Linux Permissions

Permissions

"Rules in Linux that determine who can access a file or directory and what actions they can perform."

Permission Groups

"The three categories of users that permissions apply to: Owner

Owner

"The user who owns the file or directory. Permissions apply specifically to this user."

Group

"The group assigned to the file or directory. Permissions apply to users within that group."

Others (All Users)

"All remaining users on the system who are neither the owner nor part of the assigned group."

Read (r)

"Permission that allows a user to view the contents of a file or list the contents of a directory."

Write (w)

"Permission that allows a user to modify a file or create or delete files inside a directory."

Execute (x)

"Permission that allows a user to run a file as a program or access (enter) a directory."

id Command

"A command used to display a user’s identity information including UID

chmod

"A command used to modify the permissions (mode) of a file or directory."

umask

"A command used to set the default permissions for newly created files and directories."

su

"A command that allows a user to temporarily switch to another user account

sudo

"A command that allows a permitted user to execute a specific command as another user

chown

"A command used to change the ownership of a file or directory."

chgrp

"A command used to change the group ownership of a file or directory."

passwd

"A command used to change a user’s password."

Regular File (-)

"Indicated by a dash in ls -l; represents a standard file."

Directory (d)

"Indicated by d in ls -l; represents a directory."

Symbolic Link (l)

"Indicated by l in ls -l; represents a symbolic link."

Character Special File (c)

"Indicated by c in ls -l; handles data as a stream of bytes such as a terminal."

Block Special File (b)

"Indicated by b in ls -l; handles data in blocks such as a hard drive."

Octal Notation

"A numeric method of representing file permissions using three digits for Owner

0

"Represents no permissions (---)."

1

"Represents execute permission only (--x)."

2

"Represents write permission only (-w-)."

3

"Represents write and execute permissions (-wx)."

4

"Represents read permission only (r--)."

5

"Represents read and execute permissions (r-x)."

6

"Represents read and write permissions (rw-)."

7

"Represents read

777

"Grants full permissions to everyone; not recommended for security."

755

"Owner has full access; group and others have read and execute permissions."

700

"Only the owner has full access; others have no permissions."

666

"All users can read and write the file."

644

"Owner can read and write; group and others can only read."

600

"Owner can read and write; others have no permissions."

Directory 777

"All users can list

Directory 755

"Owner has full access; others can list files but cannot create or delete them."

Directory 700

"Only the owner has access to the directory."

Symbolic Notation

"A method of changing permissions using letters instead of numbers."

u

"Represents the file or directory owner in symbolic notation."

g

"Represents the group owner in symbolic notation."

o

"Represents others in symbolic notation."

a

"Represents all users (u

u+x

"Adds execute permission to the owner."

u-x

"Removes execute permission from the owner."

+x

"Adds execute permission to all users."

o-rw

"Removes read and write permissions from others."

go=rw

"Sets group and others to have read and write permissions only."

u+x

go=rx

umask 0002

"Removes write permission from others by default."

umask 0022

"Removes write permission from group and others by default."

umask 0000

"Applies no restrictions to default permissions."

username (chown argument)

"Changes file ownership to the specified user."

username:group

"Changes file ownership to the specified user and group."

:group

"Changes only the group ownership."

username:

"Changes ownership to the specified user and assigns their login group."