So, in order to read a file, you must have execute permission on the directory containing that file, and hence on any directory containing that directory as a subdirectory, and so on, up the tree. Some examples -rwxrwxrwx a file that everyone can read, write and execute. Only the owner of a file can use chmod to change the permissions of a file. A process may be in the foreground, in the background, or be suspended. In general the shell does not return the UNIX prompt until the current process has finished executing.
Some processes take a long time to run and hold up the terminal.
Backgrounding a long process has the effect that the UNIX prompt is returned immediately, and other tasks can be carried out while the original process continues executing. For example, the command sleep waits a given number of seconds before continuing. Until the command prompt is returned, you can do nothing except wait. Backgrounding is useful for jobs which will take a long time to complete. 5.4 Listing suspended and background processes When a process is running, backgrounded or suspended, it will be entered onto a list along with a job number.