man-pages/man2/execve.2

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.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
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.\"
.TH EXECVE 2 2004-06-23 "Linux 2.6.7" "Linux Programmer's Manual"
.SH NAME
execve \- execute program
.SH SYNOPSIS
.B #include <unistd.h>
.sp
.BI "int execve(const char *" filename ", char *const " argv "[], "
.br
.BI "           char *const " envp []);
.SH DESCRIPTION
\fBexecve\fP() executes the program pointed to by \fIfilename\fP.
\fIfilename\fP must be either a binary executable, or a script
starting with a line of the form "\fB#! \fIinterpreter \fR[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
\fBinterpreter\fR [arg] \fIfilename\fR.

\fIargv\fP is an array of argument strings passed to the new program.
\fIenvp\fP is an array of strings, conventionally of the form
\fBkey=value\fR, which are passed as environment to the new
program.  Both \fIargv\fP and \fIenvp\fP 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 \fBint main(int
argc, char *argv[], char *envp[])\fR.

\fBexecve\fP() 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 signal (when set to SIG_IGN) may or may not be reset to SIG_DFL.

If the current program is being ptraced, a \fBSIGTRAP\fP is sent to it
after a successful \fBexecve\fP().

If the set-user-ID bit is set on the program file pointed to by
\fIfilename\fP, 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 containing
shared-library stubs, the Linux dynamic linker
.BR 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
interpreter named in the PT_INTERP segment is used to load the needed
shared libraries.  This interpreter is typically
\fI/lib/ld-linux.so.1\fR for binaries linked with the Linux libc
version 5, or \fI/lib/ld-linux.so.2\fR for binaries linked with the
GNU libc version 2.
.SH "RETURN VALUE"
On success, \fBexecve\fP() does not return, on error \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B E2BIG
The total number of bytes in the environment 
.RI ( envp )
and argument list 
.RI ( argv )
is too large.
.TP
.B EACCES
Search permission is denied on a component of the path prefix of
.I filename
or the name of a script interpreter.
(See also
.BR path_resolution (2).)
.TP
.B EACCES
The file or a script interpreter is not a regular file.
.TP
.B EACCES
Execute permission is denied for the file or a script or ELF interpreter.
.TP
.B EACCES
The file system is mounted
.IR noexec .
.TP
.B EFAULT
.I filename
points outside your accessible address space.
.TP
.B EINVAL
An ELF executable had more than one PT_INTERP segment (i.e., tried to
name more than one interpreter).
.TP
.B EIO
An I/O error occurred.
.TP
.B EISDIR
An ELF interpreter was a directory.
.TP
.B ELIBBAD
An ELF interpreter was not in a recognised format.
.TP
.B ELOOP
Too many symbolic links were encountered in resolving
.I filename
or the name of a script or ELF interpreter.
.TP
.B EMFILE
The process has the maximum number of files open.
.TP
.B ENAMETOOLONG
.I filename
is too long.
.TP
.B ENFILE
The system limit on the total number of open files has been reached.
.TP
.B ENOENT
The file 
.I filename
or a script or ELF interpreter does not exist, or a shared library
needed for file or interpreter cannot be found.
.TP
.B ENOEXEC
An executable is not in a recognised format, is for the wrong
architecture, or has some other format error that means it cannot be
executed.
.TP
.B ENOMEM
Insufficient kernel memory was available.
.TP
.B ENOTDIR
A component of the path prefix of
.I filename
or a script or ELF interpreter is not a directory.
.TP
.B EPERM
The file system is mounted
.IR nosuid ,
the user is not the superuser, and the file has an SUID or SGID bit set.
.TP
.B EPERM
The process is being traced, the user is not the superuser and the
file has an SUID or SGID bit set.
.TP
.B ETXTBSY
Executable was open for writing by one or more processes.
.SH "CONFORMING TO"
SVr4, 4.3BSD, POSIX.1-2001.  
POSIX.1-2001 does not document the #!  behavior
but is otherwise compatible.  
.\" SVr4 documents additional error
.\" conditions EAGAIN, EINTR, ELIBACC, ENOLINK, EMULTIHOP; POSIX does not
.\" document ETXTBSY, EPERM, EFAULT, ELOOP, EIO, ENFILE, EMFILE, EINVAL,
.\" EISDIR or ELIBBAD error conditions.
.SH NOTES
SUID and SGID processes can not be \fBptrace\fP()d.

Linux ignores the SUID and SGID bits on scripts.

The result of mounting a filesystem
.I 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 
.BR exec ()
successfully.

A maximum line length of 127 characters is allowed for the first line in
a #! executable shell script. 
.\" .SH BUGS
.\" Some Linux versions have failed to check permissions on ELF
.\" interpreters.  This is a security hole, because it allows users to
.\" open any file, such as a rewinding tape device, for reading.  Some
.\" Linux versions have also had other security holes in \fBexecve\fP(),
.\" that could be exploited for denial of service by a suitably crafted
.\" ELF binary. There are no known problems with 2.0.34 or 2.2.15.

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

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