4

From what I understanding, a daemon is a background process, but daemon requires unique config file to set the environment variable.

E.g. Hadoop daemon require hadoop-env.sh to set environment variable JAVA_HOME, you can't simply get the variable from ~/.bashrc.

The reason is because of daemon as a background process means it's non-interactive, while ~/.bashrc is means to used only from interactive session, to prevent alias cp='cp -i' case.

And the latest ~/.bashrc has the safe guard on top of the file do not allow non-interactive caller, i.e. without -i option will return early:

# ~/.bashrc: executed by bash(1) for non-login shells.
# see /usr/share/doc/bash/examples/startup-files (in the package bash-doc)
# for examples
# If not running interactively, don't do anything
case $- in
    *i*) ;;
      *) return;;
esac

It make me wonder why bashrc don't divide the config files to 3 groups, such as:

  • ~/.bashrc_interactive

  • ~/.bashrc_non_interactive

  • ~/.bashrc_global #(both interactive and non interactive)

So user can simply set JAVA_HOME in ~/.bashrc_non_interactive or ~/.bashrc_global, and no need to add this environment variable in each daemon file, over and over again.

Is there any reason or restriction of why bashrc not support non-interactive on that way or any other way ? OR am I misunderstanding some concepts ?

2
  • 1
    The concepts of foreground and background refer to processes that are part of terminal login sessions, and do not strictly speaking apply to dæmons, one of whose characteristics is that they are not part of terminal login sessions. Dæmons generally aren't connected to some random unprivileged user's '.rc' files in that user's home directory. And service managers usually provide systematic ways of setting environment variables to be inherited by the dæmons that they manage. Environment directories in daemontools-family systems, for example; or Environment= settings in systemd units.
    – JdeBP
    Mar 9, 2018 at 21:05
  • 1
    For more on Java and dæmons and environment variables, see unix.stackexchange.com/questions/320314 , unix.stackexchange.com/questions/418986 , unix.stackexchange.com/questions/322698 , and of course the systemd House of Horror. (-:
    – JdeBP
    Mar 9, 2018 at 21:17

2 Answers 2

3

The conception function of ~/.bashrc file is to initiate correctly any shell which is:

  • not the login shell,
  • an interactive shell.

Clearly the function of this shell script is to initiate environment which has to change at every level of shell, for example PS1.

It is not suited to define a session or a daemon environment.

There are other shell scripts which are dedicated for such an use.

For interactive sessions, bash will search for startup files in this order:

  • /etc/profile
  • ~/.bash_profile
  • ~/.bash_login
  • ~/.profile

For non interactive sessions, for example to start a daemon, bash is not using any of the above files but is taking into account the dedicated variable BASH_ENV (see Kusalananda answer).

2

You already have the opportunity to set BASH_ENV to the pathname of a file that non-interactive shell script parse before running.

This allows you to do, in a crontab for example

@hourly BASH_ENV="$HOME/.bashrc_non_interactive" "$HOME/bin/mybashscript"

or even

BASH_ENV="$HOME/.bashrc_non_interactive"

@hourly "$HOME/bin/mybashscript"
@daily  "$HOME/bin/myotherbashscript"

$BASH_ENV is usually empty, but there's nothing stopping you from setting it globally on your server, pointing it to a file under /etc that does

if [ -f "$HOME/.bashrc_non_interactive" ]; then
    . "$HOME/.bashrc_non_interactive"
fi

However, if a script needs specific variables set, such as JAVA_HOME etc., then it may be a better idea to set BASH_ENV explicitly on a script by script basis, or to explicitly source the relevant file from within the script itself, or to just set the variables in the script. Collecting all the things any non-interactive shell may want to use in a single file may slow down scripts and will potentially also pollute the environment of scripts with things they do not need.

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