🔹 Linux System Administration Essentials 🔹 🔹 Command to check Disk… — softwarewala.ss

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🔹 Linux System Administration Essentials 🔹

🔹 Command to check Disk usage?
📌 df -h - Check disk usage in human-readable format.
📌 du -sh <directory> - Check the size of a specific directory.

🔹 Difference between ps -aux & top command?
✅ ps -aux - Provides a snapshot of active processes.
✅ top - Real-time system performance monitoring.

🔹 What are the Ways to check CPU usage?
💻 top | htop | mpstat | vmstat | sar

🔹 How to check CPU details?
📌 lscpu or cat /proc/cpuinfo

🔹 Steps to create a partition & format with a file system?
1️⃣ fdisk /dev/sdX - Create a partition.
2️⃣ mkfs.ext4 /dev/sdX1 - Format the partition.
3️⃣ mount /dev/sdX1 /mnt - Mount the partition.

🔹 Steps to create LV?
1️⃣ pvcreate /dev/sdX
2️⃣ vgcreate vg_name /dev/sdX
3️⃣ lvcreate -L 10G -n lv_name vg_name
4️⃣ mkfs.ext4 /dev/vg_name/lv_name

🔹 Steps to reduce XFS & EXT file systems?
⚠️ XFS: Cannot be reduced directly.
✅ EXT: umount, resize2fs, lvreduce, mount

🔹 Significance of .bashrc file?
📝 User-specific shell configurations & aliases.

🔹 How to check the kernel version?
📌 uname -r

🔹 How to check the Red Hat release version?
📌 cat /etc/redhat-release or cat /etc/os-release

🔹 Significance of resolv.conf file?
🌍 Configures DNS name resolution.

🔹 What is DNS? How to resolve DNS? Types of DNS records?
🔍 DNS translates domain names to IP addresses.
✅ Resolve: nslookup or dig
📌 Types: A, AAAA, CNAME, MX, TXT, PTR

🔹 Difference between Nginx & HTTP Server?
🚀 Nginx: Event-driven | Apache: Process-based

🔹 Port numbers:
🌐 HTTP: 80 | 📂 FTP: 21 | 🔐 SSH: 22 | 🔒 HTTPS: 443

🔹 What is SSH? How to generate SSH-keys?
🔐 Secure Shell protocol for remote access.
📌 Generate keys: ssh-keygen

🔹 What are Private & Public keys? How do they authenticate?
🔑 Private key (kept secret) & Public key (shared).
✅ Authentication via asymmetric encryption.

🔹 Configuration file of SSH?
📌 /etc/ssh/sshd_config

🔹 Configuration file of HTTP?
📌 /etc/httpd/conf/httpd.conf (Apache)

🔹 What is Virtual Hosting? How to configure it?
🌐 Hosting multiple sites on a single server.
📌 Configure using <VirtualHost> in Apache.

🔹 Explain ifconfig command?
🌍 Displays/configures network interfaces.

🔹 Difference between IPv4 & IPv6?
✅ IPv4: 32-bit | ✅ IPv6: 128-bit

🔹 What is a MAC address? Can we change it?
📌 Unique network identifier.
⚠️ Change: ifconfig eth0 hw ether <MAC>

🔹 How to check system uptime?
📌 uptime

🔹 How to check memory information?
📌 free -m | cat /proc/meminfo

🔹 What is SWAP?
🛠️ Virtual memory when RAM is full.

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