> For the complete documentation index, see [llms.txt](https://mrinalghimire.com.np/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mrinalghimire.com.np/assignment-1/assignment-1-solution.md).

# Assignment 1 - Solution

**Author:** Mrinal Ghimire

## 1. SSH to the Server

### Objective

Securely connect to a Linux server using SSH authentication with the **ubuntu** user by using an RSA public/private key pair.

{% stepper %}
{% step %}

### Generate an RSA Key Pair (Local Machine)

```bash
ssh-keygen -t rsa -b 4096
```

Press **Enter** to save the key in the default location (`~/.ssh/id_rsa`).

This creates:

* `~/.ssh/id_rsa` (Private Key - keep secret)
* `~/.ssh/id_rsa.pub` (Public Key - copy to the server)
  {% endstep %}

{% step %}

### View the Public Key

```bash
cat ~/.ssh/id_rsa.pub
```

Copy the entire output.
{% endstep %}

{% step %}

### Add the Public Key to the Remote Server

Login to the remote server using a password (or console access):

```bash
ssh ubuntu@192.168.1.20
```

Create the SSH directory if it doesn't exist:

```bash
mkdir -p ~/.ssh
chmod 700 ~/.ssh
```

Open the authorized keys file:

```bash
nano ~/.ssh/authorized_keys
```

Paste the copied public key, save, then set permissions:

```bash
chmod 600 ~/.ssh/authorized_keys
```

{% endstep %}

{% step %}

### Connect Using SSH

From your local machine:

```bash
ssh ubuntu@192.168.1.20
```

#### Verify

```bash
whoami
hostname
```

Expected user:

```
ubuntu
```

{% endstep %}
{% endstepper %}

### Why SSH Keys?

* More secure than passwords
* Password-less authentication
* Resistant to brute-force attacks
* Standard practice for Linux server administration

## 2. System Information

### a) CPU Cores

```bash
lscpu
nproc
```

### b) Memory

```bash
free -h
```

### c) Total Disk Space

```bash
df -h
```

### d) Disk Partitions

```bash
lsblk
```

### e) Private IP

```bash
hostname -I
```

### f) Hostname

```bash
hostname
```

### g) OS Name

```bash
cat /etc/os-release
```

### h) Kernel Version

```bash
uname -r
```

## 3. Check Cron

```bash
systemctl status cron
crontab -l
cat /etc/crontab
```

Purpose: Schedule automated tasks like backups, updates and log rotation.

## 4. Listening Ports

```bash
sudo ss -tulnp
```

## 5. Check Web Server

```bash
systemctl status nginx
systemctl status apache2
curl localhost
```

## 6. Find Users

```bash
awk -F: '$3>=1000 {print $1}' /etc/passwd
```

## 7. Ubuntu User Status

```bash
sudo chage -l ubuntu
sudo passwd -S ubuntu
```

## 8. Find `.sh` Files

```bash
find / -type f -name "*.sh" 2>/dev/null
```

## 9. Synchronize Time

```bash
sudo apt update
sudo apt install chrony -y
sudo systemctl enable chrony
sudo systemctl start chrony
sudo timedatectl set-timezone Asia/Kathmandu
timedatectl
```

## 10. Backup Script

```bash
grep -Ri "/data" /etc /home 2>/dev/null
```

Example:

```bash
#!/bin/bash
DATE=$(date +%F)
tar -czf /backup/data-$DATE.tar.gz /data
```

## 11. CPU Usage

```bash
top
htop
mpstat
```

Consider CPU utilization, load average, I/O wait, idle time and CPU cores.

## 12. Last Boot

```bash
who -b
uptime -s
```

## 13. Update System

```bash
sudo apt update
apt list --upgradable
sudo apt upgrade
sudo apt autoremove
```

## 14. Permissions

```bash
ls -ld /test
getfacl /test
```

## 15. Save Documentation

```bash
mkdir -p /home/ubuntu/Mrinal
nano /home/ubuntu/Mrinal/revision.txt
```


---

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