This post was published at 09 May 2017


All files in linux have three permissions: Read, Write and Execute.

You can modify then with chmod command.

  • For example, we add read and write permission but forbid execution:

    sudo chmod 770 file.txt


    sudo chmod +rw-x file.txt
  • Another example, we add read/write to the owner but delete all permissions for the rest of users.

    chmod u=rw,go= arch.txt 

Managing users and groups

In all machines, we should create an user to manage the system.
Best way to create users and groups, Recommended:

  • Create/Delete new group:

    sudo addgroup jclustergroup
    sudo delgroup jclustergroup
  • Add/Delete user to a specific group or system (empty):

    sudo adduser juser [jclustergroup/empty]
    sudo deluser juser [jclustergroup/empty]
  • Add/Change password to user:

    sudo passwd juser

We can use lower/upper case in names, Not recommended:

  • Create/Delete new group:

    sudo groupadd JClusterGroup
    sudo groupdel JClusterGroup
  • Create/Delete new user:

    sudo useradd Juser
    sudo userdel Juser
  • Create new user with a group named JClusterGroup with home /home/juser and with CLI /bin/bash

    sudo useradd -g JClusterGroup -d /home/Juser -m -s /bin/bash Juser
  • Change users permissions:

    sudo chown -R <username> <files>


  • Change groups permisions:

    sudo chgrp -R <groupname> <files>


  • Change actions permissions:

    sudo chmod ugo-rw+x <filename>

    We add execution permission without read/write permission.