在postgres中，当max_connect设置过大，启动的时候会报错:

FATAL:  could not create semaphores: No space left on device

创建semaphores时空间参数不够，查询官网，有这么一段解释：

HINT:  This error does *not* mean that you have run out of disk space.  It occurs when either the system limit for the maximum number of semaphore sets (SEMMNI), or the system wide maximum number of semaphores (SEMMNS), would be exceeded.  You need to raise the respective kernel parameter.  Alternatively, reduce PostgreSQL‘s consumption of semaphores by reducing its max_connections parameter.
The PostgreSQL documentation contains more information about configuring your system for PostgreSQL.
解决的方法是改小max_connect，当业务不允许的情况下，修改内核参数，max_connect相关的内核参数有：

 下面介绍如何修改内核参数

# ipcs -ls
 
------ Semaphore Limits --------
max number of arrays = 1280
max semaphores per array = 50100
max semaphores system wide = 64128000
max ops per semop call = 50100
semaphore max value = 32767
 
 
# cat  /proc/sys/kernel/sem
SEMMSL   SEMMNS         SEMOPM  SEMMNI
50100   128256000       50100   2560

postgresql出错could not create semaphores: No space left on device