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A sub-Hurd is like a
neighbor Hurd
, however, makes use of some
resources provided by another Hurd. For instance, backing store and the
console.
Sub-hurds are extremely useful for debugging core servers as it is possible to
attach to them with gdb from the parent
debugging via subhurds
). This avoids deadlock, e.g.,
when the instance of gdb stops the server but requires its use. (Note: it is
possible to use
noninvasive debugging
, but this is less
flexible.) Vice versa, it is also possible to use a subhurd to debug the
main
Hurd system, for example, the latter's root file system, but that
requires a privileged subhurd.
Howto
Quick hack: Use an existing image
Preparing your own image
Booting
Networking
Booting and shutting down
Using
Further Info
Use Cases
Debugging the Main Hurd System
Unit Testing
Howto
Quick hack: Use an existing image
You can download a Debian/Hurd image
here
and directly
boot it:
$ wget --no-check-certificate https://cdimage.debian.org/cdimage/ports/latest/hurd-i386/debian-hurd.img.gz
$ gunzip debian-hurd.img.gz
$ boot --kernel-command-line="fastboot root=pseudo-root" -T typed part:1:file:debian-hurd.img
The 'fastboot' is necessary to skip the filesystem check which fails
because the image assumes the root filesystem to be /etc/hd0s1. Once
booted, you can correct this:
root@debian:~# settrans -c /dev/pseudo-root /hurd/storeio pseudo-root
root@debian:~# echo /dev/pseudo-root / ext2 defaults 0 1 >/etc/fstab
root@debian:~# halt
From now on,
boot -T typed part:1:file:debian-hurd.img
should suffice.
Preparing your own image
To run a subhurd, you need an additional partition (or a file) with an
installed Hurd system. In principle, you can also use your main
partition in read-only mode; but this obviously will create severe
limitations. Usually, you will want a complete independent system.
The following instructions assume that the system is installed on
/dev/hd0s1
. You can use any partition instead, or in fact just a
simple file created e.g. using dd.
Creating a file used as root filesystem for the Subhurd
To create a file
my.image
of size 2 gigabytes, do
$ dd if=/dev/zero of=my.image bs=1M count=1 seek=2000
(Note that it is currently problematic to create files larger than 2
gigabytes this way.)
Using debootstrap
The system for the subhurd is a normal Hurd installation, which could just as
well run standalone. You can use any of the various possible installation
methods, or reuse an existing installation if you already have several. If
using
Debian GNU/Hurd
, the easiest is probably to use
debootstrap as root:
mke2fs /dev/hd0s6
settrans -ca mnt /hurd/ext2fs /dev/hd0s6
debootstrap sid mnt/ http://httpredir.debian.org/debian
settrans -fga mnt
Booting
If you are using a recent version of the Hurd (>= 0.9), then you can
simply boot the subhurd as an unprivileged user by issuing
boot /dev/hd0s6
(Replace
hd0s6
by the name of your partition or backing file for the subhurd.)
The partition must be unmounted (or mounted read-only) before you boot from
it!
Networking
You can provide the subhurd with a network card by passing a
-f
option to
boot
. For instance, if you have a second network card
/dev/eth1
in your
host hurd, pass
-f eth0=/dev/eth1
to make it appear as device eth0 in the
subhurd.
If you don't have a second network card, you can setup the eth-multiplexer
to share one network card. To do so, install the multiplexer
settrans -c /dev/eth0m /hurd/eth-multiplexer --interface=/dev/eth0
Then configure your main Hurd system to use a virtual network
interface (e.g.
/dev/eth0m/0
) instead. On Debian/Hurd, this can be
accomplished using
ifdown /dev/eth0
sed -i -e s#/dev/eth0#/dev/eth0m/0# /etc/network/interfaces
ifup /dev/eth0m/0
You can now pass
-f eth0=/dev/eth0m/1
to
boot
Booting and shutting down
Now the subhurd should boot just like a normal Hurd started directly from GRUB,
finally presenting a login prompt. The
boot
program serves as proxy for the
subhurd, so you can control it from the terminal where you issued the boot
command.
