Re: dd killed with USR1 right after ftruncate()

[Pádraig Brady]

Voelker, Bernhard wrote:
> Hi *,
>  
> short question:
> is there a particular reason why the signal handlers are installed after 
> ftruncate() in dd?
>  
> Long story:
> I ran dd for a new backup of my 150GB partition to an external USB drive 
> while I started
>     while kill -USR1 pid ; do sleep 30 ; done
> in a separate terminal. The target file already existed and reflected a 
> previous backup.
> After a while, dd ended with the standard USR1 signal handler.
> The only work done so far was to truncate the old output file.
> So my guess was that installing the signal handler for SIGUSR1 is done after
> the truncation. So I looked into the latest sources (coreutils-7.4) and found 
> out
> that my guess was right:
>  
>        if (ftruncate (STDOUT_FILENO, size) != 0)
>          {
>     <snipped />
>          }
>      }
>     #endif
>       }
>       install_signal_handlers ();
>  
> So why does ftruncate() before install_signal_handlers()?

What is your exact dd command please, and destination file system.
I'm a bit confused as ftruncate is not called unless you specify a
non zero seek= but that seems a bit weird from your described usage.
Also I'm confused as to why a non zero seek would take "a while".
On vfat I suppose, but that only supports 4G files, not 150G.

You're right though in that the signal handlers are installed
just around the copy. I need to double check if that's by design.

cheers,
Pádraig.