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EXECVE(2)		   Linux Programmer's Manual		     EXECVE(2)



NAME
       execve - execute program

SYNOPSIS
       #include <unistd.h>

       int execve(const char *filename, char *const argv[],
		  char *const envp[]);

DESCRIPTION
       execve() executes the program pointed to by filename.  filename must be
       either a binary executable, or a script starting with  a	 line  of  the
       form  "#! interpreter [arg]".  In the latter case, the interpreter must
       be a valid pathname for an executable which is  not  itself  a  script,
       which will be invoked as interpreter [arg] filename.

       argv  is	 an array of argument strings passed to the new program.  envp
       is an array of strings, conventionally of the form key=value, which are
       passed  as  environment to the new program.  Both argv and envp must be
       terminated by a null pointer.  The argument vector and environment  can
       be  accessed  by the called program's main function, when it is defined
       as int main(int argc, char *argv[], char *envp[]).

       execve() does not return on success, and the text, data, bss, and stack
       of  the	calling process are overwritten by that of the program loaded.
       The program invoked inherits the calling process's PID,	and  any  open
       file descriptors that are not set to close-on-exec.  Signals pending on
       the calling process are cleared.	 Any signals set to be caught  by  the
       calling process are reset to their default behaviour.  The SIGCHLD sig-
       nal (when set to SIG_IGN) may or may not be reset to SIG_DFL.

       If the current program is being ptraced, a SIGTRAP is sent to it	 after
       a successful execve().

       If  the	set-user-ID bit is set on the program file pointed to by file-
       name, and the calling process is not being ptraced, then the  effective
       user  ID	 of the calling process is changed to that of the owner of the
       program file.  i Similarly, when the set-group-ID bit  of  the  program
       file is set the effective group ID of the calling process is set to the
       group of the program file.

       The effective user ID of the process is copied to the  saved  set-user-
       ID; similarly, the effective group ID is copied to the saved set-group-
       ID.  This copying takes place after any effective ID changes that occur
       because of the set-user-ID and set-group-ID permission bits.

       If the executable is an a.out dynamically-linked binary executable con-
       taining shared-library stubs, the  Linux	 dynamic  linker  ld.so(8)  is
       called  at the start of execution to bring needed shared libraries into
       memory and link the executable with them.

       If the executable is a dynamically-linked ELF  executable,  the	inter-
       preter named in the PT_INTERP segment is used to load the needed shared
       libraries.  This interpreter is typically /lib/ld-linux.so.1 for	 bina-
       ries  linked  with  the Linux libc version 5, or /lib/ld-linux.so.2 for
       binaries linked with the GNU libc version 2.

RETURN VALUE
       On success, execve() does not return, on	 error	-1  is	returned,  and
       errno is set appropriately.

ERRORS
       E2BIG  The total number of bytes in the environment (envp) and argument
	      list (argv) is too large.

       EACCES Search permission is denied on a component of the path prefix of
	      filename	or  the	 name  of  a  script  interpreter.   (See also
	      path_resolution(2).)

       EACCES The file or a script interpreter is not a regular file.

       EACCES Execute permission is denied for the file or  a  script  or  ELF
	      interpreter.

       EACCES The file system is mounted noexec.

       EFAULT filename points outside your accessible address space.

       EINVAL An  ELF  executable  had	more than one PT_INTERP segment (i.e.,
	      tried to name more than one interpreter).

       EIO    An I/O error occurred.

       EISDIR An ELF interpreter was a directory.

       ELIBBAD
	      An ELF interpreter was not in a recognised format.

       ELOOP  Too many symbolic links were encountered in  resolving  filename
	      or the name of a script or ELF interpreter.

       EMFILE The process has the maximum number of files open.

       ENAMETOOLONG
	      filename is too long.

       ENFILE The  system  limit  on  the  total number of open files has been
	      reached.

       ENOENT The file filename or a script or ELF interpreter does not exist,
	      or  a  shared  library  needed for file or interpreter cannot be
	      found.

       ENOEXEC
	      An executable is not in a recognised format, is  for  the	 wrong
	      architecture,  or has some other format error that means it can-
	      not be executed.

       ENOMEM Insufficient kernel memory was available.

       ENOTDIR
	      A component of the path prefix of filename or a  script  or  ELF
	      interpreter is not a directory.

       EPERM  The  file	 system	 is  mounted nosuid, the user is not the supe-
	      ruser, and the file has an SUID or SGID bit set.

       EPERM  The process is being traced, the user is not the	superuser  and
	      the file has an SUID or SGID bit set.

       ETXTBSY
	      Executable was open for writing by one or more processes.

CONFORMING TO
       SVr4,  4.3BSD,  POSIX.1-2001.   POSIX.1-2001  does  not document the #!
       behavior but is otherwise compatible.

NOTES
       SUID and SGID processes can not be ptrace()d.

       Linux ignores the SUID and SGID bits on scripts.

       The result of mounting a filesystem nosuid vary	between	 Linux	kernel
       versions: some will refuse execution of SUID/SGID executables when this
       would give the user powers she did not have already (and return EPERM),
       some will just ignore the SUID/SGID bits and exec() successfully.

       A  maximum  line length of 127 characters is allowed for the first line
       in a #! executable shell script.


HISTORICAL
       With Unix V6 the argument list of an exec() call was ended by 0,	 while
       the argument list of main was ended by -1. Thus, this argument list was
       not directly usable in a further exec() call.  Since Unix V7  both  are
       NULL.


SEE ALSO
       chmod(2), fork(2), path_resolution(2), ptrace(2), execl(3), fexecve(3),
       environ(7), ld.so(8)



Linux 2.6.7			  2004-06-23			     EXECVE(2)
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