Infrastructure Knowledge Base
⬅ Back to Infrastructure KB
🔐 Linux User & Permission Management
This section covers user, group, and permission management used in Linux system administration.
👤 User Management
| Command |
Usage & Options |
useradd testuser |
Create a new user |
passwd testuser |
Set password for user |
userdel testuser |
Delete a user |
id testuser |
Show user ID, group ID, and groups |
👥 Group Management
| Command |
Usage & Options |
groupadd devgroup |
Create a new group |
usermod -aG devgroup testuser |
Add user to group; -a → append (do not remove existing groups), -G → group |
groups testuser |
Show groups of a user |
🔐 File Permissions
| Command |
Usage & Options |
ls -l |
List file permissions; -l → long format (permissions, owner, size, date) |
chmod 755 file.sh |
Change permissions; 7 → rwx (owner), 5 → r-x (group), 5 → r-x (others) |
chmod u+x file.sh |
Add execute permission; u → user, + → add, x → execute |
chown user:group file.txt |
Change file ownership; user:group → owner:group |
🔢 Permission Breakdown
| Value |
Meaning |
| 7 |
Read (r) + Write (w) + Execute (x) |
| 6 |
Read (r) + Write (w) |
| 5 |
Read (r) + Execute (x) |
| 4 |
Read only |
| 0 |
No permission |
🔥 Useful Example
| Command |
Usage & Options |
useradd devuser |
Create user |
passwd devuser |
Set password |
usermod -aG developers devuser |
Add user to group |
chmod 750 project/ |
Restrict access; owner → full, group → read/execute, others → no access |
🎯 Summary
- Manage users using
useradd, passwd, userdel
- Control access using
chmod and chown
- Use groups to manage permissions efficiently
- Always follow the principle of least privilege for security