How to prepare for job in DevOps/SRE being a freshers?
Action# 1 - Understand SDLC Models & Architecture with Agile, DevOps, SRE & DevSecOps, SOA & Micro services
1.List of SDLC Models and its Benefit. Explain with image?
Agile model
Waterfall model
Iterative model
Spiral model
V-shaped model

1. List of Software Architecture and its Benefit. Explain with image 3.What is Agile and Scrum Model of Software Developement?. Explain with image 4.What is DevOps and Why we are migrating towards DevOps? Explain with image DevOps describes a culture and set of processes that bring development and operations teams together to complete software development. It allows organizations to create and improve products at a faster pace than they can with traditional software development approaches. What is Agile? Agile is a methodology for project management and software development it's breaking up into several phases. Once the process starts the planning and executed the sdlc cycle. What is Scrum? Scrum is broken down into shorter sprints and smaller deliverable there will be a breakdown of a specific problem or issue, as well as information and advice for how to handle it, whether you are a ScrumMaster or in any of the Scrum roles. Why SRE is popular? SRE stands for Site Reliability Engineering it's also gives developers more freedom to create innovative software solutions. What is DevSecOps? Devsecops means development, security and operations. In the devops process we are also implementing security actions at same as development and operations actions called as devsecops. Top 20 Advantage of DevSecOps?

Improves our application stability, availability and security.
Faster Speed of recovery in the case of a security incident.
Focus on the application’s security from the beginning.
Improving Overall Security by enabling Immutable infrastructure which further involves security automation.
Top 20 Tools of DevSecOps?

Prisma Cloud by PaloAlto
Argon Security 3.Checkmarx
Orca Security
SonarQube
Codacy
What is Continuous Integration?
CI-Continuous Integration is a process when developers commit and merge their code daily into central repository it's automatically build and test the code.
What we wants to implement CI?
When developers committing code changes frequently by teams it's boosting the software quality and collaboration.

Top 5 tools to implement CI?
Jenkins
TeamCity
Bamboo
GitLab
What is Continuous Deployment(CD)?
What is CD?
CD - Continuous Deployment
Continuous deployment is used to deploy our software when the code commit passes in automation process it is going for
testing after that it releases software into the production environment without manual interaction.

What we wants to implement CD?
Commit the code to GIT
Run code analysis
Run unit test
Build docker container
Deploy into the test Environment
Deploy into the production Environment

Top 5 tools to implement CD?
1.Jenkins
2.Bamboo
3.Gitlab
4.Teamcity
What is Continuous Delivery(CD)?
What is CD?
CD - Continuous delivery
Continuous delivery is used to deliver our software when the code commit passes in automation process it is going
for testing after that it releases software into the production environment with manual interaction.

What we wants to implement CD?

Top 5 tools to implement CD?
Jenkins
Gitlab
Bamboo
Teamcity
Azure Devops
What is Container?
Container is a light weight operating system and it contains packages of software to run an application.
Top 5 Container Runtime Interface?

containerd
Docker
Windows
Runc
What is Docker?
Docker is an open source containerization platform. It helps developers to package applications into containers to run an applications into small set of services.

What are top 10 benefits of Docker?

Continuous Deployment and Testing
Compatibility and Maintainability
Simplicity and Faster Configurations
Multi-Cloud Platforms
Security
Isolation
Standardization and Productivity
What is Microservices?
Micro services is an architecture to divide one application into set of small services and each service run it's own process if one service having any issue the other services was not effected.

List of Principals of Microsercies?

Carry-its-own-data microservice
Transportable microservice
Single concern
Discrete
List of Microsercies Models?
Microservices allow a large application to be separated into smaller independent parts, with each part having its own realm of responsibility.

Top 20 Actions Items to miograte into Microsercies
Data migration
Network migration
Security migration

Top 15 tools for Microsercies Implementations?

