[Bug 2147120] Re: "tail -0f <file> makes tail core-dump

[Roy J]

Hi Oliver,

Thank you for reporting this bug and for providing clear reproduction
steps and backtrace details.

I have correlated your crash with the tail implementation in rust-
coreutils/coreutils-from-uutils, and it matches a known issue that is
fixed in newer source.

For developer reference, the fix is in rust-coreutils commit ac26e933b9e24ef44c25e18cc264b5f8100f8c20 (from 0.6.0-0ubuntu1), in src/uu/tail/src/tail.rs within backwards_thru_file(). The key change is the early guard for zero delimiters:
if num_delimiters == 0 { file.seek(SeekFrom::End(0)).unwrap(); return; }
This prevents the assert_eq!(counter, num_delimiters) panic path that produces left: 1 / right: 0 with tail -0f.

Version mapping:
- Questing currently publishes rust-coreutils 0.2.2-0ubuntu2.1 (still affected line)
- Resolute publishes rust-coreutils 0.7.0-0ubuntu1 (fix included)

Given that, the recommended path is to upgrade to Resolute, where this
fix is already present in the newer package line.

Because Questing is a non-LTS release with limited remaining support
lifetime, it is generally not the right target for this kind of backport
when the fix is already available in the current LTS.

If you want, we can still leave this report documented for reference,
but upgrading to Resolute is the practical resolution path.

Thanks again for the high-quality report. It made this much easier to
track down and point to a clear fix path.

** Changed in: rust-coreutils (Ubuntu)
   Importance: Undecided => Low

** Changed in: rust-coreutils (Ubuntu)
       Status: New => Incomplete

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https://bugs.launchpad.net/bugs/2147120

Title:
  "tail -0f <file> makes tail core-dump

Status in rust-coreutils package in Ubuntu:
  Incomplete

Bug description:
  1) The release of Ubuntu you are using, via 'lsb_release -rd' or
  System -> About Ubuntu

  lsb_release -rd
  Description:	Ubuntu 25.10
  Release:	25.10

  
  2) The version of the package you are using, via 'apt-cache policy pkgname' or by checking in Software Center

  apt list coreutils
  coreutils/questing,questing,now 9.5-1ubuntu2+0.0.0~ubuntu24 all [installed]

  
  3) What you expected to happen

  When issuing a tail -0f /var/log/syslog I expect tail to start with no
  output at all until the "tailed" file changes; then the newly added
  lines should be displayed.

  
  4) What happened instead

  When if run tail -0f <file> I receive an error, e.g.:

  --

  > tail -0f /var/log/syslog

  thread 'main' panicked at src/uu/tail/src/tail.rs:393:17:
  assertion `left == right` failed
    left: 1
   right: 0
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
  Aborted (core dumped)

  --

  As suggested, I did an

  > export RUST_BACKTRACE=full

  and the resulting output is:

  --

  > tail -0f /var/log/syslog

  thread 'main' panicked at src/uu/tail/src/tail.rs:393:17:
  assertion `left == right` failed
    left: 1
   right: 0
  stack backtrace:
     0:     0x5a4ecd015db9 - <unknown>
     1:     0x5a4ecce20913 - <unknown>
     2:     0x5a4ecd001fff - <unknown>
     3:     0x5a4ecd015c13 - <unknown>
     4:     0x5a4eccfde7c3 - <unknown>
     5:     0x5a4eccfde5b6 - <unknown>
     6:     0x5a4eccfdee0c - <unknown>
     7:     0x5a4ecd016b0a - <unknown>
     8:     0x5a4ecd015fd9 - <unknown>
     9:     0x5a4eccfde8fd - <unknown>
    10:     0x5a4eccd83690 - <unknown>
    11:     0x5a4eccd83a43 - <unknown>
    12:     0x5a4eccd838fa - <unknown>
    13:     0x5a4ecd1cfb41 - <unknown>
    14:     0x5a4ecd1ce469 - <unknown>
    15:     0x5a4ecce362f1 - <unknown>
    16:     0x5a4ecce38f8f - <unknown>
    17:     0x5a4ecce6cab4 - <unknown>
    18:     0x5a4ecce746f7 - <unknown>
    19:     0x5a4ecd0019f7 - <unknown>
    20:     0x5a4ecce746e5 - <unknown>
    21:     0x7af09002a575 - __libc_start_call_main
                                 at ./csu/../sysdeps/nptl/libc_start_call_main.h:58:16
    22:     0x7af09002a628 - __libc_start_main_impl
                                 at ./csu/../csu/libc-start.c:360:3
    23:     0x5a4eccd93b15 - <unknown>
    24:                0x0 - <unknown>
  Aborted (core dumped)

  --

  ProblemType: Bug
  DistroRelease: Ubuntu 25.10
  Package: coreutils-from-uutils 0.0.0~ubuntu24
  ProcVersionSignature: Ubuntu 6.17.0-20.20-generic 6.17.13
  Uname: Linux 6.17.0-20-generic x86_64
  ApportVersion: 2.33.1-0ubuntu3
  Architecture: amd64
  CasperMD5CheckResult: unknown
  CurrentDesktop: XFCE
  Date: Thu Apr  2 15:47:18 2026
  InstallationDate: Installed on 2021-10-08 (1637 days ago)
  InstallationMedia: Ubuntu 20.04.3 LTS "Focal Fossa" - Release amd64 (20210819)
  PackageArchitecture: all
  SourcePackage: coreutils-from
  UpgradeStatus: Upgraded to questing on 2025-11-17 (136 days ago)

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