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CentOS7.X下如何查看并将一个应用设置为开机启动？systemctl start slapd 只是启动，并不是开机启动。
systemctl list-unit-files|grep slap slapd.service                                 disabled systemctl enable slapd                   #需要sudo root,否则提示：Authenticating as: root Created symlink from /etc/systemd/system/multi-user.target.wants/slapd.service to /usr/lib/systemd/system/slapd.service. systemctl list-unit-files|grep slap slapd.service                                 enabled

背景：有时候我们使用systemctl命令，如简单点的systemctl start memcached来讲，出现错时，会有一些提示，但是提示的内容是变量，其并没有将参数给编译后的值放入，于是出现如下所示，但是要失败了怎么排查这些参数呢？此文就讲这个问题，如果不是为了linux开机启动提速而并行启动外，这个systemctl其本质是想接管很多东西，但也带来了很多麻烦，难怪linus对此有一定的意见，系统要保持简单，好用。像开机慢可以少开机或不关机嘛，学学人家苹果升级在半夜，你慢就慢，谁管你，从策略上就规避了，把技术搞复杂还是简单是一门哲学，而创始人的价值就在于坚守设计艺术，而不光是技术。
● memcached.service - Memcached
   Loaded: loaded (/usr/lib/systemd/system/memcached.service; enabled; vendor preset: disabled)
   Active: inactive (dead) since Fri 2018-07-20 18:48:50 CST; 19h ago
  Process: 15266 ExecStart=/usr/local/memcached/bin/memcached -u $USER -p $PORT -m $CACHESIZE -c $MAXCONN $OPTIONS (code=exited, status=0/SUCCESS)
Main PID: 15266 (code=exited, status=0/SUCCESS)

失败：
systemctl start memcached
Job for memcached.service failed because the control process exited with error code. See "systemctl status memcached.service" and "journalctl -xe" for details.




[Unit] Description=Memcached Before=httpd.service After=network.target [Service] Type=simple ExecStartPre=/bin/bash -l -c 'echo "/usr/local/memcached/bin/memcached" -u $USER -p $PORT -m $CACHESIZE -c $MAXC ONN $OPTIONS > /tmp/systemctl.debug' EnvironmentFile=-/etc/sysconfig/memcached ExecStart=/usr/local/memcached/bin/memcached -u $USER -p $PORT -m $CACHESIZE -c $MAXCONN $OPTIONS [Install] WantedBy=multi-user.target

/etc/sysconfig/memcached
PORT="11211" USER="memcached" MAXCONN="1024" CACHESIZE="64" OPTIONS=" -vv >> /data/logs/memcached/11211/memcached.log 2>&1"

systemctl daemon-reload
systemctl start memcached
systemctl status memcached.service
  Active: failed (Result: exit-code) since Sat 2018-07-21 14:35:22 CST; 5s ago
  Process: 11417 ExecStart=/usr/local/memcached/bin/memcached -u $USER -p $PORT -m $CACHESIZE -c $MAXCONN $OPTIONS (code=exited, status=71)
  Process: 11399 ExecStartPre=/bin/bash -l -c echo "/usr/local/memcached/bin/memcached" -u $USER -p $PORT -m $CACHESIZE -c $MAXCONN $OPTIONS > /tmp/systemctl.debug (code=exited, status=0/SUCCESS)
Main PID: 11417 (code=exited, status=71)

如果有错，需要挑食的参数查看 /tmp/systemctl.debug：
cat /tmp/systemctl.debug
/usr/local/memcached/bin/memcached -u root -p 11211 -m 64 -c 1024 -vv >> /data/logs/memcached/11211/memcached.log 2>&1

作者：jackxiang@向东博客 专注WEB应用 构架之美 --- 构架之美，在于尽态极妍 | 应用之美，在于药到病除
地址：https://jackxiang.com/post/9829/
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