progsys(1) — process and fork

• One or more threads.
• Can communicate through pipes, signals, networks, files.

• Each process has its Process Descriptor, which is used to keep track of the process in memory
• Stores PID, state, parent process, children, registers, address space information, open files
• Process information is usually stored in the so called Process Table, i.e. an array of PD

• Running : execution, process is using the CPU.
• Ready : process can be executed but is temporarily waiting, CPU is used by another process.
• Waiting : process can’t be executed; it is either blocked because waiting for an external event (e.g. I/O, interrupt from another process) or because scheduler assigned CPU to others.

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#include <sys/types.h>
gid_t getgid (void);
pid_t getpid (void);
pid_t getppid (void);
uid_t getuid (void);

• getpid(): returns the process ID of the calling process.
• getppid() : returns the process ID of the parent of the calling process.
• getgid() : returns the group ID of the calling process
• getuid() : returns the user ID of the calling process

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pid_t p = fork();

Remarks:

• p == 0 (Child process)
• p == -1 (Error)
• p > 0 (Parent process)