chmod [options] mode files
Changes the access permissions.
The mode parameter has three parts: group, access, and access type. group accepts
the following characters:
u
User
g
Group
o
Others
For access, grant access with + and deny it with -.
The access type is controlled by the following options:
r
Read
w
Write
x
Execute—executing les or changing to the directory
s
Setuid bit—the application or program is started as if it were started by the
owner of the le
As an alternative, a numeric code can be used. The four digits of this code are
composed of the sum of the values 4, 2, and 1—the decimal result of a binary
mask. The rst digit sets the set user ID (SUID) (4), the set group ID (2), and the
sticky (1) bits. The second digit denes the permissions of the owner of the le.
The third digit denes the permissions of the group members and the last digit
sets the permissions for all other users. The read permission is set with 4, the
write permission with 2, and the permission for executing a le is set with 1. The
owner of a le would usually receive a 6 or a 7 for executable les.
gzip [parameters] files
This program compresses the contents of les using complex mathematical algo-
rithms. Files compressed in this way are given the extension .gz and need to be
uncompressed before they can be used. To compress several les or even entire
directories, use the tar command.
-d
Decompresses the packed gzip les so they return to their original size and
can be processed normally (like the command gunzip)
108 Start-Up
