https://maciej.lasyk.info/2016/Dec/16/systemd-231-latest-in-centos-7-thx-to-facebook/

https://copr.fedorainfracloud.org/coprs/jsynacek/systemd-backports-for-centos-7/

Centos7 当前版本使用 systemd version 219 ，发布于 2015-02-16 (see NEWS)。
这么个大问题，导致很多相关功能的重要特性我们用不到，比如journald, networkd, machinectl, systemd-nspawn 等。

升级方法

wget https://copr.fedorainfracloud.org/coprs/jsynacek/systemd-backports-for-centos-7/repo/epel-7/jsynacek-systemd-backports-for-centos-7-epel-7.repo \
-O /etc/yum.repos.d/jsynacek-systemd-centos-7.repo

yum update systemd

升级完毕后，如下

[root@localhost ~]# systemctl --version
systemd 234
+PAM +AUDIT +SELINUX +IMA -APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ +LZ4 +SECCOMP +BLKID +ELFUTILS +KMOD -IDN2 +IDN default-hierarchy=hybrid