我最近对我的 18.04 LTS 安装应用了一些软件更新，现在我在重新启动期间看到以下内容：
$ cat /var/log/boot.log Scanning for Btrfs filesystems UBUNTU: clean, 700970/30883840 files, 21610032/123523840 blocks [ OK ] Found device /sys/subsystem/net/devices/br0. [ OK ] Started ifup for br0.
Starting Network Manager Script Dispatcher Service... [ OK ]
Starting Virtualization daemon...
Starting Permit User Sessions...
Starting containerd container runtime...
Starting OpenBSD Secure Shell server... [ OK ]
Reached target Network is Online.
Starting Message of the Day...
Starting Docker Application Container Engine...
Starting Hold until boot process finishes up...
Starting GNOME Display Manager...
[ OK ] Created slice User Slice of root.
[FAILED] Failed to start Session c2 of user root. See 'systemctl status session-c2.scope' for details.
[FAILED] Failed to start Session c7 of user root. See 'systemctl status session-c7.scope' for details.
[FAILED] Failed to start Session c4 of user root. See 'systemctl status session-c4.scope' for details.
[FAILED] Failed to start Session c3 of user root. See 'systemctl status session-c3.scope' for details.
[ OK ] Started Session c11 of user root.
Starting User Manager for UID 0...
[FAILED] Failed to start Session c5 of user root. See ....
systemctl 有以下说法：
$ systemctl status session-c2.scope
● session-c2.scope - Session c2 of user root
Loaded: loaded (/run/systemd/transient/session-c2.scope; transient)
Transient: yes
Active: failed (Result: resources)
Apr 21 15:50:53 dell systemd[1]: session-c2.scope: Failed to add PIDs to scope's control group: No such process
Apr 21 15:50:53 dell systemd[1]: session-c2.scope: Failed with result 'resources'.
Apr 21 15:50:53 dell systemd[1]: Failed to start Session c2 of user root.
其他有用信息：
$ uname -a
Linux dell 4.15.0-96-generic #97-Ubuntu SMP Wed Apr 1 03:25:46 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
$ cat /proc/version_signature
Ubuntu 4.15.0-96.97-generic 4.15.18
和这个：
$ systemctl --version
systemd 237
+PAM +AUDIT +SELINUX +IMA +APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ +LZ4 +SECCOMP +BLKID +ELFUTILS +KMOD -IDN2 +IDN -PCRE2 default-hierarchy=hybrid
我对 cgroups 的了解不够，无法自行进行更改...寻求帮助以尝试了解这里发生了什么。
非常感谢您的帮助，拜托！
编辑：根据要求：
$ cat /etc/default/grub
# If you change this file, run 'update-grub' afterwards to update
# /boot/grub/grub.cfg.
# For full documentation of the options in this file, see:
# info -f grub -n 'Simple configuration'
GRUB_DEFAULT=0
GRUB_TIMEOUT_STYLE=hidden
GRUB_TIMEOUT=0
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
GRUB_CMDLINE_LINUX="locale=en_US intel_iommu=on"
# Uncomment to enable BadRAM filtering, modify to suit your needs
# This works with Linux (no patch required) and with any kernel that obtains
# the memory map information from GRUB (GNU Mach, kernel of FreeBSD ...)
#GRUB_BADRAM="0x01234567,0xfefefefe,0x89abcdef,0xefefefef"
# Uncomment to disable graphical terminal (grub-pc only)
#GRUB_TERMINAL=console
# The resolution used on graphical terminal
# note that you can use only modes which your graphic card supports via VBE
# you can see them in real GRUB with the command `vbeinfo'
#GRUB_GFXMODE=640x480
# Uncomment if you don't want GRUB to pass "root=UUID=xxx" parameter to Linux
#GRUB_DISABLE_LINUX_UUID=true
# Uncomment to disable generation of recovery mode menu entries
#GRUB_DISABLE_RECOVERY="true"
# Uncomment to get a beep at grub start
#GRUB_INIT_TUNE="480 440 1"
编辑 2：将“systemd.legacy_systemd_cgroup_controller=true”添加到 GRUB_CMDLINE_LINUX_DEFAULT 后（更新 grub，然后重新启动）：
$ grep cgroup /proc/filesystems
nodev cgroup
nodev cgroup2