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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 representing the initial program (text) and initialized
     data pages.  Additional 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 arguments 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 component of path).

     The argument envp is also a pointer to a null-terminated array of character pointers to null-terminated
     strings.  A pointer to this array is normally stored in the global variable environ. These strings pass
     information 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. setgroup-ID.
     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 char-acter character
     acter 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 systemimposed
                        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 system.

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

     [ENAMETOOLONG]     A component of a pathname exceeded {NAME_MAX} characters, or an entire path name
                        exceeded {PATH_MAX} characters.

     [ENOENT]           The new process file does not exist.

     [ENOEXEC]          The new process file has the appropriate access permission, 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

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