1 .\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
2 .\" and Copyright (c) 2006 Michael Kerrisk <mtk.manpages@gmail.com>
4 .\" %%%LICENSE_START(VERBATIM)
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10 .\" manual under the conditions for verbatim copying, provided that the
11 .\" entire resulting derived work is distributed under the terms of a
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14 .\" Since the Linux kernel and libraries are constantly changing, this
15 .\" manual page may be incorrect or out-of-date. The author(s) assume no
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19 .\" which is licensed free of charge, as they might when working
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26 .\" Modified by Michael Haardt <michael@moria.de>
27 .\" Modified 1993-07-21 by Rik Faith <faith@cs.unc.edu>
28 .\" Modified 1994-08-21 by Michael Chastain <mec@shell.portal.com>:
29 .\" Modified 1997-01-31 by Eric S. Raymond <esr@thyrsus.com>
30 .\" Modified 1999-11-12 by Urs Thuermann <urs@isnogud.escape.de>
31 .\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
32 .\" 2006-09-04 Michael Kerrisk <mtk.manpages@gmail.com>
33 .\" Added list of process attributes that are not preserved on exec().
34 .\" 2007-09-14 Ollie Wild <aaw@google.com>, mtk
35 .\" Add text describing limits on command-line arguments + environment
37 .TH EXECVE 2 2012-10-27 "Linux" "Linux Programmer's Manual"
39 execve \- execute program
41 .B #include <unistd.h>
43 .BI "int execve(const char *" filename ", char *const " argv "[], "
45 .BI " char *const " envp []);
48 executes the program pointed to by \fIfilename\fP.
49 \fIfilename\fP must be either a binary executable, or a script
50 starting with a line of the form:
54 \fB#!\fP \fIinterpreter \fP[optional-arg]
58 For details of the latter case, see "Interpreter scripts" below.
60 \fIargv\fP is an array of argument strings passed to the new program.
61 By convention, the first of these strings should contain the filename
62 associated with the file being executed.
63 \fIenvp\fP is an array of strings, conventionally of the form
64 \fBkey=value\fP, which are passed as environment to the new program.
65 Both \fIargv\fP and \fIenvp\fP must be terminated by a NULL pointer.
66 The argument vector and environment can be accessed by the
67 called program's main function, when it is defined as:
71 int main(int argc, char *argv[], char *envp[])
76 does not return on success, and the text, data, bss, and
77 stack of the calling process are overwritten by that of the program
80 If the current program is being ptraced, a \fBSIGTRAP\fP is sent to it
84 If the set-user-ID bit is set on the program file pointed to by
86 and the underlying file system is not mounted
92 and the calling process is not being ptraced,
93 then the effective user ID of the calling process is changed
94 to that of the owner of the program file.
95 Similarly, when the set-group-ID
96 bit of the program file is set the effective group ID of the calling
97 process is set to the group of the program file.
99 The effective user ID of the process is copied to the saved set-user-ID;
100 similarly, the effective group ID is copied to the saved set-group-ID.
101 This copying takes place after any effective ID changes that occur
102 because of the set-user-ID and set-group-ID permission bits.
104 If the executable is an a.out dynamically linked
105 binary executable containing
106 shared-library stubs, the Linux dynamic linker
108 is called at the start of execution to bring
109 needed shared libraries into memory
110 and link the executable with them.
112 If the executable is a dynamically linked ELF executable, the
113 interpreter named in the PT_INTERP segment is used to load the needed
115 This interpreter is typically
116 .I /lib/ld-linux.so.2
117 for binaries linked with glibc 2.
118 (For binaries linked with the old Linux libc5, the interpreter was typically
119 .IR /lib/ld-linux.so.1 .)
121 All process attributes are preserved during an
123 except the following:
125 The dispositions of any signals that are being caught are
129 Any alternate signal stack is not preserved
130 .RB ( sigaltstack (2)).
132 Memory mappings are not preserved
135 Attached System V shared memory segments are detached
138 POSIX shared memory regions are unmapped
141 Open POSIX message queue descriptors are closed
142 .RB ( mq_overview (7)).
144 Any open POSIX named semaphores are closed
145 .RB ( sem_overview (7)).
147 POSIX timers are not preserved
148 .RB ( timer_create (2)).
150 Any open directory streams are closed
153 Memory locks are not preserved
157 Exit handlers are not preserved
161 The floating-point environment is reset to the default (see
164 The process attributes in the preceding list are all specified
166 The following Linux-specific process attributes are also
167 not preserved during an
174 unless a set-user-ID or set-group ID program is being executed,
175 in which case it is cleared.
182 (Since Linux 2.4.36 / 2.6.23)
183 If a set-user-ID or set-group-ID program is being executed,
184 then the parent death signal set by
189 The process name, as set by
193 .IR "ps\ \-o comm" ),
194 is reset to the name of the new executable file.
