Linux Permissions

Commands

Command	Affects	Description
chown	files & directories	change owner or group or default group
chmod	files & directories	change permissions
umask	files & directories	change default permissions

Permissions

x	Read	Write	Execute
file	can read file	can write file	can execute file
directory	can list the contents of the directory	can create files inside the directory	can step into the directory

chown

Notations

Octal

chmod 775 file

Verbose

chmod u+rw file

Special bits

Bit	Affects	Description	Octal command	Verbose command
setUID	files	execute the file as the owner of the file	chmod 2755 file	chmod u+s file
setGID	directories	newly created files inherit the group of the parent folders group	chmod 4755 directory	chmod g+s directory

umask

Changes the default permissions for a session.

umask # 0002

On Ubuntu 16.04.
The default umask is 0002.
The default file permissions are 0666.
The default directory permissions are 0777.

The default umask is subtracted from the default octal value of the file or directory.

file

0666
0002
0664

Newly created file permissions are 0664 by default.
This can be seen from a file being created having -rw-rw-r– permissions.

directory

0777
0002
0775

Newly created directory permissions are 0775 by default.
This can be seen from a directory being created having drwxrwxr-x permissions.

You can change the umask value for a session.

touch file
ls file # -rw-rw-r--
umask 0007
touch file2 
ls file2 # -rw-rw----

Advanced

If you need more fine control you can use acl.