This was being discussed at https://pagure.io/releng/failed-composes/issue/2515 , but now we know more or less what is going on, I'm filing a bug for better tracking. Rawhide composes have been failing since 2021-05-18; the last successful compose was 20210517.n.0. The failure coincides with dracut-054-5.git20210517.fc35 being tagged.

The failure mode is that when building disk images, anaconda fails to boot, instead we are dumped in the initramfs environment. This is happening because curl cannot download stage2 via https, because the CA cert bundle curl needs for SSL transactions - /etc/pki/tls/certs/ca-bundle.crt - is missing. This in turn appears to be happening because the dracut url-lib module is going wrong when it attempts to parse curl library files to find out and include the location of the certificate bundle. We see these errors in the dracut output when building the initramfs:

2021-05-20 05:55:42,867 INFO: /usr/lib/dracut/modules.d/45url-lib/module-setup.sh: line 35: /dev/fd/63: No such file or directory
2021-05-20 05:55:42,868 INFO: /usr/lib/dracut/modules.d/45url-lib/module-setup.sh: line 37: /dev/fd/63: No such file or directory
2021-05-20 05:55:42,868 INFO: /usr/lib/dracut/modules.d/45url-lib/module-setup.sh: line 35: /dev/fd/63: No such file or directory
2021-05-20 05:55:42,868 INFO: /usr/lib/dracut/modules.d/45url-lib/module-setup.sh: line 37: /dev/fd/63: No such file or directory
2021-05-20 05:55:42,868 INFO: /usr/lib/dracut/modules.d/45url-lib/module-setup.sh: line 35: /dev/fd/63: No such file or directory
2021-05-20 05:55:42,868 INFO: /usr/lib/dracut/modules.d/45url-lib/module-setup.sh: line 37: /dev/fd/63: No such file or directory
2021-05-20 05:55:42,868 INFO: /usr/lib/dracut/modules.d/45url-lib/module-setup.sh: line 35: /dev/fd/63: No such file or directory
2021-05-20 05:55:42,868 INFO: /usr/lib/dracut/modules.d/45url-lib/module-setup.sh: line 37: /dev/fd/63: No such file or directory
2021-05-20 05:55:42,868 INFO: dracut: Couldn't find SSL CA cert bundle or libnssckbi.so; HTTPS won't work.

Those errors come exactly from the block which should be including the certificate bundle in the initramfs:

    for _dir in $libdirs; do
        [[ -d $dracutsysrootdir$_dir ]] || continue
        for _lib in "$dracutsysrootdir$_dir"/libcurl.so.*; do
            [[ -e $_lib ]] || continue
            if ! [[ $_nssckbi ]]; then
                read -r -d '' _nssckbi < <(grep -F --binary-files=text -z libnssckbi "$_lib")
            fi
            read -r -d '' _crt < <(grep -F --binary-files=text -z .crt "$_lib")
            [[ $_crt ]] || continue
            [[ $_crt == /*/* ]] || continue
            if ! inst "${_crt#$dracutsysrootdir}"; then
                dwarn "Couldn't install '$_crt' SSL CA cert bundle; HTTPS might not work."
                continue
            fi
            _found=1
        done
    done

lines 35 and 37 are the two lines that do `read -r -d '' somevar < <(somecommand)` to try and initialize a variable with the output from a command. Note we see similar errors elsewhere in the dracut output from two lines in other modules that use the same `< <(somecommand)` construction:

2021-05-20 05:55:42,867 INFO: /usr/lib/dracut/modules.d/00systemd/module-setup.sh: line 168: /dev/fd/63: No such file or directory
2021-05-20 05:55:42,868 INFO: /usr/lib/dracut/modules.d/90kernel-modules-extra/module-setup.sh: line 77: /dev/fd/63: No such file or directory

so that is what seems to be the problem.

These lines were changed in https://github.com/dracutdevs/dracut/commit/8e84fa7262d5d3273684473538d94a008b5f583e . They used to just do `somevar=$(somecommand)`.

Not sure exactly why this is happening, yet.