In any multi-user operating system the files have a series of features that allow us to see them, modify them or execute them for users that we define. Although there are several alternatives for achieving this, GNU/Linux uses the traditional users and groups system, allowing us to configure the file permission in various ways. By executing ls -l we can list the permissions over the various files inside the directory we are in. Look at the folowing example line displayed on executing ls -l

-rwxr-xr-x 1 user1 group1 128931 Feb 19 2000 test.txt

From the above line, first 10 characters corresponds to file permissions and we concentrate on them for the same reason.
Character 1        : It tells us whether it is a file or a directory. ‘-‘ for file and ‘d’ for directory.
Characters 2,3,4: These are the so called rwx permissions i.e, read,write and execute permissions. And 2,3 and 4 characters include the Read More »