EXECVE(2)                   BSD System Calls Manual                  EXECVE(2)

NAME
     execve -- execute a file

SYNOPSIS
     #include <unistd.h>

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

DESCRIPTION
     execve() transforms the calling process into a new process.  The new
     process is constructed from an ordinary file, whose name is pointed to by
     path, called the new process file.  This file is either an executable
     object file, or a file of data for an interpreter.  An executable object
     file consists of an identifying header, followed by pages of data repre-
     senting the initial program (text) and initialized data pages.  Addi-
     tional pages may be specified by the header to be initialized with zero
     data;  see a.out(5).

     An interpreter file begins with a line of the form:

           #! interpreter [arg ...]

     When an interpreter file is execve()'d, the system runs the specified
     interpreter.  If any optional args are specified, they become the first
     (second, ...) argument to the interpreter. The name of the originally
     execve()'d file becomes the subsequent argument; otherwise, the name of
     the originally execve()'d file is the first argument.  The original argu-
     ments to the invocation of the interpreter are shifted over to become the
     final arguments.  The zeroth argument, normally the name of the
     execve()'d file, is left unchanged.

     The argument argv is a pointer to a null-terminated array of character
     pointers to null-terminated character strings.  These strings construct
     the argument list to be made available to the new process.  At least one
     argument must be present in the array; by custom, the first element
     should be the name of the executed program (for example, the last compo-
     nent of path).

     The argument envp is also a pointer to a null-terminated array of charac-
     ter pointers to null-terminated strings.  A pointer to this array is nor-
     mally stored in the global variable environ. These strings pass informa-
     tion to the new process that is not directly an argument to the command
     (see environ(7)).

     File descriptors open in the calling process image remain open in the new
     process image, except for those for which the close-on-exec flag is set
     (see close(2) and fcntl(2)).  Descriptors that remain open are unaffected
     by execve().

     Signals set to be ignored in the calling process are set to be ignored in
     the new process. Signals which are set to be caught in the calling
     process image are set to default action in the new process image.
     Blocked signals remain blocked regardless of changes to the signal
     action.  The signal stack is reset to be undefined (see sigaction(2) for
     more information).

     If the set-user-ID mode bit of the new process image file is set (see
     chmod(2)), the effective user ID of the new process image is set to the
     owner ID of the new process image file.  If the set-group-ID mode bit of
     the new process image file is set, the effective group ID of the new
     process image is set to the group ID of the new process image file.  (The
     effective group ID is the first element of the group list.)  The real
     user ID, real group ID and other group IDs of the new process image
     remain the same as the calling process image.  After any set-user-ID and
     set-group-ID processing, the effective user ID is recorded as the saved
     set-user-ID, and the effective group ID is recorded as the saved set-
     group-ID.  These values may be used in changing the effective IDs later
     (see setuid(2)).

     The new process also inherits the following attributes from the calling
     process:

           process ID           see getpid(2)
           parent process ID    see getppid(2)
           process group ID     see getpgrp(2)
           access groups        see getgroups(2)
           working directory    see chdir(2)
           root directory       see chroot(2)
           control terminal     see termios(4)
           resource usages      see getrusage(2)
           interval timers      see getitimer(2)
           resource limits      see getrlimit(2)
           file mode mask       see umask(2)
           signal mask          see sigaction(2), sigsetmask(2)

     When a program is executed as a result of an execve() call, it is entered
     as follows:

           main(argc, argv, envp)
           int argc;
           char **argv, **envp;

     where argc is the number of elements in argv (the ``arg count'') and argv
     points to the array of character pointers to the arguments themselves.

RETURN VALUES
     As the execve() function overlays the current process image  with a new
     process image, the successful call has no process to return to.  If
     execve() does return to the calling process, an error has occurred; the
     return value will be -1 and the global variable errno is set to indicate
     the error.

ERRORS
     execve() will fail and return to the calling process if:

     [E2BIG]            The number of bytes in the new process's argument list
                        is larger than the system-imposed limit.  This limit
                        is specified by the sysctl(3) MIB variable
                        KERN_ARGMAX.

     [EACCES]           Search permission is denied for a component of the
                        path prefix.

     [EACCES]           The new process file is not an ordinary file.

     [EACCES]           The new process file mode denies execute permission.

     [EACCES]           The new process file is on a filesystem mounted with
                        execution disabled (MNT_NOEXEC in <sys/mount.h>).

     [EFAULT]           The new process file is not as long as indicated by
                        the size values in its header.

     [EFAULT]           Path, argv, or envp point to an illegal address.

     [EIO]              An I/O error occurred while reading from the file sys-
                        tem.

     [ELOOP]            Too many symbolic links were encountered in translat-
                        ing the pathname.  This is taken to be indicative of a
                        looping symbolic link.

     [ENAMETOOLONG]     A component of a pathname exceeded {NAME_MAX} charac-
                        ters, or an entire path name exceeded {PATH_MAX} char-
                        acters.

     [ENOENT]           The new process file does not exist.

     [ENOEXEC]          The new process file has the appropriate access per-
                        mission, but has an unrecognized format (e.g., an
                        invalid magic number in its header).

     [ENOMEM]           The new process requires more virtual memory than is
                        allowed by the imposed maximum (getrlimit(2)).

     [ENOTDIR]          A component of the path prefix is not a directory.

     [ETXTBSY]          The new process file is a pure procedure (shared text)
                        file that is currently open for writing or reading by
                        some process.

CAVEAT
     If a program is setuid to a non-super-user, but is executed when the real
     uid is ``root'', then the program has some of the powers of a super-user
     as well.

SEE ALSO
     exit(2), fork(2), execl(3), sysctl(3), environ(7)

HISTORY
     The execve() function call appeared in 4.2BSD.

4th Berkeley Distribution      January 24, 1994      4th Berkeley Distribution