Running command in background using logstash exec output plugin - output

Question

Does anybody know how to run command in background using logstash exec output plugin?
I tried this configuration
input {
file {
path => "file.log"
}
}
output {
exec {
command => "./script.sh fff ggg hhh jjj kkk &"
}
}
And script content is
#/bin/bash
echo "$*" >> file.txt
So finally file.txt contains & as it is parameter: fff ggg hhh jjj kkk &

Answer 1

According to the Logstash Reference for Exec output plugin:
Use dtach or screen to make it non blocking.
I suggest you use dtach, excerpt from dtach's man page:
dtach is intended for users who want the detach feature of screen without the other overhead of screen. It is tiny, does not use many libraries, and stays out of the way as much as possible.
Example usage (as sysadmin1138 suggested, you should use the full path):
output {
exec {
command => "/usr/bin/dtach -n /tmp/session_name -Ez /absolute/path/script.sh fff ggg hhh jjj kkk"
}
}
Note 1: You probably need to install dtach first if your system does not have it by default.
Note 2: You can get full path of dtach by using which dtach command.
Note 3: Definition of -n mode from dtach's man page:
-n Creates a new session, without attaching to it. A new session is created in which the specified program is executed. dtach does not try to attach to the newly created session, however, and exits instead.
Hope that helps!

Answer 2

You seem to be doing it right, though keep in mind that the current-working-directory is not always obvious within the context of exec. A full path to the script would be much more robust. Be aware this is run by ruby's system() function, if you are interested in potential side-effects and constraints.