ulimit命令
http://man.linuxde.net/ulimit
https://www.cnblogs.com/pangguoping/p/5792075.html
How to set ulimit values
https://access.redhat.com/solutions/61334
How to Set Limits on User Running Processes in Linux
https://www.tecmint.com/set-limits-on-user-processes-using-ulimit-in-linux
CentOS/RHEL 7 系统中设置systemd service的ulimit资源限制
http://smilejay.com/2016/06/centos-7-systemd-conf-limits
关于 CentOS 7 里面 普通用户 Ulimit max user processes 值的问题
https://cloud.tencent.com/info/95ce4e180b83c4973cc70d0b0f703d12.html
Linux中最大进程数和最大文件数
https://www.cnblogs.com/lxyit/p/9204521.html
ulimit限制之nproc问题
http://www.linuxde.net/2013/03/13045.html
ulimit命令详解
https://juejin.im/entry/5b57effce51d45190f4acb43
通过 ulimit 改善系统性能
https://www.ibm.com/developerworks/cn/linux/l-cn-ulimit/index.html