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Next: Some Important Files Up: File Permissions Previous: How Unix File Permissions

Controlling Access to Your Files

There are two important commands you need to know in order to control access to your files.

The first command is the ls -l command (i.e. the ls command with the -l optiongif. When you issue the command ls -l you will get output that looks like the following:

drwxr-xr-x  2 dela          512 Feb 26 16:06 figures
-rw-r--r--  1 dela         8529 Feb 26 15:49 legal.issues.tex
-rw-r--r--  1 dela        34670 Feb 26 16:01 security.tex

The first part of each line is what matters. The first character describes what sort of file is being listed. The next nine characters show the permissions set for the file. They are to be read in groups of 3, each position representing (in order) read access, write access and execute access. Depending of whether that access is allowed, each character in a group of three is either r, w, or an x representing read, write or execute access, or if the corresponding access is denied the position will contain a -.

The first group of three describes the permissions that the owner of the file has. The second group of three describes permission that the group associated with the file has. And the third group of three describes the type of access permissions that the category ``other'' has.

The command ls -l will also list the owner of the file.

The command ls -lg will additionally list the group associated with the file.

The second command you need to know is the chmod command. This command changes the so-called access modes of your file, i.e. it changes the access permissions associated with a file.

To use it, you must specify the change you want to make to the access permissions, and you must specify the file.

To specify how you change the access permissions, you give the user category, and which permission to add or subtract. The categories are specified as u, g, o which stand of User (the owner of the file), Group (the group associated with the file), and Other. The permissions are specified via the names r, w, x (Read, Write and eXecute). To add or remove a specific permission from a certain category, simply use a + or a - character. For example the following command will add read and write access for the group, and remove read access for others to the file report.text.

chmod g+rw,o-r report.text

Another useful command, which is unique to the HSEAS, is dirperm. This command will list the current permissions to your home directory, and explain what the current permissions mean.

next up previous contents
Next: Some Important Files Up: File Permissions Previous: How Unix File Permissions

Del Armstrong
Fri Oct 25 16:31:41 EDT 1996