08-01-2009
Normally, to run a command, the shell will fork, that is, it makes a copy of itself. Both copies start to run they both know which is the parent and which is the child. The parent simply waits for the child to finish. The child overlays irself (via the exec() feature) with the disired program. It runs and (we hope) eventually finishes by calling exit. The parent then starts running again and it issues another prompt.
The main difference with a background process it that the parent does not wait. If you need to use that file you are unzipping as input for your next command, then putting the unzip in the background would be inconvienent. You would have to keep checking to see if its done. But if you have another task then there is no problem.
Once you have one program in the background, you could overdo it. Put 25 unzips in the background and the system will slow down. So don't do that.
Some programs want to ask you questions and have you type in answers. Don't put those in the background, they're not suitable background tasks.
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killall(8) System Manager's Manual killall(8)
NAME
killall - Terminates all processes started by the user, except the calling process
SYNOPSIS
/usr/sbin/killall [- | [-]signal_name | -signal_number]
/usr/sbin/killall -l
FLAGS
The hyphen character (without an argument) sends a SIGTERM signal initially and then sends a SIGKILL signal to all processes that survive
for 30 seconds after receipt of the first signal. This gives processes that catch the SIGTERM signal an opportunity to clean up. A signal
name, optionally preceded by a hyphen, sends the specified signal to processes. The hyphen character (with a signal number argument) sends
the specified signal, either a name, stripped of the SIG prefix (such as KILL), or a number (such as 9). For information about signal
names and numbers, see the signal() system call.
In the System V habitat, the optional signal number does not have to be preceded with a hyphen (-). Lists signal names in numerical order
(as given in the /usr/include/signal.h file), stripped of the common SIG prefix.
DESCRIPTION
This command provides a convenient means of killing all processes created by the shell that you control. When started by the superuser,
the killall command kills all processes that can be terminated, except those processes that started it, the kernel processes, and processes
0 and 1 (init).
Security Configuration
This command is modified in all security configurations of the system.
EXAMPLES
To stop all background processes that have started, enter: killall This sends all background processes signal 9 (the kill signal, also
called SIGKILL). To stop all background processes, giving them a chance to clean up, enter: killall - This sends signal 15 (SIGTERM),
waits 30 seconds, and then sends signal 9 (SIGKILL). To send a specific signal to the background processes, enter: killall -2 This sends
signal 2 (SIGINT) to the background processes. To list the signal names in numerical order, stripped of the SIG prefix, enter: killall -l
This displays a list of signals, which may vary from system to system.
FILES
Specifies the command path
RELATED INFORMATION
Calls: kill(2), sigaction(2), signal(2) delim off
killall(8)