Linux Operating Systems Fundamentals Study Guide: Lessons 1–4

How to use this guide

This guide combines the Lessons 1–4 chapter material. It is organized by lesson so you can connect the shell and its text tools to the software that runs on a system, the hardware and storage underneath it, and the files you manage on top of it.

Study in this order:

1. Learn the vocabulary, commands, and options in the lesson summaries.
2. Explain the key comparisons and decision rules in your own words.
3. Practice the commands in a lab VM, then revisit the high-yield distinctions across the lessons.

Many questions hinge on one exact option letter or one exact path. When a table lists an option, learn what it does and what the similar-looking options do instead.

The ideas that connect all four lessons

Linux administration is a stack of layers, and each lesson adds one:

• Lesson 1 — the shell and text: commands, help, editors, filters, regular expressions, redirection, and pipes.
• Lesson 2 — software and processes: package managers (RPM and Debian families), shared libraries, and running programs.
• Lesson 3 — hardware and storage: firmware, devices, kernel modules, partitions, LVM, filesystems, and mounting.
• Lesson 4 — files: creating, copying, moving, deleting, archiving, linking, securing, and finding files.

One rule appears in every lesson: identify the target first (which shell, which package, which device, which file), then run the command that changes it.

Lesson 1 — Exploring Linux Command-Line Tools

Linux, GNU, and distributions

• The Linux kernel was written by Linus Torvalds. It was not developed as part of the GNU’s Not Unix (GNU) project, but it grew quickly because the GNU tools (compiler, shell, utilities) were already available to build a complete system around it.
• A distribution bundles the kernel, GNU tools, and other software with a package manager and installer.
• Linux runs on many CPU architectures, including x86 (32-bit), x86-64 (64-bit, also called AMD64), and ARM. AMD is a CPU manufacturer and BSD is a separate Unix-like OS — neither is a CPU type.

The shell

• A shell reads your commands and runs them. Bash is the most common default; others include Dash, KornShell, tcsh, and Z shell.
• The prompt is output from the shell. The PS1 environment variable defines the default Bash prompt; its default is usually set in a system file such as /etc/profile or /etc/bashrc, and users can customize it.
• Command history: press the up arrow to recall recently typed commands; history lists them.
• Tab completion finishes command and file names.
• The root user’s home directory is /root. Regular users’ home directories are under /home.
• Internal (builtin) commands such as cd run inside the shell. External commands are programs found by searching the directories in PATH.

Command	Purpose
pwd	Print the working (current) directory
cd	Change directory (cd ~ or just cd goes home)
echo	Display text or a variable’s value
type / which	Show how a command name will be run / where its program is
uname -a	Display kernel, host, and CPU architecture information
uptime	Show current time, how long the system has run, logged-in users, and load averages for the past 1, 5, and 15 minutes
export / env	Export a variable to child processes / list environment variables

Getting help

Tool	What it does
man command	Opens the manual page, displayed through the less pager
man -k keyword	Searches man page names and descriptions — same as apropos keyword
whatis keyword	Searches only the Name sections of man pages (same as man -f)
info command	Hypertext-style GNU documentation
help builtin	Help for shell builtins

Text editors

Editor	Key facts
vi / vim	Modal: command mode (default), insert mode (i), and ex mode (:)
nano	Simple text-mode editor with on-screen shortcuts
emacs	Runs as a text-mode program in a text console and provides a GUI version in a graphical environment
gedit / KWrite	GUI-only editors

vi commands to know:

Keystroke	Effect
i	Enter insert mode; Esc returns to command mode
o / O	Open a new blank line below / above the current line
yy / dd / p	Yank (copy) / delete a line / paste
:w	Save (write) the file — Ctrl+S does not save in vi
:q / :wq / :q!	Quit / save and quit / quit without saving

Watch the letter case: lowercase o opens a line below the cursor and uppercase O opens one above.

