Network Executive




NetExec is  an Alto command  processor for invoking  certain subsystems
via  the Ethernet  without  using the  local  disk.  It  is  useful for
rebuilding a smashed disk and for loading diagnostic programs  when the
disk  is sick.   Its  user interface  is intentionally  similar  to the
standard Alto Executive.

The program is invoked by holding down the  and  keys
while pressing  the boot button.   You must continue  to hold  the keys
down until a small square appears in the middle of the screen, then you
can let go.  NetExec  and all of the  programs invoked by it  are boot-
format files  kept by  'boot-servers' --  programs which  implement the
Alto boot  protocol.  Most  gateways and some  other programs  (such as
Peek) contain boot-servers.

When the NetExec  arrives, it displays a  ">" and blinks its  cursor to
indicate that it is ready for commands from the user.  In parallel with
this it displays a  pair of lines near the  top of the screen  with its
name  and   version  number,  a   digital  clock,  and   the  machine's
internetwork address.

Typing "?" causes  the NetExec to display  a list of the  boot-files it
knows how to invoke.  NetExec  builds this list by probing  the network
for boot servers  and asking them what  boot files they are  willing to
give out.  There are also  some built-in functions which are  listed by
"?" as if they were boot files:

     BootDP0       Causes NetExec to  boot the operating system  on DP0
                   of the current partition.

     FileStat      Prompts you for a  boot file name and tells  you all
                   about it: its boot file number, the host  from which
                   the NetExec will obtain it, and the  key combination
                   which will boot it directly.

     Partition     prompts you  for a disk  partition number.   If this
                   number is zero,  NetExec tells you the  current disk
                   partition.  If  it is non-zero,  it attempts  to set
                   the partition to that number.  This command  is only
                   available  on  machines that  support  multiple disk
                   partitions: Dorados and D0s.

     Probe         Causes NetExec to probe the network looking for boot
                   servers.  If it discovers any new ones, it  will add
                   the new boot files  to its list.  This is  done once
                   automatically when NetExec starts, and  whenever the
                   user types an unrecognized command.

     Quit          Boots DMT

     SetTime       Causes NetExec  to probe the  network looking  for a
                   time  server.   If  it discovers  one,  it  sets the


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                   Copyright Xerox Corporation 1979


Network Executive          January 12, 1980                           2




                   Alto's   clock   from  it.    This   is   done  once
                   automatically when NetExec starts.

In  the future,  common  subsytems should  be  stored in  a  few places
throughout the network, not on every local disk; perhaps the local disk
can  be  eliminated  entirely.    Doing  so  requires  a   much  better
integration of  network and  OS facilites  than currently  exists.  The
NetExec described here is not  intended to do this.  There  are several
limitations in the current implementation:

     1)  Most  boot-files  are  quite  large.   Typical boot-
         servers have  space for only  the few  most commonly
         used programs.

     2)  Boot-servers  typically  run in  machines  with some
         other primary  purpose, such  as gateways,  and must
         not  consume  too  many  resources.   As  a  result,
         booting is slow and  only one machine can  be served
         at a time.