问题：
#journalctl
Journal file /var/log/journal/410/system@0.journal~ uses an unsupported feature, ignoring file.
-- No entries --
# systemctl --version
systemd 229
+PAM +AUDIT +SELINUX +IMA +APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ -LZ4 +SECCOMP +BLKID +ELFUTILS +KMOD -IDN
原因：
新版本journal日志采用lz4算法替代xz，若要用journal查看日志需要重新编译systemd且使能lz4。
If the output contains `-LZ4`, journal entries will not be available.
若在Ubuntu下，可直接apt install systemd安装最新编译版本即可。
参考：
https://github.com/systemd/systemd/issues/3875
https://github.com/coreos/coreos-overlay/pull/2593
https://github.com/kinvolk/rkt/commit/9310333214c6e8a575a66f170e05c8509ddca6ae