How can I start a shell process and return immediately?

Ruby
1

I want to start a Java program from a Ruby program and have the Java
program run in another process and have control returned to my Ruby
program as soon as the Java process starts up successfully.

I can do this from a shell by suffixing an ‘&’:

java -cp <main_class>&

starts the Java program in a background process thread and returns
control the shell.

When I try this from a Ruby program the program blocks until the Java
program is terminated.

2

Stephen B. wrote:

When I try this from a Ruby program the program blocks until the Java
program is terminated.

“this”? Here let’s play a little game. You try to help me. Here is
my question: I have a for loop that doesn’t work. Can you fix it?

3

Stephen B. wrote:

java -cp <main_class>&

starts the Java program in a background process thread and returns
control the shell.

When I try this from a Ruby program the program blocks until the Java
program is terminated.

I don’t know what exactly “this” is, but system(“some_command &”) works
just
fine here.

4

r8test.rb

sleep(4)
puts “Data from subprocess: 10 20 30”

main_program.rb

puts “main program”
sleep(1)

pipe = IO.popen(“ruby r8test.rb”, “w+”)

puts “main program executing while subprocess is sleeping”
Process.wait

pipe.close_write
puts pipe.gets

pipe.close_read

5

Hello,

On 9/28/07, Stephen B. [email protected] wrote:

I want to start a Java program from a Ruby program and have the Java
program run in another process and have control returned to my Ruby
program as soon as the Java process starts up successfully.

When I try this from a Ruby program the program blocks until the Java
program is terminated.

There may be another way, but the first thing that came to mind for me
was just to launch it in another thread:

Thread.new { java -cp <classpath> <main_class> }

Cameron

6

Stephen B. wrote:

  • Thanks 7stud,

IO.popen is interesting, I’m playing with your simple test programs and
reading chapter 11 in the Pickaxe book.

You can consider the sleep(4) statement in the subprocess as a stand in
for some calculation or task that takes 4 seconds to execute.

7

There may be another way, but the first thing that came to mind for me
was just to launch it in another thread:

Thread.new { java -cp <classpath> <main_class> }

  • Thanks Cameron,

That worked, I hadn’t used threads before and they were what I needed.

  • Thanks Sebastion,

I thought I had tried this:

system(“some_command&”)

and it didn’t work – but it was late and I needed to sleep – today
that works fine – so obviously I wasn’t thinking as clearly as I could
have been.

  • Thanks 7stud,

IO.popen is interesting, I’m playing with your simple test programs and
reading chapter 11 in the Pickaxe book.

8

I have another quetion related to fire off a back ground shell process
on a remote Linux.

require "net/ssh"

ssh = Net::SSH.start( '10.0.77.87', 'toor',  :password=>'logapp')
ssh.exec!("/root/test.pl &")
ssh.close
puts "I want to be here immediately, but not"

The above code hangs also because test.pl contains a long sleep and do
nothing. Can someone offer me a help?

Thank you in advance.

Enling

Stephen B. wrote:

I want to start a Java program from a Ruby program and have the Java
program run in another process and have control returned to my Ruby
program as soon as the Java process starts up successfully.

I can do this from a shell by suffixing an ‘&’:

java -cp <main_class>&

starts the Java program in a background process thread and returns
control the shell.

When I try this from a Ruby program the program blocks until the Java
program is terminated.

9

Thank you, Rob for the quick reply and help. I tried the commmand you
enclosed in the mail. It did not work out. I still got hang at the
exec() command.

Here are the options I did. They behave the same. They don’t work. By
the way, my linux system has setsid().

ssh.exec!(“setsid /root/test.pl >/tmp/test.log 2>&1”)
ssh.exec!(“setsid /root/test.pl > /dev/null 2>&1”)
ssh.exec!(“setsid /root/test.pl”)

Thanks.

Enling

Rob B. wrote:

On Jul 9, 2009, at 5:13 PM, Enling Li wrote:

The above code hangs also because test.pl contains a long sleep and do

I can do this from a shell by suffixing an ‘&’:

java -cp <main_class>&

starts the Java program in a background process thread and returns
control the shell.

When I try this from a Ruby program the program blocks until the Java
program is terminated.

If your system has the setsid (set session id) program (and the
underlying system call), then you could try:

ssh.exec!(“setsid /root/test.pl”)

or

setsid java -cp YOURCLASSPATH MainClass

but you may wish to redirect output.

ssh.exec!(“setsid /root/test.pl >/tmp/test.log 2>&1”)

-Rob

Rob B. http://agileconsultingllc.com
[email protected]

10

On Jul 9, 2009, at 5:13 PM, Enling Li wrote:

The above code hangs also because test.pl contains a long sleep and do

I can do this from a shell by suffixing an ‘&’:

java -cp <main_class>&

starts the Java program in a background process thread and returns
control the shell.

When I try this from a Ruby program the program blocks until the Java
program is terminated.

