Rescue Media
Two extra partitions hold a full Arch ISO on local disk, so recovery doesn't depend on having a USB drive on hand.
On UEFI machines the disk layout reserves two dedicated partitions by default: about 5.5GB total (512MB FAT32 + 5GB ext4), on top of whatever your root filesystem needs. Opt out of both together with the Include rescue media toggle in the installer's Options step if you're tight on disk space:
- A small FAT32 partition holding the extracted kernel and initramfs.
- A larger ext4 partition holding the fetched Arch ISO itself, as a plain file.
The installer only formats these partitions. The ISO itself (about 1.5 GiB) is downloaded in the background after first boot, once the network is up, so it doesn't hold up the install. The rescue entry appears in the boot menu once that download finishes.
On a BIOS (non-UEFI) machine the layout is different, because an MBR disk allows only three primary partitions: there is no separate FAT32 partition. The rescue kernel and initramfs are kept under /boot/rescue instead, and only the ext4 ISO partition is added.
The split exists because the bootloader (Limine) can't read ext4 and has no GRUB-style loopback command, and FAT32 has a hard 4GB per-file cap that the ISO itself would run into. After first boot, the ISO is fetched from an official mirror, checksum-verified, and wired into a permanent boot menu entry, the same mechanism the official Arch installation media itself uses to loop-mount an ISO file at boot.
The stored ISO is refreshed manually only, never automatically. A background download on every boot or update would be surprising and wasteful, and a slightly outdated rescue ISO is still far better than none at all.
A daily background check does compare the checksum of the stored ISO against the mirror's current one (a few hundred bytes, no ISO download). When a newer release exists you get a notification; click it to run Super → Sobarch → Refresh Rescue ISO. You're notified once per new release, not every day. That menu entry only appears if rescue media was set up at install; if you opted out, you never see it. From a terminal, sobarch rescue-refresh does the same refresh.
Rescue media is unavailable on a dual-boot free-space install and on T2 Macs, and the rescue partitions are not covered by disk encryption.
This is what snapshot rollback's live-ISO mode uses when there's no other way to boot the machine.