2

I'm wondering what the messages that show up at boot on Linux are.
What is this screen called?
What does all the scrolling text mean?

There are no errors, but I am just wondering what it means.

1

Generally speaking, the boot-time text messages are broken into two major categories: kernel initialization output and service startup/status output.

Kernel initialization

Kernel initialization output is often disabled by default in modern distributions by passing the quiet kernel command line parameter. In the past, it was most often displayed on boot, not unusually to aid in troubleshooting any boot problems. Now that Linux has matured, boot problems are relatively rare so hiding these by default helps reduce user information overload. As D Schlachter pointed out, these messages can be reviewed later using the dmesg command, and they are commonly logged to files stored in /var/log early during the service startup process as well (mainly to aid recovery if the system fails before everything has started up, giving access to kernel initialization details for the system from an alternate environment such as a live or rescue CD).

Examples of kernel initialization messages are:

  • RAM map of usable/unusable/reserved/etc memory regions
  • CPU details, MTRR, delay loop calibration metrics ("BogoMIPS")
  • Hardware initialization (controllers for things like ACPI, PCI, USB; results of hardware bus scans, disk partition scans, ...; ...)

Service startup

After the kernel has initialized, control of the boot process is handed over to a userland process called init. Normally on Linux, this is /sbin/init, although it is possible to pass a different init path to the kernel using the init=... parameter which will be executed in its place. This process controls the startup of non-kernel processes; things like networking, system events logging, fan control, mounting of file systems (both local and remote), hard disk monitoring, audio, server processes, UPS and laptop battery monitoring, CPU frequency stepping, etc. are launched through scripts executed by init. At some point init will start some process that makes it possible to log in to the system; this can be a text-based login process on the console, a SSH server, or a display manager that in turn launches X Window.

This is the part of the startup where on a text boot display you'll normally see a lot of processes starting up and in some manner being reported as started OK, with more or less (usually less) verbose diagnostic output in between.

And then...?

Once all services have been started, the system is ready for use. At that point you log in and start getting work done.

But what does it mean?

Your question also includes:

What does all the scrolling text mean?

There are no errors, but I am just wondering what it means.

Unfortunately, there's just too much of it, and it is too variable between systems, to be able to provide a good answer to "what does it all mean?". If you sift through it slowly, top to bottom, with some knowledge of the system's hardware layout it is usually quite possible to determine what the various kernel initialization messages actually refer to and what they mean. If there's some particular output that you just cannot figure out even after trying to search the web for relevant key words or even the entire line, you are better off asking specifically about that message and provide the context in which it appears (not the entire boot output, unless someone specifically asks for it; a dozen or so lines before and after is usually quite enough to establish the context of any kernel initialization message).

Remember that Linux, on boot, does largely the same things as any other operating system: it determines the system's basic configuration, scans for hardware, loads any appropriate drivers (unless those are built into the kernel, in which case they are already loaded), initializes the hardware, and moves on, ultimately launching the processes that provide a meaningful user interface or allow the system to perform its duties. Windows does largely the same things during its boot process, except it doesn't tell you what it's doing so if something goes wrong there's a lot less information to tell you what is wrong.

Keep in mind the distinction between the kernel's responsibilities and the responsibilities of various services (including init) and it's usually reasonably clear which part does what.

0

What you see is usually very dependent on your particular computer and Linux distro — you can read the entire text at leisure with the dmesg command (e.g. dmesg | less run in a terminal). It's usually called the 'boot screen' or the 'start-up screen'.

I don't think there's one source to figure it all out — what works best is Googling keywords from interesting entries[1].

  • See, but I don't know what is "interesting"...I'd like to understand what it all means – user341814 Jul 11 '14 at 19:44
0

In a way this is analogous to u checking your car before u take on a drive. We check fuel, battery, tires etc. Similarly Linux is preparing the computer to be used by looking at available hardware and loading necessary modules at start up or boot. To many, this many not be interesting. Yet Linux gives the user the opportunity to see if something went wrong at startup..... Windows users do have the option to view this procedure at startup and hence the strange feeling...

  • Yes.Provided my car has a computer. I was actually mentioning about cars before the microcontroller Era with all the dials and stuff where the user has to check all the metrics before startup – Prasanna Jul 11 '14 at 20:19
  • It's actually more analogous to the car's computers checking that each component of the car is operating within specifications (things like lights, oil pressure, airbags, etc.), and displaying some sort of status indication on the dashboard if there is a problem. – a CVn Jul 11 '14 at 20:21
  • If you needed to check the tires before you turned on the ignition, I'd say something was wrong with the car's design :) – a CVn Jul 11 '14 at 20:23
  • Flat tires? My cat sleeping below my car. I'd personally walk around my car to ensure that it is safe to start away. I appreciate your answer below. Gives a lot of information about the startup.... Well done – Prasanna Jul 11 '14 at 20:25

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.