For the tangent operation, you may use the Math:: Returns true if it succeeded, false otherwise. NAME should be a packed address of the appropriate type for the socket.
The TTY demystified Real teletypes in the s. Unfortunately, its importance is often overlooked, and it is difficult to find good introductory articles about it. I believe that a basic understanding of TTYs in Linux is essential for the developer and the advanced user.
What you are about to see is not particularly elegant. In fact, the TTY subsystem — while quite functional from a user's point of view — is a twisty little mess of special cases.
To understand how this came to be, we have to go back in time. History Inthe stock ticker was invented.
It was an electro-mechanical machine consisting of a typewriter, a long pair of wires and a ticker tape printer, and its purpose was to distribute stock prices over long distances in realtime. Teletypes were once connected across the world in a large network, called Telex, which was used for transferring commercial telegrams, but the teletypes weren't connected to any computers yet.
Meanwhile, however, the computers — still quite large and primitive, but able to multitask — were becoming powerful enough to be able to interact with users in realtime.
When the command line eventually replaced the old batch processing model, teletypes were used as input and output devices, because they were readily available on the market.
There was a plethora of teletype models around, all slightly different, so some kind of software compatibility layer was called for. In the UNIX world, the approach was to let the operating system kernel handle all the low-level details, such as word length, baud rate, flow control, parity, control codes for rudimentary line editing and so on.
Fancy cursor movements, colour output and other advanced features made possible in the late s by solid state video terminals such as the VT, were left to the applications.
In present time, we find ourselves in a world where physical teletypes and video terminals are practically extinct. Unless you visit a museum or a hardware enthusiast, all the TTYs you're likely to see will be emulated video terminals — software simulations of the real thing.
But as we shall see, the legacy from the old cast-iron beasts is still lurking beneath the surface. The use cases A user types at a terminal a physical teletype. The operating system contains a UART driver which manages the physical transmission of bytes, including parity checks and flow control.
But such an approach would lack the following essential features: Most users make mistakes while typing, so a backspace key is often useful. This could of course be implemented by the applications themselves, but in accordance with the UNIX design philosophy, applications should be kept as simple as possible.
So as a convenience, the operating system provides an editing buffer and some rudimentary editing commands backspace, erase word, clear line, reprintwhich are enabled by default inside the line discipline. Advanced applications may disable these features by putting the line discipline in raw mode instead of the default cooked or canonical mode.
Most interactive applications editors, mail user agents, shells, all programs relying on curses or readline run in raw mode, and handle all the line editing commands themselves. The line discipline also contains options for character echoing and automatic conversion between carriage returns and linefeeds.
Think of it as a primitive kernel-level sed 1if you like. Incidentally, the kernel provides several different line disciplines. Only one of them is attached to a given serial device at a time. Other disciplines are used for other purposes, such as managing packet switched data ppp, IrDA, serial micebut that is outside the scope of this article.
The user probably wants to run several programs simultaneously, and interact with them one at a time. If a program goes into an endless loop, the user may want to kill it or suspend it.
Programs that are started in the background should be able to execute until they try to write to the terminal, at which point they should be suspended. Likewise, user input should be directed to the foreground program only. An operating system process is "alive" has an execution contextwhich means that it can perform actions.
It has some data fields and some methods, but the only way it can actually do something is when one of its methods gets called from the context of a process or a kernel interrupt handler.
The line discipline is likewise a passive entity. Write permissions to the device file are required, so when a user logs in on a particular TTY, that user must become the owner of the device file. This is traditionally done by the login 1 program, which runs with root privileges.
The physical line in the previous diagram could of course be a long-distance phone line: This does not change much, except that the system now has to handle a modem hangup situation as well.
Let's move on to a typical desktop system. This is how the Linux console works:For Developers By Developers. SourceForge is an Open Source community resource dedicated to helping open source projects be as successful as possible.
If the file was open(2)ed with O_APPEND, the file offset is first set to the end of the file before writing. The adjustment of the file offset and the write operation are performed as an atomic step. POSIX requires that a read(2) that can be proved to occur after a write() has returned will return the new data.
Note that not all filesystems are POSIX conforming. The write is one of the most basic routines provided by a Unix-like operating system kernel.
It writes data from a buffer declared by the user to a given device, maybe a file. This is the primary way to output data from a program by directly using a system call. ; fd1 = open (argv , O_WRONLY);. The "wait" wait queue corresponds to the wait(2) syscall, so these processes will be moved to the running state whenever there's a state change in one of their child initiativeblog.com are two sleeping states: Interruptible sleep and uninterruptible sleep.
Interruptible sleep (the most common case) means that while the process is part of a wait queue, it may actually also be moved to the running.
htop explained. Explanation of everything you can see in htop/top on Linux. Last updated on January 2, #1 on Hacker News on December 2, #1 on /r/sysadmin on December 2, Free open source vulnerability checker.
13 syscall mov rax, 60 xor, rdi, rdi syscall initiativeblog.com message: db "I love you", 10 (There may be some errors for the assembly example, if anyone knows x86 feel free to suggest edits). How do I write a love letter in programming language?
Why do you love to write software?