Jan 04, 2023
Passwords are bad, and they leak, but services are slow to adopt other auth
methods - even TOTP is better, and even for 1-factor-auth (e.g using oathtool).
But even without passwords, there are plenty of other easy-to-forget secrets to
store in a big pile somewhere, like same TOTP seed values, API keys,
government ID numbers, card PINs and financial info, security answers,
encryption passphrases, and many other stuff.
Easiest thing is to dump all these into a big .txt file somewhere.
Problem: any malware, accidental or deliberate copy ("evil maid"),
or even a screen-scrape taken at an unfortunate time exposes everything!
And these all seem to be reasonably common threats/issues.
Next best thing - store that file in some encrypted form.
Even short-lived compromise can get the whole list along with the key from
memory, and otherwise it's still reasonably easy to leak both key/passphrase
and ciphertext over time separately, esp. with long-lived keys.
It's also all on-screen when opened, can be exposed/scraped from there,
but still an improvement over pure plaintext, at the expense of some added
key-management hassle.
Encrypt whole file, but also have every actual secret in there encrypted
separately, with unique key for each one:
banks:
Apex Finance:
url: online.apex-finance.com
login: jmastodon
pw: fhd.eop0.aE6H/VZc36ZPM5w+jMmI
email: reg.apexfinance.vwuk@jmastodon.me
current visa card:
name: JOHN MASTODON
no: 4012888888881881
cvv2: fhd.KCaP.QHai
expires: 01/28
pin: fhd.y6En.tVMHWW+C
Team Overdraft: ...
google account:
-- note: FIDO2 2FA required --
login/email: j.x.mastodon789@gmail.com
pw: fhd.PNgg.HdKpOLE2b3DejycUGQO35RrtiA==
recovery email: reg.google.ce21@jmastodon.me
API private key: fhd.pxdw.QOQrvLsCcLR1X275/Pn6LBWl72uwbXoo/YiY
...
In this case, even relatively long-lived malware/compromise can only sniff
secrets that were used during that time, and it's mostly fine if this ends up
being opened and scrolled-through on a public video stream or some app screencaps
it by accident (or not) - all important secrets are in encrypted "fhd.XXX.YYY" form.
Downside of course is even more key management burden here, since simply storing
all these unique keys in a config file or a list won't do, as it'll end up being
equivalent to "encrypted file + key" case against leaks or machine compromise.
Storing encryption keys defeats the purpose of the whole thing, typing them
is insecure vs various keyloggers, and there's also way too many to remember!
Solution: get some cheap FIDO2 hardware key to do all key-management
for you, and then just keep it physically secure, i.e. put it on the keychain.
This does not require remembering anything (except maybe a single PIN, if you
set one, and can remember it reliably within 8 attempts), is reasonably safe
against all common digital threats, and pretty much as secure against physical
ones as anything can be (assuming rubber-hose cryptoanalysis works uniformly
well), if not more secure (e.g. permanent PIN attempts lockout).
Given the recent push for FIDO2 WebAuthn-compatible passkeys by major megacorps
(Google/Apple/MS), and that you'd probably want to have such FIDO2 token for
SSH keys and simple+secure full disk encryption anyway, there seems to be
no good reason not to use it for securing passwords as well, in a much better way
than with any memorized or stored-in-a-file schemes for secrets/keys, as outlined above.
There's no go-to way to do this yet (afaik), but all tools to implement it exist.
Filippo Valsorda described one way to do it via plugin for a common "age"
encryption tool in "My age+YubiKeys Password Management Solution" blog post,
using Yubikey-specific PIV-smartcard capability (present in some of Yubico tokens),
and a shell script to create separate per-service encrypted files.
I did it a bit differently, with secrets stored alongside non-secret notes and
other info/metadata, and with a common FIDO2-standard hmac-secret extension
(supported by pretty much all such devices, I think?), used in the following way:
Store ciphertext as a "fhd.y6En.tVMHWW+C" string, which is:
"fhd." || base64(salt) || "." || base64(wrapped-secret)
And keep those in the common list of various important info (also encrypted),
to view/edit with the usual emacs.
When specific secret or password is needed, point to it and press "copy
decrypted" hotkey (as implemented by fhd-crypt in my emacs).
Parsing that "fhd. ..." string gets "y6En" salt value, and it is sent to USB/NFC
token in the assertion operation (same as fido2-assert cli tool runs).
Hardware token user-presence/verification requires you to physically touch
button on the device (or drop it onto NFC pad), and maybe also enter a PIN
or pass whatever biometric check, depending on device and its configuration
(see fido2-token tool for that).
Token/device returns "hmac-sha256(salt, key=secret-generated-on-device)",
unique and unguessable for that salt value, which is then used to decrypt
"tVMHWW+C" part of the fhd-string into original "secret" string (via simple XOR).
Resulting "secret" value is copied into clipboard, to use wherever it was needed.
This ensures that every single secret string in such password-list is only
decryptable separately, also demanding a separate physical verification procedure,
very visible and difficult to do unintentionally, same as with WebAuthn.
Only actual secret key in this case resides on a FIDO2 device, and is infeasible
to extract from there, for any common threat model at least.
Encryption/wrapping of secret-string to fhd-string above works in roughly same
way - generate salt value, send to token, get back HMAC and XOR it with the secret,
cutting result down to that secret-string length.
Last part introduces a small info-leak - secret length - but don't think
that should be an issue in practice (always use long random passwords),
while producing nicer short ciphertexts.
There are also still some issues with using these physical dongles in a compomised
environment, which can lie about what it is being authorized by a device,
as they usually have no way to display that, but it's still a big improvement,
and can be somewhat mitigated by using multiple tokens for different purposes.
I've wrapped all these crypto bits into a simple C fido2-hmac-desalinate tool here:
https://github.com/mk-fg/fgtk#hdr-fido2-hmac-desalinate.c
Which needs "Relying Party ID" value to compile - basically an unique hostname
that ideally won't be used for anything else with that authenticator
(e.g. "token1.fhd.jmastodon.me" for some owned domain name), which is itself
not a secret of any kind.
FIDO2 "credential" can be generated and stored on device first, using cli tools
that come with libfido2, for example:
% fido2-token -L
% fido2-cred -M -rh -i cred.req.txt -o cred.info.txt /dev/hidraw5 eddsa
Such credential would work well on different machines with authenticators that
support FIDO2 Discoverable Credentials (aka Resident Keys), with HMAC key stored
on the same portable authenticator, but for simpler tokens that don't support
that and have no storage, static credential-id value (returned by fido2-cred tool
without "-r" option) also needs to be built-in via -DFHD_CID= compile-time parameter
(and is also not a secret).
(technically that last "credential-id value" has device-master-key-wrapped
HMAC-key in it, but it's only possible to extract from there by the device
itself, and it's never passed or exposed anywhere in plaintext at any point)
On the User Interface side, I use Emacs text editor to open/edit password-list
(also transparently-encrypted/decrypted using ghg tool), and get encrypted
stuff from it just by pointing at the needed secret and pushing the hotkey to
copy its decrypted value, implemented by fhd-crypt routine here:
https://github.com/mk-fg/emacs-setup/blob/21479cc/core/fg_sec.el#L178-L281
(also, with universal-arg, fhd-crypt encrypts/decrypts and replaces pointed-at
or region-selected thing in-place, instead of copying into clipboard)
Separate binary built against common libfido2 ensures that it's easy to use
such secret strings in any other way too, or fallback to manually decoding them
via cli, if necessary.
