you might have found that sometimes you can’t -for example- copy (or write) files into X directory when you’re using your user
but at the same time you can copy files into the same X directory using the “root” user
so how do i get the permission for writing in X using any user … not root only!!
well …
have you ever wrote “ls -l” command???
if you’ve done so, have you noticed the first column of the output?!
it may look like this:
-rwxrwxrwx
1) the first (-) represent the file type, so if it’s like that (-) you’ll know that this is a file
and if it is (d), it’s a Directory
and (l) stands for Link
there are more letters but these are the most important ones
2) then the next 9 letters represent 3 partitions, they are: OWNER (u), GROUP (g), OTHER (o) respectively
each of them consists of 3 letters: rwx
r=read (access to read files)
w=write (access to write into files)
x=execute (access to run files)
let me give a simple example for using permissions:
suppose that “boody“, “3abed“, “didooofidooo” are members in a group named “group1“
and “Hunikal” & “noor” are in “group2“
“boody” created a file, then he found that the permission is -rw-rw-r–
ok what does this actually mean?!
1) this means that this is a normal file (this is why (-) is there)
2) and the owner of the file (boody) can read the file and also write into it
3) and the owner’s group (group1) can also read and write into the file, this means that “3abed” and “didooofidooo” can also read-write into this file, as they’re in the same group (group1)
3)then we’ll find that “Hunikal” and “noor” can only read the file but not write into it, as they are not the “OWNER” or in the “owner’s GROUP”, so they are from “OTHERS”
Changing Permissions
there are two ways for changing permissions
both can be done using “chmod” command
1)Char Method
if you want to change the permission of a file named “Perm” from -rwxr-xr-x to -rw-rw-r-x
we can see that we only have to change the owner’s permission (u) from rwx to rw- so we’ll use the following command
#chmod u-x Perm
then change the group’s permission (g) from r-x to rw- so we’ll use the follwing command
#chmod g-w+x Perm
actually we could change this in only one command
#chmod u-x,g-w+x Perm
2)Numeric Method
we have three primary numbers:
4, 2 and 1
4 adds r permission (read permission)
2 adds w permission (write permission)
1 adds x permission (execute permission)
so you can change a file’s permission from -rwxr-xr-x to -rw-rw-r-x using the following command
#chmod 665 file_name
6=4+2=rw-
5=4+1=r-x
so we can give a -rwxrwxrwx permission using the following command
#chmod 777 file_name
umask
from wikipedia:
umask (abbreviated from user mask) is a command and a function in POSIX environments which set the default permission modes for newly created files and directories of the current process
you can know your umask using “umask” command:
#umask
the most important thing you need to know about umask is that:
permission = 777 – umask
so if your umask equals 0022, your files’ permissions will be 777-022=755
and this means when you create a file you’ll find the file’s permission is -rwxr-xr-x (755)
changing umask
you can change the umask (for example: to 023) using “umask” command:
#umask 023
but when you restart your computer, you’ll find that the umask returned to it’s old value
so we have to edit /etc/bashrc file
#vi /etc/bashrc
and change the umask value then save the file
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that’s all
thanQ
bye
