man-pages/man2/execve.2

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.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
.\" and Copyright (c) 2006 Michael Kerrisk <mtk-manpages@gmx.net>
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.\" Modified by Michael Haardt <michael@moria.de>
.\" Modified 1993-07-21 by Rik Faith <faith@cs.unc.edu>
.\" Modified 1994-08-21 by Michael Chastain <mec@shell.portal.com>:
.\" Modified 1997-01-31 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified 1999-11-12 by Urs Thuermann <urs@isnogud.escape.de>
.\" Modified 2004-06-23 by Michael Kerrisk <mtk-manpages@gmx.net>
.\" 2006-09-04 Michael Kerrisk <mtk-manpages@gmx.net>
.\" 	Added list of process attributes that are not preserved on exec().
.\"
.TH EXECVE 2 2006-09-04 "Linux 2.6.17" "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.

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.
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.

All process attributes are preserved during an
.BR execve (),
except the following:
.IP * 4
File descriptors that are marked close-on-exec are closed
(see the description of
.BR FD_CLOEXEC
in
.BR fcntl (2)).
.\" FIXME add some statement about the effect on record locks (fcntl()).
.IP * 4
The set of pending signals is cleared
.RB ( sigpending (2)).
.IP * 4
The dispositions of any signals that are being caught are
reset to being ignored.
.IP * 4
Any alternate signal stack is not preserved
.RB ( sigaltstack (2)).
.IP * 4
Memory mappings are not preserved
.RB ( mmap (2)).
.IP * 4
Attached System V shared memory segments are detached
.RB ( shmat (2)).
.IP * 4
POSIX shared memory regions are unmapped
.RB ( shm_open (3)).
.IP * 4
Open POSIX message queue descriptors are closed
.RB ( mq_overview (7)).
.IP * 4
Any open POSIX named semaphores are closed
.RB ( sem_overview (7)).
.IP * 4
POSIX timers are not preserved
.RB ( timer_create (3)).
.IP * 4
Any open directory streams are closed
.RB ( opendir (3)).
.IP * 4
Memory locks are not preserved
.RB ( mlock (2),
.BR mlockall (2)).
.IP * 4
Exit handlers are not preserved
.RB ( atexit (3),
.BR on_exit (3)).
.PP
The process attributes in the preceding list are all specified
in POSIX.1-2001.
The following Linux-specific process attributes are also
not preserved during an
.BR execve ():
.IP * 4
The
.BR prctl (2)
.B PR_SET_DUMPABLE
flag is set,
unless a set-user-ID or set-group ID program is being executed,
in which case it is cleared.
.IP * 4
The
.BR prctl (2)
.B PR_SET_KEEPCAPS
flag is cleared.
.IP * 4
The process name, as set by
.BR prctl (2)
.BR PR_SET_NAME
(and displayed by
.IR "ps -o comm" ),
is reset to the name of the new executable file.
.IP * 4
The termination signal is reset to SIGCHLD
(see
.BR clone (2)).
.PP
Note the following further points:
.IP * 4
All threads other than calling thread are destroyed during an
.BR execve ().
Mutexes, condition variables, and other pthreads objects are not preserved.
.IP * 4
The equivalent of \fIsetlocale(LC_ALL, "C")\fP
is executed at program start-up.
.IP * 4
POSIX.1-2001 specifies that the dispositions of any signals that
are ignored or set to the default are left unchanged.
POSIX.1-2001 specifies one exception: if SIGCHLD is being ignored,
then an implementation may leave the disposition unchanged or
reset it to the default; Linux does the former.
.IP * 4
Any outstanding asynchronous I/O operations are cancelled
.RB ( aio_read (3),
.BR aio_write (3)).
.IP * 4
For the handling of capabilities during
.BR execve (2),
see
.BR capabilities (7).
.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 the set-user-ID or set-group-ID bit set.
.TP
.B EPERM
The process is being traced, the user is not the superuser and the
file has the set-user-ID or set-group-ID 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
Set-user-ID and set-group-ID processes can not be \fBptrace\fP()d.

Linux ignores the set-user-ID and set-group-ID bits on scripts.

The result of mounting a filesystem
.I nosuid
vary between Linux kernel versions:
some will refuse execution of set-user-ID and set-group-ID
executables when this would
give the user powers she did not have already (and return EPERM),
some will just ignore the set-user-ID and set-group-ID 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)