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General-discussion FAQs

Remember that what counts is not just years but rather years x people, and in this regard, the investment into GNU Hurd's development is way below that of the Linux kernel or the BSDs. Considering how many developers are (and have been) working on the Hurd, it is actually impressive that so much has been achieved in the past couple of decades with so few people.

Posted 2013-08-24 01:03:55 CEST Tags:

A good explanation is available, translated (sic) in several languages.

Posted 2013-04-13 10:36:54 CEST Tags:

The Hurd will be considerably more flexible and robust than generic Unix. Wherever possible, Unix kernel features have been moved into unprivileged space. Once there, anyone who desires can develop custom replacements for them. Users will be able to write and use their own file systems, their own `exec' servers, or their own network protocols if they like, all without disturbing other users.

A series of interesting examples is available.

The Linux kernel has now been modified to allow user-level file systems, so there is proof that people will actually use features such as these. It will be much easier to do under the Hurd, however, because the Hurd is almost entirely run in user space and because the various servers are designed for this sort of modification.

Notably, flexibility for the user:

transparent ftp

$ cd /
$ ls

personal filesystem

$ dd < /dev/zero > myspace.img bs=1M count=1024
$ mke2fs myspace.img
$ settrans myspace /hurd/ext2fs myspace.img
$ cd myspace

Just curious, but I keep seeing these (and other similar) concepts being brought up as the amazing selling points of the Hurd, but all of this is entirely doable now in Linux with FUSE or things like it.

Nowadays, at LAST, yes, partly. And only on machines where fuse is enabled. Is it enabled on the servers you have an account on?

I'm not sure if an ftp filesystem has been implemented for FUSE yet, but its definately doable; and loopback filesystems like in your second example have been supported for years.

As a normal user? And establish a tap interface connected through ppp over ssh or whatever you could want to imagine?

What, then, are the major selling points or benefits?

These were just examples, Linux is trying to catch up in ugly ways indeed (yes, have a look at the details of fuse, it's deemed to be inefficient). In the Hurd, it's that way from the ground and there is no limitation like having to be root or ask for root to add magic lines, etc.

It also for instance provides userland drivers, for instance the network drivers are actually Linux drivers running in a separate userland process.

It also for instance provides very fine-grain virtualization support, such as VPN for only one process, etc.

etc. etc. The implications are really very diverse...

Posted 2013-03-15 16:37:56 CET Tags:

GNU Hurd 0.9 has been released on 2016-12-18, along with GNU Mach 1.8, and GNU MIG 1.8. Read about the Hurd's status.

OK, but when will it be finished?

Well, is the Linux kernel considered to be really "finished"? Hurd 0.9 does work, but of course it can still become better -- beginning to contribute and joining us is the best way for you to help achieve that. :-)

Posted 2013-03-15 16:37:56 CET Tags:

How Many Developers?

Literally only half a handful works on the core of the system in their free time, and another half of handful helps with Debian GNU/Hurd and Arch Hurd packaging. Also, an additional half of handful of former developers are still available for answering technical questions, but are not participating in the current development anymore.

In the past (that is, a lot of years ago), the FSF did pay a few developers for working full time on the GNU Hurd. But that was for a limited amount of time only, and evidently, it was too little for getting the system into a competitive state. Nowadays, it's only unpaid (apart from some bounties) and free-time volunteers' work.

In contrast to the Linux kernel, there is no industry involvement in development. For one, this is a good thing: independency; no conflicts of interests. For another, it is also a bad thing: no dedicated full-time workforce -- which matters a lot.

This also answers the question "How come the Hurd still can't do (...) after so many years of development?"

Why So Few?

We can only speculate. One major problem might be that the architectural benefits are generally perceived as very abstract, with little practical benefit. We currently don't have many tools that are actually making use of all the possibilities.

Another reason is that it's been taking too long. Today, most people don't believe it will ever be ready for production use, and thus would consider involvement a waste of time. This latter point is invalid, of course, as learning can never be a waste of time. The same holds for the challenges raised by the GNU Hurd -- we can only learn and improve upon working on them.

For likely the same reasons there is no industry interest in the GNU Hurd: its advantages are too abstract and incomplete for being of interest there.

As for the scientific sector, the GNU Hurd projects was rather about using a microkernel intead of doing research on them, for example. But, there have been some projects and theses done, and some scientific papers published on GNU Hurd topics, and we're generally very interested in further such projects.

Attracting New Faces

We're an open project: any interested party (you!) are very welcome to start contributing. Mentoring is possible, too, to help you get started.

Likewise, for reaching out to new developers, we're participating in Google's Summer of Code program.

As el_presidente commented on

Developers, developers, developers, developers.

They are the people that matter at this point in time.

Posted 2010-11-25 11:55:21 CET Tags:

Before asking a question, first make an effort to find the answer to your question. A lot of questions have been asked and answered before, so please spend some time trying to solve the problem on your own (e.g. search the web, search these web pages, etc.), and show us that you did so when you ask your question.

When asking, (1) be detailed, and (2) demonstrate that you made an effort, e.g. "I am having trouble frobbing the foo. I searched the web and only found information regarding how to frob a bar, but that seems unrelated." Provide as many relevant details as possible, as well as how to reproduce the issue.

This document may help you understand some developers attitudes and social norms.

Posted 2013-04-13 10:51:47 CEST Tags:

A Microkernel has nothing to do with the size of the kernel. Rather, it refers to the functionality that the kernel provides. It is generally agreed that this is; a set of interfaces to allow processes to communicate and a way to talk to the hardware. Software drivers, as we like to call them, are then implemented in user space as servers. The most obvious examples of these are the TCP/IP stack, the ext2 filesystem and NFS. In the case of the Hurd, users now have access to functionality that, in a monolithic kernel, they could never use, but now, because the server runs in user space as the user that started it, they may, for instance, mount an FTP filesystem in their home directory.

For more information about the design of the Hurd, read the paper by Thomas Bushnell, BSG: Towards a New Strategy of OS Design.

Posted 2013-04-13 10:44:46 CEST Tags:

The Hurd is currently slower than Linux, yes. But not very much, so it is completely usable.

