incremental tar creates wrong file

[JimmyTheSaint]

I had a lot of help over at this thread to set up incremental backups with crontab. I just discovered that tar is not actually incrementing the tar files. I first created the tar files, then in crontab I have:

 cd /; tar -cpf --incremental --exclude-from=/root/ExcludeFromTar.txt mnt/PATRIOT/bkp/home.tar  home

I only just discovered that this creates a file whose filename is "/--incremental". I also tried using tar's -G switch instead of --incremental:

 cd /; tar -cpfG --exclude-from=/root/ExcludeFromTar.txt mnt/PATRIOT/bkp/home.tar  home

but this creates a file whose filename is "/G". The contents of /--incremental and /G are my home directory, but why is the target file not being updated? This is the symptom of mistaken syntax in the tar command, but I don't see what's wrong in the command I posted above. What am I missing?

[SiliconSlick]

The "f" part takes the next part as a file name. Try:

tar -cpf mnt/PATRIOT/bkp/home.tar --incremental --exclude-from=/root/ExcludeFromTar.txt home
or
tar -cpGf mnt/PATRIOT/bkp/home.tar --exclude-from=/root/ExcludeFromTar.txt home #note G comes before f and the filename is right after f

SS

[JimmyTheSaint]

D'OH! That was it--thanks. I knew it had to be something totally stupid. I've been using tar for so long and have always automatically put 'f' at the end of my switches to the point that I had no memory of the 'f' switch's actual function. I had now thought tar's syntax just required the files in that order. Of course, I see in tar's man page (way down actually) the function of the 'f' switch. It's amazing that, in 23 years of using tar, I never once ran into this mistake.

Over at the other thread, I did post that the tar files I was supposedly incrementally backing up to each night were not having their timestamps updated. This was clear and immediate evidence that I was using tar wrong, but someone posted that this was correct behavior. That's a mistake: of course incremented tar files get touched and get their timestamps updated, so I can now easily verify that crontab is running tar on schedule.