Basic Linux for DevOps

What is Linux?

Linux is a community of open-source Unix-like operating systems that are based on the Linux Kernel known for its stability, security, and versatility. It is widely used in servers, embedded systems, and personal computers and comes in various distributions, such as Ubuntu and Fedora. It was initially released by Linus Torvalds on September 17, 1991. It is a free and open-source operating system. The biggest success of Linux is Android(operating system) it is based on the Linux kernel.

Why Linux

• Multi-User & Multi-Tasking
• Open Source
• Security
• Need fewer resources

Linux Flavours

• RHEL (Red Hat Enterprise Linux)
• CentOS
• Ubuntu
• Amazon Linux
• Fedora
• Linux Mint
• OpenSUSE

Architecture of Linux

Hardware Layer

This layer consists of all peripheral devices like RAM/ HDD/ CPU etc.

Kernel

The architecture of an operating system, the kernel is the most important or heart of the operating system as it manages the communication between a machine’s hardware and its software. The visibility of the kernel’s operation is invisible and so it is not accessible to the end-user. These userspace tools only have GUI file systems, web browsers, and the Bash shell. In short, the kernel behaves as the heart of the system and manages the memory, peripheral devices, and CPU. The kernel stands at the “lowest” level of the OS***.***

Shell

It is an interface to the kernel which hides the complexity of the kernel’s functions from the users. It takes commands from the user and executes the kernel’s functions.

System Utility

It provides the functionalities of an operating system to the user. Like Screen Savers, System Monitors, Network Utilities, etc.

Application

Desktop environments do not offer any lend to the full array of applications. As mac and Windows, Linux similarly offers hundreds of high-quality feasible software that is easily available and can be installed anytime anywhere.

Linux File System Hierarchy

1. / (Root): Primary hierarchy root and root directory of the entire file system hierarchy.

• Every single file and directory starts from the root directory
• The only root user has the right to write under this directory
• /root is the root user’s home directory, which is not the same as /

2. /bin : Essential command binaries that need to be available in single-user mode; for all users, e.g., cat, ls, cp.

• Contains binary executables
• Common linux commands you need to use in single-user modes are located under this directory.
• Commands used by all the users of the system are located here e.g. ps, ls, ping, grep, cp

3. /boot : Boot loader files, e.g., kernels, initrd.

• /boot contains files that aren't used by the operating system, but by its bootloader . You'll find both files of the bootloader itself (like /boot/grub/* for Grub) and the Linux kernel (/boot/vmlinuz*) and often an associated initrd or initramfs
• When you press the power button, an electrical signal passes through your system’s motherboard and awakens the entire hardware system. As we all know, the Linux kernel works in a very different method than the traditional booting system. In Linux, the boot process includes a few steps. Which is store in /boot

4. /dev : Essential device files, e.g., /dev/null.

• These include terminal devices, usb, or any device attached to the system (Drivers, Pseudo-devices, Character Special Files and Block Special Files).
• Example: /dev/tty1, /dev/usbmon0

5. /home : Users’ home directories, containing saved files, personal settings, etc.

• Home directories for all users to store their personal files.
• example: /home/kishlay, /home/kv

6. /opt : Optional application software packages.

• Contains add-on applications from individual vendors.
• Add-on applications should be installed under either /opt/ or /opt/ sub-directory.
• Example: /opt/google/chrome (Google Chrome addons is store here)

7. /sbin : Essential system binaries, e.g., fsck, init, route.

• It contains commands used by only root user (root). Just like /bin, /sbin also contains binary executables.
• The linux commands located under this directory are used typically by system administrator, for system maintenance purpose.
• Example: iptables, reboot, fdisk, ifconfig, swapon

8. /srv : Site-specific data served by this system, such as data and scripts for web servers, data offered by FTP servers, and repositories for version control systems.

• srv stands for service.
• Contains server specific services related data.
• Example, /srv/cvs contains CVS related data.

9. /tmp : Temporary files. Often not preserved between system reboots, and may be severely size restricted.

• Directory that contains temporary files created by system and users.
• Files under this directory are deleted when system is rebooted.

1. /etc : Host-specific system-wide configuration files.
• Contains configuration files required by all programs.
• This also contains startup and shutdown shell scripts used to start/stop individual programs.
• Example: /etc/resolv.conf, /etc/logrotate.conf.

Linux Command Cheat Sheet