Take care when running the Hurd in fully-virtualized machines: virtualization software use ugly heuristics to make Linux run faster, which will not work on the Hurd (or BSD, etc.) so comparisons in virtualized environments do not really hold. Also take care of not comparing Hurd (which is currently 32bit) with a 64bit Linux execution: 64bit has much more computational and optimization possibilities than 32bit. At least, use -m32 to build a 32bit Linux version of a test for comparison.

The main reason for slowness is not because of the overhead of RPCs. It's mostly simply because less care has been done on implementing what makes Linux fast: intelligent read-ahead, carefully-tuned page cache, etc. or even just missing DMA support for your disk controller.

There is no ground reason this can not be achieved on GNU/Hurd, it has just not been a priority until now (first make it work, then make it work fast). We are currently working on multi-page pager and read-ahead, which should improve this a lot.

Posted 2013-03-17 14:20:19 CET Tags:

Please see the contributing page.

Posted 2013-03-17 14:05:28 CET Tags:

Yes and no. GNU refers to the system as a whole, while GNU/Hurd is more specific, saying that it is the GNU system running on the Hurd -- to differentiate it from the GNU system running on Linux, GNU/Linux.

Posted 2013-03-17 13:44:52 CET Tags:

It's on Savannah. See also the GNU Development Resources, for more information.

Posted 2013-03-17 13:44:52 CET Tags:

The microkernel has to provide memory management and user-level-managed page faulting, thread scheduling, and IPC.

One would have to reimplement the mach/ and sysdeps/mach/ parts of glibc and libpthread. One would have to rewrite mig to generate the new IPCs. One would have to rewrite libpager to handle paging.

All mach_ calls in glibc and hurd would need to be updated.

Quite a few other Hurd tools also assume a Mach kernel and would have to be adapted or rewritten.

Posted 2013-03-15 16:37:56 CET Tags:

Please try to reproduce bugs which are not obviously Hurd-specific on Debian GNU/Linux and then file them there.

If you find a genuine issue in Debian GNU/Hurd, please file it in our Alioth bug tracker at If you find a bug in the Hurd or GNU Mach themselves, either file a bug against the respective Debian packages, or directly at

Posted 2013-03-15 16:37:56 CET Tags:

It is a frequently asked question, which microkernel the Hurd should be based upon assuming that Mach is no longer considered state of the art, and it is well known that there has been a lot of discussion about this topic, and also some code produced, but then, years later, the Hurd is still based on GNU Mach.

Around the turn of the millenium, some of the Hurd developers began experimenting with using other microkernels for the Hurd, as they have been encountering a number of fundamental design issues with the Mach microkernel, mostly with respect to resource management problems.

At that time, L4 (Pistachio) was the prime candidate. A reimplementation of the Hurd on this microkernel looked promising, and got pretty far (running some simple POSIX programs, such as banner). However, over time some lingering design issues turned out to be fundamental problems: the original L4 is not suitable for building object-capability systems like the Hurd. Thus development was aborted in 2005.

During that process, Neal Walfield and Marcus Brinkmann started on a period of research on other microkernels, getting in deeper contact with other researchers. There was a lot of discussion, and a lot of good ideas produced, but a straight-forward port of the Hurd to such a modern microkernel (Coyotos, or the new L4 variants, for example) didn't seem feasible to them anymore: they found microkernel design and system design to be interconnected in very intricate ways, and this demanded design changes in the Hurd's core itself.

Based on this experience, the next step was to write an own microkernel instead, which Neal Walfield began doing with his experimental Viengoos project, for his research on resource management. Currently he works in another research area though, and thus Viengoos is on hold.

Note that while none of the microkernel research work is active now, the previous experiments already yielded a lot of experience, which will be very useful in the further development / improvement of the mainline (Mach-based) Hurd implementation.

For more details about this topic, please see our history page about the port to another microkernel.

Posted 2011-03-26 00:27:11 CET Tags:

GHAMP is the GNU/Hurd-based Apache, MySQL, PHP solution stack -- analoguous to GLAMP, which is based on GNU/Linux.

Pronounce it like the G in GNU, followed by a mostly silent H, and AMP as in amplifier.

Posted 2010-12-15 08:27:25 CET Tags:

Hardware/Software support FAQs

Currently, for disks Mach integrates old drivers from Linux through some driver glue code, which provide IDE disk support, and we have an AHCI driver which provides SATA support.

For network boards, we use the DDE toolkit to run linux 2.6.32 drivers in userland processes, which provides both long-term support for new hardware and safety against driver bugs. Note however that we have of course not tested all drivers, we obviously don't even have all kinds of hardware. So we can not promise that they will all work. What probably works for sure is what we usually use: the rtl8139 and e1000 drivers for instance. Firmware loading is not implemented yet.

For graphical mode, Xorg is supported, e.g. with the vesa driver. DRM is not supported yet.

Xen is also supported, both blkfront and netfront.

Posted 2013-04-13 10:36:54 CEST Tags:

As of March 2014, 79% of all Debian packages are available for Debian GNU/Hurd. Of course, testing and bug fixing is welcome, as we have obviously not tested all of them.

Generally, packages that aren't Linux-specific (see Packages That Won't Be Ported) are expected to work on GNU/Hurd too. Notably, X.Org, GNOME, KDE, Firefox work. See the guidelines document for some common build problems and their solutions.

Posted 2013-04-13 10:36:54 CEST Tags:

It is not, there is no real reason why it would be particularly slow, it is just about switching virtual addresses and registers, which all OS have to perform anyway.

A quick-and-dirty benchmark:

    #include <fcntl.h>
    #include <semaphore.h>
    #include <stdio.h>
    #include <time.h>
    #include <unistd.h>
    #include <sys/mman.h>

    sem_t *sem1, *sem2;

    void worker1(void) {
        time_t last;
        int n = 0;
        last = time(NULL);
        while(1) {
            time_t new = time(NULL);
            if (new != last) {
                printf("%d\n", n);
                n = 0;
                last = new;

    void worker2(void) {
        while(1) {

    int fd;
    void get_sems(void) {
        void *ptr = mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
        sem1 = ptr;
        sem2 = sem1+1;

    int main(void) {
        fd = open("/tmp/foo", O_CREAT|O_TRUNC|O_RDWR, 0666);
        ftruncate(fd, 4096);

        sem_init(sem1, 1, 0);
        sem_init(sem2, 1, 0);

        if (fork())
        else {

run on my current Linux system (a Core i5-10210U), gets about 300k switches per second on Linux. Running it on Hurd-in-kvm (which would supposedly be slower) gets about 400k switches per second.

