SYS‐255 Linux File Permissions - aljimenez28/champlain GitHub Wiki

Objective

Gain hands-on experience creating Linux users, groups, and directories, then applying file and directory permissions to control access.

Key Notes

ls -ld /accounting/ displays the long listing of the directory itself, showing owner, group, and their permissions.
>> is the append operator, which adds text to the end of a file without overwriting existing content.

Steps Performed

Elevate to root
```
sudo -i
```

Opens a root shell for administrative commands.

Create users
```
useradd bob
passwd bob
useradd alice
useradd charlie
```
Adds three new users and sets a password for Bob.
Inspect home directories and user database
```
ls /home
ls -ld /home
ls -ld /home/alice
ls -l /etc/passwd
```
Lists user home directories and checks /etc/passwd to confirm user creation.
Add users to the accounting group
```
usermod -aG accounting alice
usermod -aG accounting bob
```
Appends Alice and Bob to the accounting group without removing existing group memberships.
Create the accounting directory
```
mkdir /accounting
```
Makes the shared directory that will hold accounting files.
Switch to Alice to create a test file
```
su - alice
echo alice > alice.txt
cat alice.txt
ls -l
```
Logs in as Alice, creates a file, displays its contents, and lists details.
Verify directory ownership and group settings
```
ls -ld /accounting/
```
Shows current permissions for /accounting.
Change group ownership of the directory
```
chgrp accounting /accounting
```
Assigns the accounting group to the directory so group members can manage it.
Create a file inside accounting
```
echo "alice file" > /accounting/alicefile.txt
```
Creates a file owned by Alice inside the shared directory.
Secure the directory
```
chmod o-rwx /accounting/
```
Removes all permissions for others, restricting access to only the owner and accounting group.
Confirm current user and groups
```
id
```
Displays user identity and group memberships for verification.

Summary

This lab demonstrated how to:

Create and manage users and groups.
Control directory and file access using chgrp and chmod.
Verify permissions with ls -l and id. By carefully setting group ownership and restricting “others,” only the intended team members can read or modify sensitive files.