2026-04-08T19:45:00Z

Dank:

Dank: /* initramfs can't mount root */

Sometimes you need perform irregular, unpleasant tasks involving a Linux box. One generally picks up the techniques via experience. This kind of thing tends to become less necessary as one learns Linux better, and thus it's easy to lose currency. The introduction of [[systemd]], for instance, changed almost all of this shit up. Almost everything here requires access to the console, relevant only long before sshd is running (though take a look at e.g. [https://wiki.debian.org/RescueInitramfs RescueInitramfs]).

==firmware==
System firmware configuration can usually be entered by holding one of Delete, F2, or F1. A boot menu can commonly be accessed with F10.

If you need clear a firmware password, try removing the battery and unplugging the machine for 30s.

==grub==
If there is no boot delay, but you need interactive control, try holding down space (or with some versions shift) when grub comes up.

Don't go editing grub's configuration files directly if at all possible. Edit <tt>/etc/default/grub</tt> and rebuild them with <tt>update-grub</tt>. Note that <tt>update-grub2</tt> is these days just a symlink to <tt>update-grub</tt>. If what you want to change isn't available via <tt>/etc/default/grub</tt>, try to do it via <tt>/etc/grub.d</tt>. If you're directly editing <tt>grub.cfg</tt>, you're gonna have a bad time (and your changes will be blown away the next time someone runs <tt>update-grub</tt>).

Do yourself a favor and install [https://packages.debian.org/sid/memtest86+ memtest86+], which will be automatically added to your grub menu on [[UEFI]] machines.

If you're in the interactive GRUB command prompt, and wish not to be (i.e. to return to the menu), use the command <tt>normal</tt>.

==kernel command line==
The bootloader can provide command line parameters to the kernel (they can also be specified at build time, see <tt>CONFIG_CMDLINE</tt>). [[systemd]] can take many parameters off of the kernel command line.

For more output, ensure "quiet" is not present. For still more output, add "debug=vc" (by default, <tt>debug</tt> writes to <tt>/run/initramfs/initramfs.debug</tt>; this sends it to the console).

The root process can be specified using <tt>init=</tt> (this can also be specified at build time with <tt>CONFIG_DEFAULT_INIT</tt>).

Note that the kernel does not by default reboot following a panic. This can be undesirable on remote machines. <tt>panic=N</tt> will reboot N seconds after a panic, if N is positive. <tt>/proc/sys/kernel/panic</tt> exposes this.

===my video is borked===
If you can't get output to the display, [https://www.kernel.org/doc/html/latest/networking/netconsole.html netconsole] is a pretty decent method for quickly getting console output sent to another machine. You won't have ARP or routing, so the target will need be on the local broadcast domain. Specify the target MAC if you can to avoid broadcasting.

==initramfs==
Almost all distributions ship kernels making use of initramfs these days. An initramfs can be embedded directly into the kernel image (see kernel config entry <tt>CONFIG_INITRAMFS_SOURCE</tt>), but it is usually shipped as its own file instead, and specified by the bootloader. An initramfs is a (possibly compressed) <tt>cpio</tt> archive. On boot, it is unpacked into a tmpfs. The compelling advantage of initramfs is the ability to mount the true root filesystem (which might be on [[NFS]], or encrypted, etc.) from userspace, with a minimal filesystem such as userspace expects. Over time, presence of an initramfs has become more or less assumed, and is is thus now required for all manner of things (i.e. persistent block device names when specifying the root filesystem). In the absence of an initramfs, all code necessary for mounting root must be built into the kernel (i.e. not as modules).

The [https://packages.debian.org/sid/initramfs-tools initramfs-tools-core] package ships <tt>lsinitramfs</tt> and <tt>unmkinitramfs</tt> to easily list or extract the contents of an initramfs file.

You're unlikely to run into initrd these days, but it can be unpacked the same way (the difference is in how it's mounted during boot). Initramfs on Debian are named <tt>initrd-*</tt>.

If built into the kernel, there are no extra considerations for the initramfs. If it's a distinct file, it needs to live somewhere visible to the bootloader. If booting directly from [[UEFI]], it needs live in the ESP. So long as it's kept in the same directory as the kernel image, you ought be fine. Be sure to copy the initramfs along with the kernel image if you're ever backing up the kernel, or moving it to another machine, etc.

