chmod ddd filename
Every mode has a
corresponding 3-digit code number: ddd
Each digit of the
mode number sets the permission for individual's access by categories in
this order:
(u=user_owner, g=group and
o=other or world)
The digits are the sum of the permission numbers for each category of
individuals:
4 = r, (read
permission)
2 = w, (write
permission)
1 = x. (execute
permission)
0 = - (no permission for this user)
The permissions granted the individuals in each category is the sum of
the permission numbers.
Example:
To set read
write execute for individuals defined as owner_user,
To
set read no-write execute for individuals in the
group
To set read no-write execute for all the
individuals in the world
The calculation is as
follows:
Sum of permissions for u: rwx
=> 4 + 2 + 1 = 7
Sum of permissions for g:
r-x => 4 + 0 + 1 = 5
Sum of permissions for
o: r-x => 4 + 0 + 1 = 5
Which makes :
755
The command to accomplish this set of file
permissions:
chmod 755
filename
Directories:
Permissions for
directories.
read
individuals can view
the directory's contents
write
individuals
can create new files or delete files in the
directory.
(Note: an
individual with write access to a directory
can
delete files in the
directory even without write
permissions
for the
file.)
execute
individual can cd
into the directory.
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