Viewing and processing text

Command	Key facts
cat	Display or concatenate files
head / tail	First / last 10 lines by default; use tail -n 20 file for 20 lines; tail -f follows a growing log
less / more	Page through text
cut	Extract fields or characters; the default delimiter is Tab; -d sets another delimiter, -f selects fields
wc	Count lines, words, and characters; -l lines, -w words, -c bytes, -m characters (the character count)
sort / uniq	Sort lines / remove adjacent duplicates
tr	Translate or delete characters
join / paste	Merge files on a shared field / side by side
grep	Print lines matching a pattern
sed	Stream editor for scripted edits

Linux can also modify graphics files from the command line (for example, ImageMagick’s convert), not just text.

Regular expressions

Symbol	Meaning
^	Start of a line
$	End of a line
.	Any single character
*	Zero or more of the preceding item
[abc]	One character from the set
| (ERE)	Alternation — separates two strings where either one may match
+, ?, (), {} (ERE)	One or more, zero or one, grouping, counted repetition

grep -E (historically egrep) enables extended regular expressions.

grep '^root' /etc/passwd
grep -E 'error|warning' app.log

Streams, redirection, and pipes

Every program has three standard streams: STDIN (0), STDOUT (1), and STDERR (2).

Operator	Effect
>	Create or overwrite a file with standard output
>>	Append standard output to a file
2>	Create or overwrite a file with standard error
2>>	Append standard error to a file
&>	Send both standard output and standard error to a file
<	Read standard input from a file
<<	Here document — read input until a marker line
|	Pipe: send one command’s output to the next command’s input

sort < names.txt > sorted.txt
command 2>> errors.log
command > all.log 2>&1
cut -d: -f1 /etc/passwd | sort | uniq
find . -name '*.log' | xargs wc -l

Lesson 1 terms to know

kernel, GNU, distribution, x86, x86-64, shell, Bash, prompt, PS1, history, PATH, builtin, /root, uname, uptime, man, less, apropos, man -k, whatis, info, vi, command mode, insert mode, ex mode, nano, emacs, head, tail, cut, wc, sort, uniq, grep, sed, regular expression, STDIN, STDOUT, STDERR, redirection, pipe, and xargs.

Lesson 2 — Managing Software and Processes

Package systems and distributions

A package manager tracks installed files, versions, and dependencies in a database.

Package format	Used by
RPM (.rpm)	Red Hat Enterprise Linux, Fedora, CentOS, openSUSE, Mandriva
Debian (.deb)	Debian, Ubuntu, Linux Mint
Tarballs (.tgz)	Slackware
ebuilds	Gentoo (source-based Portage system)
pacman	Arch Linux

Low-level tools (rpm, dpkg) work with a single package file. High-level tools (yum/dnf, zypper, apt) use repositories and resolve dependencies automatically.

RPM and YUM

Command	Purpose
rpm -i / -U / -F	Install / upgrade or install / freshen (upgrade only if installed)
rpm -e	Erase (remove) a package
rpm -qi	Query package information
rpm -ql	List files in an installed package
rpm -qlp file.rpm	List files in a package file that has not been installed
rpm -qf /path/file	Which package owns a file
rpm -V	Verify that no installed files have been altered since installation; no output means nothing changed
rpm2cpio pkg.rpm	Convert an RPM to a cpio archive, written to STDOUT by default
yum install / remove / update	Repository-based transactions
yum search / yum info	Search / show details, including a package’s version and release
yumdownloader	Download an RPM without installing it (part of the yum-utils package)

The primary YUM configuration file is /etc/yum.conf; repositories are defined in /etc/yum.repos.d/. Newer RPM systems use dnf, which works the same way.

Debian packages and APT

Command	Purpose
dpkg -i	Install a local .deb — dpkg is the essential low-level Debian tool
dpkg -r / -P	Remove (keep configuration) / purge (remove configuration too)
dpkg -L / -S	List a package’s files / find which package owns a file
apt-get update	Refresh the package lists from repositories
apt-get upgrade	Update installed packages to the latest versions
apt-get install / remove	Install / remove with dependency resolution
apt-cache search zsh	Search package names and descriptions
apt-cache show	Show package details
dpkg-reconfigure	Rerun a package’s configuration

Watch for fake commands: apt-get search and apt-cache locate do not exist.

