Explore the core architecture of the operating system, including the kernel, memory management, and process scheduling.

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Does iOS Automatically Reconnect to Disconnected BLE Devices, or Is It App-Driven?
Does iOS Automatically Reconnect to Disconnected BLE Devices, or Is It App-Driven? I have a few questions regarding BLE device reconnections in iOS: When a BLE device gets disconnected, does iOS automatically attempt to reconnect to it, or is it the app’s responsibility to handle the reconnection logic? If the app doesn’t initiate a BLE scan, will the OS still attempt to reconnect to previously paired devices, or is manual intervention by the app necessary? What is the recommended approach to re-establish a BLE connection when: The app has been deleted. The BLE device remains connected in the iPhone's Bluetooth settings. The app is reinstalled later. Any insights or best practices would be greatly appreciated!
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Nested Hyper-V Support for VM's
Hello! I am wondering about the status of Nested Hyper-V Support for VM's? This is specifically regarding this issue with Parallels Desktop, which claims the issue is on Apple's side: Parallels Article: https://kb.parallels.com/en/116239 Within the Article, the no longer accessible previous Apple discussion post for this issue (at least I cannot access it): https://discussions.apple.com/thread/255546412 Is this something that will be fixed and supported soon? Thank you! (If this should be posted somewhere else please just let me know where!)
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Writing to /Library/Application Support
I have seen these 2 articles that I have attached below that seem to offer some assistance. But is there a more modern way to share secured information between macOS users on same machine? Entitlements File System Protections STEPS TO REPRODUCE do { let baseDir = try fileMgr.url(for: .applicationSupportDirectory, in: .localDomainMask, appropriateFor: nil, create: true).appendingPathComponent("com.MyCompany.AppName", conformingTo: .directory) try fileMgr.createDirectory(at: baseDir, withIntermediateDirectories: true, attributes: nil) } catch { Swift.print("ERROR: can't create baseDir \(baseDir)") exit(0) }
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Oct ’24
iOS Application Bluetooth Permission
Is it possible for the Bluetooth permissions of an app to be turned off due to changes in the iOS application's Bluetooth library, possibly because of Apple's security requirements or OS-related factors? There are two applications, Application A and Application B, that control Bluetooth devices. Application A uses a third-party Bluetooth library to control the Bluetooth devices. Application B also uses a third-party Bluetooth library to control the Bluetooth devices. The Bluetooth libraries used by Application A and Application B are different, but both applications work without any issues. However, when the Bluetooth library used in Application B was changed to the one used in Application A, the Bluetooth permissions for Application B sometimes turned off. Since Application A and Application B operate without any issues on their own, we believe the problem is not with the Bluetooth libraries themselves. Given the above situation, is it possible that changing the Bluetooth library used could cause the Bluetooth permissions of the app to be turned off due to Apple's security requirements or OS-related factors?
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Developing a driver to read HFS disks on MacOS Sonoma and newer
Capability to read and write ofd HFS disks on Mac has been removed since a long time. Capability to simply read was also removed since Catalina I think. That is surprising and sometimes frustrating. I still use a 90's MacBook for a few tasks and need from time to time to transfer files to newer Mac or read some old files stored on 3.5" disks. Solution I use is to read the disk on an old Mac with MacOS 10.6 (I'm lucky enough to have kept one) and transfer to USB stick or airdrop… As there is no USB port on the Macbook of course (and I have no more a working 56k modem to transfer by mail), only option if not 3,5" disk is using PCMCIA port on the MacBook for writing to an SD Card to be read in Mac Sonoma. But reading directly 3.5" disk would be great. Hence my questions for the forum: how hard would it be to write such a driver for READING only HFS on Mac Sonoma? There are some software like FuseHFS. Did anyone experience it ? Did anyone have a look at the source code (said to be open source). does anyone know why Apple removed such capability (I thought it was a tiny piece of code compared to the GB of present MacOS)? Thanks for any insights on the matter.
