Utilites: Implement nohup

[kemzeb]

This snapshot implements the nohup command-line utility.

Running it in a directory with root permissions while being anon:

[kemzeb]

One thing important to note, I have tried to run a command such as nohup sleep 8, where I would exit the terminal after invoking it to see if SIGHUP is ignored. It appears to work after the terminal has exited, but when sleep ends I will get the following stack trace:

849.832 [#0 Finalizer Task(5:5)]: Generating coredump for pid: 85
849.835 CrashDaemon(34:34): New coredump file: /tmp/coredump/Shell_85_1688272836
849.916 CrashReporter(91:91): Started Thread "Background Thread"(92)
850.585 CrashReporter(91:92): Generating backtrace took 669 ms
850.589 CrashReporter(91:92): --- Backtrace for thread #0 (TID 85) ---
850.589 CrashReporter(91:92): 0x00000011bd09a02b: [/usr/lib/libsystem.so] syscall2 +0xb (syscall.cpp:25 => syscall.cpp:24)
850.597 CrashReporter(91:92): 0x00000010ab71c50d: [/usr/lib/libc.so] abort +0x26 (stdlib.cpp:386)
850.601 CrashReporter(91:92): 0x00000010ab722a15: [/usr/lib/libc.so] __assertion_failed.localalias +0x85 (assert.cpp:34)
850.607 CrashReporter(91:92): 0x0000000bc43ceac3: [/usr/lib/libline.so.serenity] Line::Editor::get_line(AK::DeprecatedString const&) +0x473 (Error.h:202 => Editor.cpp:750)
850.614 CrashReporter(91:92): 0x0000001691239826: [/usr/lib/libshell.so.serenity] Shell::Shell::read_single_line() +0xc6 (Shell.cpp:2097)
850.619 CrashReporter(91:92): 0x0000001691239b97: [/usr/lib/libshell.so.serenity] Shell::Shell::custom_event(Core::CustomEvent&) +0x47 (Shell.cpp:2134 => Shell.cpp:2131)
850.625 CrashReporter(91:92): 0x0000000e92f4fba7: [/usr/lib/libcore.so.serenity] Core::Object::dispatch_event(Core::Event&, Core::Object*) +0x57 (Object.cpp:214)
850.631 CrashReporter(91:92): 0x0000000e92f685fb: [/usr/lib/libcore.so.serenity] Core::ThreadEventQueue::process() +0x2eb (ThreadEventQueue.cpp:111)
850.636 CrashReporter(91:92): 0x0000000e92f46953: [/usr/lib/libcore.so.serenity] Core::EventLoopImplementationUnix::exec() +0x33 (EventLoopImplementationUnix.cpp:109 => EventLoopImplementationUnix.cpp:101)
850.647 CrashReporter(91:92): 0x0000000e92f4319d: [/usr/lib/libcore.so.serenity] Core::EventLoop::exec() +0x6d (EventLoop.cpp:75)
850.654 CrashReporter(91:92): 0x000000034906fab1: [/bin/Shell] serenity_main(Main::Arguments) +0x16a1 (main.cpp:273)
850.659 CrashReporter(91:92): 0x000000034906c6ea: [/bin/Shell] main +0x14a (Main.cpp:43)
850.666 CrashReporter(91:92): 0x000000034906c888: [/bin/Shell] _entry +0x48 (crt0.cpp:50)

Note that I truncated it as I noticed that running the top command would produce the same stack trace. See #19742.

[kemzeb]

Forgot to mention that I had trouble manually testing the code path relating to the "stderr redirects to stdout" error as I had trouble porting gcc to Serenity, but will keep trying!

[kemzeb]

I converted this as a draft PR for now as it looks like I may need to make changes as to how I make my isatty checks

[kemzeb]

My most recent changes add some error handling so that I can detect if either stdout or stderr are open (the isatty() call allows me to perform this check) and some refactoring.

I have also been able to test the code path I mentioned earlier by closing stdout (just learned about the >&- operator!):

[kemzeb]

Whoops! I should be using the returned boolean value of isatty() instead of assuming that an error means false and no error means true. My recent change reflects this.

[kemzeb]

Just rebased to try out the changes made in #19749, where I found that invoking nohup sleep 8 and exiting Terminal doesn't cause Shell to crash anymore.

[kemzeb]

The most recent change includes a commit that adds the nohup man page.

[kemzeb]

Thanks!