There are times when even after you deleted a file in Linux but that didn’t reclaim space in filesystem.
Below command shows that there are few of the files which are deleted from the system but are still active and still taking the space on the disk.

[oracle@dixitdb053 /proc]# /usr/sbin/lsof |grep -i deleted
oracle 11441 oracle 19w REG 253,2 1810 3129788 /opt/oracle/diag/rdbms/dixitdb/dixitdb/trace/dixitdb_diag_11441.trc (deleted)
oracle 11441 oracle 20w REG 253,2 126 3129795 /opt/oracle/diag/rdbms/dixitdb/dixitdb/trace/dixitdb_diag_11441.trm (deleted)
oracle 30157 oracle 19w REG 253,2 14182 3129684 /opt/oracle/diag/rdbms/dixitdb/dixitdb/trace/dixitdb_vkrm_30157.trc (deleted)
dd 32592 oracle 1w REG 253,2 24238593024 3129587 /opt/oracle/diag/rdbms/dixitdb/dixitdb/trace/dixitdb_ora_31778.trm (deleted)

Here the file is available under mount point — /opt/oracle and is still 86% full.

[oracle@dixitdb053 /proc/11441/fd]# df -hk
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
31614888 6127104 23856156 21% /
/dev/mapper/VolGroup02-LogVol05
36124288 29165480 5123800 86% /opt/oracle
/dev/sda1 101086 15711 80156 17% /boot
tmpfs 1956756 0 1956756 0% /dev/shm
113.11.88.199:/vol/dixitdb053_BO
110100480 58354656 51745824 54% /db01
113.11.88.199:/vol/vol_dixitdb053_backup
104857600 55011648 49845952 53% /backup

Well, the space will be automatically reclaimed depending on the size of the file deleted.
Below are the steps in order to remove it instantly from the file system

Steps:
=============
1. Go to /proc directory which contains PID of all active processes and files.
2. login to respective PID

[oracle@dixitdb053 /proc/11441/fd]# cd /proc/32592
[oracle@dixitdb053 /proc/32592]# cd fd
[oracle@dixitdb053 /proc/32592/fd]# pwd
/proc/32592/fd

3. Check if there is a link and in the end it says deleted.

[oracle@dixitdb053 /proc/32592/fd]# ls -ltrh
total 0
lrwx—— 1 oracle oinstall 64 Mar 7 07:57 2 -> /dev/pts/1
l-wx—— 1 oracle oinstall 64 Mar 7 08:25 1 -> /opt/oracle/diag/rdbms/dixitdb/dixitdb/trace/dixitdb_ora_31778.trm (deleted)
lr-x—— 1 oracle oinstall 64 Mar 7 08:25 0 -> /dev/zero

4. Type > in the number that was shown in that line and it will release the space instantly.

[oracle@dixitdb053 /proc/32592/fd]# > 1

[oracle@dixitdb053 /proc/32592/fd]# ls -ltrh
total 0
lrwx—— 1 oracle oinstall 64 Mar 7 07:57 2 -> /dev/pts/1
l-wx—— 1 oracle oinstall 64 Mar 7 08:25 1 -> /opt/oracle/diag/rdbms/dixitdb/dixitdb/trace/dixitdb_ora_31778.trm (deleted)
lr-x—— 1 oracle oinstall 64 Mar 7 08:25 0 -> /dev/zero

5. verify it once again by listing the open files in the filesystem to see if there is still an open file with the deleted status.

Now the space is reclaimed and has been brought down to 0.

[oracle@dixitdb053 /proc/32592/fd]# /usr/sbin/lsof |grep -i deleted
oracle 11441 oracle 19w REG 253,2 0 3129788 /opt/oracle/diag/rdbms/dixitdb/dixitdb/trace/dixitdb_diag_11441.trc (deleted)
oracle 11441 oracle 20w REG 253,2 0 3129795 /opt/oracle/diag/rdbms/dixitdb/dixitdb/trace/dixitdb_diag_11441.trm (deleted)
oracle 30157 oracle 19w REG 253,2 14792 3129684 /opt/oracle/diag/rdbms/dixitdb/dixitdb/trace/dixitdb_vkrm_30157.trc (deleted)
dd 32592 oracle 1w REG 253,2 0 3129587 /opt/oracle/diag/rdbms/dixitdb/dixitdb/trace/dixitdb_ora_31778.trm (deleted)

And the mount point /opt/oracle usage went down too and reached to 17%.

[oracle@dixitdb053 /proc/32592/fd]# df -kh
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
31G 5.9G 23G 21% /
/dev/mapper/VolGroup02-LogVol05
35G 5.3G 28G 17% /opt/oracle
/dev/sda1 99M 16M 79M 17% /boot
tmpfs 1.9G 0 1.9G 0% /dev/shm
113.11.88.199:/vol/dixitdb053_BO
105G 56G 50G 54% /db01
113.11.88.199:/vol/vol_dixitdb053_backup
100G 53G 48G 53% /backup

Thanks
Prashant Dixit