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APFS snapshot revert
I'm trying to restore an APFS volume to its previous state using a snapshot created with the tmutil command. The only native Apple tool I've found for this purpose is apfs.util. According to the documentation, the correct command for this task is /System/Library/Filesystems/apfs.fs/Contents/Resources/apfs.util -R </dev/diskXsY>. However, this command is not working for me. It returns the error "No such file or directory" for any existing . If I use a valid file/dir path instead of the as an experiment, I get an "Invalid argument" error. To investigate the issue, I decided to debug apfs.util and found that the fsctl() function is responsible for these errors (ENOENT and EINVAL). The first argument passed to fsctl() is the (or file/dir path in my experiment), and the second argument is the value 0x80084A01, which corresponds to the APFSIOC_REVERT_TO_SNAPSHOT command according to xnu's source code (https://github.com/apple-oss-distributions/xnu/blob/8d741a5de7ff4191bf97d57b9f54c2f6d4a15585/bsd/vfs/vfs_syscalls.c#L174). It seems that this command is not supported by the latest versions of macOS (see https://github.com/apple-oss-distributions/xnu/blob/8d741a5de7ff4191bf97d57b9f54c2f6d4a15585/bsd/vfs/vfs_syscalls.c#L12984) and always returns EINVAL error. Is this correct? Are there any other tools available that can be used to revert APFS snapshots?
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Memory leak when using OSLogStore in a loop
Hello, I am currently working on a project that involves periodically querying OSLog to forward system log entries to a backend. While the functionality generally operates as expected, I have encountered a memory leak in my application. Through testing, I have isolated the issue to the following simplified code example: #import <Foundation/Foundation.h> #import <OSLog/OSLog.h> int main(int argc, const char * argv[]) { @autoreleasepool { while(1) { NSError *error = nil; OSLogStore *logStore = [OSLogStore storeWithScope:OSLogStoreSystem error:&error]; if (!logStore) NSLog(@"Failed to create log store: %@", error); sleep(1); } } return 0; } When running this example, the application exhibits increasing memory usage, consuming an additional 100 to 200 KB per iteration, depending on whether the build is Debug or Release. Given that Automatic Reference Counting is enabled, I anticipated that the resources utilized by logStore would be automatically released at the end of each iteration. However, this does not appear to be the case. Am I using the API wrong? I would appreciate any insights or suggestions on how to resolve this issue. Thank you.
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Kernel Panic after update of macOS
Hi I have some problems with my macOS after updating to Sonoma. I am running a intel based MacBookPro 2018. After update to Sonoma I had some Kernel panic. Log attached. Also I had some problems running my LaunchDaemon for starting macFUSE and connecting to SSHFS. This used to work before. Now, my plan forward is to restore a backup from the MacBook before update. I will restore the backup and remove any redundant/not in use .plist jobs ( especially ) LaunchDaemon jobs. When this is done I will try to update macOS again. I have many .plist jobs also Daemon. Please supply information on how I can remove any redundant / not in use .plist jobs. I belive the reason for the kernel panic was the io.macfuse.filesystems.macfuse.23 4.7.2. ( attached log ) I want to keep the io.macfuse.filesystems.macfuse.23 4.7.2 , but I want to remove other kexts not in use and other .plist not in use. Please supply info in how to identify redundant kexts not in use and redundant .plist not in use. How do I know if the induvidual kexts is needed or not ? Best regards Tormod Willassen Kernel_Panic.rtf log-file log-file
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More DispatchIO problems -- cleanup handler isn't called
I create a DispatchIO object (in Swift) from a socketpair, set the low/high water marks to 1, and then call read on it. Elsewhere (multi-threaded, of course), I get data from somewhere, and write to the other side of it. Then when my data is done, I call dio?.close() The cleanup handler never gets called. What am I missing? (ETA: Ok, I can get it to work by calling dio?.close(flags: .stop) so that may be what I was missing.) (Also, I really wish it would get all the data available at once for the read, rather than 1 at a time.)
