业务无法和数据库建立连接，上去查看，切换用户就报错
su - postgres
su: cannot set user id: Resource temporarily unavailable
看资源不紧张，怀疑内核参数设置进程数有问题
问题如下：
tail -n10 /etc/security/limits.conf
# End of file
* soft nofile 131072
* hard nofile 131072
* soft nproc 131072
* hard nproc 131072
* soft core unlimited
* hard core unlimited
* soft memlock 50000000
* hard memlock 50000000
原来是以下文件没有修改，还是1024
cat /etc/security/limits.d/90-nproc.conf
# Default limit for number of user's processes to prevent
# accidental fork bombs.
# See rhbz #432903 for reasoning.
* soft nproc 1024
root soft nproc unlimited
查看postgres用户进程,已经跑满
ps -elf | grep postgres | wc -l
1025
注意：/etc/security/limits.d/90-nproc.conf会覆盖/etc/security/limits.conf文件的配置
解决方案：
修改/etc/security/limits.d/90-nproc.conf文件
和/etc/security/limits.conf一致，都为131072，修改文件需要重启生效
所以，还要临时修改进程的资源限制，查到postgresql主进程号为2161
cd /proc/2161/
Limit Soft Limit Hard Limit Units
Max cpu time unlimited unlimited seconds
Max file size unlimited unlimited bytes
Max data size unlimited unlimited bytes
Max stack size 10485760 unlimited bytes
Max core file size unlimited unlimited bytes
Max resident set unlimited unlimited bytes
Max processes 1024 1024 processes
Max open files 131072 131072 files
Max locked memory 51200000000 51200000000 bytes
Max address space unlimited unlimited bytes
Max file locks unlimited unlimited locks
Max pending signals 126260 126260 signals
Max msgqueue size 819200 819200 bytes
Max nice priority 0 0
Max realtime priority 0 0
Max realtime timeout unlimited unlimited us
临时修改Max processes为131072
echo -n "Max processes=131072:131072" > limits
