[apple/xnu.git] / bsd / man / man2 / execve.2

.\"	$NetBSD: execve.2,v 1.9 1995/02/27 12:32:25 cgd Exp $
.\"
.\" Copyright (c) 1980, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     @(#)execve.2	8.3 (Berkeley) 1/24/94
.\"
.Dd January 24, 1994
.Dt EXECVE 2
.Os BSD 4
.Sh NAME
.Nm execve
.Nd execute a file
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fo execve
.Fa "const char *path"
.Fa "char *const argv[]"
.Fa "char *const envp[]"
.Fc
.Sh DESCRIPTION
.Fn execve
transforms the calling process into a new process.
The new process is constructed from an ordinary file,
whose name is pointed to by
.Fa path ,
called the
.Em new process file .
This file is either an executable object file,
or a file of data for an interpreter.
An executable object file consists of an identifying header,
followed by pages of data representing the initial program (text)
and initialized data pages.  Additional pages may be specified
by the header to be initialized with zero data;  see
.Xr a.out 5 .
.Pp
An interpreter file begins with a line of the form:
.Pp
.Bd -filled -offset indent -compact
.Sy \&#!
.Em interpreter
.Bq Em arg ...
.Ed
.Pp
When an interpreter file is
.Fn execve Ap d ,
the system runs the specified
.Em interpreter .
If any optional
.Em args
are specified, they become the first (second, ...) argument to the
.Em interpreter.
The name of the originally
.Fn execve Ap d
file becomes the subsequent argument;
otherwise, the name of the originally
.Fn execve Ap d
file is the first argument.
The original arguments to the invocation of the interpreter
are shifted over to become the final arguments.
The zeroth argument, normally the name of the
.Fn execve Ap d
file, is left unchanged.
.Pp
The argument
.Fa argv
is a pointer to a null-terminated array of
character pointers to null-terminated character strings.
These strings construct the argument list to be made available to the new
process.  At least one argument must be present in
the array; by custom, the first element should be
the name of the executed program (for example, the last component of
.Fa path ) .
.Pp
The argument
.Fa envp
is also a pointer to a null-terminated array of
character pointers to null-terminated strings.
A pointer to this array is normally stored in the global variable
.Va environ.
These strings pass information to the
new process that is not directly an argument to the command (see
.Xr environ 7 ) .
.Pp
File descriptors open in the calling process image remain open in
the new process image, except for those for which the close-on-exec
flag is set (see
.Xr close 2
and
.Xr fcntl 2 ) .
Descriptors that remain open are unaffected by
.Fn execve .
.Pp
Signals set to be ignored in the calling process are set to be ignored in
the
new process. Signals which are set to be caught in the calling process image
are set to default action in the new process image.
Blocked signals remain blocked regardless of changes to the signal action.
The signal stack is reset to be undefined (see
.Xr sigaction 2
for more information).
.Pp
If the set-user-ID mode bit of the new process image file is set
(see
.Xr chmod 2 ) ,
the effective user ID of the new process image is set to the owner ID
of the new process image file.
If the set-group-ID mode bit of the new process image file is set,
the effective group ID of the new process image is set to the group ID
of the new process image file.
(The effective group ID is the first element of the group list.)
The real user ID, real group ID and
other group IDs of the new process image remain the same as the calling
process image.
After any set-user-ID and set-group-ID processing,
the effective user ID is recorded as the saved set-user-ID,
and the effective group ID is recorded as the saved set-group-ID.
These values may be used in changing the effective IDs later (see
.Xr setuid 2 ) .
.Pp
The new process also inherits the following attributes from
the calling process:
.Pp
.Bl -column parent_process_ID -offset indent -compact
.It process ID Ta see Xr getpid 2
.It parent process ID Ta see Xr getppid 2
.It process group ID Ta see Xr getpgrp 2
.It access groups Ta see Xr getgroups 2
.It working directory Ta see Xr chdir 2
.It root directory Ta see Xr chroot 2
.It control terminal Ta see Xr termios 4
.It resource usages Ta see Xr getrusage 2
.It interval timers Ta see Xr getitimer 2
.It resource limits Ta see Xr getrlimit 2
.It file mode mask Ta see Xr umask 2
.It signal mask Ta see Xr sigaction 2 ,
.Xr sigsetmask 2
.El
.Pp
When a program is executed as a result of an
.Fn execve
call, it is entered as follows:
.Bd -literal -offset indent
main(argc, argv, envp)
int argc;
char **argv, **envp;
.Ed
.Pp
where
.Fa argc
is the number of elements in
.Fa argv
(the ``arg count'')
and
.Fa argv
points to the array of character pointers
to the arguments themselves.
