| Developer(s) | Apple Inc. |
|---|---|
| Initial release | July 25, 2012 |
| Operating system | macOS |
Paths set in /etc/paths are added to the PATH at startup in all shells on Mac OS X. /.bashprofile is just one of several shell scripts run by Bash at startup, and several of these are Bash-specific. Therefore, if you change your shell — Mac OS X also ships tcsh and zsh, for example — changes made to /etc/bashrc don't apply to your new shell. PATH is an infrastructure solutions company focused on helping government entities identify, develop, and implement solutions that leverage today's technology to create better efficiencies in the areas of energy, water, and operations. Our team stands ready to serve as your partner today. You need to use the command echo $PATH to display the PATH variable or you can just execute set or env to display all of your environment variables. By typing $PATH you tried to run your PATH variable contents as a command name. Bash displayed the contents of your path any way.
Gatekeeper is a security feature of the macOSoperating system by Apple.[1][2] It enforces code signing and verifies downloaded applications before allowing them to run, thereby reducing the likelihood of inadvertently executing malware. Gatekeeper builds upon File Quarantine, which was introduced in Mac OS X Leopard and expanded in Mac OS X Snow Leopard.[3][4] The feature originated in version 10.7.3 of Mac OS X Lion as the command-line utilityspctl.[5][6] A graphical user interface was added in OS X Mountain Lion and later also in version 10.7.5 of Lion.[7]
Functions[edit]
Configuration[edit]
In the security & privacy panel of System Preferences, the user has three options:
- Mac App Store
- Allows only applications downloaded from the Mac App Store to be launched.
- Mac App Store and identified developers
- Allows applications downloaded from the Mac App Store and applications signed by certified Apple developers to be launched. This is the default setting since Mountain Lion.
- Anywhere
- Allows all applications to be launched. This effectively turns Gatekeeper off. This is the default setting in Lion. Since macOS Sierra, this option is hidden by default.[8][9]
- However, this option can be re-enabled by using the 'sudo spctl --master-disable' command from the Terminal and authenticating with an admin password.
The command-line utility spctl provides granular controls, such as custom rules and individual or blanket permissions, as well as an option to turn Gatekeeper off.[6]
Quarantine[edit]
Upon download of an application, a particular extended file attribute ('quarantine flag') can be added to the downloaded file.[10] This attribute is added by the application that downloads the file, such as a web browser or email client, but is not usually added by common BitTorrent client software, such as Transmission, and application developers will need to implement this feature into their applications and is not implemented by the system. The system can also force this behavior upon individual applications using a signature-based system named Xprotect.[11]
Execution[edit]
When the user attempts to open an application with such an attribute, the system will postpone the execution and verify whether it is:
- blacklisted,
- code-signed by Apple or a certified developer,
- the code-signed contents still match the signature.
Since Mac OS X Snow Leopard, the system keeps two blacklists to identify known malware or insecure software. The blacklists are updated periodically. If the application is blacklisted, then File Quarantine will refuse to open it and recommend to the user to move it to trash.[11][12]
Gatekeeper will refuse to open the application if the code-signing requirements are not met. Apple can revoke the developer's certificate with which the application was signed and prevent further distribution.[1][3]
Once an application has passed File Quarantine or Gatekeeper, it will be allowed to run normally and will not be verified again.[1][3]
Override[edit]
To override Gatekeeper, the user (acting as an administrator) either has to switch to a more lenient policy from the security & privacy panel of System Preferences or authorize a manual override for a particular application, either by opening the application from the context menu or by adding it with spctl.[1]
Path randomization[edit]