To exit the subhurd, issue
halt
or
reboot
. This should exit it cleanly,
but for some reason it doesn't always work; sometimes it will output various
errors and then hang. If that happens, you need to kill the
boot
process
manually from a different terminal. If the
boot
process dies, the
proc server will kill all tasks belonging to the Subhurd.
Using
In the subhurd, you can do basically all the same things as in the main Hurd.
You can even set up networking: Just invoke
settrans
on the
/servers/socket/2
as usual inside the subhurd, using
/dev/eth0
, only using a different local
IP than in the main Hurd. This way, the subhurd will be able to communicate to
the outside world with its own IP -- allowing for example to do
apt-get
inside the subhurd, or to
ssh
directly into the subhurd.
If you want to access the subhurd processes from the outside, e.g. for
debugging purposes
(or to get rid of a subhurd that
didn't exit cleanly...), you need to find out how main Hurd
PID
s correspond to
subhurd processes: the subhurd processes appear in the main Hurd (e.g. if doing
ps -e
) as unknown processes, but the
PID
s are different! To
find out which process is which, you can simply compare the order -- while the
numbers are different, the order should usually match. Often it also helps to
look at the number of threads (e.g. using
ps -l
), as many servers have very
characteristic thread counts.
IRC, freenode, #hurd, 2013-08-09
btw, is there a way to get dde-based networking into a subhurd?
the wiki instructions look like they're for the mach driver
and starting the dde translator inside the subhurd does not work
for me
that's probably a good thing though
the netdde process will need privileged access to mach
for hardware access
you can't easily use netdde from a subhurd, unless with a
different nic
i usually rebuild mach with in kernel devices so both the main and
subhurd can share on nic
one*
could a port to netdde perhaps forwarded to the subhurd?
zengh da wrote the eth-multiplexer for that iirc
it's a matter of making it appear as an eth0 device on the master
port aiui
zheng*
yes, I looked at that
what is the master port?
on a plain hurd system it's the port that privileged processes can
use to access mach devices
in a subhurd, it's the same for the subhurd, to access some devices
that you choose to give access to
its real name is the "device master port"
ah yes
IRC, freenode, #hurd, 2013-08-10
teythoon: use eth-multiplexer to use the NIC within a
subhurd. that's exactly what it was created for.
I don't remember whether it's even possible to share a "raw"
netdde device... I don't think I ever tried that; and I don't remember
enough of the theory to tell whether it should be possible
but I really don't see the reason to, when eth-multiplexer is
available
(IMHO running an eth-multiplexer on top of netdde should be the
default setup in fact)
as for actually passing on the device, that should be perfectly
possible with zhengda's modified subhurd... but I don't remember whether
that was ever merged upstream
(you will definitely need that for using netdde in a subhurd,
regardless whether through eth-multiplexer or directly)
IRC, freenode, #hurd, 2013-09-15
I wonder if we can modify the boot program so that it passes
ports from the mother hurd to the subhurd
so that we could pass in a port to the eth-multiplexer
or use like /hurd/remap as the root translator for the subhurd
remap root translator
eth-multiplexer was created exactly for that iirc,
so it's probably already done somewhere
IRC, freenode, #hurd, 2013-09-16
braunr: regarding subhurd did you mean to install
sthibault/hurd-i386/debian-hurd.img.tar.gz
on a separate partition and booting using the instructions for
subhurds on the web.
gnu_srs: yes
be careful that the subhurd doesn't use the same partition as the
main hurd, that's all
what about changing fstab?
12:17 < braunr> be careful that the subhurd doesn't use the same
partition as the main hurd, that's all
gnu_srs: yes, you need to change the fstab
currently it is used for fscking stuff, so if it points to your
main partition it will cause severe corruption
gnu_srs: you also have to specify the right partition in the
servers.boot file
fstab of the subhurd image?
yes
how to unpack the .img file (just to be sure)?
gnu_srs: you don't need to, just use the img file as secondary
hard disk image
Then how should I be able to change fstab of the image?
boot your hurd box, mount the partition and change it
I missed something here: on my partition /my_chroot I have have
the file debian-hurd-20130504.img
gnu_srs: ah, you copied it to the partition, braunr meant to use
it as the secondary disk, e.g. qemu ... -hdb debian-hurd-20130504.img ...
