Permission
Groups
Each file and
directory has three user based permission groups:
owner
- The Owner permissions apply only the owner of the file or
directory, they will not impact the actions of other users.
group
- The Group permissions apply only to the group that has been
assigned to the file or directory, they will not effect the actions
of other users.
- all
users
- The All Users permissions apply to all other users on the system,
this is the permission group that you want to watch the most.
Permission
Types
Each file or
directory has three basic permission types:
You can view the access permissions of a file by doing the long
directory listing with the ls -l
command
What does the output of ls -l mean?
The very first column, the one that looks like a bunch of shows the
file type and permissions. The second column shows the number of
links (directory entries that refer to the file), the third one shows
the owner of the file, and the fourth one shows the group the file
belongs to. The other columns show the file's size in bytes, date and
time of last modification, and the filename.
The first column is organized into four separate groups, although
it certainly doesn't look very organized.
The first group consists of only one
character and it can be any of these:
d = directory
-
= regular file
l = symbolic link
s
= Unix domain socket
p = named pipe
c
= character device file
b = block device file
The next nine characters show the
file's permissions, divided into three groups, each consisting of
three characters.
The first group of three
characters shows the read, write, and execute permissions for user,
the owner of the file.
The next group shows the read,
write, and execute permissions for the group of
the file.
Similarly, the last group of three
characters shows the permissions for other, everyone
else.
In each group, the first character
means the read permission, the second one write permission,
and the third one execute permission.
The characters are pretty easy to remember.
r = read permission
w = write
permission
x = execute permission
-
= no permission
As you already noticed, dir
is a directory, because the first column begins with a d.
The owner of this directory is user
fabien
and the group owner is users.
The first three characters, rwx,
indicate the directory's owner, fabien
in this case, has full access to the directory. The user
fabien
is able to access, view, and modify the files in that
directory.
The next three characters, r-x,
indicate that all users belonging to group users
have read and execute permissions to the directory. They can
change into the directory, execute files, and view its contents.
However, because they don't have write permissions, they can't make
any changes to the directory content.
Finally, the last three characters,
r-x,
indicate that all the users who are not fabien
or don't belong into group users,
have read and execute permissions in the directory.
How to set file
permissions - numeric mode
You can set file permissions with the chmod
command. Both the root user and the file's owner can set file
permissions. Chmod
In the numeric mode, the file permissions aren't represented by
characters. Instead, they are represented by a three-digit octal
number.
4 = read (r)
2 = write (w)
1
= execute (x)
0 = no permission (-)
Let's have an example.
The highlight line you can see the file
have full access to the owner,group and others.
when command # chmod 754 test1
entered
The permission has been changed and now
the owner have ull read, write, and execute permissions (4+2+1 = 7
) ----- 7
The
group would have read and execute permissions (4+0+1=5)
-----5
The
others would have only read permissions as well(4+0+0=4)
-----4
| rwx |
7 |
| rw |
6 |
| r-x |
5 |
| r-- |
4 |
| -wx |
3 |
| -w- |
2 |
| --x |
1 |
| --- |
0 |
