Could someone explain the macOS boot sequence to me?

[pullman]

Hello

Does anyone know why Macs have a much slower section during the boot sequence? I've noticed this on all my machines and across OS:es.

The progress bar will speedily reach around 1/4 to 1/3 at which point it slows down considerably, stutters forward in small increments or even just stops for several seconds.

Then, when whatever the hurdle is that causes the slowness has been overcome, the progress bar rushes right at a similar clip as at the start.

What causes this behaviour?

I've seen this on a 2008 unibody MacBook, a 2013 MBPr, a 2015 MBA and a 2008 cMP. They all behave in this way and across the many OS versions I've used. The slowdown/stop may be slightly different in length but it's always there.

Thanks in advance for enlightening me
Philip

 

[bogdanw]

Start up in verbose mode to see where it stalls.
Mac startup key combinations
Command-V: Start up in verbose mode.
https://support.apple.com/en-us/102603

 

[pullman]

Thank you. Below is a screenshot of where the stop happens, at approx. 20 secs into the boot. The computer "hangs" at where the cursor is at the bottom. After 7-8 seconds there, it goes directly to the Apple logo again and swiftly reaches the desktop.

There process also slows down at about 8 seconds. The marked part below takes 5 seconds to pass, with each line ticking by slowly.

Can something be told from this as to the reasons?

cheers
philip

 

[bogdanw]

From Recovery
“Repair volumes, then containers, then disks”
https://support.apple.com/HT210898
https://support.apple.com/en-us/HT210898

 

[pullman]

From Recovery
“Repair volumes, then containers, then disks”
https://support.apple.com/HT210898
https://support.apple.com/en-us/HT210898

Thank you. I ran first aid in that order but no problem was found. I also ran Etrecheck which did not report any issue.

Searching around I found that the reference to "keybag" in the second screenshot (and not the cause of the longer "hang") could have something to do with previously having stored encrypted iPhone backups on the computer. A recommended solution was to reinstall via internet recovery. This was unlikely as I have not used the computer for such backups as far as I can remember.

In any event, internet recovery appears not to have helped. The boot process still slows down, verging on halting at around 1/3 in. Verbose mode reveals that it stops at the cursor (see first screenshot above) and slows down at the same keybag messages as in the second screenshot.

Really at a loss here, any thoughts on what might cause the slow-down?

 

[bogdanw]

Have you tried Apple Diagnostics?
"Use Apple Diagnostics to test your Mac" https://support.apple.com/en-us/102550

 

[NoBoMac]

FileVault on? If so, need to do the initial decrypt of the OS to do the actual boot (FV login screen is bare minimum to allow for user input).

Looks like "antiques" so yeah, not going to be peppy.

Unsupported version(s) of OS? That might be a reason and might get better answers in the "XYZ on unsupported Macs" thread.