What is the difference between /etc/rc.local and ~/.bashrc?

Question

This is a linux related problem. I have searched around but did not get a good explanation.

It seems to me that both file configure the setup when I log in, but is there any difference? I notice that there seems to be "some rule" in deciding what should go into two different files. For example, if I need to add a specific search path to $PATH, I should do it in ~/.bashrc. But if I decide to change some system setting, like

/sys/class/backlight

or

/sys/devices/cpu/cpu#/online

then I have to do this in /etc/rc.local, otherwise it will not work.

Is it because these configurations can not differ between users?

Thanks.

Answer 1

This question was asked by me a month ago, though later I realized that stack overflow is not the best site for this Linux question. Thanks for people who answered this question earlier, but I would like to add some more explanation here.

Basically there are (at least) three stages where a user may change system environment in Linux:

1. when the system boots ; This stage is most appropriate if we fancy permanent system setting , and should be made via /etc/... . For example, in my original question, the backlight , as well as on-line/off-line management of some CPUs can be set in this way, and /etc/rc.local is the right shell script I should edit. By "permanent", it means that this update will affect all users using the system.
2. when a user logs in ; This stage is most appropriate if a user only wants to change his personal Linux environment. Therefore, files under ~/ (or HOME ) should be the right place to look for. For example, ~/.profile (historically referred to as ./bash_profile or ~/bash_login ) is a shell script run at login time. ~/pam_environment is not a shell script, but useful for setting environmental variables (see Ubunte-official-wiki-environmental_variables for more information).
3. when a user starts a bash shell ; This stage is more restricted, as it only has effects inside a bash shell (as well as its child processes), hence does not affect GUI environment. So if a user is doing most of his job from a shell, then this is an appropriate stage to go for. The shell script related to this stage is ~/.bashrc . For example, environmental variables PATH can be changed here.

Hopefully this summary is more intuitive than technical.

Answer 2

The difference is in when they are run and who they're running as when run ie rc.local is run on a change of run level and it runs as root. bashrc is bash specific and run on a non login shell as a particular user.

You can find a good explanation of rc.local here

The script /etc/rc.local is for use by the system administrator. It is traditionally executed after all the normal system services are started, at the end of the process of switching to a multiuser runlevel. You might use it to start a custom service, for example a server that's installed in /usr/local. Most installations don't need /etc/rc.local, it's provided for the minority of cases where it's needed.

and you can find what you need about bashrc

man bash

When an interactive shell that is not a login shell is started, bash reads and executes commands from ~/.bashrc, if that file exists. This may be inhibited by using the --norc option. The --rcfile file option will force bash to read and execute commands from file instead of ~/.bashrc.

There's more info on bashrc in this question...

https://superuser.com/questions/49289/what-is-the-bashrc-file

Answer 3

.bashrc runs for each bash session started (ie every time you open a shell). It sounds as though you're talking of .bashrc as if it were .bash_profile which is run once per login.

Depending on what kind of setup you're running the rc.local is a legacy construct but, traditionally it was run on the last run level during start up. You can see this link for other related posts talking about rc.local .

If you're on a system running systemd this is usually included by default in the systemd package systemd-backlight.service .