summaryrefslogtreecommitdiffstats
path: root/lib/libc/sys/execve.2
blob: ba47e6d1833cb57075f5c13500d2d6f0e2e13dbf (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
.\" 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
.Fn execve "const char *path" "char *const argv[]" "char *const envp[]"
.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
.Fn execve Ap s
runs the specified
.Em interpreter .
If the optional
.Em arg
is specified, it becomes the first argument to the
.Em interpreter ,
and the name of the originally
.Fn execve Ap d
file becomes the second argument;
otherwise, the name of the originally
.Fn execve Ap d
file becomes the first argument.  The original arguments are shifted over to
become the subsequent 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 sigvec 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 [ENAMETOOLONG]
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er EINVAL
The pathname contains a character with the high-order bit set.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded 255 characters,
or an entire path name exceeded 1023 characters.
.It Bq Er ENOENT
The new process file does not exist.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.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 ENOEXEC
The new process file has the appropriate access
permission, but has an invalid magic number in its header.
.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.
.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 E2BIG
The number of bytes in the new process's argument list
is larger than the system-imposed limit.
The limit in the system as released is 20480 bytes
.Pf ( Dv NCARGS
in
.Ao Pa sys/param.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.
.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 environ 7
.Sh HISTORY
The
.Nm
function call appeared in
.Bx 4.2 .
OpenPOWER on IntegriCloud