CHMOD
CHMOD is a command for controlling Unix File Permissions. It lets you tell the system how much (or little) access it should permit to a file.
All of your files and directories have a number of attributes that are set when
they are created. To display the attributes of each file and directory in the
working directory use the "ls -la" command in your shell account. Here is an
example listing:
[user@linux sites]$ ls -la
drwxr-xr-x 16 root root 1024 Oct 20 19:56 .
drwxr-xr-x 9 root root 1024 Sep 5 22:56 ..
drwxr-xr-x 9 foo user 1024 Sep 5 22:56 dir1
drwxr-xr-x 9 foo user 1024 Sep 5 22:56 dir2
drwxr-xr-x 9 foo user 1024 Sep 5 22:56 dir3
-rw-r--r-- 9 foo user 1024 Sep 5 22:56 file1
-rw-r--r-- 9 foo user 1024 Sep 5 22:56 file2
-rw-r--r-- 9 foo user 1024 Sep 5 22:56 file3
To the far left of each file or directory name there are ten characters which
show the attributes. The first column indicates whether the entry is a directory
(d) or not (-). The other nine characters are
organized into three groups of the three.
(drwxr-xr-x) The first group pertains to
the owner (that would be you for your files).
(drwxr-xr-x) The second group pertains to
people in your group.
(drwxr-xr-x) The third group pertains to
everyone else.
Within each group of three are three characters. The first indicates read (r)
permission. The second indicates write (w) permission. The third
indicates execute (x) permission. If the permission is not present, a
``- will replace the r, w, or x.
To perform a chmod change on a file you can either do it through your shell
account or through an FTP client.
Shell
chmod mode filename
where mode is a three digit octal number. The first digit pertains to
the owners privileges. The second pertains to the groups privileges, and the
third pertains to everyone else's privileges. Each octal digit is composed of
the addition of three components. The read component is worth 4, the write
component worth 2, and the execute component worth 1. Suppose I wanted the owner
to have read, write, and execute privileges, the group to have read and write
privileges, and everyone else to have read privileges only. The octal number I
would use with chmod would be 764.
See Also
- UNIX commands
- Environment Setup
- Unix account setup
- SSH
- Shell
- Unix File Permissions
- Unix File Permissions Cookbook
- Unix Groups
