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nohup

nohup (short for no hang up) is used to run a command in the background without being affected by terminal closures.

By default (when not redirected), it outputs a file named nohup.out to the current directory. If the nohup.out file in the current directory is not writable, the output will be redirected to the $HOME/nohup.out file. If no file can be created or opened for appending, the specified command in the "command" parameter will not be executable. If the standard error is a terminal, all output from the specified command that is written to the standard error will be redirected to the same file descriptor as the standard output.

Syntax​

nohup COMMAND [ARG]... [　& ]
nohup OPTION

COMMAND: The command to be executed.

ARG: Any additional parameters that can be used to specify an output file.

&: Allows the command to be executed in the background, even after the terminal is closed.

Option explanation​

  • --help: Display help information.
  • --version: Display version information.

Common commands​

The following command executes the runoob.sh script in the background under the root directory:

nohup /root/runoob.sh &

To stop the execution, you need to use the following command to find the PID of the running script using nohup, and then use the kill command to delete it:

ps -aux | grep "runoob.sh"

The following command executes the runoob.sh script in the background under the root directory and redirects the input to the runoob.log file:

nohup /root/runoob.sh > runoob.log 2>&1 &

Explanation of 2>&1:

Redirect standard error 2 to standard output &1, and then redirect standard output &1 to the runoob.log file.

  • 0 - stdin (standard input)
  • 1 - stdout (standard output)
  • 2 - stderr (standard error output)