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Interview Questions and Answers

Unix is a proprietary operating system, while Linux is an open-source kernel. Linux distributions (e.g., Ubuntu, Fedora) are Unix-like operating systems based on the Linux kernel. Linux is inspired by, and mostly POSIX compliant with, Unix.

The boot process typically involves: BIOS/UEFI initialization, bootloader (e.g., GRUB) loading, kernel loading, initialization of system services (init or systemd), and login prompt. Systemd is the most popular init system, now. Older systems may use SysVinit or Upstart.

SELinux (Security-Enhanced Linux) is a security module that provides mandatory access control (MAC). It is configured using `semanage` and its behavior is controlled by policy files. Disable with care. Understanding the policy is key.

Firewalls are configured using tools like `iptables` (legacy, but still used) or `firewalld` (more modern). You can define rules to allow or deny traffic based on source/destination IP addresses, ports, and protocols.

Processes are managed using commands like `ps` (to view processes), `kill` (to terminate processes), `top` and `htop` (to monitor processes), and `nice` and `renice` (to adjust process priority).

Log files record system events, errors, and other important information. They are crucial for troubleshooting, security auditing, and performance analysis. Common log files include `/var/log/syslog`, `/var/log/messages`, `/var/log/auth.log`, and application-specific logs.

Use tools like `ping`, `traceroute`, `netstat`, `tcpdump`, and `nslookup`. Check firewall rules, DNS settings, routing tables, and network interface configurations. Look for errors in system logs.

Common backup methods include: using `tar` to create archives, `rsync` for incremental backups, and specialized backup software. Restoration involves extracting archives or using the restore functionality of the chosen backup tool. Consider using offsite storage.

SSH (Secure Shell) is a protocol for secure remote access to a system. You use the `ssh` command followed by the username and hostname or IP address of the remote system (e.g., `ssh user@hostname`). SSH keys provide passwordless authentication.

Use tools like `top`, `htop`, `vmstat`, `iostat`, `netstat`, `sar`, and `dstat`. Also monitoring logs (`/var/log/`) is essential. Tools like Nagios, Zabbix, and Prometheus provide more comprehensive monitoring solutions.

Software can be installed using package managers like `apt` (Debian/Ubuntu), `yum` (Red Hat/CentOS), `dnf` (Fedora), or `pacman` (Arch Linux). Alternatively, you can compile software from source code using `configure`, `make`, and `make install`.

Network interfaces are configured through configuration files (e.g., `/etc/network/interfaces` on Debian/Ubuntu, `/etc/sysconfig/network-scripts/ifcfg-*` on Red Hat/CentOS). You can also use command-line tools like `ifconfig` (deprecated) or `ip` to manage interfaces.

Common practices include: using strong passwords, regularly updating software and security patches, configuring firewalls (e.g., `iptables`, `firewalld`), disabling unnecessary services, using SSH keys for authentication, implementing intrusion detection systems (IDS), and regularly reviewing system logs.

Tasks can be scheduled using `cron`. You can edit the system-wide crontab (`/etc/crontab`) or a users crontab (`crontab -e`). Crontab entries specify the time and command to execute.

Troubleshooting steps include: checking CPU usage (`top`, `htop`), memory usage (`free`, `vmstat`), disk I/O (`iostat`), network activity (`netstat`, `tcpdump`), examining system logs (`/var/log/syslog`, `/var/log/messages`), and identifying resource-intensive processes. Analyzing application logs can also be helpful.

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 for patterns), `find` (find files), `ps` (process status), `kill` (kill processes), `df` (disk free space), `du` (disk usage), `top` (system monitoring), `ping` (network connectivity), and `ssh` (secure shell).

A Unix administrator is responsible for managing and maintaining Unix-based systems, ensuring their security, availability, and performance. This includes tasks like user management, software installation, system configuration, troubleshooting, and security patching.

Essential skills include: strong understanding of Unix/Linux operating systems, command-line proficiency, scripting (Bash, Python, etc.), networking knowledge (TCP/IP, DNS, routing), security principles, system monitoring and troubleshooting, user management, and backup/recovery procedures.

Users are managed with commands like `useradd`, `usermod`, and `userdel`. Groups are managed with `groupadd`, `groupmod`, and `groupdel`. The `/etc/passwd` and `/etc/group` files (or LDAP, Active Directory, etc.) store user and group information. Use `passwd` to set or change user passwords.

File permissions are managed using the `chmod` command. You can use numeric mode (e.g., `chmod 755 file`) or symbolic mode (e.g., `chmod u+rwx,go+rx file`). The `chown` command changes file ownership, and `chgrp` changes the group ownership.

Filters:- filters are the set of commands that take input from standard input stream i.e. stdin, perform some operations and write output to standard output stream i.e. stdout.

- Piping:- Piping is used to give the output of one command (written o

The Unix file system is a logical technique of organizing and storing huge volumes of data in an easy-to-manage fashion. A file is the smallest unit of storage for information. All of the files are separated into folders. The file system is a tree-like st

System calls in Unix are used for file system control, process control, interprocess communication etc. The primary distinction between a system call and a library call is that a system call is a function supplied by the kernel to enter kernel mode in ord

: Normally, the newline character, which is generated by the ENTER or RETURN key, acts as the signpost. The semicolon and ampersand characters, on the other hand, can be used as command terminators.

Explain with examples that sync with the job description.

Explain specific instances with respect to the job JD.

A good software engineer is someone who is not only competent to write code but also competent to create, produce and ship useful software.

NA

Use a phased life-cycle plan, Continuous validation, Maintain product control, Use the latest programming practices, Maintain clear accountability for results

Software engineering always requires a fair amount of teamwork. The code needs to be understood by designers, developers, other coders, testers, team members and the entire IT team

Schedule, Quality, Cost, Stakeholder Satisfaction, Performance

: 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

NA

Functional requirements are the specifications explicitly requested by the end-user as essential facilities the system should provide. Non-functional requirements are the quality constraints that the system must satisfy according to the project contract,

Pseudocode is an informal high-level explanation of the operating principle of a computer program. It uses the structural conventions of a normal programming language but is intended for human reading rather than machine reading

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