added boot-partition-initramfs-bloat post

2025-09-22 23:42:20 -04:00
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+---
+title: "The Case of the Bloated Boot"
+date: 2025-09-22
+lastmod: 2025-09-22
+categories: ["Blog"]
+tags: ["linux"]
+---
+When `sudo mkinitcpio -P` fails because your boot partition is full, you've got
+a fun problem. The culprit? That massive fallback initramfs taking up precious
+space on a tiny boot partition.
+
+<!--more-->
+
+# The Problem
+
+Picture this: you're dual-booting Linux and running a system update when
+suddenly `mkinitcpio` fails to generate the larger fallback image. Your boot
+partition is completely stuffed.
+
+```bash
+$ df -h /boot
+Filesystem      Size  Used Avail Use% Mounted on
+/dev/nvme0n1p1  256M  256M     0 100% /boot
+```
+
+**Yikes.** Time to investigate what's eating all that space.
+
+# Damage Assessment
+
+A quick `du -sh` reveals the usual suspects:
+
+```bash
+$ du -sh /boot/*
+157M    /boot/initramfs-linux-fallback.img
+52M     /boot/initramfs-linux.img
+16M     /boot/vmlinuz-linux
+30M     /boot/EFI
+```
+
+The fallback initramfs is **three times larger** than the normal one. But why?
+
+# The Autodetect Mystery
+
+The secret lies in one simple flag in `/etc/mkinitcpio.d/linux.preset`:
+
+```bash
+fallback_options="-S autodetect"
+```
+
+That `-S autodetect` flag skips the autodetect hook, which normally shrinks your
+initramfs by only including modules your hardware actually needs. Without it,
+mkinitcpio includes **everything**.
+
+## By the Numbers
+
+Here's what that means in practice for me:
+
+| Component          | Normal (with autodetect) | Fallback (no autodetect) |   Ratio |
+| :----------------- | -----------------------: | -----------------------: | ------: |
+| **Kernel modules** |              190 modules |            6,319 modules | **33x** |
+| **Firmware files** |                711 files |              2,996 files |  **4x** |
+| **Total size**     |                      52M |                     157M |  **3x** |
+
+The fallback image is essentially a universal boot disk that works on _any_
+hardware — your laptop, your friend's desktop, that ancient server in the
+closet. It includes drivers for RAID controllers you don't have, network cards
+from 2003, and GPU firmware for every generation of graphics hardware.
+
+# The Nuclear Option
+
+Since I never use the fallback image anyway (live USB for rescue), the
+solution was just to get rid of this:
+
+1. **Remove the fallback image** to free immediate space:
+   ```bash
+   sudo rm /boot/initramfs-linux-fallback.img
+   ```
+
+2. **Disable future generation** by editing `/etc/mkinitcpio.d/linux.preset`:
+   ```bash
+   # Change this line:
+   PRESETS=('default' 'fallback')
+   # To this:
+   PRESETS=('default')
+   ```
+
+3. **Test it works**:
+   ```bash
+   sudo mkinitcpio -P
+   ```
+
+Result: boot partition goes from 100% to 39% usage, and future kernel updates
+won't recreate the bloated fallback.
+
+# Why It Matters
+
+The autodetect hook is actually quite clever. On my system with 443MB of total
+kernel modules available, it correctly identified that I only need 190 of them
+— things like my specific WiFi driver, filesystem modules for ext4 and LVM, and
+encryption support for LUKS.
+
+The fallback includes _everything else too_: drivers for hardware I'll never own
+(_especially since this is on a laptop_), filesystem support for formats I'll
+never use, and network protocols from the dawn of time. It's the digital
+equivalent of packing for a trip by bringing your entire garage of tools "just
+in case"
+
+# The Takeaway
+
+Unless you're regularly swapping hardware or need guaranteed boot recovery from
+the initramfs itself, the fallback image is dead weight. Modern autodetection
+works well enough that most people never need it. I've personnally never, ever
+used the fallback image and for the context of this laptop probably never will
+as a bootable USB is my go-to for any and all boot issues.
+
+For those tight boot partitions in dual-boot setups, disabling fallback
+generation is it. Save the space for kernel updates that actually matter :^)
+
+And if you _do_ need recovery? Well, that's what live USBs are for, but you're
+welcome to make your own decisions.