4. useradd in Linux.md

🛠️ 1. Display Help for useradd Command

📌 Command:

useradd -h

📌 Example Output:

Usage: useradd [options] LOGIN
Options:
  -b, --base-dir BASE_DIR       🏠 Set base home directory
  -c, --comment COMMENT         📝 Add user comment
  -d, --home-dir HOME_DIR       📂 Specify home directory path
  -e, --expiredate EXPIRE_DATE  ⏳ Set account expiration date
  -g, --gid GROUP               👥 Set primary group ID
  -G, --groups GROUPS           🔄 Add secondary groups
  -m, --create-home             🏡 Create a home directory
  -M, --no-create-home          🚫 Do not create a home directory
  -s, --shell SHELL             🖥️ Set login shell
  -u, --uid UID                 🔢 Set user ID
  -p, --password PASSWORD       🔑 Set an encrypted password
  -r, --system                  ⚙️ Create a system user

✅ This helps understand all useradd options.

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🏠 2. Create a New User with Home Directory

📌 Command:

useradd -m -d /home/john john

✅ Creates user john with a home directory /home/john.

📌 Verify:

tail -n 1 /etc/passwd

Expected Output:

john:x:1001:1001::/home/john:/bin/bash

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🔑 3. Set Password for a User

📌 Command:

passwd john

✅ Sets a password for user john.

📌 For an Encrypted Password:

useradd -p $(openssl passwd -1 "MySecurePassword") user1

✅ Uses openssl to set an encrypted password.

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🎯 4. Create a User with a Specific UID

📌 Command:

useradd -u 1050 user2

✅ Creates user2 with UID 1050.

📌 Verify:

id user2

Expected Output:

uid=1050(user2) gid=1050(user2) groups=1050(user2)

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👥 5. Assign a User to a Specific Group

📌 Command:

useradd -g developers user3

✅ Creates user3 and assigns it to the developers group.

📌 Check Group:

id user3

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🔄 6. Add a User to Multiple Groups

📌 Command:

useradd -G sudo,developers user4

✅ Adds user4 to sudo and developers groups.

📌 Verify:

groups user4

Expected Output:

user4 : user4 sudo developers

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⏳ 7. Set Account Expiration Date

📌 Command:

useradd -e 2025-12-31 user5

✅ User user5 will expire on 31 Dec 2025.

📌 Verify:

chage -l user5

Expected Output:

Account expires: Dec 31, 2025

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🚫 8. Create a User Without a Home Directory

📌 Command:

useradd --no-create-home user6

✅ Creates user6 without a home directory.

📌 Verify:

ls -ld /home/user6

Expected Output: (No directory found)

ls: cannot access '/home/user6': No such file or directory

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🖥️ 9. Set Default Shell for a User

📌 Command:

useradd -s /bin/zsh user7

✅ Sets /bin/zsh as the default shell for user7.

📌 Verify:

cat /etc/passwd | grep user7

Expected Output:

user7:x:1007:1007::/home/user7:/bin/zsh

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⚙️ 10. Create a System User

📌 Command:

useradd -r systemuser

✅ Creates a system user systemuser.

📌 Verify:

id systemuser

Expected Output:

uid=497(systemuser) gid=497(systemuser) groups=497(systemuser)

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🏷️ 11. Create a User with Custom Comments

📌 Command:

useradd -c "Project Manager" user8

✅ Adds Project Manager as a comment for user8.

📌 Verify:

cat /etc/passwd | grep user8

Expected Output:

user8:x:1008:1008:Project Manager:/home/user8:/bin/bash

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🏁 12. Delete a User

📌 Command:

userdel user9

✅ Deletes user9 but keeps their home directory.

📌 Delete User and Home Directory

userdel -r user10

✅ Deletes user10 and removes /home/user10.

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🔥 Summary Table

🎯 Command	📌 Description
useradd -m john	Creates a user john with a home directory
passwd john	Sets a password for john
useradd -u 1050 user2	Creates user2 with UID 1050
useradd -g developers user3	Assigns user3 to developers group
useradd -G sudo,developers user4	Adds user4 to multiple groups
useradd -e 2025-12-31 user5	Sets an expiration date for user5
useradd --no-create-home user6	Creates user6 without a home directory
useradd -s /bin/zsh user7	Sets /bin/zsh as the shell for user7
useradd -r systemuser	Creates a system user
useradd -c "Project Manager" user8	Adds a comment for user8
userdel user9	Deletes user9 but keeps home directory
userdel -r user10	Deletes user10 and removes home directory

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