What Are Run Levels in UNIX/Linux?

What are run levels in UNIX/Linux? Related posts:How to Check OS Type and Kernel Patch Levels for AIX/Linux/Solaris? How to Unzip and Extract Tar File in Single Command in UNIX and Linux How to Automatically Set the $DISPLAY Variable for Current Session in UNIX/Linux… Related posts:

1. How to Check OS Type and Kernel Patch Levels for AIX/Linux/Solaris?
2. How to Unzip and Extract Tar File in Single Command in UNIX and Linux
3. How to Automatically Set the $DISPLAY Variable for Current Session in UNIX/Linux…