核心系统日志文件
/var/log/messages
包含系统启动时的引导盘，以及系统运行时其他状态、I/O错误、网络错误等；
该文件较大时，会被系统切割成几份；
日志切割配置文件为/etc/logrotate.conf（不要修改）
dmesg命令
它可以显示系统的启动信息，一般查看硬件问题；
dmesg | head -n5
[root@shu-test ~]# dmesg | head -n5
[ 0.000000] Initializing cgroup subsys cpuset
[ 0.000000] Initializing cgroup subsys cpu
[ 0.000000] Initializing cgroup subsys cpuacct
[ 0.000000] Linux version 3.10.0-693.el7.x86_64 (builder@kbuilder.dev.centos.org) (gcc version 4.8.5 20150623 (Red Hat 4.8.5-16) (GCC) ) #1 SMP Tue Aug 22 21:09:27 UTC 2017
[ 0.000000] Command line: BOOT_IMAGE=/vmlinuz-3.10.0-693.el7.x86_64 root=UUID=74ffca85-fbd2-4e59-954a-883c0e1b296a ro crashkernel=auto rhgb quiet LANG=zh_CN.UTF-8
[root@shu-test ~]#清空命令
dmesg -c系统启动日志
/var/log/dmesg查看正常登录日志
last命令
主要调用文件/var/log/wtmp
[root@shu-test ~]# last |head
user pts/1 192.168.188.3 Thu Feb 1 01:01 - 01:01 (00:00)
root pts/1 192.168.188.3 Wed Jan 31 22:41 - 22:42 (00:00)
root pts/0 192.168.188.1 Wed Jan 31 22:15 still logged in
reboot system boot 3.10.0-693.el7.x Wed Jan 31 22:15 - 02:06 (03:51)
root pts/0 192.168.188.1 Wed Jan 31 21:58 - down (00:16)
reboot system boot 3.10.0-693.el7.x Wed Jan 31 21:57 - 22:14 (00:17)
root pts/0 192.168.188.1 Tue Jan 30 19:21 - down (03:03)
reboot system boot 3.10.0-693.el7.x Tue Jan 30 19:03 - 22:25 (03:22)
root pts/0 192.168.188.1 Mon Jan 29 14:48 - crash (1+04:15)
reboot system boot 3.10.0-693.el7.x Mon Jan 29 14:47 - 22:25 (1+07:37)
[root@shu-test ~]#查看登录失败的日志
lastb命令
主要调用的文件/var/log/btmp
[root@shu-test ~]# lastb
user ssh:notty 192.168.188.3 Thu Feb 1 02:10 - 02:10 (00:00)
btmp begins Thu Feb 1 02:10:06 2018
[root@shu-test ~]#安全日志
/var/log/secure
无论登录是否成功都会把他记录到日志中；
[root@shu-test ~]# head -n5 /var/log/secure
Jan 30 21:25:38 shu-test polkitd[520]: Registered Authentication Agent for unix-process:3868:852626 (system bus name :1.59 [/usr/bin/pkttyagent --notify-fd 5 --fallback], object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale zh_CN.UTF-8)
Jan 30 21:25:38 shu-test polkitd[520]: Unregistered Authentication Agent for unix-process:3868:852626 (system bus name :1.59, object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale zh_CN.UTF-8) (disconnected from bus)
Jan 30 21:33:11 shu-test polkitd[520]: Registered Authentication Agent for unix-process:4296:897879 (system bus name :1.62 [/usr/bin/pkttyagent --notify-fd 5 --fallback], object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale zh_CN.UTF-8)
Jan 30 21:33:11 shu-test polkitd[520]: Unregistered Authentication Agent for unix-process:4296:897879 (system bus name :1.62, object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale zh_CN.UTF-8) (disconnected from bus)
Jan 30 21:33:44 shu-test polkitd[520]: Registered Authentication Agent for unix-process:4317:901212 (system bus name :1.63 [/usr/bin/pkttyagent --notify-fd 5 --fallback], object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale zh_CN.UTF-8)
[root@shu-test ~]#