Monthly Archives: July 2017

How to: Virtual Private Cloud in AWS

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A how-to guide for Virtual Private Cloud in AWS. Learn what is vpc, how to create, configure, and delete VPC in AWS with screenshots.

How to guide : VPC in AWS

What is VPC?

VPC is a Virtual Private Cloud. It’s your own private cloud in the public cloud. You control every aspect of VPC and its communication with the outer world. It’s like having your own datacenter which is isolated from other datacenters. When you are using cloud services, you are working inside your VPC. Servers, storage, load balancer, databases everything you create, configure is executed under your VPC. VPC gives you great flexibility to control your data privacy and security even its on cloud.

How to create VPC in AWS?

We will walk through the process of creating VPC in AWS (Amazon Web Services) cloud. By default, one VPC is created for you when you create a new account with AWS. This VPC is marked as default VPC. Whenever you are using services within AWS, this VPC will be used by default if multiple VPC exists in your account.

Check out our AWS CSA associate certificate preparation guide

Lets follow these series of screenshots to create VPC.

First login to your AWS management console and navigate to ‘VPC‘ under the category ‘Networking and Content delivery‘. See the below image. Or you can type VPC in the AWS services search bar you will be presented with VPC link.

VPC in AWS management console

Now you will be presented with VPC dashboard which shows you a summary of your VPC resources like below :

VPC dashboard showing resources details

Here click on ‘Start VPC Wizard‘. This will kick off the VPC wizard to create your VPC step by step.

Step 1 :

Choose which kind of VPC you need. You have these choices –

  1. VPC with a single public subnet
  2. VPC with public and private subnets
  3. VPC with public and private subnets with hardware VPN access
  4. VPC with private subnet only with hardware VPN access

Each choice has its own features to offer. You can see what it offers by clicking on it. We will be creating the first type of VPC in this tutorial.

Select type of VPC

Select your type of VPC on the left column and then click on Select blue button on right.

Step 2:

Here you need to configure your subnet IP ranges, hardware related stuff, etc. See below screenshot and we will understand each field one by one.

VPC configuration
  • IPv4 CIDR block: CIDR is Class-less Inter Domain Routing. It is your subnet range to be used by VPC. The IP addresses from this range will be assigned to components or services you will be using in this VPC. This is a mandatory field. You have to specify your range with subnet notation. Note that this range is configured and reachable only within your VPC.
  • IPv6 CIDR block: Optional field. You can have IPv6 support in your VPC with this. Here IP range will be automatically generated and assigned by Amazon. You do not have the privilege to choose your own.
  • VPC Name: Name of your choice. It helps you to identify this VPC in other parts of AWS within your account for configuration purposes. You can leave this blank since AWS identifies its every component by ARN (Amazon resource name). This ARN is an alphanumeric system-generated name that is not user friendly hence this field is optionally provided so that you can name your components with an easily recognizable name.
  • Public subnet’s IPv4 CIDR: This range is meant for outside world communication. Your resources will be assigned IP from this block when you want them to communicate outside VPC.
  • Availability zone: These zones are logical grouping of AWS hardware within one specified region (geographical grouping). At a one time you can select one region to work within and availability zones from that region will be listed here as a dropdown. If no zone selected, AWS will create VPC in any of the zones which has max free resources at that instant of time.
  • Subnet name: Again this one is to name your public subnet with an easily recognizable name.
  • Service endpoints: These are virtual devices in AWS. If you want any of them to add with this VPC then you can browse and select them here.
  • Enable DNS hostnames: It enables DNS names to be generated for components when they created in this VPC. These names are system generated.
  • Hardware Tenancy: Choose if you want your VPC components to be on single dedicated hardware (dedicated, physically as close as possible) or anywhere (physically may be near or long) within the zone you specified above. Dedicated tenancy assigns hardware which is the same rack or nearby racks so that you have very minimum network latency and highest performance.

Step 3 :

Click ‘Create VPC ‘ button. Your VPC will be created within seconds and you will be greeted with a screen saying “Your VPC has been successfully created. You can launch instances into the subnets of your VPC. For more information, see Launching an Instance into Your Subnet.” (link altered here with my blog post link). Click ok and you will be presented with VPC list screen as below :

VPC list

Here you can see out newly created VPC named kerneltalks_vpc! All details of this VPC can be seen here. You VPC is ready to

How to modify VPC in AWS?

After creation you can modify VPC parameters. From the VPC list shown above, select any VPC you want to edit and then click the Actions button in the header. Dropdown menu will appear to edit below parameters :

  • Delete VPC
  • Edit CIDRs
  • Edit DHCP options set
  • Edit DNS resolution
  • Edit DNS hostnames
  • Create flow log

Flow logs are created fro any resources in VPC to trace and see IP traffic flow information. The rest of the options are self-explanatory. Here you can modify VPc and delete VPC too.

Here is small GIF I created which shows all above process of creating VPC.

GIF: Create VPC in AWS

Shell scripting basics: IF, FOR and WHILE loop

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Beginners guide to learn shell scripting basics of If statement and for. while loops. The article includes small scripts of if, for and while loop.

