[Bug 1881935] Re: Minimum inode size should be raised to 256 for forward compatibility (Y2038)

[Theodore Ts'o]

This relatively simple to change the default inode size in all cases.
Look at /etc/mke2fs.conf, which is in the sources as
misc/mke2fs.conf.in.   Find the lines where the inode_size is set to
128, and change it to be 256.   (This might or might cause problems on
Hurd; since I'm not sure whether the GNU Hurd can support modern file
systems with 256 byte inodes.  Heck, the GNU Hurd implementation doesn't
support journalling or extents last I checked.)

This will double the overhead of ext4 file systems, especially on small
file systems.  This is why the default is set the way that it is.   For
really tiny thumb drives (especially the cheap ones found in the
checkout aisle of the Micro Center), they are very likely to self-
destruct within a few months, never mind 18 years.   And users might get
cranky if the amount of usable space is decreased.

It may be that for the installer, it will want to hard code the use of a
larger inode size, or specify a file system usage type hint via the -T
option which could trigger a different default in mke2fs.conf.    This
is fundamentally a policy question, not a technical issue --- and
different distributions may have different opinions about what the
defaults should be; this is why we've made it easy to customize the
defaults should be in misc/mke2fs.conf.in in the sources, as opposed to
hard-coding it in the misc/mke2fs.c source file.

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https://bugs.launchpad.net/bugs/1881935

Title:
  Minimum inode size should be raised to 256 for forward compatibility
  (Y2038)

Status in e2fsprogs package in Ubuntu:
  New

Bug description:
  mke2fs in all supported Ubuntu releases to date creates 'small' ext4
  file systems with an inode size of 128. This is said to be
  insufficient to store time stamps referring to year 2038 and later
  (when the Unix epoch exceeds a signed 32-bit integer -
  https://en.wikipedia.org/wiki/Year_2038_problem). When such file
  systems are mounted by the kernel, such as a /boot file system created
  by the Ubuntu 20.04.0 Desktop installer (ubiquity 20.04.15), the
  kernel will warn about this fact:

    kernel: ext4 filesystem being mounted at /boot supports timestamps
  until 2038 (0x7fffffff)

  Cf. https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=953494

  Admittedly, that's another 18 years, by when most systems installed
  now will be no longer in use, or will have been reinstalled.

  Also, on a /boot file system the 5.4.0-33-generic #37 Ubuntu (20.04) kernel warned about this, I was able to 
    $ touch -t 203812312359 /tmp/test
  and got
    $ ls -l /tmp/test 
    -rw-r--r-- 1 root root 0 Dez 31  2038 /tmp/test
  so this warning may not always apply, or patches may have been applied to handle this situation more gracefully already.

  Ubuntu 20.04 comes with e2fsprogs 1.45.5-2ubuntu1. Theodore Y. Ts'o
  has submitted patches for Debian's 1.45.6-1 - but (strictly speaking
  based on the changelog) these seem to be limited to documentation
  changes.

  Still, creating such file systems may seem undesirable in terms of
  forward compatibility. I therefore suggest to change the minimum inode
  size for mke2fs, as defined in /etc/mke2fs.conf, to 256 for all file
  systems which do not already use this value (maybe with the exception
  of floppies). That is, I suggest the following change to Ubuntu
  20.04's /etc/mke2fs.conf:

  Before change:
          small = {
                  inode_size = 128
                  inode_ratio = 4096
          }

  After change:
          small = {
                  inode_ratio = 4096
          }

  This assumes that the default inode size is already set to 256 further
  above.


  As a WORKAROUND, after backing up the file system (this command is not well tested, according to the lead ext4 file system developer), users can unmount the affected file system and run 
    tune2fs -I 256 /path/to/block_device
  where /path/to/block_device should be replaced by the path to the block device which contains the file system the kernel reports the warning for. For example, for the file system mounted at /boot, the 
    findmnt /boot
  command would return the block device path in the SOURCE column.

  
  Please note I prefer not to use apport for this bug report, I believe it is already sufficiently complete.

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