man2/execve.2

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   3 .\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
   4 .\" and Copyright (c) 2006 Michael Kerrisk <mtk-manpages@gmx.net>
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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@gmx.net>
  32 .\" 2006-09-04 Michael Kerrisk <mtk-manpages@gmx.net>
  33 .\"     Added list of process attributes that are not preserved on exec().
  34 .\"
  35 .TH EXECVE 2 2006-09-04 "Linux 2.6.17" "Linux Programmer's Manual"
  36 .SH NAME
  37 execve \- execute program
  38 .SH SYNOPSIS
  39 .B #include <unistd.h>
  40 .sp
  41 .BI "int execve(const char *" filename ", char *const " argv "[], "
  42 .br
  43 .BI "           char *const " envp []);
  44 .SH DESCRIPTION
  45 \fBexecve\fP() executes the program pointed to by \fIfilename\fP.
  46 \fIfilename\fP must be either a binary executable, or a script
  47 starting with a line of the form "\fB#! \fIinterpreter \fR[arg]".
  48 In the latter case, the interpreter must be a valid pathname for an
  49 executable which is not itself a script, which will be invoked as
  50 \fBinterpreter\fR [arg] \fIfilename\fR.
  51
  52 \fIargv\fP is an array of argument strings passed to the new program.
  53 \fIenvp\fP is an array of strings, conventionally of the form
  54 \fBkey=value\fR, which are passed as environment to the new
  55 program.  Both \fIargv\fP and \fIenvp\fP must be terminated by a null
  56 pointer.  The argument vector and environment can be accessed by the
  57 called program's main function, when it is defined as \fBint main(int
  58 argc, char *argv[], char *envp[])\fR.
  59
  60 \fBexecve\fP() does not return on success, and the text, data, bss, and
  61 stack of the calling process are overwritten by that of the program
  62 loaded.
  63
  64 If the current program is being ptraced, a \fBSIGTRAP\fP is sent to it
  65 after a successful \fBexecve\fP().
  66
  67 If the set-user-ID bit is set on the program file pointed to by
  68 \fIfilename\fP, and the calling process is not being ptraced,
  69 then the effective user ID of the calling process is changed
  70 to that of the owner of the program file.
  71 Similarly, when the set-group-ID
  72 bit of the program file is set the effective group ID of the calling
  73 process is set to the group of the program file.
  74
  75 The effective user ID of the process is copied to the saved set-user-ID;
  76 similarly, the effective group ID is copied to the saved set-group-ID.
  77 This copying takes place after any effective ID changes that occur
  78 because of the set-user-ID and set-group-ID permission bits.
  79
  80 If the executable is an a.out dynamically-linked
  81 binary executable containing
  82 shared-library stubs, the Linux dynamic linker
  83 .BR ld.so (8)
  84 is called at the start of execution to bring
  85 needed shared libraries into memory
  86 and link the executable with them.
  87
  88 If the executable is a dynamically-linked ELF executable, the
  89 interpreter named in the PT_INTERP segment is used to load the needed
  90 shared libraries.  This interpreter is typically
  91 \fI/lib/ld-linux.so.1\fR for binaries linked with the Linux libc
  92 version 5, or \fI/lib/ld-linux.so.2\fR for binaries linked with the
  93 GNU libc version 2.
  94
  95 All process attributes are preserved during an
  96 .BR execve (),
  97 except the following:
  98 .IP * 4
  99 File descriptors that are marked close-on-exec are closed
 100 (see the description of
 101 .BR FD_CLOEXEC
 102 in
 103 .BR fcntl (2)).
 104 .\" FIXME add some statement about the effect on record locks (fcntl()).
 105 .IP * 4
 106 The set of pending signals is cleared
 107 .RB ( sigpending (2)).
 108 .IP * 4
 109 The dispositions of any signals that are being caught are
 110 reset to being ignored.
 111 .IP * 4
 112 Any alternate signal stack is not preserved
 113 .RB ( sigaltstack (2)).
 114 .IP * 4
 115 Memory mappings are not preserved
 116 .RB ( mmap (2)).