At least until push for passkeys makes no-password WebAuthn ubiquitous enough,
this seem to be the most convenient and secure way of password management for me,
but auth passwords aren't the only secrets, so it likely will be useful way
beyond that point as well.
One thing not mentioned above are (important!) backups for that secret-file.
I.e. what if FIDO2 token in question gets broken or lost?
And how to keep such backup up-to-date?
My initial simple fix is having a shell script that does basically this:
#!/bin/bash
set -eo pipefail
echo "### Paste new entry, ^D after last line to end, ^C to cancel"
echo "### Make sure to include some context for it - headers at least"
chunk=$(ghg -eo -r some-public-key | base64 -w80)
echo -e "--- entry [ $(date -Is) ]\n${chunk}\n--- end\n" >>backup.log
Then on any updates, to run this script and paste the updated plaintext
secret-block into it, before encrypting all secrets in that block for good.
It does one-way public-key encryption (using ghg tool, but common age or
GnuPG will work just as well), to store those encrypted updates, which can then
be safely backed-up alongside the main (also encrypted) list of secrets,
and everything can be restored from these using corresponding secure private key
(ideally not exposed or used anywhere for anything outside of such
fallback-recovery purposes).
Update 2024-02-21: secret-token-backup wrapper/tool is a more modern
replacement for that, which backs stuff up automatically, and can also be used
for safely getting specific secret out of there using other PIV yubikeys
(e.g. YK Nano stuck in a laptop's USB slot).
And one more aside - since plugging devices into USB rarely aligns correctly
on the first try (USB curse), is somewhat tedious, and can potentially wear-out
contacts or snap-off the device, I've grabbed a cheap PC/SC-compatible ACR122U
NFC reader from aliexpress, and have been using it instead of a USB interface,
as modern FIDO2 tokens tend to support NFC for use with smartphones.
It works great for this password-management purpose, placing the key on NFC
pad works instead of the touch presence-check with USB (at least with cheap
Yubico Security Key devices), with some short (<1 minute) timeout on the pad
in which token stops responding with ERR_PIN, to avoid misuse if one forgets
to remove it.
libfido2 supports PC/SC interface, and PCSC lite project providing it on
typical linux distros seem to support pretty much all NFC readers in existance.
libfido2 is in turn used by systemd, OpenSSH, pam-u2f, its fido2-token/cred/assert
cli, my fido2-hmac-desalinate password-management hack above, and many other tools.
So through it, all these projects automatically have easy and ubiquitous NFC support too.
(libfido2 also supports linux kernel AF_NFC interface in addition to PC/SC
one, which works for much narrower selection of card-readers implemented by
in-kernel drivers, so PC/SC might be easier to use, but kernel interface
doesn't need an extra pcscd dependency, if works for your specific reader)
Notable things that don't use that lib and have issues with NFC seem to be
browsers - both Firefox and Chromium on desktop (and their forks, see e.g.
mozbug-1669870) - which is a shame, but hopefully will be fixed there eventually.
Nov 30, 2022
I like and use B.A.T.M.A.N. (batman-adv) mesh-networking protocol on the LAN,
to not worry about how to connect local linuxy things over NICs and WiFi links
into one shared network, and been using it for quite a few years now.
Everything sensitive should run over ssh/wg links anyway (or ipsec before wg was
a thing), so it's not a problem to have any-to-any access in a sane environment.
But due to extra frame headers, batman-adv benefits from either lower MTU on the
overlay interface or higher MTU on all interfaces which it runs over, to avoid
fragmentation.
Instead of remembering to tweak all other interfaces, I think it's easier to
only bother with one batman-adv iface on each machine, but somehow that proved
to be a surprising challenge.
MTU on iface like "bat0" jumps on its own when slave interfaces in it change
state, so obvious places to set it, like networkd .network/.netdev files or
random oneshot boot scripts don't work - it can/will randomly change later
(usually immediately after these things set it on boot) and you'll only notice
when ssh or other tcp conns start to hang mid-session.
One somewhat-reliable and sticky workaround for having issues is to mangle TCP
MSS by the firewall (e.g. nftables), so that MTU changes are not an issue for
almost all connections, but that still leaves room for issues and fragmentation
in a few non-TCP things, and is obviously a hack - wrong MTU value is still there.
After experimenting with various "try to set mtu couple times after delay",
"wait for iface state and routes then set mtu" and such half-measures - none of
which worked reliably for that odd interface - here's what I ended up with:
[Unit]
Wants=network.target
After=network.target
Before=network-online.target
StartLimitBurst=4
StartLimitIntervalSec=3min
[Service]
Type=exec
Environment=IF=bat0 MTU=1440
ExecStartPre=/usr/lib/systemd/systemd-networkd-wait-online -qi ${IF}:off --timeout 30
ExecStart=bash -c 'rl=0 rl_win=100 rl_max=20 rx=" mtu [0-9]+ "; \
while read ev; do [[ "$ev" =~ $rx ]] || continue; \
printf -v ts "%%(%%s)T" -1; ((ts-=ts%%rl_win)); ((rld=++rl-ts)); \
[[ $rld -gt $rl_max ]] && exit 59 || [[ $rld -lt 0 ]] && rl=ts; \
ip link set dev $IF mtu $MTU || break; \
done < <(ip -o link show dev $IF; exec stdbuf -oL ip -o monitor link dev $IF)'
Restart=on-success
RestartSec=8
[Install]
WantedBy=multi-user.target
It's a "F this sh*t" approach of "anytime you see mtu changing, change it back
immediately", which seem to be the only thing that works reliably so far.
Couple weird things in there on top of "ip monitor" loop are:
systemd-networkd-wait-online -qi ${IF}:off --timeout 30
Waits for interface to appear for some time before either restarting the .service,
or failing when StartLimitBurst= is reached.
The :off networkd "operational status" (see networkctl(1)) is the earliest
one, and enough for "ip monitor" to latch onto interface, so good enough here.
rl=0 rl_win=100 rl_max=20 and couple lines with exit 59 on it.
This is rate-limiting in case something else decides to manage interface' MTU
in a similar "persistent" way (at last!), to avoid pulling the thing back-and-forth
endlessly in a loop, or (over-)reacting to interface state flapping weirdly.
I.e. stop service with failure on >20 relevant events within 100s.
Restart=on-success to only restart on "break" when "ip link set" fails if
interface goes away, limited by StartLimit*= options to also fail eventually if it
does not (re-)appear, or if that operation fails consistently for some other reason.
With various overlay tunnels becoming commonplace lately, MTU seem to be set
incorrectly by default about 80% of the time, and I almost feel like I'm done
fighting various tools with their way of setting it guessed/hidden somewhere
(if implemented at all), and should just extend this loop into a more generic
system-wide "mtud.service" that'd match interfaces by wildcard and enforce some
admin-configured MTU values, regardless of whatever creating them (wrongly)
thinks might be the right value.
As seem to be common with networking stuff - you either centralize configuration
like that on a system, or deal with constant never-ending stream of app failures.
Other good example here are in-app ACLs, connection settings and security
measures vs system firewalls and wg tunnels, with only latter actually working,
and former proven to be an utter disaster for decades now.