Shared libraries

A library is a collection of software routines that other programs can use. Its licensing terms matter to programmers who link against it (for example, the LGPL).

Tool or file	Purpose
ldd program	List the shared libraries a program needs
ldconfig	Update the links and cache for shared libraries
ldconfig -n dirs	Process only the directories named on the command line, not those in /etc/ld.so.conf
ldconfig -p	Print the current cache
/etc/ld.so.conf and /etc/ld.so.conf.d/	Library search directories
LD_LIBRARY_PATH	Environment variable adding temporary search directories

Processes

• A process is a running program with a PID. The process that launches another is its parent; the new one is the child. The parent’s ID is the PPID.
• ps (for example, ps aux or ps -ef) takes a snapshot of running processes. top shows a live, sorted view. Both are text-mode tools to identify running processes. (df shows disk space and bg is a job-control command.)
• uname -a identifies the CPU architecture; /proc/cpuinfo and lscpu give full CPU details. free shows memory use.

Foreground, background, and job control

Action	How
Start in the background	Put & after the command: long_command &
List jobs	jobs
Bring a job to the foreground	fg (for example, fg %1)
Suspend the foreground job	Ctrl+Z
Resume a stopped job in the background	bg

Priority and signals

• nice -n 10 command starts a program with lower priority; renice changes a running process. Ordinary users can only lower priority.
• kill PID sends SIGTERM (15) by default; kill -9 PID sends SIGKILL, which cannot be caught. SIGHUP (1) often makes a daemon reload. killall and pkill select processes by name.

Lesson 2 terms to know

package, dependency, RPM, Debian package, tarball, ebuild, rpm, rpm -qlp, rpm -V, rpm2cpio, yum, yum info, yumdownloader, /etc/yum.conf, dnf, dpkg, apt-get, apt-cache search, library, ldd, ldconfig, /etc/ld.so.conf, LD_LIBRARY_PATH, process, PID, parent process, ps, top, &, jobs, fg, bg, nice, renice, kill, SIGTERM, and SIGKILL.

Lesson 3 — Configuring Hardware

Firmware

• BIOS is legacy firmware that usually pairs with MBR partitioning.
• UEFI is modern firmware that usually pairs with GPT and loads a boot loader from the EFI System Partition (ESP), which Linux mounts at /boot/efi. A GPT disk on a UEFI system needs this partition (typically 100–250 MB) to boot.

Devices and the kernel’s view

Location or tool	What it shows
/dev	Device files, such as /dev/sda
/proc/interrupts	Current IRQ assignments (cat /proc/interrupts)
/proc/ioports, /proc/dma	I/O port and DMA assignments
/proc/kallsyms	Available kernel symbols (/proc/ksyms on legacy systems)
/proc/sys/kernel	Kernel settings such as the release number, domain name, and location of modprobe
/sys	Devices, drivers, and buses in the kernel’s device model
lspci	PCI devices; -k shows the kernel driver modules for each device; -n shows vendor and device IDs as numbers
lsusb	USB devices; -t shows them in a tree
lsblk	Block devices (disks and partitions)

Hotplug, coldplug, and udev

• A hotplug device can be connected and removed while the computer runs, such as a USB drive.
• A coldplug device must be installed with the power off, such as a PCI card.
• udev creates device files in /dev as hardware appears. udevadm info queries the udev database about a device, and udevadm monitor shows kernel and udev events in real time.

