Initial Core 2 study project

notes/OS-9-linux-client-tools.md

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+# 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:
+
+```bash
+pwd
+```
+
+What it does:
+- Prints the current working directory.
+
+```bash
+ls
+```
+
+What it does:
+- Lists files and directories.
+
+```bash
+ls -l
+```
+
+What it does:
+- Lists files with permissions, owner, group, size, and date.
+
+```bash
+cat /etc/os-release
+```
+
+What it does:
+- Shows Linux distribution details.
+
+```bash
+cat /etc/passwd
+```
+
+What it does:
+- Shows local user account entries.
+- Each line includes username, UID, GID, home directory, and shell.
+
+```bash
+cat /etc/hosts
+```
+
+What it does:
+- Shows local hostname-to-IP mappings.
+
+```bash
+cat /etc/resolv.conf
+```
+
+What it does:
+- Shows DNS resolver settings.
+
+```bash
+cat /etc/fstab
+```
+
+What it does:
+- Shows file systems configured to mount at startup.
+
+```bash
+grep root /etc/passwd
+```
+
+What it does:
+- Searches `/etc/passwd` for lines containing `root`.
+
+```bash
+find . -name "*.txt"
+```
+
+What it does:
+- Finds `.txt` files under the current directory.
+
+```bash
+ip addr
+```
+
+What it does:
+- Shows network interfaces and IP addresses.
+
+```bash
+ip route
+```
+
+What it does:
+- Shows routes, including the default gateway.
+
+```bash
+ping -c 4 127.0.0.1
+```
+
+What it does:
+- Sends four pings to the local loopback address.
+
+```bash
+curl https://example.com
+```
+
+What it does:
+- Retrieves data from a URL.
+
+```bash
+dig example.com
+```
+
+What it does:
+- Queries DNS for detailed domain information.
+- If `dig` is not installed, try `nslookup example.com`.
+
+```bash
+traceroute example.com
+```
+
+What it does:
+- Shows the route packets take to a destination.
+- If not installed, use `tracepath example.com` if available.
+
+```bash
+top
+```
+
+What it does:
+- Shows live process and resource usage.
+- Press `q` to quit.
+
+```bash
+ps aux
+```
+
+What it does:
+- Shows running processes.
+
+```bash
+df -h
+```
+
+What it does:
+- Shows mounted file systems and free space in human-readable units.
+
+```bash
+du -h
+```
+
+What it does:
+- Shows disk usage for files/directories.
+
+```bash
+man grep
+```
+
+What it does:
+- Opens the manual page for `grep`.
+- Press `q` to quit.
+
+## Practice File Commands
+
+Use these in a temporary folder:
+
+```bash
+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:
+
+```bash
+sudo chown user:group file
+```
+
+What it does:
+- Changes file owner/group.
+
+```bash
+sudo apt update
+sudo apt install package-name
+```
+
+What it does:
+- Updates package lists and installs software on Debian/Ubuntu-based systems.
+
+```bash
+sudo dnf install package-name
+```
+
+What it does:
+- Installs software on Fedora/Red Hat-based systems.
+
+```bash
+sudo fsck /dev/device
+```
+
+What it does:
+- Checks and repairs a file system.
+- Usually run on unmounted or read-only volumes.
+
+```bash
+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?
+