在ubuntu上使用apt安装redis报错。

Job for redis-server.service failed because a timeout was exceeded.
See "systemctl status redis-server.service" and "journalctl -xe" for details.
invoke-rc.d: initscript redis-server, action "start" failed.
● redis-server.service - Advanced key-value store
   Loaded: loaded (/lib/systemd/system/redis-server.service; disabled; vendor preset: enabled)
   Active: activating (auto-restart) (Result: timeout) since Mon 2019-11-04 15:42:39 CST; 6ms ago
     Docs: http://redis.io/documentation,
           man:redis-server(1)

Nov 04 15:42:39 VM-0-2-ubuntu systemd[1]: Failed to start Advanced key-value store.
dpkg: error processing package redis-server (--configure):
 installed redis-server package post-installation script subprocess returned error exit status 1
Errors were encountered while processing:
 redis-server
E: Sub-process /usr/bin/dpkg returned an error code (1)

于是查看服务状态

# systemctl status redis-server.service

Nov 04 15:42:39 VM-0-2-ubuntu systemd[1]: Starting Advanced key-value store...
Nov 04 15:42:39 VM-0-2-ubuntu systemd[1]: redis-server.service: Can't open PID file /var/run/redis

以为是权限问题，使用sudo启动，依然如此。 嗯，这个报错信息没卵用。网上搜到类似情况，是redis默认支持IPv6地址，但是主机没有，导致报错。

打开redis.conf，发现

bind 127.0.0.1 ::1

::1是IPv6的loopback地址，对应IPv4的127.0.0.1。 因为ecs没有分配IPv6网卡地址，绑定IPv6的loopback肯定报错。于是去掉::1。再次启动

sudo systemctl start redis-server.service

搞定。

思考：

• 虽然IPv6是大趋势，但是也不能默认选项就是listen v6地址，运行环境不一定有v6地址。
• 提示只有"Can’t open PID file"，对发现问题没有帮助，引起误导。