关于mysql启动报错The server quit without updating PID file

mysql今天突然挂掉了，重启报

The server quit without updating PID file (/var/lib/mysql/VM_0_15_centos.pid)

查看日志

# cat /var/lib/mysql/VM_0_15_centos.err

发现日志里报这个错
InnoDB: mmap(137363456 bytes) failed; errno 12
百度一下发现是linux运行内存不够

 #free -m
              total        used        free      shared  buff/cache   available
Mem:            992         383         402           0         206         451
Swap:             0           0           0

果然，系统内存不够了。。。主要原因还是太穷了。。。修改mysql配置文件

#vim /usr/my.cnf

[client]
default-character-set=utf8

[mysqld]
character-set-server=utf8

my.cnf里添加

key_buffer=16K
table_open_cache=4
query_cache_limit=256K
query_cache_size=4M
max_allowed_packet=1M
sort_buffer_size=64K
read_buffer_size=256K
thread_stack=64K
innodb_buffer_pool_size = 8M

重启ok