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Connect to the /dev/tty.PL2303G-USBtoUART120 from Catalyst app
Hello, there are popular USB GPS receivers from GlobalSat called BU-353N5. It's shipped with driver application and works well. Once connected GPS receiver is visible as a /dev/tty.PL2303G-USBtoUART120 and produces NMEA codes there. I'm a developer of an offline maps application which is available for iOS and macOS using Mac Catalyst. Is it possible to connect to the /dev/tty* from mac catalyst app? Is there an entitlement for that? There are also driver sources available to work directly with USB device based on Prolific 2303, but before I'll try to integrate driver into the app I wan't to be sure there is no way to use an existing one.
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CallKit: Blocked Calls Appearing as Unanswered in iOS 18
Hello Apple Developer Community, I'm developing a call-blocking app for iOS and have encountered an issue with iOS 18. Despite calls being successfully blocked by our app's Call Directory extension, they are still appearing as unanswered calls in the native Phone app. Details: iOS version: 18 App uses CallKit and Call Directory extension Calls are blocked successfully (not ringing on device) Blocked calls show up as "Unanswered" in Phone app's recent calls list Expected behavior: Blocked calls should not appear in the Phone app's recent calls list. Actual behavior: Blocked calls appear as "Unanswered" in the recent calls list.
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NetFSMountURLSync won't mount my FTP volume
I would like to replace the deprecated method FSMountServerVolumeSync with the newer one NetFSMountURLSync. I can properly mount my FTP volume using "Connect to Server" in the Finder and with FSMountServerVolumeSync (the volume comes as read only, but it's ok). When I try to mount the FTP volume with NetFSMountURLSync I get this error message: "The share does not exist on the server. Please check the share name and then try again". But as I know I can't define the share on a FTP server. How can I fix this issue?
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Anyone who encounters "hmmtrAccessoryServerStateChange" error during Matter device commissioning?
Hello. I found that my iPhone has encountered same error continuously when I tried to commission my Eve Door & Window device. Nov 12 11:33:48 iPhone homed(Matter)[181] <Error>: Can't extract public key from certificate: src/crypto/CHIPCryptoPALOpenSSL.cpp:1911: CHIP Error 0x0000002F: Invalid argument Nov 12 11:33:48 iPhone homed(Matter)[181] <Error>: convertX509Certificate: src/credentials/CHIPCertFromX509.cpp:559: CHIP Error 0x0000002F: Invalid argument Nov 12 11:33:55 iPhone homed(HomeKitMatter)[181] <Error>: [4264877660/1(3180582119)] Couldn't get device being commissioned for network scanning: (null) Nov 12 11:33:55 iPhone homed(HomeKitDaemon)[181] <Error>: No unpaired accessory for server HMMTRAccessoryServer fa:e6:88:97:2a:ee Nov 12 11:33:55 iPhone homed(HomeKitMetrics)[181] <Error>: [4264877660/1(3180582119)] tag="hmmtrAccessoryServerStateChange" desc="Error in progress state" errorDomain="MTRErrorDomain" errorCode="1" state="19" Nov 12 11:33:55 iPhone homed(HomeKitMatter)[181] <Error>: [4264877660/1(3180582119)] CHIP Accessory pairing failed: Error Domain=MTRErrorDomain Code=1, <HMMTRAccessoryPairingEndContext, Step: HMMTRAccessoryPairingStep_GettingNetworkRequirement, Error: Error Domain=MTRErrorDomain Code=1 "The operation couldn\M-b\M^@\M^Yt be completed. (MTRErrorDomain error 1.)", Sourceerrordomain: MTRErrorDomain> Is there anyone who has experienced or solved the same error as me? Thanks.
