[ Thanks to Steve
Emms for this link. ]
“File permissions are an important concept to understand because
many users often share the resources of a Linux system. Sometimes a
single Linux machine might be ‘home’ to hundreds of different
users. Each user may want to stop others looking at their
files/directories, or to share data with some/all of the other
users of the systems. File permissions allow this to be possible.
These permissions ensure the ability to read or write individual
files is given to an authorised individual. Only the system
administrator (the ‘root’ account) has unrestricted access to all
the files. Having file permissions set correctly is an
important issue for a system administrator; many systems have been
compromised because of incorrectly set permissions.”
“The command, “chmod” lets you change the permission mode
settings of a file/directory. You also need to specify 3 digits
with the chmod command. These digits dictate what permissions will
be applied. The first digit determines the permissions for the
owner, the second digit determines the permissions for the group,
and the third for ‘others’.”
“To change the permissions of the file joind.ps we would
type:
chmod XYZ joind.ps , where XYZ represents 3 digits e.g. 666
The first digit is the sum of 4 for read permission, 2 for write
permission and 1 for execute permissions. So to give a file read
and execute permission the digit would be 5, for read only would be
4. The same principle applies to the second and third digits.”