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to POSIX.2. In particular: - don't retry for ETXTBSY. This matches what sh(1) does. The retry code was broken anyway. It only slept for several seconds for the first few retries. Then it retried without sleeping. - don't abort the search for errors related to the path prefix, in particular for ENAMETOOLONG, ENOTDIR, ELOOP. This fixes PR1487. sh(1) gets this wrong in the opposite direction by never aborting the search. - don't confuse EACCES for errors related to the path prefix with EACCES for errors related to the file. sh(1) gets this wrong. - don't return a stale errno when the search terminates normally without finding anything. The errno for the last unsuccessful execve() was usually returned. This gave too much precedence to pathologies in the last component of $PATH. This bug is irrelevant for sh(1). The implementation still uses the optimization/race-inhibitor of trying to execve() things first. POSIX.2 seems to require looking at file permissions using stat(). We now use stat() after execve() if execve() fails with an ambiguous error. Trying execve() first may actually be a pessimization, since failing execve()s are fundamentally a little slower than stat(), and are significantly slower when a file is found but has unsuitable permissions or points to an unsuitable interpreter. PR: 1487
292 lines
7.7 KiB
Groff
292 lines
7.7 KiB
Groff
.\" Copyright (c) 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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.\" @(#)exec.3 8.3 (Berkeley) 1/24/94
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.\" $Id$
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.\"
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.Dd January 24, 1994
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.Dt EXEC 3
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.Os
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.Sh NAME
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.Nm execl ,
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.Nm execlp ,
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.Nm execle ,
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.Nm exect ,
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.Nm execv ,
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.Nm execvp
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.Nd execute a file
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.Sh SYNOPSIS
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.Fd #include <unistd.h>
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.Vt extern char **environ;
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.Ft int
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.Fn execl "const char *path" "const char *arg" ...
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.Ft int
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.Fn execlp "const char *file" "const char *arg" ...
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.Ft int
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.Fn execle "const char *path" "const char *arg" ...
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.Ft int
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.Fn exect "const char *path" "char *const argv[]" "char *const envp[]"
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.Ft int
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.Fn execv "const char *path" "char *const argv[]"
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.Ft int
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.Fn execvp "const char *file" "char *const argv[]"
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.Sh DESCRIPTION
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The
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.Nm exec
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family of functions replaces the current process image with a
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new process image.
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The functions described in this manual page are front-ends for the function
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.Xr execve 2 .
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(See the manual page for
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.Xr execve 2
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for detailed information about the replacement of the current process.)
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.Pp
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The initial argument for these functions is the pathname of a file which
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is to be executed.
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.Pp
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The
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.Fa "const char *arg"
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and subsequent ellipses in the
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.Fn execl ,
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.Fn execlp ,
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and
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.Fn execle
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functions can be thought of as
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.Em arg0 ,
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.Em arg1 ,
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\&...,
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.Em argn .
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Together they describe a list of one or more pointers to null-terminated
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strings that represent the argument list available to the executed program.
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The first argument, by convention, should point to the file name associated
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with the file being executed.
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The list of arguments
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.Em must
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be terminated by a
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.Dv NULL
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pointer.
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.Pp
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The
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.Fn exect ,
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.Fn execv ,
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and
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.Fn execvp
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functions provide an array of pointers to null-terminated strings that
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represent the argument list available to the new program.
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The first argument, by convention, should point to the file name associated
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with the file begin executed.
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The array of pointers
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.Sy must
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be terminated by a
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.Dv NULL
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pointer.
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.Pp
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The
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.Fn execle
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and
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.Fn exect
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functions also specify the environment of the executed process by following
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the
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.Dv NULL
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pointer that terminates the list of arguments in the parameter list
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or the pointer to the argv array with an additional parameter.
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This additional parameter is an array of pointers to null-terminated strings
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and
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.Em must
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be terminated by a
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.Dv NULL
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pointer.
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The other functions take the environment for the new process image from the
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external variable
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.Va environ
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in the current process.
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.Pp
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Some of these functions have special semantics.
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.Pp
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The functions
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.Fn execlp
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and
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.Fn execvp
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will duplicate the actions of the shell in searching for an executable file
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if the specified file name does not contain a slash
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.Dq Li /
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character.
