重启后，mysql 不会启动。sudo service mysql start给出start: Job failed to start并且日志是空的，所以我不知道从哪里开始。我很确定权限问题得到了解决。
编辑：
所有磁盘至少有 1G 的空间，并sh -x /etc/init.d/mysql start给我：
+ set -e
+ basename /etc/init.d/mysql
+ INITSCRIPT=mysql
+ JOB=mysql
+ [ mysql = upstart-job ]
+ [ -z start ]
+ COMMAND=start
+ shift
+ [ -z ]
+ ECHO=echo
+ echo Rather than invoking init scripts through /etc/init.d, use the service(8)
Rather than invoking init scripts through /etc/init.d, use the service(8)
+ echo utility, e.g. service …mysql ×1