Kubernetes
Minikube
Istio
Amazon Simple Queue Service (SQS)
Postman
Spring Boot
Google Cloud Functions
List of Communication Methods and Protocols in Microservices?
HTTP request
lightweight asynchronous messaging

Action# 2 - Learning & become Expert in Linux

1.Top 100 Linux User Commands

1. Cat (Concatenate) This command can be used to get the contents of the file as an output in the Terminal window.
2. aptitude aptitude is highly powerful interface for Linux package management system.
3. cal You can use cal command in Terminal window to see the calendar.
4. df You can get all the information of your file system.
5. help When you execute this help command in Terminal window, it will list all built-in commands you can use in shell.
6. pwd (Print Work Directory) This command the path of the directory currently you’re working in.
7. ls When you type and execute ls command in Terminal, it will show you all the contents of the particular directory.
8. uname It displays Linux system information when executed in Terminal shell.
9. ping (Packet INternet Groper) -- It basically checks for the network connectivity between two nodes.
10. mkdir To create a new folder in any directory using Linux Terminal.
11. gzip We can compress any file from Terminal window using gzip command.
12. whatis If we wish to know for what the particular Linux command can be used.
13. who who command when executed in Terminal show the complete list of those users who are currently logged into Linux system.
14. free free command can be used to check exactly what amount of storage is free and used in physical as well as swap memory in the system.
15. top top is simple but useful command to monitor all the ongoing processes on the Linux system
16. echo echo command can be used to print any text you through with the command.
17. groups If you want to know which groups the particular user is member of then execute groups command in Terminal window.
18. head This command will list the first 10 lines of the file you through with head command.
19. man Here man stands for user manual and as the name suggests man will display the user manual for the particular command.
20. passwd You can use passwd command to change the password for self or any user
21. w w is the short and simple command which will help you view the list of currently logged in users.
22. whoami This command will help you to find out which user is logged into system or who you are logged in as.
23. history history command will list all the commands used by you in serial numbered form.
24. login If you want to switch user or want to create new session then fire this command in Terminal window and provide the details like login id and password.
25. lscpu This command will display all the CPU architecture information such as threads, sockets, cores and CPU count.
26. mv mv (move) command can be used to move one file or directory to another file or directory.
27. ps If you want to see the list of processes that are currently running for your session
28. kill You can use this command to kill the currently ongoing processes manually
29. tail tail command will display last 10 lines of the file in the Terminal window
30. cksum cksum is a command to generate the checksum value for the file or stream of data thrown with command in Linux Terminal.
31. cmp If you ever need to do byte-by-byte comparison of the two files then cmp
32. env env is a very useful shell command which can be used to display all the environment variable in the Linux Terminal window
33. hostname hostname command can be used to view the current host name and hostname can be used to change the current host name to new one.
34. hwclock You can use hwclock or hwclock –set –date
    command to view hardware clock or set it to new date.
35. lshw sudo lshw command can be used to invoke detailed hardware information of the system on which Linux is running.
36. nano nano is Linux command-line text editor just similar to Pico editor which many of you might have used for programming
37. rm rm command can be used to remove any file from the working directory.
38. ifconfig ifconfig is another useful Linux command which can be used to configure network interface on the system.
39. clear clear is simple command for Linux Terminal shell, when executed it will clear the Terminal window for fresh start.
40. su su command can be used to switch to another account right from the Linux Terminal window.
41. wget wget is very useful command to download any file from the internet and best part is download works in background
42. yes yes “your text” command is used to display a text message entered with yes command repeatedly on Terminal window until you stop it using CTRL + c
43. last When executed last command will display the list of last logged in users into the system as an output in Linux Terminal.
44. locate locate command is an reliable and arguably better alternative to find command to locate any file on the system.
45. iostat If you ever need to monitor system input/output devices it displays all the stats of the CPU as well as I/O devices in Terminal window itself.
46. kmod You can use kmod list command to manage all the Linux Kernel modules as this command will display all the currently loaded modules on the system.
47. lsusb lsusb command will show information about all the USB buses connected to the hardware and external USB devices
48. pstree pstree command displays all the currently running processes in the tree format on Linux Terminal window.