 117 .IP * 4
 118 Attached System V shared memory segments are detached
 119 .RB ( shmat (2)).
 120 .IP * 4
 121 POSIX shared memory regions are unmapped
 122 .RB ( shm_open (3)).
 123 .IP * 4
 124 Open POSIX message queue descriptors are closed
 125 .RB ( mq_overview (7)).
 126 .IP * 4
 127 Any open POSIX named semaphores are closed
 128 .RB ( sem_overview (7)).
 129 .IP * 4
 130 POSIX timers are not preserved
 131 .RB ( timer_create (3)).
 132 .IP * 4
 133 Any open directory streams are closed
 134 .RB ( opendir (3)).
 135 .IP * 4
 136 Memory locks are not preserved
 137 .RB ( mlock (2),
 138 .BR mlockall (2)).
 139 .IP * 4
 140 Exit handlers are not preserved
 141 .RB ( atexit (3),
 142 .BR on_exit (3)).
 143 .PP
 144 The process attributes in the preceding list are all specified
 145 in POSIX.1-2001.
 146 The following Linux-specific process attributes are also
 147 not preserved during an
 148 .BR execve ():
 149 .IP * 4
 150 The
 151 .BR prctl (2)
 152 .B PR_SET_DUMPABLE
 153 flag is set,
 154 unless a set-user-ID or set-group ID program is being executed,
 155 in which case it is cleared.
 156 .IP * 4
 157 The
 158 .BR prctl (2)
 159 .B PR_SET_KEEPCAPS
 160 flag is cleared.
 161 .IP * 4
 162 The process name, as set by
 163 .BR prctl (2)
 164 .BR PR_SET_NAME
 165 (and displayed by
 166 .IR "ps -o comm" ),
 167 is reset to the name of the new executable file.
 168 .IP * 4
 169 The termination signal is reset to SIGCHLD
 170 (see
 171 .BR clone (2)).
 172 .PP
 173 Note the following further points:
 174 .IP * 4
 175 All threads other than calling thread are destroyed during an
 176 .BR execve ().
 177 Mutexes, condition variables, and other pthreads objects are not preserved.
 178 .IP * 4
 179 The equivalent of \fIsetlocale(LC_ALL, "C")\fP
 180 is executed at program start-up.
 181 .IP * 4
 182 POSIX.1-2001 specifies that the dispositions of any signals that
 183 are ignored or set to the default are left unchanged.
 184 POSIX.1-2001 specifies one exception: if SIGCHLD is being ignored,
 185 then an implementation may leave the disposition unchanged or
 186 reset it to the default; Linux does the former.
 187 .IP * 4
 188 Any outstanding asynchronous I/O operations are cancelled
 189 .RB ( aio_read (3),
 190 .BR aio_write (3)).
 191 .IP * 4
 192 For the handling of capabilities during
 193 .BR execve (2),
 194 see
 195 .BR capabilities (7).
 196 .SH "RETURN VALUE"
 197 On success, \fBexecve\fP() does not return, on error \-1 is returned, and
 198 .I errno
 199 is set appropriately.
 200 .SH ERRORS
 201 .TP
 202 .B E2BIG
 203 The total number of bytes in the environment
 204 .RI ( envp )
 205 and argument list
 206 .RI ( argv )
 207 is too large.
 208 .TP
 209 .B EACCES
 210 Search permission is denied on a component of the path prefix of
 211 .I filename
 212 or the name of a script interpreter.
 213 (See also
 214 .BR path_resolution (2).)
 215 .TP
 216 .B EACCES
 217 The file or a script interpreter is not a regular file.
 218 .TP
 219 .B EACCES
 220 Execute permission is denied for the file or a script or ELF interpreter.
 221 .TP
 222 .B EACCES
 223 The file system is mounted
 224 .IR noexec .
 225 .TP
 226 .B EFAULT
 227 .I filename
 228 points outside your accessible address space.
 229 .TP
 230 .B EINVAL
 231 An ELF executable had more than one PT_INTERP segment (i.e., tried to
 232 name more than one interpreter).
