Please note that NetWitness is not tested or suggested that it be ran on CentOS 8. How you got it installed when the software is on a CentOS 7 image opens up other questions as well. Under normal circumstances the /tmp folder should not fill to capacity when using a standard NetWitness image. How large is your /tmp folder? Do you have any non-NetWitness items writing to the /tmp folder? Do not manually remove NetWitness related temp files unless specifically requested by NetWitness Support as this can cause your NetWitness instance to not work as expected.