Concurrency issue while using cp 2

[ddrillich]

Good Day,

It appeared this morning, when the beeper woke me up at 4:15 AM ;-) that while we ran the cp command on a tiny file, another process tried to read the file and didn't find the complete file - the SAX parser threw a 'Premature end of file' SAX exception.
Hours later, the SAX parser had no problem reading the same file.

So, my question is - is the cp operation an atomic one?

Regards,
Dan

 

[elgrandeperro]

mv is, cp isn't. you get what is there at the time. A small file should be nearly atomic, but there is no guarantee.

 

[Annihilannic]

I think you already know the answer. No, it isn't. I'm presuming it was attempting to read the destination file?

If it needs to be atomic, copy to a temporary filename and then rename. Seems like overkill for a tiny file though, you were probably just very unlucky on that occasion.

Annihilannic.

 

[ddrillich]

Many thanks !!

 

[Annihilannic]

egp, mv isn't atomic either if you are moving between filesystems.

Annihilannic.

 

[elgrandeperro]

Oh, yeah...right. I was thinking in the same dir.