Public bug reported:

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)

** Affects: coreutils-from (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug questing

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

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

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