201 .BR capabilities (7).
203 The termination signal is reset to
208 Note the following further points:
210 All threads other than the calling thread are destroyed during an
212 Mutexes, condition variables, and other pthreads objects are not preserved.
214 The equivalent of \fIsetlocale(LC_ALL, "C")\fP
215 is executed at program start-up.
217 POSIX.1-2001 specifies that the dispositions of any signals that
218 are ignored or set to the default are left unchanged.
219 POSIX.1-2001 specifies one exception: if
222 then an implementation may leave the disposition unchanged or
223 reset it to the default; Linux does the former.
225 Any outstanding asynchronous I/O operations are canceled
229 For the handling of capabilities during
232 .BR capabilities (7).
234 By default, file descriptors remain open across an
236 File descriptors that are marked close-on-exec are closed;
237 see the description of
241 (If a file descriptor is closed, this will cause the release
242 of all record locks obtained on the underlying file by this process.
246 POSIX.1-2001 says that if file descriptors 0, 1, and 2 would
247 otherwise be closed after a successful
249 and the process would gain privilege because the set-user_ID or
250 set-group_ID permission bit was set on the executed file,
251 then the system may open an unspecified file for each of these
253 As a general principle, no portable program, whether privileged or not,
254 can assume that these three file descriptors will remain
257 .\" On Linux it appears that these file descriptors are
258 .\" always open after an execve(), and it looks like
259 .\" Solaris 8 and FreeBSD 6.1 are the same. -- mtk, 30 Apr 2007
260 .SS Interpreter scripts
261 An interpreter script is a text file that has execute
262 permission enabled and whose first line is of the form:
266 \fB#!\fP \fIinterpreter \fP[optional-arg]
272 must be a valid pathname for an
273 executable which is not itself a script.
278 specifies an interpreter script, then
280 will be invoked with the following arguments:
284 \fIinterpreter\fP [optional-arg] \fIfilename\fP arg...
290 is the series of words pointed to by the
297 should either be absent, or be specified as a single word (i.e., it
298 should not contain white space); see NOTES below.
299 .SS Limits on size of arguments and environment
300 Most UNIX implementations impose some limit on the total size
301 of the command-line argument
305 strings that may be passed to a new program.
306 POSIX.1 allows an implementation to advertise this limit using the
308 constant (either defined in
310 or available at run time using the call
311 .IR "sysconf(_SC_ARG_MAX)" ).
313 On Linux prior to kernel 2.6.23, the memory used to store the
314 environment and argument strings was limited to 32 pages
315 (defined by the kernel constant
317 On architectures with a 4-kB page size,
318 this yields a maximum size of 128 kB.
320 On kernel 2.6.23 and later, most architectures support a size limit
321 derived from the soft
325 that is in force at the time of the
328 (Architectures with no memory management unit are excepted:
329 they maintain the limit that was in effect before kernel 2.6.23.)
330 This change allows programs to have a much larger
331 argument and/or environment list.
332 .\" For some background on the changes to ARG_MAX in kernels 2.6.23 and
334 .\" http://sourceware.org/bugzilla/show_bug.cgi?id=5786
335 .\" http://bugzilla.kernel.org/show_bug.cgi?id=10095
336 .\" http://thread.gmane.org/gmane.linux.kernel/646709/focus=648101,
337 .\" checked into 2.6.25 as commit a64e715fc74b1a7dcc5944f848acc38b2c4d4ee2.
338 For these architectures, the total size is limited to 1/4 of the allowed
340 (Imposing the 1/4-limit
341 ensures that the new program always has some stack space.)
342 .\" Ollie: That doesn't include the lists of pointers, though,
343 .\" so the actual usage is a bit higher (1 pointer per argument).
345 the kernel places a floor of 32 pages on this size limit,
349 applications are guaranteed to have at least as much argument and
350 environment space as was provided by Linux 2.6.23 and earlier.
351 (This guarantee was not provided in Linux 2.6.23 and 2.6.24.)
352 Additionally, the limit per string is 32 pages (the kernel constant
353 .BR MAX_ARG_STRLEN ),
354 and the maximum number of strings is 0x7FFFFFFF.
358 does not return, on error \-1 is returned, and
360 is set appropriately.
364 The total number of bytes in the environment
371 Search permission is denied on a component of the path prefix of
373 or the name of a script interpreter.
375 .BR path_resolution (7).)
378 The file or a script interpreter is not a regular file.
381 Execute permission is denied for the file or a script or ELF interpreter.
384 The file system is mounted
389 points outside your accessible address space.
392 An ELF executable had more than one PT_INTERP segment (i.e., tried to
393 name more than one interpreter).
396 An I/O error occurred.
399 An ELF interpreter was a directory.
402 An ELF interpreter was not in a recognized format.
405 Too many symbolic links were encountered in resolving
407 or the name of a script or ELF interpreter.
