由於 Linux 不同發行版所採用的預設管理框架的不同，Docker 在不同環境下所使用的預設配置檔案也有所不同。這給初學者帶來了極大的困惑和不便。好訊息是，Docker 官方也意識到了這個問題，所以從 V1.12 開始，引入了並行通用配置檔案 /etc/docker/daemon.json 。從此以後，使用者可以在所有平臺統一通過調整該配置檔案來調整 Docker Engine。本文對此進行簡要說明。

配置檔案

通用配置檔案 /etc/docker/daemon.json

Docker Engine V1.12 之後版本，使用者可以自行建立 daemon.json 檔案對 Docker Engine 進行配置和調整。要點如下：

• 該檔案作為 Docker Engine 的配置管理檔案, 裡面幾乎涵蓋了所有 docker 命令列啟動可以配置的引數。
• 不管是在哪個平臺以何種方式啟動, Docker 預設都會來這裡讀取配置。使使用者可以統一管理不同系統下的 docker daemon 配置。
• 相關引數的使用說明，可以參閱 man dockerd 幫助資訊，或者參閱官方文件。
• 預設配置檔案目錄及支援的引數說明：
  • Linux： /etc/docker/daemon.json, 支援的完成引數配置示例如下（最新的支援引數列表可以參閱官方文件)：{ "authorization-plugins": [], "data-root": "", "dns": [], "dns-opts": [], "dns-search": [], "exec-opts": [], "exec-root": "", "experimental": false, "storage-driver": "", "storage-opts": [], "labels": [], "live-restore": true, "log-driver": "", "log-opts": {}, "mtu": 0, "pidfile": "", "cluster-store": "", "cluster-store-opts": {}, "cluster-advertise": "", "max-concurrent-downloads": 3, "max-concurrent-uploads": 5, "default-shm-size": "64M", "shutdown-timeout": 15, "debug": true, "hosts": [], "log-level": "", "tls": true, "tlsverify": true, "tlscacert": "", "tlscert": "", "tlskey": "", "swarm-default-advertise-addr": "", "api-cors-header": "", "selinux-enabled": false, "userns-remap": "", "group": "", "cgroup-parent": "", "default-ulimits": {}, "init": false, "init-path": "/usr/libexec/docker-init", "ipv6": false, "iptables": false, "ip-forward": false, "ip-masq": false, "userland-proxy": false, "userland-proxy-path": "/usr/libexec/docker-proxy", "ip": "0.0.0.0", "bridge": "", "bip": "", "fixed-cidr": "", "fixed-cidr-v6": "", "default-gateway": "", "default-gateway-v6": "", "icc": false, "raw-logs": false, "allow-nondistributable-artifacts": [], "registry-mirrors": [], "seccomp-profile": "", "insecure-registries": [], "disable-legacy-registry": false, "no-new-privileges": false, "default-runtime": "runc", "oom-score-adjust": -500, "runtimes": { "runc": { "path": "runc" }, "custom": { "path": "/usr/local/bin/my-runc-replacement", "runtimeArgs": [ "--debug" ] } } }
  • Windows： %programdata%\docker\config\daemon.json，支援的完成引數配置示例如下（最新的支援引數列表可以參閱官方文件)：{ "authorization-plugins": [], "data-root": "", "dns": [], "dns-opts": [], "dns-search": [], "exec-opts": [], "experimental": false, "storage-driver": "", "storage-opts": [], "labels": [], "log-driver": "", "mtu": 0, "pidfile": "", "cluster-store": "", "cluster-advertise": "", "max-concurrent-downloads": 3, "max-concurrent-uploads": 5, "shutdown-timeout": 15, "debug": true, "hosts": [], "log-level": "", "tlsverify": true, "tlscacert": "", "tlscert": "", "tlskey": "", "swarm-default-advertise-addr": "", "group": "", "default-ulimits": {}, "bridge": "", "fixed-cidr": "", "raw-logs": false, "allow-nondistributable-artifacts": [], "registry-mirrors": [], "insecure-registries": [], "disable-legacy-registry": false }

不同框架的配置檔案

不同 Linux 發行版本預設使用的管理框架可能存在不同。而不同管理框架下配置檔案的架構差異，最終導致了不同環境下預設 Docker 配置檔案目錄和檔名的不同。Linux 常見管理框架下的預設配置檔案說明如下：

| 管理框架型別 | 預設使用該框架的作業系統 | Docker 預設配置檔案 | 相關操作指令 |
| - | - | - | - |
| Sysvinit | CentOS 6.x, Ubuntu 12.04 等| /etc/default/docker | CentOS: service docker restart
Ubuntu: /etc/init.d/docker restart |
| Upstart | Ubuntu 14.x,15.x 等| /etc/default/docker| restart docker |
| Systemd | CentOS 7+，Ubunt 16+，Debian，RHEl 7, Fedora, Archlinux 等| Ubuntu/CentOS/: /lib/systemd/system/docker.service
RHEL/CentOS: /usr/lib/systemd/system/docker.service | systemctl restart docker.service |

配置檔案修改說明

參閱前述說明，對配置檔案調整後，注意如下要點：

• 修改配置後，需要重啟 docker 服務生效。當前主流的 Sytemd 框架相關平臺（CentOS 7+，Ubunt 16+ 等）的重啟指令如下： systemctl daemon-reolad systemctl restart docker.service

• 配置衝突
  如果通用配置檔案 /etc/docker/daemon.json 和上述預設配置檔案中有配置衝突（相同配置項分別配置了不同值），那麼 Docker daemon 啟動時會報錯。比如，如果在 Ubuntu 16.04 系統中，同時在 /etc/docker/daemon.json 和 /lib/systemd/system/docker.service 中指定了 --dns= 屬性，那麼 Docker daemon 會啟動失敗，相關錯誤資訊示例如下：

  [root@node3 ~]# systemctl start docker.service
  Job for docker.service failed because the control process exited with error code. See "systemctl status docker.service" and "journalctl -xe" for details.
  
  [root@node3 ~]# systemctl status docker.service
  ● docker.service - Docker Application Container Engine
     Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
     Active: failed (Result: exit-code) since Wed 2017-11-15 15:57:16 CST; 2min 29s ago
       Docs: https://docs.docker.com
    Process: 30610 ExecStart=/usr/bin/dockerd -H tcp://0.0.0.0 -H fd:// --dns=223.5.5.5 --dns=223.6.6.6 (code=exited,
   Main PID: 30610 (code=exited, status=1/FAILURE)
  
  Nov 15 15:57:16 c400e32b9e7cd46aea0d484ad260f4e4a-node3 systemd[1]: Starting Docker Application Container Engine...
  Nov 15 15:57:16 c400e32b9e7cd46aea0d484ad260f4e4a-node3 dockerd[30610]: unable to configure the Docker daemon with file /etc/docker/daemon.json: the following directives are specified both as a flag and in the configuration file: dns: (from flag: [223.5.5.5  223.6.6.6], from file: [114.114.114.114 8.8.8.8])
  Nov 15 15:57:16 c400e32b9e7cd46aea0d484ad260f4e4a-node3 systemd[1]: docker.service: Main process exited, code=exite
  Nov 15 15:57:16 c400e32b9e7cd46aea0d484ad260f4e4a-node3 systemd[1]: Failed to start Docker Application Container En
  Nov 15 15:57:16 c400e32b9e7cd46aea0d484ad260f4e4a-node3 systemd[1]: docker.service: Unit entered failed state.
  Nov 15 15:57:16 c400e32b9e7cd46aea0d484ad260f4e4a-node3 systemd[1]: docker.service: Failed with result 'exit-code'.
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