system

- issue a shell command

Synopsis

#include <stdlib.h>

int system(const char *string);

Description

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(3C).

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. The standard to which the caller conforms determines which shell is used. See standards(5).

The system() function sets the SIGINT and SIGQUIT signals to be ignored, and blocks the SIGCHLD signal for the calling thread, while waiting for the command to terminate. The system() function does not affect the termination status of any child of the calling processes other than the process it creates.

The termination status of the process created by the system() function is not affected by the actions of other threads in the calling process (it is invisible to wait(3C)) or by the disposition of the SIGCHLD signal in the calling process, even if it is set to be ignored. No SIGCHLD signal is sent to the process containing the calling thread when the command terminates.

Return Values

The system() function executes posix_spawn(3C) to create a child process running the shell that in turn executes the commands in string. If posix_spawn() fails, system() returns -1 and sets errno to indicate the error; otherwise the exit status of the shell is returned.

Errors

The system() function may set errno values as described by fork(2), in particular:

EAGAIN

A resource control or limit on the total number of processes, tasks or LWPs under execution by a single user, task, project, or zone has been exceeded, or the total amount of system memory available is temporarily insufficient to duplicate this process.

ENOMEM

There is not enough swap space.

EPERM

The {PRIV_PROC_FORK} privilege is not asserted in the effective set of the calling process.

Usage

The system() function manipulates the signal handlers for SIGINT and SIGQUIT. It is therefore not safe to call system() in a multithreaded process, since some other thread that manipulates these signal handlers and a thread that concurrently calls system() can interfere with each other in a destructive manner. If, however, no such other thread is active, system() can safely be called concurrently from multiple threads. See popen(3C) for an alternative to system() that is thread-safe.

Attributes

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

See Also

ksh(1), sh(1), popen(3C), posix_spawn(3C), wait(3C), waitpid(3C), attributes(5), standards(5)