When you unmount a filesystem, you may get "device is busy error" sometimes.
Using the following steps, you can unmount safely.
# umount /testsrv1/rman
umount: /testsrv1/rman: device is busy
umount: /testsrv1/rman: device is busy
# fuser -m /testsrv1/rman
/testsrv1/rman: 31477c
# ps -eaf | grep 31477
oracle 31477 31448 0 09:52 pts/0 00:00:00 /bin/ksh
# df -h /testsrv1/rman
Filesystem Size Used Avail Use% Mounted on
testsrv1:/miszpool/mis
2.5T 1.9T 560G 78% /testsrv1/rman
# ps -eaf | grep 31477
oracle 31477 31448 0 09:52 pts/0 00:00:00 /bin/ksh
# ps -eaf | grep 31448
dbauser1 31448 31447 0 09:51 pts/0 00:00:00 -ksh
oracle 31477 31448 0 09:52 pts/0 00:00:00 /bin/ksh
# kill -9 31477
# ps -eaf | grep 31448
dbauser1 31448 31447 0 09:51 pts/0 00:00:00 -ksh
# umount -f /testsrv1/rman
# mount /testsrv1/rman
# df -h /testsrv1/rman
Filesystem Size Used Avail Use% Mounted on
testsrv1:/miszpool/mis
2.5T 1.9T 560G 78% /testsrv1/rman
# umount /testsrv1/rman
umount: /testsrv1/rman: device is busy
umount: /testsrv1/rman: device is busy
# fuser -m /testsrv1/rman
/testsrv1/rman: 31477c
# ps -eaf | grep 31477
oracle 31477 31448 0 09:52 pts/0 00:00:00 /bin/ksh
# df -h /testsrv1/rman
Filesystem Size Used Avail Use% Mounted on
testsrv1:/miszpool/mis
2.5T 1.9T 560G 78% /testsrv1/rman
# ps -eaf | grep 31477
oracle 31477 31448 0 09:52 pts/0 00:00:00 /bin/ksh
# ps -eaf | grep 31448
dbauser1 31448 31447 0 09:51 pts/0 00:00:00 -ksh
oracle 31477 31448 0 09:52 pts/0 00:00:00 /bin/ksh
# kill -9 31477
# ps -eaf | grep 31448
dbauser1 31448 31447 0 09:51 pts/0 00:00:00 -ksh
# umount -f /testsrv1/rman
# mount /testsrv1/rman
# df -h /testsrv1/rman
Filesystem Size Used Avail Use% Mounted on
testsrv1:/miszpool/mis
2.5T 1.9T 560G 78% /testsrv1/rman