Grayson Peddie's Website

Use $HOME, not /home/$USER in BASH scripts

Audience

This article is for experienced Linux users who are familar with environment variables such as $HOME and $USER. These are the Linux users who are familiar with the command line.

Problem and Solution

Here is an example not to use /home/$USER:

[gpeddie-games@epcotcenter ~]$ su - gpadmin
Password: 
mkdir: cannot create directory ‘/home/gpadmin’: Permission denied
touch: cannot touch '/home/gpadmin/Templates/Text file': No such file or directory
mkdir: cannot create directory ‘/home/gpadmin’: Permission denied
-bash: /home/gpadmin/.local/share/DaVinciResolve/configs/.version: No such file or directory
Welcome. All activities monitored at all times.
Unauthorized access is strictly prohibited.
gpadmin@epcotcenter 
  ~
$

And here's the script (/etc/profile) that illustrates an example:

# fix gnome missing 'New file' option
if [ ! -f /home/$USER/Templates/"Text file" ]
then
    mkdir -p /home/$USER/Templates
    touch /home/$USER/Templates/"Text file"
fi

# ...

# this is a hack to bypass the Davinci Resolve new install Welcome/Onboarding screen since it does not render properly and is not required.
if [ ! -f /home/$USER/.local/share/DaVinciResolve/configs/.version ];then
    mkdir -p /home/$USER/.local/share/DaVinciResolve/configs/
    echo "Onboarding.Version=10" > /home/$USER/.local/share/DaVinciResolve/configs/.version
fi

To fix this issue, simply replace all instances of /home/$USER with $HOME. I am familiar with a text editor called Vim. It's a program that runs inside a terminal, similar to the Command Prompt or PowerShell in Windows.

Before we proceed any further, let's create a backup copy of /etc/profile:

sudo cp /etc/profile /etc/profile.bak

If anything goes wrong, you now have a backup. You can simply use the cp (copy) command to restore from the backup. Now let's begin.

1. First, open the Terminal (Konsole in KDE).

2. As root (or with sudo privileges), type the following command:

   sudo vim /etc/profile

3. Type in the following command, starting with a colon:

   :%s/\/home\/$USER/$HOME/g

   The syntax for search and replace in Vim is as follows:

   :%s/search/replace/g

   Let's not concern ourselves with g at the end for now. Basically this command replaces "search" with the next text "replace." In other words, we want to replace /home/$USER with $HOME.

   Let's have a look at the script again:

   # fix gnome missing 'New file' option
   if [ ! -f $HOME/Templates/"Text file" ]
   then
       mkdir -p $HOME/Templates
       touch $HOME/Templates/"Text file"
   fi
   
   # ...
   
   # this is a hack to bypass the Davinci Resolve new install Welcome/Onboarding screen since it does not render properly and is not required.
   if [ ! -f $HOME/.local/share/DaVinciResolve/configs/.version ];then
       mkdir -p $HOME/.local/share/DaVinciResolve/configs/
       echo "Onboarding.Version=10" > $HOME/.local/share/DaVinciResolve/configs/.version
   fi

   So why would we want to replace /home/$USER with $HOME? That /home/$USER should still work!

   Let's look at the output again after we save the changes.

4. Save the changes to the /etc/profile file.

   :wq

   A : begins a command. w writes changes to the file and q quits Vim

   If you don't want to make changes to the file, then all you have to do is type :q! to exit without saving any changes.

As I mentioned, let's look at the output again when I log into my administrator account from a user account.

[gpeddie-games@epcotcenter ~]$ su - gpadmin
Password:
mkdir: cannot create directory ‘/home/gpadmin’: Permission denied
touch: cannot touch '/home/gpadmin/Templates/Text file': No such file or directory
mkdir: cannot create directory ‘/home/gpadmin’: Permission denied
-bash: /home/gpadmin/.local/share/DaVinciResolve/configs/.version: No such file or directory
Welcome. All activities monitored at all times.
Unauthorized access is strictly prohibited.
gpadmin@epcotcenter
  ~
$

Now, let's see the new output when I log back in as an administrator.