Posted 2022-12-03 11:59:08 CET Tags:

More precisely, during the Debian installation, around the extraction of the netdde package one gets:

/hurd/random: Warning: Failed to read random seed file /var/lib/random-seed: (system kern) error with unknown subsystem

This is a harmless glitch.

Posted 2021-08-11 18:50:22 CEST Tags:

Yes. The default pager recognises and respects Linux swap partitions.

Posted 2019-01-18 00:27:30 CET Tags:

There are plans for 64-bit kernelland with 32-bit userland, which will notably permit to efficiently make use of more than 2 GiB memory and provide 4 GiB userland addressing space.

A 64-bit GNU/Hurd is also coming soon, progress is tracked on 64-bit port! Hurd developers ported GNUMach to 64-bit some time ago. Then they started making significant progress on the x86_64 userland port in Feb 2023. As of May 2023, the 64-bit port works well enough to start all the essential Hurd servers, run /bin/sh, establish TCP/IP connections, and compile C. We are currently building 64-bit packages. We plan on supporting both a 32-bit and 64-bit Debian GNU/Hurd, only not both at the same time. However, there is no plan to fix the year 2038 concern on a 32-bit system.

That being said, you can always run a 32-bit version on a 64-bit machine, it just works, processes are just limited to a couple GiB available memory.

Posted 2013-04-13 10:36:54 CEST Tags:

There is a start of work on implementing a FUSE library on Hurd; its support is not updated to the latest version, but at least some fuse filesystems do work already.

Posted 2013-03-16 19:17:26 CET Tags:

The 2 GiB ext2fs limit has been removed.

IDE disk drivers however currently do not support more than 2^28 sectors, i.e. 128GiB.

The gnumach AHCI disk driver supports up to 2^48 sectors, i.e. 128PiB, but the device interface supports only 2^32 sectors, i.e. 2TiB.

You can have a bigger disk, you just should not put disk partitions beyond these limits for the drivers to be able to read from them.

Posted 2013-03-15 16:37:56 CET Tags:

Until recently, GNU Mach did not support SATA disk drives (/dev/sda etc. in GNU/Linux) natively, the only way to get those drives to work used to be to put them into compatibility mode in the BIOS, if such an option exists. GNU Mach will then recognize them as hd etc.

An AHCI driver has been added on 10th May 2013, which should bring support for a wide range of SATA controlers. Please however make sure to configure the BIOS in AHCI mode (as opposed to RAID mode).

Posted 2013-03-15 16:37:56 CET Tags:

The 830MB RAM limit has been removed, but just like any 32-bit OS without bad tricks, GNU Mach can not cope well with lots of memory. Latest versions of the Debian gnumach package will limit themselves to 3 GiB of memory. If you want more, you can twiddle the VM_MAX_ADDRESS limit between kernelland and userland in i386/include/mach/i386/vm_param.h, but glibc and the hurd servers will not cope well with less than 1 GB.

There is a 64-bit port in progress.

If you have an older version, or still experience problems with vmstat (see above) reported much less memory than you have, the best is to limit the memory it can see via GRUB's upppermem feature. Add uppermem 786432 to GRUB's Hurd entry in menu.lst.

Posted 2013-03-15 16:37:56 CET Tags:

IRC, freenode, #hurd, 2012-01-21

<chromaticwt> is it possible to transfer servers running on one microkernel
  on one machine, to another microkernel running on a different machine?
<chromaticwt> two machines will be running the complete os
<antrik> well, if the code for network-transparent IPC still existed, it
  might be possible to move a task to another machine, while keeping the
  port associations with the original system...
<antrik> if you mean actually moving it to another system, that's pretty
  much impossible in any system that has stateful interfaces
Posted 2012-01-28 15:04:40 CET Tags:

IRC, freenode, #hurd, 2012-01-13

<veganman> so there's absolutely no way, even slowly to run i386 linux code
  under hurd/i386? I have a small app, commercial, which I have to get
  running there
<veganman> no source
<braunr> no way
<braunr> you'd need to create a userspace linux server catching linux
  system calls and calling hurd specific stuff to implement them
<braunr> it doesn't exist, it may be hard to implement
<braunr> some cases will definitely be hard to implement
<veganman> so, no magic linux lxemu on windows?
<veganman> or linuxemu on plan9
<pinotree> nope
<veganman> I remember something silly, sonmone had compiled linux as a user
  application on plan9 and inserted his own binaries as
  a code object, to be run on plan9, for use on ibm hpc hardware
<veganman> it was ron minich
<veganman> I think that was it
<veganman> google for linux & cnk for additional clues
Posted 2012-01-28 15:04:40 CET Tags:

How difficult is it to port the GNU/Hurd system to run on another architecture?

The GNU/Hurd system consists of Hurd servers running as user-space processes on top of the GNU Mach microkernel. The system functionality is usually accessed through the POSIX interface that is provided by glibc and libpthread.

A whole-system port involves touching all these components, with varying degree, of course.

For a CPU architecture port, the microkernel is the most involved part, followed by glibc and the threading library.

The original Mach microkernel was portable to a number of architectures which were a lot more popular at the beginning of the 1990s than they are now.

The GNU/Hurd system is currently available for the x86 architecture. This includes emulators such as QEMU (or KVM), or VirtualBox. Besides this, there is a port for the Xen domU sub-architecture.

Further on, there are some unfinished porting attempts for the Alpha, MIPS and PowerPC architectures. These have not been completed due to little developer interest.

