Root Access

12:00 AM

Definitely worth some info on it so folks can at least rule things out; I suspect some of it is specific to my use case and circumstances; but as you say some of the generic info could point them in the right direction

Bob

@bertieb and if you really must do something - drop by here sometime, we could always use more conversation partners :P

Jul 22 at 20:47, by allquixotic

Also, whether it's a good thing or a bad thing depends on whether you're willing to participate in our conversations about bad questions, headphones, GPUs, headphones, spam, headphones, computers, smartphones, headphones, and headphones. It's pretty important to be able to talk about headphones.

bertieb

Heh, will do, may as well leave a tab open :)

Oh, I can talk about headphones!

Bob

@bertieb just knowing how to get the filename could help a lot of people, I suspect

bertieb

I'm guessing there's no IRC interface? I vaguely remember a meta question about that

Bob

hmm... shrug

@bertieb stackapps might have one

bertieb

12:02 AM

@Bob Absolutely, the invocation of windbg is a bit arcane if you aren't used to it (and just dissimilar enough from gdb to be confusing :P)

Bob

stupid thing won't link properly

[stackapps]

[stackapps.se]

[apps.se]

Ramhound

Newegg is having a sale on Tuesday :-)

Bob

urk

[sa]

@bertieb oh, could you give dS a shot?

bertieb

@Bob Just having a look at the meta posts

Bob

that specifically prints a unicode string (where lowercase s is non-unicode, apparently)

bertieb

12:05 AM

@Bob Yet more unprintables

Bob

0

Q: print a null-terminated string in windbg

Which windbg command will print string in a executable ? For now , I'm using db command but it's output is very inconvenient to copy and paste . I also tried ds command , seems not work . Many thanks !

windbg

da or du

Ramhound

anyone watch Skarknado 3?

Bob

and there's printf too: naveensrinivasan.com/2010/06/29/dumpstring-windbg

bertieb

@Bob da was the badger

Perfect printing

Bob

might want du for some localised systems (w/ unicode filenames), but that's probably close enough :P

Ramhound

12:07 AM

Why is this in the reopen queue?

11

Q: How can I get virtual desktops (like Mac's Spaces) on my Windows 7 machine?

Possible Duplicate: What is the multiple desktop utility you suggest for Windows? Virtual desktop (alt+ctrl+1,2,3,4,...) like Linux on Windows 7 I make much use of ctrl-arrows to new virtual desktops on my MacBook to get more real estate, organize like-applications and windows, and he...

windows-7 organization virtual-desktop

bertieb

du gibberish'd unfortunately

Bob

@Ramhound cause someone voted to reopen? :P

if they didn't drop a comment about why, you could just ignore it

Ramhound

without a reason?

( figured it was a review test ) lol

Bob

@PSkocik “Ubuntu isn't the problem. The window title font you're using is.” …which is “Ubuntu”. — Xufox Jul 20 at 12:47

Journeyman Geek

maybe its the edit?

Anonymous

12:16 AM

@Bob heh @bertieb more memtest, right? :)

bertieb

@PatoSáinz Welp might as well leave the computer to do something :P

So it's either that or an extended SMART test...

Anonymous

both

Bob

@bertieb I'd say test the memory first

bertieb

There's only so many hours in a night :P

Journeyman Geek

memtest can be run overnight ;p

bertieb

12:21 AM

@JourneymanGeek Ah good point, forgot SMART test can be run from within OS

It's getting late, in my defence

Journeyman Geek

(Well, and the whole point of discussing these things is so we can bounce ideas off each other

bertieb

+1

Journeyman Geek

I'd suggest a short test first

If it catches anything you save time

bertieb

@JourneymanGeek Good call, already done :)

Haven't chkdsk'd it though, if I recall correctly

Journeyman Geek

Different issues

chkdsk would catch file system errors

bertieb

12:24 AM

Aye, but at least chkdsk might catch... yeah :)

Journeyman Geek

smart catches some detectable physical issues

Bob

@bertieb I'm actually surprised chkdsk missed the dir corruption

bertieb

@Bob chkdsk was run on system drive (partition really), not storage

Bob

ahhhhhh

you had the driver on a different fs...

bit of an oversight there; I forgot to ask :P

bertieb

Aye!

