To query if package is installed or not
[root@RedHat MyData]# rpm -qa zip
zip-3.0-23.el8.x86_64
[root@RedHat MyData]# rpm -qa unzip
unzip-6.0-43.el8.x86_64
Let's understand file "/passwd"
[root@RedHat ~]# cat /etc/passwd
root:x:0:0:root:/root:/bin/bash --> Total 7 Fields
root -⇾ login name
x -⇾ Password Pointer (x means password is set)
0 -⇾ User Id
0 -⇾ Group Id
root ⇾ Comment
/root -⇾ home directory
/bin/bash -⇾ login shell
[root@RedHat ~]# cat /etc/shadow | grep admin
admin:$6$STGdn7J1zBQMEfOt$aNKAJI.11RwA05VNwxR37ggN0wesSwzux6ue.dgc6bD1oD/73cmv24oQ4NINwO4e49HvWaxjEeOAtD3BmIHqs0:18642:0:99999:7::: -⇾ Total 9 fields
Password of user admin
Password Policy
[root@RedHat ~]# cat /etc/group
root:x:0:admin -⇾ Total 4 fields
root -⇾ Group name
x : Group password is set (/etc/gshadow)
0 -⇾ Goup ID
admin -⇾ Now all the user's belong to that group will appear in last field
[root@RedHat ~]# cat /etc/gshadow
root::: -⇾ Total 4 fields just like /etc/shadow
Group name
password
admin user of group
Normal users
Note : user's email information i.e. what he receives and send is stored in /var/mail/root
This can be used to find how many users are available
[root@RedHat mail]# ls /var/mail
admin mukesh packer udaipur
Note : user file in /var/mail will present even if user is deleted.
So if you want to remove all data associated with user the use "rf"
[root@RedHat mail]# userdel -rf udaipur
[root@RedHat mail]# ls /var/mail
adminji mukesh packer
Use command "ID Root" to find id of user
[root@RedHat ~]# id root
uid=0(root) gid=0(root) groups=0(root)
[root@RedHat ~]# id admin
uid=1001(adminji) gid=1001(admin) groups=1001(admin),4(adm),190(systemd-journal)
Points to remember :
User password is stored in /etc/shadow
Group password is stored in /etc/gshadow
Comments