Linux Interview Questions for Beginners and Freshers

A free, open source, Unix-like operating system. Strictly, Linux is the kernel; a distribution such as Ubuntu or Red Hat adds tools and a package manager. It runs most servers and cloud systems.

The core of the operating system. It manages the CPU, memory, devices and processes, and gives programs a controlled way to use the hardware through system calls.

A program that reads your commands and runs them. Bash is the most common. The terminal is the window that displays the shell.

root (UID 0) has full control of the system. Normal users can change only what they have permission for, and use sudo to run single commands with administrator rights.

An absolute path starts at /, as in /home/asha/notes.txt. A relative path starts from the current folder, as in ../notes.txt.

/etc holds system configuration, /var holds changing data such as logs, and /home holds users' personal folders.

ls -a. Hidden files have names that begin with a dot. ls -la adds details.

cp -r src dest copies, mv src dest moves or renames, and rm -r folder deletes. rm is permanent, since there is no recycle bin.

cat prints a whole file, less lets you scroll through long files, head shows the start, and tail shows the end. tail -f follows a file as it grows.

A special file that points to another path, created with ln -s target name. If the target is removed, the link no longer works. A hard link (ln) is another name for the same data.

It is a file. The owner can read, write and execute, the group can read and execute, and others can only read. In numbers, it is 754.

755 is rwxr-xr-x: the owner has full access, and others can read and execute. It suits scripts and folders. 644 is rw-r--r--: the owner can write, and others can only read. It suits normal files.

chmod changes the permissions, and chown changes the owner and group.

| sends the output of one command to the input of another, as in ls | wc -l.

> replaces a file with the output, and >> adds it to the end.

grep "text" file. Add -i to ignore case, -r to search folders, -n for line numbers, and -v to invert the match.

find /path -name "file.txt". -iname ignores case, and -type f restricts it to files.

ps aux lists processes, and top shows them live. kill PID asks a process to stop, and kill -9 PID forces it.

df -h shows free disk space, du -sh folder shows a folder's size, and free -h shows memory.

sudo apt update, and then sudo apt install name. On Red Hat systems, use dnf.