.Sh RETURN VALUES
As the
.Fn execve
function overlays the current process image  with a new process image,
the successful call has no process to return to.
If
.Fn execve
does return to the calling process, an error has occurred;
the return value will be -1 and the global variable
.Va errno
is set to indicate the error.
.Sh ERRORS
.Fn execve
will fail and return to the calling process if:
.Bl -tag -width Er
.\" ==========
.It Bq Er E2BIG
The number of bytes in the new process's argument list
is larger than the system-imposed limit.
This limit is specified by the
.Xr sysctl 3
MIB variable
.Dv KERN_ARGMAX .
.\" ==========
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.\" ==========
.It Bq Er EACCES
The new process file is not an ordinary file.
.\" ==========
.It Bq Er EACCES
The new process file mode denies execute permission.
.\" ==========
.It Bq Er EACCES
The new process file is on a filesystem mounted
with execution disabled
.Pf ( Dv MNT_NOEXEC
in
.Ao Pa sys/mount.h Ac ) .
.\" ==========
.It Bq Er EFAULT
The new process file is not as long as indicated by
the size values in its header.
.\" ==========
.It Bq Er EFAULT
.Fa Path ,
.Fa argv ,
or
.Fa envp
point
to an illegal address.
.\" ==========
.It Bq Er EIO
An I/O error occurred while reading from the file system.
.\" ==========
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
This is taken to be indicative of a looping symbolic link.
.\" ==========
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded 
.Dv {NAME_MAX}
characters, or an entire path name exceeded 
.Dv {PATH_MAX}
characters.
.\" ==========
.It Bq Er ENOENT
The new process file does not exist.
.\" ==========
.It Bq Er ENOEXEC
The new process file has the appropriate access
permission, but has an unrecognized format
(e.g., an invalid magic number in its header).
.\" ==========
.It Bq Er ENOMEM
The new process requires more virtual memory than
is allowed by the imposed maximum
.Pq Xr getrlimit 2 .
.\" ==========
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.\" ==========
.It Bq Er ETXTBSY
The new process file is a pure procedure (shared text)
file that is currently open for writing or reading by some process.
.El
.Sh CAVEAT
If a program is
.Em setuid
to a non-super-user, but is executed when
the real
.Em uid
is ``root'', then the program has some of the powers
of a super-user as well.
.Sh SEE ALSO
.Xr exit 2 ,
.Xr fork 2 ,
.Xr execl 3 ,
.Xr sysctl 3 ,
.Xr environ 7
.Sh HISTORY
The
.Fn execve
function call appeared in
.Bx 4.2 .
Commit	Line	Data
9bccf70c A	1	.\" $NetBSD: execve.2,v 1.9 1995/02/27 12:32:25 cgd Exp $
	2	.\"
	3	.\" Copyright (c) 1980, 1991, 1993
	4	.\" The Regents of the University of California. All rights reserved.
	5	.\"
	6	.\" Redistribution and use in source and binary forms, with or without
	7	.\" modification, are permitted provided that the following conditions
	8	.\" are met:
	9	.\" 1. Redistributions of source code must retain the above copyright
	10	.\" notice, this list of conditions and the following disclaimer.
	11	.\" 2. Redistributions in binary form must reproduce the above copyright
	12	.\" notice, this list of conditions and the following disclaimer in the
	13	.\" documentation and/or other materials provided with the distribution.
	14	.\" 3. All advertising materials mentioning features or use of this software
	15	.\" must display the following acknowledgement:
	16	.\" This product includes software developed by the University of
	17	.\" California, Berkeley and its contributors.
	18	.\" 4. Neither the name of the University nor the names of its contributors
	19	.\" may be used to endorse or promote products derived from this software
	20	.\" without specific prior written permission.
	21	.\"
	22	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	23	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	24	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	25	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	26	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	27	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	28	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	29	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	30	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	31	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	32	.\" SUCH DAMAGE.
	33	.\"
	34	.\" @(#)execve.2 8.3 (Berkeley) 1/24/94
	35	.\"
	36	.Dd January 24, 1994
	37	.Dt EXECVE 2
	38	.Os BSD 4
	39	.Sh NAME
	40	.Nm execve
	41	.Nd execute a file
	42	.Sh SYNOPSIS
	43	.Fd #include <unistd.h>
	44	.Ft int
2d21ac55 A	45	.Fo execve
	46	.Fa "const char *path"
	47	.Fa "char *const argv[]"
	48	.Fa "char *const envp[]"
	49	.Fc
9bccf70c	50	.Sh DESCRIPTION
39037602	51	.Fn execve
9bccf70c A	52	transforms the calling process into a new process.
