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Inter Process Communciation (IPC) Process Persistence Exists as long as it is held open by a process Pipes and FIFOs TCP, UDP sockets Mutex , condition variables , read write locks POSIX memroy based semaphores Kernel Persistence Exists until kernel reboots or IPC objects is explicitly deleted Message Queues , semaphores & shared memory are at least kernel persistent File system Persistence Exis..

Temporal Multi-threading = Only one thread of instruction can execute in any given pipeline stage at a time Simultaneous Multi-threading (SMT/HT) = More than one thread of insturction can execute in any given pipeline stage at a time (super scalar architecture) #include #include #include #include #include struct mystruct{ char character; int count; }; void * f1(void *); int main(){ pthread_t tid..

Interactive Process interact constantly with their users. When input is received , the average delay must fall between 50-150ms , otherwise the user will find the system to be unresponsive. e.g) command shells, text editors, graphical applications. Batch Processes don't need user interaction and often exectue in the background and are often penalized by the scheduler. Typical batch programs are ..

A daemon is a system process that provides services to system admin w/o human intervention (cron) , provide services to OS Kernel (paged), or communciate with other porcesses (httpd). It has following characteristics: A daemon is long-lived , often created at system startup and runs until the system is shut down It runs in the backgroudn and has no controlling terminal. The lack of a controlling..

exec system call completely replaced by the new prorgam, and the new program starts executing its main function. there is no return after a successful exec call. The exec() function return only if an error has occurred. The return value is -1, and errno is set to indicate the error. #include #include #include #include int main(){ int status; pid_t cpid = fork(); if (cpid == 0){ execlp("ls", "myl..

vfork system call intended to create a new process when the purpose of the new process is to exec a new program , and it do so without fully copying the parent address space into the child. no duplication of virtual memory pages is done for child process. child shares parent's address space until it either performs exec() or call exit(). Execution of parent process is suspended until the child h..

Process ID & Parent Process ID each process has a PID , a positive integer that uniquely identifies a process on the system. once PID reached 32767 , the PID counter is reset to 300, rather than 1. The swapper or scheduler is a system prcoess having a PID of 0. It manages memory allocation for processes, swaps processes from run state to Ready Queue or other and may be to disk. The init , now sy..

Character Special Files (c) represents hardware devices that reads or writes a serial stream of data bytes. sound cards , terminal devices(tty) Block speical files (b) represents hardware devices that raeds or wirtes data in fixed size blocks. HDD, SSD, cdrom colored boxes are device drvierers , work as an interface so that OS can communciate with devices more formally. regular file is container..

default behavior of who is to display a list of currently logged in users, if there are no argument given when executing "who" command. it is basically reading from /var/run/utmp and write on terminal with appropriate format. who process open the file /var/run/utmp read a utmp strcture untill end of file display the requried fields go to step2 close file /var/run/utmp #include #include #include ..

we can iterate directory by looping through readdir() with given pointer stream. #include #include #include #include #include extern int errno; int main(){ printf("Directory scan of /home/: \n"); DIR* dp = opendir("/home"); chdir("/home"); errno = 0; struct dirent* entry; while(1){ entry = readdir(dp); if(entry == NULL && errno != 0){ perror("readdir"); return errno; } if(entry == NULL && errno ..