当系统长期连续运行时，如果没有限制系统日志大小，可能会出现硬盘被写满的情况，如果需要限制系统日志大小，可通过下面方法进行限制：
修改/etc/systemd/journald.conf
Storage=volatile
SystemMaxUse=2M
RumtimeMaxUse=2M
将日志大小限制为 2M
文件如下：
[系统未激活][root@node5-63 ~]# cat /etc/systemd/journald.conf
# This file is part of systemd.
#
# systemd is free software; you can redistribute it and/or modify it
# under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation; either version 2.1 of the License, or
# (at your option) any later version.
#
# Entries in this file show the compile time defaults.
# You can change settings by editing this file.
# Defaults can be restored by simply deleting this file.
#
# See journald.conf(5) for details.
[Journal]
Storage=volatile
#Compress=yes
#Seal=yes
#SplitMode=uid
#SyncIntervalSec=5m
#RateLimitIntervalSec=30s
#RateLimitBurst=10000
SystemMaxUse=2M
#SystemKeepFree=
#SystemMaxFileSize=
#SystemMaxFiles=100
RuntimeMaxUse=2M
#RuntimeKeepFree=
#RuntimeMaxFileSize=
#RuntimeMaxFiles=100
MaxRetentionSec=1day
#MaxFileSec=1month
#ForwardToSyslog=no
#ForwardToKMsg=no
#ForwardToConsole=no
#ForwardToWall=yes
#TTYPath=/dev/console
#MaxLevelStore=debug
#MaxLevelSyslog=debug
#MaxLevelKMsg=notice
#MaxLevelConsole=info
#MaxLevelWall=emerg
#LineMax=48K
#ReadKMsg=yes修改完成后重新启动服务
systemctl restart systemd-journald.service在系统日志中能看到修改日志大小限制成功
[系统未激活][root@node5-63 ~]# journalctl -b -u systemd-journald.service
-- Logs begin at Tue 2019-09-03 17:40:10 CST, end at Tue 2019-09-03 17:41:05 CST. --
9月 03 17:40:10 node0-63 systemd-journald[573]: Journal started
9月 03 17:40:10 node0-63 systemd-journald[573]: Runtime Journal (/run/log/journal/3fb2775f95f245879006a2b6f8c4dad7) is 8.0M, max 1.4G, 1.4G
9月 03 17:40:13 node0-63 systemd-journald[573]: Journal stopped
9月 03 17:40:14 node5-63 systemd-journald[1094]: Journal started
9月 03 17:40:14 node5-63 systemd-journald[1094]: Runtime Journal (/run/log/journal/3fb2775f95f245879006a2b6f8c4dad7) is 8.0M, max 2.0M, 0B
9月 03 17:40:14 node5-63 systemd[1]: systemd-journald.service: Succeeded.
9月 03 17:40:14 node5-63 systemd-journald[1094]: Runtime Journal (/run/log/journal/3fb2775f95f245879006a2b6f8c4dad7) is 8.0M, max 2.0M, 0B 原来是 1.4G ，修改后变成 2M。