Kernel modules

Command or file	Purpose
lsmod	List loaded modules
modinfo	Show a module’s details
modprobe	Load a module and its dependencies
modprobe -r	Remove a module and unused dependencies
insmod / rmmod	Load / remove a single module with no dependency handling; rmmod -f forces removal. The course material lists rmmod -w as the option for removing unused modules (older rmmod versions used -w to wait until a module was no longer in use)
/etc/modprobe.d/	Module configuration, including blacklist entries that stop modprobe from loading a module

Disk interfaces and device names

Interface	Linux name
PATA (older IDE)	/dev/hda, /dev/hdb (/dev/hdX)
SATA, SCSI, and USB	/dev/sda, /dev/sdb (/dev/sdX)
NVMe	/dev/nvme0n1, partition /dev/nvme0n1p1

A number after the name is a partition: /dev/sda1 is the first partition on the first SATA/SCSI disk.

Partitioning: MBR versus GPT

MBR	GPT
Up to four primary partitions; one can be an extended partition holding logical partitions	Up to 128 partitions, no primary/extended distinction
Pairs with BIOS	Pairs with UEFI; needs an ESP at /boot/efi to boot
Tools: fdisk, parted	Tools: gdisk, parted, modern fdisk

Common separate partitions: /boot, / (root), /home, /var, and swap.

LVM and RAID

LVM builds flexible storage in three layers:

Step	Command
Initialize a partition as a physical volume (PV)	pvcreate /dev/sdb1
Pool PVs into a volume group (VG)	vgcreate vgdata /dev/sdb1
Carve out a logical volume (LV)	lvcreate -L 10G -n lvapps vgdata
List PVs / VGs / LVs	pvscan or pvdisplay / vgdisplay / lvdisplay

RAID levels: 0 striping (speed, no redundancy), 1 mirroring, 5 single parity, 6 double parity, 10 mirrored stripes. RAID is not a backup.

Filesystems

Filesystem	Notes
ext4	Standard journaling Linux filesystem
XFS, JFS, ReiserFS, Btrfs	Other Linux filesystems suitable for an installation
FAT / VFAT / exFAT	Removable media shared with other systems
NTFS	Windows filesystem
HFS / HFS+	Apple filesystem — an inappropriate choice to hold most of a Linux installation
ISO-9660	Traditional CD-ROM filesystem
UDF	Newer optical format for DVDs and Blu-ray; UDF replaces ISO-9660, not the other way around

Command	Purpose
mkfs -t ext4 /dev/sdb1 or mkfs.ext4	Create a filesystem
mkswap	Prepare a partition as swap space
swapon / swapoff	Enable / disable swap space
mount / umount	Attach / detach a filesystem at a mount point
/etc/fstab	Filesystems to mount at boot; prefer UUID= or LABEL= over device names
fsck	Check and repair a filesystem (unmount it first)
df / du	Free space per filesystem / space used by files and directories
blkid	Show UUIDs, labels, and filesystem types

The initial RAM disk

An initial RAM disk (initramfs/initrd) holds the drivers the kernel needs to reach the root filesystem at boot. On CentOS 6 and later Red Hat–family systems, dracut creates it; older systems used mkinitrd.

Lesson 3 terms to know

BIOS, UEFI, EFI System Partition, /boot/efi, /dev, /proc, /sys, IRQ, /proc/interrupts, /proc/kallsyms, /proc/sys/kernel, lspci -k, lspci -n, lsusb -t, hotplug, coldplug, udev, udevadm info, udevadm monitor, kernel module, lsmod, modprobe, insmod, rmmod, /etc/modprobe.d, blacklist, PATA, SATA, /dev/sdX, MBR, GPT, primary partition, extended partition, LVM, pvcreate, vgcreate, lvcreate, pvscan, RAID, ext4, HFS, ISO-9660, UDF, mkfs, mkswap, swapon, mount, /etc/fstab, fsck, initramfs, and dracut.

Lesson 4 — Managing Files

Filenames and globbing

• Linux filenames are case-sensitive; a leading dot makes a file hidden.
• Globbing is the use of wildcards in filename specifications. The shell expands them before the command runs.