That is the same as installing another cd image, where does the
subhurd come into play?
mount the partition on the secondary hd, fix the fstab there,
mount it r/o, get the servers.boot file from the wiki, modify it so that
it points to the right partition, execute boot servers.boot /dev/partition>, probably /dev/hd1s1
BTW: unpacking was problematic: tar: debian-hurd-20130504.img:
Cannot seek to 2147696640 (2G limitations)
I wonder why you did this on your hurd system in the first
place...
I thought I could use that partition, /my_chroot as a chroot
place. So it won't work for subhurds?
well, there are several ways to setup a subhurd. one is to
already have a spare partition for that and use crosshurd or as I did
debootstrap to install a debian system there
braunr suggested an even easier way, download the .img file and
use it as secondary hard disk
you ended up doing kind of both
I tried once with debootstrap and that created a disaster...
how so?
The install errored out, and the whole filesystem (including /)
was left in a broken state. Maybe I tried
that without using a separate partition. Don't remember any
longer. So you say it's safe now?
I used it successfully to setup my subhurd
and you have your subhurd in a separate partition, installed from
there too, as root?
the web page only mentions crosshurd, and that failed for you?
yes, having a separate partition is (currently) necessary to run
a subhurd
yes, I used debootstrap as root, afaics that is necessary
and yes, as I said the other day, I tried crosshurd first and it
failed
then again, I fail to see any reason to use crosshurd these days
it's only a wrapper around debootstrap anyway, using it with
--foreign and fixing up stuff later
one has more control over the process if one uses debootstrap
directly
I still don't dare to do it yet. I'll create another image using
netinst with a separate partition and try out first.
When installing a new image using netinst.iso (2013-06-30) and
rebooting /proc does not get mounted?
gnu_srs: is that a statement or a question?
A statement.
it's not customary to end statements with question marks ;)
s/mounted?/mounted, why?/
well, you seem to be the last person to perform such an
installation, so you are in the perfect position to answer this question.
cat /var/log/dmesg?
On other images I have: fsysopts /proc; /hurd/procfs
--clk-tck=100 --stat-mode=444 --fake-self=1
gnu_srs: no, check the installation log
gnu_srs: and what does showtrans say?
showtrans /proc;
which log file to look for?
the installation log, somewhere in /var/log probably
I only find /proc in /var/log/installer/syslog, mainly printing
out errors not finding /proc/mounts
iirc the /proc translator should be set during the hurd package
configuration
you should probably look for that part in the log
Setting up translators: /hurd/exec /hurd/proxy-defpager
/hurd/pflocal (+link) /hurd/pfinet (+link) (+link) /hurd/procfs -c
/hurd/password crash-kill crash-suspend crash-dump-core crash.
that part
debootstrap: /hurd/procfs -c and in-target: /hurd/procfs -c No
errors
I don't understand what that means
please explain in more details
see: http://paste.debian.net/41195/
makes much more sense :)
Where is the 'Setting up translators' done? I cannot find
anything in /var/lib/dpkg/info/hurd* or /etc/init.d/...
/usr/lib/hurd/setup-translators, called in hurd.postinst
tks:)
Hi, when installing a new image with debootstrap to /chroot the
script boot/servers.boot is already there (as well as in /boot/ + grub)
Is it OK to use that file to boot the subhurd?
using /boot/servers.boot or /chroot/boot/servers.boot (if the
/chroot partition is unmounted it cannot be used?)
and how to unmount /chroot: umount does not work?
braunr: I'm also trying to find out what's wrong with glibc, when
my subhurd is up and running 2.13-39 (if possible)
I know I should issue settrans command, but I'm not yet fluent in
translators.
sorry:-/
Now this, after a reboot: unknown code P 30 while trying to open
/dev/hd0s3 (/chroot)
Disk write protected: use the -n option to do a read-only check
of the device.
fsysopts /dev/&hd0s1 --writable: Operation not supported??
