EXEC(2-SVR4) RISC/os Reference Manual EXEC(2-SVR4)
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
*cnup);
int execlp (const char *file, const char *arg0, ..., const
char *argn, (char *)0);
int execvp (const char *file, char *const *argv);
DESCRIPTION
exec in all its forms overlays a new process image on an old
process. The new process image is constructed from an ordi-
nary, 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. When an interpreter file is exec'd, the
system execs the specified interpreter. The pathname speci-
fied in the interpreter file is passed as arg0 to the inter-
preter. 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 char-
acter 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
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array points to a string containing the name of the file.
path points to a path name that identifies the new process
file.
file points to the new process file. If file does not con-
tain 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).
The arguments arg0, ..., argn point to null-terminated char-
acter 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 is an array of character pointers to null-terminated
strings. These strings constitute the argument list avail-
able 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.
envp is 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 cal-
ling process in the global object extern char **environ, and
it is used to pass the environment of the calling process to
the new process.
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
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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 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 superuser, the set-
user-ID and set-group-ID bits will be honored when the pro-
cess 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)].
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)]
scheduler class and priority [see priocntl(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)]
Upon successful completion, exec marks for update the
st_atime 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 com-
pletion of a subsequent call to exec.
exec will fail and return to the calling process if one or
more of the following are true:
EACCES Search permission is denied for a direc-
tory listed in the new process file's
path prefix.
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E2BIG The number of bytes in the new process's
argument list is greater than the
system-imposed limit of 5120 bytes. The
argument list limit is sum of the size
of the argument list plus the size of
the environment's exported shell vari-
ables.
EACCES The new process file is not an ordinary
file.
EACCES The new process file mode denies execu-
tion permission.
EAGAIN Total amount of system memory available
when reading via raw I/O is temporarily
insufficient.
EFAULT Required hardware is not present.
EFAULT An a.out that was compiled with the MAU
or 32B flag is running on a machine
without a MAU or 32B.
EFAULT An argument points to an illegal
address.
EINTR A signal was caught during the exec sys-
tem 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 {PATH_MAX}, or the length of a
file or path i component exceeds
{NAME_MAX} while _POSIX_NO_TRUNC is in
effect.
ENOENT One or more components of the new pro-
cess path name of the file do not exist
or is a null pathname.
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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 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 new process requires more memory
than is allowed by the system-imposed
maximum MAXMEM.
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), nice(2),
priocntl(2), ptrace(2), semop(2), signal(2), sigpending(2),
sigprocmask(2), times(2), umask(2), lockf(3C), system(3S),
a.out(4), environ(5).
sh(1), ps(1) in the User's Reference Manual.
DIAGNOSTICS
If exec returns to the calling process, an error has
occurred; the return value is -1 and errno is set to indi-
cate the error.
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