EXEC(2-SVR3) RISC/os Reference Manual EXEC(2-SVR3)
NAME
exec: execl, execv, execle, execve, execlp, execvp - execute
a file
SYNOPSIS
int execl (path, arg0, arg1, ..., argn, (char *)0)
char *path, *arg0, *arg1, ..., *argn;
int execv (path, argv)
char *path, *argv[ ];
int execle (path, arg0, arg1, ..., argn, (char *)0, envp)
char *path, *arg0, *arg1, ..., *argn, *envp[ ];
int execve (path, argv, envp)
char *path, *argv[ ], *envp[ ];
int execlp (file, arg0, arg1, ..., argn, (char *)0)
char *file, *arg0, *arg1, ..., *argn;
int execvp (file, argv)
char *file, *argv[ ];
DESCRIPTION
exec in all its forms transforms the calling process into a
new process. The new process is constructed from an ordi-
nary, executable file called the "new process file". The
new process file may be either an "interpreter script" which
begins with the characters "#!", or an a.out file.
On the first line of an interpreter script, following the
"#!", is the name of a program which should be used to
interpret the contents of the file. For instance, if the
first line contains "#! /bin/sh", then the contents of the
file are executed as a shell script. An a.out file consists
of a header, a text segment, and a data segment. The data
segment contains an initialized portion and an uninitialized
portion (bss).
There can be no return from a successful exec because the
calling process is overlaid by the new process.
When a C program is executed, it is called as follows:
main (argc, argv, envp)
int argc;
char **argv, **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 conventionally at least one and the first
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member of the 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. The path prefix for
this file is obtained by a search of the directories passed
as the environment line "PATH =" [see environ(5)]. The
environment is supplied by the shell [see sh(1) or csh(1)].
arg0, arg1, ..., argn are pointers to null-terminated char-
acter strings. These strings constitute the argument list
available to the new process. By convention, at least arg0
must be present and point to a string that is the same as
path (or its last component).
argv is an array of character pointers to null-terminated
strings. These strings constitute the argument list avail-
able to the new process. By convention, argv must have at
least one member, and it must 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. envp is terminated by a null pointer. For
execl and execv, the C run-time start-off routine places a
pointer to the environment of the calling process in the
global cell:
extern char **environ;
and it is used to pass the environment of the calling pro-
cess 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 set to the default action in the calling process
will be set to default action in the new process. Signals
set to be ignored by the calling process will be set to be
ignored by the new process. Signals set to be caught by the
calling process will be set to the default action in the new
process; see signal(2).
For signals set by sigset(2), exec will ensure that the new
process has the same system signal action for each signal
type whose action is SIG_DFL, SIG_IGN, or SIG_HOLD as the
calling process. However, if the action is to catch the
signal, then the action will be reset to SIG_DFL, and any
pending signal for this type will be held.
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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 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.
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)]
process ID
parent process ID
process group ID
semadj values [see semop(2)]
tty group 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)]
file size limit [see ulimit(2)]
utime, stime, cutime, and cstime [see times(2)]
file-locks [see fcntl(2) and lockf(3C)]
ERRORS
exec will fail and return to the calling process if one or
more of the following are true:
[ENOENT] One or more components of the new pro-
cess path name of the file do not exist.
[ENOTDIR] A component of the new process path of
the file prefix is not a directory.
[EACCES] Search permission is denied for a direc-
tory listed in the new process file's
path prefix.
[EACCES] The new process file is not an ordinary
file.
[EACCES] The new process file mode denies execu-
tion permission.
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[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.
[E2BIG] The number of bytes in the new process's
argument list is greater than the
system-imposed limit of NCARGS.
[EFAULT] Required hardware is not present.
[EFAULT] path, argv, or envp point to an illegal
address.
[EAGAIN] Not enough memory.
[ELIBACC] Required shared library does not have
execute permission.
[ELIBEXEC] Trying to exec a shared library
directly.
[EINTR] A signal was caught during the exec sys-
tem call.
[ENOLINK] Path points to a remote machine and the
link to that machine is no longer
active.
[EMULTIHOP] Components of path require hopping to
multiple remote machines.
[EINVAL] Trying to exec a file that calls for a
nonexistent interpreter.
SEE ALSO
alarm(2), exit(2), fcntl(2), fork(2), nice(2), ptrace(2),
semop(2), signal(2), sigset(2), times(2), ulimit(2),
umask(2), lockf(3C), environ(5).
sh(1) in the User's Reference Manual.
DIAGNOSTICS
If exec returns to the calling process an error has
occurred; the return value will be -1 and errno will be set
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to indicate the error.
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