Preventing access to a file being FTP'd

[TheJuiceman]

Here is what I'm wanting to do...
I have a process that FTP's a large file from a windows box to a HP-UX box. In fact there are a lot of FTP processes that occur fairly frequent in this fashion.
I have a job scheduled to run very frequently on the HP box that will grab any FTP'd file in the depository directory and process it.
Problem: How do I tell the process on the HP box to wait until the FTP process is complete before accessing the file?

[Hein van den Heuvel · Accepted solution]

I find it best to transfer the file using a temporary output name and rename to the looked-for name on succesful transfer.

You indicate 'any' FTP'd file though.
Can that be change to any file not named .transfer or .tmp ?

Or can you use a subdirectory or parallel directory during the transfer, moving when done?


hth,
Hein.

[F Verschuren]

The reaname of the file is a simple solution....

In the kernal when a file closes (so if the write is done) ther will be a trigger.
randevou router eamons pickup this singal to be sure the write is done. this is alsow a lot of work to program.

the easey way is to either use the rename (but not all ftp jops can do this nicely) ore use a extra trigger file that you put on the hp box after you pleased the large file.. if your job sees the trigger file it has to remove the trigger and does the job...

[Matti_Kurkela]

By the way, this is called (especially in database circles) a problem of _atomicity_.

"Atomic" means "indivisible" in this context.

From the viewpoint of the process that accesses the transferred files, the transfer must be an atomic operation: it must be either completely and successfully done, or it must be completely NOT done (i.e. a file must not exist at the expected location).

Moving a file within the same filesystem (or, as a special case, renaming the file) is guaranteed to be an atomic operation at the operating system level. The solutions outlined by Hein exploit this property.

MK

[Dennis Handly]

I thought ftp when transferring files gives the file no access permissions? And this is only changed when done.

[Arturo Galbiati]

Hi,
another possibility is to FTP 2 file, the real data file and a flag file and start your process only when the flag file arrives.
In this way you will be sure tocatch teh data file completed. To avoid to chnage your script you can create a new one that run the origianl script only when the flag file is present. Just my .02$ based on a same problem in the past.
HTH,
Art

[TheJuiceman]

Thanks everyone for the suggestions.