	53	The new process is constructed from an ordinary file,
	54	whose name is pointed to by
	55	.Fa path ,
	56	called the
	57	.Em new process file .
	58	This file is either an executable object file,
	59	or a file of data for an interpreter.
	60	An executable object file consists of an identifying header,
	61	followed by pages of data representing the initial program (text)
	62	and initialized data pages. Additional pages may be specified
	63	by the header to be initialized with zero data; see
	64	.Xr a.out 5 .
	65	.Pp
	66	An interpreter file begins with a line of the form:
	67	.Pp
	68	.Bd -filled -offset indent -compact
	69	.Sy \&#!
	70	.Em interpreter
2d21ac55	71	.Bq Em arg ...
9bccf70c A	72	.Ed
	73	.Pp
	74	When an interpreter file is
	75	.Fn execve Ap d ,
2d21ac55	76	the system runs the specified
9bccf70c	77	.Em interpreter .
2d21ac55 A	78	If any optional
	79	.Em args
	80	are specified, they become the first (second, ...) argument to the
	81	.Em interpreter.
	82	The name of the originally
9bccf70c	83	.Fn execve Ap d
2d21ac55	84	file becomes the subsequent argument;
9bccf70c A	85	otherwise, the name of the originally
9bccf70c A	86	.Fn execve Ap d
2d21ac55 A	87	file is the first argument.
	88	The original arguments to the invocation of the interpreter
	89	are shifted over to become the final arguments.
	90	The zeroth argument, normally the name of the
9bccf70c A	91	.Fn execve Ap d
	92	file, is left unchanged.
	93	.Pp
	94	The argument
	95	.Fa argv
	96	is a pointer to a null-terminated array of
	97	character pointers to null-terminated character strings.
	98	These strings construct the argument list to be made available to the new
	99	process. At least one argument must be present in
	100	the array; by custom, the first element should be
	101	the name of the executed program (for example, the last component of
	102	.Fa path ) .
	103	.Pp
	104	The argument
	105	.Fa envp
	106	is also a pointer to a null-terminated array of
	107	character pointers to null-terminated strings.
	108	A pointer to this array is normally stored in the global variable
	109	.Va environ.
	110	These strings pass information to the
	111	new process that is not directly an argument to the command (see
	112	.Xr environ 7 ) .
	113	.Pp
	114	File descriptors open in the calling process image remain open in
	115	the new process image, except for those for which the close-on-exec
	116	flag is set (see
	117	.Xr close 2
	118	and
	119	.Xr fcntl 2 ) .
	120	Descriptors that remain open are unaffected by
	121	.Fn execve .
	122	.Pp
	123	Signals set to be ignored in the calling process are set to be ignored in
	124	the
	125	new process. Signals which are set to be caught in the calling process image
	126	are set to default action in the new process image.
	127	Blocked signals remain blocked regardless of changes to the signal action.
	128	The signal stack is reset to be undefined (see
	129	.Xr sigaction 2
	130	for more information).
	131	.Pp
	132	If the set-user-ID mode bit of the new process image file is set
	133	(see
	134	.Xr chmod 2 ) ,
	135	the effective user ID of the new process image is set to the owner ID
	136	of the new process image file.
	137	If the set-group-ID mode bit of the new process image file is set,
	138	the effective group ID of the new process image is set to the group ID
	139	of the new process image file.
	140	(The effective group ID is the first element of the group list.)
	141	The real user ID, real group ID and
	142	other group IDs of the new process image remain the same as the calling
	143	process image.
	144	After any set-user-ID and set-group-ID processing,
	145	the effective user ID is recorded as the saved set-user-ID,
	146	and the effective group ID is recorded as the saved set-group-ID.
	147	These values may be used in changing the effective IDs later (see
	148	.Xr setuid 2 ) .
	149	.Pp
	150	The new process also inherits the following attributes from
	151	the calling process:
	152	.Pp
	153	.Bl -column parent_process_ID -offset indent -compact
	154	.It process ID Ta see Xr getpid 2
155	.It parent process ID Ta see Xr getppid 2
156	.It process group ID Ta see Xr getpgrp 2
157	.It access groups Ta see Xr getgroups 2
158	.It working directory Ta see Xr chdir 2
159	.It root directory Ta see Xr chroot 2
160	.It control terminal Ta see Xr termios 4
161	.It resource usages Ta see Xr getrusage 2
162	.It interval timers Ta see Xr getitimer 2
163	.It resource limits Ta see Xr getrlimit 2
164	.It file mode mask Ta see Xr umask 2
165	.It signal mask Ta see Xr sigaction 2 ,
166	.Xr sigsetmask 2
167	.El
168	.Pp
169	When a program is executed as a result of an
170	.Fn execve
171	call, it is entered as follows:
172	.Bd -literal -offset indent
173	main(argc, argv, envp)
174	int argc;
175	char argv, envp;
176	.Ed
177	.Pp
178	where
179	.Fa argc
180	is the number of elements in
181	.Fa argv
182	(the ``arg count'')
183	and
184	.Fa argv
185	points to the array of character pointers
186	to the arguments themselves.
