shepherd hangs whole system upon encountering error in start slot

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2 participants
  • Maxim Cournoyer
  • raingloom
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unassigned
Submitted by
raingloom
Severity
important
R
R
raingloom wrote on 18 Dec 2021 21:13
shepherd lacks error reporting
(name . Guix Bugs)(address . bug-guix@gnu.org)
20211219061320.7ef3bb8c@riseup.net
I'm writing a single-shot shepherd-service that expands the (ext4) root
file system on first boot, using the hostname service as a template,
just passing the script as a G-expression, instead of using the
forkexec constructor.
Of course there is a bug in it. Trouble is, I have no idea what it is,
because Shepherd won't tell me. :)
The VM boots and completes the ssh initialization phase and then
apparently just gets stuck. Doesn't even show a login prompt.
It's... not a great debugging experience.
I'm going to attempt to at the very least add some error reporting.
It would also be really nice if the failure modes for Shepherd services
were better documented, like what happens when the procedure passed in
the `start` field fails, or is not even a procedure, etc.
Since I never touched Shepherd internals, help would be greatly
appreciated.

ps.: I'm attaching the system definition for completeness's sake and so
that someone might point out where the error is, but honestly the exact
bug in my code does not matter for the feature. All that matters is
there is an error and it should be logged but isn't.
(define-module (raingloom machines cloud-deploy-bootstrap)) (use-modules (gnu) (gnu system nss) (guix channels) (guix modules)) (use-service-modules admin networking shepherd ssh) (use-package-modules admin bootloaders certs gnome linux networking ssh tmux tls version-control) (define disk "/dev/vda") (define partition "2") (define ext-autoexpand-service-type (let ((name 'ext-autoexpand) (desc "Automatically expand ext2 root") (modules '((ice-9 popen)))) (shepherd-service-type name (lambda (config) (shepherd-service (documentation desc) (provision (list name)) (requirement '(file-systems)) (one-shot? #t) (start (with-imported-modules (source-module-closure modules) #~(begin (use-modules #$@modules) (let ((port (open-pipe* OPEN_WRITE #$(file-append util-linux "/sbin/sfdisk") ;; don't check if the block is in use ;; it is, and we don't care. "--no-reread" disk "-N" partition))) (display ",+" port) (close-port port)) (system* $#(file-append util-linux "/sbin/partx") "--update" disk) (system* #$(file-append e2fsprogs "/sbin/resize2fs") (string-append disk partition))))))) (description desc)))) (define-public %system (operating-system (host-name "cloud-deploy-bootstrap") (timezone "Europe/Budapest") (locale "en_US.utf8") (keyboard-layout (keyboard-layout "us")) (bootloader (bootloader-configuration (bootloader grub-bootloader) (targets '("/dev/vda")) (keyboard-layout keyboard-layout))) (file-systems (append (list (file-system (device (file-system-label "cloudimg-rootfs")) (mount-point "/") (type "btrfs"))) %base-file-systems)) ;; This is where we specify system-wide packages. (packages (append (list nss-certs tmux) %base-packages)) (services (append (list (service ext-autoexpand-service-type #f) (service dhcp-client-service-type) (service openssh-service-type (openssh-configuration (openssh openssh-sans-x) (permit-root-login #t) (authorized-keys `(("root" ,(local-file (string-append (getenv "HOME") "/.ssh/id_ed25519.pub")))))))) %base-services)) ;; Allow resolution of '.local' host names with mDNS. (name-service-switch %mdns-host-lookup-nss))) %system
R
R
raingloom wrote on 18 Dec 2021 22:02
(address . 52654@debbugs.gnu.org)
20211219070207.1195510c@riseup.net
On Sun, 19 Dec 2021 06:13:20 +0100
raingloom <raingloom@riseup.net> wrote:

Toggle quote (21 lines)
> I'm writing a single-shot shepherd-service that expands the (ext4)
> root file system on first boot, using the hostname service as a
> template, just passing the script as a G-expression, instead of using
> the forkexec constructor.
> Of course there is a bug in it. Trouble is, I have no idea what it is,
> because Shepherd won't tell me. :)
> The VM boots and completes the ssh initialization phase and then
> apparently just gets stuck. Doesn't even show a login prompt.
> It's... not a great debugging experience.
> I'm going to attempt to at the very least add some error reporting.
> It would also be really nice if the failure modes for Shepherd
> services were better documented, like what happens when the procedure
> passed in the `start` field fails, or is not even a procedure, etc.
> Since I never touched Shepherd internals, help would be greatly
> appreciated.
>
> ps.: I'm attaching the system definition for completeness's sake and
> so that someone might point out where the error is, but honestly the
> exact bug in my code does not matter for the feature. All that
> matters is there is an error and it should be logged but isn't.

So the error in my config turned out to be the G-expression not
evaluating to a lambda, but the issue with Shepherd still stands.
M
M
Maxim Cournoyer wrote on 29 Apr 2023 08:18
control message for bug #52654
(address . control@debbugs.gnu.org)
87mt2qaf8k.fsf@gmail.com
retitle 52654 shepherd hangs whole system upon encountering error in start slot
quit
M
M
Maxim Cournoyer wrote on 29 Apr 2023 08:18
(address . control@debbugs.gnu.org)
87leiaaf8f.fsf@gmail.com
severity 52654 important
quit
M
M
Maxim Cournoyer wrote on 29 Apr 2023 08:22
Re: bug#52654: shepherd lacks error reporting
(name . raingloom)(address . raingloom@riseup.net)(address . 52654@debbugs.gnu.org)
87h6syaf2k.fsf@gmail.com
Hi,

I also encountered that issue, it's really puzzling.

Here's the problematic start slot that got my mpd test to hang the boot,
with the last message being "Please wait while gathering entropy to
generate the key pair;":

Toggle snippet (30 lines)
(start
(with-imported-modules (source-module-closure
'((gnu build activation)))
#~(begin
(use-modules (gnu build activation))

(let ((user (getpw #$username)))

(define (init-directory directory)
(unless (file-exists? directory)
(mkdir-p/perms directory user #o755)))

(for-each
init-directory
(cons '#$(map dirname
;; XXX: Delete the potential "syslog"
;; log-file value, which is not a directory.
(delete "syslog"
(filter-map maybe-value
(list db-file
log-file
state-file
sticker-file)))))))

(make-forkexec-constructor
(list #$(file-append package "/bin/mpd") "--no-daemon"
#$config-file)
#:environment-variables '#$environment-variables))))

The error was the lonely cons. Taking it out, the test then passed:

Toggle snippet (30 lines)
(start
(with-imported-modules (source-module-closure
'((gnu build activation)))
#~(begin
(use-modules (gnu build activation))

(let ((user (getpw #$username)))

(define (init-directory directory)
(unless (file-exists? directory)
(mkdir-p/perms directory user #o755)))

(for-each
init-directory
'#$(map dirname
;; XXX: Delete the potential "syslog"
;; log-file value, which is not a directory.
(delete "syslog"
(filter-map maybe-value
(list db-file
log-file
state-file
sticker-file))))))

(make-forkexec-constructor
(list #$(file-append package "/bin/mpd") "--no-daemon"
#$config-file)
#:environment-variables '#$environment-variables))))

Shepherd should report the error, fail that one service and attempt to
keep booting (if the service is not required by other critical ones).

--
Thanks,
Maxim
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