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execve(2) [ultrix man page]

execve(2)							System Calls Manual							 execve(2)

Name
       execve - execute a file

Syntax
       execve(name, argv, envp)
       char *name, *argv[], *envp[];

Description
       The  system  call  transforms  the calling process into a new process.  The new process is constructed from an ordinary file 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 can
       be specified by the header to be initialized with zero data.  For further information, see

       An interpreter file begins with a line of the form ``#! interpreter''.  When an interpreter file is executed the system executes the speci-
       fied interpreter, giving it the name of the originally executed file as an argument, shifting over the rest of the original arguments.

       There  can  be  no return from a successful because the calling core image is lost.  This is the mechanism whereby different process images
       become active.

       The argument argv is an array of character pointers to null-terminated character strings.  These strings constitute the argument list to be
       made available to the new process.  By convention, at least one argument must be present in this array, and the first element of this array
       should be the name of the executed program, the last component of name.

       The argument envp is also an array of character pointers to null-terminated strings.  These strings pass information to	the  new  process,
       but they are not directly arguments to the command.  For further information, see

       Descriptors open in the calling process remain open in the new process, except for those for which the close-on-exec flag is set.  For fur-
       ther information, see Descriptors which remain open are unaffected by

       Ignored signals remain ignored across an but signals that are caught are reset to their default values.	The signal stack is  reset  to	be
       undefined.  For further information, see

       Each  process has real user and group IDs and effective user and group IDs.  The real ID identifies the person using the system; the effec-
       tive ID determines his access privileges.  The system call changes the effective user and group ID to the owner of the executed file if the
       file has the set-user-ID or set-group-ID modes.	The real user ID is not affected.

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

	    Process ID		See getpid(2)
	    Parent process ID	See getpid(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 tty(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 sigvec(2)

       When the executed program begins, it is called as follows:

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

       The  argc argument is the number of elements in argv (the ``arg count'') and argv is the array of character pointers to the arguments them-
       selves.

       The envp argument is a pointer to an array of strings that constitute the environment of the process.  A pointer  to  this  array  is  also
       stored  in  the	global	environ variable.  Each string consists of a name, an equal sign ( = ), and a null-terminated value.  The array of
       pointers is terminated by a null pointer.  The shell passes an environment entry for each global shell variable defined when the program is
       called.	See for some conventionally used names.

       If returns to the calling process, an error has occurred; the return value is -1 and the global variable errno contains an error code.

Environment
   POSIX, System Five
       When  your  program  is	compiled  using the POSIX or System V environment, the effective user ID and effective group ID of the new process
       image are saved (as the saved-set-uid and saved-set-gid) for later use by the and functions.

Restrictions
       If a program's effective user ID is not the superuser, but it is executed when the real user ID is root, then the program has the powers of
       the superuser.

Diagnostics
       The system call fails and returns to the calling process under the following conditions:

       [ENOENT]       The new process file does not exist.

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

       [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.

       [ENOEXEC]      The new process file has the appropriate access permission, but it has an invalid magic number in its header.

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

       [ENOMEM]       The new process requires more virtual memory than is allowed by the imposed maximum.  For further information, see

       [E2BIG]	      The number of bytes in the new process's argument list is larger than the system-imposed limit of {ARG_MAX} bytes.

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

       [EFAULT]       The path, argv, or envp points to an illegal address.

       [EIO]	      An I/O error occurred while reading from the file system.

       [ENAMETOOLONG] A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.

       [ELOOP]	      Too many symbolic links were encountered in translating the pathname.

       [EROFS]	      If binaries cannot be executed from the file system.

       [EROFS]	      If and programs cannot be executed from the file system.

       [ESTALE]       The  file  handle  given	in the argument is invalid.  The file referred to by that file handle no longer exists or has been
		      revoked.

       [ETIMEDOUT]    A connect request or remote file operation failed because the connected party did not properly respond  after  a	period	of
		      time that is dependent on the communications protocol.

See Also
       exit(2), fork(2), execl(3), environ(7)

																	 execve(2)

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