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system(3) [centos man page]

SYSTEM(3)						     Linux Programmer's Manual							 SYSTEM(3)

system - execute a shell command SYNOPSIS
#include <stdlib.h> int system(const char *command); DESCRIPTION
system() executes a command specified in command by calling /bin/sh -c command, and returns after the command has been completed. During execution of the command, SIGCHLD will be blocked, and SIGINT and SIGQUIT will be ignored. RETURN VALUE
The value returned is -1 on error (e.g., fork(2) failed), and the return status of the command otherwise. This latter return status is in the format specified in wait(2). Thus, the exit code of the command will be WEXITSTATUS(status). In case /bin/sh could not be executed, the exit status will be that of a command that does exit(127). If the value of command is NULL, system() returns nonzero if the shell is available, and zero if not. system() does not affect the wait status of any other children. CONFORMING TO
C89, C99, POSIX.1-2001. NOTES
If the _XOPEN_SOURCE feature test macro is defined (before including any header files), then the macros described in wait(2) (WEXITSTA- TUS(), etc.) are made available when including <stdlib.h>. As mentioned, system() ignores SIGINT and SIGQUIT. This may make programs that call it from a loop uninterruptible, unless they take care themselves to check the exit status of the child. E.g. while (something) { int ret = system("foo"); if (WIFSIGNALED(ret) && (WTERMSIG(ret) == SIGINT || WTERMSIG(ret) == SIGQUIT)) break; } Do not use system() from a program with set-user-ID or set-group-ID privileges, because strange values for some environment variables might be used to subvert system integrity. Use the exec(3) family of functions instead, but not execlp(3) or execvp(3). system() will not, in fact, work properly from programs with set-user-ID or set-group-ID privileges on systems on which /bin/sh is bash version 2, since bash 2 drops privileges on startup. (Debian uses a modified bash which does not do this when invoked as sh.) In versions of glibc before 2.1.3, the check for the availability of /bin/sh was not actually performed if command was NULL; instead it was always assumed to be available, and system() always returned 1 in this case. Since glibc 2.1.3, this check is performed because, even though POSIX.1-2001 requires a conforming implementation to provide a shell, that shell may not be available or executable if the calling program has previously called chroot(2) (which is not specified by POSIX.1-2001). It is possible for the shell command to return 127, so that code is not a sure indication that the execve(2) call failed. SEE ALSO
sh(1), signal(2), wait(2), exec(3) COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at 2010-09-10 SYSTEM(3)

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system(3C)						   Standard C Library Functions 						system(3C)

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 wait- ing 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: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |Unsafe | +-----------------------------+-----------------------------+ SEE ALSO
ksh(1), sh(1), popen(3C), posix_spawn(3C), wait(3C), waitpid(3C), attributes(5), standards(5) SunOS 5.11 14 Dec 2006 system(3C)
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