sudo useradd -m peter   #create user peter
sudo passwd peter       #set peter's password (will be prompted for password)

groupadd myAppUsers     #create the myAppUsers group

sudo usermod -a -G peter myAppUsers. #add peter to the myAppUsersGroup

adduser and addgroup are interactive convenience scripts that wrap the useradd and groupadd commands.

id
id peter

groups
groups peter

List files, showing permissions and ownership information

ls -l

The permission mask is the sum of the permissions (r = 1, w = 2, x = 4) for the user (u), group (g) and others (o). Add the numbers to get the permission mask, so 7 means all of them (1+2+4=7).

Permissions are course grained, and set for exactly 3 scopes

• u (for user) to set permission for the resource owner.
• g for the resource group.
• o (for others) to set permissions for everyone else.
• a for setting all above scopes at once.

chmod u=rwx,g=rwx,o=rwx myFile.txt
chmod a=rwx myFile.txt
chmod 777 myFile.txt

You can add or remove a specific permission for a scope

chmod u+x myFile.txt
chmod u-x myFile.txt

TODO: setfacl - for working with ACLs

chown peter myFile.txt            #change owner
chgrp myAppUsers myFile.txt       #change group
chown :myAppUsers myFile.txt      #alternate syntax for chgrp
chown peter:myAppUsers myFile.txt #change owner and group

sudo commandname

su - switch user