49. sudo If you need to run any command as a root user or root permissions then just add sudo at the start of any command.
50. apt apt (Advanced Package Tool) is Linux command which helps user to interact with the packaging system.
51. zip You can use zip command to compress one or more files
52. unzip To extract files from compressed zip file use unzip command in Terminal shell.
53. shutdown You can use shutdown command to turn of the system directly from Terminal shell.
54. dir dir (directory) command can be used to view the list of all directories and folders present in current working directory.
55. cd cd command helps you to access particular directory or folder from the file system. You can also use cd .. command to go back to root.
56. reboot As the name suggests you can use reboot command to restart or shutdown the system from the Terminal window.
57. sort sort command will help you sort file or arrange any record in particular order generally according to their ASCII values.
58. tac tac command will display the contents of the file in reverse orders.
59. exit exit command can be used to close the Terminal shell window directly from the command-line.
60. ionice ionice command will help you get or set I/O scheduling class and priority for the particular process.
61. diff diff command will compare the two directories and will display difference between them
62. expr If you want to perform quick calculations during your work then expr is really useful command for you.
63. gunzip gunzip command can be used to extract or restore files compressed with gzip command.
64. hostnamectl hostnamectl command can be used to access system information, change the system hostname and other related settings.
65. iptable iptables is a simple Linux Terminal based firewall tool which helps manage both incoming and outgoing traffic using tables.
66. killall killall command will kill all the programs matching the processes name thrown with the killall command.
67. netstat To monitor incoming and outgoing network connections continuously. netstat command displays the network status, routing tables and interface statistics.
68. lsof lsof command will help you view all the open file related to your application in the Linux Terminal window itself.
69. bzip2 You can use bzip2 command in the Terminal window to compress any file to .bz2 file and use bzip2 -d command to extract the files from compressed file.
70. service We can view the status of particular service or all the services
71. vmstat vmstat command will display systems virtual memory usage on Terminal window.
72. mpstat When executed mpstat command will display all the information about CPU utilization and performance stats on Linux Terminal window.
73. usermod If you want edit or modify attributes of already created user account then usermod login is the best command for you.
74. touch We can create empty files in file system and you can also change time and date i.e. is timestamp of recently accessed files as well as directories.
75. uniq uniq is a standard Linux Terminal command when thrown with file, filters the repeated lines in the file.
76. wc wc command reads the file thrown with the command and displays word and line count of the file.
77. pmap pmap command display the memory map of the pid you provide. You can also view memory map for multiple processes.
78. rpm rpm -i .rpm command can be used to install rpm based packages on Linux. To remove rpm package use rpm -e command in Terminal shell.
79. ssh ssh acronym for Secure Shell is protocol which is used to securely connect to host system. ssh username@host
80. telnet telnet command uses telnet protocol to connect to another system as a user.
81. nice If you need to change the priority of the running processes then run nice [OPTION] [COMMAND [ARG]…] in the Linux Terminal.
82. nproc nproc [option] command will display the number of processing units allotted to the currently running process.
83. scp scp acronym for Secure Copy is the Linux command which can be used to copy files and directories between hosts on the network.
84. sleep sleep command will delay or pause the execution of command for particular amount of time i.e. specified with sleep command.
85. split If you need to breakdown large file into small file then use split [option].. [file [prefix]] command in the Linux Terminal.
86. stat You can view the status of a file or an entire file system using stat command in Linux Terminal.
87. lsblk lsblk command reads the sysfs filesystem and displays the block device information on the Terminal window.
88. hdparm Using hdparm command you can handle hard disk and other disk devices in the Linux using Terminal shell.
89. chrt chrt [option] priority [argument..] command is used for manipulating the real-time attributes of the process.
90. useradd useradd [optaons] login command will help you add user account into your system
91. userdel userdel [option] login command will let you delete any user account from the system.
92. usermod Using usermod [options] login command you can modify any user account present on the system.
93. find Locates files based on some user-specified criteria.
94. uptime shows system uptime and load average.
95. vmstat Shows system memory, processes, interrupts, paging, block I/O, and CPU info.
96. cp copying files and folders.
97. tar An archiving utility.
98. cron set up scheduled tasks to run.
99. nslookup query Internet name servers (NS) interactively.