Nov 25, 2022
Following information sources on the internet has long been compared to
"drinking from a firehose", and trying to "keep up" with that is
how I think people end up with hundreds of tabs in some kind of backlog,
overflowing inboxes, feeds, podcast queues, and feeling overwhelmed in general.
Main problem for me with that (I think) was aggregation -
I've used web-based feed reader in the past, aggregated feeds
from slashdot/reddit/hn/lobsters (at different times), and followed
"influencers" on twitter to get personally-curated feeds from there
in one bundle - and none of it really worked well.
For example, even when following podcast feeds, you end up with a backlog
(of things to listen to) that is hard to catch-up with - natually -
but it also adds increasingly more tracking and balancing issues,
as simply picking things in order will prioritize high-volume stuff,
and sometimes you'll want to skip the queue and now track "exceptions",
while "no-brainer" pick pulls increasingly-old and irrelevant items first.
Same thing tends to happen with any bundle of feeds that you try to "follow",
which always ends up being overcrowded in my experience, and while you can
"declare bankrupcy" resetting the follow-cursor to "now", skipping backlog,
that doesn't solve fundamental issue with this "following" model -
you'll just fall behind again, likely almost immediately - the approach itself
is wrong/broken/misguided.
Obvious "fix" might be to curate feeds better so that you can catch-up,
but if your interests are broad enough and changing, that's rarely an option,
as sources tend to have their own "take it or leave it" flow rate,
and narrowing scope to only a selection that you can fully follow is silly and
unrepresentative for those interests, esp. if some of them are inconsistent or
drown out others, even while being generally low-noise.
Easy workable approach, that seem to avoid all issues that I know of, and worked
for me so far, goes something like this:
- Bookmark all sources you find interesting individually.
- When you want some podcast to listen-to, catch-up on news in some area,
or just an interesting thing to read idly - remember it - as in
"oh, would be nice to read/know-about/listen-to this right now".
- Then pull-out a bookmark, and pick whatever is interesting and
most relevant there, not necessarily latest or "next" item in any way.
This removes the mental burden of tracking and curating these sources,
balancing high-traffic with more rarefied ones, re-weighting stuff according
to your current interests, etc - and you don't loose on anything either!
I.e. with something relevant to my current interests I'll remember to go back to
it for every update, but stuff that is getting noisy or falling off from that
sphere, or just no longer entertaining or memorable, will naturally slip my mind
more and more often, and eventually bookmark itself can be dropped as unused.
Things that I was kinda afraid-of with such model before -
and what various RSS apps or twitter follows "help" to track:
- I'll forget where/how to find important info sources.
- Forget to return to them.
- Miss out on some stuff there.
- Work/overhead of re-checking for updates is significant.
None of these seem to be an issue in practice, as most interesting and relevant
stuff will natually be the first thing that will pop-up in memory to check/grab/read,
you always "miss out" on something when time is more limited than amount of
interesting goodies (i.e. it's a problem of what to miss-out on, not whether you
do or don't), and time spent checking couple bookmarks is a rounding error
compared to processing the actual information (there's always a lot of new
stuff, and for something you check obsessively, you'd know the rate well).
This kind of "disaggregated buffet" way of zero-effort "controlling" information
intake is surprisingly simple, pretty much automatic (happens on its own),
very liberating (no backlog anywhere), and can be easily applied to different
content types:
Don't get podcast rss-tracking app, bookmark individual sites/feeds instead.
I store RSS/Atom feed URLs under one bookmarks-dir in Waterfox, and when
wanting for something to listen on a walk or while doing something monotonous,
remember and pull out an URL via quickbar (bookmarks can be searched via *
<query> there iirc, I just have completion/suggestions enabled for bookmarks
only), run rss-get script on the link, pick specific items/ranges/links to
download via its aria2c or yt-dlp (with its built-in SponsorBlock), play that.
Don't "follow" people/feeds/projects on twitter or fediverse/mastodon
and then read through composite timeline, just bookmark all individual feeds
(on whatever home instances, or via nitter) instead.
This has a great added advantage of maintaining context in these platforms
which are notoriously bad for that, i.e. you read through things as they're
posted in order, not interleaved with all other stuff, or split over time.
Also this doesn't require an account, running a fediverse instance,
giving away your list of follows (aka social graph), or having your [current]
interests being tracked anywhere (even if "only" for bamboozling you with ads
on the subject to death).
With many accounts to follow and during some temporary twitter/fediverse
duplication, I've also found it useful (so far) to have a simple ff-cli script
to "open N bookmarks matching /@", when really bored, and quickly catch-up on
something random, yet interesting enough to end up being bookmarked.
Don't get locked into subscribing or following "news" media that is kinda shit.
Simply not having that crap bundled with other things in same
reader/timeline/stream/etc will quickly make brain filter-out and "forget"
sources that become full of ads, <emotion>bait, political propaganda
and various other garbage, and brain will do such filtering all in the
background on its own, without wasting any time or conscious cycles.
There's usually nothing of importance to miss with such sources really,
as it's more like taking a read on the current weather,
only occasionally interesting/useful, and only for current/recent stuff.
It's obviously not a guide to something "objectively best", and maybe only
works well for me this way, but as I've kinda-explained it (poorly) in chats
before, thought to write it down here too - hopefully somewhat more coherently -
and maybe just link to later from somewhere.
Nov 18, 2022
Haven't found anything good for this on the internet before, and it's often useful
in various shell scripts where metrics or tunable numbers can get rather long:
3400000000 -> 3_400M
500000 -> 500K
8123455009 -> 8_123_455_009
That is, to replace long stretches of zeroes with short Kilo/Mega/Giga/etc
suffixes and separate the usual 3-digit groups by something (underscore being
programming-language-friendly and hard to mistake for field separator),
and also convert those back to pure integers from cli arguments and such.
There's numfmt in GNU coreutils, but that'd be missing on Alpine, typical
network devices, other busybox Linux distros, *BSD, MacOS, etc, and it doesn't
have "match/convert all numbers you want" mode anyway.
So alternative is using something that is available everywhere, like generic
AWK, with a reasonably short scripts to implement that number-mangling logic.
Human-format all space-separated long numbers in stdin, like in example above:
awk '{n=0; while (n++ <= NR) { m=0
while (match($n,/^[0-9]+[0-9]{3}$/) && m < 5) {
k=length($n)-3
if (substr($n,k+1)=="000") { $n=substr($n,1,k); m++ }
else while (match($n,/[0-9]{4}(_|$)/))
$n = substr($n,1,RSTART) "_" substr($n,RSTART+1) }
$n = $n substr("KMGTP", m, m ? 1 : 0) }; print}'
Find all human-formatted numbers in stdin and convert them back to long integers:
awk '{while (n++ <= NR) {if (match($n,/^([0-9]+_)*[0-9]+[KMGTP]?$/)) {
sub("_","",$n); if (m=index("KMGTP", substr($n,length($n),1))) {
$n=substr($n,1,length($n)-1); while (m-- > 0) $n=$n "000" } }}; print}'
I.e. reverse of the operation above.
Code is somewhat compressed for brevity within scripts where it's not the point.
It should work with any existing AWK implementations afaik (gawk, nawk, busybox
awk, etc), and not touch any fields that don't need such conversion (as filtered
by the first regexp there).
Line-match pattern can be added at the start to limit conversion to lines with
specific fields (e.g. match($1,/(Count|Threshold|Limit|Total):/) {...}),
"n" bounds and $n regexps adjusted to filter-out some inline values.
