Lab: Create a User Step-by-Step

In this lab you will create a user and their home directory step-by-step the way the adduser command does. You’ll create the following user:

  • Username: galadriel

  • Group: maiar

  • Home directory: /home/galadriel

Step 0: Install Python

The best way to generate a UNIX password from the command line is with Python. Install it with apt:

$ sudo apt install python-minimal

Step 1: Create a User

Users are added to both the /etc/passwd and /etc/shadow files. Add this line to /etc/passwd:

galadriel:x:2000:2000:Lady of Light:/home/galadriel:/bin/bash

The fields are:

  1. galadriel: User name

  2. x: Always x

  3. 2000: User ID

  4. 2000: Primary Group ID

  5. Lady of Light: Full name

  6. /etc/galadriel: Home directory

  7. /bin/bash: Login shell

Step 2: Generate a Password

The shadow file contains the hash of the users’s password and a salt for the hash. Python’s crypt library can generate the hash and salt for us. Run this command to generate a hash for Cabri11o.

$ python3 -c 'import crypt; print(crypt.crypt("Cabri11o"))'

This will generate a random salt so every hash will be different. Here’s an example:

$6$PO8tqBryUU5aZA.r$Dy0ybcqFH6aHA/vQGixiKGzKoWX2Ryh5a1aGdRqYB9U0SWpZZyUSLyMDP0Q4BonjA1c7ywdO.wktOk13KFO3T1

The salt is made of fields separated by the dollar sign ($). The fields are:

  1. $6: Encryption method (SHA-512)

  2. $PO8tqBryUU5aZA.r: Salt (chosen at random)

  3. $Dy0ybcqFH6aHA...: The hash

Copy the entire output of the command so you can paste it in the next step.

Step 3: Give the User a Password

Add this line to /etc/shadow:

galadriel:<your-hash-here>:1:0:99999:7:::

The fields are:

  1. galadriel: User name.

  2. <your-hash-here>: The hash (paste the hash here). Empty (::) allows login without a password. A star (*) disables the account.

  3. 1: Last password change. Days since Jan 1, 1970 that password was last changed. A zero forces a password change.

  4. 0: The minimum days between password changes.

  5. 99999: The maximum age of a password.

  6. 7: Password change warning days.

  7. <empty>: The number of days after password expires that account is disabled.

  8. <empty>: The number of days since January 1, 1970 that an account has been disabled

  9. <empty>: A reserved field for possible future use

Step 4: Create a Group

Add the following line to /etc/group

maiar:x:2000:

The fields are:

  1. maiar: Group name.

  2. x: Always x

  3. 2000: Group ID

Step 5: Create a Home Directory

The directory /etc/skel has the skeleton of a home directory. That’s the bare minimum files a user gets started with. Make a copy with this command:

$ sudo cp -R /etc/skel /home/galadriel

The directory is owned by root. Use chown to fix it:

$ sudo chown -R galadriel:maiar /home/galadriel/

Step 6: Test Your Work

You should be able to use su to login as Galadriel. You’ll be prompted for the password:

$ su galadriel 
Password:

Don’t use sudo to do this test!

Turn In

Turn in the following files on Canavas:

  • /etc/passwd

  • /etc/shadow

  • /etc/group