cpu

Documentation

Overview

cpu - connection to CPU server over SSH protocol

Synopsis:

cpu [OPTIONS]

Description:

On local machine useful flags are all save -remote
On remote machines, all save dbg9p, key, hostkey.

CPU is an ssh client that starts up a shell on a remote machine,
as usual; but, further, makes a namespace of the local machine
available in a private mount rooted at /tmp/cpu.
Wherever you go, there your files are.
You can, in the ssh session, do something like this:
chroot /tmp/cpu /bin/bash
and at that point, you are running a bash, imported from your local
machine, on the remote machine; it will use your .profile and
all your files are available. You can also do something like
cat /tmp/cpu/etc/hosts
if your host file is lacking; or
cp /etc/hosts /tmp/cpu/tmp
to get the /etc/hosts on the remote machine to your local machine.

The cpu client makes this work by starting a cpu command on the
remote machine with a -remote switch and several other arguments.
The local cpu starts a 9p server and, using ssh port forwarding,
makes that server available to the remote. On the remote side, the
cpu command establishes a private, unshared mount of tmpfs on /tmp;
creates /tmp/cpu; and mounts the 9p server on that directory.

CPU has many options, as shown above; most you need not worry about.
The most common invocation is
cpu -h hostname
which will start a shell and mount the 9p server in /tmp/cpu.
Note this mount proceeds over the ssh session, and further
it mounts in a private /tmp; there is little to see when
it is running from outside the ssh session

Options:

-bin string
      path of cpu binary
-d    enable debug prints
-dbg9p
      show 9p io
-h string
      host to use (default "localhost")
-hostkey string
      host key file
-key string
      key file (default "$HOME/.ssh/cpu_rsa")
-network string
      network to use (default "tcp")
-p string
      port to use (default "22")
-port9p string
      port9p # on remote machine for 9p mount
-remote
      Indicates we are the remote side of the cpu session
-srv string
      what server to run (default "unpfs")

Examples In these examples, cpu runs with warning messages enabled. The first message is a warning that cpu could not use overlayfs to build a a reasonable union mount. The next are showing you what it is mounting, the union mount having failed. These mounts are the best we could do for a reasonable compromise of wanting local resources visible (e.g. /dev) and using resources from the remote machine (e.g. /etc, /lib, /usr and so on). u-root doesn't really need /lib and /usr, and u-root's /etc is minimal by design, so this works. Also note that the user's 9p server running on the local machine is mounted at /tmp/cpu. We can turn these off at some point but for now, in early days, we may want them. Note that these messages come from the remote side. cpu to a machine with bash as your shell and run a command

cpu -sp 23 date
  2019/05/17 16:53:22 Overlayfs mount failed: invalid argument. Proceeding with selective mounts from /tmp/cpu into /
  2019/05/17 16:53:22 Mounted /tmp/cpu/lib on /lib
  2019/05/17 16:53:22 Mounted /tmp/cpu/lib64 on /lib64
  2019/05/17 16:53:22 Warning: mounting /tmp/cpu/lib32 on /lib32 failed: no such file or directory
  2019/05/17 16:53:22 Mounted /tmp/cpu/usr on /usr
  2019/05/17 16:53:22 Mounted /tmp/cpu/bin on /bin
  2019/05/17 16:53:22 Mounted /tmp/cpu/etc on /etc
  Fri May 17 16:53:23 UTC 2019

cpu to a machine and run $SHELL (since no arguments were given) NOTE: $SHELL is NOT installed on the remote machine! It (and all its .so's and . files) come from the local machine. cpu sp -23

2019/05/17 16:58:04 Overlayfs mount failed: invalid argument. Proceeding with selective mounts from /tmp/cpu into /
2019/05/17 16:58:04 Mounted /tmp/cpu/lib on /lib
2019/05/17 16:58:04 Mounted /tmp/cpu/lib64 on /lib64
2019/05/17 16:58:04 Warning: mounting /tmp/cpu/lib32 on /lib32 failed: no such file or directory
2019/05/17 16:58:04 Mounted /tmp/cpu/usr on /usr
2019/05/17 16:58:04 Mounted /tmp/cpu/bin on /bin
2019/05/17 16:58:05 Mounted /tmp/cpu/etc on /etc
root@(none):/# echo ~
/tmp/cpu/home/rminnich
root@(none):/# ls ~
IDAPROPASSWORD  go      ida-7.2  projects            salishan2019random~
bin             gopath  papers   salishan2019random  snap
root@(none):/#
# Now that we are on the node, modprobe something
root@(none):/# depmod
depmod: ERROR: could not open directory /lib/modules/5.0.0-rc3+: No such file or directory
depmod: FATAL: could not search modules: No such file or directory
root@(none):/#
# Note that, if we had the right modules on our LOCAL machine for this remote machine, we could
# insert them. This further means you can build a modular kernel in FLASH and insmod needed modules
# later (as long as your core kernel has networking, that is!). Modules could include, e.g., an AHCI
# driver.
# run the lspci command but redirect output to ~
# note it is not installed on the remote machine; it comes from our local machine.
root@(none):/# lspci
00:00.0 Host bridge: Intel Corporation 82G33/G31/P35/P31 Express DRAM Controller
00:01.0 VGA compatible controller: Device 1234:1111 (rev 02)
00:02.0 Unclassified device [00ff]: Red Hat, Inc. Virtio RNG
00:03.0 Ethernet controller: Intel Corporation 82540EM Gigabit Ethernet Controller (rev 03)
00:1f.0 ISA bridge: Intel Corporation 82801IB (ICH9) LPC Interface Controller (rev 02)
00:1f.2 SATA controller: Intel Corporation 82801IR/IO/IH (ICH9R/DO/DH) 6 port SATA Controller [AHCI mode] (rev 02)
00:1f.3 SMBus: Intel Corporation 82801I (ICH9 Family) SMBus Controller (rev 02)
root@(none):/# lspci > ~/xyz
root@(none):/# exit
# exit and notice that file is on my local machine now:
exit
rminnich@xcpu:~/gopath/src/github.com/u-root/u-root/xcmds/cpu$ ls -l ~/xyz
-rw-r--r-- 1 rminnich rminnich 577 May 17 17:06 /home/rminnich/xyz
rminnich@xcpu:~/gopath/src/github.com/u-root/u-root/xcmds/cpu$

This is init code for the case that cpu finds itself as pid 1. This is duplicative of the real init, but we're implementing it as a duplicate so we can get some idea of: what an init package should have what an init interface should have So we take a bit of duplication now to better understand these things. We also assume for now this is a busybox environment. It is unusual (I guess?) for cpu to be an init in anything else. So far, the case for an init pkg is not as strong as I thought it might be.