Another option is to do the port at a different layer: port the Hurd servers to not run on the GNU Mach microkernel, but instead on top of another microkernel. Or, even by providing a Mach emulation layer on top of a monolithic kernel. For example, there could be a port for having Mach run as a POSIX user-space process, or by implementing the Mach IPC facility (as well as several others) as Linux kernel modules. While there have been some experiments, no such port has been completed yet.

IRC, freenode, #hurd, 2013-09-05

<rah> what would be required to port the hurd to sparc?
<pinotree> port gnumach, write the sparc bits of mach/hurd in glibc, and
  maybe some small parts in hurd itself too
<rah> what would be required to port gnumach? :-)
<braunr> a new arch/ directory
<braunr> bootstrap code
<braunr> pmap (mmu handling) code
<braunr> trap handling
<braunr> basic device support (timers for example)
<braunr> besides, sparc is a weird beast
<braunr> so expect to need to work around tricky issues
<braunr> in addition, sparc is dead
<rah> mmm
<rah> it's not totally dead
<rah> the T1 chips and their decendents are still in production
<rah> the thing is I'd like to have real hardware for the hurd
<rah> and if I'm going to have two machines running at once, I'd rather one
  of them was my UltraSPARC box :-)
<braunr> rah: unless you work hard on it, it's unlikely you'll get it
<rah> braunr: of course
Posted 2011-09-14 23:21:40 CEST Tags:

The Hurd servers themselves are multithreaded, so they should be able to take benefit of the parallelism brought by SMP/Multicore boxes. This has however never been tested yet because of the following.

Mach used to be running on SMP boxes like the Intel iPSC/860, so principally has the required infrastructure. It has however not yet been enhanced to support nowadays' SMP standards like ACPI, etc. Also, GNU Mach's Linux device driver glue code likely isn't SMP-safe. As this glue code layer is not used in the Xen port of GNU Mach, the plan is to try it in this enviroment first.

That is why for now GNU/Hurd will only use one logical processor (i.e. one core or one thread, depending on the socket type).

Once this issue is solved, there are follow-up issues about multiprocessing and multithreading.

Project idea.

Posted 2011-02-22 09:48:31 CET Tags:

Many computer operating systems strive to be POSIX (Portable Operating System Interface) compliant, as it makes cross-compiling and program portability much easier than having to package something for every new distribution.

Is it favorable of rather a hindrance to be compatible to POSIX and similar standards?

A lot of things in POSIX et al. are designed for UNIX-like systems with traditional monolithic kernels.

Thus, a microkernel-based system, as ours is, has to employ a bunch of detours, for example to implement the fork system call.

On the other hand, (mostly) complying to these standards, made a really big body of software just work without any (or just trivial) porting. Especially so for command-line programs, and libraries.

But: a large part of today's user programs are not written according to POSIX et al. low-level interfaces, but against GNOME, GTK+2, and other high-level frameworks and libraries. It may be a valid option to enrich these instead of striving for total POSIX compliance -- and the high-level programs (that is, their users) may not even notice this, but we would avoid a lot of overhead that comes with wrapping the Hurd interfaces to be POSIX compliant.


Posted 2010-12-21 12:43:38 CET Tags:

Given that both Linux and GNU Hurd are using the ?ELF binary format, it is in theory possible to have a system installation where you can dual-boot using either the ?Linux kernel, or the GNU Hurd, so that everything but the kernel is shared. For this, all programs need to agree to rely on only one abstraction layer, for example the standard C library (glibc). (Additionally, for example for system calls that are not covered by glibc calls, you'd need to be able to reliably trap and emulate these.) However, Linux' and the GNU Hurd's ?ABI's have sufficiently diverged, so that this is not easy to do. That's why you can't currently install a system in this way, but you need a separate installation of the userspace suited for the Linux kernel, or the GNU Hurd.

Posted 2010-09-06 06:24:48 CEST Tags:

Running GNU/Hurd FAQs

You are apparently not running the Hurd console, only the Mach console, which Xorg does not know how to read.

Make sure to enable the Hurd console in /etc/default/hurd-console

Posted 2022-12-02 23:51:20 CET Tags:

Possibly something broke translators there. You can run

dpkg-reconfigure hurd

to rebuild entries there.

Posted 2021-08-17 00:50:52 CEST Tags:

This is due to a missing implementation of a corner case of Posix signaling for non-root processes to root processes.

One can however use the usual ctrl-alt-backspace shortcut to kill the X server.

You just need to configure it via the file: /etc/X11/xorg.conf.d/xorg-ctrl-backspace.conf

Section "InputDevice"
    Identifier "Generic KeyBoard"
        Driver "kbd"
        Option "XkbOptions" "terminate:ctrl_alt_bksp"
Posted 2021-08-15 00:20:49 CEST Tags:

This is the error message for EIEIO (pronounce E-I-E-I-O). This error code is used for a variety of "hopeless" error conditions. Most probably you will encounter it when a translator crashes while you were trying to use a file that it serves.

You can thus think of it as an equivalent of the "blue screen of the death" or "Oops"... except that it's just an error! It doesn't take your whole system away with it, only the particular operations that was going on.

The term "Buy the farm" is synonymous to "Kick the bucket," meaning "to die". More specifically, "Bought the farm" was used by the US Air Force to denote a fatal crash. To say "Computer bought the farm" is simply saying "Your computer crashed".

Sure, we could just say "Crash!", but then again, so could the Air Force.

Posted 2016-05-23 00:53:36 CEST Tags:

Old versions of emacs used to have this issue. This is fixed in emacs24.

Posted 2013-05-02 03:39:46 CEST Tags:
Posted 2013-04-13 10:36:54 CEST Tags:

Edit /etc/default/hurd-console to configure the Hurd console. See console for further information about the Hurd console.

Posted 2013-03-15 16:37:56 CET Tags:

There is no dmesg command, since the kernel does not keep a buffer of its messages. syslog however dumps them into /var/log/dmesg, so you can simply cat that.

Posted 2013-03-15 16:37:56 CET Tags:

If ps hangs, try ps -M which should still work by not getting detailed information from processes.

Posted 2013-03-15 16:37:56 CET Tags:

This happens because currently there is no way to detect console users.