100. curl
     
     Transferring data using various network protocols. (supports more protocols than wget)

101. Top 50 Linux Admin Commands

1)traceroute

This utility uses the ICMP protocol and finds the trace
2)dig

Helps you get the DNS records associated with a domain name.
3)nslookup

Command similar to dig.
4)nc

utility to debug TCP/UDP sockets.
5)telnet

It can be used to test remote connectivity on ports
6)route
Helps you get all the route table information
7)tcpdump

This utility helps you to capture network packets and analyze them for network issues.
8)lsof

list all the open files and the process information that opened it
9)hostname

To check and set the hostname of the server.
10)host
To get host DNS details
11)ping
Checks if the remote server is reachable using ICMP protocol.
12)curl
A cross-platform utility that is used to transfer data.
13)wget
Utility to download files. Can be used for troubleshooting proxy connections and connectivity.
14)ip

A replacement for ifconfig. Can be used to configure and retrieve information about systems network interfaces
15)arp

Utility to view and manage arp cache.
16)ss/netstat

Primarily used to check the connections and PID on ports and Unix sockets.
17)df -h
to check filesystems if they are full or not
18)free -m
to check memory in the server
19)ifconfig
to check interface configurations
20)netstat
displays routing tables,listening ports

1. Top 30 Linux Troublshooting

hostname -- To check and set the hostname of the server.
host -- To get host DNS details
ping -- Checks if the remote server is reachable using ICMP protocol. It also shows the round trip time of packets.
curl -- A cross-platform utility that is used to transfer data. It can be used for troubleshooting several network issues.
wget -- Utility to download files. Can be used for troubleshooting proxy connections and connectivity.
ip -- A replacement for ifconfig. Can be used to configure and retrieve information about systems network interfaces
arp -- Utility to view and manage arp cache.
ss/netstat -- Primarily used to check the connections and PID on ports and Unix sockets.
traceroute -- This utility uses the ICMP protocol and finds the hops involved in reading the destination server. It also shows the time it takes between hops.
mtr -- mtr is a mix of ping and traceroute. It also provides additional information like intermediate hosts and responsiveness.
dig -- Helps you get the DNS records associated with a domain name.
nslookup -- Command similar to dig.
nc -- utility to debug TCP/UDP sockets.
telnet -- It can be used to test remote connectivity on ports
route -- Helps you get all the route table information
tcpdump -- This utility helps you to capture network packets and analyze them for network issues.
lsof -- list all the open files and the process information that opened it

Action# 3 - Learn VirtualBox

1.What is VirtualBox?

Oracle VM VirtualBox is cross-platform virtualization software. It allows users to extend their existing computer
to run multiple operating systems including Microsoft Windows, Mac OS X, Linux, and Oracle Solaris, at the same time.

1. How to install VirtualBox in windows?

Beginning with the Installation:
Getting Started:
VirtualBox-Windows-Installation-01
Select Installation Location:

VirtualBox-Windows-Installation-02

Creating Entries and Shortcuts:

VirtualBox-Windows-Installation-03
Ready to Install:

VirtualBox-Windows-Installation-04

Installing Files and packages:

VirtualBox-Windows-Installation-05

Installing Certificates:

VirtualBox-Windows-Installation-06

Finished Installation:

VirtualBox-Windows-Installation-07

When you will open virtualbox it will look like as shown below:

List of SDLC Models and its Benefit. Explain with image
Waterfall Model
It is old method used by organization where the iteration is in year and the product has to pass development then test
if any issue comes again the process starts from first
Agile Model
Breaking a big task into smaller chunks and all the teams working together in cycles like
plan code build test and deploy review and backlog

What is Agile and Scrum Model of Software Developement?. Explain with image
Breaking a big task into smaller chunks and all the teams working together in cycles like
plan code build test and deploy review and backlog
Scrum It is framework which brings all the teams having updated the targets and working together for faster releases

What is DevOps and Why we are migrating towards DevOps? Explain with image
The whole world is running faster and people are expecting changes in the websites apps etc quickly.
So it is organization duty to adopting changing in market and deliver it quicker.
To make this DevOps methodology helps organization.
early defect detection
faster delivery
Good Collab b/w Dev team and Ops team
Think more about code
Automating of processes

