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Today I Learned

Run a program in the background on ubuntu

  1. Make it excuable: chmod +x
  2. Use no hang up: nohup /path/to/ &. nohup keep the program running even in one closes the terminal. python /path/to/ & also keeps it running in the terminal in background. But it terminates the program if one logs out. To redirect the output to another file, nohup > comp-range-de.out 2>&1& or nohup &> comp-range-de.out& for short.
  3. Check the process: ps ax | grep ps -e can list out all the running programs.

Source: How to run the Python program in the background in Ubuntu machine?

It is very important to understand the output of ps. Here is the man.

       Here are the different values that the s, stat and state output
       specifiers (header "STAT" or "S") will display to describe the state of
       a process.
       D    Uninterruptible sleep (usually IO)
       R    Running or runnable (on run queue)
       S    Interruptible sleep (waiting for an event to complete)
       T    Stopped, either by a job control signal or because it is being
       W    paging (not valid since the 2.6.xx kernel)
       X    dead (should never be seen)
       Z    Defunct ("zombie") process, terminated but not reaped by its

       For BSD formats and when the stat keyword is used, additional
       characters may be displayed:
       <    high-priority (not nice to other users)
       N    low-priority (nice to other users)
       L    has pages locked into memory (for real-time and custom IO)
       s    is a session leader
       l    is multi-threaded (using CLONE_THREAD, like NPTL pthreads do)
       +    is in the foreground process group

Meanwhile, another question is how to kill such a process.

[email protected]:~/abc/py$ ps -eaf | grep
xxx    12921 11369 99 17:05 pts/0    00:04:49 python
xxx    13040 11369  0 17:10 pts/0    00:00:00 grep --color=auto
[email protected]:~/abc/py$ kill 12921

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