There might be a case mostly observed while unmounting, you are unable to unmount a share even though as per your knowledge no one is accessing the share. The possible error which you might get is
Device busy Mount Point busy Text File is busy
In those cases you need to find out all the processes which are still accessing those paths or files which can be done using lsof or fuser command.
For example you want to find out all the process which are using /mnt
# fuser -uvm /mnt USER PID ACCESS COMMAND /mnt: root 7899 ..c.. (root)bash
or you can also use
# lsof /mnt COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME bash 7899 root cwd DIR 0,18 4096 535032 /mnt (192.168.1.11:/work)
In case you are pretty sure you want to kill all the process using /mnt run the below command
# fuser -km /mnt /mnt: 7899c
# fuser -uvm /mnt
So now none of the processes are using /mnt and it can be safely unmounted.
Search for deleted processes occupying the filesystem
Again I have seen cases where there are some deleted process which still lock the files unless their parent process or application relating to that process is completely executed. To view those files you might need to use extra parameters like as shown below
# lsof +aL1 /var COMMAND PID USER FD TYPE DEVICE SIZE NLINK NODE NAME rhn_check 31261 root 8u REG 253,2 22082560 0 327733 /var/cache/yum/prod-03-epel-x86_64-server-5-rhel5/primary.xml.gz.sqlite (deleted) rhn_check 31261 root 9u REG 253,2 78848 0 327737 /var/cache/yum/prod-03-likewise-x86_64-client-5-rhel5/primary.xml.gz.sqlite (deleted) rhn_check 31261 root 10u REG 253,2 144384 0 327741 /var/cache/yum/prod-03-mssb-x86_64-server-5/primary.xml.gz.sqlite (deleted) rhn_check 31261 root 11u REG 253,2 54056960 0 327748 /var/cache/yum/prod-03-rhel-x86_64-server-5/primary.xml.gz.sqlite (deleted) rhn_check 31261 root 12u REG 253,2 9275392 0 327752 /var/cache/yum/prod-03-rhel-x86_64-server-supplementary-5/primary.xml.gz.sqlite (deleted) rhn_check 31261 root 13u REG 253,2 582656 0 327756 /var/cache/yum/prod-03-rhn-tools-rhel-x86_64-server-5-rhel5/primary.xml.gz.sqlite (deleted)
When +L is followed by a number, only files having a link count less than that number will be listed. (No number may follow -L.) A specification of the form +L1 will select open files that have been unlinked. A specification of the form +aL1 <file_system> will select unlinked open files on the specified file system.