Developers can sign disk images that can be verified as a unit by the system. In macOS Sierra, this allows developers to guarantee the integrity of all bundled files and prevent attackers from infecting and subsequently redistributing them. In addition, 'path randomization' executes application bundles from a random, hidden path and prevents them from accessing external files relative to their location. This feature is turned off if the application bundle originated from a signed installer package or disk image or if the user manually moved the application without any other files to another directory.[8]
Implications[edit]
The effectiveness and rationale of Gatekeeper in combating malware have been acknowledged,[3] but been met with reservations. Security researcher Chris Miller noted that Gatekeeper will verify the developer certificate and consult the known-malware list only when the application is first opened. Malware that already passed Gatekeeper will not be stopped.[13] In addition, Gatekeeper will only verify applications that have the quarantine flag. As this flag is added by other applications and not by the system, any neglect or failure to do so does not trigger Gatekeeper. According to security blogger Thomas Reed, BitTorrent clients are frequent offenders of this. The flag is also not added if the application came from a different source, like network shares and USB flash drives.[10][13] Questions have also been raised about the registration process to acquire a developer certificate and the prospect of certificate theft.[14]
In September 2015, security researcher Patrick Wardle wrote about another shortcoming that concerns applications that are distributed with external files, such as libraries or even HTML files that can contain JavaScript.[8] An attacker can manipulate those files and through them exploit a vulnerability in the signed application. The application and its external files can then be redistributed, while leaving the original signature of the application bundle itself intact. As Gatekeeper does not verify such individual files, the security can be compromised.[15] With path randomization and signed disk images, Apple provided mechanisms to mitigate this issue in macOS Sierra.[8]
See also[edit]
References[edit]
- ^ abcd'OS X: About Gatekeeper'. Apple. February 13, 2015. Retrieved June 18, 2015.
- ^Siegler, MG (February 16, 2012). 'Surprise! OS X Mountain Lion Roars Into Existence (For Developers Today, Everyone This Summer)'. TechCrunch. AOL Inc. Retrieved March 3, 2012.
- ^ abcdSiracusa, John (July 25, 2012). 'OS X 10.8 Mountain Lion: the Ars Technica review'. Ars Technica. pp. 14–15. Archived from the original on March 14, 2016. Retrieved June 17, 2016.
- ^Reed, Thomas (April 25, 2014). 'Mac Malware Guide : How does Mac OS X protect me?'. The Safe Mac. Retrieved October 6, 2016.
- ^Ullrich, Johannes (February 22, 2012). 'How to test OS X Mountain Lion's Gatekeeper in Lion'. Internet Storm Center. Retrieved July 27, 2012.
- ^ ab'spctl(8)'. Mac Developer Library. Apple. Retrieved July 27, 2012.
- ^'About the OS X Lion v10.7.5 Update'. Apple. February 13, 2015. Retrieved June 18, 2015.
- ^ abcd'What's New in Security'. Apple Developer (Video). June 15, 2016. At 21:45. Retrieved June 17, 2016.
- ^Cunningham, Andrew (June 15, 2016). 'Some nerdy changes in macOS and iOS 10: RAW shooting, a harsher Gatekeeper, more'. Ars Technica UK. Archived from the original on June 16, 2016. Retrieved June 17, 2016.
- ^ abReed, Thomas (October 6, 2015). 'Bypassing Apple's Gatekeeper'. Malwarebytes Labs. Retrieved June 17, 2016.
- ^ abMoren, Dan (August 26, 2009). 'Inside Snow Leopard's hidden malware protection'. Macworld. Retrieved September 30, 2016.
- ^'About the 'Are you sure you want to open it?' alert (File Quarantine / Known Malware Detection) in OS X'. Apple Support. March 22, 2016. Archived from the original on June 17, 2016. Retrieved September 30, 2016.
- ^ abForesman, Chris (February 17, 2012). 'Mac developers: Gatekeeper is a concern, but still gives power users control'. Ars Technica. Retrieved June 18, 2015.
- ^Chatterjee, Surojit (February 21, 2012). 'OS X Mountain Lion Gatekeeper: Can it Really Keep Malware Out?'. International Business Times. Retrieved March 3, 2012.
- ^Goodin, Dan. 'Drop-dead simple exploit completely bypasses Mac's malware Gatekeeper'. Ars Technica. Archived from the original on March 20, 2016. Retrieved June 17, 2016.
Forms of energy
There are many different types of energy, which all fall into two primary forms – kinetic and potential. Energy can transform from one type to another, but it can never be destroyed or created.
