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Felitendo c308b7e286 Add a settings screen so nothing needs a text editor

All eighteen options are now reachable from the menu as a cursor list: arrows
select, Space or Right cycles a value, q goes back, changes are written
immediately. A numbered menu would have run out of digits.

Three real bugs surfaced while building it, each found by testing against an
actual pty rather than a pipe:

- Labels went through printf as format strings, so the percent sign in
  "Minimum battery level (%)" was an invalid conversion. cau_msg_in now only
  treats a message as a format string when arguments were actually passed -
  otherwise any literal % a translator writes is a trap.

- Mixing bash's line-mode read into a single-key interface left the following
  read -sn1 receiving nothing at all, reproducibly, so the screen froze after
  editing the package list. Replaced with a small line editor built on the same
  single-character reader.

- Backspace was being swallowed: in canonical mode DEL is the ERASE character
  and the line discipline consumes it, and bash returns to canonical mode
  between each read -sn1. The interface now holds non-canonical mode for its
  whole lifetime and hands the terminal back only around actions that print or
  prompt, with a trap restoring it on Ctrl-C.

Translations and config reads are memoized; the screen redraws every label on
every keypress and a fork per lookup was the reason the redraw was slow enough
to matter.

2026-08-08 16:18:59 +02:00

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cachy-auto-update

Unattended background updates for CachyOS — no password prompt, no terminal, nothing to remember.

Built for the machine you set up for somebody else and would rather not have to maintain: it updates pacman packages, AUR packages, Flatpaks and AppImages by itself, stays out of the way while they are gaming or on battery, never touches the package database while they are using pacman by hand, and only speaks up when something actually needs a human.

sudo cachy-auto-update

That opens a menu with the two switches there are:

  CachyOS Auto-Update

  Automatic updates            ON
  Notifications                ON

  Last check                   3 hours ago
  Last successful update       Sat 08 Aug 2026 04:12:03 CEST (23 packages)
  Next scheduled run           Sat 08 Aug 2026 05:00:00 CEST

  [1] Toggle automatic updates
  [2] Toggle notifications
  [3] Update now
  [4] Show log
  [5] Show current conditions
  [6] Settings
  [q] Quit

Everything is configurable from [6] Settings — a cursor list covering all eighteen options, so nothing needs a text editor. Arrow keys select, Space or Right changes a value, q goes back; changes are written immediately.

The interface is fully translated; on a German system everything above appears in German.

Install

paru -S cachy-auto-update
sudo cachy-auto-update enable

Updates are off until you enable them — a freshly installed package has no business rebuilding somebody's system before being asked.

What it updates


Repository packages	`pacman -Syu`, after `checkupdates` confirms there is work
AUR	`paru` or `yay`, whichever is installed
Flatpak	system and per-user installations
AppImages	via Gear Lever, if installed

It also trims the pacman package cache after each run (paccache, keeping the 3 most recent versions), because otherwise /var/cache/pacman/pkg grows forever — tens of gigabytes on a machine with a few large packages. Set KeepOldPackages=1 if disk space matters more than the ability to downgrade.

-git/-devel AUR packages and orphan removal exist as options but are off by default. Orphan removal deletes installed software, and "orphaned" only means nothing else depends on it — which is also true of something installed deliberately.

When it holds back

A run is postponed — and retried an hour later — when:

the battery is below 40 % (ignored on mains power; desktops without a battery are never affected),
a game is running: GameMode, a known game process, or anything holding a blocking idle inhibitor,
pacman's database is locked, or pacman/yay/paru/pamac is running.

cachy-auto-update status prints every one of these individually, which is the fastest way to find out why nothing is happening.

The machine is never restarted on its own. When a kernel update needs a restart, you get a notification saying so.

About the password question

The obvious way to automate yay/paru is to store the user's password somewhere. This does not do that, and deliberately so: anything the daemon can decrypt is exactly what an attacker who reaches the daemon already has, so the encryption would be decoration.

Instead:

The updater is a system service running as root, so pacman needs no escalation at all.
makepkg, paru and yay refuse to run as root, so the AUR step drops to a dedicated locked system account (cachy-auto-update, no password, /usr/bin/nologin, its own home under /var/lib). Only root can become it.
That account gets one line in /etc/sudoers.d/cachy-auto-update allowing it to call /usr/bin/pacman without a password — which is what lets the helper install what it built.

No user password is stored, encrypted or otherwise.

If you would rather not have that sudoers rule on the machine, set UpdateAUR=no in the config; everything else keeps working, and the rule becomes inert.