410 The process has the maximum number of files open.
417 The system limit on the total number of open files has been reached.
422 or a script or ELF interpreter does not exist, or a shared library
423 needed for file or interpreter cannot be found.
426 An executable is not in a recognized format, is for the wrong
427 architecture, or has some other format error that means it cannot be
431 Insufficient kernel memory was available.
434 A component of the path prefix of
436 or a script or ELF interpreter is not a directory.
439 The file system is mounted
441 the user is not the superuser,
442 and the file has the set-user-ID or set-group-ID bit set.
445 The process is being traced, the user is not the superuser and the
446 file has the set-user-ID or set-group-ID bit set.
449 Executable was open for writing by one or more processes.
451 SVr4, 4.3BSD, POSIX.1-2001.
452 POSIX.1-2001 does not document the #! behavior
453 but is otherwise compatible.
454 .\" SVr4 documents additional error
455 .\" conditions EAGAIN, EINTR, ELIBACC, ENOLINK, EMULTIHOP; POSIX does not
456 .\" document ETXTBSY, EPERM, EFAULT, ELOOP, EIO, ENFILE, EMFILE, EINVAL,
457 .\" EISDIR or ELIBBAD error conditions.
459 Set-user-ID and set-group-ID processes can not be
462 Linux ignores the set-user-ID and set-group-ID bits on scripts.
464 The result of mounting a file system
466 varies across Linux kernel versions:
467 some will refuse execution of set-user-ID and set-group-ID
468 executables when this would
469 give the user powers she did not have already (and return
471 some will just ignore the set-user-ID and set-group-ID bits and
475 A maximum line length of 127 characters is allowed for the first line in
476 a #! executable shell script.
480 argument of an interpreter script vary across implementations.
481 On Linux, the entire string following the
483 name is passed as a single argument to the interpreter,
484 and this string can include white space.
485 However, behavior differs on some other systems.
488 use the first white space to terminate
491 .\" e.g., FreeBSD before 6.0, but not FreeBSD 6.0 onward
492 an interpreter script can have multiple arguments,
495 are used to delimit the arguments.
499 can be specified as NULL,
500 which has the same effect as specifying this argument
501 as a pointer to a list containing a single NULL pointer.
502 .B "Do not take advantage of this misfeature!"
503 It is nonstandard and nonportable:
504 on most other UNIX systems doing this will result in an error
506 .\" e.g., EFAULT on Solaris 8 and FreeBSD 6.1; but
507 .\" HP-UX 11 is like Linux -- mtk, Apr 2007
508 .\" Bug filed 30 Apr 2007: http://bugzilla.kernel.org/show_bug.cgi?id=8408
509 .\" Bug rejected (because fix would constitute an ABI change).
512 POSIX.1-2001 says that values returned by
514 should be invariant over the lifetime of a process.
515 However, since Linux 2.6.23, if the
517 resource limit changes, then the value reported by
520 to reflect the fact that the limit on space for holding
521 command-line arguments and environment variables has changed.
524 .\" Some Linux versions have failed to check permissions on ELF
525 .\" interpreters. This is a security hole, because it allows users to
526 .\" open any file, such as a rewinding tape device, for reading. Some
527 .\" Linux versions have also had other security holes in
529 .\" that could be exploited for denial of service by a suitably crafted
530 .\" ELF binary. There are no known problems with 2.0.34 or 2.2.15.
532 With UNIX V6 the argument list of an
535 while the argument list of
538 Thus, this argument list was not directly usable in a further
541 Since UNIX V7 both are NULL.
543 The following program is designed to be execed by the second program below.
544 It just echoes its command-line one per line.
554 main(int argc, char *argv[])
558 for (j = 0; j < argc; j++)
559 printf("argv[%d]: %s\\n", j, argv[j]);
566 This program can be used to exec the program named in its command-line
578 main(int argc, char *argv[])
580 char *newargv[] = { NULL, "hello", "world", NULL };
581 char *newenviron[] = { NULL };
584 fprintf(stderr, "Usage: %s <file\-to\-exec>\\n", argv[0]);
588 newargv[0] = argv[1];
590 execve(argv[1], newargv, newenviron);
591 perror("execve"); /* execve() only returns on error */
597 We can use the second program to exec the first as follows:
601 .RB "$" " cc myecho.c \-o myecho"
602 .RB "$" " cc execve.c \-o execve"
603 .RB "$" " ./execve ./myecho"
610 We can also use these programs to demonstrate the use of a script
612 To do this we create a script whose "interpreter" is our
618 .RB "$" " cat > script.sh"
619 .B #! ./myecho script-arg
621 .RB "$" " chmod +x script.sh"
625 We can then use our program to exec the script:
629 .RB "$" " ./execve ./script.sh"
646 .BR path_resolution (7),