Journeyman Geek

12:26 AM

Oh

@Bob: Remember the ipv6 question I've been threatening to ask?

Bob

...no? :P

Journeyman Geek

never mind then. Asked it ;p

bertieb

Also, unrelatedly, how does Debian graphical installer get the system hostname? Just set it in Windows setup (different PC) and it appeared pre-filled in crunchbangplusplus setup. Does DHCP server return it based on MAC address?

Journeyman Geek

0_0

Nope?

bertieb

waves hands at question until it makes sense

Bob

12:28 AM

@JourneymanGeek oh that one

Journeyman Geek

Yeah

bertieb

Well, somehow Linux setup knew the hostname already; and I doubt it's reading Windows configuration...

Journeyman Geek

(There's suprisingly little documentation about that ._.)

Bob

@bertieb huh.

that's... interesting.

tereško

@bertieb you would have to read more about DHCP

bertieb

12:30 AM

So must be getting it from dhcp / dnsmasq server

Perhaps it does a DNS lookup of the IP it gets assigned?

tereško

it is possible that it's announcing your IP and your hostname

Bob

@bertieb I wonder if said (DNS) server would handle reverse-lookups for local IPs

you could try!

tereško

^ that

it doesnt seem all that possible

Bob

dig some.reversed.ip.in-addr.arpa

Journeyman Geek

Oh, its possible

bertieb

12:31 AM

@Bob It's one of these routers where sometimes hostname lookups work after a device disappears (reboot etc)

Journeyman Geek

just not something you would find on a home network

tereško

@JourneymanGeek it seems like too large a vector for an attack

Bob

@bertieb that's normal for most home "router"s with integrated dhcp and dns servers

Journeyman Geek

@tereško: Work uses a wierd customish thing to kickstart workstations, and that depends on our dhcp server knowing which hostname is which system

Bob

the dhcp client announces the hostname, which the dhcp server saves and passes to the dns server, which can now serve lookups for that hostname (and possibly the reverse ip)

bertieb

12:33 AM

@Bob Aye, presumably there's something in there relating to how setup is getting the hostname

Suppose I could go look up the source for debian-installer

Oh yay svn

Except it is in a git repo, just the 'historical' parts in svn

Michael Frank

12:47 AM

@Bob Until your DNS decides it's not going to recycle hostnames on the same schedule as the DHCP leases are recycled OR at all. Then you get situations like I had a couple weeks ago where I had an angry user contacted my manager because I was trying to "hack into his machine".

Turns out his workstation was listed against the IP assigned to another workstation I was actually trying to get into.

lifehacker.com/…

heh... The writer basically admits to ripping his music then offloading the physical CDs.

Then complains then iTunes chews up 4700 songs.

Bob

> iTunes

Well, there's your problem.

I re-joined the Google Play Music trial last night, hoping to get access to the YouTube music thing. Nope. Apparently not in AU yet.

Michael Frank

It was Apple Music to be specific, but it's all just tears over spilt milk.

Bob

Then I tried to use the Play Music app.

The UI is absolute shite.

And it crashed.

Multiple times.

Michael Frank

1:02 AM

Yea, it's baaaad.

Bob

I thought Spotify was glitchy, but it's perfect compared to this pile of crap.

*quickly cancels subscription*

Michael Frank

The only thing I want from Spotify is a fullscreen visualizer.

Bob

@MichaelFrank I just want it to not take 30 mins to load.

(ok, exaggeration. usually ~30 secs)

it also crashes/freezes now and then

Funnily enough, my best music experience so far has been MetroTube on a WP device.

Well, no... not quite: its playlist support is shot.

urk.

bertieb

Argh this cbpp install is booting to a black screen even in recovery mode; even ctrl+alt+f1 tty switching isn'tdoing much of anything

Bob

So many streaming services, none seem to have figured out basic music player UI.

DragonLord

1:05 AM

@FiascoLabs, are you around?

