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Damien Diederen 7c2adb1d5c nixos/lib/make-ext4-fs: Fix: `resize2fs -M' can leave insufficient slack
The root filesystem resizing step, `resize2fs -M', does not provide any
control over the amount of slack left in the result.  It can produce an
arbitrarily tight fit, depending on how well the payload aligns with
ext4 data structures.

This is problematic, as NixOS must create a few files and directories
during its first boot, before the root is enlarged to match the size of
the containing SD card.

An overly tight fit can cause failures in the first stage:

    mkdir: can't create directory '/mnt-root/proc': No space left on device

or in the second stage:

    install: cannot create directory '/var': No space left on device

A previous version of `make-ext4-fs' (before PR #79368) was explicitly
"reserving" 16 MiB of free space in the final filesystem.  Manually
calculating the size of an ext4 filesystem is a perilous endeavor,
however, and the method it employed was apparently unreliable.

Reverting is consequently not a good option.

A solution would be to create some sort of "balloon" occupying inodes
and blocks in the image prior to invoking `resize2fs -M', and to remove
these temporary files/directories before the compression step.

This changeset takes the simpler approach of simply dropping the
resizing step.

Note that this does *not* result in a larger image in general, as the
current procedure does not truncate the `.img' file anyway.  In fact, it
has been observed to yield *smaller* compressed images---probably
because of some "noise" left after resizing.  E.g., before-vs-after:

    -r--r--r-- 2 root root 607M  1. Jan 1970  nixos-sd-image-21.11pre-git-x86_64-linux.img.zst

    -r--r--r-- 2 root root 606M  1. Jan 1970  nixos-sd-image-21.11pre-git-x86_64-linux.img.zst
2021-05-31 21:35:51 +02:00
.github backport: trigger also if label is set after the merge 2021-05-28 16:36:02 +02:00
doc Merge pull request #124739 from SFrijters/doc-fetchpatch 2021-05-28 22:13:11 +02:00
lib Merge pull request #119967 from xoe-labs/da/add-lib-flake 2021-05-24 02:06:19 -03:00
maintainers Merge pull request #123426 from mattchrist/brscan5 2021-05-31 17:52:16 +02:00
nixos nixos/lib/make-ext4-fs: Fix: `resize2fs -M' can leave insufficient slack 2021-05-31 21:35:51 +02:00
pkgs Merge pull request #125029 from r-ryantm/auto-update/elinks 2021-05-31 12:54:28 -05:00
.editorconfig Merge pull request #110395 from zowoq/gemset 2021-01-22 09:31:07 +01:00
.gitattributes gitattributes: disable merge=union in all-packages 2018-03-27 11:03:03 -05:00
.gitignore git ignore __pycache__ folders 2020-08-16 11:30:11 +02:00
.version 21.11 is Porcupine! 2021-05-22 18:14:06 -07:00
COPYING COPYING: 2020 -> 2021 2021-01-03 00:49:09 +00:00
default.nix docs: add -L to remaining curl install commands 2020-09-11 12:14:07 -07:00
flake.nix flake.nix: add aarch64-darwin 2021-05-17 00:27:02 +09:00
README.md README: just IRC, not "other channels" 2021-05-23 07:52:00 -04:00

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Nixpkgs is a collection of over 60,000 software packages that can be installed with the Nix package manager. It also implements NixOS, a purely-functional Linux distribution.

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