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Reading permissions
This is a simple tutorial for any newbie to the asus Wl-700 community
How to read permissions on a Linux system
You will find as you dabble with the linux system a confusion of numbers assigned to change permissions and then the permissions write out in the form rwx rwx rwx owner user etc.....
Assignment values are 4 for read, 2 for write and 1 for execute.
so if you wanted to only have the user of a file execute it
the command you will use will be 700
giving u rwx --- --- owner users filename as the out put.
Below the make up of assigned numbers and then use the chmod command
rwx rwx rwx
4+2+1 4+2+1 4+2+1
7 7 7
;)
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Better (?) would be
Personally I prefer NOT to use the XXX (e.g. 755) syntax, as you might overwrite permission flags that already were fine as they were... Besides calculation failures might happen.. :(
The chmod command allows you to use a (from my point if view) better syntax which allows better reading and setting delta's (see the examples below for more clarity)
chmod [who][operator][permission] file/directory
(More syntaxes are possible but I wanted to keep it "simple" at first)
Who:
u User
g Group
o Other
a All
Operator:
- Take away permissions
+ Add permissions
= Assign permissions absolutely
Permission:
r read permission
w write permission
x execute permission
(And the special permissions that need a bit more knowledge:
l mandatory locking
s user or group set-ID
t sticky bit
X execute permission if the file is a directory or if there is execute
permission for one of the other user classes)
So if you want to give your mp3 files a read permission for the user (owner) without changing the other permissions you would do something like:
chmod u+r *.mp3
To remove write for Other:
chmod o-w *.mp3
To remote read/write/execute for other:
chmod o-rwx *.mp3
To add read/write for user/group and add read for other:
chmod ug+rw,o+r *.mp3
To SET (removes permissions when not in set) read/write for user/group and read for other:
chmod ug=rw,o=r *.mp3
For clarity, a chmod 770 would be:
chmod ug=rwx,o= *.mp3
and a cgmod 775 would be:
chmod ug=rwx,o=rx *.mp3
BETTER would be the following, as an execute bit on the mp3 doesn't make sense and it would only set the execute when it's a directory or already have it:
chmod ug=rwX,o=rX *.mp3
How this doesn't confuse some people, but calculating bits... I find it old fashioned!
Anyway, there is always the man page (man chmod) which will help too!! :p