The initramfs often has copies of various kernel modules, so most changes to modules require an initramfs rebuild.

===writing an initramfs===
<tt>mkinitramfs</tt> is a lower-level tool usually called via <tt>update-initramfs</tt>, controlled by the many configuration files in <tt>/etc/initramfs-tools/</tt>.

===initramfs can't mount root===
An unpleasant situation is one where initramfs fails to mount the root partition, in which case you will be dumped to the dreaded BusyBox or klibc shells (ash, as in "a shitty shell"). A day when one sees BusyBox is never a good day. If the machine is remote, you are fucked without server-style out of band access (e.g. Dell iDRAC, BMC, KVM-over-IP). Otherwise, if you have a valid root partition somewhere, you can manually continue the boot by mounting that partition to <tt>/mnt/root</tt> and running <tt>exec switch_root /mnt/root /sbin/init</tt> or its non-union equivalent. Usually this means you've specified the wrong root partition in your bootloader; check the <tt>root</tt> command line option to the kernel.

If you have [[systemd]] running in the emergency shell (its <tt>emergency.target</tt>), try manually mounting the root filesystem to <tt>/sysroot</tt> and then running <tt>systemctl restart mount-sysroot</tt>. If this succeeds, exiting the shell ought continue the boot.

==fsck on boot==

==access sans password==
Ideally, you can just provide <tt>init=/bin/sh</tt> on the kernel command line using grub's interactive mode. This will go through the end of the initramfs and invoke <tt>/bin/sh</tt> within the root filesystem.

what if we can't use interactive mode?
===systemd emergency mode with a locked root account===
If you've locked the root account with <tt>passwd -l</tt>, systemd's <tt>sulogin</tt> won't let you enter rescue mode. Use the instructions from "access sans password" above to get a shell if possible, and enable root with <tt>passwd</tt>. Reboot, and <tt>sulogin</tt> will admit you using the new password.

==all my binaries are gone==
The situation can arise that one has an active process context (we'll assume a shell) on a machine where the standard POSIX binaries are unavailable. This can happen due to e.g. a network error, a disk error, memory error, wayward <tt>rm -rf /</tt>, misadventures in package management. What can be done in such a case? Shell builtins, [[sysfs]], <tt>/dev</tt> entries, and [[proc]] usually continue to be available.
===cat without cat===
The bash shell's <tt>echo</tt> or <tt>printf</tt> builtin can be used:
<pre>
[freebird](0) $ dmesg
-bash: /usr/bin/dmesg: Input/output error
[freebird](126) $ printf "%s" "$(</proc/kmsg)"
.....
[freebird](0) $ echo "$(</proc/kmsg)"
.....
[freebird](0) $
</pre>
===reboot without reboot===
Enable and apply sysrq reboot:
<pre>echo 128 > /proc/sys/kernel/sysrq
echo b > /proc/sysrq-trigger</pre>
Alt+SysRq+B will accomplish this at the terminal if sysrq reboot is enabled. Unlike <tt>reboot</tt>, there will be no syncing and unmounting of disks.

==moving a root filesystem + bootloader==
Ideally, mount the source filesystem <tt>ro</tt>, so it's not being modified while you copy. Start assuming a clean destination filesystem (otherwise, wipe it). Using the <tt>-a</tt> flag, <tt>cp</tt> basic toplevel directories *but do not cross filesystem boundaries on the source* (i.e. if <tt>/home</tt> is on its own filesystem, do not include it below; this includes <tt>/boot/efi</tt>). Any that you skip in this fashion ought have their mountpoints created; add them to the <tt>mkdir</tt> below:

<pre>
cp -a SOURCE/{bin,boot,etc,home,lib*,root,sbin,usr} DEST/
mkdir -p DEST/{dev,proc,var/tmp,tmp}
ln -s /run DEST/var/run
ln -s /lock DEST/var/lock
chmod 1777 DEST/{var/tmp,tmp}
</pre>

ESP, bootloader, initramfs...

