c8607653d2
file. Inspired by Solaris manpage and the current NetBSD implementation as observed with the scotty package and attempts to use the earlier shell wrapper as an interpreter.
285 lines
8.8 KiB
Groff
285 lines
8.8 KiB
Groff
.\" $NetBSD: execve.2,v 1.19 2000/07/05 12:42:09 he Exp $
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.\"
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.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)execve.2 8.5 (Berkeley) 6/1/94
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.\"
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.Dd June 1, 1994
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.Dt EXECVE 2
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.Os
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.Sh NAME
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.Nm execve
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.Nd execute a file
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.Fd #include <unistd.h>
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.Ft int
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.Fn execve "const char *path" "char *const argv[]" "char *const envp[]"
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.Sh DESCRIPTION
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.Fn execve
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transforms the calling process into a new process.
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The new process is constructed from an ordinary file,
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whose name is pointed to by
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.Fa path ,
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called the
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.Em new process file .
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This file is either an executable object file,
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or a file of data for an interpreter.
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An executable object file consists of an identifying header,
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followed by pages of data representing the initial program (text)
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and initialized data pages. Additional pages may be specified
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by the header to be initialized with zero data; see
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.Xr a.out 5 .
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.Pp
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An interpreter file begins with a line of the form:
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.Pp
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.Bd -filled -offset indent -compact
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.Sy \&#!
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.Em interpreter
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.Bq Em arg
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.Ed
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.Pp
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When an interpreter file is
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.\" was .Fn execve Ap d ,
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\fBexecve\fP'd,
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the system
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.\" was .Fn execve Ap s
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\fBexecve\fP's
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runs the specified
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.Em interpreter .
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If the optional
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.Em arg
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is specified, it becomes the first argument to the
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.Em interpreter ,
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and the name of the originally
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.\" was .Fn execve Ap d
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\fBexecve\fP'd
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file becomes the second argument;
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otherwise, the name of the originally
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.\" was .Fn execve Ap d
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\fBexecve\fP'd
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file becomes the first argument. The original arguments are shifted over to
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become the subsequent arguments. The zeroth argument, normally the name of the
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.\" was .Fn execve Ap d
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\fBexecve\fP'd
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file, is left unchanged.
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The interpreter named by
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.Em interpreter
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must not itself be an interpreter file.
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.Pp
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The argument
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.Fa argv
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is a pointer to a null-terminated array of
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character pointers to null-terminated character strings.
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These strings construct the argument list to be made available to the new
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process. At least one argument must be present in
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the array; by custom, the first element should be
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the name of the executed program (for example, the last component of
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.Fa path ) .
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.Pp
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The argument
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.Fa envp
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is also a pointer to a null-terminated array of
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character pointers to null-terminated strings.
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A pointer to this array is normally stored in the global variable
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.Va environ.
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These strings pass information to the
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new process that is not directly an argument to the command (see
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.Xr environ 7 ) .
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.Pp
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File descriptors open in the calling process image remain open in
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the new process image, except for those for which the close-on-exec
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flag is set (see
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.Xr close 2
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and
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.Xr fcntl 2 ) .
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Descriptors that remain open are unaffected by
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.Fn execve .
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.Pp
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Signals set to be ignored in the calling process are set to be ignored in
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the
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new process. Signals which are set to be caught in the calling process image
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are set to default action in the new process image.
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Blocked signals remain blocked regardless of changes to the signal action.
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The signal stack is reset to be undefined (see
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.Xr sigaction 2
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for more information).
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.Pp
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If the set-user-ID mode bit of the new process image file is set
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(see
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.Xr chmod 2 ) ,
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the effective user ID of the new process image is set to the owner ID
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of the new process image file.
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If the set-group-ID mode bit of the new process image file is set,
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the effective group ID of the new process image is set to the group ID
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of the new process image file.
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(The effective group ID is the first element of the group list.)
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The real user ID, real group ID and
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other group IDs of the new process image remain the same as the calling
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process image.
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After any set-user-ID and set-group-ID processing,
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the effective user ID is recorded as the saved set-user-ID,
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and the effective group ID is recorded as the saved set-group-ID.
