execl()

Execute a file

Synopsis:

#include <process.h>

int execl( const char * path,
           const char * arg0,
           const char * arg1,
           …
           const char * argn,
           NULL );

Arguments:

path

The path of the file to execute.

arg0, …, argn

Pointers to NULL-terminated character strings. These strings constitute the argument list available to the new process image. You must terminate the list with a NULL pointer. The arg0 argument must point to a filename that's associated with the process being started.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The execl() function replaces the current process image with a new process image specified by path. The new image is constructed from a regular, executable file called the new process image file. No return is made because the calling process image is replaced by the new process image.

When a C-language program is executed as a result of this call, it's entered as a C-language function call as follows:

int main (int argc, char *argv[]);

where argc is the argument count and argv is an array of character pointers to the arguments themselves. In addition, the following variable:

extern char **environ;

is initialized as a pointer to an array of character pointers to the environment strings. The argv and environ arrays are each terminated by a null pointer. The null pointer terminating the argv array isn't counted in argc.

Multithreaded applications shouldn't use the environ variable to access or modify any environment variable while any other thread is concurrently modifying any environment variable. A call to any function dependent on any environment variable is considered a use of the environ variable to access that environment variable.

The arguments specified by a program with one of the exec* functions are passed on to the new process image in the corresponding main() arguments.

The number of bytes available for the new process's combined argument and environment lists is ARG_MAX.

File descriptors open in the calling process image remain open in the new process image, except for when fcntl()'s FD_CLOEXEC flag is set. For those file descriptors that remain open, all attributes of the open file description, including file locks remain unchanged. If a file descriptor is closed for this reason, file locks are removed as described by close() while locks not affected by close() aren't changed.

Directory streams open in the calling process image are closed in the new process image.

Signals set to SIG_DFL in the calling process are set to the default action in the new process image. Signals set to SIG_IGN by the calling process images are ignored by the new process image. Signals set to be caught by the calling process image are set to the default action in the new process image. After a successful call, alternate signal stacks aren't preserved and the SA_ONSTACK flag is cleared for all signals.

After a successful call, any functions previously registered by atexit() are no longer registered.

If the path is on a filesystem mounted with the ST_NOSUID flag set, the effective user ID, effective group ID, saved set-user ID and saved set-group ID are unchanged for the new process. Otherwise, if the set-user ID mode bit is set, the effective user ID of the new process image is set to the user ID of path. Similarly, if the set-group ID mode bit is set, the effective group ID of the new process is set to the group ID of path. The real user ID, real group ID, and supplementary group IDs of the new process remain the same as those of the calling process. The effective user ID and effective group ID of the new process image are saved (as the saved set-user ID and the saved set-group ID used by setuid()).

Any shared memory segments attached to the calling process image aren't attached to the new process image.

The new process also inherits at least the following attributes from the calling process image:

• process ID
• parent process ID
• process group ID
• session membership
• real user ID
• real group ID
• supplementary group IDs
• time left until an alarm clock signal (see alarm())
• current working directory
• root directory
• file mode creation mask (see umask())
• process signal mask (see sigprocmask())
• pending signal (see sigpending())
• tms_utime, tms_stime, tms_cutime, and tms_cstime (see times())
• resource limits
• controlling terminal
• interval timers.

If you call this function from a process with more than one thread, all of the threads are terminated and the new executable image is loaded and executed. No destructor functions are called.

Upon successful completion, the st_atime field of the file is marked for update. If the exec* function failed but was able to locate the process image file, whether the st_atime field is marked for update is unspecified. On success, the process image file is considered to be opened with open(). The corresponding close() is considered to occur at a time after this open, but before process termination or successful completion of a subsequent call to one of the exec* functions.

exec*() summary

Returns:

When execl() is successful, it doesn't return; otherwise, it returns -1 (errno is set).

Errors:

E2BIG

The argument list and the environment is larger than the system limit of ARG_MAX bytes.

EACCESS

The calling process doesn't have permission to search a directory listed in path, or it doesn't have permission to execute path, or path's filesystem was mounted with the ST_NOEXEC flag.

ELOOP

Too many levels of symbolic links or prefixes.

ENAMETOOLONG

The length of path or an element of the PATH environment variable exceeds PATH_MAX.

ENOENT

One or more components of the pathname don't exist, or the path argument points to an empty string.

ENOEXEC

The new process image file has the correct access permissions, but isn't in the proper format.

ENOMEM

There's insufficient memory available to create the new process.

ENOTDIR

A component of path isn't a directory.

Examples:

Replace the current process with myprog as if a user had typed:

myprog ARG1 ARG2

at the shell:

#include <stddef.h>
#include <process.h>

execl( "myprog", "myprog", "ARG1", "ARG2", NULL );

In this example, myprog will be found if it exists in the current working directory.

Classification:

POSIX 1003.1

See also:

abort(), atexit(), errno, execle(), execlp(), execlpe(), execv(), execve(), execvp(), execvpe(), _exit(), exit(), getenv(), main(), putenv(), spawn(), spawnl(), spawnle(), spawnlp(), spawnlpe(), spawnp(), spawnv(), spawnve(), spawnvp(), spawnvpe(), system()

Processes and Threads chapter of Getting Started with QNX Neutrino