red terminal font when root

Question

I'd like to make happen in RHEL/CentOS 7.6

anytime you do su and become root I want the terminal prompt color in that terminal to become red for the duration of that su session. Type exit to go back to being whoever you were and I want the prompt color to go back to whatever the previous color was (black).

Same for an SSH window using putty logged in over the network: initially ssh in as user and have a default white shell prompt; do an su to root and I want the prompt to become red; type exit I want the prompt to go back to white.

so far i did this but it's not working 100%, the color stays red after you type exit and leave the su session and go back to being user.

/etc/profile.d/red_root_prompt.sh

if [ $UID -eq 0 ]; then
   PS1="\e[31m[\u@\h \W]# "
else
   PS1="[\u@\h \W]# "

Is there a way to make things happen the way I want? I only want it for bash shells.

Answer 1

You can either add this to /etc/bash.bashrc or edit /etc/profile/

force_color_prompt=yes

    if [ "$LOGNAME" = root ] || [ "`id -u`" -eq 0 ] ; then
        PS1='\[\033[01;31m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[01;34m\]#\033[00m\] '
    else
        PS1='\u@\h:\w\$ '
    fi

and you will get a prompt that looks like this. If you use a white background, change the last part after # to \033[01;30m\] so you can see the command text. I included that as a second example for reference .

also if you add the following to \etc\bash.bashrc or ~/.bashrc:

export col_white='\033[00m'
export col_black='\033[01;30m'

export col_red='\033[01;31m'
export col_green='\033[01;32m'
export col_yel='\033[01;33m'
export col_blue='\033[01;34m'

You will be able to do :

$ echo -e $col_red red $col_blue blue $col_yel yellow $col_green green
 red blue yellow green

with the output looking like this:

---

EDIT: For some reason using variable expansion for the prompt breaks the carriage return (it locks it to the length of the variable, i.e. pushes it forward by n-many spaces corresponding to echo $col_blue,echo $col_white, and I have not found a good solution for this as of this moment, but using proper bracketing without variable substitution as above solves this issue.

if [ "$LOGNAME" = root ] || [ "`id -u`" -eq 0 ] ; then
    PS1="$col_red\u@\h:$col_purple\w$col_green# $col_white"
else
    PS1="\u@\h:$col_blue\w$col_yel\$ $col_white "
fi

Answer 2

for RHEL/CentOS 7.x I thought customized stuff like this was supposed to be under /etc/profile.d or in something like /etc/bashrc.local. That way any customization is preserved after updates when something like /etc/bashrc is might be changed or replaced.

for RHEL/Centos 7, I thought one should only need to put a file under /etc/profile.d/ having the corresponding suffixes for the shells they are for,

so I did /etc/profile.d/redrootprompt.sh having only

if [ "$LOGNAME" = root ] || [ "`id -u`" -eq 0 ] ; then

    PS1='[\[\033[01;31m\]\u@\h\[\033[00m\]:\w] : '

else
    PS1='[\u@\h \w] : '
fi

and this works great giving the look i wanted

it also works in a putty window which has black background and white text, but goes red after su to root and back to white on exit.