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bug#25475: tail -f behaviour
From: |
Pádraig Brady |
Subject: |
bug#25475: tail -f behaviour |
Date: |
Wed, 18 Jan 2017 18:37:01 +0000 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 |
On 18/01/17 16:39, f0rhum wrote:
> Hi
> This is about tail v5.97
> I have a log file that is updated every 5mn, a timestamped message being
> appended to a new line at the end
> On the third time an indentical message would be writen, the last line
> is replaced by "..." then the message is writen
>
> Tracking changes with tail -f stops after this, which may be intended
> behaviour as man states "as the file grows".
>
> Although, when pruning a bunch of lines from the head of the file, then a
> yet running tracking still won't update even the file size grows, like if the
> file size was
> grabbed on the very beginning of the command and never updated on each
> iteration.
>
> To be honest, I didn't try to see what happens if I prune a single line
> and see what the next 2nd and further iterations show.
I think you're saying that your file is truncated in place.
tail(1) doesn't handle that well and expects files to be increasing,
and maybe rotated (which is handled with -F).
Newer versions of tail(1) will show the whole file again once
it detects truncation (as usually a truncated file is truncated to nothing
before new data is written).
cheers,
Padraig