The system() function causes string to be given to the shell as input, as if string had been typed as a command at a terminal. The invoker waits until the shell has completed, then returns the exit status of the shell in the format specified by waitpid(2).

If string is a null pointer, system() checks if the shell exists and is executable. If the shell is available, system() returns a non-zero value; otherwise, it returns 0. If the application is standard-conforming (see standards(5)), system() uses /usr/xpg4/bin/sh (see ksh(1)); otherwise system() uses /usr/bin/sh (see sh(1)).

The system() function executes vfork(2) to create a child process that in turn invokes one of the exec family of functions (see exec(2)) on the shell to execute string. If vfork() or the exec function fails, system() returns -1 and sets errno to indicate the error.

The system() function fails if:

EAGAIN

The system-imposed limit on the total number of processes under execution by a single user would be exceeded.

EINTR

The system() function was interrupted by a signal.

ENOMEM

The new process requires more memory than is available.

The system() function manipulates the signal handlers for SIGINT, SIGQUIT, and SIGCHLD. For this reason it is not safe to call system() in a multithreaded process. Concurrent calls to system() will interfere destructively with the disposition of these signals, even if they are not manipulated by other threads in the application. See popen(3C) for a replacement for system() that is thread-safe.

See attributes(5) for descriptions of the following attributes:

ksh(1), sh(1), exec(2), vfork(2), waitpid(2), popen(3C), attributes(5), standards(5)