That makefile logic was introduced in 17153e1, almost a year ago. It is odd that it causes problems now!

If you run make V=1 in the docs/cmdline-opts directory, does it help to reveal anything about the failure that must have happened that caused manpage.tmp not to be created (but yet not cause the command to return error) ?

Thanks for the suggestion - with make V=1 I get the following;

Making all in ../docs make[2]: Entering directory '/curl/32/docs' Making all in . make[3]: Entering directory '/curl/32/docs' if test "..x" != "/curl/src/curl-8.6.0x" -a -e "/curl/src/curl-8.6.0/docs/curl.1"; then \ /usr/bin/install -c -m 644 "/curl/src/curl-8.6.0/docs/curl.1" /curl/32/docs/curl.1 \ && touch -r "/curl/src/curl-8.6.0/docs/curl.1" /curl/32/docs/curl.1; fi /curl/src/curl-8.6.0/scripts/cd2nroff /curl/src/curl-8.6.0/docs/mk-ca-bundle.md >mk-ca-bundle.1 cd cmdline-opts && /tools/gnumake/4.4.1/bin/make make[4]: Entering directory '/curl/32/docs/cmdline-opts' (rm -f ../../docs/curl.1 && cd /curl/src/curl-8.6.0/docs/cmdline-opts && /usr/bin/perl ./gen.pl mainpage abstract-unix-socket.md alt-svc.md anyauth.md append.md aws-sigv4.md basic.md ca-native.md cacert.md capath.md cert-status.md cert-type.md cert.md ciphers.md compressed-ssh.md compressed.md config.md connect-timeout.md connect-to.md continue-at.md cookie-jar.md cookie.md create-dirs.md create-file-mode.md crlf.md crlfile.md curves.md data-ascii.md data-binary.md data-raw.md data-urlencode.md data.md delegation.md digest.md disable-eprt.md disable-epsv.md disable.md disallow-username-in-url.md dns-interface.md dns-ipv4-addr.md dns-ipv6-addr.md dns-servers.md doh-cert-status.md doh-insecure.md doh-url.md dump-header.md egd-file.md engine.md etag-compare.md etag-save.md expect100-timeout.md fail-early.md fail-with-body.md fail.md false-start.md form-escape.md form-string.md form.md ftp-account.md ftp-alternative-to-user.md ftp-create-dirs.md ftp-method.md ftp-pasv.md ftp-port.md ftp-pret.md ftp-skip-pasv-ip.md ftp-ssl-ccc-mode.md ftp-ssl-ccc.md ftp-ssl-control.md get.md globoff.md happy-eyeballs-timeout-ms.md haproxy-protocol.md haproxy-clientip.md head.md header.md help.md hostpubmd5.md hostpubsha256.md hsts.md http0.9.md http1.0.md http1.1.md http2-prior-knowledge.md http2.md http3.md http3-only.md ignore-content-length.md include.md insecure.md interface.md ipfs-gateway.md ipv4.md ipv6.md json.md junk-session-cookies.md keepalive-time.md key-type.md key.md krb.md libcurl.md limit-rate.md list-only.md local-port.md location-trusted.md location.md login-options.md mail-auth.md mail-from.md mail-rcpt-allowfails.md mail-rcpt.md manual.md max-filesize.md max-redirs.md max-time.md metalink.md negotiate.md netrc-file.md netrc-optional.md netrc.md next.md no-alpn.md no-buffer.md no-clobber.md no-keepalive.md no-npn.md no-progress-meter.md no-sessionid.md noproxy.md ntlm-wb.md ntlm.md oauth2-bearer.md output-dir.md output.md parallel-immediate.md parallel-max.md parallel.md pass.md path-as-is.md pinnedpubkey.md post301.md post302.md post303.md preproxy.md progress-bar.md proto-default.md proto-redir.md proto.md proxy-anyauth.md proxy-basic.md proxy-ca-native.md proxy-cacert.md proxy-capath.md proxy-cert-type.md proxy-cert.md proxy-ciphers.md proxy-crlfile.md proxy-digest.md proxy-header.md proxy-http2.md proxy-insecure.md proxy-key-type.md proxy-key.md proxy-negotiate.md proxy-ntlm.md proxy-pass.md proxy-pinnedpubkey.md proxy-service-name.md proxy-ssl-allow-beast.md proxy-ssl-auto-client-cert.md proxy-tls13-ciphers.md proxy-tlsauthtype.md proxy-tlspassword.md proxy-tlsuser.md proxy-tlsv1.md proxy-user.md proxy.md proxy1.0.md proxytunnel.md pubkey.md quote.md random-file.md range.md rate.md raw.md referer.md remote-header-name.md remote-name-all.md remote-name.md remote-time.md remove-on-error.md request-target.md request.md resolve.md retry-all-errors.md retry-connrefused.md retry-delay.md retry-max-time.md retry.md sasl-authzid.md sasl-ir.md service-name.md show-error.md silent.md socks4.md socks4a.md socks5-basic.md socks5-gssapi-nec.md socks5-gssapi-service.md socks5-gssapi.md socks5-hostname.md socks5.md speed-limit.md speed-time.md ssl-allow-beast.md ssl-auto-client-cert.md ssl-no-revoke.md ssl-reqd.md ssl-revoke-best-effort.md ssl.md sslv2.md sslv3.md stderr.md styled-output.md suppress-connect-headers.md tcp-fastopen.md tcp-nodelay.md telnet-option.md tftp-blksize.md tftp-no-options.md time-cond.md tls-max.md tls13-ciphers.md tlsauthtype.md tlspassword.md tlsuser.md tlsv1.0.md tlsv1.1.md tlsv1.2.md tlsv1.3.md tlsv1.md tr-encoding.md trace-ascii.md trace-config.md trace-ids.md trace-time.md trace.md unix-socket.md upload-file.md url.md url-query.md use-ascii.md user-agent.md user.md variable.md verbose.md version.md write-out.md xattr.md > ./manpage.tmp && mv ./manpage.tmp ../../docs/curl.1) mv: cannot stat './manpage.tmp': No such file or directory make[4]: *** [Makefile:909: ../../docs/curl.1] Error 1 make[4]: Leaving directory '/curl/32/docs/cmdline-opts' make[3]: *** [Makefile:937: /curl/32/docs/curl.1] Error 2 make[3]: Leaving directory '/curl/32/docs' make[2]: *** [Makefile:654: all-recursive] Error 1 make[2]: Leaving directory '/curl/32/docs' make[1]: *** [Makefile:1553: all-recursive] Error 1 make[1]: Leaving directory '/curl/32/src' make: *** [Makefile:1262: all-recursive] Error 1

