summaryrefslogtreecommitdiffstats
path: root/man/man3/exec.3
blob: a94a2f1b7f8bff5cedb912b7fba1efc3932948bc (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
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
'\" t
.\" Copyright (c) 1991 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" SPDX-License-Identifier: BSD-4-Clause-UC
.\"
.\"     @(#)exec.3	6.4 (Berkeley) 4/19/91
.\"
.\" Converted for Linux, Mon Nov 29 11:12:48 1993, faith@cs.unc.edu
.\" Updated more for Linux, Tue Jul 15 11:54:18 1997, pacman@cqc.com
.\" Modified, 24 Jun 2004, Michael Kerrisk <mtk.manpages@gmail.com>
.\"     Added note on casting NULL
.\"
.TH exec 3 2024-05-02 "Linux man-pages (unreleased)"
.SH NAME
execl, execlp, execle, execv, execvp, execvpe \- execute a file
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <unistd.h>
.P
.B extern char **environ;
.P
.BI "int execl(const char *" pathname ", const char *" arg ", ..."
.B  "                /*, (char *) NULL */);"
.BI "int execlp(const char *" file ", const char *" arg ", ..."
.B  "                /*, (char *) NULL */);"
.BI "int execle(const char *" pathname ", const char *" arg ", ..."
.BI "                /*, (char *) NULL, char *const " envp "[] */);"
.BI "int execv(const char *" pathname ", char *const " argv "[]);"
.BI "int execvp(const char *" file ", char *const " argv "[]);"
.BI "int execvpe(const char *" file ", char *const " argv \
"[], char *const " envp "[]);"
.fi
.P
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.P
.BR execvpe ():
.nf
    _GNU_SOURCE
.fi
.SH DESCRIPTION
The
.BR exec ()
family of functions replaces the current process image with a new process
image.
The functions described in this manual page are layered on top of
.BR execve (2).
(See the manual page for
.BR execve (2)
for further details about the replacement of the current process image.)
.P
The initial argument for these functions is the name of a file that is
to be executed.
.P
The functions can be grouped based on the letters following the "exec" prefix.
.\"
.SS l - execl(), execlp(), execle()
The
.I "const char\ *arg"
and subsequent ellipses can be thought of as
.IR arg0 ,
.IR arg1 ,
\&...,
.IR argn .
Together they describe a list of one or more pointers to null-terminated
strings that represent the argument list available to the executed program.
The first argument, by convention, should point to the filename associated
with the file being executed.
The list of arguments
.I must
be terminated by a null pointer,
and, since these are variadic functions, this pointer must be cast
.IR "(char\ *) NULL" .
.P
By contrast with the 'l' functions, the 'v' functions (below) specify the
command-line arguments of the executed program as a vector.
.\"
.SS v - execv(), execvp(), execvpe()
The
.I "char\ *const argv[]"
argument is an array of pointers to null-terminated strings that
represent the argument list available to the new program.
The first argument, by convention, should point to the filename
associated with the file being executed.
The array of pointers
.I must
be terminated by a null pointer.
.SS e - execle(), execvpe()
The environment of the new process image is specified via the argument
.IR envp .
The
.I envp
argument is an array of pointers to null-terminated strings and
.I must
be terminated by a null pointer.
.P
All other
.BR exec ()
functions (which do not include 'e' in the suffix)
take the environment for the new process
image from the external variable
.I environ
in the calling process.
.SS p - execlp(), execvp(), execvpe()
These functions duplicate the actions of the shell in
searching for an executable file
if the specified filename does not contain a slash (/) character.
The file is sought in the colon-separated list of directory pathnames
specified in the
.B PATH
environment variable.
If this variable isn't defined, the path list defaults to
a list that includes the directories returned by
.I confstr(_CS_PATH)
(which typically returns the value "/bin:/usr/bin")
and possibly also the current working directory;
see NOTES for further details.
.P
.BR execvpe ()
searches for the program using the value of
.B PATH
from the caller's environment, not from the
.I envp
argument.