What are the different types of energy?
Types of energy can be categorised into two broad categories – kinetic energy (the energy of moving objects) and potential energy (energy that is stored). These are the two basic forms of energy. The different types of energy include thermal energy, radiant energy, chemical energy, nuclear energy, electrical energy, motion energy, sound energy, elastic energy and gravitational energy.
Thermal (Heat) Energy
Thermal energy is created from the vibration of atoms and molecules within substances. The faster they move, the more energy they possess and the hotter they become. Thermal energy is also called heat energy.
Let's go! >Chemical Energy
Chemical energy is stored in the bonds of atoms and molecules – it is the energy that holds these particles together. Stored chemical energy is found in food, biomass, petroleum, and natural gas.
Let's go! >Nuclear Energy
Nuclear energy is stored in the nucleus of atoms. This energy is released when the nuclei are combined (fusion) or split apart (fission). Nuclear power plants split the nuclei of uranium atoms to produce electricity.
Let's go! >Electrical Energy
Electrical energy is the movement of electrons (the tiny particles that makeup atoms, along with protons and neutrons). Electrons that move through a wire are called electricity. Lightning is another example of electrical energy.
Let's go! >Radiant Energy
Also known as light energy or electromagnetic energy, radiant energy is a type of kinetic energy that travels in waves. Examples include the energy from the sun, x-rays, and radio waves.
Let's go! >Light Energy
Light energy is a form of electromagnetic radiation. Light consists of photons, which are produced when an object's atoms heat up. Light travels in waves and is the only form of energy visible to the human eye.
Let's go! >Motion Energy
Motion energy – or mechanical energy – is the energy stored in objects; as objects move faster, more energy is stored. Examples of motion energy include wind, a flowing river, a moving car, or a person running.
Let's go! >Sound Energy
Sound energy is the movement of energy through substances. It moves in waves and is produced when a force makes an object or substance vibrate. There is usually much less energy in sound than in other forms of energy.
Configuration[edit]
In the security & privacy panel of System Preferences, the user has three options:
- Mac App Store
- Allows only applications downloaded from the Mac App Store to be launched.
- Mac App Store and identified developers
- Allows applications downloaded from the Mac App Store and applications signed by certified Apple developers to be launched. This is the default setting since Mountain Lion.
- Anywhere
- Allows all applications to be launched. This effectively turns Gatekeeper off. This is the default setting in Lion. Since macOS Sierra, this option is hidden by default.[8][9]
- However, this option can be re-enabled by using the 'sudo spctl --master-disable' command from the Terminal and authenticating with an admin password.
The command-line utility spctl provides granular controls, such as custom rules and individual or blanket permissions, as well as an option to turn Gatekeeper off.[6]
Quarantine[edit]
Upon download of an application, a particular extended file attribute ('quarantine flag') can be added to the downloaded file.[10] This attribute is added by the application that downloads the file, such as a web browser or email client, but is not usually added by common BitTorrent client software, such as Transmission, and application developers will need to implement this feature into their applications and is not implemented by the system. The system can also force this behavior upon individual applications using a signature-based system named Xprotect.[11]
Execution[edit]
When the user attempts to open an application with such an attribute, the system will postpone the execution and verify whether it is:
- blacklisted,
- code-signed by Apple or a certified developer,
- the code-signed contents still match the signature.
