Trying to empty file using > but the file size increasing when next append


 
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# 1  
Old 06-23-2008
Trying to empty file using > but the file size increasing when next append

AIX 5.3 / KSH

I have a Java application which creates a log file a.log. I have a KSH script which does the following action

Code:
cp a.log /directory2/b.log
> a.log

After this the file size goes to 0 as per "ls -l"

Then next time when the application writes into this file, the file size is goes to the previous before the ">" operation happened.

I tried the Code in a different style:
Code:
cp a.log /directory2/b.log
cp /dev/null a.log

No change. What is the best way to do this?

***NOTE: I cannot use rm -f/touch method for cleaning up the log file because it requires a restart of the application.
# 2  
Old 06-23-2008
Yes, some applications are written like that and if you can't stop the appl. for wrapping the log, you will have to expand the FS, if possible... or persuade people of a short downtime of some minutes once per week at night per cron to clean up and wrap.
# 3  
Old 06-23-2008
Thanks for response.

Expand FS means increasing the size of the mount?

Any idea why the log file size becomes 0 immediately I executed ">" operation ($ > a.log) and the file size resets to earlier size (some 100MB) immediately after the first byte written into the log file?

I cannot both rely on removing the file or expanding the file. The only solution I can go for is a safe cleanup of this file, without removing or renaming.

Appreciate your thoughts.
# 4  
Old 06-23-2008
I think it is exact the same size like before after you nulled it, because it is maybe cached by the appl. or something like that. Seems it accepts the writing 1st, but a file handle appears to be still open on that file that revokes the former action somehow. I am no programmer, maybe someone else can explain it in detail.

Quote:
Expand FS means increasing the size of the mount?
Yes, if that's an option for you. The appl. might crash, spit errors or something like that if it runs out of space anyway.

Quote:
I cannot both rely on removing the file or expanding the file. The only solution I can go for is a safe cleanup of this file, without removing or renaming.
You misunderstood me. When you are allowed to get a short downtime maybe once a week, depending on how fast the log is growing, or once per night, whatever, you stop the application graceful, cp that file to a.log.`date %+w` for example, compress it and just null the original like you tried already "> a.log". When your log files are set, start your appl. again.
Write a little script for this and put it as a cronjob - done.
# 5  
Old 06-23-2008
Thanks for the points and really good. I think I need to go back to Application Developers to see if they can rotate the logs cleanly...

The approach you had mentioned (using the crontab) is already in place, except that the application restart.

Thank you so much for your help... Smilie

Smilie
 
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