Numbers here will use SI prefixes, not 2^10 binary-ish increments,
like in IEC units (kibi-, mebi-, gibi-, etc), as is more useful in general,
but substr() and "000"-extension can be replaced by /1024 (and extra -iB unit
suffix) when working with byte values - AWK can do basic arithmetic just fine too.
Took me couple times misreading and mistyping overly long integers from/into
scripts to realize that this is important enough and should be done better than
counting zeroes with arrow keys like some tech-barbarian, even in simple bash
scripts, and hopefully this hack might eventually pop-up in search for someone
else coming to that conclusion as well.
Oct 21, 2022
I've been using this as a prepare-commit-msg hook everywhere for couple years now:
#!/bin/bash
msg_file=$1 commit_src=$2 hash=$3
[[ -z "$msg_file" || "$GIT_EDITOR" = : ]] && exit 0
[[ -z "$commit_src" ]] || exit 0 # cherry-picks, merges, etc
echo >>"$msg_file" '#'
echo >>"$msg_file" "# Commit dir: ${GIT_PREFIX%/}"
echo >>"$msg_file" "# Repo dir: $(realpath "$PWD")"
echo >>"$msg_file" '#'
git log -10 --format='# %s' >>"$msg_file"
Which saves a lot of effort of coming up with commit-messages, helps in
monorepos/collections and to avoid whole bunch of mistakes.
Idea is that instead of just "what is to be comitted", comment below commit-msg
in $EDITOR will now include something like this:
# On branch master
# Changes to be committed:
# modified: PKGBUILD
# new file: 9005.do-some-other-thing.patch
#
# Commit dir: waterfox
# Repo dir: /home/myuser/archlinux-pkgbuilds
#
# waterfox: +9004.rebind_screenshot_key_to_ctrl_alt_s.patch
# waterfox: fix more build/install issues
# waterfox: +fix_build_with_newer_cbindgen.patch
# waterfox: update to G5.0.1
# +re2g-git
# waterfox: bump to G4.1.4
# +mount-idmapped-git
# telegram-tdlib-purple-*: makedepends=telegram-tdlib - static linking
# waterfox: update for G4.1.1
# +b2tag-git
It helps as a great sanity-check and reminder of the following things:
Which subdir within the repo you are working in, e.g. "waterfox" pkg above,
so that it's easy to identify and/or use that as a part of commit message.
With a lot of repositories I work with, there are multiple subdirs and
components in there, not to mention collection-repos, and it's useful to have
that in the commit msg - I always try to add them as a prefix, unless repo
uses entirely different commit message style (and has one).
What is the repository directory that you're running "git commit" in.
There can be a local dev repo, a submodule of it in a larger project,
sshfs-mounted clone of it somewhere, more local clones for diff branches
or different git-worktree dirs, etc.
This easily tells that you're in the right place (or where you think you are),
usually hard to miss by having repo under local simple dev dir, and not some
weird submodule path or mountpoint in there.
List of last commits on this branch - incredibly useful for a ton of reasons.
For one, it easily keeps commit-msgs consistent - you don't use different
language, mood and capitalization in there by forgetting what is the style
used in this particular repo, see any relevant issue/PR numbers, prefixes/suffixes.
But also it immediately shows if you're on the wrong branch, making a duplicate
commit by mistake, forgot to make commit/merge for something else important
before this, undo some reset or other recent shenanigans - all at a glance.
It was a usual practice for me to check git-log before every commit, and this
completely eliminated the need for it.
Now when I don't see this info in the commit-msg comment, first thing to do is
copy the hook script to whatever repo/host/place I'm working with, as it's
almost as bad as not seeing which files you commit in there without it.
Can highly recommend this tiny time-saver when working with any git repos from
the command line.
Implementation has couple caveats, which I've added there over time:
[[ -z "$msg_file" || "$GIT_EDITOR" = : ]] && exit 0
[[ -z "$commit_src" ]] || exit 0 # cherry-picks, merges, etc
These lines are to skip running this hook for various non-interactive git
operations, where anything you put into commit-msg will get appended to it
verbatim, without skipping comment-lines, as it is done with interactive
"git commit" ops.
Canonical version of the hook is in the usual mk-fg/fgtk dumping ground:
https://github.com/mk-fg/fgtk#git-prepare-commit-msg-hook
Which might get more caveats like above fixed in the future, should I bump into
any, so might be better than current version in this post.
Oct 19, 2022
When playing some game (Starsector, probably) on the primary display recently,
having aux emacs frame (an extra X11 window) on the second one with some
ERC chat in there (all chats translate to irc), I've had a minor bug somewhere
and noticed that cursor in that frame/window wasn't of the usual
translucent-green-foreground-text color (on a dark bg), but rather stayed simply
#fff-white (likely because of some screwup in my theme-application func
within that frame).
And an interesting observation is that it's actually really good when cursor is
of a different color from both foreground-text and the background colors,
because then it easily stands out against both, and doesn't get lost in a wall
of text either - neat!
Quickly googling around for a hack to make this fluke permanent, stumbled upon
this reply on Stack Overflow, which, in addition to easy (set-cursor-color
...) answer, went on to give an example of changing color on every cusor blink.
Which seems like a really simple way to make the thing stand out not just
against bg/fg colors, but also against any syntax-highlighting color anywhere,
and draw even more attention to itself, which is even better.
With only a couple lines replacing a timer-func that normally turns cursor
on-and-off (aka blinking), now it blinks with a glorious rainbow of colors:
https://github.com/mk-fg/emacs-setup/blob/afc1477/core/fg_lookz.el#L485-L505
And at least I can confirm that it totally works for even greater/more-immediate
visibility, especially in multiple emacs windows (e.g. usual vertical split
showing two code buffers), where all these cursors now change colors and
impossible to miss at a glance, so you always know which point in code you're
jumping to upon switching there - can recommend to at least try it out.
Bit weird that most code editor windows seem to have narrow-line cursor,
even if of a separate color, given how important that detail is within that
window, compared to e.g. any other arbitrary glyph in there, which would be
notably larger and often more distinct/visible, aside from blinking.
One interesting part with a set of colors, as usual, is to generate or pick
these somehow, which can be done on a color wheel arbitrarily, with results
often blending-in with other colors and each other, more-or-less.
But it's also not hard to remember about L*a*b* colorspace and pick colors
that will be almost certainly distinct according to ranges there, as you'd do
with a palette for dynamic lines on a graph or something more serious like that.
These days I'm using i want hue generator-page to get a long-ish list of
colors within specified ranges for Lightness (L component, to stand-out against
light/dark bg) and Chroma parameters, and then pass css list of these into a
color-b64sort script, with -b/--bg-color and -c/--avoid-color settings/thresholds.
Output is a filtered list with only colors that are far enough from the
specified ones, to stand-out against them in the window, but is also sorted
to have every next color picked to be most visually-distinct against preceding ones
(with some decay-weight coefficient to make more-recent diff[s] most relevant),
so that color doesn't blink through similar hues in a row, and you don't
have to pick/filter/order and test these out manually.
Which is the same idea as with the usual palette-picks for a line on a chart or
other multi-value visualizations (have high contrast against previous/other values),
that seem to pop-up like this in surprisingly many places, which is why at some
point I just had to write that dedicated color-b64sort thingie to do it.