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Enable local network access during iOS UI test in iOS14
We are building an iOS app that connects to a device using Bluetooth. To test unhappy flow scenarios for this app, we'd like to power cycle the device we are connecting to by using an IoT power switch that connects to the local network using WiFi (a Shelly Plug-S). In my test code on iOS13, I was able to do a local HTTP call to the IP address of the power switch and trigger a power cycle using its REST interface. In iOS 14 this is no longer possible, probably due to new restrictions regarding local network usage without permissions (see: https://developer.apple.com/videos/play/wwdc2020/10110 ). When running the test and trying a local network call to the power switch in iOS14, I get the following error: Task <D206B326-1820-43CA-A54C-5B470B4F1A79>.<2> finished with error [-1009] Error Domain=NSURLErrorDomain Code=-1009 "The internet connection appears to be offline." UserInfo={_kCFStreamErrorCodeKey=50, NSUnderlyingError=0x2833f34b0 {Error Domain=kCFErrorDomainCFNetwork Code=-1009 "(null)" UserInfo={_kCFStreamErrorCodeKey=50, _kCFStreamErrorDomainKey=1}}, _NSURLErrorFailingURLSessionTaskErrorKey=LocalDataTask <D206B326-1820-43CA-A54C-5B470B4F1A79>.<2>, _NSURLErrorRelatedURLSessionTaskErrorKey=("LocalDataTask <D206B326-1820-43CA-A54C-5B470B4F1A79>.<2>"), NSLocalizedDescription=The internet connection appears to be offline., NSErrorFailingURLStringKey=http://192.168.22.57/relay/0?turn=on, NSErrorFailingURLKey=http://192.168.22.57/relay/0?turn=on, _kCFStreamErrorDomainKey=1} An external network call (to google.com) works just fine in the test. I have tried fixing this by adding the following entries to the Info.plist of my UI test target: <key>NSLocalNetworkUsageDescription</key> <string>Local network access is needed for tests</string> <key>NSBonjourServices</key> <array> <string>_http._tcp</string> </array> <key>NSAppTransportSecurity</key> <dict> <key>NSAllowsArbitraryLoads</key> <true/> </dict> However, this has no effect. I have also tried adding these entries to the Info.plist of my app target to see if that makes a difference, but it doesn't. I'd also rather not add these entries to my app's Info.plist, because the app does not need local network access. Only the test does. Does anyone know how to enable local network access during an iOS UI test in iOS14?
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Capture Screen pre-login contex on macOS 15 Sequoia
Hello, Since 2017 I provide a free and open source Remote Desktop for macOS, Windows and Linux that supports macOS 10.7 to macOS 15. Screen capture is done with CGDisplayCreateImage and works fine. But there is a problem on macOS 15 Sequoia I can not capture the screen in the pre-login context (I am referring to the login screen before the user access into his account). The screen capture in pre-login context works fine for all macOS versions except macOS 15 Sequoia. In last weeks I tried to fix the issue without success: tried CGDisplayStream tried AVCaptureScreenInput tried ScreenCaptureKit tried to sign the App (and executable) None of these work before the user login, but them works only when the user is logged in. Additional info: I run the App with "launch agent" when user is connected. I run the App with "launch daemon" when user is not connected. Any help would be greatly appreciated!
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On File System Permissions
Modern versions of macOS use a file system permission model that’s far more complex than the traditional BSD rwx model, and this post is my attempt at explaining that model. If you have a question about this, post it here on DevForums. Put your thread in the App & System Services > Core OS topic area and tag it with Files and Storage. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" On File System Permissions Modern versions of macOS have four different file system permission mechanisms: Traditional BSD permissions Access control lists (ACLs) App Sandbox Mandatory access control (MAC) The first two were introduced a long time ago and rarely trip folks up. The second two are newer, more complex, and specific to macOS, and thus are the source of some confusion. This post is my attempt to clear that up. Error Codes App Sandbox and the mandatory access control system are both implemented using macOS’s sandboxing infrastructure. When a file system operation fails, check the error to see whether it was blocked by this sandboxing infrastructure. If an operation was blocked by BSD permissions or ACLs, it fails with EACCES (Permission denied, 13). If it was blocked by something else, it’ll fail with EPERM (Operation not permitted, 1). If you’re using Foundation’s FileManager, these error are both reported as Foundation errors, for example, the NSFileReadNoPermissionError error. To recover the underlying error, get the NSUnderlyingErrorKey property from the info dictionary. App Sandbox File system access within the App Sandbox is controlled by two factors. The first is the entitlements on the main executable. There are three