What is SRE and its advantage. Explain with image 6.What is DevSecOps and explain the importance of it?
Explain with image
SRE stands for site reliable engineering where the concept of predicting the failures even before it exists in real world.
It is used to fill the gap between development teams and operations teams and identify bugs faster
fills gap between development team and operations team
check service health continuously
decrease risk of human error
continuous monitoring
DevSecOps is the methodology of integrating security within the DevOps process.
It is like having security in every step of the process.
In case of a security incident faster recovery
thinking of security from application building stage
creating immutable infra with security automation

What is differnce between DevOps vs SRE? Explain with image
The whole world is running faster and people are expecting changes in the websites apps etc quickly.
So it is organization duty to adopting changing in market and deliver it quicker.
To make this DevOps methodology helps organization.
SRE stands for site reliable engineering where the concept of predicting the failures even before it exists in real world.
It is used to fill the gap between development teams and operations teams and identify bugs faster
fills gap between development team and operations team

What is Microsercies? Explain with image
Micro services means dividing one application into small services and each service will run it's own process that means
if a service got effected others run without any issue.

What is Continuous Integration Explain with image
Continuous Integration is a process when developer commits a code into repository the code gets validate compile
test package. If any error in this process the developer team gets intimated.

What is Continuous delivery? Explain with image
Continuous delivery is the process that allows development teams to build test and release software more quickly.
It basically uses with Continuous Integration.
Continuous delivery asks for a final human check before pushing to deployment.

ACTION:2

1.Top 100 Linux User Commands
1.Top 100 Linux User Commands

To create a new folder in any directory using Linux Terminal.

