From Linux Man Pages
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.
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 filename, 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 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 /lib/ld-linux.so.1 for binaries linked with
the Linux libc version 5, or /lib/ld-linux.so.2 for binaries linked with the GNU libc version 2.
All process attributes are preserved during an execve(), except the following:
* File descriptors that are marked close-on-exec are closed (see the description of FD_CLOEXEC in fcntl(2)).
* The set of pending signals is cleared (sigpending(2)).
* The set of pending signals is cleared (sigpending(2)).
* The disposition of any signals that are being caught are reset to being ignored.
* Any alternate signal stack is not preserved (sigaltstack(2)).
* Memory mappings are not preserved (mmap(2)).
* Attached System V shared memory segments are detached (shmat(2)).
* POSIX shared memory regions are unmapped (shm_open(3)).
* Open POSIX message queue descriptors are closed (mq_overview(7)).
* Any open POSIX named semaphores are closed (sem_overview(7)).
* POSIX timers are not preserved (timer_create(3)).
* Any open directory streams are closed (opendir(3)).
* Memory locks are not preserved (mlock(2), mlockall(2)).
* Exit handlers are not preserved (atexit(3), on_exit(3)).
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 execve():
* The prctl(2) 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.
* The prctl(2) PR_SET_KEEPCAPS flag is cleared.
* The process name, as set by prctl(2) PR_SET_NAME (and displayed by ps -o comm), is reset to the name of the
new executable file.
* The termination signal is reset to SIGCHLD (see clone(2)).
Note the following further points:
* All threads other than calling thread are destroyed during an execve(). Mutexes, condition variables, and
other pthreads objects are not preserved.
* The equivalent of setlocale(LC_ALL, "C") is executed at program start-up.
* 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.
* Any outstanding asynchronous I/O operations are cancelled (aio_read(3), aio_write(3)).
* For the handling of capabilities during execve(2), see capabilities(7).
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 inter-
preter. (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 cannot 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 superuser, and the file has the set-user-ID or set-
group-ID bit set.
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.
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
Set-user-ID and set-group-ID processes can not be ptrace()d.
Linux ignores the set-user-ID and set-group-ID bits on scripts.
The result of mounting a filesystem 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 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.
RELATED
chmod(2), fork(2), path_resolution(2), ptrace(2), execl(3), fexecve(3), environ(7), ld.so(8)
CATEGORY