systemd --user fails to start while complaining about permission in ubuntu server 20.04 inside openvz 7

Info about the system.

# systemctl --version
systemd 245 (245.4-4ubuntu3.13)
+PAM +AUDIT +SELINUX +IMA +APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ +LZ4 +SECCOMP +BLKID +ELFUTILS +KMOD +IDN2 -IDN +PCRE2 default-hierarchy=hybrid

# uname -srvmpio
Linux 5.4.0 #1 SMP Mon Mar 16 15:39:59 MSK 2020 x86_64 x86_64 x86_64 GNU/Linux

# cat /proc/cmdline
quiet

# loginctl enable-linger USERNAME

Problem

System --user daemon fails to start.systemctl status shows failure. First I was getting this:

systemd[304]: Failed to create / control group: Permission denied
systemd[304]: Failed to allocate manager object: Permission denied

After googling a bit I installed libpam-cgfs via apt. With it,

systemd[1]: : Main process exited, code=exited, status=219/CGROUP
systemd[1]: : Failed with result 'exit-code'.
systemd[1]: Failed to start User Manager for UID 1001.

Various threads in google suggests a manual workaround, setting more open permission in /sys/fs/cgroup/systemd/

So I ran these.

chmod -R o+rx /sys/fs/cgroup/systemd/

This didn't work, So it added write permission at user.slice

chmod -R o+rwx /sys/fs/cgroup/systemd/

Now I can start and it starts successfully.

One of the possible diagnosis I got that if cgroups are in unified mode,this problem occurs, suggestion is to put a flag in GRUB to set cgroups to legacy mode. But obviously those doesn't apply to my case as I'm inside a openvz container and there's no grub. My cgroups seems to be running in hybrid mode.

What can I do to fix the permission or anything else to fix this? I don't think running +w is a good thing every time system boots.

Edit: Relevant threads I found googling.

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