File Permissions in Linux

Every file has a set of permissions (similar to ACLs in Windows) that determine whether a user can read, write or run that file. Running ls -l displays the permissions.

There are four parts to file’s mode.

1. Type
2. User Permissions
3. Group Permissions
4. Other Permissions

The first character is type. - means its a file, d means directories. The rest of the file’s mode contains permissions in groups of three, in order for user, group and other. We can also use octal forms for setting permissions.

r means file is readable (4)
w means file is writable (2)
x means file is executable (for scripts, etc.) (1)
- means nothing, i.e. no permissions set

## As an example
## some user has read-write
## members of somegroup have read
## others have read
-rw-r--r--  1 someuser  somegroup    64975 16 Oct  2018 somedoc.rtf

Comparing against ACLs in NTFS

1. NTFS permissions are per-user permissions, multiple users can have different rights. Linux file mode has only three - user, group and others.
2. NTFS has explicit deny rules.
3. NTFS has inheritance model.
4. NTFS has auditing capability, Linux file mode does not having anything. Though, audit tools exist.