1. cmp If you ever need to do byte-by-byte comparison of the two files then cmp
2. env env is a very useful shell command which can be used to display all the environment variable in the Linux Terminal window
3. hostname hostname command can be used to view the current host name and hostname can be used to change the current host name to new one.
4. hwclock You can use hwclock or hwclock –set –date
   command to view hardware clock or set it to new date.
5. lshw sudo lshw command can be used to invoke detailed hardware information of the system on which Linux is running.
6. nano nano is Linux command-line text editor just similar to Pico editor which many of you might have used for programming
7. rm rm command can be used to remove any file from the working directory.
8. ifconfig ifconfig is another useful Linux command which can be used to configure network interface on the system.
9. clear clear is simple command for Linux Terminal shell, when executed it will clear the Terminal window for fresh start.
10. su su command can be used to switch to another account right from the Linux Terminal window.
11. gzip We can compress any file from Terminal window using gzip command.
12. whatis If we wish to know for what the particular Linux command can be used.
13. who who command when executed in Terminal show the complete list of those users who are currently logged into Linux system.
14. free free command can be used to check exactly what amount of storage is free and used in physical as well as swap memory in the system.
15. top top is simple but useful command to monitor all the ongoing processes on the Linux system
16. echo echo command can be used to print any text you through with the command.
17. groups If you want to know which groups the particular user is member of then execute groups command in Terminal window.
18. head This command will list the first 10 lines of the file you through with head command.
19. man Here man stands for user manual and as the name suggests man will display the user manual for the particular command.
20. passwd You can use passwd command to change the password for self or any user
21. w w is the short and simple command which will help you view the list of currently logged in users.
22. whoami This command will help you to find out which user is logged into system or who you are logged in as.
23. history history command will list all the commands used by you in serial numbered form.
24. login If you want to switch user or want to create new session then fire this command in Terminal window and provide the details like login id and password.
25. lscpu This command will display all the CPU architecture information such as threads, sockets, cores and CPU count.
26. mv mv command can be used to move one file or directory to another file or directory.
27. ps If you want to see the list of processes that are currently running for your session
28. kill You can use this command to kill the currently ongoing processes manually
29. tail tail command will display last 10 lines of the file in the Terminal window
30. cksum
31. Cat (Concatenate) This command can be used to get the contents of the file as an output in the Terminal window.
32. aptitude aptitude is highly powerful interface for Linux package management system.
33. cal You can use cal command in Terminal window to see the calendar.
34. df You can get all the information of your file system.
35. help When you execute this help command in Terminal window, it will list all built-in commands you can use in shell.
36. pwd This command the path of the directory currently you’re working in.
37. ls When you type and execute ls command in Terminal, it will show you all the contents of the particular directory.
38. uname It displays Linux system information when executed in Terminal shell.
39. ping It basically checks for the network connectivity between two nodes.
40. mkdir cksum is a command to generate the checksum value for the file or stream of data thrown with command in Linux Terminal.
41. wget wget is very useful command to download any file from the internet and best part is download works in background
42. yes yes “your text” command is used to display a text message entered with yes command repeatedly on Terminal window until you stop it using CTRL + c
43. last When executed last command will display the list of last logged in users into the system as an output in Linux Terminal.
44. locate locate command is an reliable and arguably better alternative to find command to locate any file on the system.
45. iostat If you ever need to monitor system input/output devices it displays all the stats of the CPU as well as I/O devices in Terminal window itself.
46. kmod You can use kmod list command to manage all the Linux Kernel modules as this command will display all the currently loaded modules on the system.
47. lsusb lsusb command will show information about all the USB buses connected to the hardware and external USB devices
48. pstree pstree command displays all the currently running processes in the tree format on Linux Terminal window.
49. sudo If you need to run any command as a root user or root permissions then just add sudo at the start of any command.
50. apt apt is Linux command which helps user to interact with the packaging system.
51. zip You can use zip command to compress one or more files
52. unzip To extract files from compressed zip file use unzip command in Terminal shell.
53. shutdown You can use shutdown command to turn of the system directly from Terminal shell.
54. dir dir command can be used to view the list of all directories and folders present in current working directory.
55. cd cd command helps you to access particular directory or folder from the file system. You can also use cd .. command to go back to root.
56. reboot As the name suggests you can use reboot command to restart or shutdown the system from the Terminal window.
57. sort sort command will help you sort file or arrange any record in particular order generally according to their ASCII values.
58. tac tac command will display the contents of the file in reverse orders.
59. exit exit command can be used to close the Terminal shell window directly from the command-line.
60. ionice ionice command will help you get or set I/O scheduling class and priority for the particular process.
61. diff diff command will compare the two directories and will display difference between them
62. expr If you want to perform quick calculations during your work then expr is really useful command for you.
63. gunzip gunzip command can be used to extract or restore files compressed with gzip command.
64. hostnamectl hostnamectl command can be used to access system information, change the system hostname and other related settings.
65. iptable iptables is a simple Linux Terminal based firewall tool which helps manage both incoming and outgoing traffic using tables.
66. killall killall command will kill all the programs matching the processes name thrown with the killall command.
67. netstat To monitor incoming and outgoing network connections continuously. netstat command displays the network status, routing tables and interface statistics.
68. lsof lsof command will help you view all the open file related to your application in the Linux Terminal window itself.
69. bzip2 You can use bzip2 command in the Terminal window to compress any file to .bz2 file and use bzip2 -d command to extract the files from compressed file.
70. service We can view the status of particular service or all the services
71. userdel userdel login command will let you delete any user account from the system.
72. usermod Using usermod login command you can modify any user account present on the system.
73. find Locates files based on some user-specified criteria.
74. uptime shows system uptime and load average.
75. vmstat Shows system memory, processes, interrupts, paging, block I/O, and CPU info.
76. cp copying files and folders.
77. tar An archiving utility.
78. cron set up scheduled tasks to run.
79. nslookup query Internet name servers interactively.
80. curl Transferring data using various network protocols.
81. nice If you need to change the priority of the running processes then run nice [OPTION] [COMMAND [ARG]…] in the Linux Terminal.
82. nproc nproc command will display the number of processing units allotted to the currently running process.
83. scp scp acronym for Secure Copy is the Linux command which can be used to copy files and directories between hosts on the network.
84. sleep sleep command will delay or pause the execution of command for particular amount of time i.e. specified with sleep command.
85. split If you need to breakdown large file into small file then use split [option].. [file [prefix]] command in the Linux Terminal.
86. stat You can view the status of a file or an entire file system using stat command in Linux Terminal.
87. lsblk lsblk command reads the sysfs filesystem and displays the block device information on the Terminal window.
88. hdparm Using hdparm command you can handle hard disk and other disk devices in the Linux using Terminal shell.
89. chrt chrt [option] priority [argument..] command is used for manipulating the real-time attributes of the process.
90. useradd useradd [optaons] login command will help you add user account into your system
91. vmstat vmstat command will display systems virtual memory usage on Terminal window.
92. mpstat When executed mpstat command will display all the information about CPU utilization and performance stats on Linux Terminal window.
93. usermod If you want edit or modify attributes of already created user account then usermod login is the best command for you.
94. touch We can create empty files in file system and you can also
95. uniq uniq is a standard Linux Terminal command when thrown with file, filters the repeated lines in the file.
96. wc wc command reads the file thrown with the command and displays word and line count of the file.
97. pmap pmap command display the memory map of the pid you provide. You can also view memory map for multiple processes.
98. rpm rpm -i .rpm command can be used to install rpm based packages on Linux. To remove rpm package use rpm -e command in Terminal shell.
99. ssh ssh acronym for Secure Shell is protocol which is used to securely connect to host system. ssh username@host
100. telnet telnet command uses telnet protocol to connect to another system as a user.