Tweaking parameters to only get as many farthest-apart colors as needed for
blinks until cursor goes static (to avoid wasting CPU cycles blinking in an idle
window), ended up with a kind of rainbow-cursor, counting bright non-repeating
color hues in a fixed order, which is really nice for this purpose and also just
kinda cool and fun to look at.
Oct 18, 2022
A while ago as I've discovered for myself using xattrs, ACLs and capabilities
for various system tasks, and have been using those in python2-based tools
via C wrappers for libacl and libcap (in old mk-fg/fgc repo) pretty much
everywhere since then.
Tools worked without any issues for many years now, but as these are one of the
last scripts left still in python2, time has come to update those, and revisit
how to best access same things in python3.
Somewhat surprisingly, despite being supported on linux since forever, and
imo very useful, support for neither ACLs nor capabilities haven't made it
into python 3.10's stdlib, but there is now at least built-in support for
reading/writing extended attributes (without ctypes, that is), and both of these
are simple structs stored in them.
So, disregarding any really old legacy formats, parsing ACL from a file
in a modern python can be packed into something like this:
import os, io, enum, struct, pwd, grp
class ACLTag(enum.IntEnum):
uo = 0x01; u = 0x02; go = 0x04; g = 0x08
mask = 0x10; other = 0x20
str = property(lambda s: s._name_)
class ACLPerm(enum.IntFlag):
r = 4; w = 2; x = 1
str = property(lambda s: ''.join(
(v._name_ if v in s else '-') for v in s.__class__ ))
def parse_acl(acl, prefix=''):
acl, lines = io.BytesIO(acl), list()
if (v := acl.read(4)) != b'\2\0\0\0':
raise ValueError(f'ACL version mismatch [ {v} ]')
while True:
if not (entry := acl.read(8)): break
elif len(entry) != 8: raise ValueError('ACL length mismatch')
tag, perm, n = struct.unpack('HHI', entry)
tag, perm = ACLTag(tag), ACLPerm(perm)
match tag:
case ACLTag.uo | ACLTag.go:
lines.append(f'{tag.str[0]}::{perm.str}')
case ACLTag.u | ACLTag.g:
try:
name = ( pwd.getpwuid(n).pw_name
if tag is tag.u else grp.getgrgid(n).gr_name )
except KeyError: name = str(n)
lines.append(f'{tag.str}:{name}:{perm.str}')
case ACLTag.other: lines.append(f'o::{perm.str}')
case ACLTag.mask: lines.append(f'm::{perm.str}')
case _: raise ValueError(tag)
lines.sort(key=lambda s: ('ugmo'.index(s[0]), s))
return '\n'.join(f'{prefix}{s}' for s in lines)
p = 'myfile.bin'
xattrs = dict((k, os.getxattr(p, k)) for k in os.listxattr(p))
if acl := xattrs.get('system.posix_acl_access'):
print('Access ACLs:\n' + parse_acl(acl, ' '))
if acl := xattrs.pop('system.posix_acl_default', ''):
print('Default ACLs:\n' + parse_acl(acl, ' d:'))
Where it's just a bunch of 8B entries with uids/gids and permission bits in
them, and capabilities are even simpler, except for ever-growing enum of them:
import os, io, enum, struct, dataclasses as dcs
CapSet = enum.IntFlag('CapSet', dict((cap, 1 << n) for n, cap in enumerate((
' chown dac_override dac_read_search fowner fsetid kill setgid setuid setpcap'
' linux_immutable net_bind_service net_broadcast net_admin net_raw ipc_lock'
' ipc_owner sys_module sys_rawio sys_chroot sys_ptrace sys_pacct sys_admin'
' sys_boot sys_nice sys_resource sys_time sys_tty_config mknod lease'
' audit_write audit_control setfcap mac_override mac_admin syslog wake_alarm'
' block_suspend audit_read perfmon bpf checkpoint_restore' ).split())))
@dcs.dataclass
class Caps: effective:bool; permitted:CapSet; inheritable:CapSet
def parse_caps(cap):
cap = io.BytesIO(cap)
ver, eff = ((v := struct.unpack('I', cap.read(4))[0]) >> 3*8) & 0xff, v & 1
if ver not in [2, 3]: raise ValueError(f'Unsupported capability v{ver}')
perm1, inh1, perm2, inh2 = struct.unpack('IIII', cap.read(16))
if (n := len(cap.read())) != (n_tail := {2:0, 3:4}[ver]):
raise ValueError(f'Cap length mismatch [ {n} != {n_tail} ]')
perm_bits, inh_bits = perm2 << 32 | perm1, inh2 << 32 | inh1
perm, inh = CapSet(0), CapSet(0)
for c in CapSet:
if perm_bits & c.value: perm |= c; perm_bits -= c.value
if inh_bits & c.value: inh |= c; inh_bits -= c.value
if perm_bits or inh_bits:
raise ValueError(f'Unrecognized cap-bits: P={perm_bits:x} I={inh_bits:x}')
return Caps(eff, perm, inh)
p = 'myfile.bin'
try: print(parse_caps(os.getxattr(p, 'security.capability')))
except OSError: pass
Bit weird that wrappers along these lines can't be found in today's python 3.10,
but maybe most people sadly still stick to suid and more crude hacks where more
complex access permissions are needed.
One interesting thing I found here is how silly my old py2 stracl.c and
strcaps.c look in comparison - it's screenfuls of lines of more complicated
C code, tied into python's c-api, and have to be compiled wherever these tools
are used, with an extra python wrappers on top - all for parsing a couple of
trivial structs, which under linux ABI compatibility promises, can be relied
upon to be stable enough anyway.
Somehow it's been the obvious solution back then, to have compiler check all
headers and link these libs as compatibility wrappers, but I'd never bother
these days - it'll be either ctypes wrapper, or parsing simple stuff in python,
to avoid having extra jank and hassle of dependencies where possible.
Makes me wonder if that's also the dynamic behind relatively new js/rust devs
dragging in a bunch of crap (like the infamous left-pad) into their apps,
still thinking that it'd make life simpler or due to some "good practice" dogmas.
May 30, 2022
Using man <something> in the terminal as usual, I've been noticing more and
more manpages being broken by tools that produce them over the years in this one
specific way - long command-line options with double-dash are being mangled into
having unicode en-dash "–" prefix instead of "--".
Most recent example that irked me was yt-dlp(1) manpage, which looks like
this atm (excerpt as of 2022-05-30):
-h, –help
Print this help text and exit
–version
Print program version and exit
-i, –ignore-errors
Ignore download and postprocessing errors. The download
will be considered successful even if the postprocessing fails
–no-abort-on-error
Continue with next video on download errors;
e.g. to skip unavailable videos in a playlist (default)
–abort-on-error
Abort downloading of further videos if an error occurs
(Alias: –no-ignore-errors)
Update 2023-09-10: current feh(1) manpage has another issue - unicode
hyphens instead of the usual ascii hyphen/minus signs (which look similar,
but aren't the same thing - even more evil!):
OPTIONS
‐A, ‐‐action [flag][[title]]action
If you habitually copy-paste any of the long opts there into a script (or yt-dlp
config, as it happens), to avoid retyping these things, it won't work, because
e.g –help cli option should of course actually be --help, i.e. have two
ascii hyphens and not any kind of unicode dash characters.
