[转]execve() - Unix, Linux System Call

link: http://www.tutorialspoint.com/unix_system_calls/execve.htm

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 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.

RETURN VALUE

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

ERRORS

Error Code	Description
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 offilename or the name of a script interpreter. (See alsopath_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 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 ofmain was ended by -1. Thus, this argument list was not directly usable in a further exec() call. Since Unix V7 both are NULL.

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