I build both 32 and 64-bit versions of curl in parallel from a single source tree - so I think that my issue is that this common source tree /curl/src is being changed (the perl script runs in the /curl/src/curl-8.6.0/docs/cmdline-opts directory) and there is a race between the 32 and 64-bit builds to create/move the temp file in the common source tree, rather than working in their output trees of /curl/32 and /curl/64 respectively. For some reason with 8.6.0 that race seems to be more competitive!

I will change my build process so that the two parallel builds have their own modifiable source trees to confirm that resolves the issue.

We could make it use a unique temp file to reduce this risk?

diff --git a/docs/cmdline-opts/Makefile.am b/docs/cmdline-opts/Makefile.am
index e9b35ac05..08d19a015 100644
--- a/docs/cmdline-opts/Makefile.am
+++ b/docs/cmdline-opts/Makefile.am
@@ -36,9 +36,9 @@ GN_1 =
 GN_ = $(GN_0)
 
 all: $(MANPAGE)
 
 $(MANPAGE): $(DPAGES) $(SUPPORT) mainpage.idx Makefile.inc gen.pl
-       $(GEN)(rm -f $(MANPAGE) && cd $(srcdir) && @PERL@ ./gen.pl mainpage $(DPAGES) > $(builddir)/manpage.tmp && mv $(builddir)/manpage.tmp $(MANPAGE))
+       $(GEN)(rm -f $(MANPAGE) && cd $(srcdir) && @PERL@ ./gen.pl mainpage $(DPAGES) > $(builddir)/manpage.tmp.$$$$ && mv $(builddir)/manpage.tmp.$$$$ $(MANPAGE))
 
 listhelp:
        ./gen.pl listhelp $(DPAGES) > $(top_builddir)/src/tool_listhelp.c

Thanks - I've confirmed that giving each of the builds their own source tree also resolves the issue and yes appending a pid to the filename for this make rule would also prevent any interactions on this temp file.

I'm note sure how $(builddir) got expanded to '.' but because the current directory is in the source tree that means the build will be writing (albeit temporarily) to the source tree rather than under the --prefix provided on the configure.

I'm note sure how $(builddir) got expanded to '.' but because the current directory is in the source tree that means the build will be writing (albeit temporarily) to the source tree

That variable will expand to a separate directory if you build outside of the source tree. Like this:

$ mkdir this/somewhere
$ cd this/somewhere
$ ../../curl-8.6.0/configure [options]
$ make -sj

Thanks