comptia-a-plus-core2/notes/OS-9-linux-client-tools.md

OS-9: Linux Client Tools

Status: not started

Domain:

• 1.0 Operating Systems

Objective alignment:

• 1.9 Linux client tools

What You Need To Know

Linux questions on Core 2 usually test:

• Basic file navigation
• Permissions and ownership
• Important configuration files
• Package managers
• Network commands
• Process and disk usage commands
• The difference between normal user and root/admin actions

Memory Tricks

Command buckets:

• Files: ls, pwd, mv, cp, rm, find, cat
• Permissions: chmod, chown, sudo, su
• Network: ip, ping, curl, dig, traceroute
• System: top, ps, df, du, mount, fsck
• Help: man

Key files:

• /etc/passwd: user account list
• /etc/shadow: password hashes
• /etc/hosts: local name-to-IP mappings
• /etc/resolv.conf: DNS resolver settings
• /etc/fstab: file systems mounted at boot

Memory hook:

• PASS users, SHADOW passwords, HOSTS names, RESOLV DNS, FSTAB mounts.

Linux Concepts

Root:

• The all-powerful administrative account.
• User ID 0.

sudo:

• Runs one command with elevated privileges.
• Safer than staying logged in as root.

su:

• Switches to another user, often root.
• You remain that user until you exit.

Kernel:

• Core of the operating system.
• Manages hardware, memory, and processes.

Bootloader:

• Starts the operating system during boot.

systemd:

• System and service manager.
• Starts and manages services, login sessions, logging, and other system processes.

Commands To Enter

Safe commands:

pwd

What it does:

• Prints the current working directory.

ls

What it does:

• Lists files and directories.

ls -l

What it does:

• Lists files with permissions, owner, group, size, and date.

cat /etc/os-release

What it does:

• Shows Linux distribution details.

cat /etc/passwd

What it does:

• Shows local user account entries.
• Each line includes username, UID, GID, home directory, and shell.

cat /etc/hosts

What it does:

• Shows local hostname-to-IP mappings.

cat /etc/resolv.conf

What it does:

• Shows DNS resolver settings.

cat /etc/fstab

What it does:

• Shows file systems configured to mount at startup.

grep root /etc/passwd

What it does:

• Searches /etc/passwd for lines containing root.

find . -name "*.txt"

What it does:

• Finds .txt files under the current directory.

ip addr

What it does:

• Shows network interfaces and IP addresses.

ip route

What it does:

• Shows routes, including the default gateway.

ping -c 4 127.0.0.1

What it does:

• Sends four pings to the local loopback address.

curl https://example.com

What it does:

• Retrieves data from a URL.

dig example.com

What it does:

• Queries DNS for detailed domain information.
• If dig is not installed, try nslookup example.com.

traceroute example.com

What it does:

• Shows the route packets take to a destination.
• If not installed, use tracepath example.com if available.

top

What it does:

• Shows live process and resource usage.
• Press q to quit.

ps aux

What it does:

• Shows running processes.

df -h

What it does:

• Shows mounted file systems and free space in human-readable units.

du -h

What it does:

• Shows disk usage for files/directories.

man grep

What it does:

• Opens the manual page for grep.
• Press q to quit.

Practice File Commands

Use these in a temporary folder:

mkdir linux-practice
cd linux-practice
echo "Core 2 Linux practice" > notes.txt
cp notes.txt copy.txt
mv copy.txt renamed.txt
ls -l
grep Linux notes.txt
chmod u+x renamed.txt
ls -l
cd ..
rm -r linux-practice

What they do:

• mkdir creates a directory.
• cd changes directory.
• echo ... > file writes text to a file.
• cp copies a file.
• mv moves or renames a file.
• grep searches inside a file.
• chmod u+x adds execute permission for the owner.
• rm -r removes a directory and its contents.

Admin Commands To Know

Do not run these casually on important systems:

sudo chown user:group file

What it does:

• Changes file owner/group.

sudo apt update
sudo apt install package-name

What it does:

• Updates package lists and installs software on Debian/Ubuntu-based systems.

sudo dnf install package-name

What it does:

• Installs software on Fedora/Red Hat-based systems.

sudo fsck /dev/device

What it does:

• Checks and repairs a file system.
• Usually run on unmounted or read-only volumes.

sudo mount /dev/device /mnt

What it does:

• Mounts a storage device to a directory.

Windows Comparisons

• ls is like dir.
• pwd is like checking your current path in Command Prompt/PowerShell.
• top and ps are like Task Manager process views.
• df -h is like checking drive free space.
• fsck is like chkdsk.
• traceroute is like Windows tracert.
• dig is like nslookup, but usually more detailed.

Mini Lab

Goal:

• Practice common Linux commands safely.

Linux:

1. Run cat /etc/os-release.
2. Run pwd.
3. Run ls -l.
4. Run cat /etc/passwd.
5. Run cat /etc/hosts.
6. Run cat /etc/resolv.conf.
7. Run ip addr.
8. Run ip route.
9. Run df -h.
10. Run ps aux.
11. Run top, then press q.
12. Create and remove the linux-practice folder from the practice command section.

Record:

• Distribution:
• Current directory:
• Current user:
• DNS server:
• Default gateway:
• Root filesystem free space:
• One running process:
• What permission changed after chmod u+x:

Windows comparison:

1. Run dir.
2. Run taskmgr.
3. Run tracert example.com.
4. Run nslookup example.com.
5. Record which Linux commands match those Windows tools.

Quick Check Before Quiz

You are ready for the OS-9 quiz when you can answer these without looking:

• Which file lists user accounts?
• Which file stores password hashes?
• Which command changes file permissions?
• Which command shows live process/resource usage?
• Which command shows disk free space?
• Which package manager is common on Ubuntu/Debian?
• Which command gives help/manual pages?