User Management

Linux User management

Add A New User To Secondary Group

 useradd Example - 

You need to the useradd command to add new users to existing group (or create a new group and then add user). If group does not exist, create it. The syntax is as follows:
useradd -G {group-name} username

Add a new user to primary group

useradd example - 

To add a user tony to group developers use following command:

# useradd -g developers tony

# id tony

Addding a group

# groupadd developers

Add user called vivek to group developers:

# useradd -G developers vivek

Setup password for user vivek:

# passwd vivek

Please note that capital G (-G) option add user to a list of supplementary groups. Each group is separated from the next by a comma, with no intervening whitespace. For example, add user jerry to groups admins, ftp, www, and developers, enter:

# useradd -G admins,ftp,www,developers jerry

Please note that small -g option add user to initial login group (primary group). The group name must exist. A group number must refer to an already existing group.

Add a existing user to existing group

	usermod example - 
	Add existing user tony to ftp supplementary/secondary group with usermod command using -a option ~ i.e. add the user to the supplemental group(s). Use only with -G option :

# usermod -a -G ftp tony

Change existing user tony primary group to www:

# usermod -g www tony 

list all users in a group:

compgen -u

=== List all groups: ===
compgen -g

See what groups a user belongs to:

groups nameofuser

command to Show all users:
cat /etc/passwd
lastlog

ac		Print statistics about users' connect time.
accton		Turn on accounting of processes. To turn it on type "accton /var/log/pacct".
adduser		Ex: adduser mark - Effect: Adds a user to the system named mark
chage		Used to change the time the user's password will expire.
chfn		Change the user full name field finger information
chgrp		Changes the group ownership of files.
chown		Change the owner of file(s ) to another user.
chpasswd		Update password file in batch.
chroot		Run command or interactive shell with special root directory.
chsh		Change the login shell.
edquota		Used to edit user or group quotas. This program uses the vi editor to edit the quota.user and quota.group files. If the environment variable EDITOR is set to emacs, the emacs editor will be used. Type "export EDITOR=emacs" to set that variable.
faillog		Examine faillog and set login failure limits.
finger		See what users are running on a system.
gpasswd		Administer the /etc/group file.
groupadd		Create a new group.
grpck		Verify the integrity of group files.
grpconv		Creates /etc/gshadow from the file /etc/group which converts to shadow passwords.
grpunconv		Uses the files /etc/passwd and /etc/shadow to create /etc/passwd, then deletes /etc/shadow which converts from shadow passwords.
groupdel		Delete a group.
groupmod		Modify a group.
groups		Print the groups a user is in
id		Print real and effective user id and group ids.
last		Display the last users logged on and how long.
lastb		Shows failed login attempts. This command requires the file /var/log/btmp to exist in order to work. Type "touch /var/log/btmp" to begin logging to this file.
lastcomm		Display information about previous commands in reverse order. Works only if process accounting is on.
lastlog		Formats and prints the contents of the last login.
logname		Print user's login name.
newgrp		Lets a suer log in to a new group.
newusers		Update and create newusers in batch.
passwd		Set a user's pass word.
pwck		Verify integrity of password files.
pwconv		Convert to and from shadow passwords and groups.
quota		Display users' limits and current disk usage.
quotaoff		Turns system quotas off.
quotaon		Turns system quotas on.
quotacheck		Used to check a filesystem for usage, and update the quota.user file.
repquota		Lists a summary of quota information on filesystems.
sa		Generates a summary of information about users' processes that are stored in the /var/log/pacct file.
smbclient		Works similar to an ftp client enabling the user to transfer files to and from a windows based computer.
smbmount		Allows a shared directory on a windows machine to be mounted on the Linux machine.
smbpasswd		Program to change users passwords for samba.
su		Ex: su mark - Effect: changes the user to mark, If not root will need marks password.
sulogin		Single user login.
ulimit		A bash builtin command for setting the processes a user can run.
useradd		Create a new user or update default new user information.
userdel		Delete a user account and related files.
usermod		Modify a user account.
users		Print the user names of users currently logged in.
utmpdump		Used for debugging.
vigr		Edit the password or group files.
vipw		Edit the password or group files.
w		Display users logged in and what they are doing.
wall		Send a message to everybody's terminal.
who		Display the users logged in.
whoami		Print effective user id.