Bash scripting : If, FOR & WHILE loop

This article can be referred to as a beginner’s guide to the introduction of shell scripting. We will be discussing various loops that are used in shell or bash scripting. In this chapter, we will discuss on if, for and while loop of scripting: if statement, for loop and while loop.

IF statement

If the loop is a conditional loop in scripting. It is used to check some conditions and perform actions based on the condition being true or false. If the loop structure is :

if [ condition ]
then
<execute this code>
else
<execute this code>
fi

If starts with condition check, if conditions match then it will execute the following code (after then). If the condition is false then it will execute code after else. If a statement can be used without else part too.

Example :

# cat if_statement.sh
#!/bin/bash
if [ $1 -lt 100 ]
then
echo "Your number is smaller than 100"
else
echo "Your number is greater than 100"
fi

# sh if_statement.sh 34
Your number is smaller than 100

If you execute this script, the loop will read the first argument as $1 and compare it with 100. Accordingly it will display output.

Bash FOR loop

Executing the same set of commands for the number of times loops are used in scripting. One of them is for loop. It takes input as a series of values and executes the following code repeatedly for each value. For loop structure is as below :

for i in <values>
do
<execute this code>
done

Here is reads values as a variable i and then $i can be used in the following code. Once all the values processed loops stops and script proceed to the next line of code.

Example :

# cat for_loop.sh
#!/bin/bash
for i in 1 2 3 4 5
do
echo First value in the series is $i
done

# sh for_loop.sh
First value in the series is 1
First value in the series is 2
First value in the series is 3
First value in the series is 4
First value in the series is 5

You can see variable $i is being fed with different values for each run of the loop. Once all values in range processed, the loop exits.

Bash WHILE loop

While is another loop used in programming which runs on condition. It keeps on running until the condition is met. Once the condition is un-matched, it exists. It’s a conditional loop! While loop structure is :

while [ condition ]
do
<execute this code>
done

While loop starts with the condition. If the condition is met it execute the following code and then again goes to verify condition. If the condition is still met then the next iteration of code execution happens. It continues to condition falses.

Example :

# cat while_loop.sh
#!/bin/bash
count=0
while [ $count -lt 3 ]
do
echo Count is $count
count=$(expr $count + 1)
done

# sh while_loop.sh
Count is 0
Count is 1
Count is 2

In the above example we have incremental counter code. We put up a condition for while loop is it can execute till counter less than 3. You can observe output the while loops exist when the counter hits 2.

These are three widely and commonly used for scripting! If you have any suggestions/feedback/corrections for this article please let us know in the comments below.

Beginner’s guide: 4 Linux group management commands

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Learn to manage groups in Linux with these group management commands. The article includes how to create, modify, delete, and administer groups.

Group management in Linux

Groups on the Linux system are a bunch of users created for easy access/permission management. One user can be a member of one or many groups. Users will have only one primary and one/many secondary groups. In our other article we have seen user management commands in Linux/Unix. In this article we will discuss group management. There are mainly 4 commands used to manage user groups on Linux systems :

  1. groupadd
  2. groupmod
  3. groupdel
  4. gpasswd

Let’s check all these commands and fields they are responsible in /etc/group file.

groupadd command

As the name suggests, it is used to create new groups on the Linux system. groupadd command needs a group name as an argument.

# groupadd sysadmins

# cat /etc/group
sysadmins:x:502:

This command creates a group named sysadmins. A newly created group can be verified in /etc/group file. Study fields in /etc/group file here.

Several common switches which works with groupadd are :

  • -g : Specify GID of your choice
  • -o : Create a group with non-unique GID
  • -r : Create a system group. (GID will be taken from system group GID range)

groupmod command

If you want to edit parameters like name, GID, uniqueness of group which already exist in the system then you can modify group using groupmod. Below the list of the switch with their desired values should feed to this command –

  • -g : new GID
  • -o : Make it non-unique
  • -n : New name
# groupmod -n newsysadmins sysadmins
# cat /etc/group |grep sys
newsysadmins:x:502:

# groupmod -g 9999 sysadmins
# cat /etc/group 
sysadmins:x:9999:

# groupmod -o -g 3 sysadmins
# cat /etc/group |grep sys
sys:x:3:bin,adm
sysadmins:x:3:


Observe above outputs where we changed the name, gid of the group and lastly we assigned the same GID 3 (non-unique) to our group which was already existing.

groupdel command

That’s the command where group ends their life! Yes, group deletion is performed using this command. This command is pretty simple. Just supply your group name and it will be deleted from the system.

# groupdel sysadmins

gpasswd command

This command is used to administer group. Administering groups includes :

  1. Adding/removing users to/from group
  2. Setting and removing group password
  3. Making a user administrator/member of a group

Adding and removing user in the group is done with switch -a and -d followed by user name and lastly group name. Check below examples :

# gpasswd -a shri sysadmins
Adding user shri to group sysadmins

# cat /etc/group | grep sysadmin
sysadmins:x:3:shri

# gpasswd -d shri sysadmins
Removing user shri from group sysadmins

# cat /etc/group | grep sysadmin
sysadmins:x:3:


Password set is done without any switch while password removal is with -r switch as below :

# gpasswd sysadmins
Changing the password for group sysadmins
New Password:
Re-enter new password:

What is the use of group password in Linux? 

