# Linux users/groups/permissions cheatsheet

## Add user
```
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.

## Get information about a user, including the user's group memberships
```
id
id peter
```

## List groups
```
groups
groups peter
```

## File permissions
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

## Change ownership of a file or folder
```
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
```

## Execute a command with elevated rights elevated
```
sudo commandname
```

`su` - switch user