Can LIB paths be set in rc.local? Does it execute its commands after we login?

Question

1. Does rc.local execute its commands after we login?

2. Since rc.local executes its commands after the multi user runlevel completes, does it also mean that we can/should set LIB paths in it instead of setting them in .bashrc?

Answer 1

The script /etc/rc.local is invoked at the end of normal system startup. It is executed as root and has no relationship whatsoever with a user logging in. Any environment variable assignments in /etc/rc.local are available only to the processes started by /etc/rc.local; they are not available to processes started in a user's login session.

/etc/rc.local has no direct effect on a user's login session. It is normally used to mount some disks, start some services and other such tasks. It cannot be used to set up a user's environment.

First, let's look into /etc/rc.local itself:

$ cat /etc/rc.local
#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.

exit 0

rc.local is an old feature of Unix-like system, older even than the System V initialization system (the one which used the directories /etc/rc[0-6S].d). Recent Ubuntu systems used systemd to control initialization; /etc/rc.local is invoked by the systemd unit rc-local.service:

$ sudo systemctl status rc-local
● rc-local.service - /etc/rc.local Compatibility
   Loaded: loaded (/lib/systemd/system/rc-local.service; static; vendor preset: enabled)
   Drop-In: /lib/systemd/system/rc-local.service.d
       └─debian.conf
   Active: active (exited) since Fri 2017-04-28 17:44:18 EEST; 2 days ago

Apr 28 17:44:18 factissa systemd[1]: Starting /etc/rc.local Compatibility...
Apr 28 17:44:18 factissa systemd[1]: Started /etc/rc.local Compatibility.

The unit is automatically generated at boot if the file /etc/rc.local exists, and is set by default to be invoked after achieving network.target; on Debian and derivatives such as Ubuntu, a drop-in configuration file modifies this so that the unit is run after network-online.target.

This is not exactly the same as the traditional place of /etc/rc.local at the end of a multi-user runlevel initialization, but it's similar enough so that in most cases no adjustments need to be done. (Look into those files, they are text and quite understandable; to make modifications please read the systemd documentation first.)