Update:
请阅读在 GNU screen 中优雅地运行 Caddy.

Update:
好了这篇破文章不用看了, systemd/SysVinit/Supervisor 我全都试了一遍,全他妈都不行,握草他妈的守护进程这个问题真的是无力再战了,在这上面不知道浪费了多少时间.目前用 screen 守护 Caddy, 一切正常, mlgb.

环境: Fedora 25, Caddy 0.9.4.

使用来自 https://github.com/mholt/caddy/tree/master/dist/init/linux-systemd 的 caddy.service 文件,发现无法启动服务.报错信息如下:

journalctl -xe 返回:

Jan 23 12:45:39 150-95-143-145.conoha.io systemd[1]: Network Service is not active.
Jan 23 12:45:39 150-95-143-145.conoha.io systemd[1]: Dependency failed for Wait for Network to be Configured.
-- Subject: Unit systemd-networkd-wait-online.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit systemd-networkd-wait-online.service has failed.
-- 
-- The result is dependency.
Jan 23 12:45:39 150-95-143-145.conoha.io systemd[1]: systemd-networkd-wait-online.service: Job systemd-networkd-wait-online.service/start failed wit
Jan 23 12:45:39 150-95-143-145.conoha.io systemd[1]: caddy.service: Start request repeated too quickly.
Jan 23 12:45:39 150-95-143-145.conoha.io systemd[1]: Failed to start Caddy HTTP/2 web server.
-- Subject: Unit caddy.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit caddy.service has failed.
-- 
-- The result is failed.
Jan 23 12:45:39 150-95-143-145.conoha.io systemd[1]: caddy.service: Failed with result 'start-limit-hit'.

但我又发现,如果直接在终端里执行 /usr/local/bin/caddy -log stdout -agree=true -conf=/etc/caddy/Caddyfile -root=/var/tmp , Caddy 则可以正常运行,没有报错.

问题可能在于 systemd-networkd-wait-online.service 这个服务阻碍了 Caddy 的启动.我使用的操作系统是 Fedora, 默认的网络管理器似乎是 NetworkManager ,而非 systemd-networkd-wait-online.service 所需求的 systemd-networkd .尝试以下两行命令:

systemctl enable systemd-networkd
systemctl disable NetworkManager

随后 Caddy 即可正常启动.然而重启服务器后发现 SSH 连不上,惊出一身冷汗.幸好我的 VPS 提供的 VNC 连接尚可正常工作,不得已 systemctl enable NetworkManager .

随后 Caddy 社区的 @Whitestrake 大神告诉我,这两个网络管理器最好 disable 掉一个.他更推荐的办法是,保持这两个管理器的 enable 状态为默认,并修改 caddy.service 文件,使之"依赖于"(抱歉我不知道该用什么词) networkmanager-wait-online.service 服务.

我修改后的 caddy.service 文件如下所示:

[Unit]
Description=Caddy HTTP/2 web server
Documentation=https://caddyserver.com/docs
After=network-online.target
Wants=network-online.target networkmanager-wait-online.service

[Service]
Restart=on-failure
StartLimitInterval=86400
StartLimitBurst=5

; User and group the process will run as.
User=www-data
Group=www-data

; Letsencrypt-issued certificates will be written to this directory.
Environment=CADDYPATH=/etc/ssl/caddy

; Always set "-root" to something safe in case it gets forgotten in the Caddyfile.
ExecStart=/usr/local/bin/caddy -quic -log stdout -agree=true -conf=/etc/caddy/Caddyfile -root=/var/tmp
ExecReload=/bin/kill -USR1 $MAINPID

; Limit the number of file descriptors; see `man systemd.exec` for more limit settings.
LimitNOFILE=1048576
; Unmodified caddy is not expected to use more than that.
LimitNPROC=64

; Use private /tmp and /var/tmp, which are discarded after caddy stops.
PrivateTmp=true
; Use a minimal /dev
PrivateDevices=true
; Hide /home, /root, and /run/user. Nobody will steal your SSH-keys.
ProtectHome=true
; Make /usr, /boot, /etc and possibly some more folders read-only.
ProtectSystem=full
; … except /etc/ssl/caddy, because we want Letsencrypt-certificates there.
;   This merely retains r/w access rights, it does not add any new. Must still be writable on the host!
ReadWriteDirectories=/etc/ssl/caddy

; The following additional security directives only work with systemd v229 or later.
; They further retrict privileges that can be gained by caddy. Uncomment if you like.
; Note that you may have to add capabilities required by any plugins in use.
;CapabilityBoundingSet=CAP_NET_BIND_SERVICE
;AmbientCapabilities=CAP_NET_BIND_SERVICE
;NoNewPrivileges=true

[Install]
WantedBy=multi-user.target

这样, Caddy 就可以在默认使用 NetworkManager 的系统上正常启动了.(此外我还启用了 QUIC)

这个坑困扰了我好几天的时间,多亏了强大的 Caddy 社区力量才得以解决.原贴在 Cannot start Caddy as a systemd service. 感觉确实如同一些人所说, systemd 给 Linux 系统带来了一些不必要的复杂性.

以上.