On Debian GNU/Hurd systems, you need to run

# dpkg-reconfigure xserver-xorg-legacy

and select Anybody for starting X.

Posted 2013-03-15 16:37:56 CET Tags:

The distinction between / and /usr has historical reasons. Back when Unix systems were booted from two tapes, a small root tape and a big user tape. Today, we like to use different partitions for these two spaces. The Hurd throws this historical garbage away. We think that we have found a more flexible solution called union filesystems, which allow to create virtual filesystems which are the union of several other filesystems. However, support for union filesystems is still in early development.

Posted 2013-03-15 16:37:56 CET Tags:

Debian GNU/Hurd FAQs

If you want to use the apt source facility, make sure that /etc/apt/sources.list contains a line like

deb-src unstable main

... replacing de with your homeland's code.

Posted 2013-04-13 10:36:54 CEST Tags:

Open Issues FAQs

If logging in doesn't work, e.g. you enter a username, and it doesn't even prompt for a password, but directly say "Invalid password", you probably have some translators which got deconfigured for some reason. You can try to reboot in emergency mode, and run

# dpkg-reconfigure hurd

to reinstall translators.

Posted 2017-12-04 02:12:23 CET Tags:

Quite a few of them are actually benign:

/dev/hd0s1: Deleted inode 95849 has zero dtime.  FIXED.
Block bitmap differences: -(988160--988163) -(989627--989634) [...]
Free blocks count wrong for group #30 (16477, counted=16741).
Free blocks count wrong (2170675, counted=2170956).
Inode bitmap differences:  -244986 -245011 -(245107--245108) [...]
Free inodes count wrong for group #30 (4632, counted=4649).
Free inodes count wrong (880891, counted=880909).

see ext2fs dtime

/dev/hd0s1: i_file_acl_hi for inode 81872 (/proc) is 32, shoud be 0.

see e2fsck i file acl hi, fixed in e2fsprogs 1.42.13

Posted 2014-11-19 13:50:34 CET Tags:

Some applications don't themselves link against libpthread, but then load plugins which do link against libpthread. This means internally switching from single-threading to multi-threading, which is only supported since libc0.3 2.19-16~2. Previously, it would result in errors such as:

./pthread/../sysdeps/generic/pt-mutex-timedlock.c:70: __pthread_mutex_timedlock_internal: Assertion `__pthread_threads' failed.

This could be worked around by making the application link against libpthread (i.e. not only the plugin, but also the main binary), or without recompiling by explicitly pre-loading libpthread, for example:

$ LD_PRELOAD=/lib/i386-gnu/ [application]

But it should now be gone, simply upgrade libc0.3.

Posted 2013-09-26 11:33:07 CEST Tags:

If you see a db> prompt on the console, something unexpected and bad happened inside the GNU Mach kernel, which it cannot recover from. (Think of it as the equivalent of a Linux kernel oops, for example.) The db> prompt is actually the GNU Mach kernel debugger waiting for your commands. For example, you can then reboot the system by issuing the reboot command, or if you want to help analyze the problem, start by typing in the trace command, which will display the function call trace leading to the crash:


This can be decyphered by using:

$ addr2line -i -f -e /boot/gnumach 0x8007cf1 0x80071bc 0x8006831

You can then send us the whole results of the trace and the addr2line commands, as well as the exact version of the GNU Mach kernel you were running, for further investigation. More information about the GNU Mach debugger is available.

Posted 2013-04-13 10:36:54 CEST Tags:

Copying baseGNU to the virtual disk works. Even booting got through but when I try to run native-install it never gets to the very end. First time it froze on sed package, the other time on sysv-rc.

How much memory did you configure for the QEMU system? It may simply be -- I've seen this myself -- that the system runs out of memory, as at the native-install stage (I think at least) swap is not yet configured and enabled. What I've been doing is: boot (with -s), MAKEDEV hdWHATEVER in /dev/ for the swap device, run /hurd/mach-defpager, followed by swapon /dev/hdWHATEVER. Does this help?

Thank You very much, more memory solved the freezing.

Posted 2013-03-15 16:37:56 CET Tags:

In some virtual machines (e.g. VirtualBox), "probing eata on XXX" may be quite long. This is apparently due to poor efficiency of the virtualizer, not Mach. There is no such issue on real hardware or using qemu/kvm.

Posted 2013-03-15 16:37:56 CET Tags:

If you get the error bad hypermeta data when trying to mount an ext3 partition from GNU/Linux, that is usually because the file system has not been unmounted cleanly (maybe GNU/Linux got suspended to disk) and the Hurd cannot mount it as ext2 without checking. Either boot back into GNU/Linux and unmount it or you can try to run fsck.ext3 from GNU/Hurd directly.

Posted 2013-03-15 16:37:56 CET Tags:

Development FAQs

In order to ?debug translators and being able to step into glibc during it, on Debian you need the hurd-dbgsym and libc0.3-dbg packages installed. If you need to debug the initialization of the translator, start the translator like

$ settrans -Pa /foo /usr/bin/env LD_LIBRARY_PATH=/usr/lib/debug /hurd/foofs

The -P option will make it pause and you will be able to attach ?GDB to the process.

Posted 2013-03-15 16:37:56 CET Tags:

In Debian, to get ?debugging information for glibc, you need to install the libc0.3-dbg package. At the place ?GDB looks for debugging symbols by default (/usr/lib/debug/lib/), Debian's libc0.3-dbg stores only the frame unwind information used for backtracing. If you want to step into glibc while debugging, you need to add LD_LIBRARY_PATH=/usr/lib/debug to debugged program's environment (set env VAR value from the GDB command line). If that still does not work, try LD_PRELOAD=/usr/lib/debug/ instead.

Posted 2013-03-15 16:37:56 CET Tags:

Old FAQs

The Unofficial (and no longer maintained) GNU&nbsp;Hurd FAQ, Version 0.13

Contributions by:

Michael I. Bushnell <>
Len Tower <>
Trent Fisher <>
Remy Card <>
Louis-Dominique Dubeau <>

Original Document by: Derek Upham <>

Mach is a micro-kernel, written at Carnegie Mellon
University.  A more descriptive term might be a greatest-common-factor
kernel, since it provides facilities common to all ``real'' operating
systems, such as memory management, inter-process communication,
processes, and a bunch of other stuff.  Unfortunately, the system
calls used to access these facilities are only vaguely related to the
familiar and cherished Unix system calls.  There are no "fork",
"wait", or "sleep" system-calls, no SIGHUPs, nothing like that.  All
this makes it rather difficult to, say, port GNU Emacs to a Mach box.

