Difference between ctrl-z and "&" in linux

Question

My understanding is that when you are running any command (say sleep 10) within a given shell (say bash), what's happening under the hood is that a fork system call is called, and sleep 10 is now running as a child process with the parent being the bash shell I executed the sleep.

Now, if I want to send sleep to the background, I would either do sleep 10 & or run sleep 10 and press ctrl+z so the process is sent to the background. pstree shows that using any of these options, sleep keeps being a child process of the bash shell.

Now my question is, when doing this through SSH, I noted the following: If I do: sleep 999 & and sleep 888 <- followed by a ctrl+z, and the close the ssh session, only sleep 999 & survived.

Why is this? I actually was expecting one of these:

• both processes gets terminated because the parent process is gone
• both processes gets associated to init as the parent process.

Answer 1

or run sleep 10 and press ctrl+z so the process is sent to the background

No, not really. Didn't you see that big message that says "[1]+ Stopped sleep 10"? ctrl+z stops the process and returns you to the current shell. You can now type fg to continue process, or type bg to continue the process in the background. Research "bash job control" and see bash manual Job Control Basics.

Why is this?

Stopped processes are first continued SIGCONT and then SIGTERM is sent to them so they can terminate.

Bash manual is available online: https://www.gnu.org/savannah-checkouts/gnu/bash/manual/bash.html .