==External links==
* Debian wiki page for [https://wiki.debian.org/initramfs initramfs]
* Kernel documentation for [https://www.kernel.org/doc/html/latest/filesystems/ramfs-rootfs-initramfs.html Ramfs, Rootfs, and Initramfs]

Hack on

2026-01-08T04:28:46Z

Dank: /* QEMFD! (wikipedia, wolfram) also provides... */

__NOTOC__
=='''rien n'est simple, mais tout est facile'''==
[[File:Ourheroreturns.jpg|right|thumb|your humble wikist 2025-06-29]]
this is the wiki of [mailto:dankamongmen@gmail.com nick black] (aka [[User:Dank|dank]]), located at [[LOC record|33°46′44.4"N, 84°23'2.4"W (33.779, 85.384)]] in the heart of [[Atlanta|midtown atlanta]]. dankwiki's [https://www.youtube.com/watch?v=i2tukPoF2ww rollin' wit' you], though i make no guarantees of its correctness, nor its relevance, nor its timeliness. track changes using the [[Special:RecentChanges|recent changes]] page. i've revived [[dankblog|DANKBLOG]], this wiki and [[Grad_school|grad school]] having not satisfied ye olde ''furor scribendi''.

hack the planet! don't mistake my kindness for weakness.

i primarily write to force my own understanding, and remember things (a ''few'' entries are actually semi-authoritative). i'm just a [http://en.wikipedia.org/wiki/The_Rime_of_the_Ancient_Mariner disreputable Mariner] on your way to the Wedding. '''if you derive use from this wiki, consider yourself lucky, and please get confirmation before relying on my writeups to perform surgery, design spacecraft, determine whether a graph ''G'' is an [https://en.wikipedia.org/wiki/Aanderaa%E2%80%93Karp%E2%80%93Rosenberg_conjecture#Deterministic_query_complexity Aanderaa–Rosenberg scorpion], or feed your pet rhinoceros.''' do not proceed if allergic to linux, postmodern literature, nuclear physics, or cartoonish supervillainy. ■

==[[:Category:Projects|projects?]]==
Nothing that's any good works by itself, just to please you; you've got to make the Damned Thing work.

* Still growing! The world's largest(?) collection of [[computer science eponyms]].
* [[Notcurses]], a library for blingful TUIs and character graphics
* I created and taught CS4803UWS, "[[UNIX Weapons School]]", Summer 2013 at Georgia Tech.
* [[Hackery]]! (projects and open source work). The [[Personal machines|machines]]. Matrix of [[large cases]] and [[Titanium_power_supplies|Titanium PSUs]].
* The [[WORDHORDE]]. Some [[book ideas|books]] I'd like to write. Too many [[morphisms]]!
* An ambitious [[Decay_chart|chart of decays]].
* [[Grad school]] and [[CS GRE]] prep pages. You can't have grad school without [[LaTeX|XeLaTeX]]!
* [[Elemental naming]] and good [[wordlist|words]]. Ramblings on [[Dankblog|DANKBLOG]].
* [[BlackBerry]] crap. F'n [[bookshelves]]. [[PC_Fans|Fans]] from [[Noctua]], of whom I am a fan.
* What does worldwide [[TaB|TaB®]] consumption have to do with [[nuclear weapons]]?
* I found myself playing a lot of [[Pokémon_Go|Pokémon Go]] in 2025, rather to my surprise.
* My grad school [[:Media:CS8803MCAPresentation.pdf|presentations]] tended to [[:Media:CS8803DCPresentationKlaiber.pdf|run slightly]], just a little, [[:Media:CS8803DCPresentationGschwind.pdf|unorthodox]]...
** enjoy the ghastly background of my [[:Media:Libtorque-presentation.pdf|masters thesis]] presentation
** ...yep, [[Trail of Frames|still weird]] (invited lecture for the opening of [https://wiki.freesideatlanta.org/fs/Info Freeside Atlanta])
** professionally weird! [[:Media:Public_LPC2015_-_Dynamic_iSCSI_at_Scale-_Remote_paging_at_Google.pdf|"Dynamic iSCSI at Scale"]] for Google ([https://blog.linuxplumbersconf.org/2015/ 2015 Linux Plumbers' Conference])
** [[:Media:Pwl09.pdf|"Miscompiling Programs with 'Benign' Data Races"]] for [https://www.meetup.com/Papers-We-Love-Atlanta/events/bhvjlpyxnbmb/ Papers We Love Atlanta #9] 2018-10-09
** [[:Media:Multire.pdf|"Efficiently Matching Multiple Regular Expressions"]] for BetterCloud 2013-12-06
** "[https://mdco2.mini.debconf.org/talks/6-notcurses-making-terminals-do-things-that-were-never-intended/ Making Terminals do Things Never Intended]" for [[Debian]] [https://mdco2.mini.debconf.org/ MiniDebConf #2] 2020-11-20
** "[https://nick-black.com/tabpower/notcurses-fosdem-2021.pdf Notcurses: Blingful TUIs and Character Graphics]" for [https://fosdem.org/2021/ FOSDEM 2021] 2021-02-06
** "[https://debconf21.debconf.org/talks/3-proposing-a-new-d-i-disk-preparation-tool-growlight/ Proposing a New D-I Disk Preparation Tool]" for [https://debconf21.debconf.org/ DebConf21] 2021-08-28
** "[[:Media:Black - Fast Linux Networking 2023.pdf|Fast Linux Networking: DPDK and XDP]]" for Microsoft Azure Orbital 2023-02-03
** "[[:Media:Self-publishing_and_nuclear_secrets.pdf|Self-publishing and nuclear secrets]]" 2024-01-27 release party for [https://midnightssimulacra.com midnight's simulacra]
* My video channel, [[DANKTECH]].
* Other people's [[repositories|projects]]. Other people's [[programming quotes]]. ■

