systemd – Booting Process

Before going through the booting process, make sure that you know something about systemd. If you are not sure, you may refer here and then come back.

While a system is booted up by starting the RHEL 7 kernel and initial ram disk, systemd initializes the system, starting all the system services. There involves a structure for the boot process.
There are many files that depend on the boot process structure, starting with file.

1. ls -l /usr/lib/systemd/system/ will show you that this file is actually a symlink to another file

lrwxrwxrwx. 1 root root 16 Mar 24  2014 /usr/lib/systemd/system/ ->

This means executing file automatically invokes file.

2. Now, take a look at this file by vi /usr/lib/systemd/system/
You can see the three lines as shown below:

As per this file, systemd starts everything in the before starting this. “Wants” tells systemd to start the display-manager.service service after

3. It starts every service that are expected to run in RHEL multi user mode.
vi /usr/lib/systemd/system/ gives you a line as shown below:


which means systemd should start everything in prior starting services in All the services included here, actually has symlinks associated, which point to the location of the service.

4. Starts the basic services like firewalld and microcode services.
vi /usr/lib/systemd/system/ will give you a line as shown below:

Which means should be started first before proceeding with

5. As per this file, systemd starts system initialization services. This includes swap devices enabling and file systems mounting. needs to be started before since
vi /usr/lib/systemd/system/ shows you:

6. This is set to run after target based on the line below:

No services has been associated with, however units in directory import the network configuration from the initramfs, run a file system check (fsck) on the root file system when necessary, and remount the root file system based on the contents of the /etc/fstab file.

This is the structure of boot process by built by systemd. But keep in mind that this is not the way how systemd actually works 😀 .
Yes, you read it true. systemd actually runs in the opposite order of how the process is built 🙂 .
Which simply means that the order of booting up is as follows:




One thought on “systemd – Booting Process

  1. Thanks for the sensible critique. Me & my neighbor were just preparing to do a little research about this. We got a grab a book from our area library but I think I learned more from this post. I’m very glad to see such wonderful info being shared freely out there.


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