Before I delete any file in Unix, How can I check no open file handle is pointing to that file?


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# 1  
Before I delete any file in Unix, How can I check no open file handle is pointing to that file?

I know how to check if any file has a unix process using a file by looking at 'lsof <fullpath/filename>' command.

I think using lsof is very expensive. Also to make it accurate we need to inlcude fullpath of the file.

Is there another command that can tell if a file has a truely active open file handle pointing to it ? or if a file has a runtime PID associated with it?
# 2  
fuser, which is more commonly available than lsof, does this, putting the pids on stdout and the file names and flags on stderr, so you can get the pid list easily. For example:

Code:
$ for p in $( fuser . 2>/dev/null )
do
 echo
 ps -fp $p
 echo
 ptree $p
done
$


Last edited by DGPickett; 10-05-2010 at 02:12 PM..
# 3  
Nothing bad happens if you delete a file in use. It just persists on disk until the last thing using it quits, then is deleted for good.

There's no faster way to query the kernel about open files, than querying the kernel about open files. fuser works roughly the same way as lsof, so isn't really a slimmer/better workaround.
# 4  
If you want to delete a file and not have lost space if some program holds it forever, truncate it first. However, if the program appends with a high file position, all the space is reallocated and written to zeros, so there is some virtue in ensuring nobody has it open to write before you delete it.
# 5  
Thanks for pointing me to "fuser" command.

Does someone have a solaris equivalent of this script?
# 6  
Yes - it's "fuser".

And FWIW, assuming you're running on Solaris (as this is posted under the Solaris topic...), fuser on Solaris is a lot faster than lsof on Linux. The last time I looked at the lsof source code it was doing nothing more than searching through the entire /proc file system looking for a match to the file(s) it was given. The Solaris implementation of fuser operates fully inside the kernel (see /usr/include/sys/utssys.h on a Solaris box for the actual system call that does the work) and it seems to me that the Solaris kernel pretty much has to have a direct way of finding the processes that have that file open since it returns so fast - it seems way too fast to be searching unless what it's searching is really small.
# 7  
Quote:
Nothing bad happens if you delete a file in use.
My observation is different. If we delete "catalina.out" from a tomcat web server logs folder. Tomcat would not create another log,, until we restart tomcat. Where as other applications do create a new log file.

I am trying to find a safe way to do a generic log file rotation including logs like "catalina.out". Also try to know if a file is being actively used or not to make a better decision before log/file rotation.

When I query using lsof I get this -->
Quote:
> lsof ../jakarta/logs/catalina.out
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
java 1162 <UID> 1w VREG 314,7 1284251 19505649 ../jakarta/logs/catalina.out
java 1162 <UID> 2w VREG 314,7 1284251 19505649 ../jakarta/logs/catalina.out
What is the meaning of FD --> 1w 2w ?


2. What is the difference between 1w, 2w(in lsof output) Vs <PID>o (o in fuser output) ?

Quote:
> fuser -fu ../jakarta/logs/catalina.out
../jakarta/logs/catalina.out: 13601o(<userid>)

Last edited by kchinnam; 10-05-2010 at 03:32 PM.. Reason: masking secure info
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