Bob

@bertieb hmm... look at the logs from a live env?

DragonLord

Just fiddling around with Gopher...

Gopher (protocol)

The Gopher protocol /ˈɡoʊfər/ is a TCP/IP application layer protocol designed for distributing, searching, and retrieving documents over the Internet. The Gopher protocol was strongly oriented towards a menu-document design and presented an alternative to the World Wide Web in its early stages, but ultimately HTTP became the dominant protocol. The Gopher ecosystem is often regarded as the effective predecessor of the World Wide Web. The protocol was invented by a team led by Mark P. McCahill at the University of Minnesota. It offers some features not natively supported by the Web and imposes a...

bertieb

I'm trying to blindly apt-get install openssh-server but no dice :s

DragonLord

> Been on the Internet since before there was an Internet. Remember UUCP, news feeds, and Gopher?

Fiasco Labs

5k 11 26

windows-7 windows networking hard-drive windows-xp virtualbox usb

Bob

@bertieb I had something similar when installing debian on a server... had to modify the kernel params to enable something specific when switching to graphical mode, iirc

Michael Frank

1:06 AM

@bertieb a........p........t..........-0... fuck

2

bertieb

@MichaelFrank Hah! If only I knew where the problem was lying. Sudo? Asking me to confirm something on the terminal (post-install script?) first? Not allowing ctrl+alt+f1? I dunno

Bob

vmwgfx.enable_fbdev=1

bertieb

@Bob Ended up backspacing that reply; will give that a shot. Interestingly this is the first time I've had grub clobber (not provide a menu entry for) a coexisting Windows install

Even though D-I detected it/them

Bob

@bertieb you'd have to add that to the GRUB kernel params

Jun 9 at 21:08, by Bob

the vmwgfx bit is a fix for the plymouth stuff => https://lists.debian.org/debian-kernel/2013/07/msg00877.html

bertieb

@Bob Yup, just squinting at the telly to try and see which line to edit :P

Bob

1:10 AM

I had a fun time discovering that...

was setting up a completely unsupported config

(ZFS on Linux for root partition with UEFIstub boot)

bertieb

@Bob Oh I'll bet

Bob

I messed up the ZFS rootfs setup a few times

then it booted to a blank screen

thought I messed up again

took a few days to figure out I had quiet boot enabled

then it dumped stuff to the console and the screen went blank... did a video cap of the screen to read the last parts, and it was initialising plymouth iirc

off to Google and you can see the results :P

bertieb

@Bob Had a look, not a huge lot there :o One result got me to the temporary stopgap vga=768 and a console display

(I added the suffix verbatim as you listed but still was booting to blackness)

openssh-server and tightvncserver installed at any rate, should things get desperate

And an update-grub has hopefully re-added the relevant entries

DragonLord

@MichaelFrank ROTFL

Bob

@bertieb damn

@bertieb try =0? :P

apparently some systems you have to disable fbdev

I have no idea what it's actually used for, tbh

take a look at boot.log and dmesg

bertieb

1:20 AM

@Bob Will give it a shot

Bob

wiki.debian.org/bootlogd

bertieb

Interestingly, vncing doesn't give a loaded WM (openbox)

I less'd dmesg but gave up as I don't know hoow to quickly scroll on a mac kb sans pgup/dn keys :P

Bob

@bertieb tail

@bertieb or G to go to the last line

bertieb

@Bob tail was uninteresting (network init)

Righty, getting some output from integrated graphics

But just a console

So something's gone wrong with the setup somewhere

Ahhhhhh fudge

Xorg errors

I thought I left these back in the early 00s

A segfault? Oh dearie me

Jul 27 02:22:10 artemis slim[612]: (EE)
Jul 27 02:22:10 artemis slim[612]: (EE) Backtrace:
Jul 27 02:22:10 artemis slim[612]: (EE) 0: /usr/bin/X11/X (xorg_backtrace+0x56) [0x7f309fcbad46]
Jul 27 02:22:10 artemis slim[612]: (EE) 1: /usr/bin/X11/X (0x7f309fb04000+0x1baf29) [0x7f309fcbef29]
Jul 27 02:22:10 artemis slim[612]: (EE) 2: /lib/x86_64-linux-gnu/libc.so.6 (0x7f309d7f8000+0x35180) [0x7f309d82d180]
Jul 27 02:22:10 artemis slim[612]: (EE) 3: /usr/bin/X11/X (RRSetChanged+0x50) [0x7f309fc1c6d0]

