Felitendo
2eff62f9fd
Asked what happens if someone shuts the laptop down mid-update, the honest answer turned out to be poor. The inhibitor does stop them - logind refuses and falls back to org.freedesktop.login1.power-off-ignore-inhibit, which is auth_admin_keep - so the desktop answers with an administrator password prompt reading "Power off the system while an application is inhibiting this". systemd ships that string untranslated, it never mentions updates, and no KDE catalog contains any shutdown-blocked text at all. Only systemctl names the reason. So a notification now goes out before the transaction, asking for the machine to be left on. Notifications gained a tag: the result replaces the start message in place rather than stacking a second, contradictory bubble beside it. Tagged notifications also carry a queue flag. "An update is starting" is only meaningful while somebody is looking, so unlike the result it is not spooled for delivery at next login.
242 lines
9.3 KiB
Markdown
242 lines
9.3 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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[q] Quit
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```
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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 40 % (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. When a kernel update needs a
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restart, you get a notification saying so.
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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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replaced in place by the result when the run finishes, so it costs one bubble
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rather than two. This exists because of what the next paragraph does *not* do.
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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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## 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** — you get a notification, 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 everything, `shellcheck` when available, and
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validates the sudoers drop-in with `visudo -c`.
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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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