Working with Linux is mostly about using commands — and knowing what they do, how to tweak them with flags, and where things live on disk. This article collects the fundamentals you’ll use every day: how flags and manuals work, how to create/copy/move/delete files and folders, how to read permissions and switch users, and what the important root directories (/etc, /var, /root, /tmp) contain and mean for security.
TL;DR
Flags change a command’s behaviour (-a vs --all). Use --help and man to learn options.
Create files with touch, directories with mkdir. Copy with cp, move/rename with mv, delete with rm.
Read permissions with ls -l (r, w, x for owner/group / others). Use su or su -l to switch users.
/etc holds config (sensitive), /var holds logs/data, /root is root’s home, /tmp is world-writable (sticky bit).
1) Flags, switches, and manuals — how commands accept options
Short-form flags start with a single hyphen followed by a letter: -a.
Long form switches start with two hyphens and full words: --all.
Quick ways to learn a command:
ls --help
man ls
Example: ls lists directory contents by default. ls -a or ls —all shows hidden files (those that begin with .).
2) Filesystem basics — create, copy, move, delete, inspect
Create files and directories
touch note
mkdir mydirectory
touch makes a blank file; use echo, cat >, or a text editor (nano, vim) to add content.
Copy and move
cp source_file dest_file
cp -r source_dir dest_dir
mv oldname newname
mv file.txt /path/to/folder/
Remove (be careful)
rm file.txt
rm -R directory_name
rm -i file.txt
Determine a file’s type
file filename
3) Permissions 101 — reading
ls -l
Run:
ls -lh
Sample line:
-rw-r--r-- 1 alice developers 1024 Feb 19 10:37 note
Breakdown:
First character: file type (- file, d directory, l symlink).
Next nine characters: permissions in three groups of three:
Permission symbols: r (read), w (write), x (execute), - (no permission).
Useful commands:
stat file.txt
chmod 644 file.txt
chmod 755 script.sh
sudo chown user:group file.txt
4) Switching users
su allows you to become another user (requires that user’s password unless you are root).
su user2
su -l user2
su --login user2
su -l drops you into the target user’s home and loads their login environment (PATH, shell init files, etc.).
5) Common root directories — purpose, importance, and quick checks
/etc
— system configuration
Stores service and system config: network, auth, service configs.
Files of interest: /etc/passwd (accounts metadata), /etc/shadow (password hashes, root-only), /etc/sudoers and /etc/sudoers.d (sudo rules).
ls -l /etc | head
cat /etc/passwd
sudo cat /etc/shadow
Security note: /etc/shadow is sensitive — access implies root-level compromise.
/var
— variable data and logs
Contains logs (/var/log), caches, databases, spool files.
Logs show system and app activity — useful for debugging and auditing.
ls -lh /var/log | head
sudo tail -n 200 /var/log/syslog
sudo journalctl -n 200
Security note: misconfigured apps may leak secrets into logs.
/root
— root user’s home
- The admin’s home directory. Not /home/root.
ls -la /root
Security note: if you can read /root, you likely have root access.
/tmp
— temporary files (world-writable)
Meant for short-lived files; usually cleared on reboot.
Typically has sticky bit: drwxrwxrwt — anyone can create files, only owner/root can delete them.
ls -ld /tmp
[ -w /tmp ] && echo "/tmp writable" || echo "/tmp not writable"
mktemp /tmp/mytmp.XXXXXX
Security note: never trust scripts or files placed in /tmp; prefer mktemp for temporary files.
6) Compact cheatsheet (copy/paste)
<cmd> --help
man <cmd>
touch file.txt
mkdir folder
cp source dest
cp -r sourcedir destdir
mv oldname newname
rm file.txt
rm -R directory_name
rm -i file.txt
file file.txt
ls -lh
ls -la
stat file.txt
chmod 644 file.txt
chmod 755 script.sh
sudo chown user:group file.txt
su otheruser
su -l otheruser
ls -l /etc /var /root /tmp
ls -lh /var/log | head
sudo tail -n 200 /var/log/syslog
ls -ld /tmp
sudo find / -perm -4000 -type f 2>/dev/null | head
sudo find / -xdev -type d -perm -0002 -ls 2>/dev/null | head
7) Security reminders & best practices
Treat /etc/shadow, SSH keys, and config files as high-value targets. Protect them.
rm -R (or rm -rf) is destructive — double-check paths before running.
Use mktemp to create unpredictable temporary filenames (avoid race conditions).
Logs in /var/log may contain secrets; don’t expose them in public repos.
Prefer sudo for temporary elevation; avoid running a long-lived root shell unless necessary.
8) Example workflow (quick practical scenario)
- Inspect the current directory and hidden files:
ls -la
- Create a workspace, move a file into it, and verify:
mkdir workspace
mv note workspace/
ls -lh workspace
- Check if the file is text and read it:
file workspace/note
cat workspace/note
- If you need elevated config access, view /etc/sudoers safely:
sudo visudo
Final notes
This guide gives you a concise, practical foundation: flags and manuals, the basic file operations you’ll use daily, how to read and change permissions safely, and the root directories you should know about.
