Unix Permissions on CSUN Accounts

There are user-changeable permissions assigned to every directory and file in a campus Unix account that specify who has read, write, or execute privileges. Separate permissions are assigned to the user (i.e., you, the account owner), the group to which the user belongs (normally a department, such as Geography), and "other" (i.e., anyone in the world). This document provides a brief overview to help you understand the permissions associated with your account.

• Viewing and Understanding Permissions
  • Unix Directory Permissions
  • Unix File Permissions
• Standard Permissions Settings
• Changing Permissions

Viewing and Understanding Permissions

You can view the permissions that are set for the directories and files in your account by typing the following command at the prompt:

ls -al

where ls means "list" and -al modifies the list request to include "all" files (including those preceded with a dot) in the "long" format (which includes permissions).

The resulting list of files and directories will appear in the following format:

-rwxr--r--   #   userID   group   size   date   time   filename
drwxr-xr-x   #   userID   group   size   date   time   dirname

The ten characters in the first column shows the permissions for the designated file or directory name. The remaining columns give information such as userID (i.e., your login account), the group abbreviation (e.g., geog for Geography), the size of the file or directory, the date and time it was last modified, and the name of the file or directory.

In the permissions column, the first character indicates the entry type. File listings begin with a hyphen; directory listings, with the letter d. The remaining nine characters indicate the permissions themselves (in three groups of three). Character positions 2 thru 4 show user permissions — read (r), write (w), and/or execute (x); 5 thru 7, group permissions; and 8 thru 10, other permissions. A hyphen in a character position indicates a lack of permission for that item.

Table 1 and Table 2, below, describe what the various permissions mean for the user, the group, and others.

TABLE 1. Unix Directory Permissions

In the example at the beginning of this section, the permissions for the directory listing are shown as:

drwxr-xr-x

which indicates that the user has read, write, and execute priviliges and that the everyone else (group and other) has read and execute privileges. However, they cannot create or delete files in the directory.

TABLE 2. Unix File Permissions

 

WHO	WHAT THE PERMISSIONS ALLOW
USER	Read (r)	The account owner can read the file.
	Write (w)	The account owner can modify or delete the file.
	Execute (x)	The account owner can run the file as a program.
GROUP	Read (r)	Everyone in the designated group can read the file.
	Write (w)	Everyone in the group can modify or delete the file.
	Execute (x)	Everyone in the group can can run the file as a program.
OTHER	Read (r)	Anyone can read the file.
	Write (w)	Anyone can modify or delete the file.
	Execute (x)	Anyone can run the file as a program.

In the example at the beginning of this section, the permissions for the file listing are shown as:

-rwxr--r--

which indicates that the user has read, write, and execute priviliges and that everyone else (group and other) can only read the file. They cannot modify or delete the file or run it as a program.

Standard Permissions Settings

The standard settings for files and directories in a typical CSUN account are as follows.  

drwx------

-rw-------

These settings give the account owner (user) read, write, and execute access to directories and read and write access to files. Group members and others have no access at all.

Changing Permissions

The most common reason for changing account permissions on a CSUN Unix account is to allow access to Web pages that are published there. Refer to Commands for Publishing Web Pages to a Campus Account ("Setting Up Your Account") for instructions. 

Otherwise, there is typically no need for the average account owner to change the default permissions on an account, and, in fact, it may be detrimental to do so. You might inadvertently "lock yourself out" of your own account or unintentially allow access to "the world".

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August 14, 2003

Prepared by Gail Said Johnson, User Support Services

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