CODEWITHSUNDEEP
linuxbashshellubuntuasynchronous
LorenVS
LorenVS

Reputation: 12857

Asynchronous shell commands

I'm trying to use a shell script to start a command. I don't care if/when/how/why it finishes. I want the process to start and run, but I want to be able to get back to my shell immediately...

Upvotes: 134

Views: 142878

Answers (5)

mluthra
mluthra

Reputation: 211

screen -m -d $command$ starts the command in a detached session. You can use screen -r to attach to the started session. It is a wonderful tool, extremely useful also for remote sessions. Read more at man screen.

Upvotes: 8

Ani Menon
Ani Menon

Reputation: 28209

Everyone just forgot disown. So here is a summary:

  • & puts the job in the background.

    • Makes it block on attempting to read input, and
    • Makes the shell not wait for its completion.

  • disown removes the process from the shell's job control, but it still leaves it connected to the terminal.

    • One of the results is that the shell won't send it a SIGHUP(If the shell receives a SIGHUP, it also sends a SIGHUP to the process, which normally causes the process to terminate).
    • And obviously, it can only be applied to background jobs(because you cannot enter it when a foreground job is running).

  • nohup disconnects the process from the terminal, redirects its output to nohup.out and shields it from SIGHUP.

    • The process won't receive any sent SIGHUP.
    • Its completely independent from job control and could in principle be used also for foreground jobs(although that's not very useful).
    • Usually used with &(as a background job).

Upvotes: 100

Steve B.
Steve B.

Reputation: 57284

nohup cmd

doesn't hangup when you close the terminal. output by default goes to nohup.out

You can combine this with backgrounding, 

nohup cmd &

and get rid of the output, 

nohup cmd > /dev/null 2>&1 &

you can also disown a command. type cmd, Ctrl-Z, bg, disown

Upvotes: 58

pajton
pajton

Reputation: 16226

Alternatively, after you got the program running, you can hit Ctrl-Z which stops your program and then type

bg

which puts your last stopped program in the background. (Useful if your started something without '&' and still want it in the backgroung without restarting it)

Upvotes: 29

Carl Norum
Carl Norum

Reputation: 224884

You can just run the script in the background:

$ myscript &

Note that this is different from putting the & inside your script, which probably won't do what you want.

Upvotes: 146

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