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Mahbub Ferdous Bijoy
Mahbub Ferdous Bijoy

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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
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  1. add some user by using useradd command: 
$ sudo useradd userName
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  1. delete some user by using userdel command: 
$ sudo userdel userName
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  1. cahnging some user password : 
$ sudo passwd userName
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  1. if we want to know our ssh key : 
$ cat ~/.ssh/id_rsa.pub
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  1. connect your machine with remote machine via ssh : 
$ ssh -i "key-pair_fileName_PATH ubuntu@ip_address    [ubuntu or any os]
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  1. something copy from remote server: 
$ scp -i <keypair_PATH> < keypair_PATH> <user@ip_address>: filePath
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here all linux permission command:

  1. check file permission: 
$ ls -l
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  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]
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  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]
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  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]
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  1. if you want to change your user password: 
$ passwd
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  1. to see our system name : 
$ uname
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  1. to see our system name and details: 
$ uname -a
$ uname -r     [to check only version numaric ]
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  1. add a user to a group : 
$ sudo usermod -a -g groupName userName
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  1. remove a user from a group: 
$ sudo deluser userName groupName
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  1. Shows information of all the users logged in: 
$ finger
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  1. show information of a particular user: 
$ finger userName
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