I have shared my usb drive contents mounted on linux via SAMBA. when the shared file is in use at linux platform, i was able to delete/ rename the same via windows PC.

I use a FAT32 filesystem , hence changing permissions (to readonly when in use) is not taking effect.

Is there a way to lock the shared file either via smb.conf / linux commands so that simultaneous access to same file is avoided???

Following is configuration set at smb.conf file,,
workgroup = NETWORK
server string = NETWORK-SERVER
security = share
dns proxy = no
read raw = yes
write raw = yes
oplocks = yes
max xmit = 65535
dead time = 15
getwd cache = yes
ldap debug level = 0
level2 oplocks = yes
local master = yes
preferred master = yes

path = /XX/Shared Path/
writable = yes
guest ok = yes
guest only = yes
create mode = 0777
directory mode = 0777