Since Mac OS X Snow Leopard, the system keeps two blacklists to identify known malware or insecure software. The blacklists are updated periodically. If the application is blacklisted, then File Quarantine will refuse to open it and recommend to the user to move it to trash.[11][12]
Gatekeeper will refuse to open the application if the code-signing requirements are not met. Apple can revoke the developer's certificate with which the application was signed and prevent further distribution.[1][3]
Once an application has passed File Quarantine or Gatekeeper, it will be allowed to run normally and will not be verified again.[1][3]
Override[edit]
To override Gatekeeper, the user (acting as an administrator) either has to switch to a more lenient policy from the security & privacy panel of System Preferences or authorize a manual override for a particular application, either by opening the application from the context menu or by adding it with spctl.[1]
Path randomization[edit]
Developers can sign disk images that can be verified as a unit by the system. In macOS Sierra, this allows developers to guarantee the integrity of all bundled files and prevent attackers from infecting and subsequently redistributing them. In addition, 'path randomization' executes application bundles from a random, hidden path and prevents them from accessing external files relative to their location. This feature is turned off if the application bundle originated from a signed installer package or disk image or if the user manually moved the application without any other files to another directory.[8]
Implications[edit]
The effectiveness and rationale of Gatekeeper in combating malware have been acknowledged,[3] but been met with reservations. Security researcher Chris Miller noted that Gatekeeper will verify the developer certificate and consult the known-malware list only when the application is first opened. Malware that already passed Gatekeeper will not be stopped.[13] In addition, Gatekeeper will only verify applications that have the quarantine flag. As this flag is added by other applications and not by the system, any neglect or failure to do so does not trigger Gatekeeper. According to security blogger Thomas Reed, BitTorrent clients are frequent offenders of this. The flag is also not added if the application came from a different source, like network shares and USB flash drives.[10][13] Questions have also been raised about the registration process to acquire a developer certificate and the prospect of certificate theft.[14]
In September 2015, security researcher Patrick Wardle wrote about another shortcoming that concerns applications that are distributed with external files, such as libraries or even HTML files that can contain JavaScript.[8] An attacker can manipulate those files and through them exploit a vulnerability in the signed application. The application and its external files can then be redistributed, while leaving the original signature of the application bundle itself intact. As Gatekeeper does not verify such individual files, the security can be compromised.[15] With path randomization and signed disk images, Apple provided mechanisms to mitigate this issue in macOS Sierra.[8]
See also[edit]
References[edit]
- ^ abcd'OS X: About Gatekeeper'. Apple. February 13, 2015. Retrieved June 18, 2015.
- ^Siegler, MG (February 16, 2012). 'Surprise! OS X Mountain Lion Roars Into Existence (For Developers Today, Everyone This Summer)'. TechCrunch. AOL Inc. Retrieved March 3, 2012.
- ^ abcdSiracusa, John (July 25, 2012). 'OS X 10.8 Mountain Lion: the Ars Technica review'. Ars Technica. pp. 14–15. Archived from the original on March 14, 2016. Retrieved June 17, 2016.
- ^Reed, Thomas (April 25, 2014). 'Mac Malware Guide : How does Mac OS X protect me?'. The Safe Mac. Retrieved October 6, 2016.
- ^Ullrich, Johannes (February 22, 2012). 'How to test OS X Mountain Lion's Gatekeeper in Lion'. Internet Storm Center. Retrieved July 27, 2012.
- ^ ab'spctl(8)'. Mac Developer Library. Apple. Retrieved July 27, 2012.
- ^'About the OS X Lion v10.7.5 Update'. Apple. February 13, 2015. Retrieved June 18, 2015.
- ^ abcd'What's New in Security'. Apple Developer (Video). June 15, 2016. At 21:45. Retrieved June 17, 2016.
- ^Cunningham, Andrew (June 15, 2016). 'Some nerdy changes in macOS and iOS 10: RAW shooting, a harsher Gatekeeper, more'. Ars Technica UK. Archived from the original on June 16, 2016. Retrieved June 17, 2016.
- ^ abReed, Thomas (October 6, 2015). 'Bypassing Apple's Gatekeeper'. Malwarebytes Labs. Retrieved June 17, 2016.
- ^ abMoren, Dan (August 26, 2009). 'Inside Snow Leopard's hidden malware protection'. Macworld. Retrieved September 30, 2016.
- ^'About the 'Are you sure you want to open it?' alert (File Quarantine / Known Malware Detection) in OS X'. Apple Support. March 22, 2016. Archived from the original on June 17, 2016. Retrieved September 30, 2016.
- ^ abForesman, Chris (February 17, 2012). 'Mac developers: Gatekeeper is a concern, but still gives power users control'. Ars Technica. Retrieved June 18, 2015.
