On Unix and Linux systems, you would use the chmod utility to set permissions values on files and directories. You can set permissions for the user of the file or directory, the group that's associated with the file or directory, and others. The three basic permissions are:

• r: This indicates a read permission.
• w: This is for a write permission.
• x: This is the executable permission. You can apply it to any type of program file, or to directories. If you apply an executable permission to a directory, authorized people will be able to cd into it.

Do an ls -l on a file, and you'll see something like this:

-rw-rw-r--. 1 donnie donnie     804692 Oct 28 18:44 yum_list.txt

The first character of this line indicates the type of file. In this case, we see a dash, which indicates a regular file. (A regular file is pretty much every type of file that a normal user would be able to access in his or her daily routine.) The next three characters, rw-, indicate that the file has read and write permissions for the user, which is the person who owns the file. We then see rw- permissions for the group, and r-- permissions for others. A program file would also have the executable permissions set:

-rwxr-xr-x. 1 root root     62288 Nov 20  2015 xargs

Here, we see that the xargs program file has executable permissions set for everybody.

There are two ways that you can use chmod to change permissions settings:

• The symbolic method
• The numerical method