relevant groups of entitlements: The com.apple.security.app-sandbox entitlement enables the App Sandbox. This denies access to all file system locations except those on a built-in allowlist (things like /System) or within the app’s containers. The various “standard location” entitlements extend the sandbox to include their corresponding locations. The various “file access temporary exceptions” entitlements extend the sandbox to include the items listed in the entitlement. Collectively this is known as your static sandbox. The second factor is dynamic sandbox extensions. The system issues these extensions to your sandbox based on user behaviour. For example, if the user selects a file in the open panel, the system issues a sandbox extension to your process so that it can access that file. The type of extension is determined by the main executable’s entitlements: com.apple.security.files.user-selected.read-only results in an extension that grants read-only access. com.apple.security.files.user-selected.read-write results in an extension that grants read/write access. Note There’s currently no way to get a dynamic sandbox extension that grants executable access. For all the gory details, see this post. These dynamic sandbox extensions are tied to your process; they go away when your process terminates. To maintain persistent access to an item, use a security-scoped bookmark. See Accessing files from the macOS App Sandbox. To pass access between processes, use an implicit security scoped bookmark, that is, a bookmark that was created without an explicit security scope (no .withSecurityScope flag) and without disabling the implicit security scope (no .withoutImplicitSecurityScope flag)). If you have access to a directory — regardless of whether that’s via an entitlement or a dynamic sandbox extension — then, in general, you have access to all items in the hierarchy rooted at that directory. This does not overrule the MAC protection discussed below. For example, if the user grants you access to ~/Library, that does not give you access to ~/Library/Mail because the latter is protected by MAC. Finally, the discussion above is focused on a new sandbox, the thing you get when you launch a sandboxed app from the Finder. If a sandboxed process starts a child process, that child process inherits its sandbox from its parent. For information on what happens in that case, see the Note box in Enabling App Sandbox Inheritance. IMPORTANT The child process inherits its parent process’s sandbox regardless of whether it has the com.apple.security.inherit entitlement. That entitlement exists primarily to act as a marker for App Review. App Review requires that all main executables have the com.apple.security.app-sandbox entitlement, and that entitlements starts a new sandbox by default. Thus, any helper tool inside your app needs the com.apple.security.inherit entitlement to trigger inheritance. However, if you’re not shipping on the Mac App Store you can leave off both of these entitlement and the helper process will inherit its parent’s sandbox just fine. The same applies if you run a built-in executable, like /bin/sh, as a child process. When the App Sandbox blocks something, it typically generates a sandbox violation report. For information on how to view these reports, see Discovering and diagnosing App Sandbox violations. To learn more about the App Sandbox, see the various links in App Sandbox Resources. For information about how to embed a helper tool in a sandboxed app, see Embedding a Command-Line Tool in a Sandboxed App. Mandatory Access Control Mandatory access control (MAC) has been a feature of macOS for many releases, but it’s become a lot more prominent since macOS 10.14. There are many flavours of MAC but the ones you’re most likely to encounter are: Full Disk Access (macOS 10.14 and later) Files and Folders (macOS 10.15 and later) App container protection (macOS 14 and later) App group container protection (macOS 15 and later) Data Vaults (see below) and other internal techniques used by various macOS subsystems Mandatory access control, as the name suggests, is mandatory; it’s not an opt-in like the App Sandbox. Rather, all processes on the system, including those running as root, as subject to MAC. Data Vaults are not a third-party developer opportunity. See this post if you’re curious. In the Full Disk Access and Files and Folders cases, users grant a program a MAC privilege using System Settings > Privacy & Security. Some MAC privileges are per user (Files and Folders) and some are system wide (Full Disk Access). If you’re not sure, run this simple test: On a Mac with two users, log in as user A and enable the MAC privilege for a program. Now log in as user B. Does the program have the privilege? If a process tries to access an item restricted by MAC, the system may prompt the user to grant it access there and then. For example, if an app tries to access the desktop, you’ll see an alert like this: “AAA” would like to access files in your Desktop folder. [Don’t Allow] [OK] To customise this message, set Files and Folders properties in your Info.plist. This