- ^Chatterjee, Surojit (February 21, 2012). 'OS X Mountain Lion Gatekeeper: Can it Really Keep Malware Out?'. International Business Times. Retrieved March 3, 2012.
- ^Goodin, Dan. 'Drop-dead simple exploit completely bypasses Mac's malware Gatekeeper'. Ars Technica. Archived from the original on March 20, 2016. Retrieved June 17, 2016.
Forms of energy
There are many different types of energy, which all fall into two primary forms – kinetic and potential. Energy can transform from one type to another, but it can never be destroyed or created.
What are the different types of energy?
Types of energy can be categorised into two broad categories – kinetic energy (the energy of moving objects) and potential energy (energy that is stored). These are the two basic forms of energy. The different types of energy include thermal energy, radiant energy, chemical energy, nuclear energy, electrical energy, motion energy, sound energy, elastic energy and gravitational energy.
Thermal (Heat) Energy
Thermal energy is created from the vibration of atoms and molecules within substances. The faster they move, the more energy they possess and the hotter they become. Thermal energy is also called heat energy.
Let's go! >Chemical Energy
Chemical energy is stored in the bonds of atoms and molecules – it is the energy that holds these particles together. Stored chemical energy is found in food, biomass, petroleum, and natural gas.
Let's go! >Nuclear Energy
Nuclear energy is stored in the nucleus of atoms. This energy is released when the nuclei are combined (fusion) or split apart (fission). Nuclear power plants split the nuclei of uranium atoms to produce electricity.
Let's go! >Electrical Energy
Electrical energy is the movement of electrons (the tiny particles that makeup atoms, along with protons and neutrons). Electrons that move through a wire are called electricity. Lightning is another example of electrical energy.
Let's go! >Radiant Energy
Also known as light energy or electromagnetic energy, radiant energy is a type of kinetic energy that travels in waves. Examples include the energy from the sun, x-rays, and radio waves.
Let's go! >Light Energy
Light energy is a form of electromagnetic radiation. Light consists of photons, which are produced when an object's atoms heat up. Light travels in waves and is the only form of energy visible to the human eye.
Let's go! >Motion Energy
Motion energy – or mechanical energy – is the energy stored in objects; as objects move faster, more energy is stored. Examples of motion energy include wind, a flowing river, a moving car, or a person running.
Let's go! >Sound Energy
Sound energy is the movement of energy through substances. It moves in waves and is produced when a force makes an object or substance vibrate. There is usually much less energy in sound than in other forms of energy.
Let's go! >Elastic Energy
Elastic energy is a form of potential energy that is stored in an elastic object - such as a coiled spring or a stretched elastic band. Elastic objects store elastic energy when a force causes them to be stretched or squashed.
Let's go! >Gravitational Energy
The Path Of Energy Mac Os 11
Gravitational energy is a form of potential energy. Home alone (itch) mac os. It is an energy associated with gravity or gravitational force – in other words, the energy held by an object when it is in a high position compared to a lower position.
Let's go! >What is the Law of Conservation of Energy?
While it might sound complex, the First Law of Conservation of energy simply states that energy can never be created or destroyed, but it can be transformed from one type to another.
Energy can be transformed from one form to another in different ways.
Kinetic energy is the energy of a moving object.
Potential energy is energy that is stored in an object or substance.
The Law of Conservation of energy is that energy can be transformed from one form to another, but can be neither created or destroyed. Reindeer rescue mac os.
Scp[data deleted] the game mac os. Energy Transformationssee diagram…
Os Path Split
Notice that these energy transfer examples only show the useful energy transfers. However, car engines are also noisy (sound energy) and hot (thermal energy) and electric lamps also give out heat energy.
The word energy comes from the Greek word 'energeia', meaning 'activity.
The Path Of Energy Mac Os X
The use of the word 'energy' dates all the way back to the 4th century BC.
Sunlight energy is converted into the chemical energy of glucose.
The Path Of Energy Mac Os 13
Energy comes in many different types, which can be categorised into two basic forms – kinetic and potential. Energy can never be created or destroyed, but it can be transformed from one type of energy to another.
