Use systemd in Docker
Docker's official CentOS image does not provide the systemd service for the following reasons:
- Systemd requires
CAP_SYS_ADMINCapability. This means running docker--privileged. Not good for a base image.
- Systemd requires access to the cgroups filesystem.
- Using EMD has a number of unit files that don't matter in a iner, and they cause errors if they're not removed
However, in a controllable environment, we still want to use systemd to manage our services. How can we enable systemd? First, create a Dockerfile to create the base image of systemd: FROM centos: latestMAINTAINER feiskyRUN yum-y install systemd-libs # RUN yum-y updateRUN yum clean all; \ (cd/lib/systemd/system/sysinit.tar get. wants/; for I in *; \ do [$ I = systemd-tmpfiles-setup.service] | rm-f $ I; done ); \ rm-f/lib/systemd/system/multi-user.target.wants/*; \ rm-f/etc/systemd/system /*. wants/*; \ rm-f/lib/systemd/system/local-f S.tar get. wants/*; \ rm-f/lib/systemd/system/sockets.tar get. wants/* udev *; \ rm-f/lib/systemd/system/sockets.tar get. wants/* initctl *; \ rm-f/lib/systemd/system/basic.tar get. wants/*; \ rm-f/lib/systemd/system/anaconda.tar get. wants/*; VOLUME ["/sys/fs/cgroup"] CMD ["/usr/sbin/init"] Run docker build -- rm-t centos: systemd. create a systemd base image: [root @ fei ~] # Docker build -- rm-t centos: systemd.
Sending build context to Docker daemon 490 MB
Sending build context to Docker daemon
Step 0: FROM centos: latest
---> B157b77b1a65
Step 1: MAINTAINER feisky
---> Using cache
---> 4add1a12ff67
Step 2: RUN yum-y install systemd-libs
---> Using cache
---> 2bc5274f7dd2
Step 3: RUN yum clean all; (cd/lib/systemd/system/sysinit.tar get. wants/; for I in *; do [$ I = systemd-tmpfiles-setup.service] | rm-f $ I; done ); rm-f/lib/systemd/system/multi-user.target.wants/*; rm-f/etc/systemd/system /*. wants/*; rm-f/lib/systemd/system/local-fs.target.wants/*; rm-f/lib/systemd/system/sockets.tar get. wants/* udev *; rm-f/lib/systemd/system/sockets.tar get. wants/* initctl *; rm-f/lib/systemd/system/basic.tar get. wants/*; rm-f/lib/systemd/system/anaconda.tar get. wants /*;
---> Running in d132481218d7
Loaded plugins: fastestmirror
Cleaning repos: base extras updates
Cleaning up everything
Cleaning up list of fastest mirrors
---> 7a9425819396
Removing intermediate container d132481218d7
Step 4: VOLUME/sys/fs/cgroup
---> Running in d5a93c8ee296
---> 10b06676ea4d
Removing intermediate container d5a93c8ee296
Step 5: CMD/usr/sbin/init
---> Running in 6ab276a1974b
---> B519e838366f
Removing intermediate container 6ab276a1974b
Under Successfully built b519e838116f, you can create an http Service Image Based on this image. Of course, you need another Dockerfile: FROM centos: systemdMAINTAINER feiskyRUN yum-y install httpd; systemctl enable httpd. serviceRUN yum-y install mariadb-server mariadb; systemctl enable mariadb. serviceRUN yum clean allEXPOSE 80CMD ["/usr/sbin/init"] Run docker build-t http_server. to create an http image. After the image is created, run the following command to start http docker (note that -- privileged is required ):
Docker run -- privileged-d-v/sys/fs/cgroup: ro-h server. http. local-p 8081: 80-t http_server
Run the following command to enter the docker shell (where 3df7d8c59f1e is the container ID): nsenter -- mount -- uts -- ipc -- net -- pid -- target $ (docker inspect -- format "{{. state. pid} "" 605bae76456d ") or you can run the following command in the container: # docker exec 605bae76456d ps-efUID pid ppid c stime tty time CMDroot 1 0? 00:00:00/usr/sbin/initroot 15 1 0 07:33? 00:00:00/usr/lib/systemd-journaldroot 16 1 0? 00:00:00/usr/sbin/httpd-DFOREGROUNDapache 18 16 0 07:33? 00:00:00/usr/sbin/httpd-DFOREGROUNDapache 19 16 0 07:33? 00:00:00/usr/sbin/httpd-DFOREGROUNDapache 20 16 0 07:33? 00:00:00/usr/sbin/httpd-DFOREGROUNDapache 21 16 0 07:33? 00:00:00/usr/sbin/httpd-DFOREGROUNDapache 22 16 0 07:33? 00:00:00/usr/sbin/httpd-dforeground.pdf 187 1 0? 00:00:00/bin/logs-daemon -- system -- address = systemd: -- nofork -- nopidfile -- systemd-activationmysql 248 1 0? 00:00:00/bin/sh/usr/bin/mysqld_safe -- basedir =/usrmysql 404 248 1? 00:00:00/usr/libexec/mysqld -- basedir =/usr -- datadir =/var/lib/mysql -- plugin-dir =/usr/lib64/mysql/plugin -- log-error =/ var/log/mariadb. log -- pid-file =/var/run/mariadb. pid -- socket =/var/lib/mysql. sockroot 458 0 0 07:41? 00:00:00 ps-ef accessed port 8081 of the server and found that Apache started up normally.
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