The trick is, of course, to write an emulation library.  Unix programs
can then use (what they think are) POSIX system calls and facilities
while they are really using Mach system calls and facilities.

The simplest way of going about this is to take an ordinary Unix
kernel, open it up, and rip out all the machine-specific guts; any
time the Unix kernel talks to the machine, replace the code with calls
to the Mach micro-kernel.  Run this fake kernel on a Mach machine and
you end up with something that looks and acts just like Unix (even to
GNU Emacs).  Note that the Unix kernel we have implemented is just one
Really Big Mach program (called a single-server).

The Hurd, on the other hand, breaks the giant Unix kernel down into
various Mach programs running as daemons.  Working in concert with
facilities placed in the C library, these daemons provide all of the
POSIX system-calls and features; from the outside they look just like
a standard Unix kernel.  This means that, for practical purposes,
anything that you can port to Linux will also port to the Hurd.

Of course, if a user wishes to run his own daemons, he can do that as

Mach 4.0 is an enhanced version of Mach 3.0, put out by the people at
the University of Utah.  They are working on another free operating
system, and part of it includes an enhanced, more flexible version of
Mach.  The Hurd has moved to Mach 4.0, which is good, because it is a
lot easier to build than 3.0 was.

You can find more information on Mach by browsing the Hurd pages given
in the next answer, or by looking at the Project Mach and Flux
homepages at:

Carnegie Mellon University (for Mach versions before 4.0):

the University of Utah (for Mach 4.0):



?1 Yes, I know that ``micro-kernel'' is about as apt a description
as ``Reduced Instruction Set Chip'', but we're stuck with it.
Posted 2013-03-15 16:37:56 CET Tags:

            Frequently Asked Questions about the GNU Hurd

This document attempts to answer the questions that most often plague
users when they are talking about, installing, using, compiling and
developing the GNU Hurd as well as its binary distribution Debian
GNU/Hurd.  Be sure to read this before asking for help.

The GNU Hurd is under active development.
Be aware that there is a lot of work yet to be
completed; you will find bugs; your system will crash.  That said, there
is a lot of room for contributions at all levels:  development of the
Hurd and Mach proper, porting applications, writing documentation and,
most importantly, user feedback.

Should you have a question that is not answered by this document and you
feel that it should be, submit it and, if possible, with an answer.

Each section is copyright its respective author(s).  Permission is
granted to copy, distribute and/or modify this document under the terms
of the GNU Free Documentation License, Version 1.1 or any later version
published by the Free Software Foundation; with no Invariant Sections,
with no Front-Cover Texts and with no Back-Cover Texts.  A copy of the
license is included in the file COPYRIGHT.

                                                     Neal H Walfield
? Installation

??	What partition type should I use for my GNU/Hurd partitions?

{MB} You should use an ext2 filesystem.  Alternatively, you may use BSD
style ufs.  The partition type number for ext2fs is 0x83 (this is the
same as in Linux), not 0x63 (GNU HURD).  Thomas explains why 0x63 is the
wrong choice:

	One day we may have a new filesystem format, which would
	probably be called the GNU Hurd filesystem format, and might
	well use that partition code.

Regardless, as Roland points out, it is always an error to use that code
for an ext2fs partition, 

??	How do I name partitions?

{MB,NHW} I knew you would ask this.  If I had to reduce this FAQ to only
one question, I'd choose this one.  It is pretty easy, but you have to
know that there are actually several incompatibly naming convention.

First, the Hurd:  if the disk is question is a SCSI disk, you must know
the SCSI device number; if it is an IDE disk, you must know what
controller the disk is on and whether it is a master or a slave.  The
Hurd uses the BSD naming convention which, is to say, disks are ordered
according to their physical location, numerically, starting from zero.
This naming scheme is quite similar to that found in Linux.  There, the
master disk on the primary controller is designated as `hda' and the
slave as `hdb'.  On the secondary controller, the master and the slave
are designated by `hdc' and `hdd' respectively.  Under the Hurd, `hda'
would become `hd0', `hdb' would be referred to as `hd1', etc.

In the Hurd, like in BSD, partitions are called `slices' and are
numbered starting from one.  Thus, to name a particular partition, we
take the disk name, append a `s' and the partition number.  Again, this
is similar to Linux except, there is no `s'.  For instance, `hda1' would
become `hd0s1'.

GRUB, the boot loader, uses a completely different nomenclature: it
probes the BIOS and appends each disk in turn to an array.  Disks are enumerated
using zero based arrays. GRUB 2 enumerates partitions from one, while GRUB 1
used to enumerate them from zero.
The format is:
`hd (<disk>, <partition>)'.  Thus, in GRUB 2 `hd (0, 1)' refers to the first
partition on the first drive detected by the BIOS (or the second partition with
GRUB 1).  As Grub now has tab
completion, there is not a lot of guess work.

??	How much swap do I need?

{ST} The usual rule of thumb applies: the same amount as RAM, for instance.

??	Why do I get ``Operation not permitted error''?

{MB} You forgot to set the file system owner of the GNU/Hurd partition to
``hurd''.  The Hurd uses additional information in the inodes to set
translators.  To make this work, the partition must be marked as ``owned
by the Hurd''.  This is normally done by passing the `-o hurd' option to
`mke2fs' when creating ext2 system from other operating systems
(filesystems created in GNU/Hurd automatically enable this option).
If you failed to do this, you can still use the `e2os' script.

??	After `native-install' is finished, I had to write tthhiiss
	wwaayy.  In particular, I had to type `rreebboooott' to reboot.

