exec(2) DG/UX 5.4 Rel. 2.01 exec(2)
NAME
exec: execl, execv, execle, execve, execlp, execvp - execute a file
SYNOPSIS
#include <unistd.h>
int execl (const char *path,
const char *arg0, ..., const char *argn,
(char *)0);
int execv (const char *path,
char *const *argv);
int execle (const char *path,
const char *arg0, ..., const char *argn,
(char *0),
const char *envp[]);
int execve (const char *path,
char *const *argv,
char *const *envp);
int execlp (const char *file,
const char *arg0, ..., const char *argn,
(char *)0);
int execvp (const char *file,
char *const *argv);
where:
path A pointer to a pathname that identifies the new process file.
file A pointer to the new process file. If file does not contain a
slash character, the path prefix for this file is obtained by
a search of the directories passed in the PATH environment
variable [see environ(5)]. The environment is supplied
typically by the shell [see sh(1)]. If the new process file
is not an executable object file, execlp and execvp use the
contents of that file as standard input to sh(1).
arg (0 through n) Pointers to null-terminated character strings.
These strings constitute the argument list available to the
new process image. Minimally, arg0 must be present. It will
become the name of the process, as displayed by the ps
command. Conventionally, arg0 points to a string that is the
same as path (or the last component of path). The list of
argument strings is terminated by a (char *)0 argument.
argv An array of character pointers to null-terminated strings.
These strings constitute the argument list available to the
new process image. By convention, argv must have at least one
member, and it should point to a string that is the same as
path (or its last component). argv is terminated by a null
pointer.
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envp An array of character pointers to null-terminated strings.
These strings constitute the environment for the new process
image. envp is terminated by a null pointer. For execl,
execv, execvp, and execlp, the C run-time start-off routine
places a pointer to the environment of the calling process in
the global object extern char **environ, and it is used to
pass the environment of the calling process to the new
process.
DESCRIPTION
Exec in all its forms overlays a new process image on an old process.
The new process image is constructed from an ordinary, executable
file. This file is either an executable object file, or a file of
data for an interpreter. There can be no return from a successful
exec because the calling process image is overlaid by the new process
image.
An interpreter file begins with a line of the form
#! pathname [arg]
where pathname is the path of the interpreter, and arg is an optional
argument. The text following the #!, including the terminating
newline character, may not exceed 32 bytes. When an interpreter file
is exec'd, the system execs the specified interpreter. The pathname
specified in the interpreter file is passed as arg0 to the
interpreter. If arg was specified in the interpreter file, it is
passed as arg1 to the interpreter. The remaining arguments to the
interpreter are arg0 through argn of the originally exec'd file.
When a C program is executed, it is called as follows:
int main (int argc, char *argv[], char *envp[]);
where argc is the argument count, argv is an array of character
pointers to the arguments themselves, and envp is an array of
character pointers to the environment strings. As indicated, argc is
at least one, and the first member of the array points to a string
containing the name of the file.
File descriptors open in the calling process remain open in the new
process, except for those whose close-on-exec flag is set; [see
fcntl(2)]. For those file descriptors that remain open, the file
pointer is unchanged.
Signals that are being caught by the calling process are set to the
default disposition in the new process image [see signal(2)].
Otherwise, the new process image inherits the signal dispositions of
the calling process.
If the set-user-ID mode bit of the new process file is set [see
chmod(2)], exec sets the effective user ID of the new process to the
owner ID of the new process file. Similarly, if the set-group-ID
mode bit of the new process file is set, the effective group ID of
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the new process is set to the group ID of the new process file. The
real user ID and real group ID of the new process remain the same as
those of the calling process.
If the effective user-ID is root or super-user, the set-user-ID and
set-group-ID bits will be honored when the process is being
controlled by ptrace.
The shared memory segments attached to the calling process will not
be attached to the new process [see shmop(2)].
Any user specified page locking properties [see memcntl(2) with the
MCLFUTURE option] are not inherited. In effect, these will be reset
for the new process.
Profiling is disabled for the new process; see profil(2).
The new process also inherits the following attributes from the
calling process:
nice value [see nice(2)]
scheduling class and parameters [see schedsetscheduler(2)]
process ID
parent process ID
process group ID
supplementary group IDs
semadj values [see semop(2)]
session ID [see exit(2) and signal(2)]
trace flag [see ptrace(2) request 0]
time left until an alarm clock signal [see alarm(2)]
current working directory
root directory
file mode creation mask [see umask(2)]
resource limits [see getrlimit(2)]
utime, stime, cutime, and cstime [see times(2)]
file-locks [see fcntl(2) and lockf(3C)]
controlling terminal
process signal mask [see sigprocmask(2)]
pending signals [see sigpending(2)]
Any semaphores that are open in the process at the time of an exec
call are closed as if by appropriate calls to semdestroy(2).
Any per-process timers created by the calling process are deleted as
if by appropriate calls to timerdelete(2).
Upon successful completion, exec marks for update the statime field
of the file. Should the exec succeed, the process image file is
considered to have been open()-ed. 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 exec.
exec will fail and return to the calling process if one or more of
the following are true:
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EACCES Search permission is denied for a directory
listed in the new process file's path prefix.
E2BIG The number of bytes in the new process' argument
list is greater than the system-imposed maximum.
The argument list limit is the sum of the size of
the argument list plus the size of the
environment's exported shell variables.
The limit is the value of NCARGS in sys/param.h;
obtain it by calling sysconf(_SC_ARG_MAX).
EACCES The new process file is not an ordinary file.
EACCES The new process file mode denies execution
permission.
EAGAIN Total amount of system memory available when
reading via raw I/O is temporarily insufficient.
EFAULT Path, argv, or envp point to an illegal address.
EINTR A signal was caught during the exec system call.
ELIBACC Required shared library does not have execute
permission.
ELIBEXEC Trying to exec(2) a shared library directly.
ELOOP Too many symbolic links were encountered in
translating path or file.
EMULTIHOP Components of path require hopping to multiple
remote machines and the file system type does not
allow it.
ENAMETOOLONG The length of the file or path argument exceeds
{PATHMAX}, or the length of a file or path
component exceeds {NAMEMAX} while
POSIXNOTRUNC is in effect.
ENOENT One or more components of the new process
pathname of the file do not exist or is a null
pathname.
ENOEXEC The number of characters following the #! in an
interpreter header, including the terminating
newline character, exceeds 32.
ENOTDIR A component of the new process path of the file
prefix is not a directory.
ENOEXEC The exec is not an execlp or execvp, and the new
process file has the appropriate access
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permission but an invalid magic number in its
header.
ETXTBSY The new process file is a pure procedure (shared
text) file that is currently open for writing by
some process.
ENOMEM The process failed to allocate the necessary
memory resources to complete the operation.
ENOLINK path points to a remote machine and the link to
that machine is no longer active.
SEE ALSO
alarm(2), exit(2), fcntl(2), fork(2), getrlimit(2), memcntl(2),
nice(2), ptrace(2), semop(2), signal(2), sigpending(2),
sigprocmask(2), times(2), umask(2), lockf(3C), system(3S), a.out(4),
environ(5).
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