==unix==
[[File:LookForAnswers.jpg|right|thumb|link=https://nick-black.com/dankwiki/images/5/5b/LookForAnswers.jpg|i like to stay up late on the computer, looking for answers.]]
* Writing high-performance, scalable [[Fast UNIX Servers|UNIX system applications]] is my greatest passion.
* [[Linux APIs]], [[FreeBSD APIs]], [[ELF]] (which is not, in itself, an API).
* [[Power Management]]. [[Sound Software]], [[Using Unicode]].
* Keeping FreeBSD [[Updating FreeBSD|up-to-date]]. Hacking [[CUDA]] on [[Debian]].
* [[Debian]], [[Xorg hell]], [[Consoles]] and [[Framebuffer|Framebuffers]]. [[Systemd]] and [[DBus]]. Making graphs with [[dot]].
* Notes on [[MediaWiki editing|editing]] and [[MediaWiki|running MediaWiki]]. [[Core]] files happen when one dances fandango on [[core]].
* Notes on [[subversion]], but my biggest note would be to use [[git]].
* [[Linux on Dells]], [[SMART]] and [[SATA]], [[udev]], various linux-related [[hardware detritus]] (mainly random personal crap).

did autistic people design this software? BECAUSE I'M STARTING TO LOVE IT. ■

==remarks regarding computers &c==
* [[glibc]], other [[interesting libraries]], [[working with libraries]], some implementing interfaces like [[pthreads]].
* [[X Macros]], [[ISO C18]], [[rpaths]], [[GCC|gcc]] notes, [[GNU Make|gmake]] notes.
* a [[Book_list_for_streetfighting_computer_scientists|book list]] for streetfighting coders
* There's [[Buses and Ports]], of course, of course.
* Intel's [[Sandy Bridge]] and [[Nehalem]] x86 [[microarchitectures]].
** or, if you'd prefer, [[Transmeta|Transmeta's]] or [[Tilera|Tilera's]] processors.
** It's dangerous to go alone! Take [[microcode]].
* The [[cpuid]] instruction, [[SMP on x86]], [[Performance Counters]], [[simulators]].
** Simulators ought not be confused with the [[4000 Linux VT Solutions|4,000 Linux VT Solutions]]!
* Getting into [[ARM]] (which is everywhere, including [[Raspberry Pi|Raspberry Pis]]).
* Getting into [[ACPI]]. Getting into [[Arduino]]. Getting into [[Architecture]].
** I want a (PIVT, middle-endian, 27-bit word) MISD machine; until then, there's [[SIMD]].
* [[Lamport's Hash]], [[Skip Lists]], I will put thoughts about [[automata|automata here]], [[Dijkstran Method]].
* [[ROS]] seems a pretty good way to write robots, and one day automate luvvvvv
* [[Flash]] sucks. Need get a handle on [[Compiler Design]] by tomorrow's midterm.
** Now it's [[Programming Language Theory]] by tomorrow's final, heh.
* [[Trees]] for smoking and computing. [[Lock-free algorithms|lock- and wait-free]] algorithms. [[Cache-oblivious algorithms]]. [[RCU]].
* [[Allocators]] get us that free store, son (usually through a [[DRAM]]-backed VM)!
** Said VM ''might'' implement [[transactional memory]], and ''almost certainly'' works on [[pages]].
* Via [[Grover's Algorithm]], we might be able to discover the monster at the end of this quantum book.
* While we're at it, [[timer wheels]] and even [[x86 timing]].
* Let's get bipartite, bipartite...with [[bip buffers]].
* I don't much care for writing [[Gecko Addons]] (aka [http://www.mozilla.com/en-US/firefox/upgrade.html FireFox plugins]).
* [[Blum's axioms]] and [[Rice's Theorem]] are both named after people smarter than me...
** ...as are [[Chaitin's Constant]] and [[Kolmogorov complexity]], and [[Computer science eponyms|lots of other junk]]. ■