If your system has the setsid (set session id) program (and the
underlying system call), then you could try:

ssh.exec!(“setsid /root/test.pl”)

or

setsid java -cp YOURCLASSPATH MainClass

but you may wish to redirect output.

ssh.exec!(“setsid /root/test.pl >/tmp/test.log 2>&1”)

-Rob

Rob B. http://agileconsultingllc.com
[email protected]

11

On Thu, Jul 9, 2009 at 4:53 PM, Enling Li [email protected]
wrote:

Would just dropping the ssh section into it’s own thread accomplish your
task? That seems like a rather simple way of getting what you want.

John

12

I tried that before. The thread won’t solve the issue because once child
thread established it does the same way as main tread. When the main
thread terminates, the child gets killed also. It ends up nothing
happened to the shell command.

Thanks.

Enling

John W Higgins wrote:

On Thu, Jul 9, 2009 at 4:53 PM, Enling Li [email protected]
wrote:

Would just dropping the ssh section into it’s own thread accomplish your
task? That seems like a rather simple way of getting what you want.

John

13

Are you sure you are properly connecting to the server? Have you tried
just
running something like ls and getting back a result? I just tried
running a
simple script that sleeps for 100 seconds and it ran just fine after the
remote app was finished.

If that still leaves you in trouble - you might want to look into Screen
which is designed to run apps detached from the login shell so that
would
certainly be of use if needed. This is the command I use to run an app
detached - screen -D -m command.rb

John

14

John,

The key is I don’t want to wait for the remote to finish. If I wait for
remote to complete, I don’t have problem.

Thanks.

Enling

John W Higgins wrote:

Are you sure you are properly connecting to the server? Have you tried
just
running something like ls and getting back a result? I just tried
running a
simple script that sleeps for 100 seconds and it ran just fine after the
remote app was finished.

If that still leaves you in trouble - you might want to look into Screen
which is designed to run apps detached from the login shell so that
would
certainly be of use if needed. This is the command I use to run an app
detached - screen -D -m command.rb

John

15

On Jul 9, 2009, at 7:53 PM, Enling Li wrote:

Thanks.

Enling

OK, what about:

ssh.exec!(“sh -c ‘setsid /root/test.pl > /dev/null 2>&1’”)

or perhaps bash, /bin/sh, or /bin/bash in place of sh

Of course, I’m assuming that you are verifying that you can ssh
manually and run these commands yourself. (If not, get to a command
that works even after you log out manually.)

-Rob

16

Enling,

On Thu, Jul 9, 2009 at 8:06 PM, Enling Li [email protected]
wrote:

John,

The key is I don’t want to wait for the remote to finish. If I wait for
remote to complete, I don’t have problem.

Sorry I used the wrong wording - I meant that Machine A connected to
Machine
B using Net::SSH and ran a script that slept for 100 seconds. Machine A
then
disconnected without blocking and Machine B continued to execute the
script
that was sleeping away. Again make sure you are connecting because you
could
easily be not getting to the server at all - the block could just as
easily
be a connection block and not an execution block. And if you are
connecting
and still for some reason blocking - Screen is definitely the answer
because
that is exactly what is it designed for.

John

17

Enling Li wrote:

I have another quetion related to fire off a back ground shell process
on a remote Linux.

require "net/ssh"

ssh = Net::SSH.start( '10.0.77.87', 'toor',  :password=>'logapp')
ssh.exec!("/root/test.pl &")
ssh.close
puts "I want to be here immediately, but not"

The above code hangs also because test.pl contains a long sleep and do
nothing. Can someone offer me a help?

Thank you in advance.

Enling

I run long running remote tasks that return immediately with…

ssh.exec!(“nohup /root/test.pl >/tmp/test.log 2>&1 &”)

18

Andrew,

That is excellent. It resolved the issue.
Thank you very much.

Enling

Andrew K. wrote:

Enling Li wrote:

I have another quetion related to fire off a back ground shell process
on a remote Linux.

require "net/ssh"

ssh = Net::SSH.start( '10.0.77.87', 'toor',  :password=>'logapp')
ssh.exec!("/root/test.pl &")
ssh.close
puts "I want to be here immediately, but not"

The above code hangs also because test.pl contains a long sleep and do
nothing. Can someone offer me a help?

Thank you in advance.

Enling

I run long running remote tasks that return immediately with…

ssh.exec!(“nohup /root/test.pl >/tmp/test.log 2>&1 &”)

19

Rob,

That does not work either. I tried from shell befreo running the ruby
script remotely.

ssh.exec!("/bin/bash -c /usr/bin/setsid /usr/bin/perl /root/test.pl")
ssh.exec!("/bin/bash /usr/bin/setsid /usr/bin/perl /root/test.pl")
ssh.exec!("/bin/bash /usr/bin/setsid /root/test.pl")

They just don’t work from ruby Net::SSH

Thanks.

Enling
Rob B. wrote:

On Jul 9, 2009, at 7:53 PM, Enling Li wrote:

Thanks.

Enling

OK, what about:

ssh.exec!(“sh -c ‘setsid /root/test.pl > /dev/null 2>&1’”)

or perhaps bash, /bin/sh, or /bin/bash in place of sh

Of course, I’m assuming that you are verifying that you can ssh
manually and run these commands yourself. (If not, get to a command
that works even after you log out manually.)

-Rob