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Interview Questions and Answers

Common log files include: `/var/log/syslog` (system messages), `/var/log/auth.log` (authentication attempts), `/var/log/kern.log` (kernel messages), `/var/log/mail.log` (mail server logs), and application-specific logs. They contain information about system events, errors, and warnings.

Systemd is the system and service manager in modern Linux distributions. Use commands like `systemctl start `, `systemctl stop `, `systemctl restart `, `systemctl status `, and `systemctl enable ` (to start at boot).

LVM allows for flexible disk management by creating logical volumes from physical volumes. Benefits include: resizing volumes dynamically, taking snapshots, and striping data across multiple disks.

Swap space is used when physical memory is full. You can create a swap partition or a swap file. Use `mkswap` to format a partition as swap, and `swapon` to enable it. The `/etc/fstab` file defines swap space to be mounted at boot.

SELinux (Security-Enhanced Linux) is a security module that provides mandatory access control. It enforces policies that restrict the actions of processes based on predefined rules. It enhances security by limiting the damage that can be caused by compromised processes.

Common backup tools include `tar`, `rsync`, and `dd`. You can create full or incremental backups. Develop a backup strategy that includes regular backups, offsite storage, and a documented restore procedure.

Containers provide a lightweight virtualization method for isolating applications. Docker is a popular containerization platform. Use `docker pull` to download images, `docker run` to start containers, `docker build` to create images from Dockerfiles, and `docker-compose` to manage multi-container applications.

`apt` (Debian/Ubuntu): `apt update`, `apt install `, `apt remove `, `apt upgrade`. `yum`/`dnf` (Red Hat/CentOS/Fedora): `yum update`, `yum install `, `yum remove `, `yum upgrade`. These package managers automate the installation, removal, and update of software packages.

Linux permissions control access to files and directories. `r` (read), `w` (write), and `x` (execute) permissions are assigned to the owner, group, and others. Use the `chmod` command to change permissions, either numerically (e.g., 755) or symbolically (e.g., u+rwx, g+rx, o+rx).

Tools like `top`, `htop`, `vmstat`, `iostat`, `free`, and `sar` are used to monitor CPU usage, memory usage, disk I/O, and network activity. Log files in `/var/log` also provide valuable performance information.

A firewall controls network traffic in and out of a system. `iptables` is a command-line firewall tool. `firewalld` is a dynamic firewall manager that provides a higher-level interface. Configuration involves defining rules to allow or block specific ports and services.

Cron jobs schedule tasks to run automatically at specified times. Edit the crontab file using `crontab -e` to define the schedule (minute, hour, day, month, weekday) and the command to execute.

Use tools like `ping`, `traceroute`, `netstat`, `ss`, `ifconfig`/`ip`, and `nslookup` to diagnose network problems. Check DNS resolution, routing tables, and firewall rules.

Runlevels define the state of the system. Common runlevels include: 0 (halt), 1 (single-user mode), 2-5 (multi-user mode), and 6 (reboot). The default runlevel is specified in `/etc/inittab` (older systems) or managed by systemd.

Troubleshooting steps include: checking the GRUB bootloader, using a rescue disk to repair the file system, examining boot logs, and verifying hardware.

SSH (Secure Shell) provides secure remote access to a Linux system. Configuration involves editing `/etc/ssh/sshd_config`, including settings like port number, allowed users, and authentication methods (e.g., password or key-based).

Common commands include: `ls` (list files), `cd` (change directory), `mkdir` (make directory), `rm` (remove files), `cp` (copy files), `mv` (move files), `cat` (concatenate files), `grep` (search files), `chmod` (change permissions), `chown` (change ownership), `ps` (process status), `top` (system resource monitor), `df` (disk space), `du` (disk usage), `ifconfig`/`ip` (network configuration).

Linux is an open-source operating system kernel. Key advantages include: stability, security, flexibility, customizability, a large community, and cost-effectiveness (often free).

The Linux file system is hierarchical, starting at the root directory (/). Key directories include: /bin (essential commands), /boot (boot loader files), /dev (device files), /etc (configuration files), /home (user home directories), /lib (shared libraries), /media (removable media), /mnt (temporary mount point), /opt (optional software), /proc (process information), /root (root users home), /sbin (system administration commands), /tmp (temporary files), /usr (user programs and data), and /var (variable data).

Users are managed with commands like `useradd`, `usermod`, `userdel`, `passwd`, and `id`. Groups are managed with `groupadd`, `groupmod`, `groupdel`, and `gpasswd`. Configuration files are typically located in `/etc/passwd`, `/etc/shadow`, and `/etc/group`.

Bootloader.

- OS Kernel.

- Background services.

- OS Shell.

- Graphics server.

- Desktop environment.

- Applications.

Linux and Windows- Linux is an open source operating system whereas Windows OS is commercial and proprietary. Linux has access to source code and user can alter the code as per business need whereas Windows does not allow access to the source code.

LILO - LILO stands for Linux Loader that is used to load Linux into memory.

LinuxKernel - The Linux kernel is the main component of a Linux operating system (OS) and is the core interface between a computer's hardware and its processes.

Hard

The following commands can help you check memory usage in Linux -

free Command.

/proc/meminfo File.

vmstat Command.

ps_mem Command.

smem Command.

top Command.

htop Command.

glances Command.

Network interface bonding is called by many names: Port Trunking, Channel Bonding, Link Aggregation, NIC teaming, etc. It combines or aggregates multiple network connections into a single channel bonding

Puppet is an open source software configuration management and deployment tool.

repquota prints a summary of the disc usage and quotas for the specified file systems.

The cron daemon runs tasks in the background at specified times. To schedule a task using cron, you need to edit a special file called the crontab file in a text editor and add your task in it, in a particular format.

The biggest advantage of open-source software is Transparency. With OSS the source code is open and accessible to everybody, anyone can learn how the software works and what it does. Organizations may rest assured that no unwanted or hidden features have

Environment variables allow you to customize how the system works and the behavior of the applications on the system.

Use Kill Command Options to Terminate a Process.

In Unix/Linux style “shell” command line interpreters, you can type two or more commands separated by a semicolon to run them consecutively.

Explain with examples that sync with the job description.

Explain with examples that sync with the job description.

1) Choose the Right Technology when picking up a programming language, Database, Communication Channel.

(2) The ability to run multiple servers and databases as a distributed application over multiple time zones.

(3)Database backup, correctio

Object-oriented programming is a programming paradigm based on the concept of \"objects\", which can contain data, in the form of fields, and code, in the form of procedures. A feature of objects is that objects' own procedures can access and often modify

Most modern development processes can be described as agile. Other methodologies include waterfall, prototyping, iterative and incremental development, spiral development, rapid application development, and extreme programming.

The primary aim of the code review is to ensure that the codebase overall product quality is maintained over time. It helps give a fresh set of eyes to identify bugs and simple coding errors. All of the tools and processes of code review are designed to t

The most common software sizing methodology has been counting the lines of code written in the application source. Another approach is to do Functional Size Measurement, to express the functionality size as a number by performing Function point analysis.

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Different Types Of Software Testing - Unit Testing, Integration Testing, System Testing, Sanity Testing, Smoke Testing, Interface Testing, Regression Testing, Beta/Acceptance Testing.

Quality control can be defined as a \"part of quality management concentrating on maintaining quality requirements.\" While quality assurance relates to how a process is carried out or how a product is produced, quality control is more the quality managem