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Annotation of coherent/a/usr/man/COHERENT/execution, revision 1.1.1.1

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                      3: execution             Technical Information             execution
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                      8: Program execution under COHERENT is governed by the various forms
                      9: of the COHERENT system call  exec.  This call allows a process to
                     10: execute  another executable  file (load  module, as  described in
                     11: l.out.h).  The code, data and  stack of file replace those of the
                     12: requesting process.  The new stack contains the command arguments
                     13: and its environment, in the format given below.  Execution starts
                     14: at the entry point of file.
                     15: 
                     16: During a  successful exec, the system  deactivates profiling, and
                     17: resets any caught signals to SIG_DFL.
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                     19: Every process  has a real-user id, an  effective-user id, a real-
                     20: group id, and an effective-group id, as described in getuid.  For
                     21: most load  modules, exec does not change  any of these.  However,
                     22: if the  file is marked with  the set user id or  set group id bit
                     23: (see stat), exec  sets the effective-user id (effective-group id)
                     24: of the process  to the user id (group id)  of the file owner.  In
                     25: effect, this changes the file access privilege level from that of
                     26: the  real id  to that  of the  effective id.   The owner  of file
                     27: should be  careful to limit its  abilities, to avoid compromising
                     28: file security.
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                     30: exec initializes  the new stack of the process  to contain a list
                     31: of strings  which are command arguments.   execl, execle, and ex-
                     32: eclp specify arguments individually, as a NULL-terminated list of
                     33: arg parameters.  execv, execve, and execvp specify arguments as a
                     34: single NULL-terminated array argv of parameters.
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                     36: The main routine of a C program is invoked in the following way:
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                     38: 
                     39:         main(argc, argv, envp)
                     40:         int argc;
                     41:         char *argv[], *envp[];
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                     44: argc is the number  of command arguments passed through exec, and
                     45: argv is an array of the  actual argument strings.  envp is an ar-
                     46: ray of strings that comprise the process environment.  By conven-
                     47: tion, these strings  are of the form variable=value, as described
                     48: in the Lexicon entry environ.  Typically, each variable is an ex-
                     49: ported shell variable with the given value.
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                     51: execl and  execv simply pass  the old environment,  referenced by
                     52: the external  pointer environ.  execle and execve  pass a new en-
                     53: vironment env  explicitly.  execlp and execvp  search for file in
                     54: each of the directories indicated by the shell variable $PATH, in
                     55: the same way that the  shell searches for a command.  These calls
                     56: will execute a shell command file.
                     57: 
                     58: ***** Files *****
                     59: 
                     60: /bbiinn/sshh -- To execute command files
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                     63: 
                     64: COHERENT Lexicon                                           Page 1
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                     68: 
                     69: execution             Technical Information             execution
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                     72: 
                     73: ***** See Also *****
                     74: 
                     75: environ,  execl(),  execle(),  execlp(), execv(),  execve(),  ex-
                     76: ecvp(), fork(), ioctl(), signal(), stat(), technical information
                     77: 
                     78: ***** Diagnostics *****
                     79: 
                     80: None of the exec routines returns if successful.  Each returns -1
                     81: for errors,  such as if file is  nonexistent, not accessible with
                     82: execute permission, has  a bad format, or is too  large to fit in
                     83: memory.
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                    130: COHERENT Lexicon                                           Page 2
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