fork function is the primitive for creating a process.
It is declared in the header file unistd.h.
forkfunction creates a new process.
If the operation is successful, there are then both parent and child processes and both see
forkreturn, but with different values: it returns a value of
0in the child process and returns the child's process ID in the parent process.
If process creation failed,
forkreturns a value of
-1in the parent process. The following
errnoerror conditions are defined for
- There aren't enough system resources to create another process, or the user already has too many processes running. This means exceeding the
RLIMIT_NPROCresource limit, which can usually be increased; see Limits on Resources.
- The process requires more space than the system can supply.
The specific attributes of the child process that differ from the parent process are:
vforkfunction is similar to
forkbut on some systems it is more efficient; however, there are restrictions you must follow to use it safely.
forkmakes a complete copy of the calling process's address space and allows both the parent and child to execute independently,
vforkdoes not make this copy. Instead, the child process created with
vforkshares its parent's address space until it calls
_exitor one of the
execfunctions. In the meantime, the parent process suspends execution.
You must be very careful not to allow the child process created with
vforkto modify any global data or even local variables shared with the parent. Furthermore, the child process cannot return from (or do a long jump out of) the function that called
vfork! This would leave the parent process's control information very confused. If in doubt, use
Some operating systems don't really implement
vfork. The GNU C library permits you to use
vforkon all systems, but actually executes
vforkisn't available. If you follow the proper precautions for using
vfork, your program will still work even if the system uses