Thursday, 5 February 2009

Useful Unix Commands - Part 2

A selection of useful find commands

=== Find User ===

fuser displays the PIDs of processes using the specified files or file systems.
fuser command is very useful in getting rid of the .nfs files created when processes are killed. The .nfs* names refer to files that have been deleted but are still being held open by a running process.

You can find .nfs files using ls -la

rm does not work in removing .nfs files - use fuser to find the process that's locking the file and then kill the process

 /usr/sbin/fuser {filename} 


 kill -9 {pid} 


If you stop the processes that have them open, the files will be tidied-up and removed by the file server.


If you're interested a bit of general background follows:

Most operating systems, including UNIX, operate a policy of not actually removing a deleted file (and freeing up it's data blocks) until the last process that has the file open closes it. So, if a running process has a file open and you use the rm(1) command to delete the file the data blocks on the disk will not be freed up by the OS until the process that has the file open closes it.

On a UNIX host using local disk store this behaviour can manifest itself it some seemingly confusing situations. For example, you may wish to free up some space on a file system that's used 900 MB of it's 1GB quota. You have a large file, 200MB say, named myjava.jar that you believe is no longer required, but is actually currently open in your WebLogic server. Not knowing this you delete myjava.jar and do an ls(1) command to see that the file is no longer listed. However, when you use the df(1) command it still reports that 900 MB of it's 1GB quota is used because your WebLogic server still has the file open. When you shutdown the WebLogic server or the server closes the file the disk space will be released and df(1) will report 700MB of it's 1GB is used.

If the file that is removed is on NFS mounted store then it is possible for a file to be deleted on one client whilst still being open on another client. In this situation the same rule of not actually deleting the file until the last process with it open closes it still applies. However, in order for the NFS file handle used by the client that still has the file open not to be broken a filename reference must be maintained. In order to achieve this and remove the files name from the directory ( so it doesn't show up in an ls command output) the NFS file server renames the deleted file to a name beginning '.nfs'. These are the files you are seeing. When the last process with these files open dies or closes them they will be tidied up and removed. Trying to delete them before they are closed will only result in the file being renamed again.



=== Find Class within Jar file ===

To find a class within a binary jar file

 for i in `ls *.jar`; do (jar tf $i  grep '{classname}' ) && echo $i;done   


If you want to search within all subdirectories use this

 for i in `find . -name ‘*.jar’`; do (jar tf $i  grep '{CLASSNAME}' ) && echo $i;done 


=== Find string within file of name ===


find . -name *.xml -exec grep {} \;

example

find . -name web.xml -exec grep -i servlet {} \;



=== Grep within zip file without unzipping it ===


gzip -c -d {file}.gz | grep {string}

Example

gzip -c -d admin_access.log0001_4Dec08_0147.gz | grep -i adq | wc -l







=== Find process using the port ===

The easy way to do this is using netstat passing the port number

netstat -a | grep 61014

If that does not help getting a pid, run this line below


for i in `ls /proc`; do pfiles $i | grep AF_INET | grep 61014 ; done


Output:

pfiles: permission denied: 12363
sockname: AF_INET 0.0.0.0 port: 61014
pfiles: permission denied: 12384

this shows the process appearing in between pids 12363 and 12384 uses that port.

ls /proc
gives the PIDs in order as .. 12363, 12369, 12384 ..


ps -ef grep 12369
wlsuser 12369 7852 0 01:07:40 ? 4:42 /opt/bea/jdk142_05/bin/java -server -DresKBD -Xms512m -Xmx512m -XX:MaxPermSize=

gave the process details which was using the port