最近写了个小应用，运行好好的，忽然有一天连接不上，上服务器发现竟然有1000+的用户了，
systemctl status mosquitto检查下状态，发现有提示无法创建新连接，让我执行ulimit -n
结果显示65535
查看了下服务器的最大连接数设置，都是大于1024的，问题找不到就百度嘛，用mosquitto+最大连接数查到的都没解决问题，最后发现是systemctl这个软件的问题，解决方案如下
修改/etc/systemd/system/mosquitto.service
在[service]下添加
LimitNOFILE=65535
LimitNOPROC=65535
改完后
systemctl daemon-reload
systemctl restart mosquitto.service
问题解决
PS：也可以打开其它限制，可以在/etc/systemd/system.conf上看到，内容如下
# This file is part of systemd.
#
# systemd is free software; you can redistribute it and/or modify it
# under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation; either version 2.1 of the License, or
# (at your option) any later version.
#
# Entries in this file show the compile time defaults.
# You can change settings by editing this file.
# Defaults can be restored by simply deleting this file.
#
# See systemd-system.conf(5) for details.
[Manager]
#LogLevel=info
#LogTarget=journal-or-kmsg
#LogColor=yes
#LogLocation=no
#DumpCore=yes
#CrashShell=no
#ShowStatus=yes
#CrashChVT=1
#CtrlAltDelBurstAction=reboot-force
#CPUAffinity=1 2
#JoinControllers=cpu,cpuacct net_cls,net_prio
#RuntimeWatchdogSec=0
#ShutdownWatchdogSec=10min
#CapabilityBoundingSet=
#SystemCallArchitectures=
#TimerSlackNSec=
#DefaultTimerAccuracySec=1min
#DefaultStandardOutput=journal
#DefaultStandardError=inherit
#DefaultTimeoutStartSec=90s
#DefaultTimeoutStopSec=90s
#DefaultRestartSec=100ms
#DefaultStartLimitInterval=10s
#DefaultStartLimitBurst=5
#DefaultEnvironment=
#DefaultCPUAccounting=no
#DefaultBlockIOAccounting=no
#DefaultMemoryAccounting=no
#DefaultTasksAccounting=no
#DefaultTasksMax=
#DefaultLimitCPU=
#DefaultLimitFSIZE=
#DefaultLimitDATA=
#DefaultLimitSTACK=
#DefaultLimitCORE=
#DefaultLimitRSS=
#DefaultLimitNOFILE=
#DefaultLimitAS=
#DefaultLimitNPROC=
#DefaultLimitMEMLOCK=
#DefaultLimitLOCKS=
#DefaultLimitSIGPENDING=
#DefaultLimitMSGQUEUE=
#DefaultLimitNICE=
#DefaultLimitRTPRIO=
#DefaultLimitRTTIME=