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These values may be used in changing the effective IDs later (see
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.Xr setuid 2 ) .
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.ne 1i
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.Pp
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The new process also inherits the following attributes from
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the calling process:
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.Pp
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.Bl -column parent_process_ID -offset indent -compact
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.It process ID Ta see Xr getpid 2
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.It parent process ID Ta see Xr getppid 2
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.It process group ID Ta see Xr getpgrp 2
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.It access groups Ta see Xr getgroups 2
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.It working directory Ta see Xr chdir 2
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.It root directory Ta see Xr chroot 2
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.It control terminal Ta see Xr termios 4
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.It resource usages Ta see Xr getrusage 2
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.It interval timers Ta see Xr getitimer 2
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.It resource limits Ta see Xr getrlimit 2
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.It file mode mask Ta see Xr umask 2
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.It signal mask Ta see Xr sigaction 2 ,
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.Xr sigprocmask 2
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.El
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.Pp
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When a program is executed as a result of an
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.Fn execve
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call, it is entered as follows:
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.Bd -literal -offset indent
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main(argc, argv, envp)
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int argc;
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char **argv, **envp;
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.Ed
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.Pp
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where
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.Fa argc
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is the number of elements in
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.Fa argv
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(the ``arg count'')
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and
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.Fa argv
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points to the array of character pointers
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to the arguments themselves.
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.Sh RETURN VALUES
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As the
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.Fn execve
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function overlays the current process image
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with a new process image the successful call
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has no process to return to.
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If
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.Fn execve
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does return to the calling process an error has occurred; the
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return value will be -1 and the global variable
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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.Fn execve
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will fail and return to the calling process if:
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.Bl -tag -width Er
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.It Bq Er ENOTDIR
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A component of the path prefix is not a directory.
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.It Bq Er ENAMETOOLONG
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A component of a pathname exceeded
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.Dv {NAME_MAX}
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characters, or an entire path name exceeded
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.Dv {PATH_MAX}
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characters.
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.It Bq Er ENOENT
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The new process file does not exist.
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.It Bq Er ELOOP
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Too many symbolic links were encountered in translating the pathname.
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.It Bq Er EACCES
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Search permission is denied for a component of the path prefix,
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the new process file is not an ordinary file,
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it's file mode denies execute permission, or
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it is on a filesystem mounted with execution
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disabled
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.Pf ( Dv MNT_NOEXEC
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in
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.Ao Pa sys/mount.h Ac ) .
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.It Bq Er ENOEXEC
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The new process file has the appropriate access
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permission, but has an invalid magic number in its header.
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.It Bq Er ETXTBSY
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The new process file is a pure procedure (shared text)
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file that is currently open for writing or reading by some process.
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.ne 1i
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.It Bq Er ENOMEM
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The new process requires more virtual memory than
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is allowed by the imposed maximum
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.Pq Xr getrlimit 2 .
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.It Bq Er E2BIG
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The number of bytes in the new process's argument list
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is larger than the system-imposed limit.
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The limit in the system as released is 262144 bytes
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.Pf ( Dv NCARGS
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in
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.Ao Pa sys/param.h Ac ) .
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.It Bq Er EFAULT
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The new process file is not as long as indicated by
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the size values in its header.
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.It Bq Er EFAULT
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.Fa path ,
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.Fa argv ,
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or
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.Fa envp
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point
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to an illegal address.
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.It Bq Er EIO
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An I/O error occurred while reading from the file system.
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.El
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.Sh CAVEAT
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If a program is
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.Em setuid
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to a non-super-user, but is executed when
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the real
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.Em uid
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is ``root'', then the program has some of the powers
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of a super-user as well.
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.Sh SEE ALSO
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.Xr _exit 2 ,
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.Xr fork 2 ,
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.Xr execl 3 ,
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.Xr environ 7
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.Sh STANDARDS
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The
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.Fn execve
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function conforms to
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.St -p1003.1-90 .
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.Sh HISTORY
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The
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.Fn execve
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function call appeared in
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.Bx 4.2 .
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