[gpeddie-games@epcotcenter ~]$ su - gpadmin
Password: 
Last login: Sat Mar 18 11:13:52 EDT 2023 on pts/0
Welcome. All activities monitored at all times.
Unauthorized access is strictly prohibited.
gpadmin@epcotcenter 
  ~
$

How Did That Work?

Let's see the output of $USER and $HOME.

gpadmin@epcotcenter 
  ~
$ echo $USER
gpadmin
gpadmin@epcotcenter 
  ~
$ echo $HOME
/home/graysonpeddie.lan/gpadmin
gpadmin@epcotcenter 
  ~
$

Scenario

You have an Active Directory server running in a Windows Server virtual machine. You installed Nobara so that you can do content creation and play games. You wanted to join your Linux desktop to a Windows Active Directory in your home network (or a homelab, if you want to call it). This is how you install the needed packages for Nobara 36 (that's what I am running) so that you can join your Linux desktop to the Windows domain:

sudo dnf install realmd sssd sssd-tools adcli oddjob oddjob-mkhomedi
sudo realm join yourlocaldomainname.lan -U youradminusername

Replace yourlocaldomainname.lan with your local domain name and do the same for youradminusername.

So when you log into your administrator account that's part of the Domain Administrators so that you can gain sudo privileges, you might be wondering why you are getting strange output. Here it is again.

[gpeddie-games@epcotcenter ~]$ su - gpadmin
Password:
mkdir: cannot create directory ‘/home/gpadmin’: Permission denied
touch: cannot touch '/home/gpadmin/Templates/Text file': No such file or directory
mkdir: cannot create directory ‘/home/gpadmin’: Permission denied
-bash: /home/gpadmin/.local/share/DaVinciResolve/configs/.version: No such file or directory
Welcome. All activities monitored at all times.
Unauthorized access is strictly prohibited.
gpadmin@epcotcenter
  ~
$

If you look at the /etc/profile script that Linux executes when you log into your Linux account, you will notice that the developer of Nobara assumed that your home directory is /home/gpadmin and not /home/graysonpeddie.lan/gpadmin.

This is how I configure the System Security Services Daemon (SSSD, for short) which allows Linux users to log into the Windows domain from the Linux desktop. Please note that only root can read /etc/sssd/sssd.conf.

[sssd]
domains = graysonpeddie.lan
config_file_version = 2
services = nss, pam

[domain/graysonpeddie.lan]
default_shell = /bin/bash
krb5_store_password_if_offline = True
cache_credentials = True
krb5_realm = GRAYSONPEDDIE.LAN
realmd_tags = manages-system joined-with-adcli
id_provider = ad
fallback_homedir = /home/%d/%u
ad_domain = graysonpeddie.lan
use_fully_qualified_names = False
ldap_id_mapping = True
access_provider = ad
ad_gpo_access_control = permissive

Let's ignore the entire file and focus in the fallback_homedir. The %d is for the domain name that I logged into and the %u is for the username. In my case, since I logged into my Linux desktop as gpeddie-games (that's my account designed only for gaming), my full path is /home/graysonpeddie.lan/gpeddie-games and not /home/gpeddie-games.

I have all my users (only me) in a separate home folder in order to prevent any kind of conflict with local user accounts, but then I still append my local admin account with -local in order to prevent any kind of conflicts in my Linux desktop machine.

Conclusion

This is why you should never assume that all users will be in the parent folder of the home directory. The only use-case for using a $USER environment variable is if you need to get the name of the user. Referring back to the /etc/profile script, here is an example:

if [ -x /usr/bin/id ]; then
    if [ -z "$EUID" ]; then
        # ksh workaround
        EUID=`/usr/bin/id -u`
        UID=`/usr/bin/id -ru`
    fi
    USER="`/usr/bin/id -un`"
    LOGNAME=$USER
    MAIL="/var/spool/mail/$USER"
fi

After reading the script, I'm not sure why $LOGNAME and $MAIL exists in that profile. Plus, I checked to see if I can get the name of the $USER in my VPS server and there is already a $USER in the list of environment variables even though it's not listed in /etc/profile. Strange...

Anyway, I hope I can be of help and use to the people within the Linux community and I am hoping that people can learn from mistakes when getting the user's current home directory.

Article published: 2023-03-18 15:37

Categories: The World of Computers, Computers, Information Technology, Scripting and Programming,