How to Manage Systemd Services with Systemctl? An In-Depth Guide for Linux Admins


Hi friend! As a fellow Linux admin, I know how important it is to master systemd and systemctl. It can seem daunting at first, but with some guidance, you‘ll be a pro in no time!

The default system and service manager for most Linux distributions now is systemd. It replaces the old SysV init system.

Here‘s a quick overview of what systemd does:

• Runs as PID 1, the first process after kernel initialization
• Starts services in parallel for faster boot time
• Manages mount points, devices, sockets, timers, and more
• Provides advanced logging and diagnostics

According to the 2020 StackOverflow developer survey, over 75% of developers now use Linux. As Linux admins, understanding systemd is a must-have skill.

Let‘s dive in and see how to manage services with systemctl!

Units: The Building Blocks of Systemd

The configuration files that tell systemd what to manage are called units. These are located in the /lib/systemd/system directory.

There are several types of units, but for service management we care about .service units. Each service has a unit file defining its configuration.

For example, sshd.service, apache2.service, etc.

Introducing Systemctl: Your Command Line Interface

systemctl is the main tool for controlling systemd and services. It has a ton of options!

Here are some common usages I‘ll cover in this guide:

• Starting, stopping services
• Checking status
• Enabling/disabling services
• Reloading configurations
• And more!

Ok, enough background. Let‘s see systemctl in action.

Start and Stop Services

The most basic operations are starting and stopping services.

To start a service:

# systemctl start service_name

For example starting nginx:

# systemctl start nginx

To stop a running service:

# systemctl stop service_name 

Stopping nginx:

# systemctl stop nginx

Easy right? By default, systemctl will look for a .service file matching the service name you specify.

Restart and Reload Services

Sometimes you need to restart a service after making config changes. Use restart for this:

# systemctl restart service_name

Restarting nginx to apply config changes:

# systemctl restart nginx

If you only need to reload the config file without a full restart, use reload:

# systemctl reload service_name

Reloading nginx config:

# systemctl reload nginx 

Reload just rereads the config file. Restart stops and starts the process which has more overhead, so use reload when you can.

Check Service Status

While a service is running, you can check its status with:

# systemctl status service_name

For example, when nginx is running you would see:

● nginx.service - A high performance web server and a reverse proxy server
   Loaded: loaded (/usr/lib/systemd/system/nginx.service; enabled; vendor preset: disabled)
   Active: active (running) since Fri 2022-01-28 20:13:23 UTC; 41min ago
     Docs: man:nginx(8)
 Main PID: 2809 (nginx)
    Tasks: 2 (limit: 1137)
   Memory: 5.4M
   CGroup: /system.slice/nginx.service
           ├─2809 nginx: master process /usr/sbin/nginx -g pid /run/nginx.pid; error_log stderr;
           └─2810 nginx: worker process               

This shows the service is active and running. The main PID and task counts are also shown.

If the service is stopped, you‘ll see Active: inactive (dead) instead.

Enable Persistent Services

By default, services are started manually and not on boot. To start a service automatically on boot, enable it:

# systemctl enable service_name

For example, enabling nginx auto-start:

# systemctl enable nginx

To disable automatic start:

# systemctl disable service_name

Disabling nginx from auto-start:

# systemctl disable nginx

This way you can choose which services start on boot.

View System State and List Units

Beyond individual services, you can query systemd for high-level info.

To see all available unit types:

# systemctl -t help

This will show:

  Available unit types:
    service
    socket
    target
    device
    mount
    automount
    swap
    timer
    path
    slice
    scope

To show all installed unit files:

# systemctl list-unit-files

Sample output:

UNIT FILE                                     STATE   
proc-sys-fs-binfmt_misc.automount             static  
dev-hugepages.mount                           static  
dev-mqueue.mount                              static  
...
accounts-daemon.service                       enabled 
acpid.service                                 enabled
...
nginx.service                                 enabled
postgresql.service                            enabled 
...

This lists all units and their state (enabled, disabled, static, etc).

To filter for just services:

# systemctl list-unit-files --type=service

And to show only active units:

# systemctl list-units

Conclusion

I hope this overview helps you feel more confident managing services with systemctl! Let me know if you have any other questions. Systemd may seem complex at first, but with a bit of practice you‘ll be a pro in no time!

If you liked this guide and want to take your Linux skills to the next level, I highly recommend checking out this Linux Mastery course. It goes deep into system administration including systemd, networking, security, scripting, containers and more.

Anyway, thanks for reading and let me know if you have any other Linux topics you‘d like me to cover!