 233 .TP
 234 .B EIO
 235 An I/O error occurred.
 236 .TP
 237 .B EISDIR
 238 An ELF interpreter was a directory.
 239 .TP
 240 .B ELIBBAD
 241 An ELF interpreter was not in a recognised format.
 242 .TP
 243 .B ELOOP
 244 Too many symbolic links were encountered in resolving
 245 .I filename
 246 or the name of a script or ELF interpreter.
 247 .TP
 248 .B EMFILE
 249 The process has the maximum number of files open.
 250 .TP
 251 .B ENAMETOOLONG
 252 .I filename
 253 is too long.
 254 .TP
 255 .B ENFILE
 256 The system limit on the total number of open files has been reached.
 257 .TP
 258 .B ENOENT
 259 The file
 260 .I filename
 261 or a script or ELF interpreter does not exist, or a shared library
 262 needed for file or interpreter cannot be found.
 263 .TP
 264 .B ENOEXEC
 265 An executable is not in a recognised format, is for the wrong
 266 architecture, or has some other format error that means it cannot be
 267 executed.
 268 .TP
 269 .B ENOMEM
 270 Insufficient kernel memory was available.
 271 .TP
 272 .B ENOTDIR
 273 A component of the path prefix of
 274 .I filename
 275 or a script or ELF interpreter is not a directory.
 276 .TP
 277 .B EPERM
 278 The file system is mounted
 279 .IR nosuid ,
 280 the user is not the superuser,
 281 and the file has the set-user-ID or set-group-ID bit set.
 282 .TP
 283 .B EPERM
 284 The process is being traced, the user is not the superuser and the
 285 file has the set-user-ID or set-group-ID bit set.
 286 .TP
 287 .B ETXTBSY
 288 Executable was open for writing by one or more processes.
 289 .SH "CONFORMING TO"
 290 SVr4, 4.3BSD, POSIX.1-2001.
 291 POSIX.1-2001 does not document the #!  behavior
 292 but is otherwise compatible.
 293 .\" SVr4 documents additional error
 294 .\" conditions EAGAIN, EINTR, ELIBACC, ENOLINK, EMULTIHOP; POSIX does not
 295 .\" document ETXTBSY, EPERM, EFAULT, ELOOP, EIO, ENFILE, EMFILE, EINVAL,
 296 .\" EISDIR or ELIBBAD error conditions.
 297 .SH NOTES
 298 Set-user-ID and set-group-ID processes can not be \fBptrace\fP()d.
 299
 300 Linux ignores the set-user-ID and set-group-ID bits on scripts.
 301
 302 The result of mounting a filesystem
 303 .I nosuid
 304 vary between Linux kernel versions:
 305 some will refuse execution of set-user-ID and set-group-ID
 306 executables when this would
 307 give the user powers she did not have already (and return EPERM),
 308 some will just ignore the set-user-ID and set-group-ID bits and
 309 .BR exec ()
 310 successfully.
 311
 312 A maximum line length of 127 characters is allowed for the first line in
 313 a #! executable shell script.
 314 .\" .SH BUGS
 315 .\" Some Linux versions have failed to check permissions on ELF
 316 .\" interpreters.  This is a security hole, because it allows users to
 317 .\" open any file, such as a rewinding tape device, for reading.  Some
 318 .\" Linux versions have also had other security holes in \fBexecve\fP(),
 319 .\" that could be exploited for denial of service by a suitably crafted
 320 .\" ELF binary. There are no known problems with 2.0.34 or 2.2.15.
 321 .SH HISTORICAL
 322 With Unix V6 the argument list of an
 323 .BR exec ()
 324 call was ended by 0,
 325 while the argument list of
 326 .I main
 327 was ended by \-1. Thus, this
 328 argument list was not directly usable in a further
 329 .BR exec ()
 330 call.
 331 Since Unix V7 both are NULL.
 332 .SH "SEE ALSO"
 333 .BR chmod (2),
 334 .BR fork (2),
 335 .BR path_resolution (2),
 336 .BR ptrace (2),
 337 .BR execl (3),
 338 .BR fexecve (3),
 339 .BR environ (7),
 340 .BR ld.so (8)