==networking==
* Please adhere to the various [[Standards#Networking_standards|standards]] (even where [https://en.wikipedia.org/wiki/Base64#Variants_summary_table mutually contradictory])
** As one judge said to another, '' 'Be just, and if you can't be just, be arbitrary.' ''
* [[Topology Discovery]]. Online tools for [[Internet analytics]].
* [[SSHFP]] and [[LOC record|LOC]] records. [[DNSSEC]]. The Sender Policy Framework ([[SPF]]). [[VoIP]] and telephony, NAPTR records.
* Some [[TCP]] notes. [[Syncookies]]. Radio of the [[SDR|software-defined]] kind.
* [[ARP]] is no longer used in [[IPv6]], which more fully embraces [[Zeroconf|zero-configuration networking]].
* [[ICAP]] page. [[Tunneling]] (perhaps over [[VXLAN]]), [[SNMP]], [[NFS]]...
* I don't drive, but when I do, I drive via reverse engineered [[CAN bus|CAN buses]].
* [[QMI]] replaces the venerable Hayes command set aka "AT commands" for modems
* [https://nick-black.com/BIginternet Mirror] of the BIg-Internet list from ftp://munnari.oz.au
* [[Van Jacobson Channels]] get everybody all [[DPDK|hooting]] and [[XDP|hollaring]] every decade or so.
* My FCC callsign is [https://wireless2.fcc.gov/UlsApp/UlsSearch/license.jsp?licKey=5060966 KQ4ZNN]. ■

==QEMFD! ([http://en.wikipedia.org/wiki/Q.E.D. wikipedia], [http://mathworld.wolfram.com/QED.html wolfram]) also provides...==
* A page for our 2015 [https://nick-black.com/wedding/ hax0r wedding], the event of the century
** There is no page for our 2020 divorce, natch
* Documentation for [https://www.notcurses.com Notcurses], my poorly-named but always-rockin' console graphics library
* [https://www.dsscaw.com Dirty South Supercomputing], my [[WeWork|Tech Square consultancy]], launched 2019
* The [https://nick-black.com/processorzoo.html Processor Zoo], which has been wildly surpassed by [https://en.wikichip.org/wiki/WikiChip WikiChip]
* [https://nick-black.com/blog/ Sprezzablog] from my now-defunct but forever-beloved Linux distribution SprezzOS

still have any [[Questions|questions?]]

'''''quod erat motherfucking demonstrandum!''''' ■

<hr>
<div style="text-align: right;">"I have never known a greater monster nor miracle than myself." — Michel de Montaigne</div>

{{#seo:
|title=dankwiki, the wiki of nick black
|titlemode=append
|keywords=nick,black,dank,dankamongmen,dankwiki,blackwiki,notcurses,unix,nuclear,supervillain,growlight,omphalos,sprezzos,dsscaw
|description=Nick Black of Atlanta and his personal wiki of linux, computers, postmodern literature, nuclear physics, and cartoonish supervillainy.
}}