Day-3: Linux user management and permissions

1. use sudo command to see some confidential or root user access file:

$ cat /var/etc/shadow         [you cant see access denied]
$ sudo cat /var/etc/shadow        [noew you can see]
$ sudo cat /var/etc/passwd
$ sudo cat /var/etc/group

1. add some user by using useradd command:

$ sudo useradd userName

1. delete some user by using userdel command:

$ sudo userdel userName

1. cahnging some user password :

$ sudo passwd userName

1. if we want to know our ssh key :

$ cat ~/.ssh/id_rsa.pub

1. connect your machine with remote machine via ssh :

$ ssh -i "key-pair_fileName_PATH ubuntu@ip_address    [ubuntu or any os]

1. something copy from remote server:

$ scp -i <keypair_PATH> < keypair_PATH> <user@ip_address>: filePath 

here all linux permission command:

1. check file permission:

$ ls -l

1. to change any file permission by using chmod(rwx):

$ chmod +x fileName            [make executable file]
$ chmod +rwx fileName          [ make permission read,write, executable]
$ chmod -rwx fileName          [ remove all permission]
$ chmod -x fileName            [remove executable permission]

1. we can give permission by using numaric command like 777:

Description: for read - 4, write - 2, execute -1. all together 7. for 777 means 1st 7 for user, 2nd for group and 3rd for all user

$ chmod 777 fileName    [all permission for user,group and all]
$ chmod 742 fileName    [all permission for user, read for group, write for all]
$ chmod 124 fileName    [execute permission for user, write for group, read for all]
$ chmod 711 fileName    [ all permission for user, execute for groups and all]

1. modifying ownership permission :

$ sudo chown userName fileName    [it will change files user ownership]
$ sudo chgrp groupName fileName    [it will change files group ownership]
$ sudo chmod userName:groupName fileName     [it will change both user & group ownership]

1. if you want to change your user password:

$ passwd

1. to see our system name :

$ uname

1. to see our system name and details:

$ uname -a
$ uname -r     [to check only version numaric ]

1. add a user to a group :

$ sudo usermod -a -g groupName userName

1. remove a user from a group:

$ sudo deluser userName groupName

1. Shows information of all the users logged in:

$ finger

1. show information of a particular user:

$ finger userName