Bob

> It sounds like a Robot talking under water, using a mic plugged into a metal bands distortion pedal

heh

@bertieb o.O

Michael Frank

1:33 AM

@DragonLord Blind typing is the worst.

DragonLord

Gave me a good laugh, that's for sure.

Bob

@MichaelFrank It gets the job done. Until you accidentally rm -rf /*

bertieb

@Bob I don't even know at this point, and I am too tired to care! shutdown -hP now, start memtest86+ on the other one, and collapse into bed methinks

Give some serious consideration to your reward if you fancy, I do appreciate the time spent as it saved me plenty

Cheers to all, and to all goodnight!

Bob

@bertieb g'night

Michael Frank

@Bob Reminds me of that shred question from a while ago.

Bob

1:38 AM

@MichaelFrank which one was that?

Michael Frank

The guy was asking for help cause he used shred on his fathers system after a friend told him to do it.

Bob

oh god this one?

-5

Q: How to fix the computer?? Typed sudo shred -rfz ~/* (or something like that)

One &^%@&& advised me to press alt+f2 and then type the above. And i did it... on my Dad's computer. He's furious now. How to fix this?

tags shred

Michael Frank

Yea, that's it!

Guess it wasn't a friend after all...

DragonLord

What the heck is this? superuser.com/questions/945643/…

Bob

@DragonLord spam

Anonymous

1:49 AM

@DragonLord Chineese SEO

Bob

includes qq handle and a bunch of universities... I would put money on it being some ad for a tutor

>

This can be happens when your ram is of low either very high mhz, Use the cooling paste on your processor They help very much.

wot

0

A: I recently upgraded to 16GB, now my computer is slower. What can I do?

This can be happens when your ram is of low either very high mhz, Use the cooling paste on your processor They help very much.

Michael Frank

I...

I suppose it makes sense. If the RAM is very low MHz, then your computer is slow. If it's very fast, your computer gets hot and then runs slowly again.

Anonymous

@MichaelFrank and then he continues by annexing a cool protip: "use the cooling paste on your processor"

Michael Frank

@PatoSáinz Letting trade secrets slip there!

Custom PC Builders HATE him!

Anonymous

@MichaelFrank but they help very much [sic]

DragonLord

2:05 AM

superuser.com/questions/945646/… superuser.com/questions/945645/…

Appears to be a spambot.

do_os

can I ask here about MBR?

Bob

sure

do_os

I'm learning about MBR and I understand that the first 400 some bytes are boot code

but I noticed that this boot code is basically machine code

therefore it should differ based on cpu architecture

Bob

...and?

do_os

does this mean that a hdd that is recognized in IA32 will not be recognized in arm32?

Bob

2:10 AM

You'll find that legacy BIOS boot was mostly a kludge.

do_os

kludge?? what do you mean?

Bob

@do_os Yes.

do_os

you mean that what I thought is right?

Bob

In fact, what you think of as the BIOS is basically the original IBM PC BIOS.

All implementations basically try to emulate that original BIOS.

The boot code is specifically x86 because that's what the IBM PC ran on.

do_os

okay then for universal compatibility, the MBR boot code is written in IA32

Bob

2:13 AM

(well, not even x86... its ancestor)

@do_os Nope. The boot code runs in real mode.

Not even protected mode.

do_os

?? real mode protected mode??

