EP10: systemctl & Service Management in Linux

🎯 What You’ll Learn

In this episode, you’ll learn how to:

Start, stop, enable, and check services using systemctl
Understand the difference between active and enabled
Troubleshoot service failures
Practice real RHCSA scenarios

🛠 What Is `systemctl`?

systemctl is a command used to control services (also called units) on modern Linux systems using systemd.

✅ RHEL 7 and above (including RHEL 8/9) use systemd as the init system.
✅ For RHCSA, mastering systemctl is a must.

🧠 Real-World Analogy

Think of your Linux system as a factory, and services as machines.

systemctl start = Turn the machine ON now 🟢
systemctl stop = Turn the machine OFF now 🔴
systemctl enable = Tell it to automatically start every morning (at boot) ⏰
systemctl disable = Don't auto-start anymore
systemctl status = Check the machine's health ✅❌

🧪 Common RHCSA Service Management Commands

Action	Command
Start a service now	`sudo systemctl start <service>`
Stop a service	`sudo systemctl stop <service>`
Restart a service	`sudo systemctl restart <service>`
Reload (re-read config)	`sudo systemctl reload <service>`
Enable at boot	`sudo systemctl enable <service>`
Disable at boot	`sudo systemctl disable <service>`
Check status	`systemctl status <service>`

✅ Examples

Start and Enable Apache (httpd)

sudo systemctl start httpd
sudo systemctl enable httpd

Stop and Disable

sudo systemctl stop httpd
sudo systemctl disable httpd

Check Service Status

systemctl status httpd

You’ll see:

Active: active (running) ✅
Or Active: inactive (dead) ❌
Or failed 🔥 if something went wrong

🔍 Check If Service Is Enabled at Boot

systemctl is-enabled httpd

Output:

enabled = will start at boot 🟢
disabled = won’t start at boot 🔴
static = part of another unit, not standalone

📋 List All Running Services

systemctl list-units --type=service --state=running

📋 List All Services (Running or Not)

systemctl list-units --type=service

📋 List Failed Services

systemctl --failed

Very useful for troubleshooting!

🔧 View Logs with `journalctl`

To see service logs (e.g., httpd):

journalctl -u httpd

Add -xe for detailed logs:

journalctl -xe

📂 Service File Location

Most unit files live in:

/usr/lib/systemd/system/

You can view or edit them (not usually needed for RHCSA).

🧠 RHCSA Must-Know Scenario

Install a service:
```
sudo dnf install vsftpd
```
Start it:
```
sudo systemctl start vsftpd
```
Enable it at boot:
```
sudo systemctl enable vsftpd
```
Check status:
```
systemctl status vsftpd
```
Verify:
```
systemctl is-enabled vsftpd
```

⚠️ Troubleshooting Tips

Symptom	What to check
Service not running	`systemctl status`
Logs not showing	`journalctl -u <service>`
Won’t start at boot	Check `is-enabled`
Service fails silently	Try `systemctl restart` or `journalctl -xe`

✅ Summary: Know These Commands!

Purpose	Command
Start now	`systemctl start <svc>`
Stop now	`systemctl stop <svc>`
Restart	`systemctl restart <svc>`
Enable at boot	`systemctl enable <svc>`
Disable at boot	`systemctl disable <svc>`
Check status	`systemctl status <svc>`
View logs	`journalctl -u <svc>`
List services	`systemctl list-units --type=service`