Coexisting with manual package management

Before touching anything, the updater checks for /var/lib/pacman/db.lck and for a running pacman, yay, paru, pamac, pikaur, octopi or makepkg, and postpones if it finds one. On a day with no pending repository updates the real pacman lock is never taken at all, because checkupdates works against a private temporary database.

The reverse direction has an honest limit: if you start pacman while an update is already running, you will get the usual "unable to lock database" message. Nothing outside pacman can prevent that. What the updater does do is keep the window short, run at low priority, and hold a systemd-inhibit lock so a suspend or shutdown cannot land in the middle of a transaction.

A leftover db.lck from a crashed transaction is never deleted automatically — guessing wrong there corrupts a live transaction. After it has been seen unheld on several consecutive runs, you get a notification instead.

What if the machine is switched off mid-update

Three layers, in order of how much they can actually promise:

A notification goes out before the transaction starts — "Installing updates, please leave the computer switched on until this is done" — and is replaced in place by the result when the run finishes, so it costs one bubble rather than two. This exists because of what the next paragraph does not do.

Suspend and a normal shutdown are blocked. The run holds a systemd-inhibit --what=sleep:shutdown --mode=block lock, so closing the lid or picking "Shut down" cannot interrupt a transaction. Be aware of what that looks like, though: logind refuses the request and requires the polkit action org.freedesktop.login1.power-off-ignore-inhibit, which is auth_admin_keep. The desktop therefore answers a shutdown attempt with an administrator password prompt reading "Power off the system while an application is inhibiting this" — a string systemd ships untranslated, and one that never mentions updates. No KDE dialog explains the situation. Only systemctl poweroff in a terminal names the reason. That prompt is exactly why the notification above is on by default.

A hard power-off cannot be prevented by anything. Holding the power button or pulling the plug cuts power in firmware. What limits the damage is that pacman's commit phase is short (about a minute even for a 200-package upgrade) and that most of a run is downloading, where an interruption costs nothing but a partial file.

The next run repairs it. A db.lck left behind is detected and removed — but only when it is provably dead, meaning it is older than the current boot, so no process that could hold it still exists. The interrupted upgrade is then simply run again; pacman reinstalls anything that was caught half-written. A lock that is merely unheld within the same boot is never removed, only reported, because there the guess could be wrong.

This last part matters more than it sounds: without it, a single power cut during an update would leave a lock file that makes every future run defer, and the machine would stop updating silently and permanently.

On a Btrfs system with snapper and snap-pac — the CachyOS default — every pacman transaction is bracketed by a pre and post snapshot, so a genuinely broken upgrade can still be rolled back with snapper rollback.

Configuration

/etc/cachy-auto-update/cachy-auto-update.conf, one Key=Value per line, every option documented in the file. The file is parsed rather than sourced, so a stray line cannot turn into code executed by root.

Enabled=yes
Notifications=yes
UpdateInterval=1d
MinBatteryPercent=40
SkipWhenGaming=yes
UpdateAUR=yes
UpdateFlatpak=yes
UpdateAppImages=yes
AutoResolveConflicts=yes
IgnorePkg=

How package conflicts are handled

pacman -Syu --noconfirm already answers "Replace X with Y?" affirmatively, so ordinary replacements happen silently — which is the point.

What --noconfirm declines is :: X and Y are in conflict. Remove Y? [y/N], and that aborts the whole transaction. With AutoResolveConflicts=yes (the default) the transaction is retried once with that question answered too, and everything removed is written to the log.

Two things are deliberately not automated:

File conflicts (exists in filesystem) — forcing --overwrite could silently destroy something that was put there on purpose.
Reboots — you get a notification, never a surprise restart.

Signature failures trigger one keyring refresh and one retry, since a stale keyring blocks everything else until it is fixed.

Logs

cachy-auto-update log        # the last run in full
cachy-auto-update log -a     # the rolling log
journalctl -u cachy-auto-update

Both work without root.

Building from source

make && sudo make install
sudo systemd-sysusers && sudo systemd-tmpfiles --create
sudo cachy-auto-update enable

make check runs bash -n over everything, shellcheck when available, and validates the sudoers drop-in with visudo -c.

Relationship to cachy-update

cachy-update is CachyOS's interactive updater; every one of its steps sits behind a prompt and its timer only ever checks for updates and notifies. This tool is the unattended counterpart and reimplements the same command sequence non-interactively, adding the battery, gaming and lock awareness that unattended operation needs.

The two coexist. cachy-auto-update enable offers once to switch off cachy-update's own "N updates available" notification, since it becomes noise when updates install themselves.

License

GPL-3.0-or-later.

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