Bob

Real mode

Real mode, also called real address mode, is an operating mode of all x86-compatible CPUs. Real mode is characterized by a 20-bit segmented memory address space (giving exactly 1 MiB of addressable memory) and unlimited direct software access to all addressable memory, I/O addresses and peripheral hardware. Real mode provides no support for memory protection, multitasking, or code privilege levels. Before the release of the 80286, which introduced Protected mode, real mode was the only available mode for x86 CPUs. In the interests of backwards compatibility, all x86 CPUs start in real mode when...

well, if you want to get technical then it does fall under the IA32 umbrella

do_os

but wait a minute

Bob

but it's not what you'd probably think of as IA32 (protected mode, usually)

Anonymous

@Bob have you seen HCF yet?

do_os

2:15 AM

I just remembered that MBR boot code is written in 16bit instructions

Bob

@PatoSáinz HCF? Halt and catch fire?

@do_os Ya, running in real mode specifically.

Anonymous

@Bob yes, a TV show inspired by the instruction and set in the PC revolution era

do_os

I'll take a closer look on real mode

Bob

Note that protected mode also supports 16-bit code.

=> en.wikipedia.org/wiki/IA-32#Operating_modes

@do_os The four most commonly seen modes of a modern x86-64 CPU are real mode, virtual 8086 mode, protected mode and long mode.

do_os

okay I'll have to taker a closer look on that but there's a different issue that I can't understand

Bob

2:18 AM

@do_os hm? what is it?

do_os

if the mbr boot code is written in intel instructions, then how could an arm processor understand it?
1) does bios have its own processor? (doesn't seem likely)
2) does bios or something translate the intel instruction code to arm instruction?

Bob

@do_os They don't.

UEFI is cross-platform and well-specified.

Other ARM devices will have their own custom bootloaders.

BIOS is legacy and designed purely based off copying the IBM PC from around 1980.

do_os

okay I'm looking up uefi on wikipedia and I can see "As of version 2.5, processor bindings exist for Itanium, x86, x86-64, ARM (AArch32) and ARM64 (AArch64).[14] Only little-endian processors can be supported.[15]"

so then UEFI is interfacing between the 16bit MBR instructions and the arm processor?

Bob

@do_os NO

UEFI is completely new and has almost nothing to do with the legacy BIOS.

Read this: happyassassin.net/2014/01/25/…

@do_os Basically, the way UEFI is designed... it allows you to specify multiple bootloaders and it'll pick the appropriate one for the current architecture.

do_os

still reading : ) good stuff. I was always kind of confused about BIOS and UEFI

Michael Frank

2:32 AM

@PatoSáinz Love that show.

Haven't had a chance to watch season two yet though.

Bob

Whoops, correction to the above: UEFI won't pick for you, but in the event that you move a disk to another system you can simply choose a different boot entry.

Assuming the OS itself can run under either architecture.

Which is usually impossible.

Anonymous

2:48 AM

@MichaelFrank hahaha it's good... not my favourite show of all time but it's good and it's nice to see a technical show that is at least, moderately correct (cough CSI: Cyber cough)

Michael Frank

@PatoSáinz Mr. Robot does a pretty stand up job of getting it right as well.

Anonymous

@MichaelFrank never heard of it-- quick summary?

Michael Frank

@PatoSáinz You ever watched Dexter?

It's like that but computers.

Cyber security expert by day, vigilante hacker by night.

Anonymous

3:07 AM

@MichaelFrank holy shit I loved Dexter (Even though the final season was a bit of a let down)

Anonymous

will check it out

Anonymous

97% in rottentomatoes? hell yes

Anonymous

@MichaelFrank One of the series I most like is Person of Interest

Anonymous

even if it started as half-crime drama now it's just normal drama and badass action... and also they are a treat for technical people: AI ethics, NSA collection (that topic started even before Snowden), hell they don't have unrealistic "hacks": they used shellshock once to open some gates controlled by a computer

allquixotic

@JourneymanGeek No.

Michael Frank

3:26 AM

@PatoSáinz I think I ended up stopping around the time <spoiler> was killed, I keep meaning to go back and finish the series... but it just got really dark and depressing.

