chmod command
(change file permissions)
The chmod command is used to change access permissions
to files and directories.
The format is chmod permissions filename
> chmod 755 file.txt
To see what permissions a file or directory has in linux, you use the ls command with option -l (eg: ls -l) which gives a long format listing.
> ls -l
-rwxr--r-- 1 root root 765 Apr 23 09:22 file.txt
The permissions are the first 10 characters of the line (-rwxrwx---) and can be broken down as follows.
- |
rwx |
r-- |
r-- |
1 |
root |
root |
765 |
Apr 23 |
file.txt |
File type |
Owner |
Group |
All |
Links |
Owner |
Group |
Size |
Mod date |
Filename |
The r,w and x stand for...
r = read
w = write
x = execute
The first character on the line shows what type
of file or directory it is, and can be one of these things...
- = file
d = directory
l = symbolic link
b = block-type special file
c = character-type special file
p = named pipe
S = socket
s = XENIX semaphore
m = XENIX shared data (memory) file
D = Solaris door
n = HP-UX network special file
The remaining 9 characters are broken down into 3 groups of 3 characters. The first three are the permissions for the owner, the middle three are permissions for the group which has access to the file and the last three are the permissions for everybody else.