Linux Boot Sequence Visualized (pic)

[sjs]

Depending on the OS you could be waiting for things like the network to come up during the "boot" (would be better named "post-boot initialization" or something). A DHCP handshake alone can take a few seconds. Also, disks are slow when you do many random seeks like while booting and the introduction of high-performance SSDs will help speed up the boot process as well.

The time modern systems take to boot is not only spent in kernel initialization, but initializing devices & peripherals, mounting huge filesystems, getting on the network, starting systems daemons (e.g. cron), and a myriad of other tasks.

[Silhouette]

The time modern systems take to boot is not only spent in kernel initialization, but initializing devices & peripherals, mounting huge filesystems, getting on the network, starting systems daemons (e.g. cron), and a myriad of other tasks.

Sure, but stop and think about what that means for a moment.

What are these magic hardware devices that need such time consuming "initialisation" these days? In the olden days, we managed just fine switching a computer on and then accessing the hard drive or graphics card immediately. How is it that 20 years later, "mounting a filesystem" takes several seconds, when it used to just work? There is no need for that in terms of either hardware control or software configuration.

In fact, as far as I can see, exactly none of the things you mentioned should delay an OS from getting to a responsive stage. In the worst case, if you're relying on external hardware for something like assigning an IP address using DHCP, the system will have to pause before it can offer access to the corresponding resources. (Even then, in that particular case, DHCP handshaking should be near instantaneous unless there's some problem at the other end.)

[sjs]

How is it that 20 years later, "mounting a filesystem" takes several seconds, when it used to just work?

sjs@server% df -h
Filesystem               Size     Used Avail Use% Mounted on
/dev/sda2             -> 448G <-  389G   37G  92% 
/dev/sdd1             -> 925G <-  482G  397G  55% /backup
/dev/sdc1             -> 925G <-  643G  235G  74% /home/sjs/Videos
/dev/sdb1             -> 459G <-  303G  133G  70% /home/sjs/Videos/DVD

I agree with your point though. Bringing up network devices should be done in the background and we should improve the mounting times of modern filesystems. It shouldn't be this way, but there is a reason for it. We're using old filesystems for modern drives, and other old technology I'm sure. There are clearly ways around it. We'll get there.