Difference between nohup, disown and &

Using & causes the program to run in the background, so you'll get a new shell prompt instead of blocking until the program ends. nohup and disown are largely unrelated; they suppress SIGHUP (hangup) signals so the program isn't automatically killed when the controlling terminal is closed. nohup does this when the job first begins. If you don't nohup a job when it begins, you can use disown to modify a running job; with no arguments it modifies the current job, which is the one that was just backgrounded

Here is my experience trying to run soffice in the background, following a non-terminating command (e.g. tail). For this example I will use sleep 100.

In all the cases below I execute like this:

./scriptfile
<Ctl-C>

&

#!/bin/bash
/opt/libreoffice4.4/program/soffice -invisible -nofirststartwizard &
sleep 100

I see soffice logs / by pressing Ctrl-C soffice stops

nohup .. &

#!/bin/bash
nohup /opt/libreoffice4.4/program/soffice -invisible -nofirststartwizard &
sleep 100

I don't see soffice logs / by pressing Ctrl-C soffice stops

& disown

#!/bin/bash
/opt/libreoffice4.4/program/soffice -invisible -nofirststartwizard & disown
sleep 100

I see soffice logs / by pressing Ctrl-C soffice stops

setsid .. &

#!/bin/bash
setsid /opt/libreoffice4.4/program/soffice -invisible -nofirststartwizard &
sleep 100

I see soffice logs / by pressing Ctrl-C soffice DOES NOT STOP

To save space:
nohup setsid .. : does not show logs / soffice DOES NOT STOP on Ctrl-C
nohup with & disown at the end : does not show logs / soffice stops on Ctrl-C

Short answer:

• use & when you want your command to run in the background, so you can run the next one without waiting for it to finish
• use nohup if you want your command to ignore the SIGHUP signal, so when you close the terminal or log out from ssh session the process keeps running
• use disown if you forgot to run the command with nohup and want to log out without killing the process (it will disown all processes in the background). To put a process in the background and disown it:
  1. Ctrl+Z to pause process
  2. bg to put stopped process to the background
  3. disown to make process ignore terminal termination

See also the daemonize(1) utility, which handles all of the chores about running a "true background" process. As of its docs:

daemonize runs a command as a Unix daemon. As defined in W. Richard Stevens' 1990 book, Unix Network Programming (Addison-Wesley, 1990), a daemon is “a process that executes `in the background' (i.e., without an associated terminal or login shell) either waiting for some event to occur, or waiting to perform some specified task on a periodic basis.” Upon startup, a typical daemon program will:

• Close all open file descriptors (especially standard input, standard output and standard error)
• Change its working directory to the root filesystem, to ensure that it doesn't tie up another filesystem and prevent it from being unmounted
• Reset its umask value
• Run in the background (i.e., fork)
• Disassociate from its process group (usually a shell), to insulate itself from signals (such as HUP) sent to the process group
• Ignore all terminal I/O signals
• Disassociate from the control terminal (and take steps not to reacquire one)
• Handle any SIGCLD signals

Most programs that are designed to be run as daemons do that work for themselves. However, you'll occasionally run across one that does not. When you must run a daemon program that does not properly make itself into a true Unix daemon, you can use daemonize to force it to run as a true daemon.

It superseeds all of the &/nohup/disown mess.

& puts the job in the background, i.e. makes it block input from the shell, and makes the shell not wait for its completion.

nohup and disown both can be said to suppress stdin from the terminal and SIGHUP, but in different ways. nohup works when the job is initialized, disown works after the fact.

nohup also redirects stderr to stdout and stdout to $HOME/nohup.out. It does not block other signals being sent indirectly from the original shell.

disown does not redirect stdout or stderr. It simply removes the process from the shells job table, so no signals will be indirectly sent to the process from the original shell.