I know that execute a command and add & to the end would create a job and make the command execute in background.
Now I want to create a job in a bash shell. I tried
#!/bin/bash
my-job &
# some other tasks
Then I executed jobs, but I got no output. However, ps aux does show my-job is running in the background.
I want to create a job inside a script, because in some cases I want to bring the job into foreground.
jobs are usually an interactive shell concept, as there is usually a controlling terminal involved.
A shell script is executed in a non-interactive, non-login session of shell, hence no job control by default.
You can force job control inside a script, by setting:
set -m
inside the script.
From help set:
-m Job control is enabled.
Related
I need to run rsync in background through shell script but once it has started, I need to monitor the status of that jobs through shell.
jobs command return empty when its run in shell after the script exits. ps -ef | grep rsync shows that the rsync is still running.
I can check the status through script but I need to run the script multiple times so it uses a different ip.txt file to push. So I can't have the script running to check jobs status.
Here is the script:
for i in `cat $ip.txt`; do
rsync -avzh $directory/ user#"$i":/cygdrive/c/test/$directory 2>&1 > /dev/null &
done
jobs; #shows the jobs status while in the shell script.
exit 1
Output of jobs command is empty after the shell script exits:
root#host001:~# jobs
root#host001:~#
What could be the reason and how could I get the status of jobs while the rsync is running in background? I can't find an article online related to this.
Since your shell (the one from which you execute jobs) did not start rsync, it doesn't know anything about it. There are different approaches to fixing that, but it boils down to starting the background process from your shell. For example, you can start the script you have using the source BASH command instead of executing it in a separate process. Of course, you'd have to remove the exit 1 at the end, because that exits your shell otherwise.
So, I have started studying UNIX systems about a month ago and now I have a basic question about job control
How can I create a job, that will contain several processes, using only default bash commands?
jobs are usually an interactive shell concept, as there is usually a controlling terminal involved.
A shell script is executed in a non-interactive, non-login session of shell, hence no job control by default.
You can force job control inside a script, by setting:
set -m
inside the script.
From help set:
-m Job control is enabled.
echo | ping google.com &
Was fine example, because both of these processes work independently and only require pipe symbol (|) to work in sync in the background
I found that some people run a program in shell like this
exe > the.log 2>&1 &!
I understand the first part, it redirects stderr to stdout also "&" means runs the program in background, but I don't know what does "&!" mean, what does the exclamation mark mean?
Within zsh the command &! is a shortcut for disown, i.e. the program won't get killed upon exiting the invoking shell.
See man zshbuiltins
disown [ job ... ]
job ... &|
job ... &!
Remove the specified jobs from the job table; the shell will no longer report their status, and will not complain if you try to exit an interactive shell with them running or stopped. If no job is specified, disown the current job. If the jobs are currently stopped and the AUTO_CONTINUE option is not set, a warning is printed containing information about how to make them running after they have been disowned. If one of the latter two forms is used, the jobs will automatically be made running, independent of the setting of the AUTO_CONTINUE option.
I am on shared hosting and I'm trying to schedule cronjob to run every now and then. Via cPanel I scheduled to execute my script but even though that according to my host support the cronjob runs, the script doesn't seem as doing anything. The cron job command I set via cPanel is:
/bin/sh /home1/myusername/public_html/somefolder/cronjob2.sh
and the cronjob2.sh
#!/bin/bash
/home1/myusername/public_html/somefolder/node_modules/forever/bin/forever stop 0
when via SSH I execute:
/home1/myusername/public_html/somefolder/cronjob2.sh
it stops forever process as needed. From cronjob doesn't do anything.
How can I get this working?
EDIT:
So I've tried:
/bin/sh /home1/username/public_html/somefolder/cronjob2.sh >> /tmp/mylog 2>&1
and mylog entries say:
/usr/bin/env: node: No such file or directory
It seems that forever needs to run node and this cannot be found. How would I possibly fix this?
EDIT2:
Accepted answer at superuser.com. Thank you all for help
https://superuser.com/questions/763261/simple-script-run-via-cronjob-doesnt-work-but-works-from-shell/763288#763288
For cron job lines in a crontab it's not required to specify kind of shell or e.g. of perl.
It's enough, that your script contains
shebang
line.
Therefore you should remove /bin/sh from your cron job line.
Another aspect, that might cause a different behavior of your script by interactive start and by cron daemon start is possible different environment, first of all the PATH variable. Therefore check, if you script is able to be executed in very restricted environment, that is provided by cron daemon. You can determine your cron job environment experimentally by start of temporary cron job, that executes "env" command and writes its output to a file.
Once more aspect: Have you redirected STDOUT and STDERR of the cron job to a log file and read its content to analyze the issue? You can do it as follows:
your_cron_job >/tmp/any_name.log 2>&1
According to what you wrote, when you run your script via SSH, you are using bash, because this line is the first of your script:
#!/bin/bash
However, in the crontab, you are forcing the use of sh instead of bash. Are you sure your script is fully compatible with sh? Otherwise, simply replace /bin/sh with /bin/bash in your cron command and test again.
I am using bash on Ubuntu. I would like to have a shell script open a program and continue on to the next line of the shell script, even though the program has not terminated.
Adding an & to a command places it in background.
example:
/path/to/foo
/path/to/bar # not executed untill foo is done
/path/to/foo & # in background
/path/to/bar & # executes as soon as foo is started
Read more about job-control here and here
Use something like this (my-long-running-process &) . This will launch your script as a separate process in the background.
You must run the process in the background, but you must enable job-control first. Otherwise, you cannot kill or bring the process to foreground if desired.
To enable job-control, execute:
set -m
To run some task in the background, execute:
task &
To manipulate the background task, use the jobspec syntax (%[n]). For example, to kill the last launched process, execute:
kill %
Note that enabling job-control is required only if you're actually running a script (as stated in the question). If running interactively, job-control is already enabled by default.
The manpage for bash has much more information in the JOB CONTROL section.
http://ubuntuforums.org/showthread.php?t=1657602
It looks like all you have to do is add a & at the end of the line.