CODEWITHSUNDEEP
linuxprocesscrontaskschedule
Razvan
Razvan

Reputation: 10093

Linux schedule task when another is done

I have a task/process currently running. I would like to schedule another task to start when the first one finished.

How can I do that in linux ?

(I can't stop the first one, and create a script to start one task after the other)

Upvotes: 0

Views: 445

Answers (3)

n0dus
n0dus

Reputation: 151

If you want to execute your second task every time the first one is not running, the answer suggested by tink works:

watch -n 1 'pgrep <name of task1> || <task2>'

However, I wanted to run task2 only once as soon as task1 was finished. So I used:

watch -n 1 -g 'pgrep <name of task1>'; <task2>

Upvotes: 0

dmckee --- ex-moderator kitten
dmckee --- ex-moderator kitten

Reputation: 101181

You want wait.

Either the system call in section 2 of the manual, one of it's varients like waitpid or the shell builtin which is designed explicitly for this purpose.

The shell builtin is a little more natural because both processes are childred of the sell, so you write a script like:

#!/bin/sh
command1 arguments &
wait 
command2 args

To use the system calls you will have to write a program that forks, launches the first command in the child then waits before execing the second program.

The manpage for wait (2) says:

wait() and waitpid()
The wait() system call suspends execution of the current process until one of its children terminates. The call wait(&status) is equivalent to:

      waitpid(-1, &status, 0);

The waitpid() system call suspends execution of the current process until a child specified by pid argument has changed state.

Upvotes: 0

tink
tink

Reputation: 15213

Somewhat meager spec, but something along the line of 

watch -n 1 'pgrep task1 || task2'

might do the job.

Upvotes: 2

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