Safe mode

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The safe mode popup in Windows NT 4.0.

Safe mode is a diagnostic mode used by certain computer operating systems, including Microsoft Windows and Mac OS X, as well as other complex electronic devices. While an operating system is in safe mode, it will have reduced functionality, but it is easier to isolate problems because many non-core components are disabled. An installation 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 operating system 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 that has no configuration information shared with the normal operating system. For example, on Microsoft Windows, the user can choose to boot to the recovery 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 operating system from working normally. Safe mode is intended for maintenance, not functionality, and provides minimal access to features which often frustrates users who are only aware that their computer "isn't working right".

Safe mode is a troubleshooting method on most electronic devices, including cell phones and interplanetary spacecraft ^[1] which often run VxWorks.

Safe mode in Microsoft Windows is accessed by repeatedly pressing the "F8" key as the operating system boots (Microsoft's official website for Windows XP simply advises users to press "F8" once,[1] but in practice the exact moment at which to press the key can vary from computer to computer, so it is better to repeatedly press the key at one second intervals). Also, in a multi-boot environment with multiple versions of Windows installed side by side, one can press F8 at the OS selector prompt to get to Safe mode.

An equivalently minimal setting in UNIX-like operating systems is single-user mode, in which daemons and the X Window System are not started, and only the root user can log in. On Mac OS versions 6, 7, 8 and 9, a similar mode is achieved by holding down the shift key while booting, which starts the system without extensions. In Mac OS X holding the shift key after powering up puts the system in safe mode. Safe mode with networking, one of the variations of safe mode, can be used to troubleshoot network issues.

Application software sometimes offers a safe mode as well. In the PHP interpreter, safe mode offers stricter security measures. Mozilla Firefox's safe mode allows the user to remove extensions which may be preventing the browser from loading.