From a brief look, this seem to happen because of conversion from markdown and
probably not enough folks complaining about it, which is a pattern that I too
chose to follow, and make a workaround instead of reporting a proper bug :)
(tbf, youtube-dl forks have like 1000s of these in tracker, and I'd rather not add to
that, unless I have a patch for some .md tooling it uses, which I'm too lazy to look into)
"man" command (from man-db on linux) uses a pager tool to display its stuff
in a terminal cli (controlled by PAGER= or MANPAGER= env vars), which is
typically set to use less tool on desktop linuxes (with the exception of
minimal distros like Alpine, where it comes from busybox).
"less" somewhat-infamously supports filtering of its output (which is
occasionally abused in infosec contexts to make a file that installs rootkit if
you run "less" on it), which can be used here for selective filtering and fixes
when manpage is being displayed through it.
Relevant variable to set in ~/.zshrc or ~/.bashrc env for running a filter-script is:
LESSOPEN='|-man-less-filter %s'
With |- magic before man-less-filter %s command template indicating that
command should be also used for pipes and when less is displaying stdin.
"man-less-filter" helper script should be in PATH, and can look something like
this to fix issues in yt-dlp manpage excerpt above:
#!/bin/sh
## Script to fix/replace bogus en-dash unicode chars in broken manpages
## Intended to be used with LESSOPEN='|-man-less-filter %s'
[ -n "$MAN_PN" ] || exit 0 # no output = use original input
# \x08 is backspace-overprint syntax that "man" uses for bold chars
# Bold chars are used in option-headers, while opts in text aren't bold
seds='s/‐/-/g;'`
`'s/–\x08–\(.\x08\)/-\x08--\x08-\1/g;'`
`' s/\([ [:punct:]]\)–\([a-z0-9]\)/\1--\2/'
[ "$1" != - ] || exec sed "$seds"
exec sed "$seds" "$1"
It looks really funky for a reason - simply using s/–/--/ doesn't work,
as manpages use old typewriter/teletype backspace-overtype convention for
highlighting options in manpages.
So, for example, -h, –help line in manpage above is actually this sequence
of utf-8 - -\x08-h\x08h,\x08, –\x08–h\x08he\x08el\x08lp\x08p\n - with
en-dash still in there, but \x08 backspaces being used to erase and retype
each character twice, which makes "less" display them in bold font in the terminal
(using its own different set of code-bytes for that from ncurses/terminfo).
Simply replacing all dashes with double-hyphens will break that overtyping
convention, as each backspace erases a single char before it, and double-dash is
two of those.
Which is why the idea in the script above is to "exec sed" with two substitution
regexps, first one replacing all overtyped en-dash chars with correctly-overtyped
hyphens, and second one replacing all remaining dashes in the rest of the text
which look like options (i.e. immediately followed by letter/number instead of space),
like "Alias: –no-ignore-errors" in manpage example above, where text isn't in bold.
MAN_PN env-var check is to skip all non-manpage files, where "less" understands
empty script output as "use original text without filtering".
/bin/dash can be used instead of /bin/sh on some distros (e.g. Arch, where
sh is usually symlinked to bash) to speed up this tiny script startup/runs.
Not sure whether "sed" might have to be a GNU sed to work with unicode char
like that, but any other implementation can probably use \xe2\x80\x93 escape-soup
instead of – in regexps, which will sadly make them even less readable than usual.
Such manpage bugs should almost certainly be reported to projects/distros and fixed,
instead of using this hack, but thought to post it here anyway, since google
didn't help me find an exising workaround, and fixing stuff properly is more work.
Update 2023-09-10: Current man(1) from man-db has yet another
issue to work around - it sanitizes environment before running "less",
dropping LESSOPEN from there entirely.
Unfortunately, at least current "less" doesn't seem to support config file,
to avoid relying entirely on apps passing env-vars around (maybe for a good
reason, given how they like to tinker with its configuration),
so easy fix is a tiny less.c wrapper for it:
#include <unistd.h>
#include <stdlib.h>
int main(int argc, char *argv[]) {
if (getenv("MAN_PN")) setenv("LESSOPEN", "|-man-less-filter %s", 1);
execv("/usr/bin/less", argv); return 1; }
gcc -O2 less.c -o less && strip less, copy it to ~/bin or such, and make
sure env uses PAGER=less or a wrapper path, instead of original /usr/bin/less.
May 05, 2022
Alpine Linux is a tiny distro (like ~50 MiB for the whole system),
which is usually very good for a relatively single-purpose setup,
dedicated to running only a couple things at once.
It doesn't really sacrifice much in the process, since busybox and OpenRC
there provide pretty complete toolkit for setting things up to start
and debugging everything, its repos have pretty much anything,
and what they don't have is trivial to build via APKBUILD files
very similar to Arch's PKGBUILDs.
Really nice thing seem to have happened to it with the rise of docker/podman
and such single-app containers, when it got a huge boost in popularity,
being almost always picked as an OS base in these, and so these days
it seem to be well-supported to cover all linux architectures,
and likely will be for quite a while.
So it's a really good choice for an appliance-type ARM boards to deploy and
update for years, but it doesn't really bother specializing itself for each of
those or supporting board-specific quirks, which is why some steps to set it up
for a specific board have to be done manually.
Since I've done it for a couple different boards relatively recently, and been
tinkering with these for a while, thought to write down a list of steps on how
to set alpine up for a new board here.
In this case, it's a relatively-old ODROID-C2 that I have from 2016, which is
well-supported in mainline linux kernel by now, as popular boards tend to be,
after a couple years since release, and roughly same setup steps should apply
to any of them.
Current Alpine is 3.15.4 and Linux is 5.18 (or 5.15 LTS) atm of writing this.
Get USB-UART dongle (any dirt-cheap $5 one will do) and a couple jumper wires,
lookup where main UART pins are on the board (ones used by firmware/u-boot).
Official documentation or wiki is usually the best source of info on that.
There should be RX/TX and GND pins, only those need to be connected.
screen /dev/ttyUSB0 115200 command is my go-to way to interact with those,
but there're other tools for that too.
If there's another ARM board laying around, they usually have same UART
pins, so just twist TX/RX and connect to the serial console from there.
Check which System-on-Chip (SoC) family/vendor device uses, look it up wrt
mainline linux support, and where such effort might be coordinated.
Beaglebones' TI SoC at
elinux.org, RPi's site/community, ... etc etc.
There're usually an IRC or whatever chat channels linked on those too,
and tons of helpful info all around, though sometimes outdated and distro-specific.
Get U-Boot for the board, ideally configured for some sane filesystem layout.
"Generic ARM" images on Alpine Downloads page tend to have these,
but architecture is limited to armv7/aarch64 boards, but a board vendor's
u-boot will work just as well, and it might come with pre-uboot stages or
signing anyway, which definitely have to be downloaded from their site and docs.
With ODC2, there're docs and download links for bootloader specifically,
which include an archive with a signing tool and a script to sign/combine all blobs
and dd them into right location on microSD card, where firmware will try to run it from.
Bootloader can also be extracted from some vendor-supplied distro .img
(be it ubuntu or android), if there's no better option - dd that on the card
and rm -rf all typical LFS dirs on the main partition there, as well as
kernel/initramfs in /boot - what's left should be a bootloader
(incl. parts of it dd'ed before partitions) and its configs.