{MB} Funny, isn't it? In addition to the rescue `term' server in
`/tmp/console', another `term' server got started and is clobbing the
keyboard input.  After a reboot this problem vanishes as only one `term'
server will remain.  If `tar' would support translator, we would not
have this problem...  Even if you don't experience this problem right
after the installation, reboot immediately so you don't hit this bug by

? Setup

??	How do I add a swap partition?

{MB} A swap partition is also called a paging file.  Usually, it is
sufficient to add the swap partition to `/etc/fstab', just as you would
under Linux.  You can swap to a Linux swap partition and the Hurd will
honour the Linux swap signature (both versions).  The Hurd will just as
happily swap to any other raw disk space and overwrite anything it
finds.  So, be careful!

If you want to swap to a file or make sure that it checks the Linux swap
signature before, you need to edit `/boot/servers.boot'.  The syntax is
the partition device file name plus, optionally, the swap file inside an
ext2fs partition, followed by a space and then one of:
`$(add-raw-paging-file)', `$(add-linux-paging-file)',
`$(add-paging-file)'.  The first works with any partition or file and
does not honour any swap signature or other data.  The second has a
safety check and only uses the file if a Linux swap signature is found.
The third looks for a swap signature first and falls back to raw paging
if it failed to find one.  This is also the default for entries in

??	How do I set up a network?
	How do I set up a loopback device?

{MB} In the former case, be sure that GNU Mach detected your network
card.  Either way, you need to setup `pfinet'.  Documentation can be
found at:

Don't forget to fill in `/etc/resolv.conf', `/etc/hosts', etc.

Of course, you only need to do this if the installation routine didn't
do it for you.

??	Can I use the GNU/Linux version of `e2fsck' on a GNU/Hurd partition?

{MB} Yes, at least since `e2fsprogs-1.05'.  Check this with `e2fsck -V'

{NHW} Do not try to defrag your partition as this utility does not know
about translators.

??	Why are pipes not working?

{MB} `settrans -fgc /servers/socket/1 /hurd/pflocal' should help.

? Usage

??	Where is the documentation?

{NHW,MM} There are neither man pages nor info nodes for the Hurd
translators and commands.  Documentation lives inside of the binaries
and can be found by passing the `--help' option to a given command.
For instance:

	# /hurd/ext2fs --help

will tell you what types of options the ext2fs translator accepts.

The GNU/Hurd User's Guide and the GNU Hurd Reference Manual both
provide some help about the usage of and concepts behind the GNU Hurd.
You can find them, among others, at:

??	What is the login shell?

{MB} The Hurd has the concept of a not-logged in user.  This user has
neither user ids nor groups ids.  This stems from the fact that the Hurd
supports uid and gid sets and one possibility is, of course, the empty
set.  Rather than deny access in this case, filesystems in the Hurd offer a
fourth permission triplet (i.e. rwx) which is used to determine the
privileges for users with no credentials.  This, however, needs to be
enabled on a file by file basis.  By default, the `other' permission
triplet is used.

The Hurd login shell is a shell running with neither uids nor gids.  To
restrict access to your files, either enable and change the fourth
permission triplet or change the login shell of the `login' user in the
password file to `/bin/loginpr' which implements the standard login

??	How do I use non-US keyboard bindings?

{ST} On Debian Hurd, you can configure the console layout from

??	How do I enable color on the console?

{NHW} If you are using the GNU Mach microkernel, you can set your
terminal to `mach-gnu-color'.  For instance:

	# export TERM=mach-gnu-color

??	How can I enable virtual consoles?

{ST} On Debian Hurd, it is already enabled by default, and configured from

{AMS} This can be done by running the following command:

	console -d vga -d pc_kbd -d generic_speaker /dev/vcs

If something went wrong, or if you just wish to exit the Hurd console
then hitting C-A-<backspace> will exit it.

??	What are these strange pids `0`, `2', `3', `4`, and `5`?

{MB,ST} Zero is the kernel, one is the root filesystem server, two is the
`exec` server (which handles starting programs), three is the init process, four
is the `proc` processus server, five is the `auth` server (which
handles user authentication).

??	Why does `ps aux' give me strange output?

{MB,MM} Try `ps Aux'.  Indeed, under GNU/Hurd, `ps aux' doesn't list
all processes: it omits the session and group leaders, and the
processes without parent.

??	I have a hung process that I want to kill, however, `ps' is now
	hanging too.

{MB} Interrupt it and pass it the `-M' option.

{NHW} By default, `ps' gathers information from both the proc server and
the processes themselves (via their message port).  If a process it
hung, it will not be able respond to its message port and thus, ps will
wait forever.  The `-M' option instructs ps to not gather information
that would require use of the message port.

??	Why are my translators dying?

{NHW} Try passing the `-ap' flag to settrans.  By default, settrans only
sets a passive translator, therefore, no output will show up on your
terminal.  Using `-ap', however, sets both the active and the passive
translator which, means that the translator starts immediately and its
stderr is connected to you terminal.

Additionally, the biggest problem is passing relative paths to passive
translators.  You cannot predict what the current working directory of a
translator will be when it is setup as a passive translator.

??	Why can I `read' a directory?

{MB} It is important to understand that there is nothing special about a
directory under the Hurd, it is just another file.  This fits in with
the translator concept where a translator can appear as a directory but
provide also as a file.

? Trouble shooting

??	When the APM support in the BIOS spins down my disk drives, the
	Hurd is unable to wake up.  What's wrong?

{MB} APM is not supported in the current version of GNU Mach, sorry.
Please disable APM in your BIOS setup.

??	What are these messages referring to `default pager', `paging',
	and `pager request'?

{MB} The default pager handles virtual memory allocation.  If it can't
allocate a new memory page because you are out of memory, some terrible
things may happen.  Whenever you get errors referring to any of these,
you either need more memory (make sure you have swap) or you have found
a memory leak.

??	What is a gratuitous error?

{MB} This comes from `strerror(EGRATUITOUS)'.  If you check glibc's
documentation, it will say that this error code has no purpose.  This,
however, is not quite true.  You only get this when something terrible
happens.  Thomas explains:

	More precisely `EGRATUITOUS' officially means that some server
	has responded in an impossible or protocol-violating fashion.
	There are some cases in the Hurd where `EGRATUITOUS' is returned
	and probably something else should be chosen instead.

