Home / ubuntu / Questions / 102544
Accepted
Pomario
Asked: 2012-02-09 06:46:04 +0800 CST

Help understanding command line

  • 772

We are starting our Jenkins CI with the following bash command that I would like understand. Could someone explain what is doing (the only bit I get is "java -jar jenkins.war"). Thanks! 

nohup java -jar jenkins.war > $HOME/jenkins.log 2>&1 < /dev/null &
bash

2 Answers

  1. Best Answer

    The nohup means it will continue to run when you exit the shell.

    The > means redirect the standard output to a file

    The file it is being redirected to is $HOME/jenkins.log. You can find the value of $HOME by running echo $HOME

    2>&1 means redirect standard errors to standard output, so in this example will also go into $HOME/jenkins.log.

    The < /dev/null means read data in from /dev/null. So if the script is expecting input it will read that instead of waiting for user input.

    And the & means run as a background task, and return you to the command line.

    If you want more detail, ask in the comments.

    • 13 
  2. nohup

    detaches the following command from the current terminal session, which prevents the process from being closed on terminal exit.

    java

    then runs the java VM with the options

    -jar jenkins.war

    which tells java to run the main class from the jar-archive jenkins.war

    >

    forwards the standard output (what usually appears in the terminal) into the given file, in this case into $HOME/jenkins.log 

    2>&1

    means that the optput of the error channel is connected to the output of the standard output channel.

    < /dev/null

    sends "nothing" as input stream to the java command.

    Finally & forces the task into backgrount such that the control returns to the prompt.

    • 3