Linux – nohup daemon process dies when terminal is close

monit is great in this case - it runs on localhost, so you don't need a network connection to restart your daemon (in case it fails, or daemon is responsible for networking). It also has small footprint on the system, and you can use it to monitor your other daemons/disk space/etc. as well.

Create a start/stop script (similar to those in /etc/init.d/ and create symlinks for it in runlevels that your system uses for normal operation, ensuring that your daemon will start at reboot and stop at shutdown properly. If your daemon doesn't have pidfile, create one using start-stop-daemon script.

After that, install monit and create configuration for your daemon, something like this:

check process daemond with pidfile /var/run/daemond.pid
    start program "/etc/init.d/daemond start"
    stop program "/etc/init.d/daemond stop"
    if failed port 1234 type TCP for 5 times within 10 cycles then restart
    if 3 restarts within 5 cycles then alert

This configuration will ensure that if daemon stops responding on tcp port 1234, or will stop running, it will be restarted using the init script. monit will also send you an alert through email, or do other things, depending on how you configure it. Just check out monit(1) manpage.

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.