OK, I'm giving up for now, no subhurd:-( and a broken install.
Which terminal to use in rescue mode, TERM is not set,
dumb,mach,hurd does not work with nano?
e2fsck /dev/ho0s3; e2fsck: Unknown code P 2 while trying to open
/dev/ho0s3; Possibly non-existent device?
mke2fs /dev/hd0s3; /dev/hd0s3 is not a block special device.;
Proceed anyway? (y,n) n: What's going on (hd0s3 not mounted)??
anybody, help?
after removing and creating the partition again:mke2fs
/dev/hd0s3, , mke2fs: Unknown code P 13 while trying to determine
filesystem size: What's going on?
Where to find the glibc-2.13 versions which used to be at
debian-ports?.
seems they can be found on snapshot.debian.org
IRC, freenode, #hurd, 2013-09-17
teythoon: Installing subhurd via debootstrap on partition
/chroot fails miserably. Install hangs, and after reboot \rm -r
/chroot/* fails for dev and proc
Are there translators running there already? I have not
booted the subhurd.
translators for hd0s3 (/chroot) are storeio and
ex2fs.static. Do I have to stop them to be able to clean out
/chroot?
mount -v /chroot; settrans -a /chroot /hurd/ext2fs
/dev/hd0s3;
ext2fs: /dev/hd0s3: panic: main: device too small for
superblock (0 bytes);
mount: cannot start translator /hurd/ext2fs: Translator
died
Please, somebody!
don't ask to ask, just ask, right?
we've already told you everything you need
just get it right
for example, i told you to be careful about fstab so that
the subhurd wouldn't use the main hurd partition
but you managed to screw that
good job
I installed the subhurd in a partition /chroot /dev/hd0s3
using debootstrap
i don't know deboostrap, it may be broken, use the disk
image youpi maintains
ant the install screwed up with debootstrap
ok; then I cannot use a partition, but another disk in
kvm, e.g. hdb?
gnu_srs: hd1
something is fishy with glibc, definitely, that's why I'm
trying to set up a subhurd to revert to 2.13-39
hi, when trying to boot a subhurd: /hurd/ext2fs.static:
hd0s3: Gratuitous error; bye
gnu_srs: why hd0s3 ?
it should be hd1s1
I'm still using a separate partition /my_chroot
/hd0s3. Will switch to hd1 next. teythoon?
the servers.boot script use absolute
paths:/hurd/ext2fs.static and /lib/ld.so.1 /hurd/exec,
shouldn't they be relative to /my_chroot?
no
they're actually from your host
teythoon: please, how did you succeed to boot a subhurd
in a partition?
using debootstrap
gnu_srs: from my shell history:
: 1374672426:0;debootstrap sid /mnt
: 1374673020:0;cp /etc/hosts /etc/resolv.conf /mnt/etc
: 1374673048:0;cp /etc/passwd /etc/shadow /mnt/etc
teythoon: so it does work fine ?
great
yes, why wouldn't it?
gnu_srs: I then remounted that partition r/o and used
the servers.boot file from the wiki to boot it
braunr: why wouldn't it? (you do mean the debootstrap
part, don't you?)
teythoon: i don't know
i've heard it wasn't maintained any more
not being maintained is a good reason for something to
become unusable/untrustable with time
o_O it is at the heart of d-i, isn't it?
I actually do most Debian installations using
debootstrap directly
ah
ok :)
teythoon: even hurd ones ?
braunr: well, just the subhurd installation, but that
went as expected
good
Finally: I found the reason for Gratuitous error, I used
the /boot/servers.boot script,
that being different to the one on the wiki:-/
Is it possible to copy files between a host hurd and
subhurd, what about access to eth0?
Hi, when starting the subhurd I see some warnings/error:
1) A spelling error execunable-> executable
2) libports: invalid destination port
3) mach-defpager: another already running
"execunable" is not a typo, but just "exec" and "unable
..." without a space-type character
OK, sounds more plausible
Ah, the printouts are mixed, no bug
When setting up nework in the subhurd: /hurd/pfinet:
file_name_lookup /dev/eth0: Translator died
/hurd/pfinet: device_open(/dev/eth0): (os/device) no such
device
settrans: /hurd/pfinet: Translator died
IRC, freenode, #hurd, 2013-09-18
priority does not matter much
memory manager is not really surprising, there's indeed already one
what is actually the problem?
