17_Appendix_Quick_Reference – cjeledu

Practical Professional Linux

Every command here appears in the chapters. Use this as a fast lookup once concepts are familiar. A leading sudo indicates administrative rights are required.

Navigation & Files

Command	What it does
pwd	Print the current directory.
ls -lah	List all files, long form, human-readable sizes.
cd – / cd ~	Previous directory / home directory.
cp -r src dst	Copy (recursively for directories).
mv a b	Move or rename.
rm -i / rm -r	Remove (prompt) / remove a directory tree.
mkdir -p a/b/c	Create a nested directory tree.
ln -s target link	Create a symbolic link.

Viewing & Searching Text

Command	What it does
cat / less file	Show a file / page through it (q to quit).
head -n N / tail -n N	First / last N lines.
tail -f file	Follow a file live.
grep -ri term path	Recursive, case-insensitive content search.
grep -v ‘^#’ file	Show non-comment lines.
sed ‘s/old/new/g’ f	Stream search-and-replace.
awk ‘{print $1}’ f	Print the first field of each line.
sort \| uniq -c \| sort -rn	Count and rank duplicates.

Permissions & Ownership

Command	What it does
ls -l / ls -Z	Show permissions / SELinux context.
chmod 644 / 755 / 600	Common file / dir / secret modes.
chmod u+x file	Add execute for the owner.
chown -R user:group path	Recursively set ownership.
chmod 2775 dir	Setgid shared directory.

Users, Groups & Privilege

Command	What it does
id / groups	Show your IDs and group memberships.
sudo useradd -m -s /bin/bash u	Create a user with a home + shell.
sudo passwd u	Set a user’s password.
sudo usermod -aG group u	Append a user to a group.
sudo userdel -r u	Remove a user and their home.
sudo visudo	Safely edit sudo privileges.

Packages

Command	What it does
sudo apt update && sudo apt install -y pkg	Refresh and install (Ubuntu/Debian).
sudo dnf install pkg	Install (Rocky/Alma/RHEL).
apt search / dnf search term	Find a package.
sudo apt upgrade -y / sudo dnf upgrade -y	Apply updates.
sudo apt purge pkg	Remove a package and its config.

Processes & Services

Command	What it does
ps aux –sort=-%cpu \| head	Top CPU processes.
top / htop	Live process view.
kill PID / kill -9 PID	Polite / forceful stop.
pgrep name / pkill name	Find / signal by name.
sudo systemctl enable –now svc	Start now and at boot.
systemctl status svc	Service state + recent logs.
journalctl -u svc -e / -f	Service logs: end / follow.

Networking

Command	What it does
ip addr / ip route	Interfaces / routing.
ss -tulpn	Listening ports + processes.
dig name +short	Resolve a name to an IP.
ping -c 4 host	Test reachability.
curl -I url	Check a web service responds.
nc -zv host port	Test a TCP port.

Storage & Archives

Command	What it does
lsblk / blkid	Block devices / UUIDs.
df -h / du -sh path	Free space / directory size.
sudo mkfs.ext4 /dev/sdXN	Create an ext4 filesystem (erases!).
sudo mount -a	Mount all fstab entries (test).
tar -czf a.tgz dir / tar -xzf a.tgz	Create / extract a gzip archive.
rsync -a –delete src/ dst/	Mirror a directory.

Scripting & Scheduling

Command	What it does
#!/bin/bash	Shebang — selects the interpreter.
set -euo pipefail	Strict mode for safe scripts.
chmod +x script.sh	Make a script executable.
crontab -e / crontab -l	Edit / list scheduled jobs.
systemctl list-timers	List systemd timers.