mongod.log

sudo cp /dev/null mongod.log

@ip:/var/log/mongodb$ ll
total 26475944
drwxr-xr-x  2 mongodb mongodb        4096 Feb 20  2020 ./
drwxrwxr-x 12 root    syslog         4096 Sep 25 06:25 ../
-rw-------  1 mongodb mongodb 27111306733 Sep 25 17:37 mongod.log

@ip:/var/log/mongodb$ sudo cp /dev/null mongod.log

@ip:/var/log/mongodb$ ll
total 12
drwxr-xr-x  2 mongodb mongodb 4096 Feb 20  2020 ./
drwxrwxr-x 12 root    syslog  4096 Sep 25 06:25 ../
-rw-------  1 mongodb mongodb 3034 Sep 25 17:37 mongod.log