Linux Users and Group Management

Users Management:

/etc/passwd file
The file stored information about users as following

[username]:[x]:[UID]:[GID]:[Comment]:[Home directory]:[Default shell]
here x is stored user authendication / protected by shadowed (/etc/shadow).

/etc/shadow file
The shadow files contains account authendication or encripted password stored.

Adding Users:

The new user creation with display name, group name and directory.

# useradd -c “Dilliganesh K” -d /home/data -g linux -s /bin/bash ganesh

# grep ganesh /etc/passwd
# ganesh:x:1001:1001:Dilliganesh K:/home/data:/bin/bash
here -c is for display name, -d for user data stored directory, -g for group name. -s for shell with account.

more ever -e for expiration date for the user and -u for user ID to set as default stored first available ID.
Adding Password:

# passwd ganesh
Changing password for user ganesh.
New password:
Retype new password:
passwd: all authentication tokens updated successfully.

To lock user account

# passwd -l ganesh
Locking password for user ganesh.
passwd: Success

To unlock user account

# passwd -u ganesh
Unlocking password for user ganesh.
passwd: Success

To set expire date for user account

# usermod –expiredate 2018-08-10 dilliganesh

Modify Users:

To change user login name

# usermod -l dilliganesh ganesh
# grep dilliganesh /etc/passwd
dilliganesh:x:1001:1001:Dilliganesh K:/home/data:/bin/bash

To change user directory

# usermod -d /home/dilli dilliganesh
# grep dilliganesh /etc/passwd
dilliganesh:x:1001:1001:Dilliganesh K:/home/dilli:/bin/bash

To change account group from linux to hr

# grep hr /etc/group
hr:x:1002:

# usermod -g hr dilliganesh
# grep dilliganesh /etc/passwd
dilliganesh:x:1001:1002:Dilliganesh K:/home/dilli:/bin/bash

To Adding a user to a primary group and supplementary group

# usermod -g hr -G manager dilliganesh
# grep dilliganesh /etc/passwd
dilliganesh:x:1001:1002:Dilliganesh K:/home/dilli:/bin/bash

User Deleting:

To user deleting

# userdel -r dilliganesh