bug#63921: Activation snippets in reverse order, prevent boot

["Ludovic Courtès" <ludo@gnu.org>]

Booting a system reconfigured from
eed55a6544d5bda2245ec853e5fa4b28e1865bea fails with shepherd saying:

  error: while opening socket '/var/run/shepherd/socket': Address already in use

The root cause appears to be that the ‘boot’ program has expressions
reversed:

--8<---------------cut here---------------start------------->8---
$ guix gc --references $(guix gc --derivers $(readlink -f /var/guix/profiles/system-236-link)) | grep boot
/gnu/store/21ldhyrpji6lkkdxi4lgr5k9l5fr2b7l-boot.drv
$ cat $(guix build /gnu/store/21ldhyrpji6lkkdxi4lgr5k9l5fr2b7l-boot.drv)
(eval-when (expand load eval) (let ((extensions (quote ())) (prepend (lambda (items lst) (let loop ((items items) (lst lst)) (if (null? items) lst (loop (cdr items) (cons (car items) (delete (car items) lst)))))))) (set! %load-path (prepend (cons "/gnu/store/pj751v3199vmv6i6sf0szp185ryzcfdg-module-import" (map (lambda (extension) (string-append extension "/share/guile/site/" (effective-version))) extensions)) %load-path)) (set! %load-compiled-path (prepend (cons "/gnu/store/pql80c2hy38bb60c68sng74s4xa35vwk-module-import-compiled" (map (lambda (extension) (string-append extension "/lib/guile/" (effective-version) "/site-ccache")) extensions)) %load-compiled-path))))(begin (begin (false-if-exception (delete-file "/run/booted-system")) (symlink (canonicalize-path "/run/current-system") "/run/booted-system") (let loop ((fd 3)) (when (< fd 1024) (false-if-exception (let ((flags (fcntl fd F_GETFD))) (when (zero? (logand flags FD_CLOEXEC)) (fcntl fd F_SETFD (logior FD_CLOEXEC flags))))) (loop (+ fd 1)))) (execl "/gnu/store/wj5i6x3xgai7p8whwqybxwqdjdbmbzha-shepherd-0.10.99-git/bin/shepherd" "shepherd" "--config" "/gnu/store/gnjghlc3n5qbala5jfdslgfi0n3vy8v7-shepherd.conf")) (primitive-load "/gnu/store/riabgidmf6fh76klc1yam7k9j1478vvw-activate.scm") (begin (use-modules (guix build utils)) (letrec-syntax ((fail-safe (syntax-rules () ((_ exp rest ...) (begin (catch (quote system-error) (lambda () exp) (const #f)) (fail-safe rest ...))) ((_) #t)))) (fail-safe (delete-file "/etc/group.lock") (delete-file "/etc/passwd.lock") (delete-file "/etc/.pwd.lock") (setenv "GUIX_LOCPATH" "/gnu/store/5fmqijrs5f7vx8mc2q2pmq26yvhb74sm-glibc-utf8-locales-2.35/lib/locale") (setlocale LC_CTYPE "en_US.utf8") (delete-file-recursively "/tmp") (delete-file-recursively "/var/run") (mkdir "/tmp") (chmod "/tmp" 1023) (mkdir "/var/run") (chmod "/var/run" 493) (delete-file-recursively "/run/udev/watch.old")))))
--8<---------------cut here---------------end--------------->8---

Namely, (execl "…/bin/shepherd") comes before the cleanup expressions,
which is why /var/run/shepherd/socket is still around when we boot.

Ludo’.