Linux User Group

--Note : Make sure to logged in as "root" user for using usermod,useradd,userdel, groupadd,groupmod,groupdel on Linux otherwise commands will not run. 

 To pass the password with command to sudo :-

echo "password" | sudo -S -u username linux_command

to run command with another user:- su -c "command" username 

echo "k" | sudo -S -u king whoami

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## to change home directory/Login directory of a user in Linux 

usermod -d /path/to/new_home_directory -m username 

option:

-d : for new path home directory 

-m : moving all files from old home directory to new home directory 

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to add user:- useradd -m name_of_user

usermod -aG sudo username  ----------> to assign admin access to user

sudo su - username

userdel -f username -------------------> to delete user forcefully

groupadd  group_name --------------> to add group

groupdel -f group_name ------------> to force delete a group 

gpasswd -A user -M user,user,user  groupname   ----> adding users to a group 

gpasswd -d username groupname -----> removing a user from a group 

groupmod -n newgroup oldgroup  ------> renaming a group  

add user to secondary group:- useradd -G group1,group2,group3  username

add user to primary group :- useradd -g group1,group2,group3  username

add exiting user to secondary group :- usermod -a -G group_name username 

add existing user to primary group :- usermod -g group_name username 

to view passwd:- cat /etc/passwd

to view group:- cat /etc/groups

to view all user details:- id username

to view shells:- cat /etc/shells or echo $SHELL 

 

 

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Rename User in Linux

1. Ensure the user is logged out
ps -u <old_username> pkill -u <old_username>

2. Rename the User
usermod -l <new_username> <old_username>
ex. usermod -l doe john

3. Update the Home Directory
usermod -d /home/<new_username> -m <new_username>
usermod -d /home/doe -m doe

4. Rename the Group
groupmod -d <new_groupname> <old_groupname>
groupmod -d doe john

5. verfiy changes
cat /etc/passwd; cat /etc/shadow; cat /etc/group
grep <new_username> /etc/passwd
grep <new_username> /etc/group  

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To Lock the user on Linux:

sudo usermod -L <username>

This locks the account by prefixing the password hash with ! in /etc/shadow.

To Unlock the user on Linux:

sudo usermod -U <username>

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To change shell of a user in Linux:

usermod -s /path/new_shell <username>

ex. usermod -s /bin/zsh pune

verfiy changes in grep -i /etc/passwd "pune" 

 or 

sudo chsk -s /path/new_shell <username>

sudo chsh -s /bin/sh pune

verify changes in grep -i /etc/passwd "pune" 

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