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execve
Executes a file.
Syntax
#include <unistd.h>
int execve (const char *path, char *const *argv[],
cr *const envp[]);
har *const envp[]);
Parameters
path A pointer to a string containing the pathname of the
executable file that is to become the new process image. The
pathname must be terminated by a null character.
The elements of the pathname must be uppercase and must
resolve to a valid MPE/iX file, group, and account. For
example, the pathname /FINANCE/PAYROLL/JULY must resolve to
JULY.PAYROLL.FINANCE, where JULY is an executable file located
in MPE/iX group PAYROLL in MPE/iX account FINANCE.
arg0, Each of the parameters arg0, ..., argn-1 point to a string
..., argn containing an argument to the new process image. Each
argument must be terminated by a null character. The last
parameter, argn, must be a NULL pointer.
For an application to be strictly conforming, the first
parameter, arg0, must point to a string containing a filename
that identifies the executable file for the new process image.
envp[] An array of character pointers to null terminated strings.
These strings constitute the environment for the new process
image.
Return Values
No return Success.
-1 An error occurred. The current process image remains
unchanged, and errno is set to indicate the error condition.
Description
The execve() function replaces the current process image with a new
process image created from the executable file specified in pathname.
Use the execl() function if you know the exact number of arguments to be
passed to the new process image. Use the execv() function if the number
of arguments passed to the new process image might vary at run time.
If the new process image is a C program, it is entered as a C function
call having the following declaration:
int main (int argc, const char *argv[])
In the above declaration, argc is a count of the number of pointers in
the array argv[] and argv[] is an array of character pointers to the
parameters arg0 through argn. The NULL pointer terminating argv[] is not
counted in argc.
The environment for the new process image is identical to the environment
of the calling process.
If the new process image is not a C program, no information is made
available through the argument list in argv[].
The sum of the bytes used in both the argument list and environment list
must not exceed {ARG_MAX} (defined in the file <limits.h>).
File descriptors open in the calling process image remain open in the new
process image. For all file descriptors that remain open, all attributes
of the open file description remain unchanged by this function, including
file locks.
Streams open in the calling process image are not accessible in the new
process image. (However, the underlying file descriptors that remain
open, but inaccessible, are counted towards {OPEN_MAX}.)
Signals set to SIG_DFL or SIG_IGN in the calling process remain unchanged
in the new process image. All signals of the calling process whose
action is to invoke a signal handling function are set to SIG_DFL in the
new process image.
The following attributes of the new process image are set to the same
values of those of the calling process:
* process ID
* parent process ID
* process group ID
* session membership
* real user ID
* real group ID
* time remaining until a SIGALRM signal
* current working directory
* root directory
* file mode creation mask
* process signal mask
* pending signals
* tms_utime, tms_stime, tms_cutime, and tms_cstime
The executable file's st_atime time field is marked for update. The
executable file is open until the new process image terminates or
executes another of the exec() functions.
Implementation Considerations
Refer to the EPERM, EIMPL, and ENOEXEC error descriptions below.
Some MPE/iX process attributes that are not specified in the POSIX 1003.1
standard are not inherited by the new process image.
NULL terminators and pointers are counted against {ARG_MAX}. Alignment
bytes are counted against {ARG_MAX}.
The calling process's privilege level is used as the new program's
maximum privilege level.
If the calling process entered debug mode through the ;DEBUG option of
the MPE/iX CI RUN command, the new process image is also in debug mode.
Errors
If an error occurs, errno is set to one of the following values:
E2BIG CAUSE The number of bytes used by the new process image's
argument list and environment list combined is
greater than the limit of {ARG_MAX} (defined in
<limits.h>).
ACTION Reduce the size of the argument list or environment
list or both.
EACCES CAUSE One of the following:
* The calling process does not have search
permission to a component of the pathname.
* The calling process does not have execute
permission to the file.
ACTION One of the following:
* Make sure that the calling process has search
permission to all components of the pathname.
* Make sure that the calling process has execute
permission to the file.
EFAULT CAUSE The system detected a NULL or bad address in
attempting to use the pathname parameter, or the
pathname was not terminated by a null character.
ACTION Make sure that the pointer is correctly initialized.
EIMPL CAUSE The pathname did not resolve to a valid MPE/iX file,
group, and account or the pathname began with two
slashes.
ACTION Specify a valid pathname as described in the pathname
parameter description.
Table 4-0. (cont.)
ENAMETOOLONG CAUSE One of the following:
* The length of the pathname exceeds the
{PATH_MAX} limit (defined in the file
<limits.h>).
* A component of the pathname is longer than
{NAME_MAX} (defined in <limits.h>), and
{_POSIX_NO_TRUNC} is in effect for that
directory.
ACTION Make sure that both the component's length and the
full pathname length do not exceed the {NAME_MAX} or
{PATH_MAX} limits.
ENOENT CAUSE a component of the pathname for the executable file
does not exist, or pathname points to an empty
string.
ACTION Specify a valid pathname.
ENOEXEC CAUSE The program file does not have the NMPRG file code.
ACTION Make sure that the program file has the NMPRG file
code.
ENOMEM CAUSE The new process image requires more memory than the
system allows.
ACTION No action required. The new process image cannot be
created.
ENOTDIR CAUSE A component of the pathname is not a directory.
ACTION Specify a valid pathname.
Table 4-0. (cont.)
EPERM CAUSE One of the following:
* The calling process does not have the MPE/iX
process handling (PH) capability.
* The calling process has outstanding switches
to CM code, has set critical mode, has
outstanding NOWAITIO, or is holding an
operating system internal resource, or the
calling process is in a Procedure Exit
handler.
ACTION One of the following:
* Link the program file with the MPE/iX PH
capability.
* Do not execute execl() when the calling
process has outstanding switches to CM code,
has set critical mode, has outstanding
NOWAITIO, or is holding an operating system
internal resource, or in a Procedure Exit
handler.
See Also
alarm(), chmod(), _exit(), fcntl(), fork(), setuid(), <signal.h>,
sigpromask(), sigpending(), stat(), <sys/stat.h>, times(), umask, POSIX.1