Often all magic there is "which block to dd u-boot.img to", and if
Alpine Generic ARM has u-boot blob for specific board (has one for ODROID-C2),
then that one should be good to use, along with blobs in /efi and its main
config file in /extlinux - dd/cp u-boot to where firmware expects it to be
and copy those extra stage/config dirs.
Alpine wiki might have plenty of board-specific advice too, e.g. check out
Odroid-C2 page there.
Boot the board into u-boot with UART console connected, get that working.
There should be at least output from board's firmware, even without any
microSD card, then u-boot will print a lot of info about itself and what
it's doing, and eventually it (or later stages) will try to load linux kernel,
initramfs and dtb files, specified in whatever copied configs.
If "Generic ARM" files or whatever vendor distro was not cleaned-up from card
partitions, it might even start linux and some kind of proper OS, though kernel
in that generic alpine image seem to be lacking ODC2 board support and has no
dtb for it.
Next part is to drop some working linux kernel/dtb (+initramfs maybe),
rootfs, and that should boot into something interactive.
Conversely, no point moving ahead with the rest of the setup until bootloader
and console connected there all work as expected.
Get or build a working Linux kernel.
It's not a big deal (imo at least) to configure and build these manually,
as there aren't really that many options when configuring those for ARM -
you basically pick the SoC and all options with MESON or SUNXI in the name
for this specific model, plus whatever generic features/filesystems/etc
you will need in there.
Idea is to enable with =y (compile-in) all drivers that are needed
for SoC to boot, and the rest can be =m (loadable modules).
Ideally after being built somewhere, kernel should be installed via proper
Alpine package, and for my custom ODC2 kernel, I just reused linux-lts
APKBUILD file from "aports" git repository, running "make nconfig" in
src/build-... dir to make new .config and then copy it back for abuild to use.
Running abuild -K build rootpkg is generally how kernel package can be
rebuilt after any .config modifications in the build directory, i.e. after
fixing whatever forgotten things needed for boot.
(good doc/example of the process can be found at strfry's blog here)
These builds can be run in same-arch alpine chroot, in a VM or on some other board.
I've used an old RPi3 board to do aarch64 build with an RPi Alpine image
there - there're special pre-configured ones for those boards, likely
due to their massive popularity (so it was just the easiest thing to do).
I'd also suggest renaming the package from linux-lts to something unique for
specific build/config, like "linux-odc2-5-15-36", with idea there being able
to install multiple such linux-* packages alongside each other easily.
This can help a lot if one of them might have issues in the future -
not booting, crashes/panics, any incompatibilities, etc - as you can then
simply flip bootloader config to load earlier version, and test new versions
without comitting to them easily via kexec (especially cool for remote
headless setups - see below).
For C2 board kconfig, I've initially grabbed one from
superna9999/meta-meson repo, built/booted that (on 1G-RAM RPi3, that large
build needed zram enabled for final vmlinuz linking), to test if it works at all,
and then configured much more minimal kernel from scratch.
One quirk needed there for ODC2 was enabling CONFIG_REGULATOR_* options for
"X voltage supplied by Y" messages in dmesg that eventually enable MMC reader,
but generally kernel's console output is pretty descriptive wrt what might be missing,
especially if it can be easily compared with an output from a working build like that.
For the purposes of initial boot, linux kernel is just one "vmlinuz" file
inside resulting .apk (tar can unpack those), but dtbs-* directory must be
copied from package alongside it too for ARM boards like these odroids, as they
use blobs there to describe what is connected where and how to kernel.
Specific dtb can also be concatenated into kernel image file, to have it all-in-one,
but there should be no need to do that, as all such board bootloaders expect
to have dtbs and have configuration lines to load them already.
So, to recap:
- Linux configuration: enable stuff needed to boot and for accessing MMC slot,
or whatever rootfs/squashfs storage.
- Build scripts: use APKBUILD from Alpine aports, just tweak config there
and maybe rename it, esp. if you want multiple/fallback kernels.
- Build machine: use other same-arch board or VM with alpine or its chroot.
- Install: "tar -xf" apk, drop vmlinuz file and dtbs dir into /boot.
Update extlinux.conf or whatever bootloader config for new kernel files, boot that.
E.g. after dropping vmlinuz and dtbs from "linux-c51536r01" package for u-boot.bin
from Alpine's "Generic ARM" build (running efi blob with extlinux.conf support):
TIMEOUT 20
PROMPT 1
DEFAULT odc2
LABEL odc2
MENU LABEL Linux odc2
KERNEL /boot/vmlinuz-c51536r01
# INITRD /boot/initramfs-c51536r01
FDTDIR /boot/dtbs-c51536r01
APPEND root=/dev/mmcblk0p1
Idea with this boot config is to simply get kernel to work and mount some
rootfs without issues, so e.g. for custom non-generic/modular one,
built specifically for ODROID-C2 board in prev step, there's no need for
that commented-out INITRD line.
Once this boots and mounts rootfs (and then presumably panics as it can't find
/sbin/init there), remaining part is to bootstrap/grab basic alpine rootfs for
it to run userspace OS parts from.
This test can also be skipped for more generic and modular kernel config,
as it's not hard to test it with proper roots and initramfs later either.
Setup bootable Alpine rootfs.
It can be grabbed from the same Alpine downloads URL for any arch,
but if there's already a same-arch alpine build setup for kernel package,
might be easier to bootstrap it with all necessary packages there instead:
# apk='apk -p odc2-root -X https://dl.alpinelinux.org/alpine/v3.15/main/ -U --allow-untrusted'
# $apk --arch aarch64 --initdb add alpine-base
# $apk add linux-firmware-none mkinitfs
# $apk add e2fsprogs # or ones for f2fs, btrfs or whatever
# $apk add linux-c51536r01-5.15.36-r1.apk
To avoid needing --allow-untrusted for anything but that local linux-c51536r01
package, apk keys can be pre-copied from /etc/apk to odc2-root/etc/apk just
like Alpine's setup-disk script does it.
That rootfs will have everything needed for ODC2 board to boot, including
custom kernel with initramfs generated for it, containing any necessary modules.
Linux files on /boot should overwrite manually-unpacked/copied ones in earlier
test, INITRD or similar line can be enabled/corrected for bootloader,
but after cp/rsync, rootfs still needs a couple additional tweaks
(again similar to what setup-disk Alpine script does):
etc/fstab: add e.g. /dev/mmcblk0p1 / ext4 rw,noatime 0 1 to fsck/remount rootfs.
I'd add tmpfs /tmp tmpfs size=30%,nodev,nosuid,mode=1777 0 0 there as well,
since Alpine's OpenRC is not systemd and doesn't have default mountpoints
all over the place.
etc/inittab: comment-out all default tty's and enable UART one.
E.g. ttyAML0::respawn:/sbin/getty -L ttyAML0 115200 vt100 for ODROID-C2 board.
This is important to get login prompt on the right console,
so make sure to check kernel output to find the right one, e.g. with ODC2 board:
c81004c0.serial: ttyAML0 at MMIO 0xc81004c0 (irq = 23, base_baud = 1500000) is a meson_uart
But it can also be ttyS0 or ttyAMA0 or something else on other ARM platforms.
etc/securetty: add ttyAML0 line for console there too, same as with inittab.
Otherwise even though login prompt will be there, getty will refuse to ask
for password on that console, and immediately respond with "user is disabled"
or something like that.
This should be enough to boot and login into working OS on the same UART console.
Setup basic stuff on booted rootfs.
With initial rootfs booting and login-able, all that's left to get this to
a more typical OS with working network and apk package management.
"vi" is default editor in busybox, and it can be easy to use once you know to
press "i" at the start (switching it to a notepad-like "insert" mode),
and press "esc" followed by ":wq" + "enter" at the end to save edits
(or ":q!" to discard).
/etc/apk/repositories should have couple lines like
https://dl.alpinelinux.org/alpine/v3.15/main/, appropriate for this
Alpine release and repos (just main + community, probably)
echo nameserver 1.1.1.1 > /etc/resolv.conf + /etc/network/interfaces:
printf '%s\n' >/etc/network/interfaces \
'auto lo' 'iface lo inet loopback' 'auto eth0' 'iface eth0 inet dhcp'
Or something like that.
Also, to dhcp-configure network right now:
ip link set eth0 up && udhcpc
ntpd -dd -n -q -p pool.ntp.org
rc-update add anything used/useful from /etc/init.d.
There aren't many scripts in there by default,
and all should be pretty self-explanatory wrt what they are for.
Something like this can be a good default:
for s in bootmisc hostname modules sysctl syslog ; do rc-update add $s boot; done
for s in devfs dmesg hwdrivers mdev ; do rc-update add $s sysinit; done
for s in killprocs mount-ro savecache ; do rc-update add $s shutdown; done
for s in networking ntpd sshd haveged ; do rc-update add $s; done
Run rc-update show -v to get a full picture of what is setup to run when
with openrc, should be much simpler and more comprehensible than systemd in general.
sshd and haveged there can probably be installed after network works, or in
earlier rootfs-setup step (and haveged likely unnecessary with more recent
kernels that fixed blocking /dev/random).
ln -s /usr/share/zoneinfo/... /etc/localtime maybe?
That should be it - supported and upgradable Alpine with a custom kernel apk
and bootloader for this specific board.
Extra: kexec for updating kernels safely, without breaking the boot.
Once some initial linux kernel boots and works, and board is potentially
tucked away somewhere where it's hard to reach for pulling microSD card out,
it can be scary to update kernel to potentially something that won't be able
to boot, start crashing, etc.
Easy solution for that is kexec - syscall/mechanism to start a new kernel
from another working kernel/OS.
Might need to build/install kexec-tools apk to use it - it's missing on some
architectures, but APKBUILD from aports and the tool itself should work just
fine without changes. Also don't forget to enable it in the kernel.
Using multiple kernel packages alongside each other like suggested above,
something like this should work for starting new linux from an old one immediately:
# apk install --allow-untrusted linux-c51705r08-5.17.5-r0.apk
# kexec -sf /boot/vmlinuz-c51705r08 --initrd /boot/initramfs-c51705r08 --reuse-cmdline
It works just like userspace exec() syscalls, but gets current kernel to exec
a new one instead, which generally looks like reboot, except without involving
firmware and bootloader at all.
This way it's easy to run and test anything in new kernel or in its cmdline
options safely, with simple reboot or power-cycling reverting it back to an
old known-good linux/bootloader setup.
Once everything is confirmed-working with new kernel, bootloader config can
potentially be updated to use it instead, and old linux-something package
replaced with a new one as a known-good fallback on the next update.
This process is not entirely foolproof however, as sometimes linux drivers or
maybe hardware have some kind of init-state mismatch, which actually happens
with C2 board, where its built-in network card fails to work after kexec,
unless its linux module is unloaded before that.
Something like this inside "screen" session can be used to fix that particular issue:
# rmmod dwmac_meson8b stmmac_platform stmmac && kexec ... ; reboot
"reboot" at the end should never run if "kexec" works, but if any of this fails,
C2 board won't end up misconfigured/disconnected, and just reboot back into
old kernel instead.
So far I've only found such hack needed with ODROID-C2, other boards seem to
work fine after kexec, so likely just a problem in this specific driver expecting
NIC to be in one specific state on init.
This post is kinda long because of how writing works, but really it all boils
down to "dd" for board-specific bootloader and using board-specific kernel
package with a generic Alpine rootfs, so not too difficult, especially given how
simple and obvious everything is in Alpine Linux itself.
Supporting many different boards, each with its unique kernel, bootloader and
quirks seem to be a pain for most distros, which can barely get by with x86 support,
but if the task is simplified to just providing rootfs and pre-built package
repository, a reasonably well-supported distro like Alpine has a good chance
to work well in the long run, I think.
ArchLinuxARM, Armbian and various vendor distros like Raspbian provide nicer
experience out-of-the-box, but eventually have to drop support for old
hardware, while these old ARM boards don't really go anywhere in my experience,
and keep working fine for their purpose, hence more long-term bet on something
like alpine seems more reasonable than distro-hopping or needless hardware
replacement every couple years, and alpine in particular is just a great fit
for such smaller systems.
May 04, 2022
It's usually easy to get computers to talk over ethernet, but making traditional
PC hardware to talk to electronics or a GPIO line tends to be more difficult.
Issue came up when I wanted to make a smart wakeup switch for a local backup
ARM-board the other day, which would toggle separate 5V power to it and its
drive in-between weekly backups, so went on to explore the options there.
Simplest one is actually to wake up an ARM board using Wake-on-LAN, which can
then control own and peripherals' power via its GPIO lines, but don't think mine
has that.
Next easiest one (from my pov) seem to be grabbing any Arduino-ish MCU laying
around, hook that up to a relay and make it into a "smart switch" via couple
dozen lines of glue code.
Problem with that approach is that PC mobos tend not to have simple GPIO lines
easily exposed and intended for use from userspace, but there are options:
Parallel port, if motherboard is ancient enough, or if hooked-up via one of
cheap USB-to-LPT cables with tiny controller in the connector.
These have a bunch of essentially GPIO lines, albeit in a funny connector
package, and with a weird voltage, but pretty sure only really old mobos have
that built-in by now.
RS-232 COM port, likely via a header on the board.
Dunno about latest hardware, but at least ones from 6-7 years ago can still
have these.
Even though it's a serial port, they have DTR and RTS pins, which are easy
to control directly, using ioctl() with TIOCM_DTR and TIOCM_RTS flags on /dev/ttyS*.
Outside of pure bit-banging, RS-232 can usually be hooked-up to simpler
hardware's UART pins via RS232-to-TTL chip, instead of just GPIO via optocoupler.
PC Speaker!
That's a 5V signal too (PWM, sure, but still no problem to read),
and not like it's in much demand for anything else these days.
Might have to either emit/detect distinct frequency or sequence of beeps
to make sure that's not the signal of machine booting on the other side.
3-pin fan headers with a voltage level controls.
Can be a neat use for those analog pins on arduinos, though not all monitoring
chips are RE-ed enough to have linux drivers with control over fans, unfortunately.
Power on USB ports as a signal - at least some mobos can put those to sleep
via sysfs, I think, usually with per-controller level of granularity.
For my purposes, COM was available via an easy pin header, and it was easy
enough to use its control pins, with some simple voltage-level shifting
(COM itself has -12V/+12V for 0/1).
Bit of a shame that PCs don't traditionally have robust GPIO headers for users,
feel like that'd have enabled a lot of fancy cas modding, home automation,
or got more people into understanding basic electronics, if nothing else.