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The search path is the path specified in the environment by
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.Dq Ev PATH
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variable.
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If this variable isn't specified, the default path
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.Dq Ev /bin:/usr/bin:
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is
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used.
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In addition, certain errors are treated specially.
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.Pp
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If an error is ambiguous (for simplicity, we shall consider all
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errors except
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.Er ENOEXEC
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as being ambiguous here, although only the critical error
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.Er EACCES
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is really ambiguous),
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then these functions will act as if they stat the file to determine
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whether the file exists and has suitable execute permissions.
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If it does, they will return immediately with the global variable
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.Va errno
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restored to the value set by
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.Fn execve .
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Otherwise, the search will be continued.
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If the search completes without performing a successful
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.Fn execve
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or terminating due to an error,
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these functions will return with the global variable
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.Va errno
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set to
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.Er EACCES
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or
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.Er ENOENT
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according to whether at least one file with suitable execute permissions
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was found.
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.Pp
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If the header of a file isn't recognized (the attempted
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.Fn execve
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returned
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.Er ENOEXEC ) ,
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these functions will execute the shell with the path of
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the file as its first argument.
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(If this attempt fails, no further searching is done.)
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.Pp
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The function
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.Fn exect
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executes a file with the program tracing facilities enabled (see
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.Xr ptrace 2 ) .
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.Sh RETURN VALUES
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If any of the
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.Fn exec
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functions returns, an error will have occurred.
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The return value is \-1, and the global variable
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.Va errno
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will be set to indicate the error.
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.Sh FILES
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.Bl -tag -width /bin/sh -compact
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.It Pa /bin/sh
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The shell.
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.El
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.Sh ERRORS
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.Fn Execl ,
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.Fn execle ,
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.Fn execlp
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and
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.Fn execvp
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may fail and set
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.Va errno
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for any of the errors specified for the library functions
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.Xr execve 2
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and
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.Xr malloc 3 .
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.Pp
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.Fn Exect
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and
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.Fn execv
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may fail and set
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.Va errno
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for any of the errors specified for the library function
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.Xr execve 2 .
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.Sh SEE ALSO
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.Xr sh 1 ,
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.Xr execve 2 ,
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.Xr fork 2 ,
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.Xr ktrace 2 ,
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.Xr ptrace 2 ,
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.Xr environ 7 .
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.Sh COMPATIBILITY
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Historically, the default path for the
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.Fn execlp
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and
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.Fn execvp
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functions was
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.Dq Pa :/bin:/usr/bin .
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This was changed to place the current directory last to enhance system
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security.
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.Pp
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The behavior of
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.Fn execlp
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and
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.Fn execvp
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when errors occur while attempting to execute the file is not quite historic
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practice, and has not traditionally been documented and is not specified
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by the
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.Tn POSIX
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standard.
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.Pp
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Traditionally, the functions
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.Fn execlp
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and
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.Fn execvp
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ignored all errors except for the ones described above and
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.Er ETXTBSY ,
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upon which they retried after sleeping for several seconds, and
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.Er ENOMEM
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and
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.Er E2BIG ,
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upon which they returned.
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They now return for
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.Er ETXTBSY ,
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and determine existence and executability more carefully.
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In particular,
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.Er EACCES
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for inaccessible directories in the path prefix is no longer
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confused with
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.Er EACCES
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for files with unsuitable execute permissions.
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In
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.Bx 4.4 ,
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they returned upon all errors except
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.Er EACCES ,
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.Er ENOENT ,
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.Er ENOEXEC
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and
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.Er ETXTBSY .
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This was inferior to the traditional error handling,
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since it it breaks the ignoring of errors for path prefixes
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and only improves the handling of the unusual ambiguous error
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.Er EFAULT
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and the unusual error
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.Er EIO .
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The behaviour was changed to match the behaviour of
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.Xr sh 1 .
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.Sh STANDARDS
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.Fn Execl ,
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.Fn execv ,
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.Fn execle ,
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.Fn execlp
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and
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.Fn execvp
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conform to
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.St -p1003.1-88 .
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