Unix kernels provide an execution environment in which applications may run. Therefore, the kernel must implement a set of services and corresponding interfaces. Applications use those interfaces and do not usually interact directly with hardware resources. Actually, some CPUs can have more than two execution states. When a program is executed in User Mode, it cannot directly access the kernel data structures or the kernel programs. When an application executes in Kernel Mode, however, these restrictions no longer apply.
Unix / Linux - Signals and Traps
Chapter Signals - Shichao's Notes
Disclaimer: This study guide attempts to touch upon the most important topics that may be covered on the exam but does not claim to necessarily cover everything that one needs to know for the exam. Finally, don't take the three hour time window in the title literally. Data communication, the process of conveying information from one place to another, existed long before computers and dates back to earliest recorded history. As various pre-computer techniques for conveying data reliably over distances were invented, so too were a number of underlying mechanisms that proved to be useful in digital networks. The most basic form of message delivery is moving a message from one entity person to another. This is known as point-to-point , or unicast delivery. Transmitting a single message so that everyone gets it is known as a broadcast.
UNIX programming examples
Screen is a full-screen window manager that multiplexes a physical terminal between several processes, typically interactive shells. There is a scrollback history buffer for each virtual terminal and a copy-and-paste mechanism that allows the user to move text regions between windows. When screen is called, it creates a single window with a shell in it or the specified command and then gets out of your way so that you can use the program as you normally would.
It appears that when using streams with chunk sizes which exceed the high water mark for the stream, a drain event is no longer emitted. As a result, streams with sufficient data will hang indefinitely. This appears to affect fastput, fastget, put and possibly get operations. A bug report hass been logged against the ssh2-streams library as issue UPDATE : The author of the upstream ssh2 and ssh2-streams module has decided on a re-write of the ssh2 module to address the above issues as well as some other design limitations and to allow the module to better fit in with newer versions of node.