Dockerの設定ファイルはどこ！！

デフォルトでdockerの起動時オプションはどこにあるのでしょうか。
Linuxディストロや環境によって、いくつかパターンがあるようです。

#CentOS
docker.serviceというファイルがどこかにあるはずです。サービスの構成ファイルをいじれば起動時オプションが変えられます

わたくしの場合

/usr/lib/systemd/system/docker.service

にありました。

ほかにも、次のようなケースがあるようです

/usr/lib/systemd/system/docker.service

/etc/systemd/service/docker.service

/lib/systemd/system/docker.service

/usr/lib/systemd/system/docker.service

あるいはオプション用ファイルがすでにある場合があります

/etc/default/docker

#Ubuntu

/etc/init

/etc/init/docker.conf

/etc/init.d/docker

/lib/systemd/system/docker.service

あるいは設定を/etc/docker/daemon.jsonを操作して行う場合もあります。

#docker.service (CentOS7)
ExecStartをいじれば起動オプションをつけられる。

[Unit]
Description=Docker Application Container Engine
Documentation=https://docs.docker.com
BindsTo=containerd.service
After=network-online.target firewalld.service containerd.service
Wants=network-online.target
Requires=docker.socket

[Service]
Type=notify
# the default is not to use systemd for cgroups because the delegate issues still
# exists and systemd currently does not support the cgroup feature set required
# for containers run by docker
ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock  -H 0.0.0.0:5555
ExecReload=/bin/kill -s HUP $MAINPID
TimeoutSec=0
RestartSec=2
Restart=always

# Note that StartLimit* options were moved from "Service" to "Unit" in systemd 229.
# Both the old, and new location are accepted by systemd 229 and up, so using the old location
# to make them work for either version of systemd.
StartLimitBurst=3

# Note that StartLimitInterval was renamed to StartLimitIntervalSec in systemd 230.
# Both the old, and new name are accepted by systemd 230 and up, so using the old name to make
# this option work for either version of systemd.
StartLimitInterval=60s

# Having non-zero Limit*s causes performance problems due to accounting overhead
# in the kernel. We recommend using cgroups to do container-local accounting.
LimitNOFILE=infinity
LimitNPROC=infinity
LimitCORE=infinity

# Comment TasksMax if your systemd version does not supports it.
# Only systemd 226 and above support this option.
TasksMax=infinity

# set delegate yes so that systemd does not reset the cgroups of docker containers
Delegate=yes

# kill only the docker process, not all processes in the cgroup
KillMode=process

[Install]
WantedBy=multi-user.target
~                                                                                                                                                             
~                                              

#再読み込みと再起動 CentOS7

[root@localhost ~]# systemctl daemon-reload
[root@localhost ~]# service docker restart

プロセス確認

ps aux | grep docker | grep -v grep

#Ref
http://docs.docker.jp/engine/articles/configuring.html
https://forums.docker.com/t/how-to-change-dockerd-h-configuration-on-ubuntu-16-04/32631/3
https://qiita.com/masato/items/e967e531e75101796c30