Anonymous

@MichaelFrank maybe that's the point hahaha

Anonymous

@MichaelFrank dexter and his unending hopeless monologue

Michael Frank

Yea absolutely, but I wasn't enjoying it because it was getting me down. That's not really what I want my entertainment

Anonymous

@MichaelFrank nice <spoiler> there (it's still in the edit history anyway)... well I understand you completely: my mood is really swinging and a six hour Dexter marathon can really ruin the rest of my day but the solution is to compartmentalize in that case

Michael Frank

@PatoSáinz Yea, I know. It's just much harder to accidentally see. :)

The_IT_Guy_You_Don't_Like

3:55 AM

someone is constantly spamming SU, like this post superuser.com/questions/945684/…

Michael Frank

@The_IT_Guy_You_Don't_Like They're getting flagged and removed pretty quickly.

The_IT_Guy_You_Don't_Like

yeah i am flagging them too but for long can we do this ?

Michael Frank

@The_IT_Guy_You_Don't_Like Generally it doesn't last long.

The_IT_Guy_You_Don't_Like

They seem to have stopped now

nope

one more came just now

Braiam

4:12 AM

@MichaelFrank well, you can thank your friends at The Tavern specially smokey

The_IT_Guy_You_Don't_Like

They are at war, thanks won't do. they deserve a salute ;)

nhinkle

4:28 AM

The situation is under control ish.

Regarding the Chinese fake diploma spam, they all had some Chinese characters in common which have been added to the blacklist. Should stop it for now; please flag as spam AND with an "other" message if you see any more.

2

The_IT_Guy_You_Don't_Like

cool

nhinkle

It may take a few minutes for the blacklist change to go into effect, so in the meantime keep flagging if more show up.

The_IT_Guy_You_Don't_Like

5:10 AM

ran out of flags

do_os

uh guys could you help me understand the difference between UEFI boot manager and GRUB?

Normal Human

@nhinkle BTW, it's impossible to flag a post both as spam and "other": one flag prevents the other. Flagging as spam...

Bob

@do_os One's implemented by the firmware. The other is just a normal program.

As soon as the firmware hands control over to the bootloader, the bootloader can do whatever it wants. The firmware no longer cares.

do_os

@Bob hey your back!

Bob

@do_os yea, went out for lunch

In the most basic system, the Linux kernel itself is actually a UEFI bootable file (see UEFIstub). You can set the UEFI boot entry to load the Linux kernel directly with the appropriate parameters.

do_os

5:24 AM

@Bob okay so I read the link you gave me but the behavior of uefi boot manager confuses me. The uefi boot manager has its own menu entries and the ability to detect and load different OSs. Isn't this what GRUB does?

Bob

In a more complex system, you might put GRUB in between the two.

That's technically not ideal for UEFI, but that's how it was traditionally done and most distros have not changed.

@do_os GRUB was designed back in the PC BIOS days.

Before UEFI existed.

do_os

aha..

Bob

Nowadays, UEFI can do most of what GRUB does.

Most, not all.

GRUB still offers certain advantages (especially because it's easier to configure from a Linux system, but that's more because no-one really bothered to develop the UEFI tools properly). It's a bit more flexible.

But in many cases, it's only used because it was traditionally used.

GRUB has its own drawbacks: now you have another component to keep updated and working.

do_os

So then if a GRUB is used in a uefi system, how would the process look like?
my wild guess is: UEFI -> go to partition containing GRUB -> execute GRUB -> GRUB load kernel

Bob

I actually went with UEFIstub for my server because GRUB didn't understand the ZFS filesystem enough. The Linux kernel UEFIstub booted directly into a kernel with the appropriate filesystem drivers baked in.

@do_os Pretty much. Except it's more UEFI -> EFI System Partition (ESP) -> GRUB (on the ESP) -> GRUB does its thing

once you reach GRUB, it does more or less the same thing across both legacy BIOS and UEFI systems.

do_os

5:28 AM

so then it the above process is the case, it would require a separate and exclusive but small EFI partition for GRUB?

Bob

@do_os Yes.

But even without GRUB you'd still need an ESP for whatever bootloader you use.

do_os

About ESP, I also have a question. Does ESP mean just any partition with filesystem that the UEFI boot manager can recognize?