system only displays this alert once. It remembers the user’s initial choice and returns the same result thereafter. This relies on your code having a stable code signing identity. If your code is unsigned, or signed ad hoc (“Signed to Run Locally” in Xcode parlance), the system can’t tell that version N+1 of your code is the same as version N, and thus you’ll encounter excessive prompts. Note For information about how that works, see TN3127 Inside Code Signing: Requirements. The Files and Folders prompts only show up if the process is running in a GUI login session. If not, the operation is allowed or denied based on existing information. If there’s no existing information, the operation is denied by default. For more information about app and app group container protection, see the links in Trusted Execution Resources. For more information about app groups in general, see App Groups: macOS vs iOS: Fight! On managed systems the site admin can use the com.apple.TCC.configuration-profile-policy payload to assign MAC privileges. For testing purposes you can reset parts of TCC using the tccutil command-line tool. For general information about that tool, see its man page. For a list of TCC service names, see the posts on this thread. Note TCC stands for transparency, consent, and control. It’s the subsystem within macOS that manages most of the privileges visible in System Settings > Privacy & Security. TCC has no API surface, but you see its name in various places, including the above-mentioned configuration profile payload and command-line tool, and the name of its accompanying daemon, tccd. While tccutil is an easy way to do basic TCC testing, the most reliable way to test TCC is in a VM, restoring to a fresh snapshot between each test. If you want to try this out, crib ideas from Testing a Notarised Product. The MAC privilege mechanism is heavily dependent on the concept of responsible code. For example, if an app contains a helper tool and the helper tool triggers a MAC prompt, we want: The app’s name and usage description to appear in the alert. The user’s decision to be recorded for the whole app, not that specific helper tool. That decision to show up in System Settings under the app’s name. For this to work the system must be able to tell that the app is the responsible code for the helper tool. The system has various heuristics to determine this and it works reasonably well in most cases. However, it’s possible to break this link. I haven’t fully research this but my experience is that this most often breaks when the child process does something ‘odd’ to break the link, such as trying to daemonise itself. If you’re building a launchd daemon or agent and you find that it’s not correctly attributed to your app, add the AssociatedBundleIdentifiers property to your launchd property list. See the launchd.plist man page for the details. Scripting MAC presents some serious challenges for scripting because scripts are run by interpreters and the system can’t distinguish file system operations done by the interpreter from those done by the script. For example, if you have a script that needs to manipulate files on your desktop, you wouldn’t want to give the interpreter that privilege because then any script could do that. The easiest solution to this problem is to package your script as a standalone program that MAC can use for its tracking. This may be easy or hard depending on the specific scripting environment. For example, AppleScript makes it easy to export a script as a signed app, but that’s not true for shell scripts. TCC and Main Executables TCC expects its bundled clients — apps, app extensions, and so on — to use a native main executable. That is, it expects the CFBundleExecutable property to be the name of a Mach-O executable. If your product uses a script as its main executable, you’re likely to encounter TCC problems. To resolve these, switch to using a Mach-O executable. For an example of how you might do that, see this post. Revision History 2024-11-08 Added info about app group container protection. Clarified that Data Vaults are just one example of the techniques used internally by macOS. Made other editorial changes. 2023-06-13 Replaced two obsolete links with links to shiny new official documentation: Accessing files from the macOS App Sandbox and Discovering and diagnosing App Sandbox violations. Added a short discussion of app container protection and a link to WWDC 2023 Session 10053 What’s new in privacy. 2023-04-07 Added a link to my post about executable permissions. Fixed a broken link. 2023-02-10 In TCC and Main Executables, added a link to my native trampoline code. Introduced the concept of an implicit security scoped bookmark. Introduced AssociatedBundleIdentifiers. Made other minor editorial changes. 2022-04-26 Added an explanation of the TCC initialism. Added a link to Viewing Sandbox Violation Reports.  Added the TCC and Main Executables section. Made significant editorial changes. 2022-01-10 Added a discussion of the file system hierarchy. 2021-04-26 First posted.
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