转自：http://sloger.info/posts/systemd-failed-to-start-redis-in-gentoo
今天启动 Redis 时阻塞很长时间，之后显示启动失败，启动状态如下。
systemd[1]: redis.service start operation timed out. Terminating.
systemd[1]: Failed to start A persistent key-value database.
systemd[1]: Unit redis.service entered failed state.
看了下 service 文件，发现 Systemd 启动命令如下
ExecStart=/usr/sbin/redis-server /etc/redis.conf
手动运行这条命令，发现是正常的，所以猜想是 service 文件的问题，后来发现只需要把 [Service] 部分的 Type=forking 注释掉就行了。
[Service]
# Type=forking
# PIDFile=/var/run/redis/redis.pid
ExecStart=/usr/sbin/redis-server /etc/redis.conf
User=redis
Group=redis
之后重新加载 Service 文件并启动 Redis 服务
sudo systemctl daemon-reload
sudo systemctl start redis
Man pages 对 Systemd 服务启动类型 Type 的解释如下
If set to forking, it is expected that the process configured with ExecStart= will call fork() as part of its start-up. The parent process is expected to exit when start-up is complete and all communication channels are set up. The child continues to run as the main daemon process. This is the behavior of traditional UNIX daemons. If this setting is used, it is recommended to also use the PIDFile= option, so that systemd can identify the main process of the daemon. systemd will proceed with starting follow-up units as soon as the parent process exits.
因为 Redis 配置文件里配置的是daemonize off