Managing users and permissions in Linux Systems.

Here I’ll teach you how to manage users, groups and change permissions onfiles and directories in Linux.

Permissions

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
  

  Or:

  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.