This question comes to many of us. Hardly rather no one uses this feature at all. The idea must be to secure a group from non-member users. But since a group password should be known to all group members, it actually doesn’t make any sense to use it. Then you might ask then why group passwords exist in the first place? It may be just following the user (password security) model to groups as well to maintain symmetry in design. I mean it’s just my thought. Let me know if you have any other reason which suits group password existence!

Making any user administrator of the group grants him the privilege to administer the group. Member, the user is just a member of the group and can not administer it. You can make user administrator of the group with -A switch and member with -M. By default, the user is added to the group as a member

# gpasswd -A shri sysadmins
# gpasswd -M shri sysadmins

Those are all group management commands in Linux with their most used switches. Let us know any addition/correction/feedback in the comments!

Finger command in Linux

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Learn how to get user details by using finger command in Linux. List of switches for finger command and list of parameter information in this article.

Finger command howto!

The finger is a user information lookup program in Linux. It is used to get system user details like the user, home directory, last login, user shell, etc. This command is useful to see these parameters which otherwise you have to look under /etc/passwd and last login records.

Sometimes you will not find finger command in your out of box distribution. You can install a finger package and proceed to use this command. Sample output of installation on Redhat for your reference.

# yum install finger
Loaded plugins: amazon-id, rhui-lb, search-disabled-repos, security
Setting up Install Process
epel/metalink                                                                                                                         |  15 kB     00:00
epel                                                                                                                                  | 4.3 kB     00:00
epel/primary_db                                                                                                                       | 5.9 MB     00:04
rhui-REGION-client-config-server-6                                                                                                    | 2.9 kB     00:00
rhui-REGION-rhel-server-releases                                                                                                      | 3.5 kB     00:00
rhui-REGION-rhel-server-releases/primary_db                                                                                           |  56 MB     00:00
rhui-REGION-rhel-server-releases-optional                                                                                             | 3.5 kB     00:00
rhui-REGION-rhel-server-releases-optional/primary_db                                                                                  | 5.4 MB     00:00
rhui-REGION-rhel-server-rh-common                                                                                                     | 3.8 kB     00:00
Resolving Dependencies
--> Running transaction check
---> Package finger.x86_64 0:0.17-40.el6 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

=============================================================================================================================================================
 Package                      Arch                         Version                              Repository                                              Size
=============================================================================================================================================================
Installing:
 finger                       x86_64                       0.17-40.el6                          rhui-REGION-rhel-server-releases                        22 k

Transaction Summary
=============================================================================================================================================================
Install       1 Package(s)

Total download size: 22 k
Installed size: 27 k
Is this ok [y/N]: y
Downloading Packages:
finger-0.17-40.el6.x86_64.rpm                                                                                                         |  22 kB     00:00
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
  Installing : finger-0.17-40.el6.x86_64                                                                                                                 1/1
  Verifying  : finger-0.17-40.el6.x86_64                                                                                                                 1/1

Installed:
  finger.x86_64 0:0.17-40.el6

Complete!

Finger command requires the username as an argument. Without any switch finger shows below details.

# finger shrikant
Login: shrikant                         Name: Shrikant Lavhate
Directory: /home/ec2-user               Shell: /bin/bash
On since Wed Jul  5 00:31 (EDT) on pts/0 from 59.184.183.234
No mail.
No Plan.

It displays –

  1. Login: Login id
  2. Name: Comment in /etc/passwd against that user
  3. Directory: Home directory of the user
  4. Shell: The user login shell
  5. Last login time and IP from where he/she was logged in
  6. Email status
  7. Plan : (the content of .plan file in user’s home directory)

Email status can be one of the below –

  • No Mail. :  if there is no mail at all
  • Mail last read DDD MMM ## HH:MM YYYY (TZ):  if the person has
    looked at their mailbox since new mail arriving
  • New mail received … : Same as above
  • Unread since … :  if the user has new mail

Finger command switches

Finger command supports a few switches. The above output without any switch is the same output for the switch -l (multi-line listing). It also displays the content of the files .plan, .project, .pgpkey, and .forward from the user’s a home directory if they exist.

Another switch is -s which can be used for more information like terminal name, write status, idle time, login time and contact details, etc.

# finger -s  shri
Login     Name              Tty        Idle  Login Time   Office     Office Phone
shri      Shrikant Lavhate   *     *    No     logins

In this output you can see * for :

  • terminal: When the unknown device
  • Write status: If write permission is denied
  • login and idle time: If nonexistent

The last switch is -m which prevents user matching. Finger command matches the supplied user name in userid and user comment details. To avoid matching it in comment details and only check-in user ids this switch can be used.

Finger can even be used to lookup remote user information by using user@host format.