please click here for more advanced Linux Find command usage