How to flush stdout for a process under nohup

If you're using Bash, you can run disown -h job

disown

disown [-ar] [-h] [jobspec ...]

Without options, each jobspec is removed from the table of active jobs. If the -h option is given, the job is not removed from the table, but is marked so that SIGHUP is not sent to the job if the shell receives a SIGHUP. If jobspec is not present, and neither the -a nor -r option is supplied, the current job is used. If no jobspec is supplied, the -a option means to remove or mark all jobs; the -r option without a jobspec argument restricts operation to running jobs.

When you exit an interactive bash login shell, it sends a SIGHUP to all children unless the shell option huponexit is set to off.

When most userland processes receive a SIGHUP, they will exit.

When you disown -h, you are marking the process to prevent bash from sending a SIGHUP on exit regardless of the shell options. You could have also prefixed the command with nohup to reproduce this same behavior.

As far as STAT D:

An uninterruptible sleep state is a sleep state that cannot handle a signal (such as waiting for disk or network IO (input/output)).