Bob

EFIStub (sorry, it's not called UEFIstub, stupid brain) basically acts as its own bootloader

@do_os No. It's a partition with a specific GPT GUID.

Or a specific MBR partition ID, but that's heavily not recommended.

The GPT's partition type is a GUID, which can encode a humongous number of partition types.

MBR has only something like 256 possibilities.

do_os

hmm I'll look more into that

what about .efi files? I didn't quite understand what this really does. I understand that the UEFI boot manager detects these files but what does these .efi file contain? Does it contain instructions to load the kernel in that partition?

Bob

EFI System partition

The EFI System partition (ESP) is a partition on a data storage device (usually a hard disk drive or solid-state drive) that is used by computers adhering to the Unified Extensible Firmware Interface (UEFI). When a computer is powered up and booted, UEFI firmware loads files stored on the ESP to start installed operating systems and various utilities. An ESP needs to be formatted with a file system whose specification is based on the FAT file system and maintained as part of the UEFI specification; therefore, the file system specification is independent from the original FAT specification. ESP...

> The globally unique identifier (GUID) for the EFI System partition in the GUID Partition Table (GPT) scheme is C12A7328-F81F-11D2-BA4B-00A0C93EC93B, while its ID in the MBR partition table scheme is 0xEF.

nhinkle

5:33 AM

Update on the chinese spam situation: Devs are aware of the issue and working on a longterm solution. A stopgap measure is in place which should prevent any further spam for the time being, but if you do see any more continue spam-flagging and let us know.

3

Bob

@do_os ...didn't that blog post before explain all this? o.O

Anyway, it's just a generic executable file (in the COFF format, which is similar to a Windows PE [.exe]).

The UEFI firmware just starts running the arbitrary code contained in that file.

There are two major differences compared to how a legacy BIOS runs its boot code.

1. UEFI will jump into protected (or long) mode. The .efi must match. Legacy BIOS stayed in real mode and the boot code had to do the switch.

2. The UEFI standard provides a well-defined format, location and amount of storage available. It also provides a way to have multiple bootloaders with a well-specified firmware-level manager.

Compare to legacy BIOS, where those were not specified anywhere. A lot of BIOS firmware did similar things, but OS and bootloader developers really had no guarantees.

But apart from the the general principle is the same.

Set up the environment (where UEFI does more than BIOS), and pass control over to the bootloader.

From that point the bootloader has full control and can do whatever it wants.

do_os

so an example of bootloader could be GRUB?
and when does .efi fit in your summarized UEFI booting process?

Bob

@do_os Yes, GRUB is a bootlaoder.

UEFI -> EFI System Partition (ESP) -> GRUB (on the ESP, as a .efi file) -> GRUB does its thing

The entry point into GRUB would be the .efi file.

do_os

aha got it

thanks a bunch!!

Bob

Once control has jumped into this entry point, GRUB can do whatever.

It could load (or jump into) another file if it wants.

Also, it doesn't have to end in .efi, I think. .efi is necessary for auto-discovery, but you can manually add boot entries at any path. Maybe even non-ESP paths (I haven't tried).

But in the general case you can expect most loaders to be .efi in the standard path.

@nhinkle I see no spam.

Either the blacklist is working, or some people are watching very closely.

do_os

5:43 AM

ah so then when UEFI boot manager has menu-like entries that describe multiple paths to boot from, this is actually managed in the UEFI screen which pops when you press F5 or F12 at the early stage of booting?

IOW, changing the boot order in UEFI boot manager is actually the same thing as changing the boot priority in the so-called "BIOS screen"(the one that pops up when F5, F12 or something like this is pressed)

nhinkle

5:56 AM

@Bob it comes in waves, we've been removing it in waves superuser.com/questions/945724/…

Bob

@do_os More or less, yes.

Another difference is you can actually manage EFI boot entries from within your OS (EFI vars).

And the legacy BIOS boot menu only supported whole disks. EFI supports multiple bootloaders on one disk.

do_os

@Bob again, many thanks. I now have a better chance to understand booting problems of my own laptop

Bob

@nhinkle coincidentally, from the sidebar:

@do_os Hm? What issues are you having?

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