If you want to find the system ID of the user type: id username You can check what groups a user belongs to by using the "groups" command. groups <username> To create a user with the default groups type: sudo adduser --add_extra_groups username Fedora: sudo adduser -m username To delete a user and its primary group type: sudo deluser username To delete user and files in the user's home directory along with the home directory itself and the user's mail spool (Fedora). sudo userdel -r username To add an existing user to an existing group type: sudo usermod -a -G thegroupname theusername sudo usermod -a -G thegroupname theusername sudo useradd -G thegroupname theusername Use gpasswd: sudo gpasswd -a theusername thegroupname To remove user billybob from the group hillbilly. gpasswd -d billybob hillbilly To give user billybob administrative rights to the group hillbilly. gpasswd -A billybob hillbilly To Change a users primary group type: useradd -g www joebob To show users that are in a group named joebob type: getent group joebob To temporarily lock or unlock a user account, use the following syntax, respectively: sudo passwd -l username sudo passwd -u username If you want to use the GUI you will have to install the gnome-system-tools sudo apt-get install gnome-system-tools Here are a few ways to run it once it is installed type: sudo users-admin Press Alt+F2 Type sudo users-admin Press Enter. Press Ctrl+Alt+T. Type sudo users-admin Press Enter. If you want to add a group type: sudo groupadd foo sudo addgroup groupname If you want to delete a group type: sudo delgroup groupname User Profile Security when a new user is created, the adduser utility creates a brand new home directory named /home/username, respectively. The default profile is modeled after the contents found in the directory of /etc/skel, which includes all profile basics. If your server will be home to multiple users, you should pay close attention to the user home directory permissions to ensure confidentiality. By default, user home directories in Ubuntu are created with world read/execute permissions. This means that all users can browse and access the contents of other users home directories. This may not be suitable for your environment. To verify your current users home directory permissions, use the following syntax: ls -ld /home/username The following output shows that the directory /home/username has world readable permissions: drwxr-xr-x 2 username username 4096 2007-10-02 20:03 username You can remove the world readable permissions using the following syntax: sudo chmod 0750 /home/username Some people tend to use the recursive option (-R) indiscriminately which modifies all child folders and files, but this is not necessary, and may yield other undesirable results. The parent directory alone is sufficient for preventing unauthorized access to anything below the parent. A much more efficient approach to the matter would be to modify the adduser global default permissions when creating user home folders. Simply edit the file /etc/adduser.conf and modify the DIR_MODE variable to something appropriate, so that all new home directories will receive the correct permissions. DIR_MODE=0750 After correcting the directory permissions using any of the previously mentioned techniques, verify the results using the following syntax: ls -ld /home/username The results below show that world readable permissions have been removed: drwxr-x--- 2 username username 4096 2007-10-02 20:03 username Password Policy A strong password policy is one of the most important aspects of your security posture. Many successful security breaches involve simple brute force and dictionary attacks against weak passwords. If you intend to offer any form of remote access involving your local password system, make sure you adequately address minimum password complexity requirements, maximum password lifetimes, and frequent audits of your authentication systems. Minimum Password Length By default, Ubuntu requires a minimum password length of 4 characters, as well as some basic entropy checks. These values are controlled in the file /etc/pam.d/common-password, which is outlined below. password required pam_unix.so nullok obscure min=4 max=8 md5 If you would like to adjust the minimum length to 6 characters, change the appropriate variable to min=6. The modification is outlined below. password required pam_unix.so nullok obscure min=6 max=8 md5 The max=8 variable does not represent the maximum length of a password. It only means that complexity requirements will not be checked on passwords over 8 characters. You may want to look at the libpam-cracklib package for additional password entropy assistance. Password Expiration When creating user accounts, you should make it a policy to have a minimum and maximum password age forcing users to change their passwords when they expire. To easily view the current status of a user account, use the following syntax: sudo chage -l username The output below shows interesting facts about the user account, namely that there are no policies applied: Last password change : Jan 20, 2008 Password expires : never Password inactive : never Account expires : never Minimum number of days between password change : 0 Maximum number of days between password change : 99999 Number of days of warning before password expires : 7 To set any of these values, simply use the following syntax, and follow the interactive prompts: sudo chage username The following is also an example of how you can manually change the explicit expiration date (-E) to 01/31/2008, minimum password age (-m) of 5 days, maximum password age (-M) of 90 days, inactivity period (-I) of 5 days after password expiration, and a warning time period (-W) of 14 days before password expiration. sudo chage -E 01/31/2008 -m 5 -M 90 -I 30 -W 14 username To verify changes, use the same syntax as mentioned previously: sudo chage -l username The output below shows the new policies that have been established for the account: Last password change : Jan 20, 2008 Password expires : Apr 19, 2008 Password inactive : May 19, 2008 Account expires : Jan 31, 2008 Minimum number of days between password change : 5 Maximum number of days between password change : 90 Number of days of warning before password expires : 14 Other Security Considerations Many applications use alternate authentication mechanisms that can be easily overlooked by even experienced system administrators. Therefore, it is important to understand and control how users authenticate and gain access to services and applications on your server. SSH Access by Disabled Users Simply disabling/locking a user account will not prevent a user from logging into your server remotely if they have previously set up RSA public key authentication. They will still be able to gain shell access to the server, without the need for any password. Remember to check the users home directory for files that will allow for this type of authenticated SSH access. e.g. /home/username/.ssh/authorized_keys. Remove or rename the directory .ssh/ in the user's home folder to prevent further SSH authentication capabilities. Be sure to check for any established SSH connections by the disabled user, as it is possible they may have existing inbound or outbound connections. Kill any that are found. Restrict SSH access to only user accounts that should have it. For example, you may create a group called "sshlogin" and add the group name as the value associated with the AllowGroups variable located in the file /etc/ssh/sshd_config. AllowGroups sshlogin Then add your permitted SSH users to the group "sshlogin", and restart the SSH service. sudo adduser username sshlogin sudo /etc/init.d/ssh restart
MakeUser Function for .bashrc file:
makeuser () { if [ $# -eq 0 ] then echo "Usage: makeuser username." else sudo adduser --add_extra_groups $1 fi }