Wildcard	Matches
?	Exactly one character
*	Zero or more characters
[abc], [a-z]	One character from a set or range

Basic file commands

Command	Key facts
ls	Display the names of files in a directory; -l long listing, -a hidden files, -i inode numbers
pwd	Display the directory you are working in
touch file	Create a new empty file if it doesn’t exist, or update the timestamps of an existing one
mkdir -p	Create a directory and any missing parents
cp	Copy; -R/-r recursive (includes subdirectories), -i/--interactive prompt before overwriting, -p/--preserve keep ownership and timestamps, -a/--archive also copies a whole tree
mv	Move or rename; -i prompts before overwriting, -f forces
rm	Delete files; -r recursive, -i prompt, -f force
rmdir	Delete an empty directory

An ordinary user cannot delete any file on the system with rm. Deleting a file requires write and execute permission on the directory that contains it; only root can delete everything.

Example: copy a directory and all its subdirectories to a USB drive.

cp -R ~/important /media/usb

Compression and archives

Tool	Key facts
gzip / gunzip	.gz; fast, but compresses less than bzip2
bzip2 / bunzip2	.bz2; smaller files than gzip, slower
xz / unxz	.xz; usually the smallest files
zip / unzip	.zip; archives and compresses; -9 is maximum compression, -1 fastest
tar	Archives directory trees: c create, x extract, t list, f archive file, v verbose, z gzip, j bzip2, J xz
cpio	Archive tool that reads a file list from standard input
dd	Copies raw blocks (if= input, of= output)

zip -9 trip.zip holiday.tif desc.txt
tar -czvf project.tgz Project/
tar -zxf project.tgz

Links

• A hard link (ln source newname) is a second name for the same inode. It cannot cross filesystems or point to a directory.
• A symbolic link (ln -s target linkname) stores a path to another file. It can cross filesystems and breaks if the target is deleted.

Ownership and permissions

• chown user:group file changes the owner (and group); chgrp group file changes the group only.
• Permissions are read (4), write (2), and execute (1) for the owner, group, and others. chmod 750 file means rwxr-x---.
• Symbolic form: chmod u+x, chmod g-w, chmod o=, chmod a+r.
• umask removes permissions from new files (base 666) and directories (base 777). With umask 022, files are 644 and directories are 755.
• Special bits: SUID (run as the file’s owner), SGID (run as the file’s group, or new files inherit a directory’s group), and the sticky bit (users can delete only their own files in a shared directory like /tmp).

The Filesystem Hierarchy Standard (FHS)

Directory	Contents
/bin, /sbin	Essential commands (often merged into /usr)
/boot	Kernel and boot loader files
/etc	System configuration files
/home	Users’ home directories
/root	Root user’s home directory
/usr	Installed programs that run on the system, plus their libraries and shared data
/var	Changing data: logs, mail queues, caches
/tmp	Temporary files
/opt	Add-on software packages
/media	Mount points for removable media such as USB flash drives (most distributions)
/mnt	Temporary mount point for administrators

Finding files

Command	How it searches
locate	Searches a database of filenames (mlocate.db in /var/lib/mlocate/) for a name or name fragment; refresh it with updatedb
whereis	Searches a limited set of directories for a command’s binary, source, and man page
which	Finds the program that runs from your PATH
find	Searches the live filesystem by any criteria

find tests to know:

Test	Meaning
-name '*.log'	By filename pattern
-user alice / -uid 1000	Files owned by a user (by name or by user ID)
-group / -gid	Files owned by a group
-size +1G	Larger than 1 GB (+ = more than, - = less than; units k, M, G)
-type f / -type d	Regular files / directories
-perm	By permission bits

find / -size +1G
find /home -user alice -type f
find / -perm /6000 -type f 2>/dev/null

Lesson 4 terms to know

case-sensitive, hidden file, globbing, wildcard, ls, pwd, touch, mkdir, cp -R, cp -i, --interactive, mv -i, rm, rmdir, gzip, bzip2, xz, zip -9, tar, cpio, dd, hard link, symbolic link, inode, chown, chgrp, chmod, umask, SUID, SGID, sticky bit, FHS, /usr, /var, /etc, /media, locate, updatedb, whereis, which, find, -user, -uid, and -size.