Safe Mode is a diagnostic mode used by certain computer operating systems such as Microsoft Windows, Mac OS X and other complex electronic devices. While the computer is in safe mode, it will have reduced functionality, but it is easier to isolate problems because many non-core components are disabled. A computer that will only boot into its safe mode typically has a major problem, such as disk corruption or the installation of poorly configured software that prevents the computer from successfully booting into its normal operating mode.
Though it varies by operating system, typically safe mode loads as few executable modules as possible and usually disables devices except for the minimum necessary to display information and accept input. Safe mode can also take the form of a parallel "miniature" operating system which has no configuration information shared with the normal operating system. For example, on the Microsoft Windows operating system the user can choose to boot to the command console, a small text-based troubleshooting mode kept separate from the main operating system (and can also be accessed by booting the install CD), or to various "safe mode" options that run the dysfunctional operating system but with features such as video drivers and networking disabled.
Safe mode typically provides access to utility and diagnostic programs so a user can troubleshoot what is preventing the computer from operating normally. Safe mode is not intended to be functional and provides minimal access to features which often frustrates users who are only aware that their computer "isn't working right".
To access safe mode in Windows, hold down the F8 key while booting. An equivalently minimal setting in Linux is called single-user mode, in which daemons and X11 are not started and only the root user can log in. On Mac OS versions 7, 8 and 9, a similar mode is achieved by holding down the shift key while booting, which starts the system without extensions. Safe mode with networking, one of the variations of safe mode can be used to troubleshoot network issues.
Safe Mode is also a mode in PHP with stricter security measures. It can be switched on or off.
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