[Shell: Foreground <--> Background] #sh #fg #bg

background.sh

# https://askubuntu.com/questions/8653/how-to-keep-processes-running-after-ending-ssh-session -- nohup, disown

##### `&` (BACKGROUND) #####
# foreground task (blocking)
ping localhost > /dev/null 
# background task (non-blocking)
ping localhost > /dev/null & # returns [<jobNo>] <PID>

##### `jobs` (SHOW RUNNING BG JOBS) #####
ping localhost > /dev/null & # --> [1] 107
ping localhost > /dev/null & # --> [2] 128
jobs # --> [1] & [2] details 

##### `fg`/`bg` (SWAP FG/BG FOR A RUNNING JOB) #####
fg %1 # brings [1] to the fg --> `ping localhost > /dev/null`
bg %1 # sends [1] to the bf --> `ping localhost > /dev/null &`

##### PAUSE/SUSPEND JOB (<Ctrl+Z>) #####
# regain control of the terminal by suspending a job by pressing <Ctrl+Z> while it has the fg
fg %1
<Ctrl+Z> # --> [1] Stopped
bg %1

##### `kill`/`killall`/`pkill` (KILL[ALL] JOB) #####
ping localhost > /dev/null & # --> [3] 110
kill %3 # --> [3] Terminated
killall ping # kills [1] and [2]
sleep 88888 & # --> [4] 148
pkill -15 sleep # kill with SIGTERM (15) (SIGKILL is 9)