How can I launch a new process that is NOT a child of the original process?

Question

(OSX 10.7) An application we use let us assign scripts to be called when certain activities occur within the application. I have assigned a bash script and it's being called, the problem is that what I need to do is to execute a few commands, wait 30 seconds, and then execute some more commands. If I have my bash script do a "sleep 30" the entire application freezes for that 30 seconds while waiting for my script to finish. I tried putting the 30 second wait (and the second set of commands) into a separate script and calling "./secondScript &" but the application still sits there for 30 seconds doing nothing. I assume the application is waiting for the script and all child processes to terminate. I've tried these variations for calling the second script from within the main script, they all have the same problem: - nohup ./secondScript & - ( ( ./secondScript & ) & ) - ( ./secondScript & ) - nohup script -q /dev/null secondScript & I do not have the ability to change the application an…

Accepted Answer

The typical way of doing this in Unix is to double fork. In bash, you can do this with

```
( sleep 30 & )
```

`(..)` creates a child process, and `&` creates a grandchild process. When the child process dies, the grandchild process is inherited by init.

If this doesn't work, then your application is not waiting for child processes.

Other things it may be waiting for include the session and open lock files:

To create a new session, Linux has a `setsid`. On OS X, you might be able to do it through `script`, which incidentally also creates a new session:

```
# Linux:
setsid sleep 30

# OS X:
nohup script -q -c 'sleep 30' /dev/null &
```

To find a list of inherited file descriptors, you can use `lsof -p yourpid`, which will output something like:

```
sleep   22479 user    0u   CHR 136,32      0t0       35 /dev/pts/32
sleep   22479 user    1u   CHR 136,32      0t0       35 /dev/pts/32
sleep   22479 user    2u   CHR 136,32      0t0       35 /dev/pts/32
sleep   22479 user    5w   REG  252,0        0  1048806 /tmp/lockfile
```

In this case, in addition to the standard FDs 0, 1 and 2, you also have a fd 5 open with a lock file that the parent can be waiting for.

To close fd 5, you can use `exec 5>&-`. If you think the lock file might be stdin/stdout/stderr themselves, you can use `nohup` to redirect them to something else.

How can I launch a new process that is NOT a child of the original process?

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