In this tutorial I am going to explain some basic Linux command ” useradd, userdel, usermod, groupadd, last and lastb” that help to Linux beginner users as well as advanced users.
useradd command used to create a new user or updates default new user information. Below are the some example:
Add new user called sagar with default settings
# useradd sagar
Create new user with home directory in /opt
# useradd sagar -d /opt/sagar
Disable user account, In below example account will be disable from 28/4/2017.
# useradd sagar-e 2017-04-28
Set Warning to change password after after password expired, system will allow the user to login for 7 days with warning.
# useradd sagar -f 7
Set user (sagar) group as admin
# useradd sagar -g admin
Create user with the given encrypted password. Without password account will disabled.
# useradd sagar -p $1$d7
Change user shell C as the default login shell for the sagar.
# useradd sagar -s /bin/csh
userdel command to delete a user account and user’s related files.
Delete the user account
# userdel sagar
Delete the user account together with their home directory and all files inside it.
# userdel -r sagar
Delete the user with home directory as well file, forcefully even user is still login,
# userdel -f sagar
usermod command is used to modify the user account.
Create new home directory for sagar in /var/sagar and move old home directory contents to this directory.
# usermod -d /var/sagar sagar
Disable user account, In below example account will be disable from 20/8/2018.
# usermod -e 2018-08-28
Set warning to change password after after password expired, system will allow the user to login for 7 days with warning.
# usermod -f 7 sagar
Set sagar’s initial group as infra
# usermod -g infra sagar
Set the new password for the sagar
# usermod -p $3$32d
Set BASH as default login shell for the sagar.
# usermod -s /bin/bash sagar
Lock the user’s password
# usermod -L sagar
Unlock the user’s password
# usermod -U sagar
groupadd command is used to create new group.
Create a new group on the system.
# groupadd sales
last command is used to show list of last logged in users.
List all entries
Show who were all logged through tty2
# last tty2
Show the all entries of Jim user
# last Jim
Display only last 7 entries
# last -7
Hide the Host Name field from output.
# last -R
Show hostname field in last column.
# last -a
Display the IP Address of Remote Host.
# last -i
List all entries up-to Aug 18 12:00:00 2016
# last -t 20160818120000
lastb command is used to display a list of recent bad login attempts ” from /var/log/btmp log file “.
The syntax for lastb is same as useradd but the login given is for an already existing user. Below are the some commonly used options.
- -d : Change the user’s home directory.
- -c : Update the comment for the user.
- -g : Change the user primary group.
- -a -G : Add the user to one or more supplemental group.
- -G : Change the supplemental groups to only the list of groups and remove any other supplemental groups.
- -s : Change the default shell for the user.
- -u : Update the user’s UID number.
- -L : Lock the account by disabling the password.
- -U : Unlock the account and re-enabling its previous password.
I hope this article will help to learn some basic Linux command. If you have any queries and problem please comment in comment section.