.P
If the specified filename includes a slash character, then
.B PATH
is ignored, and the file at the specified pathname is executed.
.P
In addition, certain errors are treated specially.
.P
If permission is denied for a file (the attempted
.BR execve (2)
failed with the error
.BR EACCES ),
these functions will continue searching the rest of the search path.
If no other file is found, however,
they will return with
.I errno
set to
.BR EACCES .
.P
If the header of a file isn't recognized (the attempted
.BR execve (2)
failed with the error
.BR ENOEXEC ),
these functions will execute the shell
.RI ( /bin/sh )
with the path of the file as its first argument.
(If this attempt fails, no further searching is done.)
.P
All other
.BR exec ()
functions (which do not include 'p' in the suffix)
take as their first argument a (relative or absolute) pathname
that identifies the program to be executed.
.SH RETURN VALUE
The
.BR exec ()
functions return only if an error has occurred.
The return value is \-1, and
.I errno
is set to indicate the error.
.SH ERRORS
All of these functions may fail and set
.I errno
for any of the errors specified for
.BR execve (2).
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.na
.nh
.BR execl (),
.BR execle (),
.BR execv ()
T}	Thread safety	MT-Safe
T{
.na
.nh
.BR execlp (),
.BR execvp (),
.BR execvpe ()
T}	Thread safety	MT-Safe env
.TE
.SH VERSIONS
The default search path (used when the environment
does not contain the variable \fBPATH\fR)
shows some variation across systems.
It generally includes
.I /bin
and
.I /usr/bin
(in that order) and may also include the current working directory.
On some other systems, the current working is included after
.I /bin
and
.IR /usr/bin ,
as an anti-Trojan-horse measure.
The glibc implementation long followed the traditional default where
the current working directory is included at the start of the search path.
However, some code refactoring during the development of glibc 2.24
.\" glibc commit 1eb8930608705702d5746e5491bab4e4429fcb83
caused the current working directory to be dropped altogether
from the default search path.
This accidental behavior change is considered mildly beneficial,
and won't be reverted.
.P
The behavior of
.BR execlp ()
and
.BR execvp ()
when errors occur while attempting to execute the file is historic
practice, but has not traditionally been documented and is not specified by
the POSIX standard.
BSD (and possibly other systems) do an automatic
sleep and retry if
.B ETXTBSY
is encountered.
Linux treats it as a hard
error and returns immediately.
.P
Traditionally, the functions
.BR execlp ()
and
.BR execvp ()
ignored all errors except for the ones described above and
.B ENOMEM
and
.BR E2BIG ,
upon which they returned.
They now return if any error other than the ones
described above occurs.
.SH STANDARDS
.TP
.B environ
.TQ
.BR execl ()
.TQ
.BR execlp ()
.TQ
.BR execle ()
.TQ
.BR execv ()
.TQ
.BR execvp ()
POSIX.1-2008.
.TP
.BR execvpe ()
GNU.
.SH HISTORY
.TP
.B environ
.TQ
.BR execl ()
.TQ
.BR execlp ()
.TQ
.BR execle ()
.TQ
.BR execv ()
.TQ
.BR execvp ()
POSIX.1-2001.
.TP
.BR execvpe ()
glibc 2.11.
.SH BUGS
Before glibc 2.24,
.BR execl ()
and
.BR execle ()
employed
.BR realloc (3)
internally and were consequently not async-signal-safe,
in violation of the requirements of POSIX.1.
.\" https://sourceware.org/bugzilla/show_bug.cgi?id=19534
This was fixed in glibc 2.24.
.\"
.SS Architecture-specific details
On sparc and sparc64,
.BR execv ()
is provided as a system call by the kernel
(with the prototype shown above)
for compatibility with SunOS.
This function is
.I not
employed by the
.BR execv ()
wrapper function on those architectures.
.SH SEE ALSO
.BR sh (1),
.BR execve (2),
.BR execveat (2),
.BR fork (2),
.BR ptrace (2),
.BR fexecve (3),
.BR system (3),
.BR environ (7)