2.Top 50 Linux Admin Commands
1)info

Display information about given command
2)env

Display environment variable for currently logged-in user
3)netstat

Display network status
4)df
Display filesystem information
6)du

Display usage
7)init

Allow to change server bootup
8)nano

command line editor
9)man

information about all commands
10)uptime

Show how long server is running
11)users

show username who are currently logged in
12)pkill

Kill a process
13)wget
Download file from network
14)ftp or sftp

Connect remote ftp host
15)free
Show memory status
16)top

Display processor activity of system
17)last
Display user's activity in the system
18)ps

Display about processes running on the system
19)Shutdown
Shutdown and reboot system
20)nslookup
Check domain name and IP information
21)shred

Delete a file by over writing its content
22)cat

Display, copy or combine text files
23)pwd

Print path of current working directory
24)locate

Finding files by name on system
25)chown

Change ownership of a file
26)alias
To short a command
27)echo
Display text
28)mount

Mount a filesystem
29)ifconfig
Display configuration
30)traceroute

Trace existing network
31)sudo
Run a command as a root user
32)route

List routing table for your server
33)ping
Check connection by sending packet test packet
34)find
Find location of files/directories
35)users

Show current logged in user
36)who

Same as w but doesn't show current process
37)ls

List all the files
38)tar

Compress directories
39)grep
Search for a string in a file
40)su

Switch from one to another user
41)awk

Search lines for a given pattern
42)iostat
Display I/O statistics
43)vmstat
Display VM statistics
44)useradd
To add user to the server
45)userdel
To delete a user in the server
46)last
show a listing of last logged in users
47)w
show a list of currently loggedin user sessions
48)ssh
secure command line access to remote linux systems
49)service
command to start and stop services
50)ln
create symbolic links to other files

3.Top 30 Linux Troubleshooting

1)traceroute

This utility uses the ICMP protocol and finds the trace
2)dig

Helps you get the DNS records associated with a domain name.
3)nslookup

Command similar to dig.
4)nc

utility to debug TCP/UDP sockets.
5)telnet

It can be used to test remote connectivity on ports
6)route
Helps you get all the route table information
7)tcpdump

This utility helps you to capture network packets and analyze them for network issues.
8)lsof

list all the open files and the process information that opened it
9)hostname

To check and set the hostname of the server.
10)host
To get host DNS details
11)ping
Checks if the remote server is reachable using ICMP protocol.
12)curl
A cross-platform utility that is used to transfer data.
13)wget
Utility to download files. Can be used for troubleshooting proxy connections and connectivity.
14)ip

A replacement for ifconfig. Can be used to configure and retrieve information about systems network interfaces
15)arp

Utility to view and manage arp cache.
16)ss/netstat

Primarily used to check the connections and PID on ports and Unix sockets.
17)df -h
to check filesystems if they are full or not
18)free -m
to check memory in the server
19)ifconfig
to check interface configurations
20)netstat
displays routing tables, listening ports