How to make ncsim overwrite .trn file every time it runs?

hi, it's been some years I'm doing RTL simulation.
when I run ncsim, the wave file (trn) file is generated with incrementing numbers like below.

ckim@stph45:~/Neuro/convhw] ls tb_conv.shm
tb_conv-1-1.trn tb_conv-3-1.trn tb_conv-5-1.trn tb_conv-7-1.trn
tb_conv-1.dsn tb_conv-3.dsn tb_conv-5.dsn tb_conv-7.dsn
tb_conv-2-1.trn tb_conv-4-1.trn tb_conv-6-1.trn tb_conv-8-1.trn
tb_conv-2.dsn tb_conv-4.dsn tb_conv-6.dsn tb_conv-8.dsn

The recordvar setup is like this in verilog testbench.

// simulation dump
initial begin
$recordsetup(
"design = tb_conv",
"directory = tb_conv.shm",
//"version = 1",
//"compress", # this degrades the speed considerably.
//"run = 1"
);
$recordvars(
"depth=1",
tb_conv,
//"depth=0",
//tb_conv.sdcard0,
//tb_conv.sdc0,
);
$recordon;
$display("#sim started");
end

How can I make ncsim not make new .trn file every time it runs? (to overwrite to the existing trn file, like I used to see years back..)