2fe8fb192f
There is important information about booting non-ack images in docs/UPDATING. ack/aout-format images can't be built any more, and booting clang/ELF-format ones is a little different. Updating to the new boot monitor is recommended. Changes in this commit: . drop boot monitor -> allowing dropping ack support . facility to copy ELF boot files to /boot so that old boot monitor can still boot fairly easily, see UPDATING . no more ack-format libraries -> single-case libraries . some cleanup of OBJECT_FMT, COMPILER_TYPE, etc cases . drop several ack toolchain commands, but not all support commands (e.g. aal is gone but acksize is not yet). . a few libc files moved to netbsd libc dir . new /bin/date as minix date used code in libc/ . test compile fix . harmonize includes . /usr/lib is no longer special: without ack, /usr/lib plays no kind of special bootstrapping role any more and bootstrapping is done exclusively through packages, so releases depend even less on the state of the machine making them now. . rename nbsd_lib* to lib* . reduce mtree
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.\" $NetBSD: execve.2,v 1.40 2010/05/31 12:16:20 njoly 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. 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 February 24, 2008
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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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.In 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.
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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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.Fn execve Ns d
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the system 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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.Fn execve Ns d
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file becomes the second argument;
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otherwise, the name of the originally
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.Fn execve Ns d
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file becomes the first argument.
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The original arguments are shifted over to become the subsequent arguments.
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The zeroth argument, normally the name of the
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.Fn execve Ns 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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(See
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.Xr script 7
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for a detailed discussion of interpreter file execution.)
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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.
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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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In the case of a new setuid or setgid executable being executed, if
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file descriptors 0, 1, or 2 (representing stdin, stdout, and stderr)
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are currently unallocated, these descriptors will be opened to point to
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some system file like
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.Pa /dev/null .
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The intent is to ensure these descriptors are not unallocated, since
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many libraries make assumptions about the use of these 3 file descriptors.
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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 new process.
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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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.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
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.Dq 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 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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.Dv ( NCARGS
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in
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.Ao Pa sys/param.h Ac ) .
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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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its 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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.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 EAGAIN
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A
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.Xr setuid 7
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process has exceeded the current resource limit for the number of
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processes it is allowed to run concurrently.
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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; or
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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 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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.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 ENAMETOOLONG
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A component of a pathname exceeded
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.Brq Dv NAME_MAX
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characters, or an entire path name exceeded
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.Brq 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, or
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the new process file is a script starting with
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.Li #!
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and the script interpreter does not exist.
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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 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 ENOTDIR
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A component of the path prefix is not a directory.
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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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.El
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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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.Xr script 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 first appeared in
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.At v7 .
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.Sh BUGS
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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
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.Dq root ,
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then the program has some of the powers of a super-user as well.
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