So these are merely warnings?
gnu_srs: yes
Real problems are I cannot set up networking, e.g. wget ...:
Connecting to ... failed: Address family not supported by protocol.
gnu_srs: did you give the subhurd a network card?
How?
and do I need to set up fstab, for now it's empty.
I just installed the base with dbootstrap
gnu_srs: -f option of boot
e2fsck will need fstab for sure
otherwise it can't divine what should be checked
Why is the /boot/servers.boot different from the subhurd one on
the wiki? Is it used at all, I thought grub was in charge.
it's not used at all
maybe better to put in the subhurd one there then, with a
comment?
no, since /boot/servers.boot is supposed to be used for machine
boot
not subhurd boot
what about putting a copy of the suhurd one there, with a
different name?
probably a good idea, yes
matter of making it happen
the wiki page on subhurd does not say how to set up networking,
only that you can do it.
matter of adding the information
I remember it's the -f option of boot
make it work, and add the information for others
I could try, but don't know how to add a network card to the
subhurd, and e.g. how to set up swap
see -f option
of boot?
"gnu_srs: -f option of boot"
if you could read what we write, that'd make things happen way
faster
yes I saw your comment above, it was just to be 100% sure:-D
device_file=/dev/eth0 or something else?
eth0 is used by the host already
did you read boot --help ?
iirc it's not a problem, both will receive all frames
yes I did
then I don't see where you took device_file from
at least in that form
--device=device_name=device_file
that means rather something like --device=foo=bar
so -f /dev/eth0 is correct usage then?
didn't you see that in what I wrote, there was a "=" in there?
-f is the short option, --device is the long, I don't see the
need for = in the short option?
in the long option there are *two* =
yes, but in the short no?
why not?
long -> short usually drops one =
to summarize: -f=/dev/eth0 or --device=eth_sub=/dev/eth0?
why shouldn't there be a eth_sub in the short version?
10:15:49) youpi: long -> short usually drops one =
yes, it drops the =
but nothing else
if the long option needs some information, the short needs it too?
-?
correct now? -f eth_sub=/dev/eth0 or --device=eth_sub=/dev/eth0?
yes
k!
Further Info
Read about using a subhurd for
debugging purposes
Roland's tutorial about
running a subhurd
Use Cases
Debugging the
Main
Hurd System
Note: This only works with privileged subhurds.
A subhurd can be used for debugging the
main
Hurd system. This works as long
as the subhurd doesn't use any services provided by the main Hurd. For
example, if you already have a subhurd running at the time it happens, you can
use that one to debug a deadlocked
ext2fs
root file system in
the
main
Hurd.
For this, you need to get a handle to the main Hurd's
ext2fs
translator
's
PID
, but this is no problem, as currently
PID
s are visible across subhurd boundaries. (It is a
open issue hurd
whether this is the right thing to do in
virtualization
contexts, but that's how it currently is.)
Unit Testing
freenode, #hurd channel, 2011-03-06:
From
unit testing
it could be interesting to have scripts that automatically start a
sub-hurd to do the tests
though that'd catch sub-hurd issues :)
so a sub-hurd is a hurd that I can run on something that I know
works(like linux)?
Virtual machine I would think
and over a network connection it would submit results back to
the host :p
* foocraft brain damage
sub-hurd is a bit like chroot
except that it's more complete
oh okay
i.e. almost everything gets replaced with what you want, except the
micro-kernel
that way you can even test the exec server for instance, without
risks of damaging the host OS
and we know the micro-kernel works correctly, right youpi?
well, at least it's small enough that most bugs are not there
1) all tests run in subhurd 2) output results in a place in the
subhurd 3) tester in the host checks the result and pretty-prints it 4)
rinse & repeat
the output can actually be redirected iirc
since you give the sub-hurd a "console"