Configuration files

• Configuration files - define environment for startup, global environment for programs, etc.

• Windows:
  • MSConfig
  • Registry

• Understanding Linux configuration files (IBM)

• man bash discusses bash config files.

Hierarchy

Often instructions can be put in multiple places and you may not notice the difference, depending on how you work.

Hierarchy is:

1. OS system-wide files (not to be modified, rebuilt in OS upgrades)
2. Local install system-wide files (modified by local sysadmins for all users)
3. Personal config files (in home dir, apply to one user, edited by one user)

Personal config files

These are run in login shell (e.g. ssh) or login to GUI:

file	type	notes
$HOME/.profile	global	Change PATH in here.
$HOME/.bash_profile	bash specific	See below.

This is run in non-login shell (e.g. new terminal in GUI):

file	type	notes
$HOME/.bashrc	bash specific	Set aliases in here. Change prompt in here

.bashrc may or may not also be run by login shell. It depends on setup.

.bash_profile

• ssh will only run .bash_profile not .bashrc
• GUI terminal will only run .bashrc not .bash_profile

Solution for those setups:
Get .bash_profile to run the commands in .bashrc (and maybe run the commands in .profile too).
Put the following in .bash_profile:

  
source $HOME/.profile
source $HOME/.bashrc

DCU Linux setup can change from year to year, so experiment with:

• Putting commands in one of the 3 files.
• Getting one of the 3 files to call another one.
• Seeing what happens on ssh.
• Seeing what happens on GUI terminal.

How to change the PATH

• How to change the PATH

How to set up aliases

Put lines like this in .bashrc:

alias h="history"
alias cds="cd /users/tutors/mhumphrysdculab/share"

This text substitution at the command-line is more efficient than starting up a program to do the job.
In fact, in the case of the change directory alias, a program won't work since a program can't change the directory of the parent process that called it.

How to change the prompt

export PS1='[student] \w> '

• bash prompt format
• Useful switches include: \h \H \u \w \W

PROMPT_COMMAND

• "set" shows this variable:

   PROMPT_COMMAND=_prompt_command 

  pointing to this function:

   _prompt_command () { .... } 

• This means that every time the shell prompts me, it calls function _prompt_command
• If you look at the code for the function:

   type _prompt_command 

  you see that it resets the prompt every time.
• So to set my own prompt, we need to redefine PROMPT_COMMAND or _prompt_command

Put something like the following into .bashrc:

_prompt_command () 
{ 
    local exit_status="$?";
    export PS1='[student] \w> '
    return $exit_status
}

Is customisation useful?

1. Make the prompt on the production server something dramatic like:

    [WARNING: PRODUCTION SERVER] > 

2. Make the production ssh session background colour red, as a warning of where you are.
3. Never rm directories. Just rename them. You can delete them later, when everything is working. You can delete them a month later. What's the hurry?
4. To continue that idea, obviously your normal backups should work, but if you just rename directory, your backup is sorted already!
5. Never type rm dir or other dangerous commands raw. Put them in scripts. The script will do the error checking of host, database, directory. Only run the scripts.
6. e.g. Don't update your website by copying files to production with cp, mv, rm. One day you will type the sequence wrong, or on the wrong server, or in the wrong dir. Put it all in a script.