Linux服务器：如何使用nohup确保作业正常运行？

Question

What I know and what I've tried: I have a script in R (called GAM.R) that I want to run in the background that outputs .rdata, .pdf, and .jpg files. Running this from the command line is relatively simple:

$ Rscript GAM.R

However, this code takes a very long time to run so I would love to send it to the background and let it work even after I have logged out and turned the computer off. I understand this is pretty easy, as well, and my code would look like this:

$ nohup Rscript GAM.R >/dev/null 2>&1 &

I used this to see if it was working:

$ fg
nohup Rscript GAM.R > /dev/null 2>&1

The problem: I don't know how to check if the code is working (is there a way I can see its progress?) and I don't know where the outputs are going. I can see the progress and output with the first code so I must not be too far off. It doesn't seem that the second code's outputs are going where the first code's outputs went.

Answer 1

Your command line is diverting all output to /dev/null aka, The Bit Bucket.

Consider diverting it to a temporary file:

   $ nohup Rscript GAM.R >/tmp/GAM.R.output 2>&1 &

Then you can tail /tmp/GAM.R.output to see the results, it will show the last 10 lines of the file by default. You can use tail -f to show the end of the file, plus new output in real time.

Note, the /tmp/ filesystem is not guaranteed to exist between reboots. You can put the file somewhere else (like ~/GAM.R.output if you need to be sure.

Note, however, that if you turn your computer off, then all processing gets aborted. For this to work your machine must continue to run and not go to sleep, or shutdown.

Answer 2

What you are doing is that with the > you are redirecting the output of your script to /dev/null and by doing 2>&1 you are redirecting the error output to the same place. Finally nohup executes your process and detach it from the current terminal.

So to sum up what you are doing is creating a process and redirecting its output and error output to a file called null that is stored under /dev .

To answer your question I suggest you redirect your outputs to a folder that you can access as normal user and not super user. Then to make sure that everything is ok you can print this file.

For example you can do :

nohup Rscript GAM.R >/home/username/documents/output_file 2>&1 &

and then to see the file from a terminal you can do:

cat /home/username/documents/output_file

Lastly I don't think that your program will keep on running if your turn off your pc and I don't think there is a way to do that.

Answer 3

If you want to run your program in the background and access the output of the program you can easily do that by writing

exec 3< <(Rscript GAM.R)

And then when you wish to check the output of the program run

cat <&3 # or you can use 'cat /dev/fd/3'

Answer 4

Excellent! Thanks everyone for your helpful answers, particularly @Greg Tarsa. Ultimately I needed to use:

$ nohup Rscript GAM.R >/usr/emily/gams/2017_03_14 2>&1 & 

The above is used to run the script and save the screen output to emily/gams (called "2017_03_14", a file to be made by the command, not a folder as I had origionally thought). This also outputs my .rdata, .pdf, and .jpg output filesf from the script to usr/emily.

Then I can see progress and running programs using:

$ tail -f 2017_03_14 #Shows the last 10 lines of the program's progress
$ ps #shows your running projects
$ ps -fu emily #see running projects regardless of session, where username==emily

In the spirit of completeness, I can also note here that to cancel a process, you can use:

$ kill -HUP processid #https://kb.iu.edu/d/adqw