Linux – Alternative for “tail -f” that follows filename


I have some logs being generated using a timed rotating file logger. This logs to a file called tool.log, and at midnight, moves this to tool.log.<date> and starts a new tool.log.

I have a tail -f tool.log running on the machine to keep an eye on the logs, but at midnight, when tool.log is renamed to tool.log.<date>, tail continues to watch the renamed file.

What I'm hoping for is a tool that is similar to tail, but will continue to monitor the file named tool.log, rather than following the inode.

Does something like this exist? If not, I can write my own in Python for this purpose.

Best Answer

Some implementations of tail have an option for this; here's the description from the man page for GNU tail:

same as --follow=name --retry

-f, --follow[={name|descriptor}]
output appended data as the file grows; -f, --follow, and --follow=descriptor are equivalent

keep trying to open a file even when it is or becomes inaccessible; useful when following by name, i.e., with --follow=name

As this option isn't specified by POSIX, you can't depend on it everywhere. Some known implementations:

  • GNU - has -F as described above
  • Mac OS X, FreeBSD and NetBSD - have a similar -F option with the same effect
  • OpenBSD - -f is enough (if the file is replaced (i.e., the inode number changes), tail will reopen the file and continue)
  • Solaris - no equivalent
  • Busybox - -F is available in recent versions, but must be compiled with ENABLE_FEATURE_FANCY_TAIL (it's not compiled-in by default)
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