execve() - Unix, Linux System Call

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Copyright © 2014 by tutorialspoint
execve - execute program
#include <unistd.h> 
int execve(const char *filename, char *const argv[], 
           char *const envp[]); 


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

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 signal (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
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.  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
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.
On success, execve() does not return, on error -1 is returned, and
errno is set appropriately.
SVr4, 4.3BSD, POSIX.1-2001. 
POSIX.1-2001 does not document the #!  behavior
but is otherwise compatible. 
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.
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.
chmod (2)
chmod (2)
fork (2)
fork (2)
path_resolution (2)
path_resolution (2)
ptrace (2)
ptrace (2)
ld (8)
ld (8)

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