If you can reproduce this error message, please report it.

??	What does ``/dev/hd0s1: MOUNTED READ-ONLY; MUST USE `fsysopts
	--writable''' mean?

{NHW} In this case, /dev/hd0s1 was not unmounted cleanly.  The Hurd
will, on boot up, run ``fsck -p'' on any partitions that it finds in
/etc/fstab, so, you may want to consider adding this partition to that
file.  If you are sure that the partition is fine, you can run:

	# fsysopts /home --writable

to ask the translator sitting on /home to change from read-only to
read/write mode.  Note that the command is being sent to the filesystem
and not the store (e.g. /dev/hd0s1).

??	When GNU/Hurd crashes, GNU Mach automatically reboots.  Is
	there anyway I can make it pause so I can write down the error?

{MB} Pass the `-H' option to init (add it to the boot command line), and
`init' will tell Mach to enter the kernel debugger instead to rebooting
it.  At the debugger prompt (`db>'), you can type `reboot' any time to
reboot the system.

? Porting

??	Is porting easy?

{NHW} Porting applications to GNU/Hurd is relatively easy assuming the
application is POSIX compliant as GNU/Hurd does its best to be a
conforming operating system.

The most common error made by programmers is assuming the MAXPATHLEN and
PATH_MAX are defined.  On most operating systems this is set to a few
thousand, however, on GNU/Hurd, there is no maximum and thus, this is
not set.  The correct thing to do is to submit a patch to the upstream
author that allocates memory dynamically.

? Compiling

??	Where can I get the source?

{AMS} Instructions on how to download the CVS tree from Savanah are
available at

{NHW} To get the source to the latest debian package, look on any
debian mirror.

??	Can I cross compile?


{NHW} Yes.  If you are running Debian GNU/Linux on IA32, this is quite
easy as there is a cheap cross compiler available; all that is required
is installing the gcc-i386-gnu and mig-i386-gnu Debian packages.  When
running configure, you will have to specify tools directly:

	# MIG=/usr/bin/i386-gnu-mig CC=/usr/bin/i386-gnu-gcc \
	  ../src/hurd/configure ...

If you are running another distribution, you will have to do this the
long way.  You can find instructions at the Cross Compiling HOW-TO
available at:

Farid Hajji <> also talks about his experiences

??	Any general tips?

{NHW} Yeah, building in the source tree is untested.  Try:

	# ../src/hurd/configure ...

? Development

??	What is OSKit-Mach?

{NHW,FH} There have once been two versions of GNU Mach developed: GNU Mach
1.x and GNU Mach 2.x, formerly known as OSKit-Mach.  The former uses
the drivers from Linux 2.0.x while the latter uses the University of
Utah's OSKit library for drivers.  You can find out more about the
OSKit library at:

The project didn't work out too well, so development has again been halted.

??	Where is the documentation?

{NHW} There were several books written on the Mach kernel.  The
information that they contain is still mostly pertinent and should be
considered required reading for potential hackers.  They can be found

The documentation for the Hurd is quite inadequate.  The starting of a
book, ``The GNU Hurd'' is in the doc directory in the Hurd source.  You
can read this using:

	# info hurd

The authoritative place is, of course, the source code; that does not,
however, mean that we would not welcome more documentation.  To get
started, take a look at <hurd>/doc/navigating.

??	How do I make sure that my code is POSIX compliant?

{NHW} Unfortunately, you have to buy the POSIX standard from IEEE.  The
Single Unix Specification version 2, a superset of POSIX, is available
for free on the Internet.  Try:

??	Who do I submit patches to?

{NHW} If they are against the Hurd, Mach or MiG, send a patch to the
bug-hurd mailing list.

If they are against other packages, the Debian BTS is a good place.  In
this case, be sure to advise the debian-hurd mailing list of the bug.

??	In what format should patches for the Hurd and GNU Mach be?

{MB} All patches should be sent in unified context diff format (option
`-u' to GNU diff).  It is helpful for us if you also use the `-p'
option which includes information about the function changed by a
patch.  Changes that are similar can be grouped together in one file,
but unrelated changes should be sent in seperate files.  The patches
can be included in the message or as a MIME attachement.  They should
not be compressed and/or archived unless they are very large, and if
they are very large it is probably better to store them on-line at
some place and only sent an URL.

Write a ChangeLog entry for each change, following the format of the
existing files.  Here is an example:

	2000-12-02  Marcus Brinkmann  <>

		* ops.c (op_readlink): Before returning, check if the buffer
	        pointed to by transp is ours.  If not, munmap it.
	        (op_read): Likewise for bp.
	        (op_readdir): Don't alloca a buffer here.  Instead initialize
	        BUF and BUFSIZE to 0 and let the server (eh, MiG) do it.
	        munmap BUF before returning.

The file name and the name of the function changed should always be
spelled out completely, and not abbreviated or otherwise mangled (like
foo.{c,h}), because that would make searching for all changes to a
file or function impossible.  Local variable names are all
capitalized.  There are two spaces between sentences.  You can use
``C-x 4 a'' in Emacs to add a new ChangeLog entry.  If you do that
with the mark being in a function, Emacs will automatically fill in
the file and function name for you.

Do not send in a patch for the ChangeLog file.  Rather include the
ChangeLog entries in the message that contains the patch.  Patches for
ChangeLog files often conflict.

If you have the original source tree in the directory `hurd-orig', and
the modified source tree in the directory `hurd', the following
command will produce a good patch (please make sure there are no extra
files like backups in the modified tree, or leave away the option
`-N').  You will need to collect the ChangeLog entries seperately.

	# diff -x ChangeLog -Nurp hurd-orig hurd

Answers were given by (in chronological order):
* {NHW} Neal H Walfield  <>
* {MB} Marcus Brinkmann  <>
* {AMS} Alfred M. Szmidt <>
* {OK} Ognyan Kulev	 <>
* {FH} Frédéric Henry	 <>
* {MM} Manuel Menal	 <>
* {ST} Samuel Thibault	 <>
Posted 2013-03-15 16:37:56 CET Tags: