Felitendo
f9cd8a0ace
Three stretches of a run had no way to report anything, and the bar handled each of them badly. pacman prints nothing at all between "starting full system upgrade" and the transaction it eventually prepares. On a 161-package backlog that silence ran to three minutes and nineteen seconds, and the bar spent all of it frozen on "0 of 161" - a counter seeded from checkupdates before there was anything to count. Working out the upgrade is now a step of its own, with a label and deliberately no item count, because the number was the part that was lying. A step that turns out to have no work is dropped from the bar instead of being handed its share for nothing. Packages already in the cache are never announced by pacman, so a run that only has to unpack used to jump thirty points the moment unpacking started; the same went for AUR with nothing pending and for machines with no Gear Lever or no Flatpaks. pacman's output is line-buffered through stdbuf. Writing to a log rather than a terminal, libc released it in 4KB blocks - around a hundred and sixty "upgrading foo..." lines at a time - so the bar sat still and then leapt to the end of the step in one poll. What is left is work whose length genuinely cannot be known: resolving a transaction, and an AUR helper compiling for a quarter of an hour. Those now creep along a curve that approaches the end of their step without reaching it. The item counter stays put throughout - it is the field that would be lying if it moved - and any real report overtakes the creep. A bar that has not moved since it appeared is read as a hang, and somebody who reads it that way reaches for the power button mid-update. The bar is also monotonic now. Dropping a step rescales the run, and the conflict-recovery loop restarts pacman and its tally from the top; both are honest, neither is a reason to show a bar that retreats.
327 lines
14 KiB
Markdown
327 lines
14 KiB
Markdown
# cachy-auto-update
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Unattended background updates for CachyOS — no password prompt, no terminal,
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nothing to remember.
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Built for the machine you set up for somebody else and would rather not have to
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maintain: it updates pacman packages, AUR packages, Flatpaks and AppImages by
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itself, stays out of the way while they are gaming or on battery, never touches
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the package database while they are using `pacman` by hand, and only speaks up
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when something actually needs a human.
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```bash
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sudo cachy-auto-update
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```
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That opens a menu with the two switches there are:
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```
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CachyOS Auto-Update
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Automatic updates ON
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Notifications ON
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Last check 3 hours ago
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Last successful update Sat 08 Aug 2026 04:12:03 CEST (23 packages)
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Next scheduled run Sat 08 Aug 2026 05:00:00 CEST
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[1] Toggle automatic updates
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[2] Toggle notifications
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[3] Update now
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[4] Show log
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[5] Show current conditions
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[6] Settings
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[q] Quit
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```
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Everything is configurable from **[6] Settings** — a cursor list covering all
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eighteen options, so nothing needs a text editor. Arrow keys select, Space or
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Right changes a value, `q` goes back; changes are written immediately.
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The interface is fully translated; on a German system everything above appears
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in German.
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## Install
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```bash
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paru -S cachy-auto-update
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sudo cachy-auto-update enable
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```
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Updates are **off** until you enable them — a freshly installed package has no
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business rebuilding somebody's system before being asked.
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## What it updates
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|---|---|
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| Repository packages | `pacman -Syu`, after `checkupdates` confirms there is work |
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| AUR | `paru` or `yay`, whichever is installed |
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| Flatpak | system and per-user installations |
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| AppImages | via [Gear Lever](https://github.com/mijorus/gearlever), if installed |
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It also trims the pacman package cache after each run (`paccache`, keeping the
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3 most recent versions), because otherwise `/var/cache/pacman/pkg` grows
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forever — tens of gigabytes on a machine with a few large packages. Set
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`KeepOldPackages=1` if disk space matters more than the ability to downgrade.
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`-git`/`-devel` AUR packages and orphan removal exist as options but are off by
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default. Orphan removal deletes installed software, and "orphaned" only means
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nothing else depends on it — which is also true of something installed
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deliberately.
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## When it holds back
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A run is postponed — and retried an hour later — when:
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- the battery is below 30 % (ignored on mains power; desktops without a battery
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are never affected),
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- a game is running: GameMode, a known game process, or anything holding a
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blocking idle inhibitor,
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- pacman's database is locked, or `pacman`/`yay`/`paru`/`pamac` is running.
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`cachy-auto-update status` prints every one of these individually, which is the
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fastest way to find out why nothing is happening.
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The machine is **never** restarted on its own. A kernel update that needs a
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restart is reported by `cachy-auto-update status`, not by a notification: the
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running kernel loses its module tree the moment pacman unpacks the new one, so
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a bubble would arrive while the run is still building AUR packages and pulling
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Flatpaks — and reads as an invitation to restart in the middle of it.
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## About the password question
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The obvious way to automate `yay`/`paru` is to store the user's password
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somewhere. This does not do that, and deliberately so: anything the daemon can
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decrypt is exactly what an attacker who reaches the daemon already has, so the
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encryption would be decoration.
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Instead:
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- The updater is a **system service running as root**, so `pacman` needs no
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escalation at all.
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- `makepkg`, `paru` and `yay` refuse to run as root, so the AUR step drops to a
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dedicated **locked system account** (`cachy-auto-update`, no password,
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`/usr/bin/nologin`, its own home under `/var/lib`). Only root can become it.
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- That account gets one line in `/etc/sudoers.d/cachy-auto-update` allowing it
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to call `/usr/bin/pacman` without a password — which is what lets the helper
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install what it built.
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No user password is stored, encrypted or otherwise.
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If you would rather not have that sudoers rule on the machine, set
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`UpdateAUR=no` in the config; everything else keeps working, and the rule
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becomes inert.
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## Coexisting with manual package management
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Before touching anything, the updater checks for `/var/lib/pacman/db.lck` and
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for a running `pacman`, `yay`, `paru`, `pamac`, `pikaur`, `octopi` or `makepkg`,
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and postpones if it finds one. On a day with no pending repository updates the
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real pacman lock is never taken at all, because `checkupdates` works against a
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private temporary database.
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The reverse direction has an honest limit: if you start `pacman` *while* an
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update is already running, you will get the usual "unable to lock database"
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message. Nothing outside pacman can prevent that. What the updater does do is
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keep the window short, run at low priority, and hold a `systemd-inhibit` lock so
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a suspend or shutdown cannot land in the middle of a transaction.
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A leftover `db.lck` from a crashed transaction is never deleted automatically —
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guessing wrong there corrupts a live transaction. After it has been seen
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unheld on several consecutive runs, you get a notification instead.
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## What if the machine is switched off mid-update
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Three layers, in order of how much they can actually promise:
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**A notification goes out before the transaction starts** — "Installing
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updates, please leave the computer switched on until this is done" — and is
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withdrawn again when the result arrives, so it costs one bubble rather than
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two. This exists because of what the next paragraph does *not* do.
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**A progress bar sits in the notification area for the whole run**, the same
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one Dolphin puts there while it copies files: which step is running, which
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package is being unpacked, how far along the whole thing is. A twenty-minute
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run that shows nothing looks indistinguishable from a hung one, and that is
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what gets a machine switched off in the middle of a transaction. See
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[The progress bar](#the-progress-bar).
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**Suspend and a normal shutdown are blocked.** The run holds a
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`systemd-inhibit --what=sleep:shutdown --mode=block` lock, so closing the lid or
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picking "Shut down" cannot interrupt a transaction. Be aware of what that looks
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like, though: logind refuses the request and requires the polkit action
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`org.freedesktop.login1.power-off-ignore-inhibit`, which is `auth_admin_keep`.
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The desktop therefore answers a shutdown attempt with an **administrator
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password prompt** reading *"Power off the system while an application is
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inhibiting this"* — a string systemd ships untranslated, and one that never
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mentions updates. No KDE dialog explains the situation. Only `systemctl
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poweroff` in a terminal names the reason. That prompt is exactly why the
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notification above is on by default.
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**A hard power-off cannot be prevented by anything.** Holding the power button
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or pulling the plug cuts power in firmware. What limits the damage is that
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pacman's commit phase is short (about a minute even for a 200-package upgrade)
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and that most of a run is downloading, where an interruption costs nothing but
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a partial file.
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**The next run repairs it.** A `db.lck` left behind is detected and removed —
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but only when it is *provably* dead, meaning it is older than the current boot,
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so no process that could hold it still exists. The interrupted upgrade is then
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simply run again; pacman reinstalls anything that was caught half-written. A
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lock that is merely unheld within the same boot is never removed, only
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reported, because there the guess could be wrong.
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This last part matters more than it sounds: without it, a single power cut
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during an update would leave a lock file that makes every future run defer,
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and the machine would stop updating silently and permanently.
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On a Btrfs system with `snapper` and `snap-pac` — the CachyOS default — every
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pacman transaction is bracketed by a pre and post snapshot, so a genuinely
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broken upgrade can still be rolled back with `snapper rollback`.
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## How long notifications stay
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A message that means the machine still needs you — an update failed, the
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package database is locked, packages had to be held back — **stays until you
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dismiss it**. That kind of message is only worth sending if it is still there
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when you come back to the machine.
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Everything else times out on its own, a successful update included. Nothing
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should have to be clicked away for having gone right.
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Set per message rather than left to the notification daemon. Daemons do keep
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critical-urgency messages up and the spec asks them to, but that is a *should*,
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it says nothing about the normal-urgency messages here that still need somebody
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to act, and urgency separately controls sound and do-not-disturb bypass — a
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different question. Queued messages delivered at the next login keep the same
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distinction.
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## The progress bar
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While a run is working, the notification area carries a live entry — headline,
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item count, percentage, and the package currently being unpacked under
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*Details*. It is not a notification but a **job**, the same mechanism Dolphin
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uses for file copies, which is what gets you a bar rather than a line of text.
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Two things about how it is put together:
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- The desktop ties a job to the D-Bus connection that asked for it, and
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withdraws the job the moment that connection closes. One-shot bus clients —
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`gdbus`, `busctl`, `dbus-send` — therefore cannot drive one at all, since
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every invocation is a fresh connection that closes immediately. So a small
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helper (`cachy-auto-update-progress`) runs inside each graphical session for
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the length of the update, holding the connection open and taking instructions
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on stdin. It needs **python-gobject**; without it there is simply no bar and
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nothing else changes.
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- Working out the upgrade, downloading it and unpacking it are three separate
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steps. The first is the one that used to look broken: between
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`:: Starting full system upgrade...` and the transaction it eventually
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prepares, pacman prints nothing at all, and on a large backlog that silence
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runs to minutes. A counter frozen at "0 of 161" reads as a stuck update, so
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that stretch carries a label and deliberately no counter. On a domestic line
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the download is then the longest of the three, and calling the whole thing
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"installing" would leave the bar at 4% for six minutes.
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- A step that turns out to have no work is dropped from the bar rather than
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handed its share for nothing. Packages already in the cache are never
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announced, so a run that only has to unpack skips the download step outright
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instead of leaping 30% the moment unpacking starts — and likewise for AUR
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with nothing pending, or a machine with no Flatpaks. The weights only ever
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have to be right about the steps that actually run.
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- pacman's output is line-buffered through `stdbuf`. Writing to a log rather
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than a terminal, libc would hand it over in 4 KB blocks instead, and 4 KB of
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`upgrading foo...` is on the order of a hundred and sixty packages arriving
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at once — which is how a bar comes to sit still and then jump to the end.
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- Neither counted phase gets a counter from pacman on an unattended run, so
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both are counted a line at a time — `foo-1.2-1-x86_64 downloading...` and
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`upgrading foo...`. The database sync just before prints the same shape
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(` core downloading...`) with the suffix that would give it away already
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stripped, so counting starts only after pacman's `:: Retrieving packages...`
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header. pacman's other `(n/m)` sequences — checking keys, package integrity,
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loading files — each count to the same total, so only the transaction verbs
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are followed; otherwise the bar would reach the end three times before the
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first package was unpacked.
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This is Plasma's job interface. On a desktop that does not implement it the
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helper exits quietly and the ordinary notifications carry on as before.
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## Configuration
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`/etc/cachy-auto-update/cachy-auto-update.conf`, one `Key=Value` per line, every
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option documented in the file. The file is parsed rather than sourced, so a
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stray line cannot turn into code executed by root.
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```ini
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Enabled=yes
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Notifications=yes
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UpdateInterval=1d
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MinBatteryPercent=40
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SkipWhenGaming=yes
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UpdateAUR=yes
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UpdateFlatpak=yes
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UpdateAppImages=yes
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AutoResolveConflicts=yes
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IgnorePkg=
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```
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## How package conflicts are handled
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`pacman -Syu --noconfirm` already answers "Replace X with Y?" affirmatively, so
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ordinary replacements happen silently — which is the point.
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What `--noconfirm` declines is `:: X and Y are in conflict. Remove Y? [y/N]`,
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and that aborts the whole transaction. With `AutoResolveConflicts=yes` (the
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default) the transaction is retried once with that question answered too, and
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everything removed is written to the log.
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Two things are deliberately *not* automated:
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- **File conflicts** (`exists in filesystem`) — forcing `--overwrite` could
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silently destroy something that was put there on purpose.
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- **Reboots** — `status` tells you one is due, never a surprise restart.
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Signature failures trigger one keyring refresh and one retry, since a stale
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keyring blocks everything else until it is fixed.
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## Logs
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```bash
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cachy-auto-update log # the last run in full
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cachy-auto-update log -a # the rolling log
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journalctl -u cachy-auto-update
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```
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Both work without root.
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## Building from source
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```bash
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make && sudo make install
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sudo systemd-sysusers && sudo systemd-tmpfiles --create
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sudo cachy-auto-update enable
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```
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`make check` runs `bash -n` over every shell file, `py_compile` over the
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progress helper, `shellcheck` when available, and validates the sudoers drop-in
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with `visudo -c`.
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Everything is optional at runtime and degrades to doing less rather than
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failing: `pacman-contrib` for `checkupdates`, an AUR helper, `flatpak`, Gear
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Lever, `libnotify` for notifications, and `python-gobject` for the progress bar.
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## Relationship to cachy-update
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[cachy-update](https://github.com/CachyOS/cachy-update) is CachyOS's interactive
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updater; every one of its steps sits behind a prompt and its timer only ever
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*checks* for updates and notifies. This tool is the unattended counterpart and
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reimplements the same command sequence non-interactively, adding the battery,
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gaming and lock awareness that unattended operation needs.
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The two coexist. `cachy-auto-update enable` offers once to switch off
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cachy-update's own "N updates available" notification, since it becomes noise
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when updates install themselves.
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## License
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GPL-3.0-or-later.
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