Bug 1731772

# lsmod | grep binfmt
binfmt_misc            20480  0

# strace /usr/lib/systemd/systemd-binfmt 
execve("/usr/lib/systemd/systemd-binfmt", ["/usr/lib/systemd/systemd-binfmt"], 0x7ffceb6697c0 /* 25 vars */) = 0
brk(NULL)                               = 0x5573cbc01000
arch_prctl(0x3001 /* ARCH_??? */, 0x7ffd09d38c30) = -1 EINVAL (Invalid argument)
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
... skipped ...
getrandom("\x45\x7d\x70\x70\x10\x1b\x1e\x0e\x3a\xb8\x45\x6b\x49\x22\xa9\x39", 16, GRND_NONBLOCK) = 16
openat(AT_FDCWD, "/etc/binfmt.d", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_DIRECTORY) = 3
fstat(3, {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
getdents64(3, /* 3 entries */, 32768)   = 80
getdents64(3, /* 0 entries */, 32768)   = 0
close(3)                                = 0
openat(AT_FDCWD, "/run/binfmt.d", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_DIRECTORY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/local/lib/binfmt.d", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_DIRECTORY) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/binfmt.d", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_DIRECTORY) = 3
fstat(3, {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
getdents64(3, /* 2 entries */, 32768)   = 48
getdents64(3, /* 0 entries */, 32768)   = 0
close(3)                                = 0
openat(AT_FDCWD, "/proc/sys/fs/binfmt_misc/status", O_WRONLY|O_NOCTTY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/etc/binfmt.d/wine.conf", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=119, ...}) = 0
read(3, "# Pre-PE Windows Executables\n:wi"..., 4096) = 119
openat(AT_FDCWD, "/proc/sys/fs/binfmt_misc/windows", O_WRONLY|O_NOCTTY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/proc/sys/fs/binfmt_misc/register", O_WRONLY|O_NOCTTY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
writev(2, [{iov_base="Failed to add binary format: No "..., iov_len=54}, {iov_base="\n", iov_len=1}], 2Failed to add binary format: No such file or directory
) = 55
read(3, "", 4096)                       = 0
openat(AT_FDCWD, "/proc/sys/fs/binfmt_misc/windowsPE", O_WRONLY|O_NOCTTY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/proc/sys/fs/binfmt_misc/register", O_WRONLY|O_NOCTTY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
writev(2, [{iov_base="Failed to add binary format: No "..., iov_len=54}, {iov_base="\n", iov_len=1}], 2Failed to add binary format: No such file or directory
) = 55
close(3)                                = 0
exit_group(1)                           = ?
+++ exited with 1 +++

Looks like systemd doesn't mount the necessary FS:

# grep binfmt /proc/mounts
<empty>

# mount binfmt_misc -t binfmt_misc /proc/sys/fs/binfmt_misc
# grep binfmt /proc/mounts
binfmt_misc /proc/sys/fs/binfmt_misc binfmt_misc rw,relatime 0 0

Now I wonder why all of this has to be done manually.

# systemctl start systemd-binfmt
# systemctl status systemd-binfmt
● systemd-binfmt.service - Set Up Additional Binary Formats
   Loaded: loaded (/usr/lib/systemd/system/systemd-binfmt.service; static; vendor preset: disabled)
   Active: active (exited) since ; 14s ago
     Docs: man:systemd-binfmt.service(8)
           man:binfmt.d(5)
           https://www.kernel.org/doc/html/latest/admin-guide/binfmt-misc.html
           https://www.freedesktop.org/wiki/Software/systemd/APIFileSystems
  Process: 15855 ExecStart=/usr/lib/systemd/systemd-binfmt (code=exited, status=0/SUCCESS)
 Main PID: 15855 (code=exited, status=0/SUCCESS)

I don't have the autofs module enabled in the kernel:

# journalctl -b | grep -i auto
localhost systemd[1]: Failed to find module 'autofs4'
localhost systemd[1]: Starting of Arbitrary Executable File Formats File System Automount Point not supported.

This bug appears to have been reported against 'rawhide' during the Fedora 31 development cycle.
Changing version to '31'.

This bug appears to have been reported against 'rawhide' during the Fedora 31 development cycle.
Changing version to 31.

So many comments, so much attention, WTF??

This is how I "solved" this bug seeing that no one gives a f:

1) sudo systemctl mask proc-sys-fs-binfmt_misc.automount
2) sudo cp -a /usr/lib/systemd/system/systemd-binfmt.service /etc/systemd/system
3)

--- /usr/lib/systemd/system/systemd-binfmt.service	2019-09-03 12:59:59.000000000 +0000
+++ /etc/systemd/system/systemd-binfmt.service	2019-09-17 08:56:18.357965085 +0000
@@ -14,7 +14,6 @@
 Documentation=https://www.freedesktop.org/wiki/Software/systemd/APIFileSystems
 DefaultDependencies=no
 Conflicts=shutdown.target
-After=proc-sys-fs-binfmt_misc.automount
 Before=sysinit.target shutdown.target
 ConditionPathIsReadWrite=/proc/sys/
 ConditionDirectoryNotEmpty=|/lib/binfmt.d
@@ -28,3 +27,7 @@
 RemainAfterExit=yes
 ExecStart=/usr/lib/systemd/systemd-binfmt
 TimeoutSec=90s
+
+ExecStartPre=/usr/sbin/modprobe binfmt_misc
+ExecStartPre=-/usr/bin/mount -t binfmt_misc binfmt_misc /proc/sys/fs/binfmt_misc

Normally, the way that this works is that:
1. proc-sys-fs-binfmt_misc.automount is pulled in by sysinit.target (it is statically enabled)
2. systemd-binfmt.service only runs if it has something to do, potentially triggering the next point
3. when /proc/sys/fs/binfmt_misc/ is accessed, proc-sys-fs-binfmt_misc.mount is started
4. proc-sys-fs-binfmt_misc.mount mounts the filesystem which also causes binfmt_misc to be loaded

Since you disabled autofs, step 1 doesn't happen, so steps 3-4 don't happen and nothing loads
the module. You can make things work by adding proc-sys-fs-binfmt_misc.mount as a dependency:
# /etc/systemd/system/systemd-binfmt.service.d/dep.conf
[Unit]
Requires=proc-sys-fs-binfmt_misc.mount
After=proc-sys-fs-binfmt_misc.mount

If you customize a kernel like that, you have to take the necessary steps to adjust certain
units. Sorry, but when you do this in Fedora, you're on your own.

I'll file a patch to add After=proc-sys-fs-binfmt_misc.mount to systemd-binfmt.service upstream.
This will not fix your issue, but it'll make it slightly nicer to handle, because then it will
be enough to enable proc-sys-fs-binfmt_misc.mount in any way, and systemd-binfmt.service will
be ordered appropriately after it.

FEDORA-2019-66b24a298e has been submitted as an update to Fedora 30. https://bodhi.fedoraproject.org/updates/FEDORA-2019-66b24a298e

systemd-241-12.git323cdf4.fc30 has been pushed to the Fedora 30 testing repository. If problems still persist, please make note of it in this bug report.
See https://fedoraproject.org/wiki/QA:Updates_Testing for
instructions on how to install test updates.
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2019-66b24a298e

systemd-241-12.git323cdf4.fc30 has been pushed to the Fedora 30 stable repository. If problems still persist, please make note of it in this bug report.