187	.Sh RETURN VALUES
188	As the
189	.Fn execve
2d21ac55 A	190	function overlays the current process image with a new process image,
2d21ac55 A	191	the successful call has no process to return to.
9bccf70c A	192	If
9bccf70c A	193	.Fn execve
2d21ac55 A	194	does return to the calling process, an error has occurred;
2d21ac55 A	195	the return value will be -1 and the global variable
9bccf70c A	196	.Va errno
	197	is set to indicate the error.
	198	.Sh ERRORS
39037602	199	.Fn execve
9bccf70c A	200	will fail and return to the calling process if:
9bccf70c A	201	.Bl -tag -width Er
2d21ac55 A	202	.\" ==========
	203	.It Bq Er E2BIG
	204	The number of bytes in the new process's argument list
	205	is larger than the system-imposed limit.
	206	This limit is specified by the
	207	.Xr sysctl 3
	208	MIB variable
	209	.Dv KERN_ARGMAX .
	210	.\" ==========
9bccf70c A	211	.It Bq Er EACCES
9bccf70c A	212	Search permission is denied for a component of the path prefix.
2d21ac55	213	.\" ==========
9bccf70c A	214	.It Bq Er EACCES
9bccf70c A	215	The new process file is not an ordinary file.
2d21ac55	216	.\" ==========
9bccf70c A	217	.It Bq Er EACCES
9bccf70c A	218	The new process file mode denies execute permission.
2d21ac55	219	.\" ==========
9bccf70c	220	.It Bq Er EACCES
2d21ac55 A	221	The new process file is on a filesystem mounted
2d21ac55 A	222	with execution disabled
9bccf70c A	223	.Pf ( Dv MNT_NOEXEC
	224	in
	225	.Ao Pa sys/mount.h Ac ) .
2d21ac55	226	.\" ==========
9bccf70c A	227	.It Bq Er EFAULT
	228	The new process file is not as long as indicated by
	229	the size values in its header.
2d21ac55	230	.\" ==========
9bccf70c A	231	.It Bq Er EFAULT
	232	.Fa Path ,
	233	.Fa argv ,
	234	or
	235	.Fa envp
	236	point
	237	to an illegal address.
2d21ac55	238	.\" ==========
9bccf70c A	239	.It Bq Er EIO
9bccf70c A	240	An I/O error occurred while reading from the file system.
2d21ac55 A	241	.\" ==========
	242	.It Bq Er ELOOP
	243	Too many symbolic links were encountered in translating the pathname.
	244	This is taken to be indicative of a looping symbolic link.
	245	.\" ==========
	246	.It Bq Er ENAMETOOLONG
	247	A component of a pathname exceeded
	248	.Dv {NAME_MAX}
	249	characters, or an entire path name exceeded
	250	.Dv {PATH_MAX}
	251	characters.
	252	.\" ==========
	253	.It Bq Er ENOENT
	254	The new process file does not exist.
	255	.\" ==========
	256	.It Bq Er ENOEXEC
	257	The new process file has the appropriate access
	258	permission, but has an unrecognized format
	259	(e.g., an invalid magic number in its header).
	260	.\" ==========
	261	.It Bq Er ENOMEM
	262	The new process requires more virtual memory than
	263	is allowed by the imposed maximum
	264	.Pq Xr getrlimit 2 .
	265	.\" ==========
	266	.It Bq Er ENOTDIR
	267	A component of the path prefix is not a directory.
	268	.\" ==========
	269	.It Bq Er ETXTBSY
	270	The new process file is a pure procedure (shared text)
	271	file that is currently open for writing or reading by some process.
9bccf70c A	272	.El
	273	.Sh CAVEAT
	274	If a program is
	275	.Em setuid
	276	to a non-super-user, but is executed when
	277	the real
	278	.Em uid
	279	is ``root'', then the program has some of the powers
	280	of a super-user as well.
	281	.Sh SEE ALSO
	282	.Xr exit 2 ,
	283	.Xr fork 2 ,
	284	.Xr execl 3 ,
2d21ac55	285	.Xr sysctl 3 ,
9bccf70c A	286	.Xr environ 7
	287	.Sh HISTORY
	288	The
	289	.Fn execve
	290	function call appeared in
	291	.Bx 4.2 .