In an ssh session on a server I started some bash processes (that start other processes) in the background with & and redirected their stdin / stdout to file (<dev/null >mylog.out).
The processes are not listed under jobs and ps -T shows only one bash process and ps itself.
Most of the (child) processes are run by user root but are all linked to a specific TTY pts/20.
If I close the ssh session, will the processes and their children be sent the HUP signal or will they continue running? If yes, how could I completely detach them?
If you put a process in the background the process will ignore the SIGHUP command. So the process will continue to run.
Test results:
Login and run bash script o.sh in background and exit:
system:10.11.2.122 > o.sh &
system:10.11.2.122 > exit
Login back into system and check o.sh process:
system:10.11.2.122 > ps -ef | grep o.sh
root 19115 1 0 10:10 ? 00:00:00 /usr/local/bin/bash /root/scripts/o.sh
root 27774 20197 0 10:23 pts/2 00:00:00 grep o.sh
This method daemonises a running process.
With bash, this behavior is dependent on the huponexit shell option. These, and other option settings, can be seen using the shopt command on CentOS/RedHat 6.7.
huponexit appears to be off by default on CentOS/RedHat 6.7.
A subset of the output of shopt:
histappend off
histreedit off
histverify off
hostcomplete on
huponexit off
interactive_comments on
lithist off
login_shell on
mailwarn off
no_empty_cmd_completion off
nocaseglob off
nocasematch off
nullglob off
So to answer your questions:
If I close the ssh session, will the processes and their children be sent the HUP signal or will they continue running?
That depends on your huponexit setting. If huponexit is off, then no and process will continue to run. Otherwise, yes.
If yes, how could I completely detach them?
Use the nohup command when executing the process.
nohup your_process &