在通常的Linux服务器中，有一些服务本身没有日志，只能通过 tail -f /var/log/messages来查看其运行日志，比如nrpe server。但是，如果想在docker容器中实现这个功能就需要费点事了。具体步骤如下：
1、安装rsyslog
# yum -y install rsyslog
2、启动syslog服务
# rsyslogd
3、测试是否在messages中生成日志
# logger "Hello World"
结果发现，在messages中只有一下一行："Aug 1 11:31:37 f2570fed2149 rsyslogd: [origin software="rsyslogd" swVersion="7.4.7" x-pid="73" x-info="http://www.rsyslog.com"] start"，故可认定其未工作。原因是：“The problem was that in RHEL7 and Fedora we now use journald, which listens on /dev/log for incoming messages. In RHEL7 and Fedora, rsyslog actually reads messages from the journal via its API by default.But not all docker containers run systemd and journald. (Most don’t). In order to get the rsyslogd to work the way the user wanted, he would have to modify the configuration file, /etc/rsyslog.conf”。
解决办法如下：
1、修改syslog配置—— # vi /etc/rsyslog.conf
、注释掉 $ModLoad imjournal
、设置 $OmitLocalLogging 为 off
、注释掉 $IMJournalStateFile imjournal.state
2、提交容器至镜像，重新创建容器
[root@localhost home]# docker commit f2570fed2149 centos_with_syslog:v1.
830e298b4c103f70154ec9c8ceae44ec4602ed22063dae8e13a3f9aff4c3260a
[root@localhost home]# docker run -d -p : -v /dev/log:/dev/log -ti centos_with_syslog:v1. /run.sh
dc2eb83e80ced6f553eb1dd7032489d37b4d934a9126f61dfbd4d6a2243e98f1
3、测试验证
[root@localhost home]# docker exec -ti dc2eb83e80ced6f553eb1dd7032489d37b4d934a9126f61dfbd4d6a2243e98f1 /bin/bash
[root@dc2eb83e80ce /]# logger "hello everyone"
[root@dc2eb83e80ce /]# exit
exit
[root@localhost home]# tail -f /var/log/messages （注意实在宿主机上的messages文件中查看日志）
Aug :: localhost docker: time="2015-08-01T19:57:51+08:00" level=info msg="-job log(exec_start: /bin/bash , dc2eb83e80ced6f553eb1dd7032489d37b4d934a9126f61dfbd4d6a2243e98f1, centos_with_syslog:v1.0) = OK (0)"
Aug :: localhost docker: time="2015-08-01T19:57:51+08:00" level=info msg="POST /v1.18/exec/9ae97d0666bf5abcd8d95eb87d10c5d013a0f006c2cb1adc7ff8f7baaacf14fc/resize?h=37&w=191"
Aug :: localhost docker: time="2015-08-01T19:57:51+08:00" level=info msg="+job execResize(9ae97d0666bf5abcd8d95eb87d10c5d013a0f006c2cb1adc7ff8f7baaacf14fc, 37, 191)"
Aug :: localhost docker: time="2015-08-01T19:57:51+08:00" level=info msg="-job execResize(9ae97d0666bf5abcd8d95eb87d10c5d013a0f006c2cb1adc7ff8f7baaacf14fc, 37, 191) = OK (0)"
Aug :: localhost logger: hello everyone