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Ask the Argus

Booting Sandbox Part III

Experimenting With fstab

Synopsis

In this entry I refer again to the lab Shevek has made me, found at the bottom of this page. As has been the case with this particular sandbox, there is no guide or context, so I have Shevek make me a lesson plan and guide. Of all the booting labs thus far, this one actually works the way Shevek intended. We explore modifying /etc/fstab, remdiate the fault, and dive into the mechanics of systemctl.

Questions & Objectives
  1. I want to understand what fstab is and it's role in booting.
  2. I will deliberately miscofigure fstab to see it's effects.
  3. I will then reconfigure the system so that it is returned to normal operation.
  4. What is the nature of systemctl?
Process

    1. As the sandbox has been a huge dissapointment with regards to interactiveness, I immediately just have Shevek make me a guided lesson for this section of the lab: fstab. I will say this, I at least appreciate that he is having me do this in the order of the boot chain so I become more familiar with it.

      fstab Lesson Plan 1

      fstab Lesson 1
      fstab lesson 1

      fstab Lesson Plan 2

      fstab Lesson 2
      fstab lesson 2

      fstab Lesson Plan 3

      fstab Lesson 3
      fstab lesson 3

      fstab Lesson Plan 4

      fstab Lesson 4
      fstab lesson 4

      fstab Lesson Plan 5

      fstab Lesson 5
      fstab lesson 5

      fstab Lesson Plan 6

      fstab Lesson 6
      fstab lesson 6

      fstab Lesson Plan 7

      fstab Lesson 7
      fstab lesson 7

      fstab Lesson Plan 8

      fstab Lesson 8
      fstab lesson 8

    2. I follow Sheveks instructions and the lab functions as intended. I have to become root before I can modify the file. I then access /etc/fstab and add a mount to the mix. Next, I reboot to see the results. I remount root as writtable, then I access /etc/fstab and change it back to it's original state. Lastly, I tell systemd to continue boot with systemctl.

      Modifying fstab 1

      Modifying fstab 1
      Modifying fstab 1

      Modifying fstab 2

      Modifying fstab 2
      Modifying fstab 2

      Modifying fstab 3

      Modifying fstab 3
      Modifying fstab 3

      Modifying fstab 4

      Modifying fstab 4
      Modifying fstab 4

      Modifying fstab 5

      Modifying fstab 5
      Modifying fstab 5

      Modifying fstab 6

      Modifying fstab 6
      Modifying fstab 6

      Modifying fstab 7

      Modifying fstab 7
      Modifying fstab 7

      Modifying fstab 8

      Modifying fstab 8
      Modifying fstab 8

      Modifying fstab 9

      Modifying fstab 9
      Modifying fstab 9

      Modifying fstab 10

      Modifying fstab 10
      Modifying fstab 10

      Modifying fstab 11

      Modifying fstab 11
      Modifying fstab 11

    3. And it's that simple. Things went smoothly for a change, but I still have questions about what exactly I am doing when I use systemctl. I have Shevek break it down for me. It would appear systemctl is a means of controlling systemd.

      systemctl Explained 1

      systemctl Explained 1
      systemctl Explained 1

      systemctl Explained 2

      systemctl Explained 2
      systemctl Explained 2

      systemctl Explained 3

      systemctl Explained 3
      systemctl Explained 3

      systemctl Explained 4

      systemctl Explained 4
      systemctl Explained 4

      systemctl Explained 5

      systemctl Explained 5
      systemctl Explained 5

      systemctl Explained 6

      systemctl Explained 6
      systemctl Explained 6

      systemctl Explained 7

      systemctl Explained 7
      systemctl Explained 7

    4. As I have made a habit of doing, I say back to Shevek what my understanding from this lesson is. As is always the case, I'm close, but not quite. He refines it and clarifies the things I don't quite understand.

      fstabLesson Review 1

      fstab Review 1
      fstab Review 1

      fstabLesson Review 2

      fstab Review 2
      fstab Review 2

      fstabLesson Review 3

      fstab Review 3
      fstab Review 3

      fstabLesson Review 4

      fstab Review 4
      fstab Review 4
Conclusions

Corrupting fstab is relatively straight forward and simple, but has devastating implications for the system. If unable to mount something, the system will drop into emergency mode. If it fails to mount root, it defaults to dracut. If it fails to mount another item, it defaults to systemd. The root filesystem needs to be made writtable in systemd emergency shell before fstab can be corrected. systemctl is a useful tool for managing systemd.

Shevek's Haiku

Readonly root waits,
A single line breaks the boot —
Mount, mend, rise again.

Sandbox

Shevek7