Advanced File and User Management in Linux

In Linux systems, file management and user permissions are critical for system security and organization.

In this guide, we’ll explore advanced file operations, user management, and authorization techniques.

1️⃣ Advanced File Management

🔹 List files and directories

ls -lah

🔹 Shows detailed listing including hidden files.

🔹 Find large files

find /var/log -type f -size +100M

🔹 Lists files larger than 100MB in the specified directory.

🔹 Search files containing specific keywords

grep -rl 'error' /var/log

🔹 Shows log files that contain the word 'error'.

🔹 Monitor file contents in real time

tail -f /var/log/syslog

🔹 Follows live updates to the system log.

🔹 Compress directory into archive

tar -czvf backup.tar.gz /home/user/

🔹 Compresses the specified folder into an archive file.

2️⃣ Advanced User Management

🔹 Add a new user

sudo useradd -m -s /bin/bash new_user

🔹 Creates user with home directory and shell.

🔹 Set user password

sudo passwd new_user

🔹 Delete user

sudo userdel -r new_user

🔹 Removes user and home directory.

🔹 Create group and add user

sudo groupadd developers
sudo usermod -aG developers new_user

🔹 Creates a group and adds user to it.

🔹 List user groups

groups new_user

🔹 Grant sudo/root privileges

sudo usermod -aG sudo new_user

🔹 Adds user to sudoers group.

3️⃣ File and Directory Permissions

🔹 View file permissions

ls -l file.txt

🔹 Sample output:

-rw-r--r-- 1 user user 1234 Mar 1 12:34 file.txt

Explanation:

• r (read), w (write), x (execute)
• -rw-r--r-- → Owner (rw-), Group (r--), Others (r--)

🔹 Change file permissions

chmod 644 file.txt  # Owner can write, others can read only
chmod 755 script.sh  # Everyone can execute, only owner can write

🔹 Change file ownership

sudo chown new_user:new_group file.txt

🔹 Changes file owner and group.

4️⃣ Advanced Authorization and Access Control

🔹 Grant specific access to a user

setfacl -m u:new_user:rwx secret_file.txt

🔹 Assigns custom permissions to a specific user.

🔹 View file ACL permissions

getfacl secret_file.txt

🔹 Displays advanced permissions for the file.