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User administration Commands
useradd <username>
passwd <username>
While using the above commands of creating a user it reflects to three files /etc/passwd,/etc/group,/etc/shadow
/etc/passwd
sysadmin:x:500:500:Sys:/home/sysadmin:/bin/bash
/etc/shadow
sysadmin:$1$L6icvM39$i9FdAwunWV9Xkw2nO0F.Y0:14880:0:99999:7:::
/etc/group
sysadmin:x:503:
whereas unpriviledged users uid&gid will start from 500
The uid&gid between 1-499 will be for system users and groups uid&gid for processing a system process
Usage of Usermod command
To Add the Comment Entry
# usermod -c <Comment><User Name>
To Change the home directory
# usermod –d <Home Directory><User Name>
To Change the User ID
# usermod –u <New UID><User Name>
To Change the Group ID
# usermod –g <Existing GID><User Name>
To add users to a Supplementary Group
# usermod -G pp2 pp3 [ Adding user pp3 to group pp2 ]
# usermod -G pp2 pp1 [ Adding user pp1 to group pp2 ]
To change the User’s login name
# usermod -l <New Login Name><User Name>
To change a user's shell
# usermod -S /sbin/nologin <User Name>
Alternate way of changing a shell is by giving command in prompt as chsh
# chsh <UserName>
To lock a user's passwd
# usermod -L sysadmin
To Unlock a users passwd
# usermod -U sysadmin
# userdel
# userdel -r
To delete a User [ This is will not remove the User’s Home Directory. ]
# userdel <User Name>
To delete a User including Home Directory.
# userdel -r < User Name>
Group Administration Commands
To add a group
# groupadd <groupname>
To change a group
# groupmod <newgroupname><oldgroupname>
To delete a group
# groupdel <groupname>
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